In the rolling process of general thin-walled elliptical heads, the phenomenon of bulging often occurs in the parts with larger curvature of the head. A circular integral rolling die is used to first pre press the large curvature parts near the folded edge of the head, making the billet into a flat bottomed pot shape, and then press it into shape with a convex die.
In this way, in areas with larger curvature, due to pre pressing into a certain geometric shape, there is a cold work hardening phenomenon in the pre pressing area, which enhances the rigidity of the billet during deformation and prevents the occurrence of bulging.
During the pressing process, when preloading, it is not necessary to make a separate preloading mold. The pressure ring of other specifications of head molds can be used, but its outer edge should be rounded, and the outer diameter should be 100-200mm smaller than the inner diameter of the mold itself, so that it is pressed exactly at the starting position before the head is formed, thus avoiding the occurrence of starting phenomenon.