Process stability of parallel turning processes

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To increase the productivity of machining processes, lathes with multiple tool turrets are used increasingly. These turning machines are characterized by the possibility of simultaneous engagement of multiple tools on a single rotating work piece. Either the tool engagements takes place at different areas of a work piece or the cutting is carried out simultaneously on the same cutting surface.In both cases, process instabilities in the form of chattering may occur. Chattering is a self-excited and self-reinforcing regenerative phenomenon, resulting from interactions between the dynamic behavior of the machine tool structure and the cutting process.So far, there is a lack of research in the field of process stability of parallel turning processes. In previous studies from WZL a major influence of the transfer compliance on the process stability during double spindle milling could already be detected. The transfer compliance describes the displacement on a second tool as a result of a force on the first tool. Parallel turning processes using multiple blades in the same cutting plane induce mutual excitations due to the shared cutting surface waviness.The goal of this research project is the determination, modeling and interpretation of the stability behavior of parallel turning processes. The influence of the radial angular position between the cutting tools on the process stability is expected to be significant, because this angle directly affects the stability-relevant tool dead time. Subsequently, this angle will be varied continuously to generate a time variant dead time (analogously to active spindle speed variation techniques). This is done by extending the commonly used process-machine interaction models. Using a time-domain simulation, time variant process parameters may be investigated. A test bench was already designed to investigate the underlying parameters and to validate the simulation results. This test bench comprises of two single mass oscillators, which are adjustable in their angular positions. Using the test bench, the machine behavior can be reduced to that of a single mass oscillator. Thus, the research will be focused primarily on simulative prediction of process machine interaction. Using the virtual model, suitable optimization strategies for increasing the stable chip removal rates will be derived and validated. Finally, the insights gained by the aforementioned procedures are used to create a simulation model of an industrial turning machine with multiple tool turrets, which will be experimentally validated.