No abstract

No abstract

Peripheral milling is extensively used in manufacturing processes, especially in aerospace industries where end mills are used for milling of wing parts and engine components. The generation of complex shapes with high quality for various types of materials is the main advantage of milling in contrast to other machining processes. During the milling process, the occurrence of self-excited vibrations or chatter may cause reduction in material removal rate (MRR), damage to the tool and spindle bearing or may result in poor dimensional accuracy and surface finish of the work-piece. In this paper, milling process is modeled as two degrees of freedom (2DOF) system in which the tool wear and process damping effects are considered. To suppress regenerative chatter (or self-excited vibrations), optimum tunable vibration absorbers (in x-y directions) are designed. A sophisticated optimization algorithm is developed to determine the optimum values of the absorber parameters (their mass and stiffness). The effects of tool wear, process damping and absorbers are investigated on the frequency response of the system. Results are presented in the time and frequency domains. According to the results, both of the tool wear and process damping play as stabilizing factors of the dynamic system; under regenerative chatter and unstable machining conditions. However, tuned vibration absorbers are implemented to achieve the global stable conditions. The robustness and efficiency of deigned absorbers are investigated for the uncertain dynamic model. It is shown that after implementation of the absorbers, higher material removal rate (MRR) can be achieved while the stability of the nominal and uncertain processes is guaranteed.

Due to exibility of thin plates, high-amplitude vibrations are observed when they are subjected to severe dynamic loads. Because of the extensive application of circular plates in industry, attenuating the undesired vibrations is of foremost importance. In this paper, Adaptable Vibration Suppressors (AVSs) as a semi-active control approach were utilized to suppress the vibrations in a free circular plate under the concentrative harmonic excitation. Using mode summation method, the mathematical model of the hybrid system including the plate and an arbitrary number of vibration suppressors was analyzed. By developing a complex multiple-loop algorithm, optimum values for the parameters of AVSs (sti ness and position) were achieved such that the plate de ection was comprehensively minimized. According to the results, AVSs acted e ciently in suppressing the vibrations in resonance/non-resonance conditions. It was also observed that optimum AVSs reduced the plate de ection over a broad spectrum of excitation frequencies. Finally, since the algorithm was developed in a general user friendly style, design of AVSs could be extended to other shapes of plates with various boundary conditions and excitations.