Injection molding method and injection molding machine

An injection molding method for a resin that contains an added component, the method comprising:

• a plasticizing step of:
• supplying a resin raw material and the added component which is reinforcing fibers, to a cylinder in which the resin raw material is melt to generate a molten resin and the added component is supplied in the molten resin to form a molten resin containing the added component, the cylinder being equipped with a screw and a vent hole, the screw being able to rotate normally and reversely around a rotating axis,
• transporting the molten resin containing the added component to a downstream side of the cylinder, and placing the screw at the downstream side of the cylinder,
• forcibly retreating the screw placed at the downstream side of the cylinder without rotating the screw, as a first retreat operation, to form a first space at a downstream side of the screw in which no molten resin containing the added component is present,
• after the first retreat operation, normally rotating the screw, as a first normal rotation operation, and filling the first space with the molten resin containing the added component,
• after the first normal rotation operation, reversely rotating the screw, as a first reverse rotation operation, to apply a shearing force to the molten resin containing the added component in a direction different from a direction at the first normal rotation operation, and dispersing the added component in the molten resin,
• after the first reverse rotation operation, forcibly further retreating the screw without rotating the screw, as a second retreat operation, to form a second space at the downstream side of the screw in which no molten resin containing the added component is present, and placing the screw to a predetermined position,
• after the second retreat operation, normally rotating the screw, as a second normal rotation operation, and filling the second space with the molten resin containing the added component,
• after the second normal rotation operation, reversely rotating the screw, as a second reverse rotation operation to apply a shearing force to the molten resin containing the added component in a direction different from a direction at the second normal rotation operation, and further dispersing the added component in the molten resin;
• and
• an injecting step of injecting the molten resin containing the added component at the downstream side of the screw into a cavity,
• wherein
• in a plasticizing step, the added component is supplied to the cylinder through the vent hole when the molten resin generated in the cylinder is transported under the vent hole, and in the first and second reverse rotation operations, the screw reversely rotates at prescribed timing and for a prescribed period.