基于数值模拟的注射成型聚碳酸酯热/流动残余应力的壁厚特性

Effect of Wall Thickness on Thermal-Induced/Flow-Induced Residual Stresses of Injection Molded Polycarbonate Parts Based on Numerical Simulation

分别基于线性黏弹性模型和可压缩黏弹本构模型,采用相应的有限差分法和有限体积法作为控制方程的离散方法,以计算注射成型制品的流动残余应力和热残余应力。实现了对3 mm,7 mm和11 mm厚度注射成型聚碳酸酯平板的流动残余应力和热残余应力的数值模拟,并结合注射成型实验,分析了薄壁/厚壁制件流动残余应力、热残余应力和总残余应力的分布规律差异。计算结果表明,热残余应力区主要围绕平板边缘分布,中心区域的热残余应力明显低于边缘部分。随壁厚的增加,热残余应力逐渐上升,高残余应力分布面积明显增加,当壁厚从3 mm增加到11 mm,分布面积至少增加2倍以上;流动残余应力均表现为沿熔体流动方向递减的规律。随壁厚的增加,流动残余应力显著降低。当壁厚从3 mm增加到11 mm,最大流动残余应力从15 MPa降低到1.5 MPa,下降幅度达到90%;随着壁厚的增加,流动残余应力对平板总残余应力的贡献逐渐降低,热残余应力的贡献则逐渐增大。对于3 mm薄壁制件,流动残余应力占绝对主导地位;当平板厚度增加至7 mm时,近浇口区流动残余应力主导,远浇口区热残余应力主导;对于11 mm厚壁制件,热残余应力占绝对主导地位。不同壁厚平板的残余应力分布的数值模拟与实验结果吻合度较好,表明文中的数值模拟方法可以有效计算残余应力。

Based on the linear viscoelastic model and compressible viscoelastic constitutive model,the finite differ-ence method and finite volume method were used as the discrete methods of the governing equations to calculate the flow-induced residual stresses and thermal-induced residual stresses of injection molded products,respectively.Numeri-cal simulation of the flow-induced residual stresses and thermal-induced residual stresses of 3 mm,7 mm and 11 mm in-jection molded polycarbonate sheets were realized.Combined with the injection molding tests,the difference in the dis-tribution of flow-induced residual stresses,thermal-induced residual stresses and total residual stresses of thin-walled/thick-walled parts were analyzed.The calculation results show that the thermal-induced residual stress area is mainly dis-tributed around the edge of the plate,and the thermal-induced stresses in the central area are significantly lower than in the edge.As the wall thickness increases,the thermal-induced stresses gradually increase,and the distribution area of high residual stresses is increased significantly.When the wall thickness is increased from 3 mm to 11 mm,the distribu-tion area has more than doubled at least.Flow-induced stresses decrease along the melt flow direction.As the wall thick-ness increases,the residual flow-induced stresses is decreased significantly.When the wall thickness is increased from 3 mm to 11 mm,the maximum flow-induced stresses drop from 15 MPa to 1.5 MPa,and the decrease rate reaches 90%.As the wall thickness increases,the contribution of the flow-induced stresses to the total residual stresses of the plates gradually decreases,while that of the thermal-induced stresses gradually increases.For 3 mm thin-walled part,the flow induced stresses are absolutely dominant.When the thickness of the plate is increased to 7 mm,the flow-induced stress-es in the area near the gate are dominated,and the thermal-induced stresses in the area far away from the gate are domi-nated.For 11 mm thick-walled parts,the thermal residual stresses are absolutely dominant.The numerical simulation re-sults of the residual stress distribution of the plates with different thicknesses are in good agreement with the experimen-tal results,indicating that the numerical simulation method in this paper can effectively predict the residual stresses.