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Development of Ultra-precision Machining Technology and Corresponding Strategies Introduction Ultra-precision machining technology is one of the main directions of development in modern machinery manufacturing. It plays a crucial role in improving the performance and quality of electromechanical products as well as in the development of high-tech technologies, and has become a key technology for success in international competition. Ultra-precision machining refers to processing with sub-micron precision (dimensional error of 0.3–0.03 µm, surface roughness of Ra 0.03–0.005 µm) and nanometer-level precision (accuracy error of 0.03 µm, surface roughness less than Ra 0.005 µm). The process methods and technical measures employed to achieve these finishes are known as superfinishing technology. Due to issues such as measurement technology, environmental protection, and materials, this technology is collectively referred to as ultra-precision engineering. Ultra-precision machining mainly includes three fields: · · Ultra-precision turning, such as that using diamond tools, can be used to manufacture various mirror surfaces. It has successfully solved the processing of large parabolic mirrors used in laser nuclear fusion systems and astronomical telescopes. · Ultra-precision grinding and lapping processes such as the surface treatment of coatings on high-density hard disk drives and the processing of integrated circuit substrates. · Ultra-precision special machining, such as the patterning on large-scale integrated circuit chips, is carried out using electron beam or ion beam etching, with line widths reaching 0.1µm. When processed using a scanning tunneling electron microscope (STM), the line width can reach 2–5 nm. 2 Overview Abroad The United States was the first country to develop ultra-precision machining technology. As early as 1962, the United States developed an ultra-precision hemispherical turning machine that used a single-point diamond tool for mirror-like machining of aluminum alloys and oxygen-free copper. The spindle’s rotational accuracy was 0.125µm; when turning a hemisphere with a diameter of Ø100mm, the dimensional accuracy was ±0.6µm and the surface roughness was Ra0.025µm. In 1984, a large-scale optical diamond lathe was developed, capable of machining large parts weighing 1350 kg and with a diameter of 1625 mm. The roundness and flatness of these parts reached 0.025 µm, while the surface roughness was Ra0.042 µm. This machine tool incorporates a number of new technologies, such as multi-path laser measurement feedback control, measurement of workpiece deformation using a capacitive micrometer, a 32-bit CNC system, friction-driven feed, and a heat exchanger for temperature control. Leveraging its existing mature unit technologies, the United States managed to assemble a small ultra-precision machining lathe of the BODTM type in just two weeks; this lathe uses single-crystal diamond tools with a tool tip radius of 5–10 nm to achieve machining with a thickness of 1 nm. Nevertheless, the United States has recently continued to regard micrometer- and nanometer-scale processing technologies as one of its key technologies, which is sufficient to show its emphasis on this technology. The UK was one of the first countries to engage in research on ultra-precision machining technology. Since 1979, vertical ultra-precision diamond turning machines have been developed for manufacturing metal mirrors used in X-ray telescopes. The mirror is required to have a surface roughness of less than 6 nm, with the accuracy within a range of 30 mm, and an overall shape accuracy of less than 1 µm. To ensure superfinishing, this machine tool incorporates many new technologies. For example, encapsulated synthetic granite is used as the foundation for the machine tool (with a total weight of 48 tons); X and Z axes driven by permanent-magnet DC torque motors, offering a rotational accuracy of 0.1 µm in both radial and axial directions; a rotating worktable supported by air bearings; an HP5501 laser interferometer with a resolution of 0.015 µm; a measurement and compensation system for the size and shape accuracy of workpieces on the X and Z axes, composed of an HP9826 computer and other components; a piezoelectric tool micro-feed device; and a 16-bit CNC control system. The UK began implementing its nanotechnology program in the early 1980s, establishing a Strategic Committee on Nanotechnology. Cranfield University is the second institution in the world to be able to manufacture high-stiffness (2kN/µm) air-bearing precision bearings and spindle systems for large-scale ultra-precision machining machines. www.stonebuy.com China Stone Network Japan’s research and development in ultra-precision machining technology lags behind that of the United States by 20 years, but it is developing rapidly thanks to the attention and efforts devoted to it by relevant parties. Unlike the United States, Japan has developed ultra-precision machining technology solely for civil industrial purposes, ranging from machine tools for processing polyhedral mirrors to those for fine machining of magnetic heads and disk end faces, and further developing into machine tools for aspheric surface processing and for machining short-wavelength X-ray mirrors. In 1986, Japan included nanotechnology as one of the six key topics in its research program for advanced technologies. Japan launched a large-scale **research program** to invest 25 billion yen in the research and development of micro-mechanics over a period of 10 years, starting in 1991. Under this project, the lathe-type ultra-precision milling machine developed through collaboration between FANUC and the University of Electro-Communications achieved the fine machining of free-form surfaces using cutting methods for the first time in the world. This milling machine features a frictionless servo system and a CAD/CAM system for microfabrication, with a minimum CNC resolution of 1nm. In the fine milling of a complex surface with a diameter of 1 mm and a height difference of 30 µm, a surface roughness of Ra0.058 µm was achieved. Main performance of the machine tool: The minimum resolution of the X and Z axes is 1 nm, while the minimum resolutions of the C and B axes are 0.0001° and 0.00001° respectively. When the maximum air supply pressure to the spindle is 6×106 Pa, its rotational speed is 55,000 r/min. A tool for micro-cutting is a single-crystal diamond pseudo-spherical end mill. The tip radius is 0.01 mm, the half-tip angle is 75°, and the center of the tip arc is offset by 0.1 mm from the axis line. There are over a dozen manufacturers of ultra-precision machine tools in Japan. Their products are mostly measured using CNC systems with a resolution of 0.01µm and laser interferometers; in terms of nanoscale lithography, Japan is ahead of the United States and holds a leading position in the world. The machining precision of super-finishing machines has reached the sub-micron level (below 0.1µm), with a surface roughness of Ra0.01µm. The highest-grade machines are used in the production of very large-scale integrated circuits, where the line width can reach 0.3µm. The ultra-precision machining machines in Germany, the Netherlands, and Taiwan, China are also at the world’s advanced level. For example, Philip Company developed the Colath super-precision turning machine, with a maximum machining diameter of Ø200mm and a length of 200mm; its shape accuracy is 0.5µm, and the surface roughness is Ra0.02µm. Germany mainly focuses on ultra-precision measurement technology. The highest technical levels achieved in ultra-precision machining worldwide at present are as follows: machining precision of 0.025µm and surface roughness of Ra0.0045µm, which means that we have entered an era of nanoscale machining precision. In terms of measurement technology, for measuring small displacements: the resolution of capacitive probes can reach 0.5 nm (for a range of 15 µm) and 0.1 nm (for a range of 5 µm), with a linear error of less than 0.1% ； The resolution of the optoelectronic fiber optic probe can reach 0.5 nm (with a range of 30 µm), and its linear error is 5% ； The resolution of a scanning tunneling microscope (STM) can reach 0.01 nm (at a range of 20 mm) ； The resolution of the X-ray interferometer also reaches 0.003 nm (at a range of 200 µm). For the measurement of large lengths, the resolution of the heterodyne laser interferometer can reach 1.25 nm (range: ±2.6 m) ； The resolution of the helium-neon laser (for laboratory use) can reach 0.01µm (with a range of 2mm) ； The resolution of the moiré optical scale can reach 10 nm (with a range of 1 m), and its accuracy is 1 µm/m. For angle measurement, the resolution of the moiré fringe angular optical scale is 0.005\" within a range of 360°, with an accuracy of 0.1\", thus meeting the requirements of nanoscale processing technology in terms of measurement. 3 Microfabrication using STM: The scanning tunneling microscope (STM) is used to etch and modify various surfaces at the nanoscale, enabling nanofabrication, which is an important area of its application. There are mainly two types of methods for surface processing using STM: the first type involves directly writing dots, lines, or specified graphic symbols on the surface of metals, semiconductors, or insulators. The specific method typically involves applying a voltage pulse to the tip while the STM is operating in current-mode, or suddenly reducing the distance between the tip and the sample, thereby causing structural changes such as pits and hills on the surface of the sample beneath the tip. The second category of methods involves using the electron beam of STM to induce chemical reactions, thereby depositing metal materials in the surface microregion beneath the tip. The first STM was developed by G. Bining in 1981. Now, the structure of these devices, as well as their shock resistance, stability, and resolution, are all becoming increasingly improved. In principle, STM, like conventional electron beams, can be used for planar lithography in the manufacture of solid-state devices. Its advantage is that it can display the structural morphology of the surface, with atomic-scale resolution ； The electron energy involved is low (