Liparoti Sara, De Piano Giorgia, Salomone Rita, Pantani Roberto
Department of Industrial Engineering, University of Salerno, via Giovanni Paolo II 132, 84084 Fisciano, Italy.
Materials (Basel). 2023 Sep 3;16(17):6053. doi: 10.3390/ma16176053.
Micro-injection molding (µIM) is a widespread process for the production of plastic parts with at least one dimension, or feature, in the microscale (conventionally below 500 µm). Despite injection molding being recognized as a robust process for obtaining parts with high geometry accuracy, one last occurrence remains a challenge in micro-injection molding, especially when junctions are present on the parts: the so-called weld lines. As weld lines are crucial in determining mechanical part performances, it is mandatory to clarify weld line position and characteristics, especially at the industrial scale during mold design, to limit failure causes. Many works deal with weld lines and their dependence on processing parameters for conventional injection molding, but only a few works focus on the weld line in µIM. This work examines the influence of mold temperature on the weld line position and strength by both experimental and simulation approaches in µIM. At mold temperatures below 100 °C, only short shots were obtained in the chosen cavity. At increased mold temperatures, weld lines show up to a 40% decrease in the whole length, and the overall tensile modulus doubles. This finding can be attributed to the reduction of the orientation at the weld line location favored by high mold temperatures. Moldflow simulations consistently reproduce the main features of the process, weld line position and length. The discrepancy between experimental and simulated results was attributed to the fact that crystallization in flow conditions was not accounted for in the model.
微注塑成型（µIM）是一种广泛应用的工艺，用于生产至少有一个尺寸或特征处于微观尺度（传统上低于500µm）的塑料零件。尽管注塑成型被认为是一种能够获得具有高精度几何形状零件的可靠工艺，但在微注塑成型中仍有一个问题是挑战，特别是当零件上存在连接处时：即所谓的熔接线。由于熔接线对于确定机械零件性能至关重要，因此必须明确熔接线的位置和特性，尤其是在模具设计的工业规模阶段，以减少故障原因。许多研究涉及熔接线及其对传统注塑成型工艺参数的依赖性，但只有少数研究关注微注塑成型中的熔接线。这项工作通过实验和模拟方法研究了模具温度对微注塑成型中熔接线位置和强度的影响。在模具温度低于100°C时，在所选择的型腔中只能获得短射料。随着模具温度升高，熔接线全长减少达40%，整体拉伸模量翻倍。这一发现可归因于高模具温度有利于减少熔接线位置处的取向。Moldflow模拟能够一致地再现该工艺的主要特征、熔接线位置和长度。实验结果与模拟结果之间的差异归因于模型中未考虑流动条件下的结晶现象。
