PURPOSE:To prevent the generation of burr or a cut powder due to punching by completing the reduction of nozzle touch pressure before raising cutting pressure. CONSTITUTION:A receiving die and sprue bush 7 and a punching die 17 are moved toward an injection nozzle 10 while the molded product therebetween are held by changing over a three-position direction change-over valve 13 and a two-position change-over direction change-over valve 20 in such a state that molds 3, 4 are clamped during the pressure holding and cooling process after molding. At this time, shearing is performed between the fixed mold 3 and the punching die 17 to carry out gate cutting. This punching is performed by such a way that the nozzle touch pressure pressing the receiving die and sprue bushing 7 is reduced by the injection nozzle 10 while gate cutting pressure is generated by a cylinder 18 to form the difference pressure between the gate cutting pressure and the nozzle touch pressure. When the start order of a gate cutting process is received, an in-mold punching apparatus starts nozzle touch pressure reducing operation first. At this time, a delay timer is counted in parallel and the gate cutting pressure is raised at the point of time when the nozzle touch pressure is completely lowered to a predetermined level to carry out gate cutting operation.
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