Today, numerical-controlled machine tools are used for flexible machining of increasingly individualized products. The selection of the most economic tool, machining strategy and clamping position is part of the manufacturing operations planning and bases on the employees’ practical knowledge. The NC programmer is supported by current CAM systems with material removal simulation and collision detection. This early validation avoids damages and increases the productivity of the machines. The benefit of simulations can be increased by a better model accuracy. In common CAM systems the machine behaviour is often insufficiently reproduced; for example, the dynamic characteristics of axes, the tool change and the chronological synchronization are simplified or neglected. In view of complex operations, a slow trial run on the real machine or substantial safety margins are necessary. The described deficits can be solved by virtual machine tools. Thereby a virtual numerical control and a detailed machine kinematic is used for an accurate simulation. The result is an error-free NC program which can be directly used on the real machine. In addition, the exact processing time is determined and supplied for the operations scheduling and dispatching. Furthermore, virtual machine tools provide promising approaches for an automated optimization of machining operations and machine set up. Parameters for the optimization of the processing time are, for example, different clamping positions or tooling arrangement. Simulating several parameters requires lots of computational power. Hence, the vision of the project ,,InVorMa“ is a cloud application, which supports the operation planning, scheduling and dispatching of machine tools. A computer cluster (cloud) provides noticeably faster results than a single computer. Therefore, the machine tools and the manufacturing equipment of the user are cloned one-to-one in the cloud. The manufacturing documents are optimized by the cloud application before they are forwarded to the shop floor. The optimization involves the NC program for each machine as well as the distribution of orders. The practical knowledge of the manufacturing planner and the results of the optimizations are pre-processed for reuse by an integrated knowledge base.