The failure mechanisms of hot forging dies

摘要

This paper describes the phenomena taking place on the surface of the dies used for hot forging. Because of this paper's limited space only changes in the tool surface layer during the forging of a gear wheel, as most representative, are presented. Similar changes were observed in the case of the other two investigated closed die forging processes, i.e. the forging of a cover and a yoke, respectively. The research was aided by FEM, which supplied a lot of information about the forging conditions. The most intensive wear of the tools occurs in the place of their longest contact with the material being forged, regardless of the number of produced forgings. The research has shown that the one of the most adversely factor affecting the investigated forging process is thermomechanical fatigue which results in fine cracks quickly developing into a network of cracks extending over the entire tool/forged material contact surface. Also the abrasive wear of the investigated die is high due to the intensive flow of the material in the presence of abrasive oxide particles and tools bits created by thermomechanical fatigue. An attempt to model the abrasive wear using the Archard model is presented.