Friction in sheet forming with soft and hard tooling

Abstract

Comparative studies were conducted with the drawbead‐simulation (DBS) test on a bare steel, a galvannealed steel, three electrogalvanized steels, and a hot‐dip galvanized steel as representatives of the major classes of steel sheets used in the automotive industry. Drawbeads of bare, plasma‐nitrided and hard chromium‐coated tool steels were prepared with various surface finishes. The zinc alloy Kirksite represented the soft tooling used in die tryout. A low‐viscosity mineral oil, neat and compounded with oleic acid or a borate compound, served as lubricant. Correlation between friction on hard and soft surfaces was governed primarily by the extent and stability of a zinc transfer layer on the hard beads. Kirksite may be regarded as the equivalent of a very stable, more hard and less reactive transfer film. Correlation was generally better when the sheet surface was capable of entrapping the lubricant, when oleic acid (a boundary additive) was absent, borate (a parting compound) was present, and the plowing component of friction was low.

A technical note on an experimental device to measure friction coefficient in sheet metal forming

“…As far as the latter topic is regarded, it is well-known that Coulomb model is probably the most appropriate classic frictional model to be utilized in sheet metal forming simulations with respect, for instance, to the shear-factor one [2]. Nevertheless, the frictional coefficient µ has to be properly chosen in order to proper model the frictional conditions at the sheet metal-dies interfaces.…”