In the metal cutting process, usually use cutting fluid. The heavy use of cutting fluid has brought great harm to the environment and human health, forcing people to continue to research and develop new technologies to change the status quo. Therefore, in recent years, green manufacturing technology has become an international research hotspot.
Green cutting technology is an integral part of green manufacturing. It means that it has no toxic and side effects (or side effects are small) on the ecological environment and the small environment of the processing site, and a small amount of “three wastes” (exhaust gas, waste liquid and Waste slag) cutting technology that can be recycled or naturally degraded at the end of the chain to meet the environmental protection requirements of no pollution and harmless to human health and the environment.
For green cutting, a series of international standards have been formulated accordingly. In April 1996, the International Mechanical Society formulated the ISO14000 international standard for clean processing. Countries such as Germany, the United States, Canada, and Japan have also formulated stricter industrial emission standards, further restricting the use of cutting fluids. The discharge and treatment of cutting fluid as toxic waste and chips with cutting fluid greatly increase the cost of recycling and processing, and the costs associated with cutting fluid account for about 17% of the processing cost.
pollution-free, clean and low-energy green manufacturing is the development direction of machinery manufacturing in the 21st century. Therefore, research and development of new green cutting technology to reduce the pollution caused by cutting fluid to the environment, and to seek green and environmentally friendly cooling and lubrication technology are important topics for the promotion and application of green cutting technology. Green cutting technology meets the requirements of the sustainable development strategy and will surely promote the sustainable and healthy development of the machinery industry.
2 Dry cutting
Dry cutting means that no cutting fluid is used during the cutting process, which completely eliminates the negative effects of the cutting fluid and is a green cutting processing method that meets the ecological requirements. Its main advantages are: no pollution to the atmosphere and water environment; no residue on the swarf, which reduces the cost of cleaning treatment; it is harmless to human health and does not damage the skin or cause allergies. Dry cutting technology is currently mainly used in the processing of cast iron parts, and the promotion and application of other aspects are being further researched and developed.
The implementation of dry cutting needs to meet certain conditions, mainly including:
(1) The machine tool is required to have good thermal stability and high rigidity, otherwise it is difficult to guarantee the machining accuracy.
(2) puts forward new requirements for cutting tools. It mainly includes the choice of tool materials and the design of tool geometric parameters. Because dry cutting does not use cutting fluid, the cutting temperature is very high. Only tool materials with good thermal conductivity, high temperature resistance and high hardness can meet the processing requirements. At present, CBN and PCD are the most widely used tool materials in dry cutting. The application of tool coating technology (CVD and PVD coating technology, nano coating technology, etc.) can extend the tool life and better meet the requirements of dry cutting. Optimizing the geometric parameters of the tool can improve the machining accuracy and prolong the service life of the tool, and is also one of the important means to promote the development of dry cutting technology.
At present, there are still many deficiencies in the dry cutting technology and technical difficulties that restrict its popularization and application. Due to the loss of cutting fluid lubrication, cooling, auxiliary chip removal, etc., the load on the tool during processing increases, the cutting temperature increases, the tool-chip interface is in full two-phase solid contact, and the tool wear process is extremely complicated. Both the tool and the workpiece are prone to thermal deformation, resulting in a shortened tool life and reduced surface quality. In addition, for the machine tool itself, since the thermal balance cannot be maintained, the bed, column, etc. of the machine tool also undergo deformation that cannot be ignored due to the increase in temperature.
The development of dry cutting technology mainly depends on the improvement and improvement of the performance of machine tools and tools, namely:
(1) Improve machine performance. On the one hand, improve the thermal stability and resistance to thermal deformation of the machine tool; on the other hand, by increasing the spindle speed of the machine tool, developing high-speed (ultra-high-speed) dry cutting technology to greatly improve production efficiency, reduce cutting force, and obtain good Surface finish quality.
(2) Develop new tool materials and coating technology. By improving the thermal conductivity, heat resistance, self-lubricity and wear resistance of the tool material, the tool life is extended and the machining accuracy of dry cutting is guaranteed.
3 Liquid nitrogen cooling cutting
Liquid nitrogen cooling cutting is an advanced cutting technology that uses the characteristics of liquid nitrogen to form a local low temperature (or ultra-low temperature) in the cutting zone, thereby changing the physical and mechanical properties of the workpiece material and making it beneficial for processing. Research by Dr. SYHong of White State University on liquid nitrogen cooling turning shows that cemented carbide tool materials can maintain good cutting performance under liquid nitrogen cooling cutting conditions. The ZYWang turning silicon nitride ceramics test at Lincoln University showed that under liquid nitrogen cooling, tool wear can be reduced by approximately 4 times, and the surface roughness value of the workpiece can be reduced by more than 6 times. Liquid nitrogen cooling cutting is very beneficial for the processing of difficult-to-machine materials such as titanium alloys, low alloy steels, mild steels, and some high plastic (tough) composite materials.
At present, the liquid nitrogen cooling cutting technology mainly has the following problems to be solved:
(1) Liquid nitrogen storage, transportation and other costs bring additional costs;
(2) The lubricity of liquid nitrogen is insufficient during cutting;
(3) The safety of the use of liquid nitrogen requires special attention;
(4) The surface of the workpiece cut at ultra-low temperature has strong chemical activity, and it will quickly rust when exposed to air, so the problem of rust prevention of the workpiece must be solved;
(5) Further research is needed on the low-temperature cutting performance of different workpiece materials and the cutting characteristics of tools.
4 steam cooling cutting
Steam cooling cutting is a cutting method that sprays superheated steam into the cutting area to achieve cooling and lubrication. Its cutting system consists of water vapor generating device, water vapor transmission and control system and machine tool system. Former Soviet scholars PodgorkvVV and GodelviskiVA proposed this cutting method in the 1990s. Harbin Institute of Technology has also done preliminary research on this, and has achieved certain results. Studies have shown that water-cooled cutting can reduce the cutting force and the surface roughness of the workpiece, significantly reduce the cutting temperature, generate more regular and reasonable chips, and improve the lubricity. Water vapor is inexpensive and pollution-free, and it is a good green lubricant. At present, the technology is still in the research stage, mainly with the following problems:
(1) The steam generating device consumes a large amount of energy, and further research is needed on a steam generating device with low energy consumption, good thermal insulation, and simple and reasonable structure.
(2) The lubrication mechanism of water vapor needs further study, and the lubrication model of the cutting process is not yet clear.
(3) It is still necessary to carry out a large number of cutting performance tests and studies on different workpiece materials, select reasonable processing parameters and determine the optimal spray angle and flow rate.
5 gas jet cooling cutting
Gas jet cooling cutting is a cutting method in which a certain pressure of jet gas flushes the processing area to obtain a cooling effect. Japanese scholars have done more research work on this processing method. my country East China Shipbuilding Institute has also done research in this area and achieved good results. Studies have shown that gas jet cooling cutting has benefits in terms of cooling effect, workpiece machining quality and tool life. At present, domestic research on this technology is still in its infancy, and the following research work must be carried out:
(1) Optimized design of cutting parameters of gas jet cooling (including gas pressure, temperature, air flow velocity, nozzle diameter and spray direction, etc.).
(2) Analysis and research on the cutting mechanism of gas jet cooling.
(3) A large number of experimental studies on the gas jet cooling cutting performance of different workpiece materials are still needed.
6 Low temperature air-cooled cutting
Low temperature air-cooled cutting is a cutting technology that uses cold air of -10℃~-100℃ to wash the processing area during the process, thereby reducing the temperature of the tool and the workpiece. Its cutting system is mainly composed of cold wind generating device and cutting processing system. Japan’s research on this technology is earlier and the level of development is higher. In 1996, Prof. Kazuhiko Yokogawa began a comprehensive study of low-temperature air-cooled cutting. Domestic Chongqing University has also conducted such research and achieved certain results. Studies have shown that low-temperature air-cooled cutting can significantly reduce the temperature of the cutting zone, improve the wear resistance of the tool, extend the service life of the tool, improve the quality of the processed surface, and have no pollution to the environment.
There are still some problems in the research of this technology. First of all, low-temperature cold air cutting has different effects on different processed materials, and domestic research work in this area has been carried out less, lacking test data, and it is difficult to provide scientific and reasonable cutting parameters. Secondly, the cooling and lubrication system of this method is relatively complicated, which is not conducive to popularization and application. Third, this method only has a cooling function and no lubrication function (if a small amount of cutting oil is added to the cold wind, it can solve the problem of lubricity, but the
has a certain influence, which belongs to quasi-green cutting). In addition, the noise emitted during use is large. Finally, there is a lack of systematic experimental research on air-cooled cutting technology, and there is no quantification and optimization of a series of technical parameters. The cutting performance of different materials under different conditions needs further study.
Low-temperature air-cooled cutting technology has certain application prospects, but the following topics must be further researched and developed:
(1) Develop low-temperature air-cooling devices with low energy consumption, high efficiency, large adjustment range and no pollution.
(2) Conduct systematic research. A large number of experimental studies were conducted on the low-temperature cutting performance of different materials under different conditions, and the experimental data was collated and analyzed to prepare for the next study.
(3) Adjust the structure of the machine tool, improve the adaptability to the low-temperature air-cooling system, and promote the small-scale application of low-temperature air-cooling cutting technology in the machinery industry.
7Minimum lubrication (MQL) cutting
Minimal Quantities of Lubricant (MQL) cutting refers to a cutting processing method in which compressed air and a very small amount of lubricating fluid are mixed and vaporized and sprayed to the processing area for effective lubrication. It can greatly reduce the amount of cutting fluid (generally only 0.03 ~ 1.2L/h), can effectively reduce the friction between the tool and the workpiece, the tool and the chip, prevent adhesion, extend the life of the tool, and improve the quality of the processed surface. At present, this technology is mainly used for drilling, reaming, tapping, deep hole drilling, milling of aluminum alloy face, etc. of cast iron, steel and aluminum alloy.
During processing, the oil and gas mist formed in the air by the lubricating oil is harmful to the environment and human health. A joint study by Cicinati University and Techsolve Inc. in the United States shows that when milling and drilling AISI/SAE4340 steel parts at a dosage of 11ml/min and 6.5L/min on a TongilTNV-80CNC vertical machining center, the lower At the cutting speed and the metal removal rate, the generation rate of oil mist particles in the air caused by MQL is 340~3300 times that of the traditional pouring method when drilling, and 100~140 times when it is milling. Therefore, the use of MQL cutting technology must add closure, ventilation and air freshening facilities on the machine tool, which will inevitably bring some additional costs.
Combining the current research and development status, the following research directions of MQL cutting technology are proposed:
(1) In-depth study of the formation mechanism of oil mist particles, and put forward effective and practical protective measures. Through technical measures, the concentration of oil mist particles in the atmosphere is minimized to achieve quasi-green cutting that is harmless (or least harmful) to humans and the environment.
(2) Strengthen the design and research of MQL oil mist generating device. At present, most MQL devices use compressed air as the carrier of oil mist. It is difficult to control the size and distribution of oil mist particles. Therefore, the design of the transmission unit and the oil mist control port will be the focus of research.
(3) Because both cutting parameters and cutting speed will affect the generation rate of oil mist particles, a lot of research is still needed on the effect of cutting parameters on the generation rate of oil mist particles.
8 Conclusion
This article gives a systematic introduction and analysis of some common branch technologies in the field of green cutting technology. Among them, dry cutting, liquid nitrogen cooling cutting, steam cooling cutting, gas jet cooling cutting and low temperature air cooling cutting are all green cutting technologies; minimum lubrication (MQL) cutting technology and low temperature with a small amount of cutting oil added in cold wind Cold air cutting technology belongs to quasi-green cutting technology. Green cutting technology can improve the tool life and processing quality, and it has no pollution to the environment and harm to human health. It has achieved good results in practical applications and is the future development direction of the field of metal cutting. At present, high-speed (ultra-high-speed) dry cutting technology and the development of pollution-free ecological cutting fluid are the development priorities of green cutting technology. In the development process of manufacturing in the 21st century, green cutting technology will surely get faster development and wider application.