Friction and wear mechanisms during hot stamping of AlSi coated press hardening steel

Abstract

With increasing demand for light-weight constructions and improved safety standards, hot stamping becomes a desirable process to produce high strength steel parts. However, for an effective process design, a thorough understanding of tribological interactions between the tool surface and the sheet metal is of major importance. The goal of this paper is to characterize tribological interactions between the tool and the sheet metal coating during hot stamping and furthermore to investigate the different phenomena which affect the local friction coefficient and tool wear.For this purpose, the friction and wear mechanisms occurring during hot friction draw tests between the uncoated tool steel and the AlSi-coated press hardening steel (PHS) at 700°C are investigated. Most importantly, the mutual interaction between the friction and tool wear mechanisms is probed. The results show complex friction and wear mechanisms with several phenomena taking place simultaneously and/or in quick succession within the strip-tool contact system. Cumulative wear effects are also found to occur from one draw test to the next as a result of different phenomena. Furthermore our results show that abraded tool material could embed in the relatively soft sheet coating which subsequently causes ploughing marks on the tool. These interactions manifest a change in the friction mechanism as material transfer takes place from sheets to the tool. Our results provide a clear insight on the sheet metal–tool interactions during the hot stamping process. These results can be used for a more realistic modelling of the hot stamping process and its optimization.