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Automated mold design for reaction injection molding

Authors He, Yong-Jun
Issue Date 2001
Summary Casting and molding are popular manufacturing processes that transform molten materials into designed solid shapes. A gate and a mold cavity (impression) are the two necessary components of a molding process. Proper selection of a location for the gate is a challenging issue, which is commonly conducted by complex thermal and fluid simulations. In addition, mold pieces (cavities) generation from a given molded part usually consumes much time and labor as CAD software provides very limited functions for mold design. A simple and effective automation system of mold design is needed to dramatically reduce the cycle time of developing new products. The objective of this thesis is to propose a design framework for automated gate location selection and mold shape (cavity) generation. Reaction injection molding (RIM) is a molding process becoming more popular as it has wide applications and superior processing conditions. The critical requirement in RIM is that the filling time is short enough to allow the curable resins to fill up the mold before polymerization. Besides increasing injection pressure, proper selection of a gate location is an important element to achieve this requirement. From a geometric point of view, the geodesic center of a molded part is a good candidate for a gate location as it gives the shortest flow length. However, the geodesic center of a 3-D object is difficult to obtain. The Surface Contraction Method (SCM) proposed in this thesis is to approximate the geodesic center. This method, which is implemented on a voxel-based model representing a 3-D object, suffers easily from artificial breakages. To prevent artificial breakages, three breakpoint-checking rules were developed to guarantee the connectivity of the surface contracted object. This enables the object to contract smoothly into the approximate geodesic center without artificial breakages. The SCM was applied to several illustrative cases and the resultant gate locations are in line with physical expectations. Experiments were also conducted to verify the effectiveness of the SCM. Many researchers considered mold shape (cavity) generation as simply looking for parting lines. However, parting lines alone cannot fully define the mold cavity in cases with inner parting lines. In the thesis, the concept of a contact line is introduced to fully define the mold cavity with inner parting lines. A draft angle can also be added to the mold halves to reduce the difficulty of assembly. In order to automate the process of mold shape generation, new algorithms implemented on the voxel model are proposed. The algorithms determine not only the parting lines, but also the surface points of the cavities of mold halves.
Note Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2001
Language English
Format Thesis
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