4. Tool superhard material <br> <br> superhard materials diamond and cubic boron nitride means (CBN), which is several times higher than the hardness of other tool materials. Diamond is the hardest substance in nature, and CBN is second only to diamond. In recent years, superhard tool materials have developed rapidly.
Diamond tool materials are divided into five categories: natural diamond (ND); synthetic polycrystalline diamond (PCD) and synthetic single crystal diamond; synthetic polycrystalline diamond compact (PCD/CC); diamond coated tool (CD); diamond thick Membrane tool (FCD). The crystal anisotropy of ND must be selected in the appropriate direction when using the knife. Synthetic diamond is isotropic, its hardness is lower than ND, but its strength and toughness are higher than ND.
Diamond tools can efficiently process non-ferrous and non-metallic materials such as non-ferrous metals such as copper and tungsten and their alloys, ceramics, hard alloys, various fiber and particle reinforced composites, plastics, rubber, graphite, glass and wood. Wait, but diamonds don't cut steel and other iron metals.
TFD has a good comprehensive performance, and has the advantages of natural diamond and artificial polycrystalline diamond. It is firmly combined with the substrate and is easy to re-grind many times, so it has good application value and development prospects. The manufacturing method of CBN is similar to PCD or PCD/CC. Using cubic boron nitride as raw material, polycrystalline CBN or composite sheet CBN/CC is prepared by high temperature and high pressure. CBN is mainly used for processing hardened steel, high hardness cast iron and other hard metal and non-metal materials.
It is foreseeable that diamond tools will have great development in the 21st century. In addition to the inability to process steel and iron metal, it has a very good application value in the processing of non-ferrous metals and non-metallic materials. For example, aluminum-silicon pistons in the automotive industry and non-ferrous metal precision parts in the aerospace industry are inseparable from diamond tools. The author believes that in the future, artificial single crystal gold stone tools and CD, TFD diamond coating (coating) tools will have a great development.
In recent years, CBN manufacturers have improved and the cost has been reduced. At the same time, the toughness has been significantly improved by changing the ratio of the hard phase to the binder phase and the type of binder material. In recent years, the processing of steam brake hubs (ash cast) and metallurgical rolls (hardened and high hard) has been widely used. I believe that CBN tools will have a great development. By the end of the 21st century, it is likely to replace a considerable number of carbide tools and ceramic tools, making it one of the most widely used tool materials. From a technical point of view, CBN should improve the defects that are not significant when processing general hardness and medium hard materials.
In recent years, a new type of superhard tool material has emerged. A carbon nitride (CxNy) film can be deposited on a high speed or cemented carbide tool by magnetron sputtering, which can reach or exceed the hardness of the diamond according to the modulus of the body. Other properties are also very similar to diamonds. Applying this film to high-speed tools (such as twist drills) to machine steel, the tool life can be increased by 8 to 10 times before coating. Coating on carbide inserts also has a certain effect, but not as significant as high-speed tools. Therefore, CxNy coated tools are also an important development direction for future tools.
A brief history of the development of tool materials <br> <br> ancient times have used stone and copper alloy as a tool material. After the European industrial revolution in the mid-18th century, cutting tools were always made of carbon tool steel; in 1865, alloy tool steel was invented. However, as the requirements for processing efficiency increase, the performance of the above two tool steel materials is insufficient.
High-speed steel was invented in 1898. The appearance of this new material increased the cutting speed and cutting efficiency by 4 times and 2.5 times compared with carbon tool steel and alloy tool steel. From the end of the 19th century to the beginning of the 20th century, high-speed steel has made a leap in the level of cutting, which has promoted the rapid development of machinery manufacturing in the United States and the world, and produced huge economic benefits.
Efforts to find new tool materials with higher performance have never stopped. From the mid-1920s to the early 1930s, tungsten-cobalt and tungsten-titanium-cobalt-based cemented carbides appeared. During the Second World War, due to the high-volume, high-efficiency production of weapons, the United States, Britain, and Sudan countries have partially used carbide tools. In China, after the liberation, a small amount of cemented carbide was introduced from the Soviet Union. After the mid-1950s, it began to produce itself and was widely used.
In the second half of the 20th century, the mechanical properties of workpiece materials continued to increase, the variety and batch size of products increased, the requirements for processing accuracy increased, and the structure and shape of workpieces continued to be complicated and diversified. Carbide tools in dealing with these new challenges Played a major role. Moreover, many new varieties have emerged in the cemented carbide itself, and the performance has been continuously improved. However, it is brittle, has insufficient toughness, and is much less machinable than high-speed steel. It can only be used for turning tools and milling cutters at the beginning, and later expanded to other tools, making it difficult to use all the tools. Because high-speed steel can manufacture all kinds of tools, it always occupy a large position, and high-speed steel has also developed many new varieties, and the cutting performance has been greatly improved compared with the original varieties.
Until recently, high-speed steel and cemented carbide were still the two most used tool materials, but the proportion of cemented carbide has expanded to 60%. It can be seen that after half a century of "striking the land", the cemented carbide has occupied such a vast position, and it should have been unexpected. However, it still cannot meet the requirements of ultra-precision machining of modern high-hardness workpiece materials, so alumina ceramics appeared in the 1930s, and later silicon nitride ceramics. In the 1950s and 1960s, artificial cubic boron nitride and synthetic polycrystalline diamond were produced, which were significantly harder than other tool materials. Ceramics have a slightly higher hardness than cemented carbides, but their toughness and workability are inferior to those of hard alloys.
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