Representation of material behaviour in finite element methods of modelling sheet forming processes

Abstract

Recent progress in the evolution of sheet metal forming from a craft based into a science based technology is reviewed. Examples of methods used in the first phase of application of finite element modelling techniques, to press forming operations which involve stretching and deep drawing over metal tools at ambient temperatures, are considered from the viewpoint of the user, rather than that of the programme designer. Because the interactions between material and process variables which influence performance in sheet forming are exceptionally complex, the requirements for accurate modelling can be very demanding. In some applications, knowledge of the plastic behaviour of the material and of frictional conditions is not yet sufficient to meet the requirements for accurate prediction. Recent experimental and theoretical work which is aimed at refining descriptions of plastic behaviour and of frictional conditions is outlined. It is expected that the degree of elaboration in constitutive equations representing material behaviour which is necessary to give the required accuracy in prediction will vary quite widely with differences in both the process and the material used. It is suggested that, when the capabilities of available modelling techniques are better established by practical trials, a rational approach to the selection of an appropriate finite element methods formulation and constitutive relationship to meet specific requirements could be based on more discriminating classifications of both materials and processes.