1 Introduction

Every time a new piece is forged, the residual life of the dies involved in the forming operation decreases due to wear phenomena until the maximum allowed wear is reached: at this point the dies must be substituted or, if possible, reworked. To forecast the wear level is a fundamental task in cost definition for the piece produced.

Wear can be correlated to several working parameters and mainly to sliding length, normal pressure and tool hardness according to Archard's model [ARC 53].

The aim of the present paper is to analyse the influence of friction on these variables and, consequently, on die wear in a hot forging operation, particularly the stamping of a flange. The information derived from the model, once validated, can be utilised to correctly design the dies and define the process variables.

In particular the steps followed during the present research have been:

• to define a suitable wear model;

• to implement this model in an F.E.M. program;

• to validate this model with experimental tests;

• to extend the results of the model in forecasting the material behaviour varying the friction factor.

The wear model, found in literature, has already been applied in turning and extrusion, furnishing appreciable results [CER 95, PAI 95]. Particularly, wear of the dies is mainly considered abrasive due to very hard particles placed between piece and die which progressively...