Simulation of a multi-stage forming process to investigate failure in the formed part
Goniwe, Nicholas Sandisile
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The purpose of this study is the optimisation of the stamping analysis process in order to investigate the possible reasons for the part failure. (Altan & Vasquez, 2000) have conducted similar research to optimise a forming process. However, they focussed on dies for a forging process and in this study, we are looking at cold forming and this study is also different in that we are trying to reduce the number of stages while maintaining the formability. Formability is based on the dimensional conformance of the final part with additional criteria being the thinning, appearance of wrinkling, dynamic effects leading to the localisation of strain, cracking and residual stress. A numerical modelling procedure that is close enough to the real process is used to investigate the effects of changes in the frictional contact that would correspond to lubrication and also the effect of adding draw beads to the forming tools to change the frictional contact. We also investigated the effect of using a different material in terms of meeting the design requirements. Experimental results for comparison are available for certain of the stamping processes investigated that were tested in pre-production. The finite element simulation is used to account for all residual thinning, stress and strain of the multi-stage forming process to ensure optimum thickness changes of the sheet at each stage. The variations of material and manufacturing parameters are established to accurately predict the behaviour of this specific forming process. The material model required to meet physical experiments is deduced from the results of standard tensile tests and fitted to the Hill’s 48 Law for Work Hardening. The commercial packages Ls-Dyna with Dynaform and Pam-Stamp software are used for the simulation to produce 2 results for comparison.