US Patent 7775907 Method for manufacturing golf club head

A method for manufacturing a hollow golf club head is disclosed, wherein a metallic main frame provided with a top opening and a bottom opening, a metallic crown plate and a metallic sole plate are prepared. The sole plate is placed in the bottom opening. A die is inserted into the inside of the main frame through the top opening. A protrusion of the sole plate is crushed onto the edge portion of the main frame around the bottom opening, by the use of the inserted die. Then the top opening is closed by the crown plate. The specific gravity SGm and proof stress YSm of the main frame, the specific gravity SGs and proof stress YSs of the sole plate, and the specific gravity SGf of the face plate satisfy: SGf=<SGm<SGs and YSs<YSm.