Suction pressure casting method

A suction pressure casting method comprising

• using a casting device to carry out suction pressure casting in which molten metal is pressurized and poured into a cavity of a metal mold and the cavity is suctioned and exhausted, the casting device including
• a holding furnace in which molten metal is accumulated,
• the metal mold that forms the cavity together with a core,
• a molten-metal pressurizing device including a pressurized gas tank for supplying pressurizing gas into the holding furnace, and
• a suction-exhaust device for suctioning and exhausting an interior of the cavity, the suction-exhaust device including a vacuum pump, a first exhaust pipe in communication with the cavity, a second exhaust pipe in communication with the core, a first exhaust valve provided in the first exhaust pipe, and a second exhaust valve provided in the second exhaust pipe;
• setting a preset decompression pattern of the suction-exhaust device in advance according to a casting process;
• comparing the preset decompression pattern to a measured pressure pattern of the cavity and the core that is measured during actual casting, the measured pressure pattern comprising a first time period from a start of pouring of the molten metal to a completion of pouring, a second time period from the completion of pouring the molten metal to when a solidified film of the molten metal is formed in a periphery of the core, and a third time period from the formation of the solidified film of the molten metal in the periphery of the core to when the suctioning and exhausting of the cavity is stopped;
• calculating a corrected decompression pattern of the suction-exhaust device based on a difference between the preset decompression pattern and the measured pressure pattern;
• and
• correcting the preset decompression pattern at a time of a subsequent casting cycle by using the corrected decompression pattern, the corrected decompression pattern of the suction-exhaust device being calculated based on the difference between the preset decompression pattern and the measured pressure pattern, and at which time period the measured pressure deviates from the preset decompression pattern being displayed by a display device;
• using a preset pressurizing pattern of the molten-metal pressurizing device set in advance according to the casting process;
• and
• in the second time period, calculating the corrected decompression pattern such that the difference between the measured pressure of the core and the molten metal pressure of the periphery of the core determined from the preset pressurizing pattern of the molten-metal pressurizing device becomes a predetermined value or less,
• the preset decompression pattern and the corrected decompression pattern being patterns for controlling opening amounts of the first and second exhaust valves.