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Key words: superhard material, synthetic diamond, cubic boron nitride, tool grinding, grinding
Development and Applications in Machining Industry
Of Superhard Materials in China
Li Zhihong et al
Abstract:The development and applications in machining industry of superhard materials in China are introduced. The excellent properties and application fields of the synthetic diamond and cubic boron nitride (CBN) are indicated, and some practical examples in machining are also described. The importance of further researching,developing and extending the applying fields of superhard materials is pointed out.
Keywords:superhard material synthetic diamond CBN cutting tool abrasive grinding
I. Overview <br>
Synthetic diamond and cubic boron nitride (CBN) are collectively referred to as superhard materials. In 1963, Zhengzhou Abrasives Grinding Research Institute successfully developed the first synthetic diamond in China under the cooperation of the Brother Institute. In 1966, it completed the intermediate test and put into mass production. In that year, it produced 10,000 carats of synthetic diamond. In the same year, the institute successfully developed China's first cubic boron nitride (CBN). Since then, China has the ability to mass produce superhard materials.
From the birth of China's superhard materials to the end of the 1980s, the output increased slowly, and it experienced a stage of perfecting the production process and gradually improving the product quality from scratch. At the end of the 1980s, with the rapid growth of demand for China's stone processing industry, super-hard materials entered a stage of rapid development. In 1997, the annual output reached 500 million carats, ranking first among the world's largest producers of super-hard materials.
Diamond is the hardest material known in the world, and has many excellent properties such as high thermal conductivity, high insulation, high chemical stability, high temperature semiconductor characteristics, etc. It can be used for high-quality processing of non-ferrous metals such as aluminum and copper, especially suitable for Processing hard and brittle non-metallic materials. Cubic boron nitride is a superhard material with hardness second only to diamond. It has excellent properties such as high hardness, high thermal stability and high chemical stability. It is especially suitable for processing hard, tough and difficult to process metal materials. Diamond and cubic boron nitride also have good infrared transmittance and wide forbidden band width. In recent years, they have been used as functional materials to make high-tech products such as transparent windows and high-temperature semiconductors, and are widely used in advanced industries such as electronics and aerospace.
Except for a small part of superhard materials used directly for grinding, polishing, coating and other processes, most of them are made into various tools for different industrial fields (see Table 1). .jpg)
Second, the development of China's superhard materials
1. Synthetic Diamond China's first professional manufacturer of synthetic diamond and its products, the sixth grinding wheel factory, was put into production in 1969, marking the entry of China's synthetic diamond into the industrial production stage. In 1970, China's synthetic diamond production was 460,000 carats. In 1980, the output reached 4.5 million carats, which increased nearly 10 times in 10 years. In 1990, the output was 35 million carats, an increase of about 8 times compared with 1980. After entering the 1990s, China's diamond production has entered a period of rapid development (see Figure 1). This development momentum is mainly driven by the booming development of the stone processing industry. In addition, the use of PCD composite sheets for drilling and cutting and diamond grinding wheels for grinding has also played a significant role. China's synthetic diamond production increased by 14 times between 1990 and 1997, becoming the world's largest producer of synthetic diamonds, and also promoted the development of stone, glass, refractory materials, geological drilling and other industries, and made important contributions to China's economic construction. .jpg)
Although China's synthetic diamond production ranks first in the world, there is still a big gap between product quality and developed countries. The main performance is that the impact strength and high-temperature impact strength of the product are low, and there are many impurities and defects, which can be used to manufacture high strength of saw blades. Diamond only accounts for about 20% of the total product, while RVD and MBD products account for about 80%.
2. Cubic boron nitride cubic boron nitride (CBN) has excellent physical, chemical and mechanical properties such as high hardness, high wear resistance, high thermal conductivity and heat resistance, low friction coefficient, and is particularly suitable for use in iron group metal materials. Processing is an excellent material for improving productivity and processing quality, and has been widely used in industrialized countries. China's CBN products have been in existence for 32 years, but they have been slow to develop over the past 20 years from 1966 to 1989. After entering the 1990s, the rapid development of China's automobile and motorcycle industry has provided a powerful driving force for the development of CBN, and the output has increased significantly (see Figure 2). .jpg)
From 1990 to the present, the average annual growth rate of China's CBN production is 25%, which greatly exceeds the annual growth rate of CBN consumption in developed countries by 15%, but it is very different from the developed countries in the application field and application level. The grinding equipment manufacturing process and equipment are not perfect, the quality and performance of the grinding tools are unstable, and the special grinding machine and grinding process are not matched.
3. Diamond film A diamond film is a superhard film prepared on a non-diamond substrate by chemical vapor deposition (CVD) or other methods. It can be used not only for making all kinds of diamond tools, but also as a functional material for making acoustic sensors, speaker diaphragms, infrared windows, X-ray detection windows, etc., and it is widely used. Internationally, since the early 1970s, trial production of diamond films has been carried out and the research and development of diamond films has been rapidly set off. China began this research in the mid-1980s and has been included in the national "863 Program". It has been able to prepare diamond films of 80mm and 2mm thick, and has achieved a lot of results in applied research, but it is still generally In the development stage, it has not yet reached the stage of industrial application. It is expected that diamond film will be the main material of the 21st century diamond industry, and scientists from all over the world are making unremitting efforts to industrialize diamond film.
Third, the application of superhard material products in mechanical processing
1. Application of diamond products Diamond abrasives and their products are mainly used to process various difficult-to-machine materials such as stone, glass, cement products, refractory materials, ceramics, wood, and hard alloys, ferrosilicon alloys. The application ratio of China's diamond abrasives and their products in various fields is shown in Figure 3. .jpg)
Diamond products are only used in the field of machining only 10%, mainly used for turning and grinding. Diamond knives are equipped with turning tools, milling cutters, boring tools, etc., more than 80% are used in the automotive and motorcycle industries, others are used in household appliances, gas, general machinery and other fields.
(1) Diamond cutters Diamond cutters are mainly used in the automotive and motorcycle industries to process skirts, pin holes, cylinder blocks, gearboxes, carburetor, etc. of engine pistons. Due to the high silicon content (10% or more) of these components, and most of them are produced in large quantities by pipeline, the service life of the tool is high, and the hardness of the diamond tool is difficult. The durability of the diamond tool is hard alloy. 10 to 50 times the tool can ensure the dimensional stability of the part, and can greatly improve the cutting speed, processing efficiency and surface quality of the workpiece. Table 2 and Table 3 compare the practical application results of diamond boring tool and diamond milling cutter and cemented carbide tool. .jpg)
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The research and production of superhard materials in China is developing rapidly, and the application of superhard materials in mechanical processing has also achieved good results, and the application prospect is very broad. The main problem currently exists is that product quality needs to be improved, and the promotion and application work is not enough. In the future, on the one hand, we should increase the promotion and application of super-hard materials; on the other hand, we must strengthen research and development, improve the quality of super-hard materials, increase the types of products, strengthen after-sales service, and narrow the gap with developed countries as soon as possible. Play an important role in the machining of superhard materials.
Development of superhard materials in China and its application in machining
Abstract : This paper introduces the development of superhard materials in China and its application in mechanical processing. The performance characteristics, application range and application examples of synthetic diamond and cubic boron nitride are described. The importance of further strengthening the research, development, promotion and application of superhard materials is pointed out.