Process planning for the productive machining of complex shaped parts is a comprehensive activity where the dynamic behaviour of a machine tool, workpiece and the process setting has to be taken into account. The predictive process-oriented machine tool digital twin is a digital simulation tool enabling full control of the process results with respect to the adjustment of the whole machining system and the machining process. The paper defines and describes four different levels of such a digital twin according to its complexity. An overview of key elements and modelling techniques employed for creating the process digital twins is provided. The strategy for implementing the process digital twin as an enhancement of the NC machining process planning chain is presented. Selected use cases in the field of mould machining or thin walled blade machining are used for the method demonstrated.