Hydro-rim deep-drawing processes of hardening and rate-sensitive materials

The conventional deep drawing process is limited to a certain limit drawing ratio (LDR) beyond which rupture will ensue. An asymptotic solution of the complete governing equations of this process indicates that this relativel y low LDR results from the steep build-up of radial tensile stress with max imum value at the die lip. This tensile stress is significantly enhanced by interfacial friction along the die/flange and by high speed of the operati ng load and thus holds responsible for premature ruptures. The intention of this work is to examine the possibilities of relaxing the above limitation , aiming towards a process with an 'unlimited drawing ratio'. The ideas whi ch may lead to this goal are: (a) exerting an external fluid pressure on the outside rim of the blank ("H ydro-rim process") to reduce radial stress and to decrease, in parallel, th e interfacial friction, (b) increasing the blank temperature to a level at which the material is mo re rate sensitive, and thus less prone to early failure. The benefits of th ese ideas are examined via parametric analysis of the solution and with exp eriments in deep drawing processes. A clear outcome from the solution is that if changes in the material proper ties (strain hardening, strain-rate sensitivity, yield stress, etc.) can be controlled, say, by controlling the temperature and/or the operating speed , the process can reach higher drawing ratios with substantially less assis ted fluid pressure. (C) 2000 Elsevier Science Ltd. All rights reserved.