Sikailo M. Eliminating vibrations when final milling on CPC machines

This dissertation is devoted to solving the problem of vibration during milling with end mills on CNC machines. There are passive and active methods for reducing vibrations during milling, but they require intervention in the design of the machine and/or tool, which is costly and non-universal. The effect of reducing vibrations can also be achieved by selecting "vibration-free" cutting modes, which can be depicted on a petal diagram of stability. This has become possible due to the widespread use of CNC machines and modern tool materials, which allows us to expect significant efficiency from the implementation of this approach for most cutting processes. In production, this mode is most often found by experimental trial and error. It is possible to determine the "vibration-free" cutting mode beforehand, at the stage of preparing the control program, using a stability diagram. However, to solve this problem, there are still no simple, effective methods and computer tools that can be used directly in production. There are several methods for creating a stability diagram, but due to the lack of a general model of the cutting process with regard to the backlash in elastic TOC, the adequacy of the process representation is lost. The experimental method is more accurate, but it is not universal because it is used for a specific machine, workpiece, and tool. To identify such cutting modes, a software application was created that automatically builds a diagram of the stability of the milling process. The software application is based on the developed mathematical model of the 4th order final milling process, which takes into account the closedness of the elastic dynamic system in the form of a single-mass system with two degrees of freedom and additionally closed due to positive feedback in two coordinates through the delay function. The stability limit is determined by the new Nyquist stability criterion. The process is modeled in both time and frequency space. A methodology and hardware are proposed to identify the dynamic characteristics of the technological processing system, namely, the frequency of natural oscillations, stiffness, and the oscillation damping coefficient. To test the results obtained, an experiment consisting of two stages was conducted. At the first stage, the dynamic parameters of the machine-workpiece-tool system were identified and a stability diagram was automatically generated. At the second stage, the workpieces were processed at cutting modes that correspond to the obtained stability diagram. The results showed the effectiveness of the new Nyquist stability criterion and the resulting stability diagram. The work consists of five chapters in which the main results of the thesis are presented and substantiated.