Warpage control of thin-walled injection molding using local mold temperatures

Currently, 3C products are required to be lightweight, portable, and convenient. Injection molding is among the most used techniques for mass production in plastic processing industries; however, producing thinner parts that do not warp is challenging. Although plastic components warp for numerous complicated reasons, warpage primarily is caused by variations in shrinkage during the injection process of plastic part manufacturing. Material properties, part design, mold design, and processing conditions are factors influencing variations in the part shrinkage. For example, inconsistent thickness in component geometry, poor sprue-runner-gate or cooling design in the injection mold, and improper molding condition settings may cause plastic parts to warp excessively. Warpage causes unpredictable component shapes, which may cause poor assembly quality. Although mold cooling achieved by adjusting mold temperatures improves warpage, the conventional single mold temperature setting for each male or female mold plate limits the cooling capability. Therefore, this paper describes local mold temperature settings for a cooling system that can prevent severe warpage in an asymmetric plastic cover for handheld communication devices. The neutral axis theory is introduced to analyze the temperature distribution in the cross section of a part, and then predict the warping trend. Through simulation and experiments conducted in this study, the feasibility of using an effective local mold temperature setting in a cooling system to reduce part warpage was verified.