Distribution characteristics and influencing factors of the frequency-domain response of a vehicle–track vertical coupled system

Employing theory on vehicle-track coupled dynamics, the equation of motion of a vehicle-track vertical coupled system was established by combining frequency analysis and symplectic mathematics. The frequency response of the vehicle-track vertical coupled system was calculated under the excitation of the German low-interfer- ence spectrum, and the effects of the vehicle speed, vehicle suspension parameters, and track support parameters on the frequency response of the coupled system were studied. Results show that, under the excitation of the German low- interference spectrum, the vertical vibration of the car body is mainly concentrated in the low-frequency band, while that of the bogie has a wide frequency distribution, being strong from several Hertz to dozens of Hertz. The vertical vibrations of the wheel-rail force, wheelset, and track structure mainly occur at a frequency of dozens of Hertz. In general, the vertical vibration of the vehicle-track coupled system increases with vehicle speed, and the vertical vibrations of the car body and bogie obviously shift to higher frequency. Increasing the vehicle suspension stiffness increases the low- frequency vibrations of the vehicle system and track struc- ture. With an increase in vehicle suspension damping, the low-frequency vibrations of the car body and bogie and the vibrations of the wheel-rail vertical force and track structure decrease at 50-80 Hz, while the mid-frequency and high- frequency vibrations of the car body and bogie increase. Similarly, an increase in track stiffness amplifies the vertical vibrations of the wheel-rail force and track structure, while an increase in track damping effectively reduces the vertical vibrations of the wheel-rail vertical force and track structure.

Determination of optimal geometrical parameters of peripheral mills to achieve good process stability

This paper focuses on optimization of the geo-metrical parameters of peripheral milling tools by takinginto account the dynamic effect. A substructure synthesistechnique is used to calculate the frequency responsefunction of the tool point, which is adopted to determinethe stability lobe diagram. Based on the Taguchi designmethod, simulations are first conducted for varying com-binations of tool overhang length, helix angle, and teethnumber. The optimal geometrical parameters of the tool aredetermined through an orthogonal analysis of the maxi-mum axial depth of cut, which is obtained from the pre-dicted stability lobe diagram. It was found that thesequence of every factor used to determine the optimal toolgeometrical parameters was the tool overhang length, teethnumber, and helix angle. Finally, a series of experimentswere carried out as a parameter study to determine theinfluence of the tool overhang length, helix angle, and teethnumber on the cutting stability of a mill. The same con-clusion as that obtained through the simulation wasobserved.