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RAPID prototyping, NEW product development, PROTOTYPES, RAW materials, SHEAR waves, PHOTOPOLYMERIZATION, MANUFACTURING processes, and FINITE element method

Stereolithography is one of the rapid prototyping processes which uses a photopolymer as the raw material to build prototypes. The photopolymer absorbs energy by selective laser exposure. The curing effect starts when the absorbing energy exceeds a critical value, and the process is called photopolymerisation. The photopolymerisation changes the phase from liquid to solid. The cured volume can expand and then shrink on cooling. The process parameters such as the scanning speed, scanning path, scanning pitch, and the slicing thickness, lead to different shrinkage and curl distortion, so, the photopolymerisation process is a dynamic material behaviour. In this study, a dynamic finite element simulation code has been developed to simulate the photopolymerisation process. The simulated result for a suspended beam which corresponds to the process parameters shows that a short raster causes less curl distortion than a long raster. The experimental result agrees very well with the simulated result. [ABSTRACT FROM AUTHOR]

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, MANUFACTURING processes, MATHEMATICAL optimization, and NEW product development

Rapid prototyping (RP) is an emerging technology that has been implemented in many spheres of industry – particularly in the area of new product development. Growth of this field has been rapid in recent years. Stereolithography (SL) is one of the most popular RP process used for rapid tooling applications. There are several process parameters contributing to the strength of an SL product. The contribution of three parameters; namely, layer thickness, post curing time and orientation are most significant. In light of this concern, an attempt has been made to study and optimize these process parameters for maximum part strength, and develop an empirical relationship between process parameters and part strength through design of experiments (DOE). The proposed DOE is verified with the data of experiments conducted under standard conditions. [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]

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]