Developing of galling during the forming and its improvement by physical vapour depositing

In sheet metal stamping, galling is initiated and developed aggressively at the mould radius, where sheet metal undergoes large plastic deformation. This study sheds light on correlating the level of sheet plastic deformation with galling initiation on the mould surface. The 3D topography facilitated the observation of galling evolution process on the surface of quenched/tempered mould. The observation on the sliding sheet counterpart showed that with larger plastic deformation, zinc-coated surface tended to become rough and a large number of intermittent micro-cracks formed, leading to earlier initiation of galling. Furthermore, the surface of mould was treated by physical vapour depositing (PVD) of CrN. In the specific sliding tests under the same level of plastic deformation, critical total slid distance at which galling initiated was increased significantly. The major factor causing galling initiation on the PVD(CrN)-coated mould was identified.