articles+ search results

Laser-based directed energy deposition (L-DED) is a rising field in the arena of metal additive manufacturing and has extensive applications in aerospace, medical, and rapid prototyping. The process parameters, such as laser power, scanning speed, and layer thickness, play an important role in controlling and affecting the properties of DED fabricated parts. Nevertheless, both experimental and simulation methods have shown constraints and limited ability to generate accurate and efficient computational predictions on the correlations between the process parameters and the final part quality. In this paper, two data-driven machine learning algorithms, Extreme Gradient Boosting (XGBoost) and Random Forest (RF), were applied to predict the tensile behaviors including yield strength, ultimate tensile strength, and elongation (%) of the stainless steel 316L parts by DED. The results suggest that both models successfully predicted the tensile properties of the fabricated parts. The performance of the proposed methods was evaluated and compared with the Ridge Regression by the root mean squared error (RMSE), relative error (RE), and coefficient of determination (R2). XGBoost outperformed both Ridge Regression and Random Forest in terms of prediction accuracy. [ABSTRACT FROM AUTHOR]

3D printing is a constantly expanding technology that represents one of the most exciting and disruptive production possibilities available today. This technology has gained global recognition and garnered considerable attention in recent years. However, technological breakthroughs, particularly in the field of material science, continue to be the focus of research, particularly in terms of future advancements. The 3D printing techniques are employed for the manufacturing of advanced multifunctional polymer composites due to their mass customization, freedom of design, capability to print complex 3D structures, and rapid prototyping. The advantages of 3D printing with multipurpose materials enable solutions in challenging locations such as outer space and extreme weather conditions where human involvement is not possible. Each year, numerous research papers are published on the subject of imbuing composites with various capabilities such as magnetic, sensing, thermal, embedded circuitry, self-healing, and conductive qualities by the use of innovative materials and printing technologies. This review article discusses the various 3D printing techniques used in the manufacture of polymer composites, the various types of reinforced polymer composites (fibers, nanomaterials, and particles reinforcements), the characterization of 3D printed parts, and their applications in a various industries. Additionally, this review discussed the limitations of 3D printing processes, which may assist future researchers in increasing the utility of their works and overcoming the shortcomings of previous works. Additionally, this paper discusses processing difficulties, anisotropic behavior, stimuli-responsive characteristics (shape memory and self-healing materials), CAD constraints, layer-by-layer appearance, and void formation in printed composites. Eventually, the promise of maturing technology is discussed, along with recommendations for research activities that are desperately required to realize the immense potential of operational 3D printing. [ABSTRACT FROM AUTHOR]

DIGITAL image correlation, METAL fibers, RAPID prototyping, POISSON'S ratio, METAL powders, FINITE element method, and DIGITAL images

Recently, metals have been processed with fused filament fabrication (FFF) printers, in the form of mixture of metal powder and a polymeric binder. This new area of additive manufacturing is called metal-fused filament fabrication (metal FFF), and it is characterized by several advantages: low cost of manufacturing for small batches, ease of use, lower cost of energy and lower risks compared to the main metal additive manufacturing technologies. Being a novel technique, it is of great importance to understand the mechanical behaviour of the fabricated parts to reach the potential applications. In this work, the mechanical response of parts printed by metal FFF was analysed by means of digital image correlation (DIC) technique. This latter allowed to better highlight the anisotropic mechanical behaviour of the FFF parts when varying some 3D printing parameters, such as building orientation and number of wall layers and enabled a complete characterization of material useful for numerical calculation and finite element analysis. With this aim, 316L stainless steel filament and a consumer 3D printer were used for the fabrication of tensile test specimens. Three different building orientations and three different numbers of wall layers were evaluated. Results obtained from the tensile tests conducted with the DIC system highlighted the anisotropy of the strain behaviour when varying building orientation and printing strategy. More in details, flatwise and sideways configurations returned higher values of tensile strength, elongation at break and Poisson's ratio compared to upright one, while the increase of number of wall layers, in some cases, caused a decrease of the mechanical properties. [ABSTRACT FROM AUTHOR]

3-D printers, HALL effect transducers, DETECTORS, MACHINE learning, COMPUTER printers, and MAGNETS

Desktop fused filament fabrication (FFF) 3D printers have been growing in popularity among hobbyist and professional users as a prototyping and low-volume manufacturing tool. One issue these printers face is the inability to determine when a defect has occurred rendering the print unusable. Several techniques have been proposed to detect such defects, but many of these approaches are tailored to one specific fault, use expensive hardware, and/or use machine learning algorithms which can be sensitive to ambient conditions making them unreliable. This paper proposes a novel, low-cost system, named MTouch, to accurately detect millimeter-scale defects that tend to make prints unusable. MTouch uses an actuated contact probe designed with a low-power solenoid, magnet, and hall effect sensor. This sensor is used to check for the presence, or absence, of the printed object at specific locations. The MTouch probe demonstrated 100% accurate readings, which was significantly higher than the 74% achieved using a repurposed commercially available bed leveling touch probe (the BLTouch). Additionally, algorithms were developed to detect common print failures such as layer shifting, bed separation, and filament runout using the MTouch probe. In head-to-head testing against a commercially available print defect detection system (The Spaghetti Detective), the MTouch was able to detect faults 44% faster on average while only increasing the print time by 8.49%. In addition, MTouch was able to detect faults The Spaghetti Detective was unable to identify such as layer shifting and filament runout/jam. [ABSTRACT FROM AUTHOR]

Generally, machining of polymeric microfluidic devices is a one-step manufacturing process. It is economical compared to lithography and can be used for batch production and rapid prototyping. However, surface properties are modified during machining due to the viscoelasticity property of polymers and the mechanical nature of fractures. In this present work, the manufacturing capability of the mechanical micromachining process of polymers has been explored. Surface characteristics like surface roughness, surface energy, and burr formation are investigated. Surface quality is chosen as a contributing factor for defining the manufacturing capability as it is one of the significant factors influencing the physics of fluid flow in microchannels. In the present work, several manufacturing methods, such as 3D printing, hot embossing, photolithography, and mechanical micromachining, were considered. The surface energy of various surfaces machined using the abovementioned methods is evaluated and compared. It has been observed that mechanical micromachining is the most suitable methods as they have less wettability with lower surface energy. Further investigations are carried out by machining microfluidic devices using polymethylmethacrylate (PMMA) and polycarbonate (PC) materials, as they are extensively used in biomedical applications. Surface roughness was measured on the PMMA and PC surfaces after milling. The surface roughness values and surface energies are used for evaluating the suitability of the machining process to fabricate microfluidic devices. Microfluidic devices with serpentine channels were machined on PMMA with a depth of 50 µm and width of 200 µm for evaluating inertial focusing in the channels. These devices were further evaluated for blood cell separation at different dilution rates. It is observed that PMMA is the preferable choice for fabricating microfluidic devices using mechanical micro-milling. [ABSTRACT FROM AUTHOR]

DIGITAL twins, FUSED deposition modeling, 3-D printers, RAPID prototyping, VIRTUAL machine systems, and WEB-based user interfaces

Additive manufacturing is often used in rapid prototyping and manufacturing, allowing the creation of lighter, more complex designs that are difficult or too expensive to build using traditional manufacturing methods. This work considers the implementation of a novel digital twin ecosystem that can be used for testing, process monitoring, and remote management of an additive manufacturing–fused deposition modeling machine in a simulated virtual environment. The digital twin ecosystem is comprised of two approaches. One approach is data-driven by an open-source 3D printer web controller application that is used to capture its status and key parameters. The other approach is data-driven by externally mounted sensors to approximate the actual behavior of the 3D printer and achieve accurate synchronization between the physical and virtual 3D printers. We evaluate the sensor-data-driven approach against the web controller approach, which is considered to be the ground truth. We achieve near-real-time synchronization between the physical machine and its digital counterpart and have validated the digital twin in terms of position, temperature, and run duration. Our digital twin ecosystem is cost-efficient, reliable, replicable, and hence can be utilized to provide legacy equipment with digital twin capabilities, collect historical data, and generate analytics. [ABSTRACT FROM AUTHOR]

GLOBAL optimization, RAPID prototyping, ENGINEERING design, INJECTION molding, MANUFACTURING processes, GENETIC algorithms, and CHEMICAL molding

Injection molding (IM) is a versatile manufacturing process capable of rapid prototyping and mass-producing high-quality polymer parts. The present study mainly investigates the challenge of designing multiple molding gates on the complex arbitrary part surface in 3D. Currently, this problem is a challenge in mold design and engineering experience still plays an important role in designing the molding gates. To reduce the human intervention in the design process, the present study proposed a novel methodology with the following major steps: 1) using Poisson disk sampling (PDS) to preselect candidate gate locations automatically within the suitable gating region specified by designers; 2) using a space-filling initialization strategy and efficient global optimization to find the optimal gate locations. In the present setting, the molding gate design problem is formalized as a discrete optimization problem. The PDS is employed to construct the discrete solution space and EGO is used to efficiently search through a large solution space for the best design. To further promote optimization efficiency, a parallel implementation of EGO is also proposed. The effectiveness of the proposed methods is validated in two design cases. The results demonstrate the proposed EGO and Parallel EGO method is superior that the Genetic Algorithm (GA) and Surrogate Optimization (SO). Moreover, the proposed Parallel EGO converges faster than all other alternatives. [ABSTRACT FROM AUTHOR]

FOOT orthoses, FLEXIBLE manufacturing systems, RAPID prototyping, MACHINE learning, PSYCHOLOGICAL feedback, ELECTRONIC data processing, and TIME management

Mold design and construction is typically the most time-consuming and costly process in the fabrication of custom freeform product surfaces. Reconfigurable molds reduce this time and cost; however, some opportunities for improvement in reconfigurable systems are still possible in design by reducing system complexity and reconfigure time for a target application. A novel "multi-actuated optimized reconfigurable freeform surface (MORFS)" mold is proposed for the following key targets to (1) design the system for a targeted application, e.g., custom foot orthoses (CFOs), (2) reduce system complexity, (3) reduce system reconfigure time, and (4) ensure accuracy. The MORFS design process involves the following steps: (1) data processing, segmentation, normalization, and dimensionality reduction; (2) design of a novel mechanical subassembly; (3) development of a finite element (FE) flexible shell model of the manufacturing surface mold; (4) design optimization; and (5) development of a machine learning (ML)-based feedback control algorithm. The developed MORFS mold is 29% less complex, and 60% faster as compared with the benchmark study while maintaining the desired accuracy, i.e. mean error ≤ 1 mm. Furthermore, the accuracy of the optimized MORFS mold is also increased up to 39% as compared with the unoptimized configuration. The mechanical subassembly of the MORFS mold is improved by conducting design optimization, i.e., the number of actuators is reduced. Furthermore, the system reconfigure time is reduced significantly by using the FE model based ML control algorithm. The proposed design methodology ensured the desired accuracy of the surface construction for a target application. This case study is limited to the construction of freeform surfaces for CFOs; however, the proposed MORFS design methodology may be used to improve the time, complexity, and cost aspects of manufacturing in different areas including aerospace, automotive, biomechanics, and civil. [ABSTRACT FROM AUTHOR]

MARTENSITIC stainless steel, STEEL walls, MANUFACTURING processes, THERMAL properties, STAINLESS steel, METALS, and WIRE

Additive manufacturing is often seen as a novel alternative compared to well-consolidated, subtractive, and formative manufacturing processes. Its presence in the industrial environment is rapidly increasing, and its performance and flexibility may be the answer for present-day fabrication challenges, combining solutions to minimize environmental impacts without losing competitiveness or product quality. Arc welding-based additive manufacturing (also known as wire arc additive manufacturing, WAAM) has been gaining prominence in the current Industry 4.0 scenario. For the advancement of this technology, multiple output analysis of the pertinent welding processes is essential, especially regarding studies applied to materials such as high-strength and high-cost steels. In this paper, a study was conducted with the AISI 420 alloy and CMT variants of the GMAW process applied to additive manufacturing of thin walls, comparing them with conventional GMAW process. The welding processes and deposited welds used were analyzed on electrical, thermal, morphological, and metallurgical aspects. In the end, CMT Advanced and CMT Pulse variants stood out as opposite extremes, whereby CMT Advanced presented the best performance in relation to wall height and heat input. CMT and conventional GMAW produced good and significantly similar results, highlighting the stability of CMT. [ABSTRACT FROM AUTHOR]

SHEET metal, METALWORK, SHEET metal work, AEROSPACE industries, MICROELECTRONICS, and WATER jets

Nowadays the development of innovative processes is a major challenge for industries which want to prototype functional workpieces. Incremental sheet forming (ISF) is a good alternative for sheet metal prototyping to ensure flexibility, accuracy of the part produced, and cost effectiveness. A derived process, the Water Jet Incremental Sheet Forming (WJISF), has been undergoing development since 2001 and this paper purpose to give its state of the art. Different eclectic industrial fields could be concerned by WJISF process: automotive, micro-electronics, medical, and aerospace industry, for example. As the ISF process, the WJISF device needs a multi-axial machine, but it also needs a pressure pump with a sufficient flow rate and pressure. In an environmental point of view, this process can be seen as a "green" one giving that the water can be recycled and there is no lubricant. A general methodology has been defined to rigorously investigate this process and focus on researchers' teams, technological feasibility, numerical simulations, machine-tool uses, and real parts manufacturing. The study presented here provides summarizing evidence, especially technological windows, which give quick view of the actual knowledges and will help scientists and industrials to find WJISF parameters related to their needs. A lot of simple tests have been carried out with numerical and experimental comparisons. Nevertheless, few real parts have been manufactured, and the complex shape obtained by WJISF remains a scientific field to explore. [ABSTRACT FROM AUTHOR]

FUSED deposition modeling, MOLDING materials, FLEXURAL strength, INJECTION molding, GLASS fibers, FLEXURE, and CARBON fibers

Vacuum casting (VC) is a promising technique used for the production of functional plastic parts due to its fast production of high-quality prototypes. However, the mechanical properties of the fabricated products are affected by the composition of the molding materials. Additive manufacturing (AM) is also widely applied for low-volume prototyping applications. However, the mechanical properties of the fabricated products are affected by both build directions and printing angles. To investigate the difference in flexural strength of parts between vacuum casting and fused deposition modeling, glass fiber (GF) and carbon fiber (CF) are added to the matrix materials of polyurethane (PU) for improving the flexural strength of the molded products and three different printing angles and two build directions were applied in AM process. It was found that the flexure strength of the specimen fabricated by VC is generally greater than that of the specimen fabricated by AM. The highest flexure strength of the specimen fabricated by VC is 141 MPa, whereas the highest flexure strength of the specimen fabricated by FDM is only 102.7 MPa. The addition of short GF to the PU will increase the flexural strength. The flexural strength can be increased by about 41% when the PU is added with 4 wt.% short GF. The flexural strength can be increased by about 4.8% when the PU is added with 1 wt.% long GF. In contrast to above results, the flexural strength will be reduced when the PU is added with more than 2 wt.% long GF. On the contrary, the flexural strength can not be improved when the short CF or long CF is added to the PU. Finally, the flexural strength of the plastic prototype made by VC technology is superior to that of the plastic prototype made by FDM since the mechanical properties of the plastic prototype made by the FDM are affected by the build direction and printing angle. [ABSTRACT FROM AUTHOR]

POLYETHER ether ketone, COMPUTER simulation, POLYLACTIC acid, RAPID prototyping, TEMPERATURE, HEAT transfer, and FUSED deposition modeling

Material extrusion additive manufacturing is one of the widely used rapid prototyping technology, which produces parts with complex shapes and structures by continuous deposited strands. In previous studies, the influence of process parameters on product performance was experimentally studied, while morphological evolutions of strands, particularly considering the temperature variation, were not well understood. In this study, the mesostructure formed by parallel strands during continuous non-isothermal deposition flows was comprehensively studied by numerical simulations and experimental methods. The numerical model simulated the complete process of flow, deposition, bonding, and heat transfer for the representative materials, polyether ether ketone (PEEK), and polylactic acid (PLA). The quantitative comparison of the strands cross-sectional size measured by experiments and simulations was presented, and the results were consistent. The results showed that increasing the reheating temperature can considerably improve the strand-to-strand bonding. The effects of gap distance, printing speed, and strand-to-strand distance on the mesostructures of PEEK and PLA were comprehensively investigated and compared. Additionally, the simulation and experiment results provided detailed information regarding the porosity and bonding degree, which significantly affects product performance. [ABSTRACT FROM AUTHOR]

WRINKLE patterns, FINITE element method, STRENGTH of materials, and SHEET-steel

Roll forming is increasingly used in the automotive industry for the manufacture of structural and crash components from ultra-high-strength steel (UHSS). Springback and end flare are common shape defects in roll forming and increase with material strength. The conventional roll forming process is limited to the manufacture of components with a uniform cross section while flexible roll forming can produce parts with variation in width and depth. In this paper, the flexible roll forming of an automotive component from three different high-strength sheets of steel is investigated. The experiments are carried out with a flexible roll forming prototyping facility and combined with finite element analysis. The study shows that the flexible roll forming of high-strength automotive components is possible. Springback and end flare depend on the material strength and the forming sequence and can be reduced with a flexible forming approach where the material is first overbent followed by bending back. Wrinkling of the flange was observed but the severity of wrinkling reduced with an increasing number of forming passes. [ABSTRACT FROM AUTHOR]

BIOCERAMICS, 3-D printers, DENTURES, BIOMEDICAL materials, and THREE-dimensional printing

The introduction of ceramic materials in the medical field is becoming a vital necessity because of its stable physicochemical characteristics, high biocompatibility, and good osteoconductivity. On the contrary, machining ceramic components is difficult, owing to their extreme hardness and brittleness. Additive manufacturing (AM) technologies are an appropriate alternative to obtain the complex shapes of implants, which can have porous structures. Thus, since the development of 3D printing, direct ink writing (DIW) is one of the most promising and inexpensive techniques for shaping free-form ceramic medical components such as prostheses or dental implants from liquids or pastes. However, the assurance of performance criteria of the extrusion system for simultaneous usage becomes the major challenge for most direct ink writing (DIW) platforms, for instance for printing large parts, for multi-material printing, to decrease printing time, and to increase efficiency in terms of motor usage and weight of the extruders. To address the current deficiencies, a new extrusion system is designed for a 3D printing machine for ceramics that is compatible with different low-cost, open-source 3D printers. The proposed extrusion model enables printing with a loader with different syringes simultaneously, without stopping the operational process while switching the syringe. It adopts three subsystems. The automatic syringe loading system, which is operational to manually receive several syringes of the same or different volumes, allows the syringe feeding system to be loaded and unloaded once the syringe is empty. The syringes are automatically transferred to the holding system using an arm. The holding system allows the fixing of the syringe in order to perform printing with ceramic material. Pugh concept analysis was used to select the optimum design shape. After that, the 3D CAD environment was used to combine the strength of Pugh's method and the design space. This brings a new concept into the mechanical design field for 3D printers, which is in line with the technological trends prevalent in the industry. [ABSTRACT FROM AUTHOR]

MARAGING steel, MECHANICAL heat treatment, RIETVELD refinement, CARBON steel, HEAT treatment, and FACTORIAL experiment designs

Maraging steels (MS) are widely used materials for heavy-duty applications and are considered an alternative to carbon hardened steels when high strength and good toughness is needed. Their processing through additive manufacturing (AM) technologies offers additional high-value opportunities, for instance, in the rapid prototyping or fabrication of tooling and inserts, and in the repair of molds and dies as well as in maintenance applications. This work studied the maraging 300 steel (18Ni-300) deposited by the laser cladding (LC) process. The experimental design was based on a 23-full factorial design used to determine the optimum processing windows, using a constant powder feed rate. After that, samples with optimal process parameters were manufactured to determine the influence of deposition strategy and aging heat treatments on structural and mechanical properties (i.e., macrohardness). Results indicated the influence of crucial process parameters (i.e., laser power, velocity, and laser spot size) on the track's geometrical characteristics. The processing windows also revealed that particular combinations of these parameters' values produced LC tracks with the minimum dilution with either maximum height or maximum width, which is desirable for manufacturing and repair applications. Although the as-built samples did not show significant differences in their hardness, they showed a considerable difference in their austenitic phase content due to a combined effect between the sample's geometry and deposition pattern. Aging heat treatments between 460 and 490 °C (4–8 h) resulted in the maximum hardness value (~55HCR) with an austenite content below 6 wt% calculated by Rietveld analysis. Finally, SEM and EDS analysis were carried out; it was found that the austenite located in the boundaries of the solidification structures is rich in Mo, Ti, and Ni for the samples in the as-built condition, while for the samples with aging, the highest content of austenite rich in Ni and Mo was obtained with aging at 530 °C. [ABSTRACT FROM AUTHOR]

METALLIC wire, GAS metal arc welding, WIRE, RAPID prototyping, and ULTRAMICROELECTRODES

Wire arc additive manufacturing (WAAM) is well suited for the manufacture of sizeable metallic workpieces featuring medium-to-high geometrical complexity due to its high deposition rate, low processing conditions limit, and environmental friendliness. To enhance the current capability of the WAAM process for fabricating structures with complex geometry, this paper proposes a robot-based WAAM strategy adapted specifically for fabricating freeform parts with wire structures composed of multiple struts. Contributions in this work include: (i) The study of bead modelling, which establishes optimal welding parameter selection for the process; (ii) the novel manufacturing strategy, including the adaptive slicing methodology and height control system for accurately depositing every single strut; and (iii) detailed manufacturing procedures for multi-strut branch intersections as well as the collision-free path planning to control the overall fabrication process. To verify the effectiveness of this proposed WAAM approach, two complex wire structures were fabricated successfully, indicating the feasibility of the proposed fabrication strategy. [ABSTRACT FROM AUTHOR]

FUSED deposition modeling, RAPID prototyping, EXTRUSION process, RAPID tooling, MANUFACTURING processes, and FINITE element method

Additive manufacturing has evolved from a rapid prototyping tool to a set of manufacturing processes for functional parts. One of their most outstanding features is the ability to build complex geometry parts. However, their industrial application is limited because these parts exhibit heterogeneous and porous micro/mesostructures with anisotropic behavior. These structural characteristics, mainly porosity, are strongly related to the building parameters. In this work, a computational multiscale homogenization approach was implemented to determine the mechanical properties of unidirectional and criss-cross mesostructures generated by a material extrusion process (MEP). Representative volume elements (RVE) for simplified and real-like pore geometries were created to model the mesostructures and to perform the multiscale analysis. Stiffness tensor for each RVE was obtained and graphically represented to observe the mechanical properties as a function of the orientation. A great influence of the pore geometry on mechanical properties was observed. Finally, by comparing with experimental data, the results obtained were validated. [ABSTRACT FROM AUTHOR]

DRAWING (Metalwork), SHEET metal, MASS production, METALWORK, RAPID prototyping, and SHEET metal work

Due to the change from mass production to mass personalized production and the resulting intrinsic product flexibility, the automotive industry, among others, is looking for cost-efficient and resource-saving production methods to combining global just-in-time production. In addition to geometric manufacturing flexibility, additive manufacturing offers a resource-saving application for rapid prototyping and small series in predevelopment. In this study, the FDM process is utilized to manufacture the tooling to draw a small series of sheet metal parts in combination with the rubber pad forming process. Therefore, a variety of common AM polymer materials (PETG, PLA, and ABS) is compared in compression tests, from which PLA is selected to be applied as sheet metal forming die. For the rubber pad forming process, relevant processing parameters, i.e., press force and rubber cushion hardness, are studied with respect to forming depth. The product batch is examined by optical evaluation using a metrological system. The scans of the tool and sheet metal parts confirm the mechanical integrity of the additively manufactured die from polymer and thus the suitability of this approach for small series in sheet metal drawing processes, e.g., for automotive applications. [ABSTRACT FROM AUTHOR]

FUNCTIONALLY gradient materials, FINITE element method, MATHEMATICAL optimization, FOAM, PHENOMENOLOGICAL biology, and STRUCTURAL optimization

Weight reduction is one of the main concerns when designing any component as it reduces material cost and green house gas emissions, among other aspects. Several numerical approaches exist in the literature with the objective of having any component with known mechanical loading become optimized in terms of mass minimization and stiffness maximization. Thus, the objective of this work is the development of optimized structures maintaining the same geometry by means of cellular materials, namely the gyroid infill, and generating functionally graded cellular structures with higher stiffness-to-weight ratio. Remodelling algorithms based on biological phenomena, namely bone growth, as well as Bi-evolutionary structural optimization (BESO) were employed to obtain the density map allowing the material functional gradient distribution. Smoothing functions were tested as a possibility of enhancing stiffness as abrupt density changes are avoided. The gyroid infill was characterized in order to create a phenomenological law based on bone remodelling laws. The gyroid law was implemented on the analysis FEMAS (opens-source, academic and educational FEM and meshless method software) software which presented the density map as an output. Each gradient consisted on areas at a similar density being concatenated into one solid. The different solids, at different density levels, are assembled thus creating the material functional gradient. Lastly, simulations consisted on three distinct and benchmark flexural load cases. Specimens were printed using FFF technology in PLA (E = 3145 MPa, ν = 0.3) having then been tested experimentally according to the appropriate load case. Numerical results correlated with the experimental results in terms of accuracy between theoretical and experimental stiffness where there was a greater accuracy for the specimens subject to a Four-Point bending load case, where only a 16% gap was verified between numerical and experimental flexural stiffness. [ABSTRACT FROM AUTHOR]

INDUSTRY 4.0, CONCURRENT engineering, MANUFACTURING processes, FACTORIES, VIRTUAL prototypes, SHARED workspaces, and OFFSHORE wind power plants

Smart manufacturing, tailored by the 4th industrial revolution and forces like innovation, competition, and changing demands, lies behind the concurrent evolution (also known as co-evolution) of products, processes and production systems. Manufacturing companies need to adapt to ever-changing environments by simultaneously reforming and regenerating their product, process, and system models as well as goals and strategies to stay competitive. However, the ever-increasing complexity and ever-shortening lifecycles of product, process and system domains challenge manufacturing organization's conventional approaches to analysing and formalizing models and processes as well as management, maintenance and simulation of product and system life cycles. The digital twin-based virtual factory (VF) concept, as an integrated simulation model of a factory including its subsystems, is promising for supporting manufacturing organizations in adapting to dynamic and complex environments. In this paper, we present the demonstration and evaluation of previously introduced digital twin-based VF concept to support modelling, simulation and evaluation of complex manufacturing systems while employing multi-user collaborative virtual reality (VR) learning/training scenarios. The concept is demonstrated and evaluated using two different wind turbine manufacturing cases, including a wind blade manufacturing plant and a nacelle assembly line. Thirteen industry experts who have diverse backgrounds and expertise were interviewed after their participation in a demonstration. We present the experts' discussions and arguments to evaluate the DT-based VF concept based on four dimensions, namely, dynamic, open, cognitive, and holistic systems. The semi-structured conversational interview results show that the DT-based VF stands out by having the potential to support concurrent engineering by virtual collaboration. Moreover, DT-based VF is promising for decreasing physical builds and saving time by virtual prototyping (VP). [ABSTRACT FROM AUTHOR]

RAPID prototyping, RAPID tooling, TOOL-steel, and MECHANICAL properties of condensed matter

Hybrid moulds are an increasingly considered alternative for prototype series or short production runs. This type of tools resorts on the use of Rapid Prototyping and Tooling (RPT) to produce the moulding elements (blocks or other inserts). This study was developed using a hybrid injection mould with exchangeable moulding elements that were produced by additive manufacturing (AM), namely vacuum epoxy casting, stereolithography and ProMetal. A full steel tool was also used as a reference. The processing conditions for the polypropylene moulded parts using the hybrid mould were monitored for pressure, temperature and ejection force. The hybrid mould performance was assessed in terms of pressure and temperature evolution during the injection cycle and the AM moulding elements for physical integrity. The data from the polypropylene moulded parts and the moulding inserts are compared with structural and rheological simulations using ANSYS Workbench and MOLDEX 3D. The results show that the hybrid mould performance and the structural integrity of the moulding elements depend on the properties of the materials used. The moulding shrinkage, when resin cores are used, is also affected by the core deformation caused by the injection pressure. [ABSTRACT FROM AUTHOR]

RAPID prototyping, JEWELRY industry, PARAMETRIC modeling, 3-D printers, CASE studies, and STEREOLITHOGRAPHY

The new research and technologies that have ensured the digitalization of industries and the introduction of smart manufacturing are still characterized by poorly studied processes. In particular, communication and integration between different platforms, which form the ecosystem of smart manufacturing, are subject to various communication problems. The research conducted and propounded in this article is based on the implementation of an integrated manufacturing system that involves parametric modeling, optimization, and additive manufacturing. The ecosystem analyzed guarantees communication between IT platforms such as Rhino-Grasshopper, for parametric modeling, and PreForm, slicing software for Formlab's stereolithographic 3D printers. For this purpose, C# scripts have been implemented in order to solve optimization problems in 3D modeling of objects and to guarantee integration between the two platforms. The latter script is configured as a real add-in for Rhino whose advantages are easily demonstrated thanks to the large number of recursive operations that are automated. [ABSTRACT FROM AUTHOR]

INTERSECTION numbers, ALGORITHMS, TOPOLOGY, TRIANGLES, COMPUTATIONAL geometry, and INTERSECTION graph theory

To date, slicing algorithms for additive manufacturing is the most effective for favourable triangular mesh topologies; worst-case models, where a large percentage of triangles intersect each slice plane, take significantly longer to slice than a like-for-like file. In larger files, this results in a significant slicing duration, when models are both worst cases and contain more than 100,000 triangles. The research presented here introduces a slicing algorithm which can slice worst-case large models effectively. A new algorithm is implemented utilising an efficient contour construction method, with further adaptations, which make the algorithm suitable for all model topologies. Edge matching, which is an advanced sorting method, decreases the number of sorts per edge from n total number of intersections to two, alongside additional micro-optimisations that deliver the enhanced efficient contour construction algorithm. The algorithm was able to slice a worst-case model of 2.5 million triangles in the 1025s. Maximum improvement was measured as 9400% over the standard efficient contour construction method. Improvements were also observed in all parts in excess of 1000 triangles. The slicing algorithm presented offers novel methods that address the failings of other algorithms described in literature to slice worst-case models effectively. [ABSTRACT FROM AUTHOR]

3-D printers, POLYLACTIC acid, DIGITAL image correlation, MODULUS of rigidity, MANUFACTURING processes, and YOUNG'S modulus

3D printing by fused filament fabrication (FFF) provides an innovative manufacturing method for complex geometry components. Since FFF is a layered manufacturing process, effects of process parameters are of concern when plastic materials such as polylactic acid (PLA), polystyrene and nylon are used. This study explores how the process parameters, e.g. build orientation and infill pattern/density, affect the mechanical response of PLA samples produced using FFF. Digital image correlation (DIC) was employed to get full-field surface-strain measurements. The results show the influence of build orientation and infill density is significant. For on-edge orientation, the tensile strength and Young's modulus were 55 MPa and 3.5 GPa respectively, which were about 91% and 40% less for the upright orientation, demonstrating a significant anisotropy. The tensile strength and Young's modulus increased with increasing infill density. In contrast, different infill patterns have no significant effect. Considering the influence of build orientation, based on the experimental results, a constitutive model derived from the laminate plate theory was employed. The material parameters were determined by tensile tests. Results demonstrated a reasonable agreement between the experimental data and the predictive model. Similar anisotropy to tension was observed in shear tests; shear modulus and shear strength for 45° flat orientation were about 1.55 GPa and 36 MPa, whereas for upright specimens they were about 0.95 GPa and 18 MPa, respectively. The findings provide a framework for systematic mechanical characterisation of 3D-printed polymers and potential ways of choosing process parameters to maximise performance for a given design. [ABSTRACT FROM AUTHOR]

ROBOTICS, TACTILE sensors, OPTICAL fiber detectors, FIBER Bragg gratings, MANUFACTURING processes, OPTICAL gratings, and ARTIFICIAL skin

Modern industrial processes aim for the continuous production of small volumes tailored to the customer's needs. Machines and robotic platforms have to be more and more adaptable, flexible, and able to cope with complex scenarios where sensing and manipulation capabilities are the key technology to succeed. The literature has plenty of capacitive, resistive, piezoelectric, and piezoresistive sensors used as tactile or force sensors. All of them present some drawbacks like non-linear behavior, sensitivity to temperature or electromagnetic noise, and hysteresis, among others. Other sensing systems are bulky and hard to integrate, sometimes jeopardizing the dexterity and manipulability of the gripper. In this context, the manuscript proposes fiber Bragg grating (FBG) optical fiber as a tactile sensing element to capture the interaction forces during material handling and object manipulation since it has numerous advantages compared with the other sensing devices. The work also offers a methodology to easily integrate the fiber in industrial grippers and introduces a set of tests useful to characterize the sensors. Custom gripper fingers have been realized in rapid prototyping to present a pictorial example of such an integration. Finally, the essay presents some experiments that assess the capability of a tactile sensor based on FBG optical fiber showing as it can correctly perceive the contact forces (NRMSE = 0.75%) and can recognize the material of the object that is being manipulated. The authors believe that the application of optical fiber sensor as tactile feedback can be useful in industrial scenarios to enable complex manipulation activities. [ABSTRACT FROM AUTHOR]

CLOSED loop systems, RAPID prototyping, and MANUFACTURING processes

Additive manufacturing encompasses a set of low-cost and highly versatile tools used to prototype and fabricate three-dimensional (3D) objects with ease. In most of the additive manufacturing techniques, materials are deposited layer by layer until a 3D object is reproduced. Several additive manufacturing techniques have been developed in the previous decade, and the application of additive manufacturing has increased in various industrial sectors. However, there are still drawbacks associated with additive manufacturing techniques, necessitating further study and development. In this study, we review the techniques and materials used in additive manufacturing. The vast majority of additive manufacturing processes are still based on open-loop control or implement some local controllers for specific variables (such as temperature), making them susceptible for errors. This study presents a review of the different additive manufacturing techniques, examples of academic and commercial efforts to improve the control systems for additive manufacturing, as well as the application of additive manufacturing in different fields such as aerospace, electronics, arts, and biomedical. The article ends highlighting the advantages of utilizing a closed-loop control system in additive manufacturing and discussing the work needed for further development. [ABSTRACT FROM AUTHOR]

RAPID prototyping, INVESTMENT casting, ELECTRIC metal-cutting, MANUFACTURING processes, ELECTRODES, FEASIBILITY studies, MACHINING, and FABRICATION (Manufacturing)

This study fabricates a roughing electrode of electrical discharge machining (EDM) using a rapid prototyping (RP) system and investment casting technology, which reduces the overall time that is required for fabrication and the cost of the manufacturing process for a selected electrode. Pro/E (3D CAD) software is used to design the electrode prototype, which has a complex appearance, and to transform the CAD model into stereolithography (STL) format. An RP machine (Zcorp 402 3DP) is used to construct a gypsum-based powder model. After a sealing process using the permeation of resin, the water resistance and strength of the gypsum-based material are increased. The manufacturing process then involves creating a wax model with a gypsum electrode that is strengthened by resin permeation by casting a vulcanized silicone molding. The brass electrode is fabricated using investment casting technology. The results of an EDM test show that the brass electrodes with RP that are manufactured perform well and the total time that is required to machine the EDM electrode using RP is 15.8% less than the time that is required for a CNC machining process. [ABSTRACT FROM AUTHOR]

SHOE design, EXPERIMENTAL design, HEEL (Anatomy), NEW product development, REVERSE engineering, MANUFACTURING processes, NANOFABRICATION, and FOOT orthoses

Digital techniques are a strategic tool to design new commercial products, reducing time and waste. This is particularly relevant for shoe manufacturing and, in particular, for high-heeled shoes, for which a trade-off between comfort and attractiveness is difficult to achieve. This paper offers a new set of tools to design high-heeled shoes that exploits the synergies between modeling and experiments, aiming at predicting the comfort of such products, improving the manufacturing process by optimizing the design step. As a case study, two actual commercial 11-cm-heel shoe models, differentiated by the openness of the front side, were used to deploy the digital design procedure. A finite-element model was implemented by combining the outcomes from reverse engineering techniques, to reconstruct the foot and shoe topologies, and the experimental characterization of the materials used for the final shoe products. Pressure maps on the toes and the footbed were used as benchmarks for a comparison with experiments, made with commercial sensorized insoles. Non-uniform pressures for both shoe models were observed, with highest values for the closed-shaped specimen that presented peaks of ≈ 160 kPa on the footbed and ≈ 140 kPa on the external toes. The here presented digital approach has the potential to improve the design process that will not require the traditional fabrication of countless handicraft prototypes, saving time and the associated prototyping costs. Finally, although this work focused on a niche of the shoe market, this approach may be extended to other products, which customization has a key role in the manufacturing process. [ABSTRACT FROM AUTHOR]

FOCUSED ion beams, OPTICAL glass, MATERIALS science, RAPID prototyping, SEMICONDUCTOR materials, and OPTICAL fibers

Focused ion beam (FIB) milling is widely used in fields such as the semiconductor industry and materials science research. The direct writing and small feature size also make FIB milling attractive for rapid prototyping of novel photonic structures. In this manuscript, we describe in detail a FIB milling procedure which enables high-resolution fabrication of complex micro- and nanostructures with precise geometry control. Two different procedures (for 2D and 3D structures) are described and implemented on the tip of a glass optical fiber for fabricating diverse structures embedded on or below the tip surface. The procedures described here can be easily adjusted and implemented on any conductive or non-conductive substrate. [ABSTRACT FROM AUTHOR]

MANUFACTURING processes, LASER beams, LASERS, POWDERS, and BULK solids

Laser powder–based directed energy deposition (DED) is a specific additive manufacturing process that offers an effective way to fabricate parts via simultaneous delivery of powders and laser beam. It has been developing greatly in the recent decades and being widely used for manufacturing, prototyping, and repairing. Complex physical events take place during the manufacturing process and have great impacts on its overall performance. To build high-quality parts through the laser powder–based DED process, its physical insights and process parameters need to be understood and optimized, for which modeling provides an efficient way. This article gives a review of the modeling work for the laser powder–based DED process, in which the models developed for powder stream and its interaction with laser beam, melt-pool, and bulk heating are discussed in detail. Different modeling approaches and methods towards overall and specific physical processes of the laser powder–based DED are analyzed and compared. Suggestions towards the modeling are also given at the end. [ABSTRACT FROM AUTHOR]

MACHINING, MANUFACTURED products, COST control, CONSTRUCTION materials, PRODUCT costing, and ELECTROCHEMICAL cutting

In this competitive world, industries are looking for smart technologies to compete; these technologies help R&D people to explicit the ideas and bring the product to the market at shorter lead times and with affordable cost. Each AM machine has its own unique capabilities in manufacturing a product, utilising materials, material intake and wastages. Machine and material costs are the significant parameters, which play a major role in cost estimation of the prototypes. Costs of both machine and materials are prime factors in AM and it can be helpful for cost reduction due to their uniqueness. However, an alternate strategy is being concentrated on process optimization and consumption of material to reduce the overall cost of the prototype. In this paper, multi criterion decision making (MCDM) technique, namely, best-worst method (BWM), was adopted to select the suitable material for the product. This is along with the end user expectations in AM. In the initial phase, the suitable machine to be selected from the available machines is based on the parameters like cost, accuracy, variety of materials and material wastage. From the variety of materials, the suitable material was selected based on the respondent requirement. The criteria that influenced more in the overall cost of the product manufacture through AM is identified and used. According to BWM, the criteria to be selected by the decision maker based on the respondent expectations are identified. In BWM method, pairwise comparisons are carried out between the best and worst criterion suggested by the decision makers, as that it leads to the selection of the suitable material. Here, a demonstration of such a selection is detailed; this is certainly based on the respondent requirements. The result attained through the proposed methodology can be varied based upon the respondent requirements and further machine availabilities. In conclusion, the end result helps to identify the suitable machine and build materials for the prototype to be produced based on the respondent requirements. [ABSTRACT FROM AUTHOR]

ELECTRIC metal-cutting, LASER sintering, SELECTIVE laser sintering, METALLIC composites, OPEN-circuit voltage, COPPER electrodes, WORKPIECES, and X-ray spectrometers

Nowadays, additive manufacturing (AM)-based rapid prototyping (RP) is used as a convenient route for making tool electrodes required in electrical discharge machining (EDM). AM enables direct fabrication of complex shaped EDM electrode in comparatively less time in contrast to subtractive machining processes. In this study, an EDM electrode is prepared directly by selective laser sintering (SLS) process using metal matrix composite of aluminium (Al), silicon (Si) and magnesium (Mg). To study the performance of the prepared RP tool electrode in electrical discharge machining, titanium is used as workpiece material and EDM-30 oil as dielectric medium during machining. The performance of the prepared tool electrode is compared with conventional copper and graphite tool electrodes. Experiments have been conducted changing EDM process parameters viz. open circuit voltage (V), peak current (Ip), duty cycle (τ) and pulse duration (Ton) along with three tool electrodes such as RP, graphite and copper tool electrodes. The performance measures considered during the experimental study are material removal rate (MRR), tool wear rate (TWR), average surface roughness (Ra), white layer thickness (WLT), surface crack density (SCD) and micro-hardness (MH) on white layer. SEM and EDX of the machined surface reveal that tool material is generally eroded and deposited on the machined surface with formation of metal carbides. However, tool erosion is more pronounced in case of RP tool electrode. XRD analysis reveals the formation of titanium carbides on the machined surface resulting in increase in the micro-hardness of white layer. Discharge current and tool type are found to be significant parameters influencing the performance measures considered in the study. The surface produced when machined with RP tool electrode exhibits superior surface characteristics while graphite tool electrode produces better MRR and TWR. [ABSTRACT FROM AUTHOR]

RAPID prototyping, MANUFACTURING processes, FUSED deposition modeling, RESIDUAL stresses, and BOX-Jenkins forecasting

This paper proposes a novel data-driven approach for predicting and optimizing the additive manufacturing process parameters. The integrated scheme consists of three popular algorithms: (1) group method for data handling (GMDH) as the engine of neural networks, (2) autoregressive integrated moving average (ARIMA) for characterizing spatial collinearity of the multiple response, and (3) indirect optimization on the basis of self-organization (IOSO) to adopt the emerged correlated multi-response optimization problem. As a numerical case study, a computer-generated fused deposition modeling data tested the introduced algorithms. The finite element (FE) simulation model consists the multi-layer residual stresses as targets, in respect of printing speeds as process parameters. The residual stresses predicted by the low-order integrated ARIMA-GMDH variants correlate well with the FE simulations. This approach provides a viable data-driven alternative for computationally based rapid prototyping and additive manufacturing processes. [ABSTRACT FROM AUTHOR]

THREE-dimensional printing, RAPID prototyping, PRINTING, and BEHAVIOR

Although 3D printing was invented in 1984, it was not until recent years that it captured the imagination of everyone from industry experts to at-home hobbyists. Three-dimensional printing, also known as additive manufacturing or rapid prototyping, constructs an object by accumulating materials layer by layer. In recent years, 3D printing technology has been dramatically developed with respect to materials, printer, and process, which laid a foundation for 4D printing. Four-dimensional printing is the targeted evolution of the 3D-printed structure, concerning shape, property, and functionality. The object is produced by 3D printing firstly. Then, the object can self-deform, self-assemble, self-disassemble, self-repair, and change property or functionality over time when the external stimuli are imposed on it. This review mainly introduces the stimulus, types of shape-shifting behaviors, mechanisms of deformation, and applications of 4D printing. [ABSTRACT FROM AUTHOR]

SHAPE memory alloys, SHAPE memory effect, PREDICTION models, ARTIFICIAL neural networks, and LASERS

Shape memory alloys (SMAs) have been applied for various applications in the fields of aerospace, automotive, and medical. Nickel-titanium (NiTi) is the most well-known alloy among the others due to its outstanding functional characteristics including superelasticity (SE) and shape memory effect (SME). These particular properties are the result of the reversible martensite-to-austenite and austenite-to-martensite transformations. In recent years, additive manufacturing (AM) has provided a great opportunity for fabricating NiTi products with complex shapes. Many researchers have been investigating the AM process to set the optimal operational parameters, which can significantly affect the properties of the end-products. Indeed, the functional and mechanical behavior of printed NiTi parts can be tailored by controlling laser power, laser scan speed, and hatch spacing having them a crucial role in properties of 3D-printed parts. In particular, the effect of the input parameters can significantly alter the mechanical properties such as strain recovery rates and the transformation temperatures; therefore, using suitable parameter combination is of paramount importance. In this framework, the present study develops a prediction model based on artificial neural network (ANN) to generate a nonlinear map between inputs and outputs of the AM process. Accordingly, a prototyping tool for the AM process, also useful for dealing with the settings of the optimal operational parameters, will be built, tested, and validated. [ABSTRACT FROM AUTHOR]

THREE-dimensional printing, THREE-dimensional display systems, LITHOGRAPHY, INDUSTRIAL marketing, SURFACE finishing, AIRCRAFT industry, and AEROACOUSTICS

Stereolithography (SLA)-based three-dimensional (3D) printing is widely used in both industrial and consumer markets for prototyping and concept validation. It also plays an important role in aircraft industry as it offers advantages in surface finish and high precision. Despite the extensive usage, the combination of large volume, high resolution, and high speed is hard to achieve. This paper presents a 3D printing technology that allows a UV projector to continuously cure resin while scanning over the build area. To print large objects, 3D models are sliced into layer-by-layer, high-resolution image "maps". Each "map" is further divided into sub-region images that are dynamically exposed to the photocurable materials and synchronized with the scanning of the projector, causing a still exposure pattern to appear on the build area. Therefore, large objects with delicate details can be printed layer-by-layer. As such, customized build volumes on a large scale (greater than 1 m3) can be achieved with micro-scale features. Along with a wiping system, this technique is compatible with various materials, leading to the direct manufacturing of final parts from photocurable materials. Furthermore, this technique shows advantages over existing large-scale DLP printing methods regarding both printing speed and material flexural properties. This technique can be implemented at design workflow in the aerospacing industry by facilitating design communication, validation, pre-production, and even assisting in producing final parts. [ABSTRACT FROM AUTHOR]

VIRTUAL reality, COMPUTER-aided design, SOFTWARE development tools, COLLISIONS (Physics), FEATURE extraction, and INDUSTRY 4.0

Assembly validation is a key part of product design. Current methods, such as physical prototyping are time-consuming and do not offer immediate validation results. Assembly motion simulation systems have been proposed as a solution to this problem. However, widespread adoption of such systems is hindered due to their ties to proprietary computer aided design (CAD) software or expensive and often cumbersome hardware. Recently, virtual/augmented reality (VR/AR) technologies and simulation have been heralded as two of the key enabling factors of Industry 4.0. Collective interests in these technologies by industry and community have brought many low-cost software and hardware tools to the market, which opens a gateway to achieving assembly validation at a much lower cost. This paper presents an assembly validation system that is independent of CAD packages, interoperable and implemented using relatively low-cost and commercially available hardware and software tools. The system features intuitive bare-hand manipulation of part models through a virtual hand model that tracks the hands. Collision detection and physics modelling allow for hand-part and part-part interactions to be natural, thus validating assembly interactions. An assembly feature extraction algorithm has also been implemented to analyse the planar face features of the part models to detect possible mating assembly features between parts concerned. A constraint management system considers identified mating features and determines the allowable motion of parts once constraints are applied and removed. Pulling force is used to facilitate the removal of constraints. [ABSTRACT FROM AUTHOR]

MANUFACTURING processes, LABOR costs, INDUSTRY 4.0, VIRTUAL reality, COST accounting, VIRTUAL reality software, and MIXED reality

Digital manufacturing concept is gaining a lot of attention and popularity due to its enormous benefits. It is considered as one of the pillars or component of Industry 4.0. With the advancements in technology, digital manufacturing is becoming a reality rather than a concept only. It is applied to various stages of the manufacturing process such as design, prototyping, and assembly training. Virtual reality (VR) is a cog in a wheel of digital manufacturing. It can be used in various phases of manufacturing. Planning and conducting assembly operations account for the majority of the cost of a product. It is difficult to design and train assembly operations during the early stages of product design. Assembly is a vital step in manufacturing, so firms provide training to their employees and it costs them time and money. Therefore, this research work extends VR applications in manufacturing by integrating concepts and studies from training simulations to the evaluation of assembly training effectiveness and transfer of training. VR provides a platform for "learning by doing" instead of learning by seeing, listening, or observing. A series of user-based evaluation studies are conducted to ensure that the virtual manufacturing assembly simulation provides an effective and efficient means for evaluating assembly operations and for training assembly personnel. Different feedback cues of VR are implemented to evaluate the system. Moreover, several case studies are used to assess the effectiveness of VR-based training. The results of the study reveal that participants trained by VR committed fewer errors and took lesser time in actual product assembly when compared against the participant from traditional or baseline training group. [ABSTRACT FROM AUTHOR]

INDUSTRIAL robots, MANUFACTURING processes, REINFORCEMENT learning, MULTISENSOR data fusion, RAPID prototyping, INDUSTRY 4.0, and ROBOTS

In recent years, the applications of industrial robots are expanding rapidly due to Industry 4.0 oriented evolutions, ranging from automobile industry to almost all manufacturing domains. As demands with rapid product iterations become increasingly fluctuant and customized, the assembly process of industrial robots faces new challenges including dynamic reorganization and reconfiguration, ubiquitous sensing, and communication with time constraints, etc. This paper studies the industrial robot assembly process modeling, planning, and scheduling based on real-time data acquisition and fusion under the framework of advanced shop-floor communication and computing technologies such as wireless sensor, actuator network, and edge computing. Taking the assembly of industrial robots as the specific object, the multi-agent model of industrial robot assemble process is established. Then, the encapsulation, communication, and interaction of agents with real-time data acquisition and fusion are studied. Based on multi-agent reinforcement learning approach, an intelligent planning and scheduling algorithm for industrial robot assembly is proposed, and a simulation case is presented to demonstrate the proposed model and algorithm. [ABSTRACT FROM AUTHOR]

ELASTOMERS, THERMOPLASTICS, THERMOPLASTIC composites, POLYETHYLENE terephthalate, FRACTOGRAPHY, ULTIMATE strength, and POLYMERS

Due to the layer-by-layer nature of additive manufacturing, fabricated parts suffer from an anisotropic behavior with reduced mechanical performance when compared to traditional manufacturing. One specific mechanical property, folding endurance, requires both low flexural strength and simultaneously high elongation to achieve the flexibility needed to sustain repetitive bending. The present work provides an analysis of selected thermoplastics' flexural capacity, including nylon (PA), polyethylene terephthalate (PETG), polylactide (PLA), thermoplastic polyurethane (TPU), polypropylene (PP), polyethylene (PE), and a TPR blend (ABSMG94: SEBS-g-MA 25:75), in order to evaluate the maximum number of folding cycles and load capacity sustained by a living hinge. A fractographic analysis was performed using scanning electron microscopy and computed tomography. Similar to the performance of injected molded products, the experimental results demonstrated that three of the tested materials behaved well in the context of a large number of folding cycles prior to an eventual detachment into two pieces; TPR blend, 244,424 cycles; PP endured one million cycles; and TPU, more than two million cycles, while the remaining materials failed to survive more than 1000 cycles. The hinges failure analysis revealed a wide variety of fracture morphologies and failure modes. In regard to the load capacity, PLA, PETG, and nylon provided the highest results in the ultimate strength of an axial static force applied (790.61 N, 656.06 N, and 652.75 N respectively), while the TPR blend was the highest (398.44 N) of the elastomeric materials (PP, TPU, and TPR blend). The evaluated materials demonstrated enough flexibility for use in specific applications such as stretchable electronics and wearable applications. [ABSTRACT FROM AUTHOR]

FOIL stamping, BORON steel, SCANNING electron microscopes, LOW temperatures, HARDNESS testing, and TENSILE tests

This paper demonstrates the promise of a new low-temperature hot stamping process with pre-cooling for 22MnB5 boron steels. It is the first time for the new process being successfully implemented for producing an automotive demonstrator component assisted with thorough experimental studies. The studies mainly include hot forming experiments carried out on an industrial prototyping line, post-form examinations, and in-die quenching tests. Automotive B-Pillar components with two designed drawing depths (50 and 64 mm) were hot stamped at a wide range of temperatures and forming speeds, through both the conventional hot stamping processes and the new processes with pre-cooling applied. For the as-formed B-Pillars, 3D shape scanning was conducted to investigate the thickness distribution of the components; uniaxial tensile testing, hardness testing, and scanning electron microscopes (SEM) observation were conducted to assess the final mechanical properties and microstructures. To understand the benefit of the low-temperature hot stamping in reducing cycle time, a separate set of in-die quenching experiments were designed and carried out, with combinations of three different process parameters: workpiece start quenching temperature, initial tool temperature, and die-workpiece contact pressure. The results of this work confirmed that low-temperature hot stamping could be performed successfully in producing complex-shaped components, such as automotive B-Pillars, with much reduced cycle time. [ABSTRACT FROM AUTHOR]

AUGMENTED reality, INDUSTRY 4.0, OPTICAL head-mounted displays, GAS industry, and MANUFACTURING processes

Augmented Reality (AR) is one of the nine key technologies of Industry 4.0 and one of the most promising innovation accelerators that in the next years will bring smart factories to a higher level of efficiency. In this context, the paper presents an AR tool that improves and increases the efficiency of data collection and exchange of information among different professional figures involved in the design and production processes of products for the oil and gas sector. In fact, prototyping and labour-intensive activities usually require modifications and improvements to be made on-site that should be sent as feedback to the technical office. To this end, the proposed AR tool supports workers at the workplace to easily detect and annotate design variations made during their working activities and furthermore to formalize and automate the collecting and transferring of this data to the designers in order to prevent loss of information. Field experimentation has been carried out with end-users to evaluate their acceptance by means usability studies, based on objective and subjective metrics, and personal interviews. Experimental results show that the proposed AR tool provides medium-to-high levels of usability and has been positively accepted by all the participants involved in the study. [ABSTRACT FROM AUTHOR]

WAGES, MACHINE tools, DIAMOND turning, RAPID prototyping, OPTICS, MACHINING, and HYPERSPECTRAL imaging systems

Advancements in diamond turning technology with tool servo configurations enables the generation of precise freeform surfaces. However, the profile accuracy is mainly limited due to non-availability of an efficient tool path compensation techniques and precise alignment methods. The aim of this study is focused on developing a tool path compensation routine for slow tool servo machining of freeform optics. A seven-order polynomial freeform surface, designed for hyperspectral imaging is selected for experimentation. Alignment strategy by utilizing the available fiducials is presented to ensure the precise re-mounting of surface during machining and metrology. The contact type profilometer is used to measure the fabricated surface by taking 25 numbers of two-dimensional raster scans at an interval of 0.5 mm. The scans are then stitched to get the 3D surface measurement. The residual form error map is used to compensate the tool path. Significant reduction in form error, i.e., from peak to valley (PV) of 9.27 to 0.75 μm with surface finish (Ra) of 11.82 nm, is achieved by performing four machining iterations of compensation. The simulation studies are also presented to investigate the effects of various misalignments on manufacturing accuracies. The developed compensation process is effective for fast convergence of form error and to manufacture the precise freeform optics for various imaging and non-imaging applications. [ABSTRACT FROM AUTHOR]

3-D printers, THREE-dimensional printing, MANUFACTURING processes, EXTRUSION process, PRINT materials, and RAPID prototyping

Since the advent of 3D printing in the mid-1980s, additive manufacturing has grown steadily and found numerous applications across all types of industries. More recently, the industry has seen a spur of growth as the terms of the original patents expired and new companies entered the market. While there exist several different methods of additive manufacturing, polymer-based material extrusion 3D printing (also known as fused filament fabrication) has become one of the most widely used ones due to its lower cost, ease of use, and versatility. While development has greatly expanded the material availability and improved the quality of prints, material extrusion 3D printers have often faced a challenge in physical scaling. There are inherent design hurdles to the extrusion process when the print starts to grow larger. This paper aims to study the market landscape of extrusion-based 3D printing technology for polymer-based material as well as challenges faced in upscaling this technology for industrial applications. A prototype large-scale material extrusion 3D printer has been designed, constructed, and then tested to gain experimental data on large-scale 3D printing using thermoplastic polymers as a printing material. Results of testing and experimentation verified certain key design elements and how they can improve large-scale 3D printing. Testing also revealed how large diameter nozzles for the hot end introduce challenges not seen in small-scale 3D printers. This paper also seeks to consolidate available information pertaining to large-scale 3D printing into one comprehensive document. [ABSTRACT FROM AUTHOR]

STAINLESS steel, IRON & steel plates, LASERS, LASER beams, and RAPID prototyping

Laser forming is an innovative technique that uses a defocused laser beam to form sheet metal by thermal stresses rather than external forces. This offers excellent and promising potential applications in rapid prototyping, straightening, aligning, and adjusting of macro/micrometallic components. However, the undesirable edge effects in laser forming reflect that the bending angle is not constant along the scanning line. This paper presents an analytical study of edge effects in laser bending of AISI 304 stainless steel plate. Experimental and numerical investigations aimed at understanding the effects of the triangular beam geometry with different aspect ratios were clearly demonstrated. A validated thermal model was developed, and different sets of FE simulations were carried out by varying heat input values and aspect ratio of laser beam with constant scanning speed. It is evident that triangular beam with highest aspect ratio was preferable to produce a higher bending angle with lesser edge effect at higher power intensity. It is found that triangular beam geometries are more effective in minimizing the bending angle variation compared with the circular beam. [ABSTRACT FROM AUTHOR]

VIBRATION tests, AUTOMOBILE supply stores, AIRPLANE testing, COST analysis, ERROR analysis in mathematics, and MANUFACTURING industries

Single-point incremental forming has potential applications in prototyping and custom part manufacture for a range of industries including automotive and aerospace. For components with vertical walls, multiple passes are required to achieve a reasonable residual strain distribution and to accommodate large material strains without failure. In this paper, various multistage strategies were evaluated experimentally, and a complex C-channel fixture designed for aircraft vibration testing was successfully manufactured. Design guidelines for flat-base geometries are provided along with the rules for high-quality toolpath generation. A separate set of experiments was conducted comparing hemispherical and flat tools, and a flat tool was selected as being the most suitable for flat-base parts. The typical thickness variation developed in components and a geometrical error analysis are also presented. The response of the developed component to annealing and effect of this process on final geometrical errors are also reported. Cost analyses from design to development stage of the component are also presented. This work will be of practical interest to anyone seeking to bridge the gap between prototyping and large-scale production for complex flat-bottomed part geometries with single-point incremental forming. [ABSTRACT FROM AUTHOR]

HYDROSTATIC stress, RAPID prototyping, TECHNOLOGY, SURFACE roughness, AGRICULTURAL technology, and COMMERCIAL product testing

This study proposed and evaluated a highly precise method employing various diameters and shapes of punch to manufacture right-angled square-bodied products. In this method, a trough is not only engraved on the die but also designed into the punch. Five diameters and shapes of the punch were collocated with a circular trough around the square shape of a die cavity. In the tests, a ram descended to a fixed level, and part of the billet was forced into the trough without touching its bottom. This causes high hydrostatic stress on the cutting edge of the die. The pressure substantially reduces the occurrence of fractures in test products. The punch with a square trough engraved on its face produced a product with favorable shape and precision compared with other punch shapes. The results revealed that the proposed method can produce a product with a long and burnished surface with a roughness of 0.02–0.12 μm. The tolerance band for the width and thickness ranges from IT1 to IT3, and that for the right angle is 0.02–0.06°. The proposed method is a new rapid prototyping technology and has greater levels of precision than conventional manufacturing methods. [ABSTRACT FROM AUTHOR]

VIRTUAL prototypes, WIRE, CONES, and MATHEMATICAL models

To solve the problems involving several forming movements and the complex sharpening structures required for the flank face of a traditional grinding wheel-sharpening twist drill, a new method based on the wire electrical discharge machining is here proposed and a mathematical model of twist drill flank faces formed by wire electrical discharge machining (WEDM) is established. Based on the forming principle of the conical flank face of twist drills and the processing characteristics of the wire-cutting machine, a wire-cutting and forming device was designed and its motion analyzed. Using the UG NX (Unigraphics NX) software, a virtual prototype of the wire-cutting and forming device was established, with the simulation and measurement analysis performed using the VERICUT software. After analyzing the feasibility of its motion, the wire-cutting and forming device was developed and the wire-cutting and forming test was conducted. The feasibility of the device was analyzed by measuring the angle of the drill tip and the surface quality of the flank face of the twist drill. The utility model has a simple structure and provided us with a new idea and solution for the "grinding" of the twist drill. [ABSTRACT FROM AUTHOR]

LASERS, CERAMIC materials, MANUFACTURING processes, and CAD/CAM systems

Quasi-tangential laser processing, also called laser turning, is increasingly applied for various applications. Specifically, its ability to generate complex geometries with small feature sizes at high precision and surface quality in hard, brittle, and electrically non-conductive materials is a key benefit. Due to the geometric flexibility, the process is well suited for prototyping in hard-to-machine materials such as ceramics, carbides, and super-abrasives. However, the lack of advanced software solutions for this novel process hitherto limited the exploitation of the potential. Here, we discuss a unique computer-aided manufacturing approach for synchronous 7-axes laser manufacturing with quasi-tangential strategies. This gives the peerless possibility to process arbitrary geometries, which cannot be manufactured with conventional techniques. A detailed description of the path calculation with derivation and procedures is given. The generated machine code is tested on a laser manufacturing setup consisting of five mechanical and two optical axes. Following, a processed cylindrical ceramic specimen with a continuously varying profile along a helical path is presented. The profile is constituted by a rectangular over half-spherical to a triangular groove with defined pitch on the helix. This demonstrator provides the validation of the presented CAM solution. Measurements of the produced specimen show high adherence with the target geometry and an average deviation below 10 μm. [ABSTRACT FROM AUTHOR]

RAPID prototyping, SHEET-steel, ELECTRIC currents, TITANIUM, and SHEET metal

Single point incremental forming (SPIF) is an emerging forming process for rapid prototyping and manufacturing of complex components from sheet metals. Recently, the use of electric current for the local resistance heating of the deformation area has attracted much attention in SPIF. In order to further study the electric hot incremental sheet forming (EHISF), in the present research, the effect of utilizing various lubricants on the formability of Ti-6Al-4V, AA6061, and DC01 sheet metals is experimentally investigated by forming a truncated cone under different feed rates, vertical pitches, and electric currents. To this end, the Taguchi design of experiment (DOE) and the analysis of variance (ANOVA) are employed. The results showed that the formability of Ti-6Al-4V and AA6061 sheets can be improved using the EHISF. For both the sheets, the lubricant and the electric current have significant effects on the maximum achievable forming depth. In addition, the formability of the DC01 sheet is highly affected by the lubricant and the feed rate. The results of the DC01 sheet showed that at the considered wall angle, the maximum forming depth in the EHISF does not change, compared to the cold SPIF, but the thickness distribution of the formed part at a higher temperature is more uniform. [ABSTRACT FROM AUTHOR]

RESIDUAL stresses, POWDERS, RESIDUAL stresses measurement, TOOL-steel, MELTING, and LASER beams

The occurrence of residual stresses in selective laser melting (SLM) presents challenges that limit the capability of the process to manufacture parts at industrial scale. These stresses can have irreversible effects such as warping and cracking of parts during and post manufacturing. One of the most important SLM parameters that should be controlled carefully in order to effectively manage residual stresses is the scanning strategy. This study presents an evaluation of four different scanning strategies, namely the island, successive, successive chessboard and least heat influence (LHI) scanning strategies with respect to their influence on residual stresses and distortions. All the scanning strategies were investigated by melting single tracks on tool steel substrates without powder. Measurement of residual stresses was performed on selected positions on the substrates before and after exposure to the laser beam using the x-ray diffraction technique. The successive chessboard scanning strategy was found to contribute to the least average residual stresses, and lowered residual stress by up to 40% relative to the default island scanning strategy. Further to this, the influence of the successive chessboard and island scanning strategies on distortions was evaluated. Similar to the residual stress findings, the successive chessboard contributed to lower form deviations compared to the island strategy. The scanning strategies were also evaluated based on their impact on total scanning times, with the successive chessboard strategy showing slightly lower scanning time than that for the island and LHI chessboard strategies. [ABSTRACT FROM AUTHOR]

RAPID prototyping, MANUFACTURING processes, SPLINES, SIMPLE machines, DEVELOPMENTAL biology, and PROSPECTING

For successful development of the intelligent manufacturing of freeform surfaces using STEP-CNC with online toolpath generation capability, it is required to make a choice of the optimal representation of a 3D model which will be used for machining. Traditionally, most existing CAD-CAM systems use NURBS to design freeform surfaces and to perform toolpath generation in order to machine them. The introduction of T-splines to CAD systems and some reported results of using them in manufacturing makes it possible to consider T-splines, or more generally T-NURCCs (Non-Uniform Rational Catmull-Clark Surfaces with T-junctions), as a good solution for the development of the STEP-NC-based manufacturing of freeform surfaces because of their advantages over NURBS. Therefore, this paper gives an overview of the main arguments in favor of choosing the T-spline surface representation for integration within STEP-CNC systems. We examine the prospects for T-splines to become an integral part of modern manufacturing systems, and highlight some important properties of T-splines which are the most beneficial for manufacturing processes. The paper presents the results of the development of a complete T-spline-enabled STEP-CNC system which can strategically support online toolpath generation for three-axis ball end machining of simple T-spline surfaces using four different freeform strategies defined in ISO 14649-11. These results represent the implementation of the first stage of the development process of intelligent STEP-CNC systems, and in the future more research is needed in this direction. [ABSTRACT FROM AUTHOR]

ALUMINUM alloys, WAGES, ROBOTIC path planning, SHEET metal, and RAPID prototyping

Incremental sheet forming (ISF) is a new and rapid forming process which produces parts without using specific die. One of the key challenges is geometric accuracy especially for complex sheet metal parts. In the presented work, a typical non-axisymmetric part of AA5052 with stepped feature was studied through orthogonal experiments with 4 parameters in 4 levels to determine the optimal process parameters for better geometric accuracy. Based on the optimum process parameters, the strategy on further reducing geometric deviation was investigated, and the compensation was made on each tool path during multi-pass incremental forming. The intermediate configurations were designed to avoid the interaction of different features and improve the smoothness of material flow. Based on the proposed methodology, the geometric accuracy of non-axisymmetric part with stepped feature has been obviously improved, particularly at the stepped feature. [ABSTRACT FROM AUTHOR]

THREE-dimensional printing, CONCEPTUAL design, FREQUENCY selective surfaces, METAL coating, ROBOTICS, SURGICAL robots, and MEDICAL robotics

In this paper, a novel concept of robotic manipulator is developed for direct additive manufacturing on non-planar surfaces. The application scenario is the metal coating of the internal surface of radome systems, using frequency selective surface patterns. The manipulator is presented from the design, modeling, and control point of view. It is developed following an application-driven approach, meaning that the requirements from the application and the additive manufacturing technology are translated into the design specifications of the robotic system. Simulation results demonstrate that the proposed control strategy based on a decentralized architecture is satisfactory to accurately control the motion of the robotic mechanisms along the trajectory foresees by the direct additive manufacturing task. [ABSTRACT FROM AUTHOR]

THREE-dimensional printing, THREE-dimensional display systems, TECHNOLOGY, and MANUFACTURING processes

In 2014, NASA, in partnership with Made In Space, Inc., launched the first 3D printer to the International Space Station (ISS). Results of the first phase of operations for this mission demonstrated the use of the fused filament fabrication (FFF) process for 3D printing in a microgravity environment. Previously published results indicated differences in density and mechanical properties of specimens printed in microgravity and those manufactured with the printer prior to its launch to ISS. Based on extensive analyses, these differences were hypothesized to be a result of subtle changes in manufacturing process settings rather than a microgravity influence on the FFF process. Phase II operations provided an opportunity to produce additional specimens in microgravity, evaluate the impact of changes in the extruder standoff distance, and ultimately provide a more rigorous assessment of microgravity effects through control of manufacturing process settings. Based on phase II results and a holistic consideration of phase I and phase II flight specimens, no engineering-significant microgravity effects on the process are noted. Results of accompanying material modeling efforts, which simulate the FFF process under a variety of conditions (including microgravity), are also presented. No significant microgravity effects on material outcomes are noted in the physics-based model of the FFF process. The 3D Printing in Zero G Technology Demonstration Mission represents the first instance of off-world manufacturing. It represents the first step toward transforming logistics for long-duration space exploration and is also an important crew safety enhancement for extended space missions where cargo resupply is not readily available. This paper presents the holistic results of phase I and II on-orbit operations and also includes material modeling efforts. [ABSTRACT FROM AUTHOR]

ELECTRIC heating systems and REVERSE engineering

The single-point incremental forming process is an emerging process, which presents an alternative to the conventional sheet metal-forming processes like stamping and drawing. It is known to be perfectly suited for prototyping and small series. The incremental forming process offers the possibility of manufacturing medical prosthesis or implants specific to each patient, which are more comfortable and guarantee better performance. A reverse engineering approach associated with single-point incremental forming process in order to produce a titanium prosthesis of human skull is developed. It allows guaranteeing the high degree of customization required. In this paper, several novel warm forming experimental setup equipped with instruments to measure efforts and temperature monitoring is proposed. This new warm setup is feasible and makes it easy to monitor force and temperature sheet at forming; it gives it the ability to be exploited in the industry of manufacturing titanium alloy medical shapes. The real geometry of a skull prosthesis is re-constructed from a laser scanning technique, and specific treatments are performed until a CAD model is obtained. From it, the forming punch trajectories have been defined, and skull prostheses are manufactured using the technology of single-point incremental forming in titanium material at different temperatures. [ABSTRACT FROM AUTHOR]

CASTING (Manufacturing process), RAPID prototyping, STAINLESS steel, POLYSTYRENE, LASER sintering, and STEREOLITHOGRAPHY

Rapid casting is the product of digital, information, and optimization of casting technology. It mainly includes rapid prototyping and virtual manufacturing. In order to shorten the production cycle of a stainless steel closed impeller casting, the wax pattern was made by high impact polystyrene (HIPS) with a selective laser sintering and photosensitive resin with stereolithography (SL). In order to prevent the formation of shrinkage defects, different gating systems designed to examine the molten metal flow and solidification behavior during the pouring and solidification process. The results show that pouring temperature is 1550 °C and pouring speed is 0.75 m/s, which is favorable for filling impeller castings, and can avoid casting defects. The optimized gating system prevented surface shrinkage and interior defects. The optimized gating systems have been verified by experiment, and the rapid casting has been realized based on 3D printing wax pattern and simulation optimization. This rapid casting can reduce processing time and costs, and enhance casting quality in the foundry industry. [ABSTRACT FROM AUTHOR]

CLOUD computing, THREE-dimensional printing, RAPID prototyping, MANUFACTURING processes, and RESEARCH & development

At present, some service platforms for 3D manufacturing encounter problems, including the low level of integration with digital design ability, the single character of cooperative printings, the uneven distribution of 3D printing resources, and the high 3D design requirements of users. To overcome these issues, a cloud service platform for the seamless integration of digital design and rapid prototyping manufacturing was established using ASP.NET, WebGL, WebSocket, and SQL Server in combination with C# language and JavaScript. The goals were to realize a design and rapid prototyping of mechanical equipment parts that are browser based and provide online digital design services, such as the parametric design of key parts, downloading of models, format conversion, and virtual assembly. The client application layer, server processing layer, database layer, and working machine end application layer of this cloud 3D printing platform were set up. The result of the design module could be printed remotely in 3D. Practical application showed that the platform could effectively improve the R&D and design speed of the parts and components of the mechanical equipment and reduce the effort of designers. In particular, this platform would be suitable for users without a 3D design background. The design and rapid prototyping parts of the platform satisfied the dimensional precision required by enterprises, which provides an important basis for the further verification of the design correctness for small- and medium-sized enterprises and has high application value. [ABSTRACT FROM AUTHOR]

RELIABILITY in engineering, VIRTUAL prototypes, MULTIBODY systems, ANALYTICAL mechanics, and FAILURE mode & effects analysis

The reliability analysis is a quantification of the sources of failures in a product, with emphasis on the most significant contributors towards the overall product unreliability. As the reliability analysis of complex products is very crucial for analyzing the behavior of the products, many researches have been focused on it in recent decades with a result of many valuable contributions. However, current researches always focus on rigid product, while the product is always a rigid-flexible coupling multibody system, which could affect the accuracy of reliability analysis. This paper is devoted to virtual prototyping-based approach to a fuzzy Failure Mode, Effects, and Criticality Analysis (FMECA) with the consideration of rigid-flexible coupling virtual prototyping model. This paper discussed proposed approach in detail with three steps: the traditional FMECA method, the fuzzy FMECA method, and the rigid-flexible coupling-based analysis for FEMCA. The cold heading machine is given as an example which demonstrates that the methodology is helpful to reliability analysis. The physical prototyping is also carried out to demonstrate the product reliability. [ABSTRACT FROM AUTHOR]

AUTOMOTIVE engineering, FINITE element method, STRENGTH of materials, CAST-iron, and THREE-dimensional printing

Lightweight engineering is a current topic in mechanical industry. The mass reduction is a common design objective to reduce product cost and environmental impacts. Virtual prototyping tools are widely applied to study new lightened solutions and check the compliance with regulations and standards. However, an integrated approach, involving simulations and life-cycle analysis, is necessary to support design optimization and decision-making. The scope of this study concerns the definition of an Ecodesign approach to support the lightweight engineering of cast iron parts through the redesign of the product shape. In particular, this paper deals with the optimization of a ductile cast iron manhole. The test case shows a redesign method which considers structural analysis with environmental impacts. The structural analysis has been evaluated using a finite element method tool. In particular, the simulation results have been compared and validated with physical tests. The environmental analysis is based on the methodology provided by the standardized ISO 14040:2006 and ISO 14044:2006. The proposed LCA study considers the phases of manufacturing and transport related to one ductile iron product. The described manufacturing phase is related to a Chinese foundry which produces roughly 12,000 tons of ductile cast-iron castings. The results show the possibility to achieve about 20% of mass reduction for one casting. Considering such mass decreasing, the related reduction in terms of carbon emission is about 7%. Summarizing, this paper shows a design approach to integrate the structural improvements with the reduction of the environmental impacts related to a lighter weight casting. [ABSTRACT FROM AUTHOR]

MICROSTRUCTURE, MECHANICAL properties of metals, THREE-dimensional printing, DIRECT metal laser sintering, and TENSILE strength

Additive manufacturing (AM) started as a rapid prototyping (RP) technology to aid in visualizing and validating designs in the design process. However, with the recent improvements in metal AM parts, functional parts can be manufactured using laser-based AM. Currently, metal AM parts have comparable mechanical properties to traditional manufacturing parts. 15-5PH stainless steel and Inconel 718 are two of the most commonly used metals in laser-based AM, and they have a high modulus of elasticity and tensile strength and can be precipitate hardened to increase their strength and hardness by heat treatment. These properties make 15-5PH stainless steel and Inconel 718 suitable for many industrial applications such as aerospace and automotive. However, due to the nature of AM, AM parts usually suffer from anisotropy. In this paper, the mechanical properties such as tensile strength, modulus of elasticity, yield strength, and ductility are investigated at various elevated temperatures up to 350 °C and compared with the mechanical properties at room temperature using specimens printed in three different orientations to capture the effect on the anisotropy. In addition to that, the microstructure of the specimens is studied to investigate the influence of elevated temperature on the specimens. [ABSTRACT FROM AUTHOR]

POLYLACTIC acid, FUSED deposition modeling, CARBON-black, GRAPHENE, and TEMPERATURE coefficient of electric resistance

This study characterizes the microstructure and temperature dependence of resistance of two commercially available electrically conductive polylactic acid (PLA) composites for fused deposition modeling (FDM): PLA-carbon black and PLA-graphene. No microstructural changes were observed between the filament and the printed parts; however, the resistivity of the filament was found to drop by four to six times upon FDM. Also, compared to the resistivity of individual extruded wire, the resistivity of the printed parts was found to be up to 1500 times higher for PLA-graphene and up to 300 times higher for PLA-carbon black. The raw PLA-carbon black filament and printed wire showed a positive temperature coefficient of resistance (α) value between ~ 0.03 and 0.01 °C−1, which makes them more suitable for sensor development. The raw PLA-graphene filament and printed wire did not exhibit a significant α, which makes them more suitable for printing wires. However, the parts made with multilayer FDM exhibited a negative or a negligible α up to a certain temperature prior to exhibiting a positive α; further, these α values were significantly lower than those obtained for the filaments before or after extrusion. These findings enable proper selection of commercial conductive FDM filaments for enabling quicker prototyping of electronics and sensors. [ABSTRACT FROM AUTHOR]

SHEET metal, SPRINGBACK (Elasticity), DIES (Metalworking), MACHINING, and MANUFACTURING processes

Sheet metal structures produced by bending are extensively used in a wide variety of industries. Rapid production of such workpieces is well sought after for low production volume demands. An effective and practical way to reduce springback is through compensating die dimensions, which has proved to be economic for large production scenario. However, in the environment of rapid production, part dimensions and/or material composition change frequently and hence new dies have to be designed and made to address these changes even if they are minor. Such situation inevitably incurs significant effort and high expenditure on determining appropriate die dimensions and fabricating new dies, and therefore imposes both time and financial burdens on producing angular sheet metal workpieces particularly at very low production volumes. This paper presents an effective and economic way of prototyping sheet metal workpieces with angular dimensional accuracy maintained, however without the need of creating new dies. The methodology extends from the author's previous work on angular dimension improvement as reported by Li and Sekar (Proceedings of the 2016 Manufacturing Science and Engineering Conference, MSEC2016, 2016) to the rapid prototyping of sheet metal structures and process planning of bending-machining hybrid process. Three case studies are provided in the paper and the outcome shows that the methodology is capable of prototyping angled sheet metal workpieces with existing dies that are not designed nor compensated for the prototype models. [ABSTRACT FROM AUTHOR]

TISSUE engineering, CRYSTALLOGRAPHIC shear, BIOACTIVE glasses, MICROSTRUCTURE, and FABRICATION (Manufacturing)

This paper reports a study on the development of bioactive glass powders for biofabrication of scaffolds by an additive manufacturing technique, three-dimensional printing (3DP). Several formulations of the glass were developed from the CaO·P2O5·TiO2 system and prepared on the basis of the results for the commercial powder characterization (average particle size, particle size distribution, microstructural and crystallographic analysis). For printing the glass models in the prototyping machine, a virtual model defined as the “standard model” was produced in commercial powder, and a systematic study of the relevant processing parameters (binder composition, formulation of powder, saturation level in the shell and core, bleed compensation, and printed layer thickness) was carried out in order to determine the most suitable conditions for the fabrication of porous structures for tissue engineering applications. The printed glass models were sintered through specific thermal programs and then characterized in terms of dimensions, structure, morphological features, and mechanical properties. Finally, the sintered models were submitted to mineralization tests in simulated physiological media. In this work, it was demonstrated that it is possible to use a printing machine to manufacture 3DP glassy porous structures with suitable features for tissue engineering applications as temporary scaffolds. The mechanical properties of the produced structures and its mineralization capability in physiological fluids suggest that they have potential to be used in bone tissue regeneration under low load-bearing situations. [ABSTRACT FROM AUTHOR]

INTRAOCULAR lenses, MANUFACTURING processes, TREATMENT of cataracts, REFRACTIVE errors, and RAPID prototyping

Intraocular lens implantation surgery is the only approach for cataract treatment at present. Apart from removing the cloudy lens, correction of refractive errors becomes the second main function of intraocular lenses. This paper systematically summarizes the intraocular lenses in terms of its material, design, manufacturing and evaluation. The next generation of intraocular lenses with customized freeform surfaces is highlighted from the lens design viewpoint. The status of processing and measurement methods is presented for both current intraocular lenses and future freeform lenses. Finally, the research perspectives are outlined. [ABSTRACT FROM AUTHOR]

MACHINING, SCHEDULING, MATHEMATICAL decoupling, and RAPID prototyping

The feedrate scheduling of parametric interpolator is one of the most important factors for a high-performance CNC machining, since it directly concerns the machining efficiency, machining accuracy, and cutting stability. In this paper, an adaptive feedrate scheduling method with limited contour error and axis jerks is proposed for free-form contour machining based on a strategy of moving knot sequence. The analytical relations between dynamic contour error and feedrate are first derived explicitly, and then the formula of maximum feedrate limit under confined contour error and axis jerks is yielded using a numerical decoupling scheme. Consequently, the maximum feedrate limit satisfying the above constraints is obtained for each predefined parametric segment of the tool path. Further, a bidirectional scanning algorithm is employed to globally adjust the local minimum feedrate values of all feedrate segments. On the basis of feedrate segments with local minimum value and maximum recommendation value, an exact knot sequence configuration method for the B-spline curve, which is used to express the initial feedrate profile, is proposed. Finally, a simple feedrate relaxation algorithm is performed to generate the final feedrate profile with entirely limited contour and axis jerks by utilizing a strategy of moving knot sequence. The proposed feedrate scheduling method is validated by several typical experimental tests, and the results demonstrate the effectiveness and reliability of the proposed method. [ABSTRACT FROM AUTHOR]

BEVEL gearing, GEOMETRY, FABRICATION (Manufacturing), MANUFACTURING processes, and THREE-dimensional printing

The growth of additive manufacturing technology allows the fabrication of complete functional devices with complex geometries with ease and low cost. This technology allows the fabrication of pieces that could not be made in the past with traditional manufacturing techniques, in this case, bevel gears with exact spherical involute (ESI). Focusing on this issue, this paper presents a method for the geometric design and fabrication of practical industrial-like ESI bevel gears with variable surface detail. The definition of the tooth profiles on back cones is proposed introducing a projection procedure for straight and spiral toothing. An in-house-developed software package was developed to test the method, and a pair of plastic examples were fabricated on a generic 3D printer. A comparison between the fabricated pinion and its STL model was conducted for validation purposes. Mean deviations of 0.22 and 0.15mm were obtained for the whole model and for the contact surfaces comparison, respectively. Thus, the fabrication of bevel gears using AMT is achieved, and can be implemented to a specific application using a particular additive manufacturing technique. [ABSTRACT FROM AUTHOR]

RAPID prototyping, COMPUTER-aided process planning, PRODUCTION planning, MILLING machinery, and MILLING-machines

Feature recognition is an important function of computer-aided process planning (CAPP) system. The freeform feature recognition works performed so far have resulted in successful classification and recognition of freeform surface-based features, but the works do not classify and recognize freeform volumetric features. The research works like automatic generation of delta volume (DV) for volumetric features, finishing, and roughing process were successful when applied to regular form parts, but generated a complex DV for roughing process when applied to freeform parts. Also, the DV generation works do not generate DV for freeform features. So an effort is made (i) to newly classify freeform volumetric features and develop an algorithm to automatically generate DV for freeform volumetric features; (ii) to automatically recognize freeform volumetric features by a set of conditions and colour coding concept; and (iii) to determine the level of complexity and milling machine selection. The problem of complex DV is overcome by generation of sub-delta volume for transition (SDVT). The algorithm is able to recognize freeform volumetric features and the DV’s quantitative data, exploded view, and labelling will aid the downstream activities of CAPP system. The algorithm validation result shows a percentage error of 0.005% for complex part like impeller. [ABSTRACT FROM AUTHOR]

SHEET metal, ULTRASONICS, VIBRATION (Mechanics), METALWORK, and RAPID prototyping

The incremental sheet forming (ISF) is an innovative dieless forming process featured with high formability and short lead time which is suitable for rapid prototyping and small volume production. The integration of ultrasonic (US) vibration into the ISF process can significantly reduce the forming force and bring other benefits. In this work, the impacts of process parameters including the sheet material, US power, feeding speed, and tool diameter, on force reduction and temperature increment were studied. The force reduction contains two components—the stress superposition-induced force reduction and acoustic softening-induced force reduction. The stress superposition-induced force reduction was analyzed by finite element simulation while the total force reduction was detected by experiments since currently, the unknown mechanism of the acoustic softening cannot be modeled. The temperature increment was measured by a high-speed infrared camera. The results show that the force reduction can go up to 56.58% and the temperature increment can be as high as 24.55 °C. In general, the material with a higher yield stress results in a higher force reduction and a higher temperature increment. A higher US power or a lower feeding speed can significantly enhance the force reduction and the interface temperature increment. The tool with a smaller diameter has a comparable effect as a larger tool, but a larger vibration amplitude is required. [ABSTRACT FROM AUTHOR]

MACHINING, MACHINE tools, RAPID prototyping, K-means clustering, and MANUFACTURING processes

Due to the geometric complexity, tool orientations usually change dynamically during freeform surface machining with 5-axis machine tool. As the kinematic performance of the rotary axes is usually weaker than that of the linear axes, the real cutting speed is difficult or even impossible to reach the desired level, which further leads to low machining efficiency. This paper presents a region-based 3 + 2-axis machining toolpath generation method with 5-axis machine tool. The surface is first divided into several preliminary sub-surfaces using K-means clustering algorithm. A post processing procedure is then carried out to optimise the preliminary sub-surfaces to ensure the machinability. For each sub-surface, gouging-/collision-free tool orientations are first calculated and then the optimal combination of the fixed tool orientation and the feed direction is determined by maximising the average machining strip width for toolpath generation. The proposed method is tested by a case surface and the comparisons to some other traditional methods are also provided. [ABSTRACT FROM AUTHOR]

THREE-dimensional printing, COMPUTER scheduling, PARTICLE swarm optimization, QUADRATIC programming, and RAPID prototyping

The problem of service matching and scheduling in cloud manufacturing (CMfg) is complex for different types of manufacturing services. 3D printing, as a rapidly developing manufacturing technology, has become an important service form in the CMfg platform due to its characteristics of personalized manufacturing. How to solve the task scheduling problem for distributed 3D printing services in CMfg needs further research. In this paper, a service transaction model of 3D printing services in CMfg is built. Based on the service transaction model, we propose 3D printing service matching strategies and matching rules of different service attributes, including model size, printing material, printing preciseness, task cost, task time, and logistics. To reduce the delivery time of tasks from service suppliers to service demanders, a 3D printing service scheduling (3DPSS) method is proposed to generate optimal service scheduling solutions. In 3DPSS, optimization objective, constraints, and optimization algorithm are presented in detail. Experimental results show that the average task delivery time of 3DPSS is shorter than that of typical scheduling methods, such as particle swarm optimization, pattern search, and sequential quadratic programming, when the amounts of tasks change. [ABSTRACT FROM AUTHOR]

COMPUTER-aided design, ALGORITHMS, TOPOLOGY, HOLES, and RAPID prototyping

The existing method to determine the parting direction for core and cavity of two-plate mold is usually limited to decided types of direction. This limitation reduces the capability of the existing method to select the best parting direction for a 3D CAD model of an object. This paper introduces a new algorithm for another alternative that overcomes the limitation and takes less computational time by using the boundary representation (B-rep) of a visibility map to determine the parting direction. By extracting the geometric and topological information of a visibility (V) map, a B-rep entity is created to represent the V-map, which replaces the existing method that uses convex hull algorithms. To illustrate the capability of the algorithm, the 3D CAD model of objects with regular and freeform faces, holes, protrusion, and depression is presented. [ABSTRACT FROM AUTHOR]

THREE-dimensional printing, COMPUTER-aided design, MANUFACTURING processes, RAPID prototyping, and ROBOTICS

Additive manufacturing (AM, generally called 3D printing) has attracted great research interests due to its ability to build complex shapes. It transforms design files to functional products through slicing and material accumulation. Typically, the planar slicing strategy is used in AM to convert CAD model into accumulating layers. However, when building overhang structures and curved parts, it often needs support structures and generates a large number of planar layers, which lead to the fact that it spends more time in manufacturing. To reduce the need for support structures and decrease the number of layers, this paper presents two nonplanar slicing approaches: a decomposition-based curved surface slicing strategy and a transformation-based cylinder surface slicing method. The former is implemented based on STEP models and the latter is capable of slicing mesh models. The feasibility of the proposed methods are validated by printing two parts with a robotic fused deposition modelling system. [ABSTRACT FROM AUTHOR]

SURFACE roughness, THREE-dimensional printing, MANUFACTURED products, RAPID prototyping, and SURFACES (Technology)

A theoretical formula for surface roughness of layer-based manufactured parts in additive manufacturing is developed considering a more accurate definition of the centerline by minimizing the total arithmetic deviations of the actual surface profile. The developed model is experimentally validated, and it is compared with those that are used in common practices. Considering the uncontrolled process variables and the complexity of the numerical solutions, the analytical and experimental results show satisfying agreement. A methodology is also developed to decide whether the objective surface slope is feasible with the current number of layers and how the layers need to be laid down to achieve the desired surface accuracy. The methodology yields more accurate small features on the surfaces of the layer-based manufactured products. [ABSTRACT FROM AUTHOR]

THREE-dimensional printing, EXTRUSION process, MATHEMATICAL optimization, HIGH energy forming, and RAPID prototyping

A problem with the planning solutions for the additive manufacturing material extrusion process is a lack of optimization strategies to improve upon the standard raster and contour tool paths. Bead deposition tool paths can cause unwanted voids, which in turn creates a set of potential failure points within the finished product. This paper aims to identify, minimize, and manage void regions during the tool path generation. The goal is to minimize voids in each layer and to prevent stacked void regions, i.e., avoid creating an internal chimney. Material extrusion processes, with a wide selection of nozzle sizes (0.4 to 21 mm), are considered suitable candidates for this solution. The mathematical model is established based on the component geometry and the available build options for a given machine-material configuration. A C++ program has been developed to select a set of standard (available) tool path parameters to determine the optimal output process variables (bead width, raster angle, and the overlap percentage). Case studies are presented to show the merits of this approach. [ABSTRACT FROM AUTHOR]

THREE-dimensional printing, MANUFACTURING processes, HOOKS, BAGS, FUSED deposition modeling, and RAPID prototyping

This paper deals with design for manufacturing (DFM) approach for additive manufacturing (AM) to investigate simultaneously the different attributes and criteria of design and manufacturing. The integrated design approach is provided in the product definition level and it gradually maps the customer requirements to the final product model. The main contribution of this paper is an interface processing engine that is an interface between the product model and manufacturing model. This study uses the Skin-Skeleton approach to model the first definition of the product and model the material flow of AM technology as the manufacturing process. This engine is developed through analysis of all AM technologies and identification of their parameters, criteria, and drawbacks. In order to evaluate some product and process parameters, a multi-objective problem is formulated based on the analysis of all AM technologies; production time and material mass are optimized regarding mechanical behavior of the material and roughness of product. The approach is validated by a case study through a bag hook example. From its requirement specification to the proposed approach, this article defines an optimized product and its manufacturing parameters for fused deposition modeling (FDM) technology. [ABSTRACT FROM AUTHOR]

THREE-dimensional printing, RAPID prototyping, CASTING (Manufacturing process), RESIDUAL stresses, and STRAINS & stresses (Mechanics)

A rib-enforced shell mold for castings is proposed to replace the traditional dense mold. The 3D printing methods of sand mold make this new mold design a reality. The rib-enforced shell mold has been applied to cast a stress frame specimen of Al alloy A356. The effects of rib-enforced shell sand mold and traditional dense mold on the cooling of this casting have been investigated and compared. The results show that the cooling efficiency of the casting increases significantly by using rib-enforced shell mold, and approximately 40% cooling time is saved in natural condition and 35% further is saved in air blowing condition for the stress frame specimen before shakeout. This mold makes it possible to adjust the cooling condition of interested locations. It ensures fast and uniform cooling of the casting which can improve production efficiency and reduce deformation and residual stresses of the casting. Temperature distribution in the rib-enforced shell sand mold during the solidification was measured by an infrared imaging camera. The produced casting has good dimensional accuracy and surface quality. Meanwhile, nine-tenths of the sand is saved per mold. [ABSTRACT FROM AUTHOR]

MANUFACTURING processes, SELECTIVE laser sintering, CEMENT admixtures, SINTERING, and LASER power transmission

Selective laser sintering (SLS) is a modern rapid prototyping method with which 3D objects with complex geometries can be manufactured precisely through the sintering of powders’ thin layers using the laser power. The effective manufacturing parameters in SLS are laser power, scanning speed, scan-spacing, and the part-bed temperature. In this work, selective laser sintering (SLS) is used to manufacture a composite material from white cement additives and polyamide 12 (PA12) and then, the influence of energy density (controlled by laser power, scanning speed, and scan-spacing) on the dimensions, density, mechanical properties, and morphology of sintered specimens is investigated. The criteria for obtaining optimum manufacturing parameters are the part dimensional accuracy, maximum density, and maximum strength. Hence, the optimum energy density for producing parts with maximum density and enhanced strength has been determined experimentally. The tensile, compressive, and flexural testing methods are used to evaluate the effects of laser power on the fabricated parts. The results show that the optimum energy density of 0.051 J/mm2 could achieve the highest density of sintered parts without any degradation of binder material. Also, it is found that a combination of a 0.051-J/mm2 energy density and 10% weight fraction of white cement is sufficient enough to enforce significant improvements on the mechanical properties of PA12-sintered specimens. [ABSTRACT FROM AUTHOR]

TORSIONAL vibration, ANISOTROPY, EXTRUSION process, MECHANICAL behavior of materials, THREE-dimensional printing, and SHEAR strength

Several reports have studied the mechanical properties of the material extrusion additive manufacturing process, specifically referred to as fusion deposition modeling (FDM) developed by Stratasys. As the applications for 3D printed parts continue to grow in diversity (e.g., gears, propellers, and bearings), the loading conditions applied to printed parts have become more complex, and the need for thorough characterization is now paramount for increased adoption of 3D printing. To broaden the understanding of torsional properties, this study focused on the shear strength of specimens to observe the impact from additive manufacturing. A full factorial (42) design of experiments was used, considering the orientation and the raster angle as factors. XYZ, YXZ, ZXY, and XZY levels were considered for the orientation parameter, as well as 0°, 45°, 90°, and 45°/45° for the raster angle parameter. Ultimate shear strength, 0.2% yield strength, shear modulus, and fracture strain were used as response variables to identify the most optimal build parameters. Additionally, stress-strain diagrams are presented to contrast elastic and plastic regions with traditional injection molding. Results demonstrated an interaction of factors in all mechanical measured variables whenever an orientation and a raster angle were applied. Compared to injection molding, FDM specimens were similar for all measured torsion variables except for the fracture strain; this led to the conclusion that the FDM process can fabricate components with similar elastic properties but with less ductility than injection molding. The orientation in YXZ with the raster angle at 00 resulted in the most suitable combination identified in the response optimization analysis. [ABSTRACT FROM AUTHOR]

ADAPTIVE sampling (Statistics), RAPID prototyping, COORDINATE measuring machines, SURFACES (Technology), and SURFACES (Physics)

The components with freeform surface are widely used in industrial fields. The machining quality of freeform surface becomes increasingly significant. Coordinate measuring machine (CMM), as a conventional dimensional measuring instrument, is commonly used to inspect freeform surface. The sampling strategy, consisting of distribution of sampling points and sample size, is important to the effectiveness and accuracy of the measurements performed on CMM. The present work aims at proposing an improved adaptive sampling strategy based on a machining error model (MEM) for freeform surface inspection on CMM. The machining error model is built to determine the distribution of sampling points adaptively. In addition, Hammersley sequence is adopted to address the aliasing problem. Experiments are performed to compare presented strategy with four well-known sampling strategies. Results prove that the MEM is valid and the present strategy is reliable and effective. [ABSTRACT FROM AUTHOR]

RAPID prototyping, SURFACES (Physics), and ADAPTIVE sampling (Statistics)

The original version of this article contained a mistake. Yincun Sang has been corrected to Yicun Sang. The presentation is corrected above. [ABSTRACT FROM AUTHOR]

ACRYLONITRILE butadiene styrene resins, THREE-dimensional printing, RAPID prototyping, COMPRESSIVE strength, and ELASTICITY

Acrylonitrile butadiene styrene (ABS) specimens manufactured by fused deposition are tested under uniaxial compression in order to judge the effectiveness of printing orientation, density, and filler patterns in terms of stiffness and strength per printing time. The compressive properties of the 3D printed materials along the three orthogonal directions are studied on cylindrical specimens filled with honeycomb and rectangular patterns. In order to achieve different densities, five filler percentages (0, 20, 30, 40, and 100%) are employed for each type of structure. Specimens filled with honeycomb patterns are stiffer and stronger than those with rectangular patterns only when they are oriented along the applied load. However, structures with rectangular patterns only require roughly half of printing time of those filled honeycomb cells, which yields effective rectangular structures with high elastic properties per printing time. Stress-strain curves reveal that compressive strength and stiffness increase with respect to the structure density. Patterns printed along the loading direction present higher strength and stiffness than on the other orthogonal orientations. Local buckling and compressive failure mechanisms are identified for light weight and heavy structures, respectively. A combination of shear and local buckling failure appeared in honeycomb structures printed transversely with relative densities around 20-40%. [ABSTRACT FROM AUTHOR]

MANUFACTURING processes, RAPID prototyping, STAINLESS steel, TITANIUM alloys, and RESIDUAL stresses

Metal additive manufacturing has employed several technologies and processes to advance from rapid prototyping to rapid manufacturing. Additive manufacturing technologies compete with traditional manufacturing methods through their ability to produce complex structures and customized products. This paper aims to study the characteristics of stainless steel 316L (UNS S31603) parts produced using a selective laser melting machine. In the aerospace industry, turbine blades are typically manufactured from nickel-based alloys, titanium alloys, and stainless steels. Several geometries typical of airfoil blades were examined. The main goal is to investigate the material characteristics and surface features of the airfoil blades. The study included the geometrical errors, surface microstructures, material compositions, material phases, and residual stresses of the samples produced. The characteristics of the parts produced were investigated based on experimental observations. The paper also discusses the influence of the part dimension and orientation on the profile error, surface microstructure, and residual stress. [ABSTRACT FROM AUTHOR]

MACHINING, MICROSTRUCTURE, FABRICATION (Manufacturing), RAPID prototyping, and TECHNOLOGY

Fast tool servo (FTS) in ultra-precision machining (UPM) is an enabling and efficient technology for fabricating optical freeform surfaces or microstructures with submicrometric form accuracy and nanometric surface finish. There are many kinds of FTS in the different driving principle to present their various performances currently. Their kernel technologies influence the machining ability and accuracy of freeform surfaces, consequently receiving much research attention and interest. These technologies are generally summarized as the development of FTS structure, the advanced control algorithms, tool path planning, machining condition monitoring, and surface measurement and error compensation. This paper aims to survey the current state of the art in machining freeform optics by FTS. An analysis of the principle, performance, and application of FTS machining with regard to freeform optics is presented. And the key machining technologies for optical freeform surfaces by FTS are then introduced in detail. The challenges and opportunities for further studies are concluded according to the FTS machining difficult of optical freeform surfaces finally. [ABSTRACT FROM AUTHOR]

RAPID prototyping, MILLING (Metalwork), SURFACE roughness, GRINDING & polishing, and MACHINING

The tool path used for polishing applications with characteristic of physically uniform coverage, which is similar to the iso-scallop path in milling operations, is significantly important to facilitate uniform material removal and acquire low surface roughness and consistent surface quality. In this paper, tool path planning method for physically uniform coverage instead of traditional geometrically uniform coverage of polishing path based on scanning mode is further investigated and an efficient iterative approximation algorithmis proposed. Then a complete spiral path generation strategy for small tool polishing of freeform surface is presented, which uses a cyclic iteration correction and driving method to produce spiral path with physically uniform coverage. At the same time, this strategy uses surface expansion and re-parameterization techniques to avoid edge effect in polishing. The effectiveness and robustness of the developed polishing path generation technique are proved by case studies. And the superiority of the planned polishing path over the traditional path in promoting uniformity of material removal is examined through the practical application of polishing. [ABSTRACT FROM AUTHOR]

MACHINING, RAPID prototyping, PRODUCTION planning, MANUFACTURING processes, and CUTTING (Materials)

In a typical multi-pass machining process of freeform surfaces, especially at the roughing stage, the constant Z level strategy is typically used. Under this strategy, the inevitably formed islands where the tool has to travel between increase the machining time as the tool has to air-cut between them. Moreover, the uneven intermediate geometry left on the islands leads to sharp changing of chip load and jeopardizes the finish surface quality. To avoid the staircase-like intermediate geometry of the islands and most of all for the ultimate goal of maximizing the machining efficiency, in this paper we present a method of variable-depth of cut multipass tool path generation for multi-axis machining of mesh surfaces. By parameterizing the cut volume to a unit uvw cubic parametric domain, the multi-pass process planning task turns to finding an optimal sequence of w level parameters. To solve the optimization problem, we introduce a machining efficiency indicator--the average material removal rate (AMRR). The w level parameters are obtained by iteratively solving the maximization problem regarding AMRR. The preliminary computer simulation and real physical cutting experiments show that substantial savings in total machining time could be achieved by the proposed method as compared to the traditional constant Z level method. [ABSTRACT FROM AUTHOR]

DIAMOND cutting, CUTTING (Materials), RAPID prototyping, FREQUENCIES of oscillating systems, and ACTUATORS

For diamond cutting of die steel, it has been shown that ultrasonic vibration-assisted cutting can reduce the chemical wear of diamond tool due to the discontinuous contact between the cutting tool and the workpiece. In this paper, a novel structure of transducer is designed by using free-form surface for ultrasonic vibration-assisted ultra-precision turning die steel. It has two interesting characteristics: The vibration direction of cutting tool tip can be changed by altering vibration frequencies; it can produce an elliptical vibration with only longitudinal vibration actuator. In addition, the structure of this transducer is simple and compact. Finally, several experiments were conducted to demonstrate the effectiveness of this system by diamond ultra-precision turning of STAVAX steel to a mirror surface. [ABSTRACT FROM AUTHOR]

SHEET metal work, METAL formability, RAPID prototyping, MANUFACTURING processes, and PRODUCT design

Incremental sheet forming (ISF) processes like single-point incremental forming (SPIF) have been majorly studied since the beginning of the 2000s. Besides the applications in the prototyping field, ISF processes can also be used in the manufacture of unique parts and small batches. This capability led to new business possibilities, enabling the development of exclusive or custom products. Despite being a free-form manufacture process, ISF has some geometric limitations, mainly due to the forming mechanics and formability limit of the materials. Thus, it is important to establish well-defined guidelines to grant a feasible design. This paper presents a knowledge basis to design and manufacture ISF parts, mainly by SPIF. The possible part configurations and the design orientation are settled, allowing for a suitable part development. The hardware to perform incremental forming operations is outlined and the forming process is described, presenting alternative solutions. The process modelling is completed with a brief description of methods to improve part quality. [ABSTRACT FROM AUTHOR]

THREE-dimensional printing, BREAKAGE, shrinkage, etc. (Commerce), FUSED deposition modeling, RAPID prototyping, and COORDINATE measuring machines

An interior design methodology to compensate for the shrinkage in the holes of artifacts fabricated with desktop 3D printers employing fused deposition modeling process is presented in this study. In the conventional way of compensating, the initial geometry is scaled according to the predictive and statistical models so that the critical dimensions will be more accurate when the part is cooled down. The proposed method employs a completely different paradigm. It constructs various interior structures to compensate for the shrinkage in the holes according to the geometric attributes of the artifacts. In other words, the method utilizes shrinkage as a tool to compensate for the shrinkage. Printed interior line segments, which are directly connected to the perimeter of the hole, simply pull the hole towards the inside of the artifact. In result, the dimensional accuracy of the hole is improved considerably. The measurements with a coordinate measuring machine and the numerical analysis revealed that the proposed design approach can decrease the dimensional error substantially compared to the conventional 3D printed parts. [ABSTRACT FROM AUTHOR]

THREE-dimensional printing, HIGH resolution imaging, TIME to market (New products), PRODUCT costing, and COMPUTED tomography

Additive manufacturing (AM) technique can help reduce time, cost, and complexity of the manufactured parts apart from adding functionality. This work explores AM techniques, namely fused deposition modeling (FDM) and PolyJet printing to fabricate a free-form structure with embedded electrical components. Both additive manufacturing technologies are discussed, analyzed, and compared. Another additive manufacturing method is then employed to print the electronic circuitry inside to connect the components. High-resolution X-ray computed tomography (CT) is employed to investigate the dimensional accuracy of the printed parts. This work demonstrates an innovative approach to construct arbitrary 3D objects with fully functional electronic circuits. [ABSTRACT FROM AUTHOR]

TURBINE blades, BLADES (Hydraulic machinery), INCONEL, CHROMIUM-iron-nickel alloys, and TENSILE strength

In the frame of additive manufacturing of metals, laser powder-bed fusion is investigated in this paper as an advanced industrial prototyping tool to manufacture Inconel 718 turbine blades at a predesign stage before flow production. Expediting of the evaluation of any upgrade to the part is aimed. To this purpose, possible anisotropy of manufacturing is preliminarily investigated via tensile testing at room and elevated temperature as a function of the sloping angle with the building plate; the normalized strength is given and compared with similar studies in the literature. Positioning and proper supporting in manufacturing are discussed; the parts are further investigated to assess their compliance with the intended nominal geometry. [ABSTRACT FROM AUTHOR]

POLYSTYRENE analysis, COMPUTER simulation, ELECTROMECHANICAL analogies, CUTTING (Materials), and TITANIUM alloys

In the present paper, experimental and numerical studies of a newly developed process of Hot-Blade Cutting used for free forming of double-curved surfaces and cost effective rapid prototyping of expanded polystyrene foam is carried out. The experimental part of the study falls in two parts. The first presents a number of large-scale cutting samples combining linear cuts with and without inclination measured from the horizontal direction of cutting, while in the second, the thermal phenomena in the process are studied based on infrared measurements of the hot-blade tool made by observation during the cutting process. A novel measurement method for determination of kerfwidth (i.e., the gap space after material removal) applying a commercially available large-scale optical 3D scanning technique was developed and used. A one-dimensional thermo-electro-mechanical numerical model for Hot-Blade Cutting similar to the one previously proposed by Petkov and Hattel (Int J Machine Tools Manuf 107:50-59 2016) for Hot-Wire Cutting of Polystyrene foam is used to simulate the process and describe the effects taking place within the hot-blade during different cutting procedures. The obtained results are graphically presented and discussed in relation to the aim for higher geometrical accuracy of the Hot-Blade Cutting process. [ABSTRACT FROM AUTHOR]

RAPID tooling, MANUFACTURING processes, and INJECTION molding of metals

Reduction of the time and cost during the research and development stage of a new product is an important issue. Rapid tooling techniques can reduce the time to market compared to conventional machining approaches. In general, reduction in cooling time plays an important role on cycle time in manufacturing time. Wax injection mold fabricated from aluminum-filled epoxy resin can be employed for small-batch productions of wax patterns. However, the cooling time is much longer compared to metallic wax injection molds due to poorer thermal conductivity. In this study, three kinds of cooling-channel layouts were employed to fabricate wax injection molds for low-pressure wax injection molding using rapid prototyping and rapid tooling techniques. The effects of three kinds of wax injection molds on the cooling time during the low-pressure wax injection molding were investigated. It was found that the reduction in cooling time about 87% can be obtained when a wax injection mold with conformal cooling channels is compared to a conventional wax injection mold fabricated by Al-filled epoxy resin. The manufacturing cost reduction for a wax injection mold with high cooling efficiency about 63% can be obtained using the method proposed in this work. [ABSTRACT FROM AUTHOR]

THREE-dimensional printing, MANUFACTURING processes, and STATISTICAL reliability

In recent years, additive manufacturing (AM) has undergone a rapid growth, therefore several processes based on different working principles (e.g. photopolymerization, sintering, extrusion, material jetting, etc) are now available and allow to manufacture parts using a wide range of materials. Consequently, the so-called benchmark artifacts are necessary to assess the capabilities and limitations of each AM process or to compare the performance of different processes. This paper focuses on the benchmark artifacts for evaluating the geometrical performance of AM processes and proposes an extensive review of the available literature, analyzing the design of such test parts in detail. The investigated test parts are classified according to the process aspect that they are able to evaluate (dimensional/geometrical accuracy, repeatability, minimum feature size) and the combination AM process/materials for which they have been used. In addition, the paper draws a summary of guidelines to design benchmark artifacts for geometrical performance evaluation. [ABSTRACT FROM AUTHOR]

RAPID prototyping, METAL extrusion, METALWORK, METALWORKING machinery, and METAL industry

A rapid prototyping and high-precision technology for manufacturing a linear motion (LM) guideway is proposed in this paper. In this technology, a trough is laid on the die, and a ram is used to press the billet before extrusion to produce high hydrostatic stress on the cutting edge of the die. The punch diameter is designed to be larger than the die hole but smaller than the die diameter. Hence, the action of the punch traveling downward to extrude the billet can increase the hydrostatic pressure around the cutting edge of the punch and die, thereby eliminating product fracture. LM rails of linear guides were formed using an experimental test, in which all the product processes were completed in only a few minutes. The results indicated that this approach can extrude a part of the linear guide with an excellent burnished surface. The test range for the roughness of the burnished surface was R = 0.03-0.21 μm, and the tolerance band for the width and thickness ranged from IT1 to IT4. This novel approach provides a more rapid prototyping technology as well as precise sizes higher than those obtained using traditional manufacturing methods. [ABSTRACT FROM AUTHOR]

SHEET metal, RAPID prototyping, COMPUTER simulation, GEOMETRY, and MANUFACTURING processes

Incremental sheet forming is a flexible forming process where a tool is programmed to follow predetermined tool paths to create sheet metal parts. It is ideal for rapid prototyping and low-volume production. Modeling incremental sheet forming and predicting forming forces can significantly benefit product design and process development. Existing force prediction methods are either inaccurate or too time consuming. The goal of this research is to identify an efficient force prediction strategy based on experimental observations of forming forces. It was found that by creating a near-finished part geometry as a starting point of numerical simulation, forming forces can be predicted with satisfactory accuracy and efficiency. The proposed strategy was validated and further demonstrated in forming of parts having different geometries. As the simulation strategy can be completed in a fraction of the full simulation time, it can be adopted to guide the development of incremental sheet forming parts. [ABSTRACT FROM AUTHOR]

RIBBONS, RAPID prototyping, CONTACT mechanics, GRINDING & polishing, and COMPUTER algorithms

This paper presents a new polishing path planning method for physically uniform overlap of polishing ribbons instead of traditional geometrically uniform coverage of polishing path on freeform surfaces, which attempts to achieve the even material removal on the polished surface in consideration of contact mechanics in polishing process. The polishing ribbon is defined as the ribbon with varying width generated by continuous contact areas along the polishing path. The boundary extraction algorithm (BEA) is proposed to determine the specific polishing ribbon boundary which is next to the to-be-planned path. The path extraction algorithm (PEA) is given to predict the location of the adjacent polishing path. Those BEA and PEA make the overlap of polishing ribbons along two adjacent polishing paths physically uniform. Proposed polishing path planning is implemented for a typical freeform surface and the polishing paths with physically uniform overlap of polishing ribbons between two adjacent paths are obtained, while the under-polishing and over-polishing phenomena occur when the traditional scanning path is applied. In addition, the comparative experiments and analysis are also conducted and the experimental results further verify the feasibility of the proposed polishing path to promote even material removal. [ABSTRACT FROM AUTHOR]

LASER ablation, RAPID prototyping, GALVANOMETER, OPTICAL scanners, and ARC length

Texture patterns are fabricated on the surface of freeform parts in order to improve the performance, and to meet special functional requirements. Due to its low processing efficiency and poor processing accuracy and quality, the conventional mechanical processing cannot fully meet the requirements of the texture pattern processing on parts surface. A novel laser cross-scale micro-3D processing technology, named laser ablation by projective galvanometer scanning (LPAGS), which can fabricate texture patterns on freeform surface with high efficiency and precision has been developed in this paper. The new method is based on the combination of multi-axis machine tool and 3D galvanometer scanning laser processing head. An equal arc length projection was adopted to establish reasonable and undistorted processing model on freeform surface. By reasonable division plan, freeform surface was divided into sub-areas, sub-layers and sub-blocks. Patterns on each sub-area were converted into 2D scanning processing path by reverse projection. By systematically studying the effect of the variation of surface curvature on the focused laser spot shape, energy distribution in laser spot, the criterions of surface partition which satisfy the processing dimensional accuracy and quality were given. The experimental results demonstrate the effectiveness of this method in fabricating texture patterns on large-scale freeform surface. [ABSTRACT FROM AUTHOR]

RAPID prototyping, PROTOTYPES, MANUFACTURING processes, COMPUTER simulation, and PRODUCTION engineering

The incremental sheet forming processes (ISF) are attracting lots of attentions due to their advantages on rapid prototyping, without special dies and short lead time. The numerical simulation can be a valid method to investigate the forming process and predict the defects. In this study, an extended fully coupled ductile damage model with mixed nonlinear hardening was used to simulate the ISF process. At the same time, the yield surface distortion was also considered in this model, which can enhance the capability of modeling metallic material behavior under complex loading paths. Afterwards, some simulations were conducted with the proposed model. Additionally, one tension-shear orthogonal loading test was assigned on the one representative element in order to investigate the loading path effect during ISF process. By comparing the equivalent plastic strain and ductile damage evolution of the blank, the influence of the yield surface distortion on the ISF process was proved. [ABSTRACT FROM AUTHOR]

RAPID prototyping, PROTOTYPES, MANUFACTURING processes, SURFACE finishing, FINISHES & finishing, and SURFACE preparation

Toolpath planning for irregular-shaped compound freeform surfaces remains a challenge. This work presents a new approach for compound surface finishing by treating the toolpath planning task as a traveling salesman problem (TSP). The concept of curvature map is proposed. With this concept, the curvatures of the surface patches are recorded to corresponding cells of the map and then the path intervals are determined. The CC points as well as the normal vectors are calculated on the mesh model of the compound surface with a linear algorithm. The obtained CC points are linked as cities in LKH, in which the distance function is redefined to cope with the illegal linking problems. With LKH, tool retractions are no longer necessary. The resulted toolpath is capable of covering the whole compound surface with only one pass. The proposed toolpath generation method is more forgiving on the input. It does not require the surfaces to be perfectly conform on the joining boundaries. Several compound surface examples have been used to verify the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]