During conventional injection moulding, the holding pressure curve is controlled via pressure transducers on the injection axis. Influences such as, for instance, viscosity fluctuations in the melt owing to humidity, lubricants or colour additives, but also screw wear are not taken into account. These influencing variables, however, inevitably lead to pressure losses in the mould and consequently to fluctuations in part quality. In 1988, ARBURG therefore already developed the so-called “integrated injection process control”,
in which the holding pressure curve was controlled in real time via a pressure sensor in the mould. In addition to improved reproducibility of part quality the number of start-up cycles can also be reduced significantly using this method.
Injection process control operates with base points which are mutually interconnected to form a polygon outline.
This also allows a theoretical ideal characteristic to be followed by the machine.
The applicability of the target curve determined in this manner, however, depends largely on the parameterisation of the controller. This in turn is significantly determined by the flow paths in the mould up to the sensor. For process optimisation, therefore, a high degree of control technology expertise is required.
The principle of reference curve control is based on the idea of recording the internal mould cavity pressure curve of a moulded part deemed to be of good quality and employing this as a target characteristic. The adjustment curve of the controller is also recorded. This not only significantly simplifies determination of the target characteristic, the parameterisation of the controller is also facilitated considerably. With this method, the injection moulding process can thus be stabilised quickly and conveniently to produce a specified part quality. From practice for practice – this is the principle of reference curve control.