Abstract: The traditional cutting methods and their influence on external systems are analyzed. The key technologies of dry cutting, including tool technology, machine tool technology, quasi-dry cutting technology, green cutting fluid technology and its application, are proposed. .
Manufacturing is the material basis for national economic and social development, the main force for promoting national technological progress, the pillar industry for creating social wealth, and an important embodiment of a country's comprehensive national strength. While modern manufacturing brings unprecedented material civilization to mankind, in the process of natural resource exploitation and processing, in the process of using industrial products, wastes such as waste gas, waste residue and waste liquid are thrown to nature at will, resulting in The serious pollution of the environment has led to an ecological crisis characterized by depletion of resources and environmental degradation. According to statistics, more than 70% of the emissions from environmental pollution come from the manufacturing industry, which generates about 5.5 billion tons of non-hazardous waste and 700 million tons of hazardous waste each year. The issue of sustainable development has become one of the central issues facing human society in the 21st century. The advanced manufacturing model that realizes the sustainable development of manufacturing industry--green manufacturing is the future development direction of the manufacturing industry. Therefore, green cutting is one of the key technologies for green manufacturing, and it is of great significance for its in-depth study. The author focuses on the key technologies and applications of green cutting.
1 Traditional cutting methods and their influence on external systems Traditional metal cutting, especially in CNC machine tools, machining centers and automated production lines with high degree of automation, is carried out in a large number of wet cutting methods using cutting fluids. The use of cutting fluids is very extensive. The cutting fluid has functions such as cooling, lubrication and auxiliary chip removal, which plays an important role in prolonging the service life of the tool and improving the surface quality of the workpiece. The cutting fluids currently used are mainly divided into oil-based cutting fluids containing no water and water-based cutting fluids mainly composed of water. Oil-based cutting fluids have good lubricating properties and poor cooling performance, while water-based cutting fluids are reversed.
The large-scale use of cutting fluid in wet cutting has become increasingly prominent in the external system, mainly including the following aspects.
1.1 Pollution ecological environment Cutting fluid is the root cause of pollution caused by the mechanical processing industry, which seriously affects the implementation of green manufacturing, circular economy and sustainable development strategy.
The harm of cutting fluid to the environment is mainly the pollution of water resources by its waste liquid. Mineral oil is one of the main components of cutting fluids. It has poor biodegradability and can remain in water and soil for a long time. If the oil content in the water is greater than 10-5, the marine plants will die, and the oil content of 3×10-4 will cause the freshwater fish to die. In addition, the cutting fluid also contains environmentally harmful additives such as S, P, and Cl. Untreated cutting fluid is discharged into rivers, lakes and seas, causing serious damage to the ecological environment; even if the discharged waste liquid is subjected to strict mineral oil recovery, its long-term accumulation in water cannot be ignored. The cutting fluid will remain more or less on the chips, and a large amount of accumulated chips will pollute the soil; when the chips are recycled, the toxic and harmful chemical components of the cutting fluid will also pollute the environment.
1.2 Harm to human health The oil mist generated by the cutting fluid and the pungent odor emitted by the cutting fluid can cause harm to the operator's respiratory system. Additives such as sodium nitrite rust inhibitor, phenolic fungicide, and formaldehyde compound added to the water-based cutting fluid to improve cutting performance are toxic, and long-term exposure may cause cancer. The degreasing effect of mineral oil and surfactant can cause dryness, cracking and redness of the skin and induce various skin diseases. Specialized research by General Motors of the United States has shown that operators who are in direct contact with cutting fluids suffer from respiratory diseases more than those who do not directly contact cutting fluids and those who never work on machine tools.
1.3 Increasing manufacturing costs The large use of cutting fluids increases production costs and is not conducive to companies to improve their core competitiveness. Research by the Japan Precision Engineering Association shows that the cost of using cutting fluids accounts for about 16% of the cost of manufacturing parts, and the cost of grinding fluids is as high as 30% of the manufacturing cost, including cutting fluids and adhesive tapes due to environmental requirements. The cost of harmless processing of the cutting fluid is only 4% of the manufacturing cost.
2 Green cutting is an inevitable choice for sustainable manufacturing. In the past 10 years, people have been exploring ways to eliminate the negative impact of traditional wet cutting methods on external systems, and increasingly recognize that Dry Cutting is to reduce manufacturing costs and implement green. An important way to manufacture and develop ecological industries and achieve sustainable development of manufacturing.
2.1 Dry cutting technology and its characteristics Dry cutting is a process that does not use any cutting fluid during the cutting process. It is a technological innovation for traditional cutting methods. Compared to wet cutting, it is a green cutting and cleaning manufacturing process that controls pollution from the source. It eliminates the negative impact of the use of cutting fluid on external systems and has the following characteristics:
1. It does not pollute the ecological environment and does not pose a hazard to the health of the workers.
2. The formed chips are clean, non-polluting and easy to recycle.
3. It saves the transportation, recycling and filtration costs associated with cutting fluid, simplifies the production system and reduces production costs.
2.2 Green cutting is the inevitable choice for the sustainable development of the manufacturing industry The traditional environmental governance method is the end-of-pipe governance. The reality of the global ecological deterioration is that this kind of governance method cannot fundamentally realize the protection of the environment. To solve this problem, you must manage it from the source. Specific to the manufacturing industry, it is required to consider the impact of the product's entire life cycle on the environment, maximize the use of raw materials, energy, reduce harmful waste and solid, liquid, gas emissions, select green materials, implement green design, green technology, Green packaging, green use and green recycling. It can be seen that green cutting is an important part of the sustainable development of the manufacturing industry.
In 1996, the International Organization for Standardization officially promulgated the ISO 14000 environmental management series of standards. In order to implement the ISO 14000 environmental management series of standards, green manufacturing should be implemented at every stage of the product life cycle. Therefore, green cutting is also a requirement for implementing the ISO 14000 environmental management series of standards.
3 Key technologies for green cutting Dry cutting is more wet cutting. Due to the lack of cooling fluid, lubrication and auxiliary chip removal, the friction between the tool, the workpiece and the chip is intensified, the tool wear is intensified, and the cutting force and cutting heat are increased. The sharp increase, the temperature in the cutting zone rises sharply; at the same time, the machining accuracy and the surface quality of the workpiece deteriorate. However, by improving tooling techniques, machine performance and cutting processes, the adverse effects of dry cutting can be eliminated. According to statistics, in the European industry, there are currently 10% to 15% of the processing has adopted the dry cutting process.
3.1 Dry cutting tool technology Dry cutting process Because the cutting fluid is not used, whether the tool can withstand huge cutting heat is the key to dry cutting. Generally take the following measures.
1. Adopting new green tool materials Dry cutting conditions require excellent thermal properties of the tool material, high red hardness and thermal toughness, good adhesion resistance, thermal shock resistance and wear resistance. Ceramic knives (Al2O3, Si3N4) and cermets (Cermet) have good red hardness and are suitable for general purpose dry cutting, but these materials have poor thermal toughness and are not suitable for interrupted cutting, ie suitable for drying. Cutting is not suitable for dry milling. Cubic boron nitride (CBN) material is second only to diamond, with a hardness of 3200-4000 HV. It has high wear resistance, thermal stability and chemical stability. It is suitable for ferrous materials and alloys such as hardened steel and martensite. Dry cutting of cast iron, hardened bearing steel and nickel-chromium alloy. Polycrystalline diamond (PCD) material has a hardness of about 2 times that of CBN. It has good thermal conductivity and small thermal expansion coefficient. It is suitable for high-speed dry cutting of copper-aluminum alloy, non-metal materials and composite materials. It is an important tool for ultra-precision cutting. . Ultrafine grained carbide has good toughness and heat resistance and is also suitable for dry cutting. In addition, whisker toughening ceramics formed by adding 20% ​​to 30% SiC whiskers to the Al2O3 matrix, the reinforcing phase SiC whiskers can block or change the direction of crack development, and the toughness of the tool is greatly improved, which is a great potential for development. Dry cutting tool material.
2. Green tool coating technology Dry cutting tool coating technology is to improve the performance of the tool by applying one or more layers of special properties to the tool base. Coating the surface of the tool reduces the friction factor between the tool, the workpiece and the chip, reduces the cutting force, improves the tool life and improves the surface quality of the workpiece. The coating has a function similar to the cutting fluid, which isolates the tool from the heat of cutting, thus maintaining the rigidity and sharpness of the blade for a long time. In high-speed dry cutting, high temperatures have a large catalytic effect on the chemical reaction, so the coating can also protect the tool material from chemical reactions.
At present, there are two main types of coatings for dry cutting tools: one is a "hard" coating, such as TiC, TiN and Al2O3, which has the advantages of high hardness and good wear resistance. Among them, TiC coated tools have strong resistance to flank wear, and TiN coated tools have ideal anti-crater function. One type is “soft†coatings, such as MoS2, WS, etc. These coated tools are also called “self-lubricating toolsâ€. The friction factor between the tool, workpiece and chip is very low, only about 0.01, which can be reduced. Cutting force and cutting temperature. For example, the “MOVIC†soft coating technology developed by Guhring in Germany is to apply a layer of MoS2 on the surface of the tool to improve the durability of the tool.
The tool coating can also be coated with a soft/hard combination, ie a “hard†coating such as TiN is applied to the tool, and then a “soft†coating such as MoS2 is applied to form a multi-coated tool to make the coating The tool has high hardness and wear resistance, and has the characteristics of small friction factor and easy chip flow. Currently, there are as many as 13 layers of coated tools.
3. Optimizing Tool Geometry Parameters To meet the technical requirements for dry cutting for chip breaking and chip removal, tool geometry parameters must be optimized. First, reduce the contact area between the tool and the surface of the workpiece. For example, the drill bit should reduce the reverse cone and the helix angle for smooth chip removal. Second, consider the maximum lubricity of the tool surface to prevent the formation of built-up edge.
When performing dry cutting in closed spaces such as dry drilling and dry reaming, the chip pocket space of the tool and the taper of the back cone should be increased.
Dry cutting can also use special tools such as heat pipe tools and self-cooling tools to reduce tool temperature.
3.2 Structural design of dry cutting machine The research shows that the lubricating fluid of cutting fluid is only 10%, and its main function is heat dissipation and chip removal. Therefore, the structural design of dry cutting machine tools should consider two main problems: one is the rapid emission of cutting heat, and the other is the rapid discharge of chips. The machine bed is made of heat-stable structure and material, which can greatly reduce the adverse effects of cutting heat. Proper insulation measures such as the use of insulation materials to make chip flutes can reduce the transfer of cutting heat during chip removal. Here are a few quick chip removal designs that have been successfully applied to dry cutting:
1. Use debris to remove debris. The traditional drilling is carried out from top to bottom. By improving the layout of the machine, it is possible to drill from bottom to top and use the cutting fluid without gravity to assist the chip evacuation.
2. Using the siphon phenomenon, the dry air sucks the chips out of the air and does not require cutting fluid.
3. The chip evacuation condition can also be improved by using a vacuum or jet system.
3.3 Quasi-dry cutting technology Because dry cutting has strict technical requirements for tools, workpieces and machine tools, the application range is narrow. In the case where full dry cutting is not possible, Minimal Quantity Lubrication (MQL), also known as Near Dry Cutting, can be used to minimize the amount of cutting fluid when the cutting operation is optimal. . The method is to mix and atomize compressed air with a certain pressure (0.3~1 MPa) and a small amount of lubricating liquid (50-125 mL/h, and the cutting fluid consumption of normal jet lubrication reaches 6 L/min) to form an oil mist, and then spray at a high speed. It goes to the cutting zone for cooling and lubrication. MQL technology is mainly divided into two types: aerosol external lubrication and internal lubrication. Currently, MQL technology is mainly used for drilling, reaming and tapping of cast iron, steel and aluminum alloys.
3.4 Green cutting fluid dry cutting has significant advantages but limited application range. Quasi-dry cutting technology also requires a small amount of cutting fluid. For a long period of time, most cutting operations are inseparable from cutting fluid and cannot achieve complete green cutting. . Therefore, the development and promotion of green cutting fluids is still of great significance. Green cutting fluid is a human- and environmentally friendly cutting fluid whose residual waste oil and additives are completely degradable in nature. In the near future, we should focus on the development of low-toxic, low-pollution green cutting fluids. In the long run, we should pursue non-toxic, non-polluting green cutting fluids. The current green cutting fluid technologies used are:
1. Replace mineral oil with degradable vegetable oils and ester oils. Vegetable oil is a renewable resource that can be completely degraded in nature and is harmless to humans and the environment; the biodegradation rate of ester oil can reach 90% to 100%.
2. Replace harmful additives with low-toxic, low-pollution or even non-toxic, non-polluting biodegradable green additives.
3. Develop water-based cutting fluids instead of oil-based cutting fluids.
4 Application of Green Cutting Dry cutting technology originated in Europe and has been widely used in Europe and America. This is related to the developed manufacturing industry in Europe and America and the increasingly strong environmental protection concept. The research on dry cutting technology in China has started. Guangdong University of Technology, Tsinghua University, Zhengzhou Abrasives Grinding Research Institute and Chengdu Tool Research Institute have systematically studied superhard tool materials and tool coating technology. Dry cutting technology has been applied in the following aspects.
4.1 Dry Cutting of Cast Iron Casting is usually done without cutting fluid and is always dry-cut to increase its productivity. For example, ceramic or CBN tools for high-speed dry cutting, the heat generated quickly accumulates at the front end of the tool, and the cutting heat is pushed toward the workpiece, so that the material in the cutting zone reaches a red hot state, the yield strength of the cast iron component decreases, the cutting speed and the feed rate The increased speed has greatly improved the cutting efficiency of cast iron materials. This is the so-called "Red Crescent" cast iron dry cutting technology, which has been applied in the United States. Under normal circumstances, the metal removal rate (turning) of cast iron is 16cm3/min, while the "red Crescent" dry cutting technology can be increased to 49cm3/min, the cutting speed can reach 914~1219m/min, and the feed rate is 1270~ 5080mm/min.
4.2 Dry cutting of aluminum alloys Aluminum alloys have been widely used in the automotive industry and aerospace industry due to their good corrosion resistance, high specific strength, good electrical conductivity and thermal conductivity.
The aluminum alloy has a high heat transfer coefficient and a large thermal expansion coefficient. It absorbs a large amount of cutting heat during cutting, and its hardness and melting point are relatively low. Therefore, during the cutting process, the cutter and the chip are prone to sticking to form a built-up edge, which becomes A technical problem that must be solved when aluminum alloy is dry-cut. The best way to solve this problem is to use high-speed dry cutting technology. In high-speed cutting, 95% to 98% of the cutting heat is transferred to the chips, and the chips are partially melted at the interface with the tool rake face, so the chips are easily separated from the workpiece, reducing the cutting force and making it difficult. Forming built-up edge.
5 Conclusion Cutting technology is a key technology in the machining industry, and its development level determines the appearance of a country's machinery manufacturing industry. Dry cutting is an innovative green manufacturing process compared to wet cutting, which effectively solves the adverse effects of cutting fluid. It is of great significance to reduce processing costs, protect the ecological environment from pollution sources, and achieve sustainable development of manufacturing.
Dry cutting technology is a systematic project involving technical cooperation and technological innovation in many fields such as tools, machine tools, processes and materials, not just by using cutting fluid. For example, the choice of tool material and coating technology is closely related to the workpiece material. The dry cutting technology of aluminum alloy is the result of the combination of ultra-high speed machining technology and dry cutting technology. The development of dry cutting technology is in the ascendant. With the rapid development of various super-hard and high-temperature tool materials and coating technologies, it will certainly promote the in-depth research and popularization of dry cutting technology.
Manufacturing is the material basis for national economic and social development, the main force for promoting national technological progress, the pillar industry for creating social wealth, and an important embodiment of a country's comprehensive national strength. While modern manufacturing brings unprecedented material civilization to mankind, in the process of natural resource exploitation and processing, in the process of using industrial products, wastes such as waste gas, waste residue and waste liquid are thrown to nature at will, resulting in The serious pollution of the environment has led to an ecological crisis characterized by depletion of resources and environmental degradation. According to statistics, more than 70% of the emissions from environmental pollution come from the manufacturing industry, which generates about 5.5 billion tons of non-hazardous waste and 700 million tons of hazardous waste each year. The issue of sustainable development has become one of the central issues facing human society in the 21st century. The advanced manufacturing model that realizes the sustainable development of manufacturing industry--green manufacturing is the future development direction of the manufacturing industry. Therefore, green cutting is one of the key technologies for green manufacturing, and it is of great significance for its in-depth study. The author focuses on the key technologies and applications of green cutting.
1 Traditional cutting methods and their influence on external systems Traditional metal cutting, especially in CNC machine tools, machining centers and automated production lines with high degree of automation, is carried out in a large number of wet cutting methods using cutting fluids. The use of cutting fluids is very extensive. The cutting fluid has functions such as cooling, lubrication and auxiliary chip removal, which plays an important role in prolonging the service life of the tool and improving the surface quality of the workpiece. The cutting fluids currently used are mainly divided into oil-based cutting fluids containing no water and water-based cutting fluids mainly composed of water. Oil-based cutting fluids have good lubricating properties and poor cooling performance, while water-based cutting fluids are reversed.
The large-scale use of cutting fluid in wet cutting has become increasingly prominent in the external system, mainly including the following aspects.
1.1 Pollution ecological environment Cutting fluid is the root cause of pollution caused by the mechanical processing industry, which seriously affects the implementation of green manufacturing, circular economy and sustainable development strategy.
The harm of cutting fluid to the environment is mainly the pollution of water resources by its waste liquid. Mineral oil is one of the main components of cutting fluids. It has poor biodegradability and can remain in water and soil for a long time. If the oil content in the water is greater than 10-5, the marine plants will die, and the oil content of 3×10-4 will cause the freshwater fish to die. In addition, the cutting fluid also contains environmentally harmful additives such as S, P, and Cl. Untreated cutting fluid is discharged into rivers, lakes and seas, causing serious damage to the ecological environment; even if the discharged waste liquid is subjected to strict mineral oil recovery, its long-term accumulation in water cannot be ignored. The cutting fluid will remain more or less on the chips, and a large amount of accumulated chips will pollute the soil; when the chips are recycled, the toxic and harmful chemical components of the cutting fluid will also pollute the environment.
1.2 Harm to human health The oil mist generated by the cutting fluid and the pungent odor emitted by the cutting fluid can cause harm to the operator's respiratory system. Additives such as sodium nitrite rust inhibitor, phenolic fungicide, and formaldehyde compound added to the water-based cutting fluid to improve cutting performance are toxic, and long-term exposure may cause cancer. The degreasing effect of mineral oil and surfactant can cause dryness, cracking and redness of the skin and induce various skin diseases. Specialized research by General Motors of the United States has shown that operators who are in direct contact with cutting fluids suffer from respiratory diseases more than those who do not directly contact cutting fluids and those who never work on machine tools.
1.3 Increasing manufacturing costs The large use of cutting fluids increases production costs and is not conducive to companies to improve their core competitiveness. Research by the Japan Precision Engineering Association shows that the cost of using cutting fluids accounts for about 16% of the cost of manufacturing parts, and the cost of grinding fluids is as high as 30% of the manufacturing cost, including cutting fluids and adhesive tapes due to environmental requirements. The cost of harmless processing of the cutting fluid is only 4% of the manufacturing cost.
2 Green cutting is an inevitable choice for sustainable manufacturing. In the past 10 years, people have been exploring ways to eliminate the negative impact of traditional wet cutting methods on external systems, and increasingly recognize that Dry Cutting is to reduce manufacturing costs and implement green. An important way to manufacture and develop ecological industries and achieve sustainable development of manufacturing.
2.1 Dry cutting technology and its characteristics Dry cutting is a process that does not use any cutting fluid during the cutting process. It is a technological innovation for traditional cutting methods. Compared to wet cutting, it is a green cutting and cleaning manufacturing process that controls pollution from the source. It eliminates the negative impact of the use of cutting fluid on external systems and has the following characteristics:
1. It does not pollute the ecological environment and does not pose a hazard to the health of the workers.
2. The formed chips are clean, non-polluting and easy to recycle.
3. It saves the transportation, recycling and filtration costs associated with cutting fluid, simplifies the production system and reduces production costs.
2.2 Green cutting is the inevitable choice for the sustainable development of the manufacturing industry The traditional environmental governance method is the end-of-pipe governance. The reality of the global ecological deterioration is that this kind of governance method cannot fundamentally realize the protection of the environment. To solve this problem, you must manage it from the source. Specific to the manufacturing industry, it is required to consider the impact of the product's entire life cycle on the environment, maximize the use of raw materials, energy, reduce harmful waste and solid, liquid, gas emissions, select green materials, implement green design, green technology, Green packaging, green use and green recycling. It can be seen that green cutting is an important part of the sustainable development of the manufacturing industry.
In 1996, the International Organization for Standardization officially promulgated the ISO 14000 environmental management series of standards. In order to implement the ISO 14000 environmental management series of standards, green manufacturing should be implemented at every stage of the product life cycle. Therefore, green cutting is also a requirement for implementing the ISO 14000 environmental management series of standards.
3 Key technologies for green cutting Dry cutting is more wet cutting. Due to the lack of cooling fluid, lubrication and auxiliary chip removal, the friction between the tool, the workpiece and the chip is intensified, the tool wear is intensified, and the cutting force and cutting heat are increased. The sharp increase, the temperature in the cutting zone rises sharply; at the same time, the machining accuracy and the surface quality of the workpiece deteriorate. However, by improving tooling techniques, machine performance and cutting processes, the adverse effects of dry cutting can be eliminated. According to statistics, in the European industry, there are currently 10% to 15% of the processing has adopted the dry cutting process.
3.1 Dry cutting tool technology Dry cutting process Because the cutting fluid is not used, whether the tool can withstand huge cutting heat is the key to dry cutting. Generally take the following measures.
1. Adopting new green tool materials Dry cutting conditions require excellent thermal properties of the tool material, high red hardness and thermal toughness, good adhesion resistance, thermal shock resistance and wear resistance. Ceramic knives (Al2O3, Si3N4) and cermets (Cermet) have good red hardness and are suitable for general purpose dry cutting, but these materials have poor thermal toughness and are not suitable for interrupted cutting, ie suitable for drying. Cutting is not suitable for dry milling. Cubic boron nitride (CBN) material is second only to diamond, with a hardness of 3200-4000 HV. It has high wear resistance, thermal stability and chemical stability. It is suitable for ferrous materials and alloys such as hardened steel and martensite. Dry cutting of cast iron, hardened bearing steel and nickel-chromium alloy. Polycrystalline diamond (PCD) material has a hardness of about 2 times that of CBN. It has good thermal conductivity and small thermal expansion coefficient. It is suitable for high-speed dry cutting of copper-aluminum alloy, non-metal materials and composite materials. It is an important tool for ultra-precision cutting. . Ultrafine grained carbide has good toughness and heat resistance and is also suitable for dry cutting. In addition, whisker toughening ceramics formed by adding 20% ​​to 30% SiC whiskers to the Al2O3 matrix, the reinforcing phase SiC whiskers can block or change the direction of crack development, and the toughness of the tool is greatly improved, which is a great potential for development. Dry cutting tool material.
2. Green tool coating technology Dry cutting tool coating technology is to improve the performance of the tool by applying one or more layers of special properties to the tool base. Coating the surface of the tool reduces the friction factor between the tool, the workpiece and the chip, reduces the cutting force, improves the tool life and improves the surface quality of the workpiece. The coating has a function similar to the cutting fluid, which isolates the tool from the heat of cutting, thus maintaining the rigidity and sharpness of the blade for a long time. In high-speed dry cutting, high temperatures have a large catalytic effect on the chemical reaction, so the coating can also protect the tool material from chemical reactions.
At present, there are two main types of coatings for dry cutting tools: one is a "hard" coating, such as TiC, TiN and Al2O3, which has the advantages of high hardness and good wear resistance. Among them, TiC coated tools have strong resistance to flank wear, and TiN coated tools have ideal anti-crater function. One type is “soft†coatings, such as MoS2, WS, etc. These coated tools are also called “self-lubricating toolsâ€. The friction factor between the tool, workpiece and chip is very low, only about 0.01, which can be reduced. Cutting force and cutting temperature. For example, the “MOVIC†soft coating technology developed by Guhring in Germany is to apply a layer of MoS2 on the surface of the tool to improve the durability of the tool.
The tool coating can also be coated with a soft/hard combination, ie a “hard†coating such as TiN is applied to the tool, and then a “soft†coating such as MoS2 is applied to form a multi-coated tool to make the coating The tool has high hardness and wear resistance, and has the characteristics of small friction factor and easy chip flow. Currently, there are as many as 13 layers of coated tools.
3. Optimizing Tool Geometry Parameters To meet the technical requirements for dry cutting for chip breaking and chip removal, tool geometry parameters must be optimized. First, reduce the contact area between the tool and the surface of the workpiece. For example, the drill bit should reduce the reverse cone and the helix angle for smooth chip removal. Second, consider the maximum lubricity of the tool surface to prevent the formation of built-up edge.
When performing dry cutting in closed spaces such as dry drilling and dry reaming, the chip pocket space of the tool and the taper of the back cone should be increased.
Dry cutting can also use special tools such as heat pipe tools and self-cooling tools to reduce tool temperature.
3.2 Structural design of dry cutting machine The research shows that the lubricating fluid of cutting fluid is only 10%, and its main function is heat dissipation and chip removal. Therefore, the structural design of dry cutting machine tools should consider two main problems: one is the rapid emission of cutting heat, and the other is the rapid discharge of chips. The machine bed is made of heat-stable structure and material, which can greatly reduce the adverse effects of cutting heat. Proper insulation measures such as the use of insulation materials to make chip flutes can reduce the transfer of cutting heat during chip removal. Here are a few quick chip removal designs that have been successfully applied to dry cutting:
1. Use debris to remove debris. The traditional drilling is carried out from top to bottom. By improving the layout of the machine, it is possible to drill from bottom to top and use the cutting fluid without gravity to assist the chip evacuation.
2. Using the siphon phenomenon, the dry air sucks the chips out of the air and does not require cutting fluid.
3. The chip evacuation condition can also be improved by using a vacuum or jet system.
3.3 Quasi-dry cutting technology Because dry cutting has strict technical requirements for tools, workpieces and machine tools, the application range is narrow. In the case where full dry cutting is not possible, Minimal Quantity Lubrication (MQL), also known as Near Dry Cutting, can be used to minimize the amount of cutting fluid when the cutting operation is optimal. . The method is to mix and atomize compressed air with a certain pressure (0.3~1 MPa) and a small amount of lubricating liquid (50-125 mL/h, and the cutting fluid consumption of normal jet lubrication reaches 6 L/min) to form an oil mist, and then spray at a high speed. It goes to the cutting zone for cooling and lubrication. MQL technology is mainly divided into two types: aerosol external lubrication and internal lubrication. Currently, MQL technology is mainly used for drilling, reaming and tapping of cast iron, steel and aluminum alloys.
3.4 Green cutting fluid dry cutting has significant advantages but limited application range. Quasi-dry cutting technology also requires a small amount of cutting fluid. For a long period of time, most cutting operations are inseparable from cutting fluid and cannot achieve complete green cutting. . Therefore, the development and promotion of green cutting fluids is still of great significance. Green cutting fluid is a human- and environmentally friendly cutting fluid whose residual waste oil and additives are completely degradable in nature. In the near future, we should focus on the development of low-toxic, low-pollution green cutting fluids. In the long run, we should pursue non-toxic, non-polluting green cutting fluids. The current green cutting fluid technologies used are:
1. Replace mineral oil with degradable vegetable oils and ester oils. Vegetable oil is a renewable resource that can be completely degraded in nature and is harmless to humans and the environment; the biodegradation rate of ester oil can reach 90% to 100%.
2. Replace harmful additives with low-toxic, low-pollution or even non-toxic, non-polluting biodegradable green additives.
3. Develop water-based cutting fluids instead of oil-based cutting fluids.
4 Application of Green Cutting Dry cutting technology originated in Europe and has been widely used in Europe and America. This is related to the developed manufacturing industry in Europe and America and the increasingly strong environmental protection concept. The research on dry cutting technology in China has started. Guangdong University of Technology, Tsinghua University, Zhengzhou Abrasives Grinding Research Institute and Chengdu Tool Research Institute have systematically studied superhard tool materials and tool coating technology. Dry cutting technology has been applied in the following aspects.
4.1 Dry Cutting of Cast Iron Casting is usually done without cutting fluid and is always dry-cut to increase its productivity. For example, ceramic or CBN tools for high-speed dry cutting, the heat generated quickly accumulates at the front end of the tool, and the cutting heat is pushed toward the workpiece, so that the material in the cutting zone reaches a red hot state, the yield strength of the cast iron component decreases, the cutting speed and the feed rate The increased speed has greatly improved the cutting efficiency of cast iron materials. This is the so-called "Red Crescent" cast iron dry cutting technology, which has been applied in the United States. Under normal circumstances, the metal removal rate (turning) of cast iron is 16cm3/min, while the "red Crescent" dry cutting technology can be increased to 49cm3/min, the cutting speed can reach 914~1219m/min, and the feed rate is 1270~ 5080mm/min.
4.2 Dry cutting of aluminum alloys Aluminum alloys have been widely used in the automotive industry and aerospace industry due to their good corrosion resistance, high specific strength, good electrical conductivity and thermal conductivity.
The aluminum alloy has a high heat transfer coefficient and a large thermal expansion coefficient. It absorbs a large amount of cutting heat during cutting, and its hardness and melting point are relatively low. Therefore, during the cutting process, the cutter and the chip are prone to sticking to form a built-up edge, which becomes A technical problem that must be solved when aluminum alloy is dry-cut. The best way to solve this problem is to use high-speed dry cutting technology. In high-speed cutting, 95% to 98% of the cutting heat is transferred to the chips, and the chips are partially melted at the interface with the tool rake face, so the chips are easily separated from the workpiece, reducing the cutting force and making it difficult. Forming built-up edge.
5 Conclusion Cutting technology is a key technology in the machining industry, and its development level determines the appearance of a country's machinery manufacturing industry. Dry cutting is an innovative green manufacturing process compared to wet cutting, which effectively solves the adverse effects of cutting fluid. It is of great significance to reduce processing costs, protect the ecological environment from pollution sources, and achieve sustainable development of manufacturing.
Dry cutting technology is a systematic project involving technical cooperation and technological innovation in many fields such as tools, machine tools, processes and materials, not just by using cutting fluid. For example, the choice of tool material and coating technology is closely related to the workpiece material. The dry cutting technology of aluminum alloy is the result of the combination of ultra-high speed machining technology and dry cutting technology. The development of dry cutting technology is in the ascendant. With the rapid development of various super-hard and high-temperature tool materials and coating technologies, it will certainly promote the in-depth research and popularization of dry cutting technology.
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