Development of ultra-precision machining

The development of ultra-precision machining has gone through the following three stages.

(1) The 1950s to 1980s were the period of technological creation. In the late 1950s, in order to meet the needs of the development of advanced technologies such as aerospace and national defense, the United States took the lead in developing ultra-precision machining technology, and developed the ultra-precision cutting technology of diamond tools-single point diamond turning (SPDT) technology, also known as "micro-inch technology", which was used to process large spherical and aspheric parts of laser nuclear fusion mirrors, tactical missiles and manned spacecraft. Since 1966, unionCarbide, Philips and LawrenceLivemoreLaboratories have successively launched their own ultra-precision diamond lathes, but their application is limited to the experimental research of a few large companies and research institutions, and their products are mainly processed for national defense or scientific research purposes. During this period, diamond lathes were mainly used to process soft metals such as copper and aluminum, as well as workpieces with complex shapes, but only axisymmetric workpieces such as aspherical mirrors. (2) The 1980s and 1990s were the initial stages of folk industrial application. In the 1980s, the US government promoted several private companies Moore Special Tool and Pneumo Precision to start the commercialization of ultra-precision machining equipment, while several Japanese companies such as Toshiba and Hitachi and Cmfield University in Europe also launched products one after another, and these equipment began to manufacture general private industrial optical components. But at this time, ultra-precision machining equipment is still noble and scarce, mainly in the form of special machine tools. During this period, in addition to diamond lathes for processing soft metals, ultra-precision diamond grinding for processing hard metals and hard and brittle materials was also developed. This technology is characterized by ductile grinding of brittle materials with extremely small cutting depth by using high rigidity mechanism, so that hard metals and brittle materials can obtain nano-scale surface roughness. Of course, its processing efficiency and the complexity of the mechanism can't be compared with diamond lathe. In the late 1980s, through the "Laser Nuclear Fusion Project" of the Department of Energy and the "Advanced Manufacturing Technology Development Plan" of the armed forces, the United States invested a lot of money and manpower to develop ultra-precision diamond cutting machine tools, and realized micro-inch ultra-precision machining of large parts. The large optical diamond lathe (LODTM) developed by LLNL National Laboratory has become a classic in the history of ultra-precision machining. This is a vertical lathe with a maximum machining diameter of 1.625m and a positioning accuracy of 28nm. It has the ability of online error compensation, and can realize machining with a length exceeding 1m and a straightness error of only 25nm. (3) The 1990s is the mature period of folk industrial application. Since 1990, due to the vigorous development of automobile, energy, medical equipment, information, photoelectricity, communication and other industries, the demand for ultra-precision machining machine tools has increased sharply. Industrial applications include aspheric optical lenses, Fresnel lenses, ultra-precision molds, magnetic heads of disk drives, processing of disk substrates and cutting of semiconductor wafers. During this period, the related technologies of ultra-precision machining equipment, such as controller, laser interferometer, air-bearing precision spindle, air-bearing guide rail, oil-bearing guide rail and friction-driven feed shaft, have gradually matured. Ultra-precision machining equipment has become a common production machinery and equipment in industry, and many companies, even small companies, have introduced mass production equipment. In addition, the precision of the equipment gradually approaches the nanometer level, the processing stroke becomes larger, and the processing application gradually expands. In addition to diamond lathe and ultra-precision grinding, ultra-precision five-axis milling and flying cutting technology have been developed, which can process non-axisymmetric aspheric optical lenses. Europe, America and Japan are the world's first ultra-precision machining power, but the research focus is different. Europe and the United States, especially the United States, have been investing heavily in the processing of large-aperture mirrors for large-scale ultraviolet and X-ray detection telescopes for decades. For example, the space development plan promoted by NASA aims to manufacture reflectors with a height exceeding 1m and to detect short waves such as X-rays (OO.6565,438+0 ~ 30 nm). Because of the high energy density of X-ray, it is necessary to make the surface roughness of the mirror reach the order of angstrom to improve the reflectivity. The material of this kind of mirror is silicon carbide, which has light weight and good thermal conductivity, but the hardness of silicon carbide is very high, so ultra-precision grinding and other methods must be adopted. Compared with the United States and Britain, the research on ultra-precision machining technology in Japan started late, but it is the country with the fastest development of ultra-precision machining technology in the world today. The applications of ultra-precision machining in Japan are mostly civilian products, including office automation equipment, video equipment, precision measuring instruments, medical instruments, artificial organs and so on. Japan has advantages in ultra-precision machining technology of small and ultra-small electronic and optical parts in sound, light, image and office equipment, even surpassing the United States. Ultra-precision machining in Japan started with diamond cutting of aluminum and copper wheels, and then concentrated on mass production of computer hard disk magnetic sheets, followed by rapid diamond cutting of polygon mirrors used in laser printers and other equipment, and then ultra-precision cutting of optical components such as aspherical lenses. The aspheric lens used in EastnlanKodak digital camera, which went on sale in 1982, has attracted wide attention in Japanese industry. Because 1 aspheric lens can replace at least three spherical lenses, the optical imaging system is miniaturized and lightweight, and can be widely used in photoelectric products such as cameras, video recorders, industrial televisions, robot vision, CD, vcd, DVD and projectors. Therefore, the precision forming of aspheric lens has become a research hotspot in Japanese optical industry. Although with the changes of the times, the ultra-precision machining technology is constantly updated, the machining accuracy is constantly improved, and the research focus of different countries is also different, but the factors that promote the development of ultra-precision machining are essentially the same. These factors can be summarized as follows. (1) Pursuing high-quality products. In order to make the storage density of magnetic sheet higher or the optical performance of lens better, it is necessary to obtain a surface with lower roughness. In order to make the function of electronic components work normally, it is required that the processed metamorphic layer does not remain on the processed surface. According to the technical requirements put forward by the American Microelectronics Technology Association (SIA), the next generation computer hard disk magnetic head requires surface roughness Ra ≤ 0.2 nm, surface scratch depth h≤lnm, and surface roughness Ra ≤ 0. 1 NMP. 1983 Taniguchi summarized the machining accuracy of each period and predicted its development trend. Based on this, BYRNE described the development of machining accuracy after 1940s.

(2) Pursuing product miniaturization. With the improvement of machining accuracy, the size of engineering parts decreases. From 1989 to 200 1 year, and from 6.2kg to10.8 kg, the high integration of electronic circuits requires reducing the surface roughness of silicon wafers, improving the accuracy of lenses for circuit exposure and the motion accuracy of semiconductor manufacturing equipment. The miniaturization of parts means that the ratio of surface area to volume is getting bigger and bigger, and the surface quality and integrity of workpieces become more and more important.

(3) Pursuing high reliability of products. Reducing surface roughness can improve the wear resistance of parts, improve their working stability and prolong their service life. Si3N4 is used for high-speed and high-precision bearings. The surface roughness of ceramic balls is required to reach several nanometers. The processed metamorphic layer is active in chemistry and easy to be corroded, so from the point of view of improving the corrosion resistance of parts, it is required that the metamorphic layer produced by processing should be as small as possible. (4) Pursuing high performance of products. The improvement of mechanism motion accuracy is beneficial to slow down the fluctuation of mechanical performance and reduce vibration and noise. Good surface roughness can reduce the leakage and loss of machines that need high sealing performance, such as internal combustion engines. After World War II, the aerospace industry required some parts to work in high temperature environment, so it used titanium alloy, ceramics and other difficult-to-machine materials, which put forward a new topic for ultra-precision machining.