The effect of lubricant selection on galling in a model wear test

Abstract

Galling is a known failure mechanism in sheet metal forming (SMF) processes. As a result of this wear process, the amount of waste increases, the production process becomes hard to control and eventually expensive maintenance is required in order to continue production. Delaying or avoiding galling mechanisms by optimising the contacting materials and lubricant is therefore of high industrial importance. The presented work focuses on the effect of lubricant selection on galling, using a model wear test: the TNO slider-on-sheet tribometer. With this tribometer, galling mechanisms are studied using tool steel in sliding contact with lubricated deep draw steel DC 06. The wear data obtained with the test method agrees well with a general framework of lump initiation, lump growth and scoring (galling). Experimental data clearly demonstrates that a low coefficient of friction at the start of the experiment is not a reliable indicator for galling prevention. Hence, lubricant evaluation should be done based upon long-term testing instead of on short-term testing. Comparative results with a lubricant set shows that the TNO slider-on-sheet model wear test is suited for ranking forming lubricants with respect to their ability to avoid material transfer.