Modelling wall boundary conditions in an elasto-viscoplastic material forming process

The numerical simulation of a hot metal or soft material processing operati on, for optimising the design and operating variables, critically depends o n the boundary conditions associated with the walls of the equipment. With advancements in finite element methods, more accurate determination of the field variables governing material flow in forming processes involving comp lex interfacial boundary conditions and realistic material constitutive mod els has become feasible. This paper describes a finite element study of the effect of wall boundary conditions on the upsetting of plasticine as a model for hot metal. The wal l boundary and intrinsic how characteristics for the model material are the n used to investigate the effects of introducing a vibration assisted tooli ng method. The aim was to modify the wall boundary conditions in a way that reduced the forming force. A comparison between experimental and computed results, for the relationshi p between the forming force and tool displacement and for flow visualisatio n, demonstrate very close agreement, if deformation is performed under supe rimposed vibration, the mean stress necessary to maintain plastic flow decr eases appreciably in comparison with that for purely static deformation, an d this decrease is accurately predicted by the FE models. (C) 2000 Elsevier Science B.V. All rights reserved.