Due to an increasing number of setting parameters of current manufacturing systems increasing efforts are required to achieve a high product quality. At the Institute of Plastics Processing (IKV) a concept for a self-optimising injection moulding machine is being developed. Next to the natural process variations (caused by the limited accuracy of the machine) systematic disturbances like the fluctuating environmental conditions or variations in material viscosity influence the reproducibility of the injection moulding process. The conventional control of the injection moulding process is based on machine variables, which cannot compensate these process fluctuations and thus a constant part quality cannot be guaranteed. The aim of the self-optimising processing method is to compensate the effects of such process fluctuations, to ensure a repeatable process at the place of moulded part formation. So a constant part quality can be achieved. The usage of the so called pvT-optimisation in combination with a closed-loop cavity pressure control allows a systematic consideration of variable boundary conditions of the process. In addition, the effort required to set up the process can be significantly reduced. The pvT-optimised processing method enables the compensation of thermal disturbances and pressure fluctuations. In addition, the influence of variations in material viscosity on process variables are presented, occurring when using recycled material. Changing temperature and pressure of the material during the processing should compensate the variations in material viscosity. An effect analysis of viscosity-relevant process parameters like melt temperature, mould temperature and injection velocity links with the process parameters to the quality like part weight and part warpage. It shows a good correlation between the injection velocity and the part weight. Thus, the part weight can be estimated by adapting the injection velocity.