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In this paper, based on the above analysis, a new simula¬tion system for RP molds is developed. The proposed system focuses on predicting part distortion, which is dominating defect in RP-molded parts. The developed simulation can be applied as an evaluation tool for RP mold design and process opti¬mization. Our simulation system is verified by an experimental example.
Although many materials are available for use in RP tech¬nologies, we concentrate on using stereolithography (SL), the original RP technology, to create polymer molds. The SL pro¬cess uses photopolymer and laser energy to build a part layer by layer. Using SL takes advantage of both the commercial domi¬nance of SL in the RP industry and the subsequent expertise base that has been developed for creating accurate, high-quality parts. Until recently, SL was primarily used to create physical models for visual inspection and form-fit studies with very limited func¬tional applications. However, the newer generation stereolitho¬graphic photopolymers have improved dimensional, mechanical and thermal properties making it possible to use them for actual functional molds.
2 Integrated simulation of the molding process
2.1 Methodology
In order to simulate the use of an SL mold in the injection molding process, an iterative method is proposed. Different soft¬ware modules have been developed and used to accomplish this task. The main assumption is that temperature and load bound¬ary conditions cause significant distortions in the SL mold. The simulation steps are as follows:
1 The part geometry is modeled as a solid model, which is translated to a file readable by the flow analysis package.
2 Simulate the mold-filling process of the melt into a pho¬topolymer mold, which will output the resulting temperature and pressure profiles.
3 Structural analysis is then performed on the photopolymer mold model using the thermal and load boundary conditions obtained from the previous step, which calculates the distor¬tion that the mold undergo during the injection process.
4 If the distortion of the mold converges, move to the next step. Otherwise, the distorted mold cavity is then modeled (changes in the dimensions of the cavity after distortion), and returns to the second step to simulate the melt injection into the distorted mold.
5 The shrinkage and warpage simulation of the injection molded part is then applied, which calculates the final distor¬tions of the molded part.
In above simulation flow, there are three basic simulation mod¬ules.
2. 2 Filling simulation of the melt
2.2.1 Mathematical modeling
In order to simulate the use of an SL mold in the injection molding process, an iterative method is proposed. Different software modules have been developed and used to accomplish this task. The main assumption is that temperature and load boundary conditions cause significant distortions in the SL mold. The simulation steps are as follows:
1. The part geometry is modeled as a solid model, which is translated to a file readable by the flow analysis package.
2. Simulate the mold-filling process of the melt into a photopolymer mold, which will output the resulting temperature and pressure profiles.
3. Structural analysis is then performed on the photopolymer mold model using the thermal and load boundary conditions obtained from the previous step, which calculates the distortion that the mold undergo during the injection process.
4. If the distortion of the mold converges, move to the next step. Otherwise, the distorted mold cavity is then modeled (changes in the dimensions of the cavity after distortion), and returns to the second step to simulate the melt injection into the distorted mold.