Development of the hottest natural diamond tool te

Introduction

diamond is the crystal of a single carbon atom, and its crystal structure belongs to the equiaxed face centered cubic system (a crystal system with the highest atomic density). Because the bond between carbon atoms in diamond is SP3 hybrid covalent bond, it has strong binding force, stability and directivity. The unique crystal structure makes diamond have the highest hardness, rigidity, refractive index, thermal conductivity, excellent wear resistance, corrosion resistance and chemical stability in nature

the excellent characteristics of natural diamond can meet most of the requirements of precision and ultra precision cutting for tool materials, and it is an ideal precision cutting tool material. The uniform crystal structure of natural diamond without internal grain boundary makes the cutting edge theoretically reach the flatness and sharpness of atomic level, and the cutting ability is strong, the precision is high, and the cutting force is small; The hardness, wear resistance, corrosion resistance and chemical stability of natural diamond ensure the super long service life of the tool, ensure continuous and long-term normal cutting, and reduce the impact of tool wear on the accuracy of parts; Its high thermal conductivity can reduce the cutting temperature and the thermal deformation of parts. Therefore, natural diamond, as a superhard tool material, plays an important role in the field of machining and has been widely used, especially in the field of ultra precision machining (such as machining various mirrors used in atomic nuclear reactors and other high-tech fields, navigation gyroscopes used in missiles or rockets, computer hard disk substrates, accelerator electron guns and other ultra precision parts), Using natural diamond tools has obvious advantages over traditional processing methods in both price and accuracy. Table 1 shows the comparison results of the accuracy and price of processing various mirrors with natural diamond tools and traditional grinding and polishing methods. Table 1 Comparison of processing accuracy and price between natural diamond tools and grinding and polishing methods

processing cost of processing objects (USD) traditional processing methods diamond turning infrared aspheric mirror rpvflir aspheric mirror medical special FLIR mirror X-ray celestial telescope 500000 ~ 1000000 (glass) 60000 (metal) 100mm parabolic mirror processing cost accuracy (m) 30.6 processing time 12 months and 3 weeks

except in high-tech fields, The application of natural diamond tools in the processing of ordinary industrial and civil products has also increased year by year. It has developed from the traditional processing of watch parts to the processing of aluminum pistons, jewelry, pen making, high gloss signs, non-ferrous metal ornaments, etc. it can be said that natural diamond tools have gone deep into various fields of mechanical processing and play an increasingly important role

on the other hand, due to the unique properties of natural diamond, it is very difficult to process it. Due to the extremely high hardness of natural diamond, special methods must be used for grinding, which also has high requirements for the skills of operators; Due to the good chemical stability of natural diamond, it was impossible to weld it for a long time in the past, and only large particles of diamond could be clamped by mechanical methods, resulting in the waste of diamond materials and the high price of cutting tools, which also affected the accuracy of cutting tools and parts

in the past hundred years, scientific and technological personnel have conducted long-term research and development on the important role, application prospects and implementation methods of diamond cutting tools in machining, and achieved fruitful results. Next, the development of natural diamond tool technology is reviewed in stages, the latest cutting-edge technology of diamond tools is introduced, and the future development trend is discussed

2 traditional processing technology of natural diamond tools

natural diamond tools were developed after World War II to meet the processing needs of watch precision parts, light ornaments and jewelry carving. Their manufacturing technology originated from the grinding and polishing technology of diamond jewelry. Its development has brought major changes in watches and related manufacturing technology

the grinding and polishing process of diamond jewelry is as follows: the upper surface of the cast iron grinding plate is coated with grinding paste mixed with diamond powder and olive oil, and the diamond powder is embedded in the micro pores of the cast iron surface. The diamond jewelry fixed on the fixture sliding plate is ground on the high-speed rotating grinding plate by the self weight of the fixture

when using diamond jewelry processing method to grind natural diamond tools, the following special processes need to be completed:

1) blade treatment and detection: the quality of the blade will directly affect the quality of the processed parts

2) orientation: place the most severely worn surface of the tool on the hardest crystal surface of the diamond to maximize the service life of the tool. The traditional orientation method generally adopts naked eye orientation

3) clamping: in the cutting process, natural diamond tools must bear the cutting force from all directions. In order to ensure continuous and stable cutting, diamond tools must be firmly installed on the tool bar. Since diamond brazing technology had not been invented at that time, mechanical clamping was only available

because the traditional diamond tool processing method has simple process and low equipment cost, it is still used for rough machining of diamond tools today. In order to further improve the processing technology of diamond tools, scientific and technological personnel have conducted a lot of research on the physical and chemical properties of diamond crystals, the grinding mechanism of diamond tools, the formation mechanism of cutting edges, cutting theory, brazing technology, precision grinding equipment and other topics for half a century, which has laid a solid foundation for the development of ultra precision processing technology of natural diamond tools. Many research topics are still continuing today

3 ultra precision machining technology of natural diamond tools

in the late 1970s, in the research of laser nuclear fusion technology, a large number of high-precision soft metal mirrors need to be machined, and the surface roughness and shape accuracy of soft metal are required to reach the ultra precision level. If the traditional grinding and polishing processing methods are adopted, not only the processing time is long, the cost is high, the operation is difficult, but also it is not easy to achieve the required accuracy. Therefore, it is urgent to develop new processing methods. Driven by the actual demand, the ultra precision mirror cutting technology of natural diamond has developed rapidly. Based on the existing diamond turning technology, the mirror cutting technology has been formed and developed into a special technology by improving the accuracy and rigidity of machine tools, strictly controlling the vibration and temperature drift during processing, and developing ultra precision natural diamond tools. As one of the key technologies of ultra precision mirror cutting, natural diamond tool technology has made significant innovation and development in theory and practice, which is mainly reflected in the following aspects:

3.1 development of ultra precision diamond tools

1) the polishing edge is introduced between the main cutting edge and the sub cutting edge, so that the theoretical roughness of the machined surface is close to zero and the polishing edge is 500 × Or no defects when tested under a higher power microscope

2) the machining accuracy of the key angle of diamond tool reaches 2 "

3) the arc accuracy of the arc cutter used for turning the inner surface reaches the order of microns

3.2 development of precision grinding equipment

because the traditional grinding equipment can no longer meet the processing requirements of ultra precision diamond tools, an arc and blade grinder using air bearings has been developed, and its grinding accuracy can reach 0.1 M

3.3 precision orientation technology and equipment

the purpose of diamond tool orientation is not only to make the tool have the longest service life, but also to minimize the friction between the tool flank and the machined surface and the stress of the cleavage surface near the blade. Therefore, a more precise X-ray diffractometer is needed for orientation

3.4 invention of vacuum brazing technology

vacuum brazing is one of the most important breakthroughs in diamond tool manufacturing technology. On the one hand, the traditional mechanical clamping method may lead to micro displacement and vibration of diamond tools in cutting, which will affect the machining quality; On the other hand, due to the high chemical stability of diamond itself, it is difficult to realize welding by reacting with other metals under normal conditions, that is, diamond is non weldable. In order to solve this contradiction, after long-term research and exploration, we finally found the specific conditions of brazing diamond (high vacuum environment) and brazing alloy (silver based alloy with titanium as the active element)

3.5 establishment of tool wear mechanism

through research, it is found that in the cutting process, the wear of diamond tools is mainly chemical bonding wear, and there are a small amount of mechanical wear and other forms of wear. The establishment of tool wear mechanism determines the tool orientation principle: place the crystal surface with the best chemical stability on the back face of the tool

3.6 systematic research on mechanical grinding methods

3.7 progress in diamond theoretical research

through in-depth research on diamond theory, the macroscopic plastic deformation of diamond was found (in the past, it was thought that diamond had only a small amount of elastic deformation but no plastic deformation); The micro impurities in diamond crystal are studied. According to the different impurities, diamonds are divided into four categories, so different kinds of diamonds can be selected according to different uses; In addition, through systematic theoretical research on the fracture characteristics, cleavage characteristics and surface formation mechanism of diamond, a large number of data have been obtained, various theories have been formed, and a more scientific and profound understanding of diamond has been obtained

the development characteristics of diamond tool technology at this stage are: because diamond tools are used in national defense, high-tech and other fields, they have received a lot of capital investment, used cutting-edge equipment, instruments and the latest scientific methods in research, and made a leap forward development

4 the latest processing technology of natural diamond tools

in the late 1980s, micro machinery as a new research field has developed rapidly. When machining micro parts used for manufacturing micro robots (such as 0.1mm micro precision gears, 0.3mm micro motors, etc.) by mechanical methods, the arc radius of the tool tip is required to be 3 ~ 5 m, and the arc accuracy can be controlled, and the tool service life can be quite long

from the analysis of tool materials, only single crystal diamond is undergoing clinical trials in Germany and Switzerland, but diamond can meet the above requirements. At the same time, after nearly a decade of rapid development, the theory and technology of diamond tools have been accumulated, and they basically have the ability to develop the above-mentioned high-precision tools. However, there is still a gap between the requirements of diamond tools processed by the above-mentioned ultra precision machining technology and micro machining tools, and more advanced machining methods need to be further developed. In recent years, various chemical mechanisms have been developed to grind diamond tools. The following three machining methods can reach the atomic level

4.1 thermochemical method

the mechanism of thermochemical method is: when the temperature is 800 ℃, if the diamond surface contacts with iron, the carbon atoms in the diamond crystal can get rid of the constraints of their own lattice and diffuse into the lattice of iron crystal

the grinding process using thermochemical method is as follows: heat the iron grinding disc to 800 ℃ in hydrogen atmosphere to make the diamond contact with the grinding disc and slide relatively. The utilization of new carbon materials in the diamond lattice is an inevitable trend of development, and atoms will diffuse into the iron crystal lattice to achieve the purpose of grinding diamond; Carbon atoms entering the iron lattice react with hydrogen to produce methane, which is emitted into the air with the gas flow. The grinding speed of thermochemical method is 40 ~ 2000 atomic layers per second

4.2 vacuum plasma chemical polishing

first, a layer of fine-grained silicon oxide is coated on the surface of the grinding disc by vacuum plasma physical vapor deposition, and then on the high fidelity