Effect of coupling misalignment fault on vibration response and machined surface topography in ultra-precision lathe turning

In machining process of the ultra-precision turning lathe, the vibration of the spindle is closely related to the machining quality. Coupling misalignment is one of the most common faults that lead to vibration problems of the spindle. Most of the studies on the misalignment of coupling focus on the vibration response in radial direction, and the axial motion of spindle is rarely studied. In this paper, the model of a machining system with misaligned coupling is established. Each part of the system has complete 6 degree-of-freedom (DOF) of motion, and system’s responses when idling and cutting are simulated. Furthermore, the machined surface topography is simulated according to the responses results. It is found that there are abundant low-order harmonics besides the operating frequency in the vibration of the spindle, both in the radial and axial direction. These harmonics in response will be reflected to the surface through the relative motion of the spindle and the cutting tool. The influence of spindle’s angular vibration on the surface is also especially noteworthy. Meanwhile, an experiment is carried out that the vibration of the spindle is detected by the capacitive displacement sensor, and the surface topography is directly measured by a laser interferometer. The experimental results verify this relationship between the vibration and the machined surface. This study is of considerable significance to deeply understand the influence of misalignment on rotor’s motion and machined surface. The research results also have value for spindle error diagnosis and machined surface prediction.