Micro milling - investigations on process structure interactions

At the IWF and the MMD of the Technische Universität Berlin a prediction model is developed, that predicts process machine interactions (PMI) during the micro milling process on a 3 axis micro milling machine tool. The dynamic process forces due to the discontinuous cutting conditions and the deviation of the tool center point (TCP) represent the most important parameters within the prediction model. Both of them are determined experimentally. The micro milling process is different from macro cutting. Chip thickness and grain sizes of different materials are in the range of the cutting edge radius. Moreover, the commonly used spindle speed is very high. The cutting edge engagement leads to a high frequency excitation of the entire structure. The paper describes research activities to model the micro milling process. The prediction model contains two major parts, the structure model and the process model. The 2D model is implemented into Matlab/Simulink as a differential equation of motion. Process forces are calculated based on the Kienzle/Victor equation. By transferring the forces to the structure model dynamic loads are imposed on the machine structure. The structure's response in the form of deviations of the tool center point (TCP) results in a changed chip thickness. By that the simulation circle is closed. The edge roundness caused by tool wear and the helix angle of the tool are also taken into account. Using common and alternative measurement techniques as proposed, in situ measurement is possible. Future research work will focus on the connection of the structure and process model Non-linear structure parts will be treated and implemented by FE software.