Hydraulic system for a toggle-type plastic injection molding machine

Abstract

An improved computer controlled hydraulic system for a conventional toggle-operated plastic injection molding machine comprising an injection assembly and a mold clamping assembly. The hydraulic system includes a first low volume pump and a second high volume pump connected between a reservoir of hydraulic fluid and a pressure and flow control manifold. The output of the pressure and flow control manifold is connected to an injection control manifold, in turn conected to and operating the instrumentalities of the injection assembly. The output of the pressure and flow control manifold is also connected to a clamping control manifold, in turn connected to and operating the cylinder of the clamping assembly. An isolation manifold is connected between the pressure and flow control manifold and the clamping control manifold. A third low volume pump is connected between the reservoir and the isolation manifold. The isolation manifold is also connected to the reservoir. When unactuated, the isolation manifold connects the output of the pressure and flow control manifold directly to the clamping control manifold and recirculates the third pump to reservoir, when the machine is to perform sequential cycles such as conventional injection molding or conventional coining. When actuated, the isolation manifold disconnects the clamping manifold from the pressure and flow control manifold and connects the third pump to the clamping control manifold, enabling the machine to perform a coining cycle with individual and simultaneous clamping and injection control, and precise and repeatable position and speed control of the coining step.