Minimizing distortion during extrusion using adaptable dies

Warping, twisting, underfill, and/or distortion during the extrusion are challenging problems. The goal of the present paper is to develop a criterion and use an adaptable die design methodology that will allow the prediction of extrusion die shapes that produce minimum distortion in axisymmetric product. Distortion in the final extrusion product is the axial displacement experienced by an initially straight and transverse line after it has passed completely through the deformation zone. Four possible criteria for use in the die design scheme (based on deviations from ideal flow) are developed. These criteria are: (1) average axial displacement, (2) average shear strain, (3) average effective strain, and (4) volumetric effective strain rate deviation. Each of these criteria is presented in mathematical form, which can easily be incorporated into an analysis of extrusion die design. Two of the four criteria are viable and can be used to determine optimal die shapes via the adaptable design method. The average effective strain criterion can be used to minimize the effective strain distribution in the finished product. The volumetric effective strain rate deviation criterion tries to create a uniform effective strain rate field in the deformation zone, and minimizes the distortion in the final product. The extrusion die shape, which produces the minimum effective strain in the product, is different from the shape for minimum distortion. This finding is contradictory to the concept that, to minimize distortion, one should minimize redundant strain. Based on the use of the volumetric effective strain rate deviation criterion, extrusion dies, which minimize distortion, are established using the adaptable die design methodology.