精密注塑成型制品的收缩率预测分析

Prediction analysis of shrinkage for precision injection molded parts

注塑行业的制品收缩率的控制是控制产品质量的主要因素。本文针对目前的注塑成型收缩率预测方法及模具设计时收缩率计算的不足,应用CAE模拟技术及Moldflow等软件工具,提出了基于Moldflow的注塑制品收缩规律的模拟实验研究。本文塑件对2个支脚和孔的位置和形状精度要求较高,因此,对于注塑过程中的收缩范围,要有一个比较精确的控制。塑料供应商所提供的收缩率的取值范围收缩率最小值0.004,最大值为0.0065。通过分析注塑成品的收缩机理,掌握注塑成型制品的收缩规律,结合塑料供应商所提供的注塑材料平均收缩率,对模具表面温度、熔体温度、保压时间3个工艺参数分别进行设置。调整后的体积收缩率由25.21%变为13.70%,减少将近一半。从关键尺寸图可以看到,调整后的关键尺寸代号21338的预期值几乎等于希望值,再结合报告查看尺寸在X方向上的收缩值,发现制品的希望值为111.60而预期值为112.40。预期值和希望值相差很小,可以满足要求。而预测错误图的预期值和希望值相差有些加大,但也在允许范围内。预测注塑成型制品各点收缩率定量值的方法,解决了目前数值模拟方法所存在的各材料常数难以获取的问题。在注塑材料的收缩率范围由塑料供应商提供的条件下,注塑成型制品的收缩率根据模具成型结构通过数值模拟在理想注塑工艺条件下的注塑成型过程而得到。得到的结论与实际情况非常接近。使塑件在注塑成型过程中所产生的收缩率最理想。

The control of shrinkage rate in injection molding industry is a major factor in product quality control. The method of sutdy on simulation experiment for shinkage laws of injection molding products based on Moldftow software was conducted by simulatin technology of CAE and Moldftow software facilities, considernig prediction means of shrinkage and shortcomings of calculating shrinkage in the design mold. Because of the high precision of the position and shape of two feet and holes, the contraction in the process of injection molding should be precisely controled. Shrinkage range provided by the suppliers of plastic is between 0.004 and 0.0065. By analyzing the contraction mechanism of the injection molding, the contraction laws of injection molding products can be controled. Incorporating the materials＇ average shrinkage provided by plastic suppliers,three process parameters including the mold surface temperature, the melt temperature and the packing time were set. After adjusting the volume shrinkage reduced from 25.21% to 13.70%, reduced by nearly half. It can be seen from the key size figure that the adjusted critical value of the expected size of code 21338 was almost equal to the desired value. Incorporating the X direction shrinkage in the report we could find out the desired value was 111.60 while the expected value was 112.40. There was little difference between the desired value and the expected value, so it was content to requirements. The difference between the expected value of forecast error and the desired value was greater, but it was also permitted. The difficulty in obtaining the material constants in current numerical simulation was settled by predicted the injection molding products＇ shrinkage. Shrinkage of injection molded products could be obtained in numerical simulation for ideal conditions injection molding process, in case of the shrinkage range was provided by the suppliers of plastic. Conclusions was very close to the actual situation. The best shrinkage during injection process could be produced.