Dents are caused by local internal shrinkage after gate sealing or injection of missing material. The indentation or micro indentation on the surface of injection molded products is an old problem in the injection molding process. Dents are generally caused by an increase in the local shrinkage rate of plastic products due to an increase in wall thickness. They may appear near external sharp corners or at sudden wall thickness changes, such as protrusions, reinforcing ribs, or behind supports, and sometimes also in some uncommon areas.The fundamental cause of dents is the thermal expansion and contraction of the material, as thermoplastic materials have a relatively high coefficient of thermal expansion. The degree of expansion and contraction depends on many factors, among which the properties of the plastic, the maximum and minimum temperature ranges, and the holding pressure of the mold cavity are the most important factors. The size and shape of injection molded parts, as well as cooling speed and uniformity, are also influencing factors.
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