Wrinkling behaviour of different grades of annealed commercially pure aluminium sheets when drawing through a conical die

This paper deals with the deep drawing of circular blanks of three different grades of annealed, commercially pure aluminium sheets of different grades, namely ISS 19000, ISS 19600 and ISS 19660, having a thickness of 2.00 mm, into cylindrical cups through Conical die using a flat bottomed punch. It is well established that the use of a Conical die can enhance the limiting draw ratio compared with that obtainable in a conventional drawing operation. When a Conical 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. For the present work, annealed aluminium sheets of different diameters are drawn through a conical die under dry lubrication condition, until the appearance of a first stage wrinkle. Here, an attempt is made to relate the percentage amount of draw obtainable in the drawing process with the initial diameter of the blank. It is also shown that the onset of wrinkling takes place when the percentage change in thickness reaches a critical value, this value being found to be generally different for both air cooled and furnace cooled aluminium sheets.