Thin-walled hollow shapes offer a means to increase structural stiffness without increasing structural weight. The production of these shapes is usually by extrusion. During the extrusion process, the metal is heated to temperatures in excess of one-half the melting point. After extrusion, the shapes may cool slowly on a run-out table or be quenched at the press. The cooling results in distortion and the precipitation of alloying elements establish the material strength. The extruded shape may or may not have the desired shape or strength levels for a given design.
Subsequent heat treatment may be required to achieve the desired strength for the part. The heat treating practice increases the temperature of the part. The part is rapidly cooled after withdrawal from the heat-treating furnace. The quenching operation achieves the desired strength levels through precipitate control and restores the material strength. However, the rapid cooling results in further distortion of the part.
The major question in developing design models for the quench distortion of closed extruded shapes is the modeling of the members and the inelastic behavior of the members. We present results of a finite element model for the deformation of closed thin-walled extrusions. The results demonstrate the need for accurate constitutive models for the inelastic material behavior. We also present results to show how the constraint in the extrusion direction influences the predicted results of the deformation. Finally, we present a strategy for the simplified analysis of the quench distortion of thin-walled parts.
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