The development of the hottest ultra precision mac

2022-08-02
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The development of ultra precision machining and the analysis of several factors affecting surface quality

precision and ultra precision manufacturing engineering are developed to meet the development needs of cutting-edge high technology. It is the embodiment of a country's important economic and technological strength and the basis for the implementation of other high and new technologies. See Table 1 for the division of precision and ultra precision machining categories

ultra precision manufacturing technology is one of the core technologies for the development of various industrial countries. The reason why advanced countries have been leading in high-tech fields (such as national defense industry, integrated circuit, information technology industry, etc.) is that these countries attach great importance to and develop ultra precision manufacturing technology

ultra precision manufacturing technology is developing with the development of measurement technology. Renishaw, Heidenhain, Sony and other companies have developed measuring elements with a resolution of 1nm; The measuring instruments of HP, Taylor and Zygo can meet the needs of nano measurement. Table 1 Classification of machining precision by machining precision

ultra precision manufacturing technology has been widely used in the world. Related to the national defense industry, such as attitude bearings and telemetry components for artificial satellites, Hubble Space Telescope (HST) sent into space, aircraft engine rotor blades, etc; Silicon wafer processing related to integrated circuit (IC) (the machined surface roughness Ra of silicon wafer is generally less than 2nm, and the maximum requirement is 0.1nm); In addition, the precision of lithography equipment and silicon wafer processing equipment is required to be sub micron and nano scale. The surface roughness of the missile inertial instrument, the laser gyroscope plane mirror and the infrared guided missile mirror should reach the nanometer level. In addition, the surface shape manufacturing accuracy requirements of optical non spherical surface parts have been met λ/(30-50), the surface roughness shall be ≤ 0.5nm

1 development of ultra precision manufacturing technology

1962 Union Carbide developed the first ultra precision lathe. With the support of the U.S. Department of energy, LLI laboratory and Y-12 factory cooperated to successfully develop a large ultra precision diamond lathe (dtm-3 type) in 1983. The maximum diameter of the machine tool is ¢ 2100mm, and the resolution of the multi-channel laser interferometry system is 2.5nm. In 1984, LLL laboratory successfully developed lodtm large diamond lathe. The maximum diameter that the machine tool can process is ¢ 1625mm x 500mm, and the weight is 1360kg. The resolution of the dual frequency laser measurement system adopted is 0.7nm, and the static accuracy of its main shaft is: radial runout ≤ 25nm, axial displacement ≤ 51nm. The two machine tools of LLL laboratory are currently recognized as the highest level of ultra precision machine tools in the world

the nancenter ultra precision lathe developed by cupe (crankfield unit for Precision Engineering) has been produced in batch. Its spindle accuracy is ≤ 50nm and the surface shape accuracy of machined workpiece is ≤ 0.1 μ m。

after Taylor company merged with pneumo company, it mass produced nanoform 250 ultra precision lathes. The products occupy a large part of the application market of international ultra precision machining and are leading products in technology

since the 1990s, ultra precision milling and polishing technologies have been developed in several developed countries. Individual laboratories can reach a very high level, especially the nano manufacturing technology contained therein, which has attracted great attention. Companies and institutions that have developed ultra precision milling and nano polishing manufacturing technologies well include m00re in the United States, tayl0r in the United Kingdom, Zeiss, LOH, Schneider in Germany, Nachi, Toshiba in Japan, Philips in the Netherlands, etc

many domestic units are engaged in research and production of ultra precision machining equipment and instruments, such as Beijing Machine Tool Research Institute, Tsinghua University, Changsha University of defense technology, Harbin Institute of technology, Xi'an Jiaotong University, 303 institutes, etc

the ultra precision machine tool produced by Beijing Machine Tool Research Institute is characterized by good spindle performance, accuracy of nm and stiffness of 350n/μ m; Straightness of slide plate ≤ 0.1 μ m/200mm; The surface roughness of machined parts is small, and the turning milling surface can be less than 1nm; The motion system has high resolution, which can reach nanometer level; High degree of commercialization. The types of machine tools include: jcs-027 ultra precision lathe, nam-800 ultra precision lathe, square300 ultra precision milling machine and sphere 200 ultra precision spherical machining machine

the model of ultra precision machine tool developed by Harbin Institute of technology is HCM, with spindle accuracy ≤ 50nm and radial stiffness of 220n/μ m. Axial stiffness 160n/μ m. The Z direction of the guide rail enables the electronic product to make a further progress in its inherent reliability during the description and development (spindle) straightness ≤ 0.2 μ M/100 mm, X-direction (tool rest) straightness ≤ 0.2 μ M/100mm, perpendicularity in X and Z directions ≤ 1 ", machining workpiece accuracy, surface accuracy (roundness) ≤ 0.1 μ m。

ultra precision manufacturing technology will develop in three directions: (1) under the demand of cutting-edge technology and products, develop new processing mechanism and enter into nano and sub nano processing precision. (2) With the development of the national economy and the improvement of people's living standards, we should enter the main battlefield of the national economy and improve the country's economic strength. For example, automobile manufacturing, computers, communication networks, optical discs, household appliances, etc. are closely dependent on the support of ultra precision manufacturing technology. (3) With the development of modern manufacturing technology, the characteristics of interdisciplinary and composite machining technology are becoming increasingly prominent. Precision machining and ultra precision machining will not only develop as an independent discipline, but also appear in the form of more interdisciplinary disciplines, and even form new disciplines. For example, precision special machining technology and nano manufacturing technology include many disciplines. The development of ultra precision manufacturing technology will promote the development of major fields of the national economy and high-tech related fields

2 analysis of several factors affecting surface machining quality

surface characteristics are the main content of controlling the surface quality of industrial products, and they are the synthesis of some typical deviations on the actual surface. Ultra precision plus spherical surface quality mainly includes roughness, waviness and surface shape accuracy, which are divided according to the spatial scale and frequency of surface measurement. A complex surface profile can be divided into three types of spatial frequency components: low frequency component (surface shape), high frequency component (surface roughness) and intermediate frequency component (waviness) between the two

because the surface quality of parts is the most important factor affecting their service performance. For the optical surface, the surface shape error reflects the accuracy of the direction of light after passing through the surface. The waviness and roughness are related to the surface scattering. In particular, the waviness is related to the small angle scattering. For the imaging system, small angle scattering will produce astigmatism, blur the image surface and reduce the resolution of the system; For the reflection system, waviness reflects the degree of non-uniformity of the surface, which will cause uneven specular reflection and scattering, which is very important in some applications

in ultra precision turning, many factors affect the surface machining quality. Such as the geometric parameters of the tool, the rotation accuracy of the spindle, the motion accuracy of the slide, the natural vibration and vibration isolation, and the system stability. These factors have certain regularity, and these regular influencing factors have an impact on the surface processing quality with their inherent rules. In order to realize ultra precision turning, the cutting parameters must be optimized, so it is necessary to predict the surface roughness to be obtained. Through the research on the theory of the analysis model of the influencing factors of surface roughness, we can further study the machine tool, unit parts, cutting tools, cutting mechanism and cutting technology

2.1 analysis model and theory

nano ultra precision cutting generally refers to the ultra precision cutting process with cutting depth of 0.1-5nm and RA ≤ 10nm. In this cutting state, the cutting parameters of the tool and the workpiece to be cut are atoms, which determines the different molecular sizes of the tensile fixture used. Therefore, the research on nano scale ultra precision cutting process involves the energy conversion, structural change, molecular dynamics and thermodynamic processes of the non-uniform system composed of materials, as well as the machining process that will greatly increase the export share to emerging countries in the non-linear state

2.1.1 molecular dynamics model

the basic principle of molecular dynamics simulation is to establish a particle system to simulate the microscopic phenomena studied. The interaction between molecules in the system is determined according to quantum mechanics. The core problem of molecular dynamics simulation is to calculate the mechanical properties of related particles. Its basic assumptions are as follows: t: (1) the motion of all particles follows the laws of classical Newtonian mechanics; (2) The interaction between particles satisfies the superposition principle. The molecular dynamics model is shown in Figure 1

Fig. 1 molecular dynamics model

for a physical system with a particle number of N, the Hamiltonian form of its mechanical description can be written as

the Hamiltonian function quantity is

in equations (1) - (3), Qi and PI are the generalized coordinates and momentum of the ith particle respectively, MI is the mass of the particle, and u is the total potential energy function of the system. The Newton equation described by the system mechanics is in the form of

in equations (4) and (5), FI is the resultant force on the ith particle; RI is the position coordinate of the particle

in molecular dynamics simulation, the selection of potential function is very important, which determines the calculation workload and the approximation between the calculation model and the real system. In the calculation, the corresponding potential function should be selected for different materials considering the interaction between polyatomic valence bonds and quantum effects

2.1.2 dislocation theory based on molecular dynamics

dislocation theory analysis based on molecular dynamics provides an effective method to reveal the essence of various phenomena in crystals. Dislocation is essentially a special configuration of atoms, and its formation causes are complex. According to the study of dislocation theory, the movement and interaction of dislocation are the main reasons for the formation of fault source. The main mechanism of dislocation formation is as follows:

(1) the dislocation stacking theory was proposed by Stroh, which means that the dislocation stacking causes stress concentration, and finally forms a wedge-shaped crack source, increasing the wedge thickness until a crack is formed

(2) dislocation reaction theory this is a crack nucleation model with less energy consumption proposed by Cottrell according to the dislocation reaction law. The theory proposes a dislocation reaction mechanism in which dislocations moving in two intersecting slip planes converge along the intersection line to form cracks

(3) tengtian dislocation destruction theory there are two rows of edge dislocations with different symbols on the two slip planes, which are relatively displaced under the action of shear stress. When the distance between the two slip planes is less than 10 atomic distances, they will merge and destroy to form cracks

(4) crack mechanism of screw dislocation the screw dislocation gets cut step, the cut step produces holes, and the holes develop into the crack core

The study of

molecular dynamics model and dislocation theory shows that if only the fracture mechanism is studied, the fracture surface in ultra precision cutting is a molecular surface morphology. If it is made of ordinary materials, the thickness of the fracture layer is about 0 nm。 Therefore, in ultra precision cutting with a surface roughness Ra of 10 nm, the influence of the quality of the fracture surface on the surface quality of the machined part is not the main factor. However, after ultra precision machining has entered the nanometer order of magnitude, it has become an important influencing factor

2.2 research on Influencing Factors of surface quality

in ultra precision machining, there are many factors affecting the surface quality, including cutting performance of materials, spindle motion accuracy, slide motion accuracy, natural vibration and vibration isolation, tool and cooling, cutting parameters and environmental conditions. These factors affect the machining process of workpiece with their complex laws, and the laws of these factors also have fractal properties. If the surface roughness is set B, other influencing factors

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