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Development trend of precision ultra-precision machining technology

2018-07-13 Administrator home station clicks:

Development trend of precision ultra-precision machining technology

1. The basic theory and experiment of ultra-precision machining technology should be further developed

The basic theory of ultra-precision machining technology refers to that the process can be mastered after understanding and mastering the description of the basic rules and phenomena of ultra-precision machining, and the expected results can be obtained. For example, in the early 1990s, Japanese scholars processed the thinnest continuous chip images on the DTM3 of LLNL with diamond turning tool. At that time, the cutting thickness of 1nm was considered to be the highest in the world, and no breakthrough has been made till now (as shown in figure 4). Then, what is the limit scale of ultra-precision cutting, how can the material be removed at this time, and in addition, the multi-physical quantity/of the ultra-precision processing system in force, heat, electricity, magnetism, gas, etc.

The new theory is needed to support the mechanism of the complex field coupling, the dynamic characteristics of the system, the dynamic accuracy and the stability of the system.

Along with the development of computer technology, molecular dynamics simulation technology in the 1990 s in areas such as physics, chemistry, material science and tribology, got very good application, the United States, Japan and other countries the first application of the technology research nanoscale machining process, starting at the beginning of the 21st century in some colleges and universities domestic application of molecular dynamics simulation study of cutting and grinding process, the cutting process of atomic size, transient, to a certain extent, reflects the microscopic material removal mechanism, but it remains to be seen in the experiment.

The processed materials and process methods are also expanding

Titanium alloy is one of the most commonly used material in aviation, hydrogen as harmful impurity elements on the performance of the use of titanium alloy is extremely adverse effects, such as the cause of titanium alloy hydrogen embrittlement and stress corrosion and delayed fracture, etc., but in recent years, research has shown that by reasonable control effectively hydrogen permeability, phase transition and the hydrogen process, such as for titanium alloy organization structure changes, which can improve the processing performance, to improve the surface quality and processing efficiency. Black metal is often thought to be also unable to use natural diamond ultra-precision machining, over the years has been in a variety of technology was studied, such as the use of cryogenic fluid (liquid nitrogen or carbon dioxide) cryogenic cooling cooling cutting area are turning, the ultrasonic vibration cutting black metal, diamond coated tools, etc., using gas nitriding and ion nitriding process on steel processing, but the above methods have so far unable to engineering application. In recent years, the machinability of the surface of the processed materials has been changed by ion implantation, and high-efficiency ultra-precision cutting of hard brittle materials such as silicon has been realized.

The development of anti-fatigue manufacturing technology puts forward a new development direction for ultra-precision processing technology. The precision processing technology of ultra-hard materials requires to control the damage, structure, stress state and other parameters of surface and subsurface. For example, the hardness of aircraft engine bearing material M50NiL after surface treatment exceeds HRC70. With the application of monocrystalline turbine discs and monocrystalline turbine blades in aero engines, the processed materials are required to have no remelted layer and metamorphic layer, which puts forward new requirements for precision machining process. With the increase of the Mach number of the missile, the anti-abrasion performance of the head cover material is required to be improved. It has developed from infrared material to sapphire material and even diamond material, and its shape has also developed from spherical to aspheric surface and even freeform surface.

3. Ultra-precision machining technology of functional surface of micro-nano structure

Microstructure with a specific function surface topology shape, the structure size is generally 10 to 100 microns, surface shape accuracy is less than 0.1 microns, its surface microstructure has the texture structure rules, Gao Shenkuan ratio, determine the characteristics of geometric features, such as groove arrays, micro lens array, the structure of the pyramid array, etc., these make surface microstructure components has certain function, can communicate the physical and chemical properties of materials, such as adhesion, grinding, lubricity, wear resistance, or have a specific optical performance, etc. For example in the aviation and aerospace craft processing the micro-nano structure formation on the surface of macro function surface, not only can reduce the vehicle is in wind resistance, friction, reduce friction, also can avoid the formation of ice and improve air kinetics and thermodynamics function, so as to achieve growth, extended range, noise reduction and other purposes, and specific surface microstructure characteristics can also play a stealth function, enhance the penetration ability.

The most typical example for civilian use was the addition of a few microstructures to the swimwear of swimmers, commonly known as sharkskin swimwear, which resulted in a significant improvement in the athletes' performance and led to the fina having to ban the high-tech swimwear. Function surface and microstructure in optical system, display device, concentrated photovoltaic industry, traffic signs, signs, lighting and other fields are widely used, such as LCD backlight module of various optical diaphragm, key-module - backlight module, diffusion of light guide plate plate, a good film, etc., to the Fresnel lens concentrator photovoltaic solar CPV systems, road signs with microstructure optical diaphragm structure, a new generation of LED lighting efficient light distribution, etc.

Parts design and manufacturing in the future will increase the function of a surface structure design and manufacturing, through design and processing in parts surface microstructure of different shapes, thus improve the parts function such as mechanics, optics, electromagnetism and enters a higher school, it will be an important application field of micro-nano manufacturing, the international society for nano manufacturing, established in 2006 by experts to discuss and agree, the core technology of nano manufacturing will from now to MEMS technology gradually turned to the ultra precision machining technology.

4. Ultra-precision machining began to pursue high efficiency

Since the development of ultra-precision machining technology, to guarantee the final accuracy of some key parts, it was not aimed at processing efficiency at the beginning, but more focused on precision and surface quality. For example, the initial processing cycle of some optical components was "year". However, with the increase of the size and number of parts, the efficiency of ultra-precision machining is required. In order to constantly improve the observation object range and resolution, for example, need to constantly increase the diameter of astronomical telescope, it's same day version of Moore's law, namely every several years, a doubling of the calibre of the optical telescopes, such as built in 1917, is located in the United States the Hooker telescope mount Wilson observatory diameter of 2.5 m, is the world's largest telescopes; By 1948, it was replaced by the Hale telescope with a caliber of 5m; The newly built Keck telescope, which was built in 1992, has a caliber of 10m and is still playing a big role. The giant astronomical telescope OWL main mirror, with a diameter of 100m, is composed of 3,048 hexagonal spherical reflectors and the secondary mirror is composed of 216 hexagonal planar reflectors with a total weight of about 1-15,000 t. According to the current processing technology, it may take hundreds of years to complete. In addition, the laser fusion ignition (NIF) requires more than 7,000 400mm square KDP crystals, and the processing time cannot be imagined without efficient ultra-precision processing technology. Therefore, it is necessary to develop new ultra-precision machining equipment and ultra-precision machining technology to meet the demand of efficient ultra-precision machining.

5. Ultra-precision machining technology will develop to the extreme direction

With the progress of science and technology, new requirements have been put forward for ultra-precision machining technology, such as the extremely high precision of extremely large parts, extremely high precision of extremely small parts and features, extremely high precision of extremely complex environment, extremely high precision of extremely complex structure, etc.

The VLT mirror, a very large telescope under development at the European southern observatory, is a piece of zero-expansion glass with a diameter of 8.2m and a thickness of 200mm. REOSC takes charge of the processing, adopts the processing technology such as milling mill and small grinding head polishing, the processing cycle is 8-9 months, and finally meets the design requirements. At present, many new ultra-precision processing technologies, such as stress disc polishing, magnetorheological polishing and ion beam polishing, provide technical support for large mirror processing. The functional surface size of the micro-nano structure mentioned above is small to several microns. For example, the characteristic size of the flexible arm of the sensitive element in the micro-inertial sensor is 9 plus or minus m, while the dimensional accuracy is required to be plus or minus 1 plus m.

Developed by the national bureau of standard measurement nanometer three coordinate measuring machine (molecular measuring machine) is how to achieve in a very complex environment of high precision measurement of typical examples, the instrument measuring range 50 mm x 50 mm x 100 microns, the precision achieved 1 nm, and strict with environment, the innermost shell 17 plus or minus 0.01 ℃, the temperature control shell adopts active vibration isolation, high vacuum level working environment keep 5-1.0 x 10 pa, the outermost shell is used for noise isolation, then the whole structure is installed on the air spring for passive vibration isolation. Some of them can not even be expressed by equation (such as assigned surface). However, due to its excellent optical performance, its application range has been expanding in recent years. However, the design, manufacture and detection of optical parts of free surface have yet to be further developed.

Ultra precision machining technology will develop to ultra precision manufacturing technology

Ultra-precision machining technology is often used in the final work procedure, or a few parts but now some parts in the field of the whole manufacturing process or the entire product development process are used ultra precision technology, including super precision machining, precision assembly debugging and ultra precision detection, the most typical example is the United States national ignition facility (NIF).

In order to solve the human energy crisis, all countries are studying new energy technologies, which use the fusion reaction of deuterium and tritium to generate huge energy available without any radioactive pollution. This is the U.S. national ignition project. China has also started this research, known as the shenguang project. The whole system of NIF is about the size of two football fields, and there are 192 intense laser beams entering the target chamber with a diameter of 10m, and finally the energy is concentrated on the target pellet with a diameter of 2mm. This requires an extremely large number of laser mirrors (more than 7000 pieces), extremely high precision and surface roughness (otherwise a strong laser will burn the lens), extremely high precision of transmission path debugging and installation, and extremely high control requirements of working environment. For a target with a diameter of 2mm, the thickness of the wall is only 160 diameters m, of which the diameter of the inflatable hole is 5 diameters m, with a sunk hole with a diameter of 12 diameters m and 4 depths m. The difficulty of microhole machining lies in its large depth diameter ratio and variable cross section, which can be processed by electric discharge, femtosecond laser, focusing ion beam, or ultra-precision machining by atomic force microscope. The symmetry error of spatial geometry position of each laser in the system should be less than 1%, the time consistency error of reaching the surface of the laser should be less than 30fs, and the consistency error of laser energy intensity should be less than 1%. Such a complex and high-precision system reflects the ultra-precision manufacturing technology from the moment of component processing and assembly and debugging. The new theory is needed to support the mechanism of the complex field coupling, the dynamic characteristics of the system, the dynamic accuracy and the stability of the system.