粉末注射成形两相流动三维数值模拟及粉末与粘结剂的分离

摘要

分析齿轮零件粉末注射成形(PIM)实验成形坯密度分布以及成品容易出现飞边和塌陷的位置特点。根据粉末注射成形技术工艺过程的特点给出PIM的双流体模型及初边界条件，基于计算流体力学软件CFX对I型拉伸试样和齿轮零件的PIM两相流动过程进行三维数值模拟。根据数值模拟结果，对PIM充模流动过程中粉末和粘结剂两相速度的变化曲线进行对比分析，证实I型拉伸试样和齿轮零件的PIM充模过程中多个位置发生过不同程度的粉末与粘结剂两相分离现象。对模腔中多个不同结点处发生粉末与粘结剂两项分离的现象进行分析比较。结果表明：PIM充模过程中位于远离浇口狭窄模腔内的点容易产生两相分离现象，粉末与粘结剂两相分离现象只发生在相应位置被充填初期的一段时间内，且不同位置发生的两相分离持续时间也不同。%The density distribution and sink defects location characteristics of powder injection molding (PIM) green parts for a gear part were analyzed. According to characteristics of PIM process, mathematical models of two­phase flow with proper initial and boundary conditions were given for PIM filling process. Three­dimensional numerical simulations of two­phase flow in PIM filling process were carried out for a tensile test specimen and a gear part using the CFD software CFX. Based on the numerical simulation results, the velocity variation curves of powder and binder during the filling process were compared and analyzed. The powder­binder two­phase separation of different degrees was confirmed happening during PIM filling process for the tensile test specimen and gear part. The binder­powder separation phenomena observed at different locations of the cavity were compared and analyzed. The results show that powder­binder separation phenomenon is more possible to occur at those points far from the inlet and locates in the narrow regions of cavity. The powder­binder separation occurs only at the initial stage of the time when the corresponding position is filled and time duration of two­phase separation is different for different locations.