精密注塑制品残余应力的试验研究及其计算

注塑残余应力对精密注塑制品的力学性能和光学性能等有重要影响,是精密注塑制品质量控制的关键指标之一。为研究注塑成形过程中残余应力的发展,以丙烯腈—丁二烯—苯乙烯共聚物(Acrylonitrile butadiene styrene,ABS)塑料为研究对象,对其模内蠕变行为进行试验研究。将热弹性模型计算的收缩应变与试验测量的收缩应变之间的差值定义为制件的模内蠕变,得到注塑工艺条件对模内蠕变的影响规律。在此基础上构建计算精密注塑制品残余应力的蠕变模型。模型中的材料弹性模量可由Tait方程计算得到,粘壶系数采用反演方法计算得到。利用该模型结合薄壳有限元法对ABS平板注塑件残余应力进行计算,对计算结果进行试验验证,并与普通的松弛模型计算进行比较。计算结果表明,该模型的计算精度高于普通的松弛模型,是解决精密注塑制品残余应力预测问题的新的有效方法。

Experiments and Calculation of Residual Stress for Precision Injection Molded Part

Residual stress of the injection molded polymers is a key factor of quality control on precision injection molded part and has important effect on the mechanical and optical properties of the molding.To investigate the development of this residual stress,the in-cavity creep experiment of acrylonitrile butadiene styrene(ABS) is carried out and its in-cavity creep behavior is studied.In-cavity creep is defined as the variance of shrinkage which is calculated by thermal elastic model with measured in the experiments.General rules are learnt that injection processing conditions affect in-cavity creep of the molding.Based on the experimental results,a creep model for calculating residual stress of the molding is built.The elastic module of material is calculated with Tait equation and the viscous factor calculates with inversion method.The residual stress of injection molded plate made by ABS with this model integrated thin shell finite element method is calculated,and calculation result is verified by the experiments and compared with stress relaxation.The results show that the new model is more accurate than general relaxation model and that is a new effective way to predict the residual stress of precision injection moldings.