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

The numerical simulation of a hot metal or soft material processing operation, for optimising the design and operating variables, critically depends on 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 complex interfacial boundary conditions and realistic material constitutive models 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 wall boundary and intrinsic flow characteristics for the model material are then used to investigate the effects of introducing a vibration assisted tooling 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 relationship between the forming force and tool displacement and for flow visualisation, demonstrate very close agreement. If deformation is performed under superimposed vibration, the mean stress necessary to maintain plastic flow decreases appreciably in comparison with that for purely static deformation, and this decrease is accurately predicted by the FE models.