Mold clamping unit and injection molding apparatus

An injection molding apparatus comprising:

• a mold having a fixed mold plate and a movable mold plate;
• an injector for injecting a plasticized resin into a cavity of said mold closed;
• and
• a mold clamping unit for opening and closing said mold,
• wherein said mold clamping unit comprises:
• a mold clamping cylinder which is driven by supply or discharge of a working fluid, and moves said movable mold plate between a fully open position in which said movable mold plate is separated by a predetermined distance from said fixed mold plate and a closed position in which said movable mold plate is in contact with said fixed plate;
• mold opening means for applying a mold opening force of a predetermined magnitude to said movable mold plate in the direction from said closed position toward said fully open position and moving said movable mold plate from said closed position to a predetermined half-open position located between said closed position and said fully open position;
• switching means for switching a mold clamping force generated by said mold clamping cylinder between a first mold clamping force which is larger than said mold opening force and a second mold clamping force which is smaller than said mold opening force by switching the supply pressure of said working fluid supplied to said mold clamping cylinder;
• and
• control means for controlling said mold opening means and said switching means.