Control method for injection molding machine and injection molding machine

An injection molding machine comprising:

• a heating barrel in which a resin material is heated and becomes molten resin;
• a screw that is disposed rotatably in the heating barrel, and movable in an axis direction of rotation in the heating barrel;
• a back pressure detection unit that detects a back pressure as a pressure of the molten resin ejected by the screw in the heating barrel;
• and
• a control unit that controls rotation of the screw and movement of the screw by moving the screw backward while rotating the screw to feed the molten resin along a length of the heating barrel and accumulate a quantity of molten resin to be used in an injection cycle, the control unit determines a back pressure of the accumulated quantity of molten resin based on the back pressure detected by the back pressure detection unit,
• wherein during a metering process before the metering process is completed, the control unit is configured to decelerate a rotational speed of the screw at a same time as a backward movement speed of the screw is decelerated,
• wherein the control unit is configured to stop backward movement of the screw at completion of the metering process,
• wherein the metering process is a process of accumulating a quantity of the molten resin to be used in an injection cycle,
• wherein the control unit is configured to control the rotational speed and a rotation direction of the screw so that the back pressure detected by the back pressure detection unit becomes a target pressure lower than the back pressure of when the metering process is completed when a target time is reached, and
• wherein the control unit is configured to control an injection of the accumulated molten resin into a mold after reaching the target time.