Overview

Application to a Backward Extrusion Process

Gilles Arnold, Olivier Hubert and Ren Billardon
LMT-Cachan, Cachan, France

Martin Dutko
Rockfield Softward Ltd, Swansea, Wales, UK

1. Introduction

The prediction of damage in an industrial forging process can be of great interest for the optimisation of the forging steps in order to avoid or limit the initiation of defects induced by plastic deformation. This paper presents some results of a study performed during the FORMAS BRITE-EURAM project [FORMAS]. The process considered is a single step backward extrusion of a tube with internal teeth (Figure 1).

Figure 1: CAD image of the piece after forging

The material used in the present paper is a 16 Mn Cr 5 steel. An analysis of the microstructure has been performed and shows two kinds of inclusions that could influence damage evolution: cementite nodules homogeneously distributed and MnS sulfides strongly elongated in the extrusion direction of the bar (Figure 2). Lemaitre's isotropic ductile damage model [LEM 85a, LAD 84, LEM 92] has been chosen to describe the damage evolution.

Figure 2: a) Elongated MnS inclusions and cementite nodules as observed inside the same specimen (etched and polished), b) Nodules of cementite in the ferritic matrix as observed after ductile failure in tension

2. Damage measurements and identification

Measurement of damage through the direct evaluation of the surface of the defects is very difficult and strongly dependent on the surface polishing conditions. Various indirect evaluations have been proposed through the measurements of the...