FE simulation of the influence of thermal and elastic effects on the accuracy of cold-extruded components

The thermal and elastic behaviour of both the component and the forming tool have a significant effect on accuracy of high-precision forming operations. FE simulation of material flow, temperature distribution, die deflection and dimensional variation of the component during extrusion, punch retraction, component ejection and cooling was conducted using a coupled thermo-mechanical approach for the forward extrusion of pure aluminium and low-carbon steel in tools of steel. Heat generated by the deformation of the work material and that generated by friction at the component–die interface, heat transfer from the component to the die, cooling of the component, die deflection due to elasticity and temperature changes and the dimensional variation of the component resulting from thermal and elasticity factors with different process conditions were investigated. The results show that the thermal and elastic behaviour of the process have a significant influence on the accuracy of formed components not only during tool loading and unloading, but also during component ejection and cooling. The thermal behaviour of the component has a greater impact on component form errors than has the elastic behaviour of the tool and the component for aluminium components. For low-carbon steel, the elastic behaviour of the tool and the component has a more dominant influence on the accuracy of the component. Changes in the process conditions including the punch velocity, the interfacial friction, the die transition radii and the die land also affect the accuracy of the component. Temperature changes in the die during a single forming cycle do not cause significant changes in its dimension; consequently, die deflection is dependent mainly on the elastic deformation.