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Thermal analysis for injection molding of thermoplastics

Chi-Joan Yu, University of Massachusetts Amherst


The goals of this study are to increase the accuracy and consistency of the simulated results of the Computer Aided Engineering (CAE) cooling analysis software for injection molding and to develop a relative cooling time table for commonly used thermoplastics. The CAE cooling analysis software will then be useful in increasing the efficiency of design and manufacturing. The relative cooling time table will be useful to selected the appropriate material in order to reduce the production cost. Due to the lack of knowledge about thermal contact resistance and specification of process parameter inputs of Polycool II--a cooling simulation software for injection molding, the simulation data of Polycool II have a very poor agreement with the field or experimental data. This work addresses these issues. This study is comprised of the following components: to obtain the thermal contact resistance (TCR) between the injection molded part and the mold; to determine the ejection temperature of the parts; to study how process parameters affect TCR and ejection temperature; to study the relative cooling time of material; and to study the effects of using a specific material on the production cost. Experiments were conducted to obtain temperature distributions, cooling time, part thickness, and the inside cavity pressure distributions for a large number of injection molded parts. The temperature distribution was used as the boundary condition in the thermal analysis for each experiment. The cooling time data were used to determine the ejection temperature, to formulate an equation for obtaining the relative cooling time for the materials not included in the experiments, and to develop the relative cooling time table. The relative cooling time is defined as the ratio of the cooling time of the material to the cooling time of general purpose Polystyrene (PS) where both materials are used to produce the same part. The inside cavity pressure distributions provided the information needed to explain the TCR behavior. Thermal analyses were performed to obtain the bulk temperature distributions of the parts and the thermal contact resistance (TCR) between the parts and the mold. The bulk temperature distribution was used to determine the ejection temperature, which is defined as the bulk temperature of part at the moment when the part is ejected. The TCR data were used in Polycool II and significantly increased the accuracy and consistency of the simulated data. The significant improvement of the simulated results has been demonstrated by using three examples.

Subject Area

Mechanical engineering

Recommended Citation

Yu, Chi-Joan, "Thermal analysis for injection molding of thermoplastics" (1990). Doctoral Dissertations Available from Proquest. AAI9035422.