AN ANALYSIS OF THE EXTRUSION OF BIMETALLIC TUBES BY NUMERICAL-SIMULATION

This paper presents a numerical analysis of a high temperature extrusi on process applied to bimaterial tubes made of two pre-bonded metallic materials with different plastic properties. The analysis has been ca rded out for different geometries and material combinations by using a FE code. An elasto-plastic behaviour with strain rate dependence has been assumed. A parameter related to the void growth rate at the bimat erial interface has been considered for fracture prediction during the extrusion operation. The influence of the different extrusion variabl es, namely the yield stress ratio, the location and relative thickness of the layers and the die angle, has been assessed. As a conclusion o f the analysis, the yield stress ratio between the two materials turns out to be the most critical parameter of the process. Besides, the th ickness fluctuations of the harder layer in the final product have bee n analysed for several material combinations. Those fluctuations can l ead to an unacceptable geometrical heterogeneity under certain conditi ons. The results of the FE calculations are in reasonable agreement wi th the scarce data available from similar industrial operations. In sh ort, the paper shows that use of FE calculations can be a pre-screenin g tool for the selection of material couples and extrusion conditions for the production of sound bimetallic tubes, before being engaged in very costly full-scaled trials.