Active chatter control techniques in peripheral milling

The research work presented in this thesis tackles different aspects of the chatter control problem in peripheral milling. These aspects include chatter detection, suppression, and avoidance.;A new method for detecting chatter is introduced. The method is based on using the spindle drive current signal, an application that has been thought not possible by researchers in the field due to the limited bandwidth. Different chatter detection signals are compared based on their capabilities and sensitivities. Comparisons include the acceleration, sound, and cutting force signals, as well as the current signal. Statistical methods are used for analyzing experimental data. The current signal was proven to have a high sensitivity to chatter development. Also, it had the maximum signal to noise ratio. This makes it a preferred signal, overall, for chatter detection in industrial applications.;Two fuzzy logic controllers, proportional and proportional derivative, are designed to select combinations of amplitude and frequency of spindle speed modulation based on a measure of process instability, the R-value. The implementation aspects of the controllers are addressed. The performance of the controllers is compared with that of a bang-bang controller. The effects of the cutting parameters on the controllers' performance are investigated using statistical methods, and discussed using the stability chart of the milling process. The analysis of variance of experimental data indicated that the increase in the immersion adversely affects the controllers' performance while other cutting parameters have no significant effect. Also, the interaction of the spindle speed and the geometry of cut was shown to have a significant effect on the controllers' performance. By analyzing experimental data using the stability chart of half immersion down milling, it was found that the controllers' performance was dependent on the position of the operating point with respect to stability lobes. Experimental data and simulations showed that the delay time of the control action degraded the controllers' performance. An advanced interface card is necessary to solve this problem.;A new method for identifying the locations of stability lobes is introduced. The method depends on ramping the spindle speed while observing the pattern of the R-value. A control system for avoiding chatter in peripheral milling is developed and implemented. The system ramps the spindle speed when chatter is detected. Based on the fluctuations in the R-value, the system selects a favourable spindle speed at which chatter ceases or the degree of system instability decreases. The system was tested under different cutting conditions. Experimental results showed that this system is very successful in both avoiding chatter and alleviating its effects, and reducing the degree of system instability.