Look-Ahead to Minimize Energy Costs of CNC Milling Machines for a Volatile Energy Price

Due to the rising share of renewable energy sources in the energy market (e.g. 40 % in Germany 2018) the power grid has to be stabilized by other sources of balancing power than conventional power plants and the volatility of the energy price is expected to increase. Production machines in the industry have unused energy flexibilities in their production processes. Those flexibilities like the differences in energy consumption between various machining processes or even between single processing steps could be used for demand-side management. This paper presents an approach on how to model and control the energy consumption of CNC (Computerized Numerical Control) machines. While in previous studies on energy flexibilities, mainly high energy-consuming auxiliary units are investigated, the focus of this publication is to use explicitly the flexibilities inside the process. The main idea is to optimize automatically the production process to a certain volatile energy price without significantly delaying the process, increasing the workload on the shop floor with additional tasks or jeopardizing (much) the workpiece quality. The proposed method uses a material removal simulation in combination with an energy model of the flexibilized machine tool, to be able to model the energy consumption of each processing step, and its dependencies to other steps. The energy costs can be reduced by scheduling the various processing steps. The precondition for the “look ahead” is a workpiece model, a model of the machine and a tool model which are described in this publication. Therefore, it is not only suitable for series production but also for small batch production. The approach is especially interesting for long production processes (>>1 h) or a market with highly volatile energy prices.