The effect of shrinkage induced interface gap on the thermal contact resistance between the mold and plastic in injection molding

Accurate modeling of the heat transfer from the relatively hot plastic to the relatively cold injection mold is essential to obtain accurate simulation of the injection molding process. The thermal contact resistance is one parameter that affects the heat transfer in injection molding and is difficult to measure from laboratory experiments. In injection molding the thermal contact resistance in the post filling stage is shown to depend on the gap formed between the part and the mold wall due to part shrinkage. It is shown from shrinkage calculations that the thermal contact resistance is a time and space (location on the part surface) dependent parameter and its value can vary by orders magnitude during each molding cycle. The effects of this variation on the molding process are discussed.