To provide a stack molding die for injection molding, wherein the front part and the rear part of a first sprue are passed through at molding; when the molded material is cooled and a forming is finished, the die is naturally opened at the same time when the front and rear part of the sprue are separated to form an aperture; and as a result, since a resin leaks from the part of the aperture, the aperture is removed for preventing the resin leaking.
When the die is opened, piston heads movable on a parting line part A as a center are made to face each other and set to be a shape as pushing one another. The side face of the piston head is made for sliding and engaging with a cylinder to exhibit a valve effect. On injecting a molten resin, a pass way for a resin flow is automatically formed by the resin pressure, and on pressure reducing after the filling of the resin is finished and a gate is solidified, the piston head part is returned to the parting line face A. When the die is opened, namely when the front part and the rear part of the first sprue are separated, a leak of the resin is prevented by realizing a valve effect owing to sliding and engaging with the cylinder. The die has such a structure, and the operation method therefor is provided.
SOEJIMA MASATO
SUZUKI JO
SUZUKI JO