Direct and Indirect Extrusion of Sintered Preform at the End of Stroke

The paper reports a theoretical investigation into various aspects of cold forming through conical converging die at the end of stroke. At this stage of the process, there occur some phenomena that require discussion. A well-known defect in extrusion is cavity formation at the center on the back of the billet, a process that begins as the billet is shortened. The cavity gradually increases in diameter and depth, transforming the emerging rod into a pipe of increasing inner diameter, with the result that this portion of the product is discarded. This defect can be reduced or eliminated if dies of smaller cone angles are used. The results so obtained are discussed critically to illustrate the interaction of various process parameters involved and are presented graphically.