Abstract
An upper-bound formula was developed to analyze the backward-extrusion forging of regular polygon cup-shaped components. An admissible spherical velocity field has been suggested for the early stage of the extrusion process. This stage was facilitated by substitution of a nosed punch with cylindrical surface instead of a flat one. The optimum nose contour was determined by the minimization technique. On the other hand, by this method the semi-prism angle of dead zone was calculated. For the final stage of the process, an admissible cylindrical velocity field has been applied. In any stage of the process, by increasing the number of polygonal sides, the upper-bound results approaches that of circular cups which was obtained by other investigators. The comparison of analytical results to that of experimental investigations showed excellent agreement.
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