The rotation accuracy of the aerostatic spindle can easily be affected by shaft shape errors due to the small gas film clearance. Thus, the main shaft shape errors with the largest scale—that is, the roundness and cylindricity errors—are studied in this paper, and a dynamic mathematical model is established with the consideration of the roundness, cylindricity errors, and spindle speed. In order to construct the shaft model, the discrete coefficient index of the shaft radius based on roundness measurement data are proposed. Then, the simulation calculations are conducted based on the measured cylindricity data and the constructed shaft model. The calculation results are compared with the spindle rotation accuracy measured using the spindle error analyzer. The results show that the shaft with a low discrete coefficient is subjected to less unbalanced force and smaller rotation errors, as obtained by the experiment.

In regards to the problem of tubing precision separation, the high-efficiency precision separation method for tubing under eccentric wheel high-speed rotational bending fatigue loading is proposed, which aims to promote the initiation of fatigue cracks at the root of the annular V-notch on the tubing surface. Research on the stress concentration effect of the annular notch on the tubing surface is carried out. The design of the notch takes into account the characteristics of tubing precision separation. The numerical simulation calculation includes four kinds of notches, namely, annular V-notch, annular U-notch, asymmetric V-notch towards the blanking end direction 45°, and asymmetric V-notch away from the blanking end direction 45°. The crack propagation lengths produced by each notch under the same experimental conditions are investigated experimentally. According to the findings, the annular V-notch is suitable for this separation method. By analyzing the theoretical stress concentration factor of the annular V-notch on the tubing surface, three main parameters affecting the annular V-notch root stress field are determined, namely, notch angle, notch depth, and notch root base angle radius. Through calculation and analysis, the influence law of tubing annular V-notch angle, notch depth, and notch root base angle radius on the stress concentration effect is obtained. Based on the process characteristics of tubing precision separation, the ideal tubing annular V-notch geometric parameter is presented within a reasonable value range. For the validation experiment of tubing precision separation, 45# steel, 304 stainless steel, and T2Y copper tube are selected, respectively. Finally, a great tubing precision separation effect is achieved, which verifies the reasonable selection of the tubing surface annular V-notch geometric parameter.

Aiming at the difficulties of efficient and precise separation of metal tubes. For tubing fatigue fracture precision separation, this paper proposes a tubing precision separation process under eccentric wheel rotational bending fatigue loading. Mechanical properties experiments for 304 stainless steel tubing are carried out. On this basis, the J-C constitutive model of 304 stainless steel tubing fatigue fracture is established. In addition, the tubing stress at different rotation angles of the eccentric wheel and the axial stress at four positions of the tubing V-groove section are analyzed, and the process of the tubing precision separation is simulated. According to the results, the axial stress of the tubing V-groove section changes basically symmetrically, and the stress is the largest at the smallest distance from the eccentric wheel excircle axis. During fatigue loading cycles from 0 to 500, the crack growth rate of tubing outer ring is greater than that of the inner ring. With the increase in loading cycles, the crack surface gradually changes from smooth to undulating. Finally, an obvious final fracture region appears, which is consistent with the experimental results.

Traditional separation methods for thick-walled metal tubes include turning and sawing, which suffer from wasted raw material and low efficiency. In view of this, this paper proposes a new process of using impact load to promote crack generation and tube separation. Based on the principles of radial repeated impact load, stress concentration effect and fatigue fracture, the rapid initiation and stable expansion of tube fatigue crack are promoted. In addition, the crack initiation mechanism of the tube V-notch root cracks under radial repeated load when the tube is in a restrained state. For the experimental study of the GCr15 steel tube, a multistep decline frequency time tube separation control curve with an initial frequency from 4 Hz to 31 Hz and termination frequency from 1 Hz to 8.5 Hz was designed, and the precision tube separation device is loaded by pneumatic fatigue shock to achieve tube precision separation. In addition, a tube fracture quality evaluation method is proposed. According to the test results, the stress concentration effect of V-notch can significantly reduce the average stress in the process of tube fatigue separation and accelerate the generation of microcracks. Under the continuous action of repeated impact load, the loading method of multistep decline can effectively control the rapid crack initiation and stable expansion of the GCr15 tube V-notch root crack. Moreover, the tube final fracture region has relatively small defects, which can obtain good fracture quality.