Patent ID: 7347965

Claim:
An apparatus for injection molding wherein raw material is plasticized in an injection unit and injected therefrom into at least one mold cavity, the injection unit comprising a plunger, the plunger being translated with accumulation of plasticized material to be injected and being advanced to inject the accumulated plasticized material into the mold cavities, the apparatus comprising: a) 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; b) 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 c) 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.