Injection molding machine and method for injection molding

A method for injection molding of an injection molding machine, comprising:

• a step of supplying a resin material into a plastication cylinder of a plastication device, wherein a material inlet from which a resin material is supplied from a starved feeder including a feed cylinder and a rotatably provided feed screw and a vent hole from which gas is discharged are formed on the plastication cylinder, and a plastication screw is arranged to rotate freely in the plastication cylinder, and melts and sends the resin material supplied from the material inlet,
• a step of melting and sending the resin material by the plastication screw of the plastication device,
• a step of sending the resin material to an injection device which comprises an injection cylinder and an injection plunger, wherein the resin material is sent from the plastication cylinder to the injection cylinder through a junction which communicates the plastication cylinder and the injection cylinder, and the injection plunger is arranged to advance and retreat freely in the injection cylinder, retreats to meter the resin material, and advances to inject the resin material after metering;
• a step of controlling at least the plastication screw and the injection plunger according to predetermined molding conditions by a controller,
• a step of switching from normal conditions to vent-up suppression conditions by the controller when the vent up is detected by a vent up sensor, and performing a control of molding by referring to operating situations that are fed back, wherein the normal conditions are the molding conditions which are normal, and the vent-up suppression conditions are the molding conditions for suppressing the vent-up, and
• the vent-up suppression conditions comprise the followings:
• increasing a rotational speed of the plastication screw to be higher than a rotational speed of the plastication screw in the normal conditions,
• reducing a rotational speed of the feed screw to be lower than a rotational speed of the feed screw in the normal conditions,
• reducing a back pressure applied to the injection plunger to be lower than a back pressure applied to the injection plunger in the normal conditions,
• using retreat-metering when the retreat-metering is not performed in the normal conditions, wherein the retreat-metering is a control to apply, a force in a retreat direction in addition to a pressure of the resin material to the injection plunger to move the injection plunger at a predetermined retreat speed in the metering, and
• increasing the retreat speed of the injection plunger to be higher than the retreat speed of the injection plunger in the normal conditions when the retreat-metering is performed in the normal conditions.