A Novel Approach to Control Switchover Between Injection and Holding Phase for a Hydraulic Injection Moulding Machine

The repeatability of injection moulding machines has been a focus point since the 1970's. An important part of the moulding process, when utilizing secondary over point, is the switchover between the velocity and pressure-controlled phase. Minimizing the transients in the response increases the moulding quality. A novel switchover method is presented in this paper, based on a hydraulic injection moulding machine. Controlling the flow into each of the injection cylinder chambers combined with a cascaded control structure makes it possible to execute a fully controlled switchover with a single parameter related to the permissible time duration of the pressure settling period. The controllers are implemented on an industrial state of the art injection moulding machine, and the results show good agreement with theory. The response time and transients are minimized. It is further experimentally verified that it is possible to tune the desired switchover duration. The method furthermore simplifies the task for the moulding machine operator, when setting up a new mould, as it is possible to control the dynamics of the switchover with a single parameter.