Research Status and Development of Green Cutting Technology

1. introduction
Environment, resources and population are the three major problems facing today's society. Relying on scientific and technological progress, realizing money-saving and efficiency, reducing waste emissions, and establishing a development model of production, consumption, environment and resources have become the only way for the sustainable development of human society. In the 21st century, it is imperative to implement green manufacturing in the manufacturing industry. Cutting machining as a manufacturing industry is an important and widely used processing method is facing new challenges. In this context, green cutting technology came into being.
In the traditional cutting process, a large amount of cutting fluid is required to be cast in the cutting zone for cooling, lubrication, cleaning, chip removal, rust prevention and the like. With the high concern of human society for environmental protection, the negative impact of using cutting fluid can not be ignored. These effects are mainly manifested in: 1 the large use of cutting fluid increases the manufacturing cost. In the European automotive industry, the cost of cutting fluid accounts for 16.9% of the total manufacturing cost, including the cost of purchasing cutting fluid, equipment costs for cutting fluids, maintenance and waste disposal costs. Tool costs account for only 7.5% of total manufacturing costs. 2 The cutting fluid contains mineral oil and environmentally harmful additives such as sulfur, phosphorus and chlorine. If it is not treated or improperly treated before discharge, it will cause environmental pollution. 3 cutting fluid poses a threat to the health of operators, it will induce a variety of skin diseases and respiratory and lung diseases. Green cutting technology is a processing technology that fully considers environmental and resource issues. It requires that it be done throughout the entire process. Environmental pollution is minimal and resource utilization is highest. At present, the research on green cutting at home and abroad mainly focuses on dry cutting, low temperature cutting, green wet cutting and so on.

2. Dry cutting
Dry cutting refers to a method of consciously reducing the use or absence of cutting fluids in order to protect the environment and reduce costs during machining. There are two types of dry cutting, one is dry cutting without cutting fluid at all, and the other is quasi-dry cutting with gas mixed with a small amount of lubricant instead of cutting fluid. It uses minimum amount of lubrication (Minimal Quantity) Lubrication, MQL) technology. Quasi-dry cutting with MQL technology is suitable for situations where dry cutting cannot be fully realized, such as grinding and machining of difficult-to-machine materials. After quasi-dry machining, the tool, workpiece and chips are kept dry and the chips can be recycled without treatment.
At present, the research on dry cutting mainly focuses on the following aspects.

2.1 Dry-cutting tool research Since the dry cutting temperature is much higher than the wet cutting, in order to achieve dry cutting, the tool material must have high red hardness, wear resistance, thermal toughness and thermochemical stability. And the coefficient of friction between the chips, the workpiece and the tool should be as small as possible. The tool structure should be easy to chip, and the tool strength and impact toughness should be high. Current tool materials for dry cutting include ultrafine grained cemented carbide, diamond, cubic boron nitride, and coated cemented carbide.
Nanocoatings tools developed by American scholars can be used in different combinations of materials (such as metal/metal combinations, metal/ceramic combinations, ceramic/ceramic combinations, solid lubricants/metal combinations, etc.) to meet different Functional and performance requirements. The nano-coating provides a significant increase in the hardness and toughness of the tool, with excellent resistance to friction and wear and self-lubricating properties.
Sumitomo Electric Industries Co., Ltd. has developed a tool material capable of dry-cutting hardened steel at a relatively high speed - Boron Abrasive (Cubic Boron Nitride Abrasive Tool trade name) BNX10, BNX25. Boron Abrasive BNX10 is suitable for high speed continuous dry cutting of hardened steel. An example of the outer diameter machining of the shaft shows that the BNX10 achieves a higher machined surface finish and stable dimensional accuracy than the ceramic tool, and the tool life is greatly improved. Boron Abrasive BNX25 improves the defect resistance and crater wear resistance by optimizing the particle size and content of CBN and using special ceramic materials as the bonding phase. It is suitable for high-speed interrupted cutting of hardened steel. An example of high-speed machining of the outer diameter of the sleeve material shows that the life of the BNX25 tool is improved under high-speed cutting conditions compared to conventional tool materials.
Deng Jianxin et al. developed Al203/TiB2 ceramic tool materials using TiB2 as additive and Al203 as matrix. The ceramic tool was used for high-speed dry cutting test of hardened steel. The results show that when the cutting speed is greater than 12Om/min, the tool begins to exhibit high-temperature self-lubricating performance. The composition of the self-lubricating film is the oxidation of TiB2 in Al203/TiBz ceramic tool. The object can act as a solid lubricant on the surface of the tool, thereby reducing the friction of the rake face, reducing the adhesive wear of the tool, improving the wear resistance of the tool, and having good anti-friction and anti-wear effects.
Yang Haidong et al. used the NT15 matrix carbon nitride film coating tool to dry and turn silicon-aluminum alloy. The test results show that the blade tip is very small, the surface roughness of the workpiece is small, and the service life of the tool is much higher than that of the hard alloy. .

2.2 Research on Dry Cutting Mechanism Liu Xianli et al. proposed the concept of critical hardness by dry cutting test of hardened bearing steel GCrI5 with different hardness, and obtained 50HRC to distinguish the critical hardness of hard cutting and ordinary cutting GCrl5. The conclusion. From the point of view of cutting heat, the hard dry cutting mechanism of hardened steel is the softening mechanism of the metal layer being cut. The cutting temperature plays a decisive role in the softening effect of the metal, and the hardness of the workpiece decreases with the increase of the cutting temperature. Further affecting the formation and quality of the machined surface. Studies have shown that when the hardened material hardness is higher than 50HRC, the cutting mechanism changes due to the metal softening effect, and thus the cutting force, the residual stress distribution on the machined surface and the generation of the white layer change. Existing cutting theory can not explain the variation of cutting temperature.
In high-speed dry cutting, the US Makino company proposed the "Red Crescent" dry cutting process. The mechanism is that due to the high cutting speed, the generated heat is concentrated in the front of the tool, so that the workpiece material near the cutting zone reaches a red hot state, resulting in a significant decrease in yield strength, thereby improving the material removal rate. Currently, tools such as PCBN and ceramics are mainly used to implement this process.

2.3 Application of dry cutting Because dry cutting is beneficial to environmental protection and reduce processing costs (saving machining costs by 10% to 15%), the research and development of dry cutting technology is receiving more and more attention. Currently, about 10% in Europe. ~15% of batch machining has adopted dry or quasi-dry cutting technology.
From the processing method point of view, turning, milling, hobbing and other processing applications are more dry cutting. Japanese firm vine Iron Works developed KC250H used dry-type carbide hob hobbing and performs high-speed processing at a cold hobbing cooling lubricant trace lubrication conditions, the conventional wet hobbing (KA220-type) and high-speed steel compared hobbing, the processing speed increased 2.3 times, the gear machining accuracy has also been significantly improved.
In terms of the workpiece material, cast iron because of the high melting point, thermal diffusivity, and most suitable for dry cutting. Spur Lachmund test results and ceramic tools and tool CNB high-speed cutting of cast iron indicated that since the CNB having high thermal conductivity can quickly remove heat of the workpiece, and therefore more suitable for high-speed cutting tool CNB cast iron materials than ceramic tool. Aluminum and aluminum alloys are difficult materials for dry cutting. However, through the use of MQL-lubricated high-speed quasi-dry cutting, breakthroughs have been made in solving chip and tool bonding and thermal deformation of aluminum parts. parts of the quasi-dry cutting production line put into operation. For difficult-to-machine materials, processing techniques using laser-assisted dry cutting have been developed.

3. Low temperature cutting
Low-temperature cutting is the use of low-temperature fluids such as liquid nitrogen, liquid carbon dioxide and cold air to spray into the cutting area of ​​the processing system, resulting in local low-temperature or ultra-low temperature conditions in the cutting zone, using the low-temperature brittleness of the workpiece under low temperature conditions to improve the machinability of the workpiece. , tool life and workpiece surface quality. According to different cooling media, low temperature cutting can be divided into cold air cutting and liquid nitrogen cooling cutting.
The low-temperature cold air cutting method is to spray a low-temperature airflow of -20 ° C to -30 ° C (or even lower) to the processing part of the cutting edge, and mix a small amount of vegetable lubricant (10 to 20 ml per hour) to cool down, The role of chip removal and lubrication. Compared with conventional cutting, low-temperature cold-air cutting can improve machining efficiency, improve the surface quality of the workpiece, and have almost no pollution to the environment. The machining center of Yasuda Industrial Co., Ltd. uses a structure in which a heat-insulated air duct is inserted into the center of the motor shaft and the arbor shaft, and a low-temperature cold air of 30 ° C is used to directly lead to the cutting edge. The structure greatly improves the cutting conditions and is beneficial to the implementation of the low temperature cold air cutting process. Yokokawa and Hiroshi studied the cold air cooling in turning and milling. In the milling test, the water-based cutting fluid, normal temperature wind (+10 ° C) and cold air (a 30 ° C) were compared respectively. The results show that the tool durability is significantly improved by cold air cutting. In the turning test, the tool wear rate during cold air (20 ° C) cutting was significantly lower than that at normal temperature (+20 ° C).
Chen Decheng et al. used a micro-vegetable lubricating oil and cold-air cutting method to test the high-silicon aluminum alloy of difficult-to-machine materials. The results show that this method can reduce tool wear, improve the surface quality and avoid water solubility. Tool wear due to circulation of silicon crystal particles in the cutting fluid when cutting oil. Chen Decheng et al. also carried out the test of cutting stainless steel under the condition of cold air cooling and trace vegetable oil lubrication. The results show that this method prolongs the service life of the tool, can inhibit the generation of built-up edge, improve the surface precision and save Go to the waste treatment system to achieve green cutting.
There are two main applications for liquid nitrogen cooling cutting. One is to use a bottled pressure to spray liquid nitrogen directly into the cutting zone like a cutting fluid; the other is to use a liquid nitrogen heated evaporation cycle to indirectly cool the tool or workpiece. Nitrogen is the most abundant component in the atmosphere. As a by-product of the oxygen industry, nitrogen is abundant in resources. Since liquid nitrogen is directly volatilized into a gas and returned to the atmosphere, it does not leave any pollution. At present, low temperature cutting is mainly used in the processing of difficult-to-machine materials such as titanium alloy, high-manganese steel and hardened steel. KP Raijurkar used H13A cemented carbide tools and liquid nitrogen circulation cooling tools to test the low temperature cutting of titanium alloy. The test results show that compared with the traditional cutting method, the tool wear is significantly reduced, and the cutting temperature is reduced by 30%. The surface finish quality of the workpiece is greatly improved. Wan Guangmin used low-temperature cutting test on high-manganese steel by indirect cooling method. The results show that when low-temperature processing of high-manganese steel by indirect cooling method, the impact force of the tool is reduced, the tool wear is reduced, and the work hardening phenomenon is improved. The surface quality of the workpiece is also improved. Wang Lianpeng et al. used liquid nitrogen spray method to cry harden 45 hardened steel on CNC machine tools. The test results show that the use of liquid nitrogen spray low temperature processing 45 hardened steel can improve tool durability and improve workpiece surface quality.

4. Green wet cutting
Green wet cutting refers to the use of high-performance, long-life, low-pollution, and degradable new green cutting fluids, minimizing the amount of cutting fluid and waste liquid, increasing the number of times the cutting fluid is recycled, and implementing it. Harmful treatment, so as to achieve the cutting requirements of green environmental protection. At present, the research on green wet cutting mainly focuses on the following aspects:

4.1 Development of high-performance, long-life, low-pollution cutting fluids Micro-emulsions are widely used in developed countries, and environmentally-friendly cutting fluids are being researched. Mobil Chemical Company of the United States has developed an emulsion called Mobilment AquaRho, which incorporates a composition containing phosphorus, nitrogen and boron, which has a service life of more than 45 months.
In China, the use of water-based cutting fluids is becoming wider and wider, and it has begun to transition from emulsion to synthetic cutting fluids and microemulsions with good performance and long life. Mineral oils are gradually biodegradable vegetable oils and synthetic esters. Replaced. Ionic cutting fluid is a new type of water-soluble cutting fluid. Its mother liquor is prepared from anionic, nonionic surfactants and inorganic salts, and has a good cooling effect. Liu Zhenchang et al. developed a low-toxic, low-pollution low-temperature (ie, low-condensation point) cutting fluid. The cutting fluid has good low-temperature fluidity, excellent cooling performance and good lubricating performance, and can effectively inhibit bacterial growth, greatly prolong the service life of the cutting fluid, thereby reducing the discharge of cutting waste liquid, and utilizing the environment. Protection has good social benefits. Shanghai Haiying Chemical Industry & Trade Co., Ltd. has developed a high-tech green environmental protection coolant - MCT lubrication coolant, which has good lubrication, cooling performance and good anti-rust and anti-corrosion properties, and is non-toxic and non-irritating. Sexual, non-polluting.

4.2 Research on “Minimum Lubrication” Technology The minimum amount of lubrication (MQL) technology refers to the use of cutting fluid during cutting, the cutting work is in the best condition (ie, the tool life is not shortened, the surface quality is not reduced). Achieve the least.
The University of Michigan technical research in the United States on the appropriate amount of cutting fluid in the cutting process, trying to meet the processing requirements, the minimum amount of cutting fluid, the cost associated with cutting fluid is also minimized. In the tests performed by Ford Motor Company, they tested and studied the concentration of cutting fluid, workpiece material, tool type and geometric parameters, and analyzed the surface roughness, built-up edge and cutting force of the workpiece. The most appropriate amount of cutting fluid was obtained through experiments. The Thyssen manufacturing company in the United States has studied the "minimum lubrication" processing technology, so that the cutting fluid or aerosol acts on the processing area through the cutter, and the flow rate of the cutting fluid is controlled by the CNC program, and good results are obtained. Wang Chengyong and others used a minimum lubrication technique to drill a variety of composite panels. When drilling aluminum-titanium multi-layer composite board, the friction and wear of the titanium plate cutting chip will cause the aluminum plate hole to be flared, and the aperture fluctuation amplitude and average aperture value increase and may be out of tolerance. The test uses the least amount of lubrication technology, using coated tools and processing with retracting chips and reaming, reducing the width of the land, increasing the feed angle and using the stepped shaft to ensure the processing quality of the hole.

4.3 Research on Coolant Purification Treatment Technology In general, the coolant is recycled, and it should be purified before it is recycled, including filtration and sterilization. Guo Cheng et al. conducted a test on the grinding fluid under the ultra-high-speed grinding condition of CBN grinding wheel by diatomite deep filtration method. The results show that the diatomite filtration method has high precision and efficiency, and is suitable for colloidal and viscous. Filtration of materials. The Research Department of Xi'an Institute of Technology has developed a purification device that does not discharge coolant. The device includes a drum scraper magnetic separator and an electronic ozone sterilizer. The combination of the two can achieve zero discharge of the coolant, thus eliminating the mechanical Environmental pollution caused by the discharge of coolant during processing, and the cutting fluid can be saved.

5. in conclusion
Dry cutting technology has been applied to mature non-ferrous metals and alloys and cast iron, the problem still exists, especially in the application of dry cutting steel materials of high strength steel, mainly for serious tool wear, material and structure of the tool Higher requirements and higher costs. At the same time, it is common in the cutting that the dust and chip processing are difficult, and the machine tool is easy to rust.
At present, low temperature cutting is only used in the processing of some difficult materials such as titanium alloy, high manganese steel and hardened steel. Compared with the traditional cutting method, the cost of low temperature cutting is high, so reducing the cost becomes a prerequisite for the promotion and application of low temperature cutting. At the same time, the rust prevention of machine tools is also a problem to be considered.
Green wet cutting is currently a more feasible processing method. The development of new environmentally friendly cutting fluid I, the rational use of cutting fluid and the purification of waste liquid have become problems to be solved.
The 21st century calls for green manufacturing, and clean production requires green processing. As a new topic, green cutting is gaining more and more attention. Although there are still many problems to be solved in dry cutting, low temperature cutting, green wet cutting, etc., their superiority is gradually reflected in comparison with traditional processing methods. Green cutting will be an important part of future green manufacturing. .

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