Title: Injection molding control system

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Abstract: An injection molding control provides for the programmable control of ram velocity as a function of the position of the ram through closed-loop feed-back of the measured actual velocity. Closed-loop feed-back of the actual mold cavity pressure overrides the velocity program in an analog fashion to stop the ram when a preset cavity pressure has been attained associated with a desired charge size. Programmable control of the ram screw speed and/or back pressure during injection as a function of ram position or time is used to impart a predetermined temperature profile to the charge along the length thereof while it is in the barrel prior to injection. This enables controlled variation in density of the molded article throughout its volume to achieve desired levels in preselected characteristics such as surface wear, gloss, resolution and the like. A closed-loop servo system responsive to hydraulic pressure on the ram, including a flow divider valve which meters flow between the ram pressure chamber and a drain tank, provides accurate and continuous control of injection, hold and back pressure to enhance product quality; smooth pressure transitions between different ram pressure levels utilized in the molding cycle to avoid undesirable effects due to ram overshoot; simultaneous flow and pressure increase during injection when ram velocity falls below programmed level thereby avoiding sluggish response characteristics when restoring ram velocity; and reduction in number of hydraulic components required to effect the injection, hold, and back pressure functions.


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