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Metal cutting is the most basic, widest and heaviest level in industrial production. It is directly related to the efficiency of machining, the quality of products and the manufacturing process. It directly affects the efficiency and cost of industrial production. As one of the basic equipments for cutting, metal cutting tools play a key role in the development of mechanical manufacturing technology. With the emergence of new tool materials such as ceramics, synthetic diamonds, cubic boron nitride, and coated cemented carbides, metal cutting and tooling technology has entered the development of high-speed cutting and development as the basic process and equipment of modern manufacturing technology. A new stage of development characterized by new cutting processes and accelerated tool structure changes.
1 Cutting performance of new ceramic tools
In the cutting process, the quality of the cutting performance of the tool is determined, and the material, shape and tool structure of the cutting part of the tool are often analyzed. The analysis of the tool material is based on the traditional cemented carbide. With the continuous development of modern industrial technology, traditional cemented carbide tools are difficult or impossible to achieve processing of certain high-strength, high-hardness materials, and ceramic tools have good wear resistance and red hardness. Dry processing of high hardness materials. Even at a high temperature of 1200 to 1350 ° C, the cutting can be continued, and the affinity with the metal is small, the chips are less likely to stick to the knife, the built-up edge is less likely to occur, and the surface roughness value is small. It is also capable of high-speed cutting, reducing the number of tool changes and dimensional errors due to tool wear, and greatly improving productivity and product quality.
According to foreign reports, ceramic knives have been developed very rapidly in industrialized countries, and some have reached more than 10% of the total tool composition ratio. In the United States, when hot-hardened ceramic tools are used to process chilled cast iron (HRC66) and high-temperature alloys, the amount of cutting used is high (v=610m/min, ap=6mm, s=0.5mm/r), which greatly improves productivity. Although the research level of ceramic knives in China is not worse than that of foreign countries, the actual application development is slow. According to relevant materials reports before 1994, at that time, the proportion of domestic ceramic knives accounted for less than 1% of total knives, and it was widely used in foreign countries. Industrial and CNC machine tools are the opposite. They are also mainly used for rough machining of hard-to-cut workpieces such as water pumps and rolls, which are less used in precision machining.
As early as the mid-to-late period of the 1970s, Tsinghua University successfully developed silicon nitride (Si3N4) ceramic knives, and was the first in the world to use hot-pressed (Si3N4) ceramic knives for a variety of difficult-to-machine materials (quenching) Hard steel, chilled cast iron, hot dielectric graphite, glass reinforced plastic, etc.) have been processed and applied in various processes (car, milling, thread turning, screw picks, etc.), which has attracted the attention and interest of academic circles at home and abroad. And some famous magazines in other countries have reported and affirmed this achievement. Today, the composite nitriding ceramic tool developed by Tsinghua Fangda has high hardness and strength, as well as excellent wear resistance, red hardness and oxidation resistance. Sex. The ceramic blade has a room temperature hardness value of HRA92.5-94. The bending strength has reached 750-1000 MPa, and the cutting can be performed even at a cutting temperature of 1200 to 1450 °C. The cutting speed is 3 to 10 times higher than that of cemented carbide, the cutting durability is increased by 10 to 100 times, the cutting efficiency is improved by 3 to 10 times, and the superhard material with a hardness of up to HRC65 can be processed, and the price is also cheaper than that of foreign countries. The ceramic blade of Tsinghua Fangda won the Gold Cup Award at the Beijing International Exposition in 1991. The grades and performance of some ceramic blades are listed in the table below.
Ceramic blade grades and performance tables
(Note: The parameters in the table are from Beijing Fangda Ceramics Co., Ltd.)
2 Advantages of cutting new workpieces with ceramic tools
Ceramic knives have many advantages. Although the processing materials and cutting speed range are much larger than those of ordinary cemented carbide tools, the cutting performance will change greatly as the parts to be cut change. The best ceramic insert model must be optimized for the material properties and construction of the part being machined. At present, FD01 ceramic inserts have become the main tool for rough machining all kinds of high-hard alloy cast iron and chilled cast iron in many factories. However, when cutting high-hard alloy steel materials, FD01 ceramic inserts wear long swarf due to long chips, causing crater wear on the rake face. Make it chip. At the same time, because the FD01 is not conductive, the shape of the blade cannot be cut by the wire, which limits the scope of use. The FD03 composite Si3N4 ceramic insert, which has appeared after the addition of carbides and other components, has a slightly lower strength but increased wear resistance, making it suitable for high-speed cutting. The Al2O3-TiCN cermet insert FD22, which has been developed to meet the requirements for finishing hardened steel, has reached a new level. When cutting 40Cr hardened steel with FD22 cermet blade, the durability is much better than other ceramic blades. Longer cutting times and fewer grinding locks. For example, when the FR22 cermet cutter is used to harden the 86CrMoV7 steel roll of HRC58-63, the cutting distance Lm15420m and the surface roughness Ra1 are processed at v=60m/min, f=0.2mm/r and ap=0.8mm. At .6μm, it fully meets the requirements of rough grinding by fine car. Therefore, the use of new ceramic knives can improve processing efficiency, greatly save processing time and power, and can obtain greater economic benefits, and can save a lot of precious metals such as W, Co and Ti. Moreover, the production of traditional cemented carbide tools consumes a large amount of strategic metals such as W, Co, Ti, etc., which are scarce on the earth. Ceramic cutting tools are based on the most abundant elemental silicon (Si) in the earth's crust. Therefore, ceramic tools have Broad application prospects.
3 Application analysis of new ceramic tools
Due to its durability, high hardness and chemical stability, ceramic tools are suitable for dry cutting of cast iron and tempered steel, as well as for modern high-speed cutting processes. Manufacturing is the main source of environmental pollution, and exploring the new dry cutting technology by utilizing the advantages of existing tool materials is one of the trends in the future development of metal cutting. In recent years, especially in industrialized countries, we have attached great importance to dry cutting. In order to implement environmental protection, we are vigorously researching, developing and implementing this new processing method. For a long time, the application of cutting fluid has been an important process factor to improve tool life and processing quality, but it has also led to the deterioration of the ecological environment, but also increased manufacturing costs. According to the statistics of American companies, in the cooling processing system, the cutting fluid accounts for 14% to 16% of the total cost, and the tool cost accounts for 2% to 4%. Therefore, the developed countries such as the United States, Germany, and Japan attach great importance to the research of dry processing. According to the test, under normal circumstances, such as reducing the use of cutting fluid can save 10% to 15% of processing costs. In the European industry, about 10 to 15% of the cutting operations have adopted dry cutting. Therefore, the future development of cutting processing is to use cutting fluid as little as possible. For the design of dry cutting tools, the geometrical angle of the tool, tool material, blade coating, etc. should be considered. Ceramic and cermet tools have the characteristics of heat resistance, high temperature hardness and good chemical stability, so they are suitable for dry cutting. Cast iron and hardened steel. With the development of metal cutting technology, the precision of the blank manufacturing of parts and the realization of less cutting without parts are a development trend of modern manufacturing technology. The use of ceramic knives can achieve the use of car grinding, reduce the process, shorten the process route, improve productivity, especially for the processing of some inner and outer rings of rolling bearings. When using and sharpening ceramic tools, the ceramic tool grades and tool geometry should be correctly selected according to the difference between the workpiece material and the processing method. Generally choose a larger tool nose arc radius (r = 1.2 ~ 2.0mm), a larger chamfer angle (25 ~ 35 °); the blade is generally made of synthetic diamond grinding wheel, sharpening on the ordinary tool grinding machine, the grinding wheel granularity can be Choose 18 0~240#, the saw edge can not appear in the cutting edge of the tool, the roughness of the sharpening is not lower than Ra=1.6μm, and it is repaired with diamond stone grinding paste, in the high-speed large feed cutting or roughing rough processing The machine tool must have sufficient power and rigidity, and the tool should be ground with a negative chamfer. The ceramic tool should be fed slowly before cutting into the material to be processed to prevent the initial chipping.
4 Conclusion
Ceramic knives have a very high wear resistance, it has better chemical stability than cemented carbide, can be cut at high speed and will last longer, and the average efficiency is 3~10 than that of cemented carbide tools. Times. It can realize the efficient "hard machining technology" and "dry cutting technology" by car grinding, milling and polishing, and improve the surface quality of parts. The realization of dry cutting has broad application prospects for controlling environmental pollution and reducing manufacturing costs. It is foreseeable that the new ceramic tools will greatly promote the development of cutting machining in the direction of high speed, high efficiency and high precision. Its popularization and application will bring changes to the metal cutting process, change the traditional tool materials and cutting technology, and save. Working hours, electricity, machine tools and production area of ​​30% to 70%, saving strategic precious metals, resulting in huge economic benefits.
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Tag: Ceramic tool High speed cutting Tool material Cutting fluid Chip
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