| 摘要 |
PROBLEM TO BE SOLVED: To form an annular cooling passage with high reliability within the thickness of a piston of an internal combustion engine. SOLUTION: A piston molding body 1 having an annular reinforced part 3 formed by impregnating a molten aluminum alloy into a porous body ring 31 and solidifying is formed by pressure fitting an annular body 4 formed by connecting in an endless state a tube member in which a soluble solid material 5 is filled to the inside of a metal porous body ring 31, supporting them to the inside of a piston casting mold, pouring the molten aluminum alloy in the mold and solidifying under pressure, a communicating hole 12 extending in the shaft direction of the piston molding body 1 and reaching the tube member is formed, the soluble solid material 5 is dissolved and removed, and a top ring groove 2 is formed within the region of the annular reinforced part 3.
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