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LIQUID crystal displays, LIQUID crystal devices, NEW product development, MANUFACTURING processes, LITHOGRAPHY, RAPID prototyping, FINITE element method, and COMPUTER simulation

In many investigations, a liquid crystal display (LCD) has been used as the photo mask in a stereolithography system. The LCD mask has the potential to increase the speed of rapid prototyping (RP) fabrication as well as to reduce the system cost. Compared to the conventional laser-scanning technique used in 3D systems stereolithography apparatus (SLA), the reaction heat of layer curing is released as the area is exposed, and it is higher than that of the laser scanning in which the reaction heat only releases point-by-point. On the other hand, mask type stereolithography has a more serious shrinkage effect than the other methods and requires further analysis. This paper analyses the shrinkage deformation of the mask type stereolithography process. A simulation code based on the dynamic finite-element method has been developed to predict the 3D shrinkage and to monitor the RP fabrication, which consists of three stages of simulation which include the pre-processor, the analytic processor and the post-processor. In order to fabricate experimental parts, a mask type stereolithography system has been assembled. The principle of the experimental apparatus is also briefly described. For evaluation of the experimental and simulation results, a thin shell wall rectangular part was fabricated and measured. The simulation program developed has been proved to be in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

RAPID prototyping, PROTOTYPES, INDUSTRIAL design, ENGINEERING design, and ENGINEERING models

The rapid prototyping (RP) process is the fastest and most feasible method for prototype construction. However, with the use of any material or build method the phenomenon of volume shrinkage is unavoidable. It is known that volume shrinkage and curl distortion are the major causes that lead to poor accuracy of the built prototype. Subsequently, in order to improve the precision of dimension and volume shrinkage, more expensive equipment is used on the market. Also, it is expensive and inefficient to obtain better process parameters through trail and error in the RP process. In order to improve the precision of dimension, reduce the processing cost and the frequency of trail and error, this study first induces the concept of computer-aided engineering (CAE) into the processing of RP, which uses a dynamic finite element simulation code to simulate the photopolymerization process, so as to reduce the time for selecting the processing parameters and obtain the distortion data. Second, by means of reverse distortion compensation to obtain a new CAD model, then it is sent to a RP machine for the actual prototyping processes, so as to obtain a more accurate precision. Finally, in order to confirm this method and restriction in experimental equipment, the stereolithography process and simple laser scanning path are chosen as examples. The results of the simulation and experiment prove that the method proposed herein is effective. It not only can reduce the cost of equipment but also obtain a better precision of dimension on final-parts at the same time. Besides, it is believed that this research method can be promoted to other materials or build methods in RP fabrication . [ABSTRACT FROM AUTHOR]

RAPID prototyping, PROTOTYPES, MANUFACTURING processes, POLYMERS, and POLYMERIZATION

Stereolithography (SL) is one of the rapid prototyping (RP) systems that use liquid photopolymer resin as the raw material for building prototypes. The photopolymer type of the RP system employs lasers to selectively expose the surface of the liquid resin. The absorbance of energy leads to photo-polymerization that transfers the liquid resin into solid. Subsequently, the phenomenon of volume shrinkage is unavoidable, and the curl distortion changes with the different laser scan paths, even affecting the geometric profile of the final-parts. The volume shrinkage and curl distortion are the major causes that lead to poor accuracy of the built prototype. In order to understand and improve the curl distortion and the geometric profile, so as to find a simple and suitable laser scan path. This paper first of all uses simulation and experiment to explore the deformation and shrinkage during the process of photo-polymerization while the liquid resin uses a laser beam to carry out single line scanning or single layer scanning in liquid free surface, and further understands the final change of geometric profile. Secondly, it investigates into the curl distortion and changes of geometric profile occurred in the three-dimensional part by different scan paths. Finally, a simple, proper, and effective laser scan path planning is suggested to decrease the curl distortion, and promote the dimension accuracy and the profile of the final-parts. Besides, this paper also mentions the feasibility of multi-optical processing. [ABSTRACT FROM AUTHOR]

MANUFACTURING processes, GENETIC algorithms, COMBINATORIAL optimization, PRODUCTION engineering, INDUSTRIAL engineering, and PRODUCTION methods

Genetic algorithms (GAs) have gained wide research and applications in production scheduling fields, but the efficiency and effectiveness of a GA significantly depend on its parameters and operators. In contrast to the rich research on determination of optimal and adaptive parameters, little research has been done on determining optimal combination of genetic operators. Different from the traditional way by trial and error, this paper presents a novel and systematical approach based on ordinal optimisation (OO) and optimal computing budget allocation (OCBA) technique to determine optimal combination of genetic operators for flow shop scheduling problems. Simulation results show that the proposed methodology is able to determine optimal combination of genetic operators and simultaneously to provide a good solution with reasonable performance evaluation for scheduling problem. [ABSTRACT FROM AUTHOR]

RAPID prototyping, PROTOTYPES, MICROSTRUCTURE, HIGH resolution spectroscopy, SCANNING systems, and LITHOGRAPHY

A high-resolution stereolithography (SL) system for fabricating small objects with complex microstructures has been developed. This novel SL system consists of a single mode He-Cd laser, an improved optical scanning system, a novel recoating system and a control system. A laser light spot with the diameter of 12.89 μm on the focal plane is obtained with the improved optical scanning system, and resin layers with the thickness of 20 μm can be built with the novel recoating system. Experimental studies were carried out to investigate the influences of the build parameters on the cured line width and depth with this novel SL system. The experimental results showed that the cured depth and width increase with the increasing ratio of laser power to scanning speed. And it is found that the cured line built using the high-resolution SL system is smaller in width and deeper in depth compared with the cured line fabricated in conventional SL system under the same scanning conditions. Based on the cured line width and depth obtained in the experiment, empirical equations predicting the cured line width and depth according to the ratio of laser power to scanning speed are established using a least-square fitting. The cured line width and depth predicted by the empirical equations provide a foundation to set up accurate line width compensation and appropriate layer thickness in the high-resolution SL system. Some small objects with microstructures have been fabricated with the new SL system. [ABSTRACT FROM AUTHOR]

LITHOGRAPHY, RAPID prototyping, ULTRAVIOLET radiation, DEGREES of freedom, and SCANNING systems

Stair-stepping is one of the major causes of poor surface finish in stereolithography (SLA) and other rapid prototyping (RP) systems. Taking this effect as an inability of conventional scanning systems, which can only fabricate layers with straight edges, the authors have studied and implemented a new SLA scanning technique. In the new method, termed slant beam rotation (SBR) scanning, an inclined beam of ultra violet (UV) light fabricates slant edges of individual layers, while an additional degree of freedom (DOF) in the scan head is used to rotate the beam inside the resin through 360 degrees to change the build angle. The data format needed to complete this scanning process has also been prepared and reported along-with the development of the stereolithography system. Through fabrications and analyses, it has been found that average surface roughness of a typical stair-stepped object reduced to 1.1 μm from 18.0 μm otherwise. [ABSTRACT FROM AUTHOR]

ALGORITHMS, PRODUCTION planning, VISCOSITY, RHEOLOGY, FLUID dynamics, and ERRORS

Recently, a multiple-material stereolithography (MMSL) system was introduced, which included the novel feature of stacking different photocurable resins to produce a multiple-material part. This process is capable of fabricating intricately detailed parts with smooth surface finish and internal structures of various colors. However, the MMSL system requires a washing process when switching materials, and this additional step increases the fabrication time and also introduces deformations in the build structure as registration errors accumulate. Consequently, reducing the number of material changeovers in this process is a priority, and the minimum number of changeovers is imposed in part by the sweep interference between layers of different materials. Fortunately, the use of low-viscosity resins permits possible fabrication without sweeping. As a result, multiple layers of one material can be continuously built without changing resins, and subsequently, a different low-viscosity material can be added without resulting in sweep obstruction with the original layers. In this paper, a stacking simulation, which determines the maximum number of layers possible to be continuously built between material changeovers, is described. This paper presents a novel interference-detection algorithm, which identifies interference by inspecting the overlap between loop segments. In addition, the algorithm successfully manages the triangulation errors that occur at a curved surface when two materials are adjacent within a layer. Finally, several practical examples are shown to verify the algorithm and provide compelling evidence that the proposed algorithm is effective and applicable in MMSL. [ABSTRACT FROM AUTHOR]

GENETIC algorithms, MULTIPLE criteria decision making, and STEREOLITHOGRAPHY

A correction to the article "Genetic-algorithm-based multi-objective optimization of the build orientation in stereolithography" which was published online on February 23, 2010 is presented.

LITERARY errors & blunders, TERMS & phrases, PUBLISHING, THREE-dimensional printing, STEREOLITHOGRAPHY, and RAPID prototyping

THREE-dimensional printing, MANUFACTURING processes, PRODUCTION planning, STEREOLITHOGRAPHY, POLYGONS, and RAPID prototyping

Additive Manufacturing (AM) is a process in which material is added layer by layer to build a physical part. In AM process planning, a stack of 2D closed contours is obtained when a 3D stereolithography (STL) model is sliced. Each slice may have a set of closed contours or polygons, each of which needs to be classified (oriented) as internal (clockwise) or external (counterclockwise) to identify where material should be added. This is not a straightforward task as the STL format does not ensure correct surface orientation of the 3D model. This work describes two methods for identifying the direction of each contour in a set, i.e., for sorting them into internal and external contours. Three alternative tests to check whether a point is inside or outside a polygon were evaluated. The tests are based on the ray-tracing principle and the classical point-in-polygon test. The proposed algorithms were devised and implemented in an AM process planning system. The methods were validated using 3D models with a variety of geometries, and the computing time for the alternative tests was compared. The results showed that the method based on the point-in-polygon tests has some advantages. [ABSTRACT FROM AUTHOR]

ANISOTROPY, STEREOLITHOGRAPHY, PHOTOPOLYMERS, RAPID prototyping, CERAMIC materials, FRACTURE mechanics, INVESTMENT casting, and MATHEMATICAL models

Photopolymer-based stereo-lithography (SL) rapid prototyping patterns with honeycomb internal structure reduce lead time and material cost for pattern manufacturing and also minimize ceramic mold residue after pattern removal in investment casting process. However, relatively larger thermal expansion of SL pattern tends to cause ceramic shell cracking during the pattern thermal removal. The anisotropy of SL pattern properties incurs different stress states of ceramic shell depending on the orientation of the honeycomb structure. In this work, a comprehensive thermo-mechanical coupled finite element model was developed to characterize the anisotropy of SL pattern and its effect on stress in investment casting shell molds. An experimental-based thermal degradation material model was developed considering anisotropy of the thermo-mechanical properties of SL pattern. The static analysis of slurry dipping and transient thermo-mechanical analysis of the pattern thermal removal process were performed. Both the pattern and ceramic shell behavior were studied and validated with experimental findings. Facesheet thickness/facesheet-to-core ratio and orientation of honeycomb structure were found to be the key factors to shell stress during pattern firing. Decreased facesheet thickness reduces stress in shell but also increases shell stress sensitivity to anisotropy of SL pattern. The developed tool provides an effective and efficient way to evaluate and optimize the structure of SL pattern for investment casting process. [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]

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]