| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem that densification of metal structure is practically impossible under the high pressure and a piston forged by using the powder alloy is expensive in a conventional gravity type piston die casting method. SOLUTION: A secondary pressure applicator 27 to press the molten metal 75 cast in a die cavity 71 and a hydraulic cylinder 25 to drive the applicator are built into a die 11 of a die casting machine, the secondary pressure applicator 27 is advanced toward the die cavity 71 from the direction perpendicular to a top surface 3a of a head wall 3 of a piston 1 after the molten metal 75 is cast and before it is solidified, and the molten metal in a molten metal storage recess 19 is thereby pressed into the molten metal 75 in the die cavity 71 to make the structure denser. Since the die cavity 71 is substantially sealed, the secondary pressurization can be realized. The metal structure becomes most dense at the head wall 3, and its location and direction agree with the location and direction in which the explosive energy in the cylinder is directly applied to the piston 1.
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