八字形零件渐进成形机理分析

Analysis on incremental forming mechanism for figure-eight part

利用三层实体单元和壳单元,对非对称类零件(八字形零件)的渐进成形过程进行数值模拟,研究了成形过程中板料不同区域的厚度变化、应力状态以及各区域应变分量占比与演化历史,并对零件的两个特征截面——中部截面和拐角截面进行了比较。结果表明:渐进成形具有局部变形特征,工具头附近区域的应变值剧烈增加,远离工具头区域的应变值缓慢增加并逐渐趋于平稳;成形角度虽然相同,但八字形零件成形后的中部减薄程度比拐角严重;中部与拐角截面正应变分量占比大致相同,前者的xy平面切应变ε12占比较大,而后者的yz平面切应变ε23占比大,说明ε12是导致中部截面减薄更严重的主因;成形过程是拉伸、剪切与弯曲效应的集合,拉伸效应与弯曲效应相互叠加,且拉伸效应对成形过程的影响最为显著;正弦定律不能完全适用于对非对称类零件厚度的预测。

Three-layer solid elements and shell elements were used for numerically simulating the incremental forming process of asymmetric part(figure-eight part)to research the thickness changes and the stress states in different regions of sheet,as wall as the proportion and evolution history of strain components in each region during the forming process,and the two characteristic sections of middle section and corner section for part were compared.The results show that the incremental forming process has local deformation characteristics,and the strain value in the area near the tool head increases sharply while the strain value in the far away the tool head slowly increases and gradually stabilizes.Although the forming angle is the same,the thickness reduction on the middle section of figure-eight part after forming is more serious than that on the corner section,the proportions of the normal strain component on the middle and corner sections are approximately the same,the former has a larger proportion for shearing strainε12 and the latter has a large portion for shearing strainε23 in yz plane which shows that theε12 is the main cause of more serious thickness reduction on the middle section.Thus,the forming process is a combination of stretching,shearing and bending effects,and the tensile effect and the bending effect are superimposed on each other.Meanwhile,the tensile effect has the most significant effect on the forming process,and the sine law cannot be fully applied to the prediction of the thickness for asymmetric part.