An injection molding apparatus comprising:
- a mold assembly incorporating a first mold member and a second mold member which open and close relative to each other and which form a mold cavity therebetween when closed, said first mold member having:
- a base member;
- a movable member supported on said base member so as to be movable relative thereto in the open and close direction of said first mold member and said second mold member, said movable member closable against said second mold member;
- biasing means for biasing said movable member relative to said base member towards said second mold member;
- a protruding portion provided integral with said base member, said second mold member having a recess portion for removably engaging with the protruding portion on said first mold member, the construction being such that said mold cavity is formed by the recess portion and the protruding portion, and a material passage is formed between said movable member and said second mold member so that a gate to said mold cavity is formed therefrom, said gate being closed by said protruding portion engaging in said recess portion,;
- a material supply apparatus for supplying mold material in a moldable condition to said material passage in said mold assembly;
- a mold clamping device with adjustable clamping force for opening and closing said first mold member and said second mold member of said mold assembly;
- filling control means for supplying mold material from said material supply device to said material passage of said mold assembly, to fill said mold cavity under conditions wherein said first mold member and said second mold member are closed with a light mold clamping force, and said movable member is closed against said second mold member, but said movable member and said base member are open;
- pressure adjustment control means for adjusting the pressure of the mold material inside said mold cavity so as to make the density of the mold material constant during filling by said filling control means, by the displacement of said movable member and said second mold member relative to said base member, as a result of an equilibrium between the pressure of the mold material inside said mold assembly, and the mold clamping force;
- measurement control means for increasing the mold clamping force to close said base member and said movable member towards each other, after adjusting the pressure with said pressure adjustment control means, so that mold material on the mold cavity side returns to said material supply device, and at the point in time of closing said gate a constant amount of mold material remains in said mold cavity;
- and
- compression control means for closing said base member and said movable member against each other after measurement control by said measurement control means, thereby compressing the mold material inside said mold cavity.