Identification of optimal process parameters in twin-spindle machining

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To increase the production capacity, twin-spindle machining centers are widely used in industry. Such a machine configuration is economically advantageous as productivity increase at approximately the same floor space and only moderately higher investment costs can be achieved. However, in practice, the removal rate is limited by the dynamic instability of the milling process. In a previous research project funded by the DFG at the Laboratory for Machine Tools (WZL) at RWTH Aachen University a significant influence of the angular position of the two spindles to each other on the process stability could be identified and demonstrated.The optimum angle position which enables a stable process with a maximum cutting depth is dependent on the machine structure and process parameters of the milling process. The determination of an optimal angle position can be done either through simulation of the machining process or series of experimental cutting tests on the machine. The effort to parameterize a simulation model as well as to run through the experimental test series is considerable. Due to the high cost for determination of stability charts or optimal angular positions, the stability limits for the present cutting processes are usually not be determined in industrial practice. If regenerative chartering occurs during the setup of series production, the machine operator usually tries to stabilize the process by varying the process parameters. If this procedure does not induce a stable process in a few tries, the cutting depth and thus the productivity will be reduced.To use the potential of the different spindle angular positions a procedure has to be developed that allows an automatic determining of the optimal angular position of tool 1 and tool 2 depending on the current process. The goal of this research project is to develop a methodology and a measurement setup with an analysis software, which allows an operator without knowledge of dynamics of machine tools or chatter theory to determine efficient process parameters. Therefore software has to be developed for analysing the occurring vibrations regarding their amplitudes in the relevant frequency range. The process with the corresponding angular displacement between the cutting tools, in which the lowest vibration amplitude can be observed in relevant frequency ranges, is identified as efficient.