Critical forming force in rotary forging and the application of tungsten carbide dies

Abstract In precision cold forming in a rotary forging press the final stage of deformation occurs at a diminishing die closure rate to give the required accuracy of form. Earlier studies have indicated that elastic distortion of the dies can result in significantly increased die contact area and forming force as compared with an ideal rigid die system. In this paper the analysis is developed to give an expression for a critical forging force below which forming will not proceed. The critical force is dependent on the elastic modulus of the dies and it is shown that by using tungsten carbide dies, with a modulus almost three times that of tool steels, the forging force can be reduced significantly. A force reduction of about 50% is achieved in upsetting experiments on strain hardened steel billets by the use of tungsten carbide instead of tool steel.