During the pressing process of thin-walled heads, the phenomenon of bulge is the key to affecting the quality of the product. During the pressing of various heads with an inner diameter of Di = 400 ~ 1500mm, the common process and mold have been changed to overcome the problem. Packing phenomenon of thin-walled head.

　　Principle of the starting phenomenon after rolling. In the rolling process of thin-walled elliptical heads, bulging usually occurs in the part with large curvature of the head. Using a ring-shaped integral rolling die, the large curvature parts near the head hem are firstly used. It is pre-pressed to make the blank into a pan shape, and then pressed by a punch.

　　During the calendering process of thin-walled elliptical heads, the packing phenomenon often occurs in the part where the curvature of the head is large. The ring-shaped integral rolling die is used to pre-compress the large curvature parts near the edge of the head. The blank is shaped into a pan and then pressed with a punch.

　　In this way, in the part with large curvature, due to the pre-pressed geometry, there is a cold work hardening phenomenon in the pre-pressed area, which enhances the rigidity during the deformation of the blank and does not cause bulging.

　　In the pressing process, when pre-pressing, it is not necessary to make another pre-pressing die, and the pressure ring of other specifications of the head mold can be borrowed, but the outer edge should be rounded, and the outer diameter should be 100 ~ 200mm smaller than the inner diameter of the die. It is just pressed on the bulging part before the head is formed, so that the bulging phenomenon can be avoided.