| 摘要 |
PROBLEM TO BE SOLVED: To obtain a metallic box body further thinned and lightened while securing the rigidity and the strength of not less than certain level with injection molding. SOLUTION: Recessing-shape parts 44-51 corresponding to projecting shape parts 21-28 in an unbalanced thickness structure formed in the surface in a metallic mold of a left metallic mold 11A or a right metallic mold 11B for forming a cavity 12, are formed on the back surface 40B of a metallic box body 40 with the recessed letters. Then, the metallic box body 40 with the recessed letters, which is further thinned in comparison with the conventional product in the average thickness and lightened without lowering the rigidity and the strength can be formed while taking a role as the ribs to these recessing-shape parts 44-51.
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