金属板料单点渐进成形极限的数值模拟预测

Prediction of Single Point Incremental Forming Limit

渐进成形(Single point incremental forming,SPIF)有着较高的成形极限,但目前对其成形极限预测研究较少。基于数值模拟得到的应力应变数据,并结合四组具体的破裂试验,应用Oyane韧性破裂准则有效地预测了厚1.5mm的LY12(M)硬质铝板的渐进成形极限;在Oyane韧性破裂准则中,当破裂积分值I=4时,预测的工件破裂起始点及成形极限图都与试验结果较为吻合。渐进成形极限远远高于传统成形方式,其'局部、交替、小增量'的变形特点,使小变形不断积累以获得大变形,'强制性'地实现变形的均匀分布,从而获得较高的成形极限。具体体现在成形过程中,应力路径跌宕起伏,应力三轴度(σh/σ)较小,不利于材料韧性破裂;局部高压力小增量叠加成形、摩擦热及良好的润滑条件保障了渐进成形件较高的塑性。

The single point incremental forming has a high forming limit,but the prediction of forming limit is few.Based on the stress-strain data from numerical simulation and combined with the four groups of fracture tests,the Oyane ductile fracture criteria are used to effectively predict the forming limit of LY12（M） hard alluminum sheet of 1.5 mm thick.In the Oyane criteria,when the integral value I amounts to four,the predicted rupture starting point of the workpieces and the forming limit diagram are more consistent with the experimental results.Incremental forming limit is much higher than conventional forming methods,due to its ＂partial,alternate,small-increment＂ deformation characteristics,so that small deformation accumulates to large deformation,＂mandatory＂ achieving a uniform distribution of deformation to gain a high forming limit.During the forming process,the stress path ups and downs,the stress triaxiality degree（σ h/σ） is small and unfavorable to the material ductile fracture;local high pressure and small feed rate,frictional heat and good lubrication conditions guarantee the high plasticity of incremental forming workpieces.