Apparatus and method for injection molding

An injection molding machine comprising:

• a) a clamp unit comprising a mold assembly having at least one mold cavity for receiving plasticized material, the clamp unit opening and closing the mold assembly to permit molding of plasticized material therein and removal of molded articles therefrom;
• b) an injection unit wherein raw material is plasticized and injected therefrom into the mold cavities, the injection unit having a plunger being translated with accumulation of plasticized material and being advanced to inject the accumulated plasticized material into the mold cavities;
• c) at least one electric motor engageable with the plunger to resist translation during accumulation of plasticized material and to advance the plunger to inject the plasticized material into the mold cavities;
• d) at least one hydraulic actuator selectably operating the plunger during a pack and hold interval following injection of plasticized material into the mold cavities to maintain a desired melt pressure while the plasticized material solidifies, the hydraulic actuators being operated to supply supplemental force when force supplied by electric motors engaged to operate the plunger is limited to maintain the operation of the motors within the applicable continuous duty rating thereof;
• and
• e) a control, the control predetermining a force required to maintain melt pressure during the pack and hold interval and a supplemental force to be supplied by the hydraulic actuators so that the motors engaged to operate the plunger will be operated within the applicable continuous duty rating thereof.