THE INFLUENCE OF FRICTION STABILITY ON THE SUCCESS OF LUBRICATED STAMPING OPERATIONS. PREDICTIVE TOOLS FROM PLANE FRICTION TESTS

摘要

This work was aimed at analysing the influence of the tribological behaviour on the onset of systematic fractures of car body parts during stamping, and at developing an alternative friction evaluation system, able to detect in advance the risk of failure by galling or seizing when stamping zinc coated (electrogalvanized or hot dip galvanized) steel sheets. The friction test reproduces the severe boundary lubrication conditions found in real practice, and also the progressive deterioration of the initial surface topography that the sheet suffers as a result of the pass through the draw-beads before reaching the die entry. Under these conditions, it was found that the initial values of the coefficient of friction have only a limited effect on the real behaviour, and that successful stamping relies mainly on the stability of the friction values as the length of sheet under pressure between the tools increases. Some index parameters obtained from this test can be used to predict in advance with high reliability the risk of lubricant breakdown and galling during real stamping.