Evaluation of Anti-galling Ability of Zinc Phosphate Coating by Backward Extrusion of Cylindrical Cup

Abstract A method using backward extrusion of a cylindrical cup to evaluate the anti-galling ability of a zinc phosphate coating is proposed. In this method, galling generation on the inner surface of the cup is judged by the rapid increase in the extrusion load in the extrusion load-stroke diagram. By using a divided punch, the tip of the punch is left at the extrusion end when the main body of the punch is returned after extrusion, thus the galling situation on the inner surface of the cup is perfectly maintained. It is confirmed that the rapid increase in the extrusion load is caused by the generation of galling, and the residual coating thickness measured by FE-AES at the galling generation position is smaller than the reduced peak height Rpk of the punch tip.