Method for making an injection-molded product having a partly thin portion

Claim 1

A method for injection molding a product having a thick-wall portion and a thin-wall portion comprising the steps of: providing a molding die including a male die and a female die disposed with respect to each other so as to define a cavity between the male die and the female die, the cavity having a cross section corresponding to the thick-wall portion of the product, the molding die also including a slide block movably disposed in one of the male die and female die and a gate for permitting the injection of molten resin material into the cavity; injecting a molten resin material of an amount larger than that required for molding the product into the cavity through the gate while maintaining said slide block in a retracted position; advancing the slide block to project into the cavity before the resin material is solidified to form the thin-wall portion of the product between a face of the slide block and a confronting portion of the molding die; defining a hollow space within the molding die communicating with said cavity substantially simultaneously with the slide block advancing step to permit excess of the resin material to be discharged from the cavity into the hollow space; and reducing a volume of said hollow space immediately after the slide block completes the advancing step to thereby increase the pressure in the resin material.

Claim 2

A method for injection molding a product having a thick-wall portion and a thin-wall portion comprising the steps of: providing a molding die including a male die and a female die disposed with respect to each other so as to define a cavity between the male die and the female die, the cavity having a cross section corresponding to the thick-wall portion of the product, the molding die also including a slide block movably disposed in one of the male die and female die and a gate for permitting the injection of molten resin material into the cavity; injecting a molten resin material of an amount larger than that required for molding the product into the cavity through the gate while maintaining said slide block in a retracted position; advancing the slide block to project into the cavity before the resin material is solidified to form the thin-wall portion of the product between a face of the slide block and a confronting portion of the molding die; defining a hollow space within the molding die communicating with said cavity substantially simultaneously with the slide block advancing step to permit excess of the resin material to be discharged from the cavity into the hollow space; and reducing a volume of said hollow space immediately after the slide block completes the advancing step to thereby increase the pressure in the resin material.