粉末注射成形过程中熔体前沿速度优化

Optimization on melt front velocity in powder injection molding

在粉末注射成形中,喂料熔体中的聚合物在充模阶段由于非均匀的熔体前沿速度将导致坯件非均匀收缩、坯件密度变小和翘曲变形。基于充填过程数值模拟提出实现在粉末注射成形过程中的注射速率优化方法,以获得均匀熔体前沿速度从而减少喂料中聚合物非均匀收缩以实现提高成形坯件密度。通过模拟熔体前沿面积变化曲线的与螺杆行程的关系,确定分级注射点;结合分级注射点对应的注射量与螺杆注射位置的对应关系,导出一个简化的分级注射参数。由模拟和实验表明,该方法能获得较为均匀的熔体前沿速度,熔体前沿速度的标准方差从优化前14.6cm/s下降到优化后的4.2cm/s;生坯平均密度由从优化前5.34g/cm3提高到优化后的5.54g/cm3,生坯样本方差由从优化前0.235g/cm3下降到优化后的0.0823g/cm3。

During the mold filling stage of powder injection molding,due to non-uniform melt front velocity,the polymer of melt t will result in the non-uniform contraction,relative low density and warpage of the green.Based on the numerical simulation of the forming phase in powder injection molding,a method used to optimize the injection rate is proposed which can make the melt front velocity more even so that the non-uniform shrinkage is lessened and the density of the green is improved.The relationship be-tween the change of the melt front area and the course of screw was established through the simulation,then the mufti-level points of the cavity were determined.Combining the relation between the injection volume and the screw＇s position respect to each injection point,a simplified math model was formulated from which the injection parameters were obtained.From the simulation and experiments,it can obtained that by the method,the melt front velocity is more even,the standard deviation of the melt front velocity is changed from 14.6 cm/s to 4.2 cm/s,the density of the green is improved from 5.34g/cm3 to 5.54g/cm3,the sample variance of the green is changed from 0.235 to 0.0823.