Significance and limitations of variable blank holding force application in deep drawing process

Abstract

Control of the blank holding force (BHF) enables control of friction on the flange during deep drawing process and significantly influences the course and process results in that way. In the paper we are presenting analysis of the influence degree of flange friction on plastic forming process and significance of variable blank holding force (VBF) like normal force as a part of that. Also, we are giving the results of experimental researches of VBF influence on deep drawing process. Cylindrical part is realized by deep drawing in conditions of: a) constant BHF application (literature recommendation), b) constant BHF application (optimized) and c) VBF application. Material is coated low carbon steel sheet and 3 regimes of friction are used (dry, oil and oil + PET foil). Drawing depths, sheet surface strains, thinning strains, drawing forces and BHF forces are monitored. We can conclude, at the end, that there is possibility of important process improving by application of VBF beside evident limitations.