Harmful self-excited vibrations called chatter occur during cutting processes (milling and turning) as a result of the trace regeneration. Moreover, dynamics of milling process is also influenced by intermittent cutting teeth during cutting. The paper presents an analysis of two-dimensional nonlinear model of milling. The analysed model takes into account susceptibility of the tool and the workpiece. The dynamics of the milling process is described by the discontinuous differential equation with a time delay, which can cause process instability for various system parameters. Therefore, stability lobes diagram was determined numerically. In order to reduce harmful vibrations the concept of the use of active piezo-elements is presented here. In addition, the work shows numerical results of chatter control in open and closed loop.
The article presents the results of an analysis of the influence of the technological parameters related to tool holder types on the vibrations occurring during the milling of AZ91D magnesium alloy. Magnesium alloys are very low-density materials and, therefore, are increasingly being considered as replacement materials for the more commonly used aluminium alloys. The tool used in the study was a carbide end mill with TiAlN coating, clamped in three different types of tool holder: ER collet, heat shrink, and Tendo E hydraulic. The milling tests used straight toolpaths at varied cutting speeds and feed per tooth values. Based on the vibration displacement and acceleration signals recorded during the machining tests, the following were analysed: maximum value, amplitude, and root mean square (RMS) value of the vibrations. As part of the study, composite multiscale entropy (CMSE) analysis was also performed, describing the level of disorderliness of the obtained vibration signals. The increase in machining parameters caused an increase in the values characterising the displacement and acceleration of the vibrations. It was noted that multiscale entropy might be an important parameter describing the vibration signal (both displacement and acceleration).
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