Key component technology for ultra-precision machining machines (figure)

1 Introduction

The development of ultra-Precision Machining machines began in the 1960s. At that time, in the United States, large-scale metal mirrors were required for the development of laser nuclear fusion experimental devices and infrared experimental devices, and it was urgent to develop ultra-precision processing technology for mirrors. Ultra-precision machine tools for cutting aluminum alloy and oxygen-free copper with a single-point diamond turning tool have emerged. In 1980, the United States first developed the three-coordinate controlled M-18AG aspherical machining machine in the world, which marked the maturity of sub-micron ultra-precision machining machine technology. The development of ultra-precision machine tools in Japan lags behind the United States for 20 years. From 1981 to 1982, the first development of multi-prism mirror processing machine tools, followed by magnetic head micro-machining machine tools, disk end-face lathes, and recently aspherical processing machines and short-wavelength X-ray mirror processing machines. Ultra-precision machine tools in Germany, the Netherlands and Taiwan are also at the advanced level in the world. Although the research and development of ultra-precision processing machine tools in China started relatively late, it has made gratifying achievements after the unremitting efforts of the vast number of precision engineering researchers. The HCM-I ultra-precision machining machine developed by the Institute of Precision Engineering of Harbin Institute of Technology has reached the international level. The performance indexes of some foreign ultra-precision machine tools and HCM-I ultra-precision machine tools are shown in Table 1. This paper focuses on the key component technologies of ultra-precision machining machines.

Table 1 Summary of performance indicators of typical ultra-precision lathes at home and abroad

2 spindle system

The spindle of the ultra-precision machining machine directly supports the movement of the workpiece or the tool during the machining process, so the rotation accuracy of the spindle directly affects the machining accuracy of the workpiece. Therefore, it can be said that the spindle is the most important component in the ultra-precision machining machine, and the accuracy of the machine tool itself can be evaluated by the accuracy and characteristics of the machine spindle. At present, the most accurate precision of the spindle of the ultra-precision machining machine tool is the hydrostatic air bearing spindle (the magnetic suspension bearing spindle has also received more and more attention, and its accuracy has been rapidly improved). The air bearing spindle has good whirling precision. The spindle run-off rotation accuracy is the shaft-line runout except for the roundness error of the shaft and the influence of the machining roughness, that is, the non-repetitive radial runout, which is static precision. At present, the precision of the high-precision air bearing spindle can reach 0.05μm and the highest can reach 0.03μm. Due to the homogenization of the pressure film supporting the rotary shaft in the bearing, the air bearing spindle can obtain higher precision than the bearing component itself. For example, the rotation accuracy of the main shaft can reach about 1/15 to 1/20 of the roundness of the bearing components such as the shaft and the bushing. Japanese scholars have shown that when the circularity of the shaft and the sleeve reaches an accuracy of 0.15 to 0.2 μm, a rotation accuracy of 10 nm can be obtained, and the rotation precision of the air bearing spindle with the highest precision manufactured by FFT is 8 nm. The roundness error of the dense jade air bearing main shaft of HCM-I ultra-precision machining machine is ≤0.1μm. In addition, the air bearing main shaft has the advantages of good dynamic characteristics, long precision life, no vibration, and a rigidity/load amount which is commensurate with the use condition. However, detailed work is required on the stiffness, heat generation and maintenance of the spindle. In order to achieve the nano-rotation accuracy of the air bearing main shaft, in addition to the shape accuracy of the air bearing shaft and bushing of 0.15 ~ 0.2μm, and then through the homogenization of the air film to achieve, it is also necessary to maintain the uniformity of the gas flowing out of the air supply hole Sex. The difference in the number of air supply holes, the distribution accuracy, the inclination of the shaft center, the convexity and concave of the bearing, the cylindricity, the surface roughness, etc., all affect the uniformity of the air flow on the bearing surface. The unevenness of the airflow is the direct cause of the slight vibration, which affects the rotation accuracy. To improve the condition of the gas supply system, the bearing material should be made of porous material. This is because the porous bearing is supplied through a myriad of small holes, which can improve the pressure distribution and improve the uniformity of air flow while improving the load carrying capacity. The uniformity of the porous material is very important. Because the cavity inside the porous air supply bearing material will form an air cavity, if it is not controlled, it will cause the air hammer to vibrate. For this reason, the surface must be blocked.

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