Mold closing unit of an injection molding machine

Claim 1

A mold closing unit of an injection molding machine which includes a stationary mold clamping plate and a movable mold clamping plate slidable along parallel guide rods relative to said stationary plate, a movable die affixed to said movable plate, a mating fixed die affixed to said stationary plate and confronting said movable die, the unit comprising a fixed, hydraulic mold closure retention cylinder, and a hydraulic traveling cylinder including a piston operable within said retention cylinder and defining therewith on opposite sides of said piston first and second pressure chambers for respectively retracting and extending said piston, said piston being connected to said movable die, and said piston being hollow so as to define a third pressure chamber, means for operating said unit comprising a hydraulic supply line connected with said first and third chambers, said supply line having a branch line leading to said second chamber, a linear amplifier having rigid hydraulically fixed feedback and comprising a multi-way valve arranged in said supply line for axial movement to control the flow of hydraulic fluid through said supply line and said branch line for closing and opening said movable die, said valve being controllable for the operation of a speed pattern specified for said movable clamping plate, an elongated threaded rotatable spindle threadedly connected with said movable mold clamping plate for axial displacement relative thereto upon rotation of said spindle, said valve being a 4/2-way valve having a valve body on said spindle for axial movement therewith upon spindle rotation, and a stepping motor coupled with said spindle for rotation thereof, said stepping motor being controllable as a function of a predetermined closing speed pattern, whereby rotation of said spindle effects the movement of said 4/2-way valve to control the flow of hydraulic fluid, the movement of said movable die effecting an oppositely directed movement of said valve via said spindle which is counteracted by said motor, and said stepping motor being switchable to an increased number of steps per revolution during mold closing when said movable plate reaches a predetermined distance from said stationary plate for slowing down the mold closing to a specified creep rate before the mold is completely closed so that the mold is closed at said creep rate, independently of the mass of said movable die and of said movable mold clamping plate.