Injection molding method and injection molding machine

An injection molding method of resin containing reinforcing fibers, comprising:

• a plasticizing process of feeding a fiber bundle and a resin raw material to a cylinder including a screw that can rotate around a rotation axis and can advance and retreat along the rotation axis, and generating molten resin by rotating the screw in a normal direction, the fiber bundle comprising the reinforcing fibers in a roving state or in a chopped strand state;
• and
• an injection process of injecting to a cavity the molten resin containing the reinforcing fibers, wherein
• in the plasticizing process;
• a shear force in a direction different from a direction of a shear force generated by rotation of the screw is applied to the fiber bundle contained in the molten resin inside a groove of the screw by a retreat operation of forcibly retreating the screw for a predetermined stroke or for a predetermined time that can form a space closer to a downstream side than a tip of the screw, so that a swirling flow is generated in the molten resin containing the reinforcing fibers in a rotation axis direction of the screw;
• and
• the retreat operation is performed, and a rotation operation of rotating the screw in the normal direction is performed after the retreat operation to thereby promote dispersion of the reinforcing bundle.

An injection molding machine that gives a shear force to reinforcing fibers fed to a cylinder by rotating a screw in a normal direction, and generates and plasticizes molten resin, the injection molding machine comprising:

• the cylinder in which a discharge nozzle is provided on a front side, and that includes a reinforcing fiber feed hole through which the reinforcing fibers are fed, the reinforcing fiber feed hole feeding a fiber bundle comprising the reinforcing fibers;
• the screw provided inside the cylinder so as to be able to rotate around a rotation axis and to be able to advance and retreat along the rotation axis;
• and
• a control unit having a control program that controls an operation of the screw, wherein
• the control unit has the control program relating to the screw and a retreat operation velocity input setting unit that can set a retreat velocity of the screw to be an arbitrary value, wherein
• in the plasticization:
• the control program applies a shear force in a direction different from a direction of a shear force generated by rotation of the screw to the fiber bundle contained in the molten resin inside a groove of the screw by a retreat operation of forcibly retreating the screw for a predetermined stroke or for a predetermined time that can form a space closer to a downstream side than a tip of the screw, so that a swirling flow is generated in the molten resin containing the reinforcing fibers in a rotation axis direction of the screw;
• and
• the control program makes the screw perform the retreat operation, and makes the screw perform a rotation operation of rotating the screw in the normal direction after the retreat operation to thereby promote dispersion of the fiber bundle.