A plasticity model for interface friction: application to sheet metal forming

Successful numerical simulations of forming operations require robust and accurate tool-workpiece interface friction models. In this paper we extend the rate-independent, isotropic, isothermal interface friction model proposed by Anand (Anand, L., 1993. A constitutive model for interface friction. Computational Mechanics 12, 197–213) to a rate-dependent formulation. Material parameters in the friction model are determined for lubricated interfaces between Al6111-T4 sheet and D2 tool steel. The lubricants used are MP404 and boric acid; the MP404 lubricant is currently used in industry, whereas boric acid has recently been proposed as a solid-film lubricant for sheet forming by Erdemir (Erdemir, A., 1991. Tribological properties of boric acid and boric acid-forming surfaces. Part i: crystal chemistry and mechanisms of self-lubrication of boric acid. Lubrication Engineering 47, 168–173). The interface friction model is implemented in the finite element code ABAQUS/Explicit (ABAQUS Reference Manual., 1999. Providence, RI), and the finite element program is used to simulate two sheet forming operations: axisymmetric cup-drawing and square pan-drawing. The predictions from the finite element simulation are shown to be in very good agreement with experimental results.