Reinforcement and toughening of the hottest and dr

2022-08-05
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Reinforcement and toughening of dry cutting tools with human understanding of resources and environment, the concepts of green manufacturing and clean production have been put forward in the field of industrial production. As the manufacturing process of mechanical products is the main link that directly consumes resources and produces waste, green processing technology has been paid more and more attention, and has become one of the important development directions of manufacturing industry in the future

at present, the greening of cutting process mainly focuses on the non use of cutting fluid. Dry cutting is an effective way to eliminate the pollution of cutting fluid and realize cleaner production. The reason why machinery manufacturing enterprises gradually cancel cutting fluid and choose dry machining is mainly due to economic and environmental considerations: in terms of economy, according to German statistical data, the cost of using cutting fluid accounts for 14% - 17% of the total cost, while the cost of cutting tools only accounts for 3% - 4% of the manufacturing cost; In addition, according to the statistics of balyers company in the United States, the consumption of cutting fluid is 3-4 times of the tool cost

in terms of environment, the use of cutting fluid will cause damage to the health of operators due to long-term exposure to grinding fluid and synthetic cutting fluid in the air, especially the mist cutting fluid. At the same time, it will also cause pollution to the workplace and local environment (water, air, soil, etc.). In recent years, dry machining has been widely used in the manufacturing industry in the United States. Half of the enterprises in Europe have adopted dry cutting technology, especially in Germany

the research shows that the development of dry cutting technology depends on the development and application of new cutting tools to a great extent

2 key technology of dry cutting tools during dry cutting, the tool should bear higher temperature than wet cutting. Dry cutting is to create the same or similar cutting conditions as wet cutting when there is no cutting fluid. The friction coefficient between the tool and chip and the contact surface between the tool and workpiece should be as small as possible, and the tool is also required to break chip and facilitate chip removal. Therefore, higher requirements are put forward for the tool, Its key technologies mainly include the following aspects: the tool should have higher strength and impact toughness, and the tool materials suitable for dry cutting can be selected, such as ultra-fine grain cemented carbide, ceramic and Cermet Tool Materials, diamond and CBN, etc; Suitable coatings can also be applied on high-speed steel and cemented carbide substrates, such as tain coating, HCN coating, tiain+m8 coating, diamond-like carbon (DLC) coating, etc; It can also improve the tool design, process, etc. to improve the strength and impact toughness of the tool

the friction coefficient between the chip and the tool should be as small as possible. During dry cutting, the high temperature generated in the cutting area will increase the chemical instability, increase the friction between the tool and the chip, slow down the chip removal speed, easily produce chip buildup, and aggravate tool wear. Therefore, it is necessary to reduce the friction coefficient between the chip and the tool. The effective method is to coat the tool surface and design the tool structure with good chip removal

the structure of the tool should be able to quickly remove chips during dry cutting. In order to ensure the processing quality of the workpiece and the service life of the tool, the tool is required to quickly discharge chips, so that the heat transferred to the workpiece and the tool is greatly reduced

the tool shall have excellent high temperature resistance. On the one hand, the tool materials with sufficient high temperature wear resistance and suitable for dry cutting conditions, such as new performance cemented carbide, polycrystalline ceramics and CBN, shall be selected; On the other hand, coating the tool is also an effective method. The role of the coating in the cutting process is like adding a force and heat isolation layer between the tool and the chip, which can prevent the heat transfer to the tool matrix, ensure that the cutting edge of the tool is sharp, so that the hardness of the tool head will not decline quickly, and greatly improve its high temperature resistance. Production practice has proved that although the heat generated in the cutting area can not be completely discharged with the chips in dry cutting, as long as the tool material, geometry and cutting parameters are reasonably selected, most of the cutting heat can be discharged with the chips and good machining results can be achieved

therefore, the tool material and structure must be reasonably selected for dry cutting. In this paper, the strengthening and toughening technology of cutting tools, one of the key technologies, is discussed

3 ways of strengthening and toughening coated tools are the most commonly used tools for dry cutting today. The total investment of the matrix is more than 160billion yuan, which is a hard alloy with good toughness. One or more layers of wear-resistant hard coatings such as tin, tic and TiAIN are coated on the matrix, playing a role of heat resistance and heat insulation. In order to reduce friction and adhesion during cutting, soft coatings such as mo+ and WC are often added on top of the hard coating to integrate the advantages of high hardness, good thermal stability of the hard coating, low friction coefficient and good self-lubricating of the soft coating. The data shows that when a blind hole is dry drilled on an alloy steel material (the hole depth is 4 times the diameter), an uncoated drill bit will be damaged when it is dry drilled. A drill bit coated with TiAIN hard coating will fail only when it is dry drilled 85 holes. A drill bit coated with TiAIN plus - C composite coating can process 108 holes

3.1.1 traditional coating method in traditional coatings, different coating materials can be combined and optimized according to the wear model. The internal (intermediate) coating usually ensures good resistance to flank wear. The most commonly used intermediate layer is Ti (C, n), which is mainly used for medium temperature chemical vapor deposition. Ai23 is usually used on the top of the intermediate layer to reduce the wear of crescent pits on the rake face and act as a thermal barrier. A thin layer of tin is usually deposited on the top surface of the composite coating to make the tool golden and help prevent wear

3.1.2 in order to improve the cutting performance of the tool and increase the hardness, strength and toughness of the tool, new tool coating materials and coatings are emerging in endlessly, among which nano coating is a more successful one. The coating can adopt different combinations of various coating materials, such as metal/metal combination, metal/ceramic combination, ceramic/ceramic combination, solid lubricant/metal combination, etc., to meet different functional and performance requirements. The properly designed nano coating can significantly increase the hardness, strength and toughness of the tool, and make it have excellent anti friction, wear and self-lubricating properties, which is suitable for all kinds of dry cutting

from the point of view of friction, lubrication and wear, the multilayer nano coatings of cemented carbide tools can be divided into four categories: (1) hard/hard combination: carbide, boration/soft combination: carbide/metal combination, such as b4c/w, sic/a, sic/wsic/ti, etc. (3) Soft/soft combination: Metal/metal combination, such as ni/cu, etc. (4) Soft/soft combination with lubricating performance: solid lubricant/metal combination, such as ms/mo, w+/w, tas/ta, mos/ai-mo, etc. Each layer of these composite coatings is composed of two materials, and the thickness is only a few nanometers. According to the needs of cutting performance and coating properties, hundreds of layers can be applied interactively, with a total thickness of 2!!. New ceramic cutting tools ceramic cutting tools are very suitable for dry cutting because of their high heat resistance and good chemical stability. However, the inherent characteristics of ceramic materials, such as high brittleness, poor strength and toughness, limit its application in dry cutting to a great extent. The development of new ceramic materials has solved this problem

3.2.1 the most effective way to improve the strength and toughness of ceramic materials is to reduce the grain size of ceramics and improve the purity of materials. In the manufacturing process of ceramic blade, especially in high-temperature sintering, there is grain growth. In order to restrain grain growth, MgO is often added to ceramic powder as an inhibitor, but the oxide forms a glass phase after sintering, which is deposited at the grain boundary to separate the grain boundary, thus reducing the grain boundary strength and prone to intergranular fragmentation. If ceramics can be sintered at low temperature, the above phenomena can be avoided without adding inhibitors, and the performance of ceramic blades can be improved

a new type of alumina ceramic powder with fine particles (0.22! M) and high purity (99.99%) is used to manufacture ceramic blades. This kind of fine powder has a large specific surface area (15.1m2/g), and it has a great surface energy during compaction. Under the action of this energy, the required temperature for sintering is significantly reduced to 1230 This means that the bases in Zhenhai, Shanghai and Nanjing are relying on the existing devices, facilities and connotation to the greatest extent to tap the potential, and do not need to add inhibitors during the preliminary work, so that there are no impurities at the grain boundary

3.2.2 the inherent brittleness of ceramic materials limits the application of carbide ceramic metal composites. Introducing fibers, whiskers, particles and other second phase materials into ceramics to improve their strength, fracture toughness and thermal stability constitutes a new type of ceramic matrix composites

carbide ceramic metal composites are one of the most widely used composites, such as tungsten carbide based cemented carbides in 1923 and titanium carbide based ceramic metal (Ni Co CR bonding alloy) in 1950s. Since the 1960s, tic and WC based steel bonded cemented carbides have been mainly used in China

the research shows that Ni, Co, Cr and Si can form a solid bond with titanium carbide and penetrate along the grain boundary, so they can play the role of bonding metal as ceramic substrate. For Ti Ni system, 1450 The wetting angle of pure Ni to tic is 30. Adding transition metals to Ni will reduce the wetting angle

co and Ni - can be used as binder for tic based ceramic metal composites. However, because the eutectic temperature of TiC-C system (1370+) is higher than that of Ti Ni system (1280+), the ceramic metal composite bonded with CO shrinks later during sintering. The growth of carbide grains in the two alloys starts at 1440 +, so the optimal sintering temperature range of TiC CO is narrower than that of TiC Ni

in ceramic metal composites, tic often adds other carbides, For example, the carbide phase composed of:/", Yiyou::: and Jia Zhen. In addition, nitrogen also has a good effect on the microstructure and properties of TiC ceramic metal composites. The composites with low nitrogen content and high carbon content have high mechanical properties. The research shows that under high temperature (about 1000+) and low stress, the ceramic matrix metal (Ni) containing tin The creep strength of the composites has exceeded that of WC composites, which is of great significance to reduce the material cost, especially in tungsten poor countries

tungsten carbide based ceramic metal (CO) matrix composites are traditional excellent cutting metal tool materials. In order to improve the cutting strength, impact toughness and stability of composites, the grain structure of ceramic (WC) is usually refined to achieve this goal. The results show that the addition of carbon to WC Co system can prevent the growth of WC grains at the sintering temperature, and VC has the most significant inhibition effect, Then, the addition of 0.015% 3.29% Cu to Cr (C2, NBC and TAC) has a significant effect on the density, grain size and mechanical properties of the composite. For example, when Cu is added, the density of the composite increases significantly. When the Cu content is 0.3:1.0, the maximum density can be reached, and the bending strength can also reach the maximum value. When the Cu content is appropriate, the growth of carbide (W, Ti, TA) grains will be inhibited, and the average size will be reduced; In addition, Cu can also improve the wettability of carbide metal liquid interface

the properties of tungsten carbide based nickel composites are relatively lower in strength and higher in plasticity than those using CO as binder. The fracture resistance increases with the increase of Ni content and WC grain size. In addition, the strength and hardness of WC based Ni composites can be improved by adding Mo2C, ZrC, HFC, etc. to WC substrate or dissolving Si, Ti, Cr, Mo, etc. in Ni. carbonization

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