| 摘要 |
A pair of main molds (13) for forming an outer peripheral surface of a piston (P) and a pair of side cores (16) for forming a pair of lightened recessed portions (5) in the piston (P) are provided. The main molds (13) and the side cores (16) are set in such as way as to form a cavity (11) corresponding to the piston (P), and the cavity (11) is filled with molten metal. After the piston (P) in the cavity (11) has solidified, the side cores (16) are caused to move downward in a direction moving them away from the central axis (Y) of the piston (P), and are separated from the lightened recessed portions (5), and at this time the side cores (16) are inclined in a direction whereby the upper ends thereof move closer to the central axis (Y) of the piston (P). Thus the cores can be separated smoothly from the lightened recessed portions without galling being caused to occur on the inner side surfaces of the lightened recessed portions. |
