Tribological investigations on aluminum alloys at different contact conditions for simulation of deep drawing processes

Abstract

The tribological condition occurring in aluminum sheet forming processes remarkably affects the part quality and the tool wear. Reliable finite element (FE) models which consider the actual contact conditions are required for successful simulation of aluminum sheet forming. Therefore, tribology experiments are vital for creating contact models which represent the actual tribological system between the tool and the blank. In this work, pin-on-plate tests using plates of aluminum alloys EN AW-5182 EN and AW-6016-T4 were performed at different nominal contact pressures, sliding velocities and surface temperatures for investigating the coefficient of friction (COF). The surface topographies of the aluminum plates, before and after the pin-on-plate tests, were investigated using an optical 3D surface profiler. The obtained COF as well as the surface topographies were imported into the TriboForm R3 software for generating a multi-factor friction model (MFFM), which was subsequently applied in deep drawing simulations using the AutoForm R8 software. The simulation results based on the MFFM were compared to the results based on friction models with constant COF. Moreover, the simulations were validated with deep drawing experiments using a cross-shaped tool at three blankholder forces. The results of the tribology experiments showed that the COF tended to decrease with increasing nominal contact pressure and sliding velocity. However, at elevated temperature the COF increased for both aluminum alloys. Observation of the surface topography after the pin-on-plate tests showed that the plastic deformation of the surface asperities increased with increasing nominal contact pressure. The simulation results based on the MFFM agreed well with the deep drawing experiments at each blankholder force in terms of forming forces, thickness variations and final geometries of the parts.