Abstract
Three principles for improvement of the square shell drawability can be summarized to be decrease in the drawing resistance Pmax, increase in the fracture strength Pcr, and uniform distribution of these forces along the circumference of the punch shoulder. In order to achieve these principles, blank shapes (huni) are selected to obtain cup with a uniform height by means of the slip-line-field method. In the application of the slip-line-field method, the calculation starts from the drawn square shell having uniform height and is performed by going back stepwise the drawing process, and thus in this way finally the blank shape is determined. Therefore, this way can rid the troublesome trial and error process needed in the usual calculation. In comparison with a square blank, the huni blank improves the deep-drawability for all the shape factors r1/l1(r1=punch corner radius, l1=distance between opposite side). particularly, the improvement is remarkable in the acute corner radius.
