Calculation Method for Analyzing the Vibration Resistance for Thin-Walled Elements

When employing end milling for the thin-walled elements, in particular aircraft gas-turbine engines, it is possible to observe their forced vibrations due to the machining discontinuity. The authors present the calculation method for determining the best performance of discontinuous milling of the given elements, which minimizes the forced vibrations' level and provides the required quality of the machined surface. The proposed method is based on the modeling of machining, considering the differences between the end milling and standard milling. The main difference lies in the discontinuity in the process of machining. The authors developed a model for determining the milling force with the considered type of machining of thin-walled elements. A dissipative system with one degree of freedom is chosen as the calculation model to investigate the forced vibrations. The experimental investigations are performed on the specially designed facilities to study the vibrations in the thin-walled structural elements in their end milling. The paper provides the calculation results, which are compared with the experimental data in the wide range of rotational spindle frequency. A satisfactory coincidence between the rotational spindle frequencies with the largest and smallest vibration amplitudes is demonstrated. The reduced analysis of roughness of the machined surface shows an evident dependence of the given parameter on the vibration amplitude. Therefore, the smallest vibration amplitude denotes the highest quality of machining. The spectrum analysis of the deviation element signal implies the presence of beats when the natural element frequency is close to the excitation frequency of its vibrations, which is the main source of their amplitude increase and degradation of the machined surface. Here the smallest vibration amplitudes are observed with the frequencies of their excitation between the resonance peaks. Thus, the analysis of the motion law of the thin-walled element during milling confirms the accuracy of modeling of the considered process and determination of its vibration stability modes.