Analyse des dégradations d’outillages de forge à chaud à l’aide de la simulation numérique

Analysis of hot forging tools damages using numerical simulation

¹ Université de Reims Champagne-Ardenne, L.A.C, Charleville-Mézières
² C.R.E.A.S, Recherches Unimélal - Ascométal, groupeUsinor, Amnéville

Abstract

Metallurgical assessments and simulations with F.E.M FORGE2, have permitted to determine the main loadings which produce the damages of hot forging tools (wear, thermal fatigue, plastic strains,...).

In this first approach, we have shown the simultaneity of thermal cracking and wear. This effect is the result of important thermal flashes generated by friction and plastic strains. The magnitude of these thermal flashes has been confirmed by experimental identification of the thermal flux. For example, between the sample deposit and the end of the hit, the thermal flux can be multiplied by forty. The use of these flux values and the tooI material fatigue behaviour in F.E.M code Systus have permitted to determine the evolution of the different spatial distributions (temperatures, thermal gradients, stresses and the plastic strains) with time. Mainly for high thermal flash, the thickness of the plasticized layer can be limited to few hundreds micrometers. This effect show that the thermo-chemical layers can influence the thermal fatigue resistance. Moreover, with a damage model, we have plotted all the thermo-mechanical data of F.E.M calculation in order to estimate the thermal fatigue life. This approach of number of hits, before the occurrence of fatigue crack permits the analyse of the working limits of the tools. For example, in our case, if we decrease the thermal flux of 5%, we multiply the fatigue life by 30.

We have seen the interest of the numerical simulation for the forecasts of the forging tools thermal damages. This approach is used by Ascoforge for optimising of the tools forging life with the process and the materials (localised coating, thermo-chemical treatments).