Improvement of quarity of a molded part using ultrasonic vibration

本研究描述了一种利用超声波振动提高模塑塑料质量的方法。当使用结晶或半结晶热塑性塑料作为模塑树脂时，模塑树脂的结晶度直接关系到它的质量，因为它的收缩率、机械强度、杨氏模量等都会根据结晶度而变化。一般来说，模具中各处的冷却速度不同，因此无法获得成型树脂的均匀结晶度。另一方面，振动似乎加速了结晶性，因为过冷水（<0 C）在振动时突然结晶。然而，振动对结晶度的影响尚未明确。因此，当用超声波振动对模具进行强制振动时，可以预期成型树脂的结晶度因振动而增加，成型树脂的质量得到改善。在本研究中，利用超声振动对成型树脂在填充、填充和冷却阶段进行振动。在这种情况下，树脂直接由顶销或间接由模具振动。采用高密度聚乙烯（HDPE）作为成型材料。从这些实验结果可以看出，振动下成型树脂的结晶度比未振动下成型树脂的结晶度有所提高，并且在振动下成型树脂的冷却速度不受振动影响。

This study describes approaches available for a method of improving the quality of molded plastics by ultrasonic vibration. When a crystalline or semi-crystalline thermoplastic is used as the molded resin, the crystallinity of the molded resin is directly related to its quality, because its shrinkage, mechanical strength, Young's modulus and so on vary according to the crystallinity. In general, the cooling speed varies from place to place in the mold, so uniform crystallinity of the molded resin cannot be obtained. On the other hand, it seems that the crystallinity is accelerated by vibration, since supercooled water (<0ﾟC) becomes suddenly crystallized when it is vibrated. However, the influence of vibration on crystallinity has not been clarified. Therefore, when the mold is forcedly vibrated by ultrasonic vibration, it can be expected that the crystallinity of the molded resin increases due to the vibration, and the quality of the molded resin is improved. In this study, the molded resin is vibrated during filling, packing and cooling stages by ultrasonic vibration. In this case, the resin is vibrated directly by an ejector pin or indirectly by the mold. High density polyethylene (HDPE) is used as the molded material. From these experimental results, it is evident that the crystallinity of the resin molded under vibration is improved in comparison with the non-vibrated molded one and that the cooling speed of the molded resin has not been affected by the vibration when the mold is vibrated.