Wrinkling of commercially pure aluminium sheet metals of different grades when drawn through conical and tractrix dies

This paper deals with deep drawing of circular blanks of annealed three different grades of commercially pure sheets namely ISS 19000, ISS 19600 and ISS 19660 having thickness 2.00 mm into cylindrical cups through conical and tractrix dies using a flat bottomed punch. It is well established that the use of either a conical die or a tractrix die can enhance the limiting draw ratio compared with that obtainable in a conventional drawing operation. When a conical or a tractrix die is employed the need for a hold-down or clamping ring is eliminated. However, this enhances the propensity of the blank to fail by wrinkling or buckling, particularly in the early stages of a drawing process in which thin sheet blanks are used. It is shown that the onset of wrinkling takes place when the ratio of the plastic strain increment reaches a critical value. This value which is determined experimentally, over which the wrinkling takes place has been shown in the form of diagrams for the above three different grades. An attempt is also made to rank the properties that appear to suppress the wrinkling. Further it is observed that the aluminium grade having high strain hardening index value, low ratio of (σu/σy) and fairly good value of high normalised hardening rate shows better resistance against wrinkling. Furnace cooled aluminium grades and drawn through the tractrix die showed better resistance against wrinkling.