板材单点渐进成形工艺数值模拟与成形缺陷研究

工具头运动轨迹的动态加载是建立板材渐进成形有限元模型的难题。首先基于DYNAFORM建立基本的有限元模型,而后直接提取数控代码中工具头的位移坐标信息并添加至关键字文件,从而实现任意复杂运动曲线的加载;数控代码规划的加工轨迹存在起刀区域集中和加工方向单一的问题,容易造成破裂和失稳缺陷。起刀区域塑性变形大,累积效应使该区域板材严重减薄,采用均布策略,并保证均布后相邻起刀点的空间距离大于塑性变形区的最大半径可避免此缺陷。同时,运用顺逆相间的加工方式避免了单一方向加工方式存在的材料堆积引起的形状失稳和棱纹缺陷。

Numerical Simulation and Flaws of Sheet Metal Single-point Incremental Forming

The definition of motion trajectory of forming tool is a puzzle when setting up a finite element method (FEM)model of single-point incremental sheet forming.On the basis of DYNAFORM software,a basic FEM model was firstly constituted,and then the displacement coordinates of the forming tool which were received from numerical control (NC)code directly were added to the keyword file of the FEM model,thus an arbitrary complicated movement trace of the forming tool could be defined.Two problems maintained in the processing tool path generating from NC code,the concentration of the tool setting points and the single machining direction,which might bring about fracture and instability flaw respectively.As the plastic deformation in the tool setting point was large,the accumulative effect of the deformation of the tool setting zone might result in the severe wall thickness reduction.The distribution method in which the distance of the two adjacent setting points must be larger than the maximum radius of the plastic zone was employed to settle this problem.Meanwhile,the forming instability flaws such as collapse and ridge,which came from material accumulation during the process with single machining direction,were overcome by utilizing the forward and backward forming method.