상계해법에 의한 원형빌렛으로부터 타원 단면을 가진제품의 압출가공의 비틀림 해석

An Upper Bound Analysis for the Twisting Phenomenon of Extrusion of Elliptical Shapes from Round Billet

A kinematically admissible velocity field is developed for the analysis of twisting of extruded products. The twisting of extruded product is caused by the linearly increased rotational velocity from the center on the cross-section of the workpiece at the die exit. In the analysis, the rotational velocity in angular direction is assumed by the multiplication of radial distance and angular velocity. The angular velocity is zero at the die entrance and is increased linearly by axial distance from die entrance. The increase rate of angular velocity is determined by the minimization of plastic work. The results of the analysis show that the angular velocity of the extruded product increase with the die twisting angle and the aspect ratio of product and friction condition and reduction area and show that angular velocity increases with the decreases in die length.