Numerical study on local contact conditions on rough surface under press hardening

The primary concern for manufacturers related to press hardening is productivity, which can deteriorate owing to wear. Severe tribological behaviours, such as abrasive and adhesive wear, lead to blank rupture, surface scratches and shape deviation of the formed parts, increasing the cost and time required for maintenance. To understand the mechanism governing tribological behaviours during consecutive stamping strokes, this study proposes a finite element (FE) simulation of the interface between the blank and tool steel. The FE simulation involves measuring the surface topography in a real stamping tool to obtain local contact conditions. The effects of the nominal pressure and range of the friction coefficient on the local contact conditions were studied. A tribological test capable of accurately reproducing the press hardening conditions was conducted to validate FE simulation. The local contact conditions in terms of contact pressure, contact area and sliding distance were found to differ from the nominal values. The proposed FE simulation involving a rough surface explores the possible length scale of the surface topography, wherein the calculated parameters are likely the main factors affecting wear. Furthermore, the correlation between the test variables and local contact conditions can help optimise the process parameters and lubricity.