熔体温度对注射成型热塑性聚氨酯制件残余应力及外形精度的影响

Influence of melt temperature on residual stress and shape accuracy of injection molded thermoplastic polyurethane part

采用光学双折射法研究注射成型过程中熔体温度对透明热塑性聚氨酯(TPU)弹性体平板制件残余应力的影响规律和作用机理。结果表明,TPU制件在近浇口区域的残余应力大于远浇口区域,整体残余应力随熔体温度上升而下降。通过对平行于熔体流动方向和垂直于熔体流动方向上的制件截面进行双折射测量发现,注射成型TPU制件具有明显的皮-芯结构和零应力层,且随熔体温度升高芯层厚度显著增加。残余应力分析结果表明在制件的芯层以流动残余应力为主,而皮层区域是流动残余应力和热残余应力叠加的结果。此外,制件的翘曲变形与残余应力的分布直接相关,TPU制件尺寸的改变主要是由于流动残余应力释放引起的。

The effects of melt temperature on the residual stress of thermoplastic polyurethane(TPU)sheets during the injection molding process were studied by birefringence.The results indicate that the residual stress in the near gate area is higher than that in the far gate area and decreases with the increase of the melt temperature.The residual stress of cross section in the two directions is characterized.The injection molded TPU sheets have obvious skin-core structure and zero stress layer.The thickness of core layer increases with the melt temperature rising.The results of residual stress analysis show that the residual stress of core layer is dominated by the flow residual stress,while it is the result of superposition of flow and thermal residual stress in the surface layer.Besides,the warpage deformation is directly related to the distribution of residual stress.The change of the dimensions of the TPU sheets is directly caused by the release of flow residual stress.