Purpose: The purpose of this study is twofold: firstly, to investigate the effect of the infill value and build orientation on the fatigue behaviour of polylactic acid (PLA) specimens made by fused filament fabrication (FFF), also known as fused deposition modelling; and secondly, to model the fatigue behaviour of PLA specimens made by FFF and similar additive manufactured parts. Design/methodology/approach: A new methodology based on filament characterisation, infill measuring, axial fatigue testing and fatigue strength normalisation is proposed and implemented. Sixty fatigue FFF specimens made of PLA were fabricated and evaluated using variable infill percentage and build orientation. On the other hand, fatigue modelling is based on the normalised stress amplitude and the fatigue life in terms of number of cycles. In addition, a probabilistic model was developed to predict the fatigue strength and life of FFF components. Findings: The infill percentage and build orientation have a great influence on the fatigue behaviour of FFF components. The larger the infill percentage, the greater the fatigue strength and life. Regarding the build orientation, the specimens in the up-right orientation showed a much smaller fatigue strength and life than the specimens in the flat and on-edge orientations. Regarding the fatigue behaviour modelling, the proposed Weibull model can predict with an acceptable reliability the stress-life performance of PLA-FFF components. Research limitations/implications: This study has been limited to axial fatigue loading conditions along three different build orientations and only one type of material. Practical implications: The results of this study are valuable to predict the fatigue behaviour of FFF parts that will work under variable loading conditions. The proposed model can help designers and manufacturer to reduce the need of experimental tests when designing and fabricating FFF components for fatigue conditions. Originality/value: A fatigue study based on a novel experimental methodology that considers the variation of the FFF process parameters, the measurement of the real infill value and the normalisation of the results to be comparable with other studies is proposed. Furthermore, a new fatigue model able to predict the stress-life fatigue behaviour of PLA-FFF components considering variable process parameters is also proposed. [ABSTRACT FROM AUTHOR]
POLYLACTIC acid, STRAIN rate, STRAINS & stresses (Mechanics), DIGITAL image correlation, TAGUCHI methods, and FUSED deposition modeling
Abstract
Purpose: This paper aims to investigate the effects of build parameters and strain rate on the mechanical properties of three-dimensional (3D) printed polylactic acid (PLA) by integrating digital image correlation and desirability function analysis. The build parameters included in this paper are the infill density, build orientation and layer height. These findings provide a framework for systematic mechanical characterization of 3D-printed PLA and potential ways of choosing process parameters to maximize performance for a given design. Design/methodology/approach: The Taguchi method was used to shortlist a set of 18 different combinations of build parameters and testing conditions. Accordingly, 18 specimens were 3D printed using those combinations and put through a series of uniaxial tensions tests with digital image correlation. The mechanical properties deduced for all 18 tests were then used in a desirability function analysis where the mechanical properties were optimized to determine the ideal combination of build parameters and strain rate loading conditions. Findings: By comparing the tensile mechanical experimental properties results between Taguchi's recommended parameters and the optimal parameter found from the response table of means, the composite desirability had increased by 2.08%. The tensile mechanical properties of the PLA specimens gradually decrease with an increase in the layer height, while they increase with increasing the infill densities. On the other hand, the mechanical properties have been affected by the build orientation and the strain rate in similar increasing/decreasing trends. Additionally, the obtained optimized results suggest that changing the infill density has a notable impact on the overall result, with a contribution of 48.61%. DIC patterns on the upright samples revealed bimodal strain patterns rendering them more susceptible to failures because of printing imperfections. Originality/value: These findings provide a framework for systematic mechanical characterization of 3D-printed PLA and potential ways of choosing process parameters to maximize performance for a given design. [ABSTRACT FROM AUTHOR]
Purpose: Liquid crystal display (LCD)-based stereolithography (SLA) technique has been used in drug delivery and fabrication of microfluidic devices and piezoelectric materials. It is an additive manufacturing technique where an LCD source has been used as a mask to project the image onto the tank filled with photo curable resin. This resin, when interacted with light, becomes solid. However, critical information regarding the energy absorption during the compression analysis of different components three-dimensional (3D) printed by SLA process is still limited. Therefore, this study aims to investigate the effect of different process parameters on the compressive properties. Design/methodology/approach: In the present study, the influence of layer thickness, infill density and build orientation on the compression properties is investigated. Four infill densities, that is, 20%, 40%, 60% and 80%; five-layer thicknesses, that is, 50 µm, 75 µm, 100 µm, 150 µm and 200 µm; and two different orientations, that is, YXZ and ZXY, have been selected for this study. Findings: It is observed that the samples printed with acrylonitrile butadiene styrene (ABS) absorbed higher energy than the flexible polyurethane (FPU). Higher infill density and sample oriented on ZXY absorbed higher energy than sample printed on YXZ orientation, in both the ABS and FPU materials. Parts printed with 80% infill density and 200 µm layer thickness resulted into maximum energy for both the materials. Originality/value: In this study, two different types of materials are used for the compression analysis using LCD-SLA-based 3D printer. Specific energy absorbed by the samples during compression testing is measured to compare the influence of parameters. The investigation of infill parameters particularly the infill density is very limited for the SLA-based 3D printing process. Also, the results of this study provide a database to select the print parameters to obtain the required properties. The results also compare the specific energy for hard and flexible material for the same combination of the process parameters. [ABSTRACT FROM AUTHOR]
METAL fibers, ALLOYS, TENSILE tests, and BENDING strength
Abstract
Purpose: The purpose of this paper is to systematically investigate the influence of build orientation on the anisotropic as-printed and as-sintered bending properties of 17-4PH stainless steel fabricated by metal fused filament fabrication (MFFF). Design/methodology/approach: The bending properties of 17-4PH alloy fabricated by low-cost additive manufacturing (MFFF) using three build orientations (the Flat, On-edge and Upright orientations) are examined at both as-printed and as-sintered states. Findings: Unlike tensile testing where the Flat and On-edge orientations provide similar as-sintered tensile properties, the On-edge orientation produces a significantly higher bending strain with a lower bending strength than the Flat orientation. This arises from the printed layer sliding due to the Poisson's effect, which is only observed in the On-edge orientation together with the alternated layers of highly deformed and shifted voids. The bending properties show that the Upright orientation exhibits the lowest bending properties and limited plasticity due to the layer delamination. Originality/value: This study is the first work to study the effect of build orientation on the flexural properties for MFFF. This work gives insight information into anisotropy in flexural mode for MFFF part design. [ABSTRACT FROM AUTHOR]
FIBERS, TEMPERATURE control, THREE-dimensional printing, HEAT transfer, and MECHANICAL properties of condensed matter
Abstract
Purpose: The performance of the parts obtained by fused filament fabrication (FFF) is strongly dependent on the extent of bonding between adjacent filaments developing during the deposition stage. Bonding depends on the properties of the polymer material and is controlled by the temperature of the filaments when they come into contact, as well as by the time required for molecular diffusion. In turn, the temperature of the filaments is influenced by the set of operating conditions being used for printing. This paper aims at predicting the degree of bonding of realistic 3D printed parts, taking into consideration the various contacts arising during its fabrication, and the printing conditions selected. Design/methodology/approach: A computational thermal model of filament cooling and bonding that was previously developed by the authors is extended here, to be able to predict the influence of the build orientation of 3D printed parts on bonding. The quality of a part taken as a case study is then assessed in terms of the degree of bonding, i.e. the percentage of volume exhibiting satisfactory bonding between contiguous filaments. Findings: The complexity of the heat transfer arising from the changes in the thermal boundary conditions during deposition and cooling is well demonstrated for a case study involving a realistic 3D part. Both extrusion and build chamber temperature are major process parameters. Originality/value: The results obtained can be used as practical guidance towards defining printing strategies for 3D printing using FFF. Also, the model developed could be directly applied for the selection of adequate printing conditions. [ABSTRACT FROM AUTHOR]
ARTIFICIAL saliva, GEOMETRY, RAPID prototyping, DETERIORATION of materials, TRANSVERSAL lines, and SHAPE memory polymers
Abstract
Additive manufacturing of polymers has evolved from rapid prototyping to the production of functional components/parts with applications in distinct areas, ranging from health to aeronautics. The possibility of producing complex customized geometries with less environmental impact is one of the critical factors that leveraged the exponential growth of this processing technology. Among the several processing parameters that influence the properties of the parts, the geometry (shape factor) is amid less reported. Considering the geometric complexity of the mouth, including the uniqueness of each teething, this study can contribute to a better understanding of the performance of polymeric devices used in the oral environment for preventive, restorative, and regenerative therapies. Thus, this work aims to evaluate 3D printed poly(ε-caprolactone) mechanical properties with different build orientations and geometries. Longitudinal and transversal toolpaths produced specimens with parallelepiped and tubular geometry. Moreover, as it is intended to develop devices for dentistry, the influence of artificial saliva on mechanical properties was determined. The research concluded that the best mechanical properties are obtained for parallelepiped geometry with a longitudinal impression and that aging in artificial saliva negatively influences all the mechanical properties evaluated in this study. [ABSTRACT FROM AUTHOR]
A. Matos, Marina, Rocha, Ana Maria A. C., Costa, Lino, Pereira, Ana I., and Universidade do Minho
Subjects
3D Printing, Additive Manufacturing, Build Orientation, and Multi-objective Optimization
Abstract
Over the years, rapid prototyping technologies have grown and have been implemented in many 3D model production companies. A variety of different additive manufacturing (AM) techniques are used in rapid prototyping. AM refers to a process by which digital 3D design data is used to build up a component in layers by depositing material. Several high-quality parts are being created in various engineering materials, including metal, ceramics, polymers and their combinations in the form of composites, hybrids, or functionally classified materials. The orientation of 3D models is very important since it can have a great influence on the surface quality characteristics, such as process planning, post-processing, processing time and cost. Thus, the identification of the optimal build orientation for a part is one of the main issues in AM. The quality measures to optimize the build orientation problem may include the minimization of the surface roughness, build time, need of supports, maximize of the part stability in building process or part accuracy, among others. In this paper, a multi-objective approach was applied to a computer-aided design model using MATLAB® multi-objective genetic algorithm, aiming to optimize the support area, the staircase effect and the build time. Preliminary results show the effectiveness of the proposed approach.
AlRedha, Sultan, Shterenlikht, Anton, Mostafavi, Mahmoud, Van Gelderen, Derreck, Lopez-Botello, Omar Eduardo, Reyes, Luis Arturo, Zambrano, Patricia, and Garza, Carlos
FRACTURE toughness, MELTING, BULK solids, LASERS, FRACTOGRAPHY, and METALLOGRAPHY
Abstract
Purpose: A key challenge found in additive manufacturing is the difficulty to produce components with replicable microstructure and mechanical performance in distinct orientations. This study aims to investigate the influence of build orientation on the fracture toughness of additively manufactured AlSi10Mg specimens. Design/methodology/approach: The AlSi10Mg specimens were manufactured using the selective laser melting (SLM) technology. The fracture toughness was experimentally determined (under ASTM E399-09) using C(T) specimens manufactured in different orientations. The microstructure of the specimens was examined using metallography to determine the effects of grain orientation on fracture toughness. Findings: The fracture toughness magnitude of manufactured specimens ranged between 36 and 50 MPam, which closely matched conventional bulk material and literature values regarding AlSi10Mg components. The C(T) specimens printed in the T-L orientation yielded the highest fracture toughness. The grain orientation and fracture toughness values confirm the anisotropic nature of SLM parts where the T-L-oriented specimen obtained the highest KIC value. A clear interaction between the melt pool boundaries and micro-slipping during the loading application was observed. Originality/value: The novelty of this paper consists in elucidating the relationship between grain orientation and fracture toughness of additively manufactured AlSi10Mg specimens because of the anisotropy generated by the different melting pool boundaries and orientations in SLM. The findings show that melt pool boundaries can behave as easier pathways for cracks to propagate and subsequently reduce the fracture toughness of specimens with cracks perpendicular to the build direction. [ABSTRACT FROM AUTHOR]
Purpose: This paper aims to investigate the structural behaviour of polylactic acid (PLA) parts fabricated by fused deposition modelling (FDM) to support the development of analytical and numerical models to predict the structural performance of FDM components and categories of similar additive manufactured parts. Design/methodology/approach: A new methodology based on uniaxial tensile tests of filaments and FDM specimens, infill measurement and normalization of the results is proposed and implemented. A total of 396 specimens made of PLA were evaluated by using variable process parameters. Findings: The infill and the build orientation have a large influence on the elastic modulus and ultimate tensile stress, whereas the layer thickness and the infill pattern have a low influence on these properties. The elongation at break is not influenced by the process parameters except by the build orientation. Furthermore, the infill values measured on the test specimens differ from the nominal values provided by the system. Research limitations/implications: The analysis of the structural properties of FDM samples is limited to uniaxial loading conditions. Practical implications: The obtained results are valuable for the structural analysis and numerical simulation of FDM components and for potential studies using machine learning techniques to predict the structural response of FDM parts. Originality/value: A new experimental methodology that considers the measurement of the real infill percentage and the normalization of the results for inter-comparison with other studies is proposed. Moreover, a new set of experimental results of FDM-PLA parts is presented and extends the existing results in the literature. [ABSTRACT FROM AUTHOR]
Purpose: The cement-filled PA12 manufactured by selective laser sintering (SLS) offers desirable mechanical properties; however, these properties are dependent on several fabrication parameters. As a result, SLS prototypes may exhibit orthotropic mechanical properties unless properly oriented in build chamber. This paper aims to evaluate the effects of part build orientation, laser energy and cement content on mechanical properties of cement-filled PA12. Design/methodology/approach: The test specimens were fabricated by SLS using the "DTM Sinterstation 2000" system at which the specimens were aligned along six different orientations. The scanning speed was 914mm/s, scan spacing was 0.15mm, layer thickness was 0.1mm and laser power was 4.5–8Watt. A total of 270 tensile specimens, 270 flexural specimens and 135 compression specimens were manufactured and the tensile, compression and flexural properties of fabricated specimens were evaluated. Findings: The experiments revealed orientation-dependent (orthotropic) mechanical properties of SLS cement-filled PA12 and confirmed that the parts with shorter scan vectors have enhanced flexural strength as compared with longer scan vectors. The maximum deviations of ultimate tensile strength, compressive strength and flexural modulus along the six orientations were 32%, 26% and 36%, respectively. Originality/value: Although part build orientation is a key fabrication parameter, very little was found in open literature with contradictory findings about its effect on mechanical properties of fabricated parts. In this work, the effects of build orientation when combined with other fabrication parameters on the properties of SLS parts were evaluated along six different orientations. [ABSTRACT FROM AUTHOR]
THREE-dimensional printing, TENSILE strength, 3-D printers, SCANNING electron microscopes, and FRACTURE mechanics
Abstract
Purpose The main purpose of this paper is to investigate the influence of build orientation on the tensile properties of PolyJet 3D printed parts. Effects on manufacturing time and total cost per part are the secondary objectives.Design/methodology/approach Solid tensile specimens were prepared as per the American Society for Testing and Materials D638 standards and were manufactured in six different orientations by using the Objet260 Connex 3D printer. VeroWhitePlus RGD835 was used as the build material, with FullCure 705 as the support material. The specimens were tested for their tensile strength and elongation. The side surface and the fracture surface were analyzed using the Field Emission Scanning Electron Microscope-SIGMA HV-Carl Zeiss with Bruker Quantax 200-Z10 EDS detector. Scanning electron microscope images of each surface were obtained at various magnifications.Findings From the study, it can be concluded that build orientation has an influence on the tensile strength and the manufacturing cost of the parts. The microstructural analysis revealed that the orientation of surface cracks/voids may be the reason for the strength.Originality/value From literature survey, it is inferred that this study is sure to be among the first few under this topic. These results will help engineers to decide upon the right build orientations with respect to print head so that parts with better mechanical properties can be manufactured. [ABSTRACT FROM AUTHOR]
AEROFOILS, ENGINEERING, WIND turbines, ENGINEERING students, and TURBINES
Abstract
A practical project undertaken by many first-year Engineering students at Lancaster University is to design, build and test a model wind turbine. Until recently it was difficult to produce convincing aerofoil shapes at small scale, but the recent acquisition of a fused-deposition modeller (FDM) has provided an opportunity to improve the accuracy of the model aerofoils that students can produce. This paper discusses the design method and tools used by the students, and the production of test blades. Particular note is made of the effects of the FDM construction on the blades, including the orientation of build and resulting surface finish, structural issues, and cost. Samples of graphics from student reports are presented, including some results for the efficiency of the turbines. [ABSTRACT FROM AUTHOR]
GENETIC algorithms, COST, COMBINATORIAL optimization, COMBINATORIAL analysis, and MATHEMATICAL optimization
Abstract
Build orientation is an important fabrication parameter in layer manufacturing (LM) since it affects the part fabrication accuracy, cost, and time. Despite its importance, orientation selection relies quite heavily on the experience and skill of the operator of the LM system, which does not guarantee optimality of the decision. In the present work, a decision support system that automates the orientation selection task is proposed. The proposed system utilizes genetic algorithms and multi-criteria optimization techniques for the definition of (near) optimum build orientation for parts fabricated with stereolithography. Build time, surface roughness, and post-processing time are considered as the main optimization criteria. [ABSTRACT FROM AUTHOR]
RAPID prototyping, NUMERICAL control of machine tools, and MACHINING
Abstract
To overcome the limitations of the layered manufacturing process, hybrid rapid-prototyping systems that allow material removal and deposition are being introduced. This approach should benefit from the advantages of conventional layered manufacturing and traditional CNC machining processes. To realize these advantages, however, an intelligent process plan must be generated. In the hybrid rapid-prototyping process, a part is decomposed into thick-layered 3D shapes, such that each layer can be machined and stacked easily. When each layer is generated from the part’s shape, the build orientation is an important factor to be considered, because it greatly influences the lead-time, the machining accuracy, and the number of tool-accessible features in each setup. In this paper, an algorithm to determine the build orientation is described. It considers the deposition process attributes and the machining process attributes simultaneously. [Copyright &y& Elsevier]
