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Automated design of injection molds to reduce warpage of injection molded parts

Byung Hak Lee, University of Massachusetts Amherst


Several design methodologies for automatically designing injection molds were developed to reduce warpage of injection molded parts. The part warpage was defined from warpage simulation, so as to represent various deformation behavior of the molded part. A concept for deliberately varying part wall thicknesses, within feasible dimensional tolerances to reduce the warpage, was introduced. The wall thicknesses, that minimized the effect of process fluctuation inherent to molding process, were obtained using the Taguchi method. The results of the example indicated that one can considerably reduce the warpage, and may also reduce material costs, by varying the wall thicknesses. A modified complex method was developed to optimize various domains in injection mold design. The modified complex method significantly reduced the part warpage with a moderate number of independent analysis evaluations for the proposed optimization of: part wall thicknesses; location and sizes of cooling channels; and process conditions. The runner system of multiple cavity molds was successfully balanced by adjusting the sizes of runners and gates using the iterative redesign method integrated with packing simulation in two case studies. A design technique for automatically determining the "best" gate location(s) of injection molds was presented in association with the three important parameters in gating design--the part warpage, the weld and meld line location at the critical areas, and the Izod impact strength at a specific region of the part. The difficulty in predicting accurate values of engineering property like Izod impact strength is that they vary throughout a part with respect to the thermomechanical history. Upon evaluating each gating design, the trained neural network computation predicts, regardless of part geometry, Izod impact strength by a non-parameteric modeling of the complex relation with thermomechanical processing histories. As the results, when the polymer resin and the part geometry were predetermined, the part warpage could be considerably reduced by the developed design tools for the part wall thicknesses, the mold systems including gating, runner, and cooling system, as well as the process conditions.

Subject Area

Mechanical engineering|Industrial engineering

Recommended Citation

Lee, Byung Hak, "Automated design of injection molds to reduce warpage of injection molded parts" (1995). Doctoral Dissertations Available from Proquest. AAI9524725.