Deep Drawing of Circular Sheet Metals with Rubber Rings : 3rd Report, On the Drawing Mechanism

Abstract

It is clarified that a neutral point exists on the contact surface between a polyurethane ring and a blank, which plays a similar role to no-slip points in rolling of sheets or upsetting of circular hollow disks. A neutral point moves radially inwards to the die opening as compression ratio of a ring increases. The direction of the frictional force acting on a blank reverses at a neutral point, and only the frictional force on the inner area of a neutral radius contributes to the deformation of a blank. A friction hill appears in the pressure distribution on the contact surface between a ring and a blank. It should be emphasized that the deformation of a blank can be advanced very much either by using powdered rosin only on the inside of a neutral radius or by using a blank with a smaller diameter than one of a polyurethane ring.