Injection molding method and injection molding device

An injection molding method which includes a cylinder having a discharge nozzle formed on a front side thereof, a single axis screw provided to be rotatable in the cylinder, and a fiber-supplying device for filling the cylinder with reinforcing fiber, and performs injection molding while separately supplying the reinforcing fiber and a resin starting material and supplying the reinforcing fiber on a side closer to the front side than the resin starting material, the method comprising:

• a plasticization process of allowing the screw to retract while rotating the screw in a normal direction to melt the resin starting material and kneading the reinforcing fiber with the melted resin starting material, thereby obtaining a predetermined amount of a kneaded product;
• and
• an injection process of discharging the kneaded product from the discharge nozzle by allowing the screw to advance,
• wherein the reinforcing fiber is supplied into the cylinder in the injection process,
• wherein the screw is rotated in the normal direction or is rotated in a reverse direction in the injection process,
• wherein the cylinder is provided with a vent hole which penetrates through a body of the cylinder from an outer peripheral surface to an inner peripheral surface thereof in order to supply the reinforcing fiber from the side closer to the front side than the resin starting material, and
• and wherein, in the injection process, a reverse rotational velocity of the screw is set so that movement of the flight of the screw in a projection region of the vent hole is equal to or smaller than one lead length of the flight.