Effects of surface treatments and lubricants for warm forging die life

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