Effects of surface treatments and lubricants for warm forging die life

In most metal forming applications, the surface treatments and lubricants are the main factors influencing die life, since they directly determine the interface friction and thermal insulation. In general, in hot and warm forging processes, the surface hardness of the die is decreased while the temperature of the die increased during repeated operations, which induce thermal softening. The thermal softening causes the plastic deformation of die despite the forming load not being changed. In this study, experiments and numerical analyses were performed under various conditions: two kinds of surface treatment, two lubricants, different initial billet temperatures and different loads: to investigate the effects on thermal softening and the amount of heat-transfer Carbon nitride (CN,), ion-nitride and no surface treatment for the dies were used and oil-based and water-based graphite were used as lubricants. Experiments were also performed to take the heat-transfer coefficient into account with the combination of surface treatments and lubricants. The coefficients determined were then used in a finite element model for the analysis of the backward extrusion process, the results produced were compared being experiment. (C) 2001 Elsevier Science B.V. All rights reserved.