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.