Abstract: In this paper, whether the macro-defect (cavitation of metal) appears or not in the　chamber corner has been analyzed during the extrusion, by using the minimum energy principle and the upper-bound approach. In this paper, the shape of workpiece is cup-cup with different outer radius. It is found that the cavitation does not appear during the extrusion in spite of the final froming stage. Our conclusion is further demonstrated according to the viewpoint of the transformation of the deformation patterns varying with the relative. Thickness of the billet bottom. The conclusion is confirmed by the experiments as well.

Key words: 杯杯型复合挤压, 复合挤压, 缺陷, 上限法原理