| In order to take full advantage of recent developments in tool materials, a method is proposed to overcome the limitations placed on the milling operation by flexibilities in the machine-tool-workpiece system. Using a new type of stability diagram developed through time-domain simulation, it is shown that by adjusting the spindle speed so that the frequency with which the teeth pass the workpiece is equal to the dominant natural frequency of the system, it is usually possible to achieve substantial improvements in stability without necessitating basic changes in the NC part program.;An algorithm is presented which is capable of making this adjustment automatically and which requires only a vibration signal from the cut, the number of teeth on the cutter, and the spindle speed. No prior knowledge of the dynamic characteristics of the machine or workpiece is required, and the algorithm is even able to respond to changing dynamic charateristics (e.g. tool changes or machining across a thin web). The selection of spindle speed is made iteratively, and adjustments in feed rate are made in order to limit the magnitude of vibrations that may develop during the selection process. It is shown through simulation and experimental work that the algorithm converges to the best speed rather rapidly if convergence is possible. Cases are enumerated where convergence is not possible, and the original part program must be altered.;The portion of the operational time of a machine which is usually required for proving part programs can be greatly reduced. Substantial gains in metal removal rate are possible using this algorithm, and the hardware required for implementation is commonly available and relatively inexpensive. |
