椭球封头冷拉深缺陷分析

起皱、局部壁厚过度减薄是封头冷拉深常见的缺陷,严重制约着拉深封头质量、成形极限的提高以及生产过程的正常进行。文章采用ABAQUS软件建立椭球封头拉深成形的三维有限元模型,并验证该模型的可靠性;发现了椭球封头拉深过程中易于出现的悬空区起皱和过度减薄两种缺陷,并分析了其形成机理,同时研究了工艺参数对缺陷产生的影响规律。研究发现,悬空区承受双向压应力区域的范围与周向压应力的大小对起皱影响明显,而切向拉应力对壁厚的减薄影响显著。增大压边力、摩擦系数和减小凹模圆角半径,可减小悬空区承受双向压应力区域的面积和周向压应力值,进而减小起皱的倾向,而过大的压边力、摩擦系数和过小的凹模圆角半径,则导致悬空区切向拉应力过大,可加剧壁厚的减薄。

Study on forming defects in deep drawing of semi-ellipsoidal end closures

Wrinkling and over-thinning of wall thickness,known as common defects in deep-drawing of end closures,affect the forming quality and forming limit greatly.A three-dimensional(3D) finite element(FE) model for deep-drawing process of semi-ellipsoidal end closure was established and its reliability was validated.It was found that wrinkling and over-thinning always take place in suspended section,and the mechanism of defects was investigated,consequently the influencing law of process parameters on defects were analyzed.The results show that the area of suspended section which undergoes compressive stresses in both tangent and circumferential directions and the value of circumferential compressive stress have obvious effect on wrinkling,and the tangent tension stress has obvious effect on wall thickness.The possibility of wrinkling decreases with the increase of blank holder force(BHF) and friction coefficient,and with the decrease of the die radius,due to the decrease of the area of suspended section undertaking the biaxial compressive stress and the value of circumferential compressive stress.When the BHF or friction coefficient is too large,or the die radius is too small,excessive tangent tension stresses would result in the suspended section,so the wall thickness would reduce significently.