Die life and lubrication in warm forging

Abstract Since the worm forging enables the processing of high strength parts with a high level of precision, it is possible to eliminate the cutting and grinding of the ball and roller grooves of the outer race of the constant velocity joints. The application of this process has been increasing each year and the size of parts made with the process continues to grow. The severity of the process including higher reduction of sectional area and higher backward extrusion length have also increased. One result is that the die life of the backward extrusion punch has decreased under conventional processing conditions. This paper deals with the development of countermeasures to improve the duration of the punch's life. Obtained results are as follows. The die life of the backward extrusion punch is affected by heat cracks and softening of the surface layer. To improve die life, it is essential that there is a dry lubrication adhesion layer which binds strongly to the die. The die temperature range which provides the appropriate lubrication adhesion layer thickness is between 200 and 300°C. The most favorable die surface temperature at the start of the lubricant spraying is 300°C. The lubricant adhesion layer can be created in the shortest time by making the lubricant spray granules small.