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According to statistics, the use cost of cutting fluid is quite expensive, adding up the cost of cutting fluid and related equipment, energy consumption, handling, labor, maintenance and materials to 7% to 17% of the total manufacturing cost. All tool costs are only 2% to 4% of the total manufacturing cost.
In 1996, the International Standards Association issued the ISO14000 series of standards for environmental management. Countries such as Germany, the United States, Canada and Japan have also developed more stringent industrial emission standards, further limiting the use of cutting fluids.
Faced with lower production costs, improved production conditions and sustainable development requirements for environmental protection, and more pressure from relevant laws, rational use of manufacturing resources, less waste, less environmental pollution, and a virtuous cycle of "green manufacturing" technology It will surely become the main development trend in the 21st century manufacturing field. 1 Principles and characteristics of green processing technology
In the process of searching for green processing technology to replace the original cutting fluid casting method, many beneficial attempts have been made to create a variety of representative cutting lubrication cooling technologies. Biostable cutting fluid, spray cooling, liquid nitrogen cooling , low temperature air cooling cutting, MQL and dry cutting. From the perspective of quality, efficiency, economy and environmental protection, each of these technologies has its own characteristics and superiority.
Dry cutting technology originated in Europe and is currently the most popular in Western European countries. LeBlond Makino Company of the United States has also developed a "red crescent" process for high-speed dry cutting of cast iron with ceramic tools and CBN tools and put it into actual production, which has achieved good economic benefits.
The implementation of dry cutting does not simply stop the use of cutting fluid. It is necessary to consider the entire process system including machine tools, workpieces, and especially tools. The new types of tools that are currently available (including tools with advanced materials, tools for coating treatment, and tools that optimize geometry and structure) provide a strong guarantee for dry cutting. Research on the properties of tool materials is also necessary. In fact, for ceramic tools, since dry cutting reduces the possibility of thermal shock and thermal fatigue, the processing effect is often better than ordinary wet cutting.
Dry cutting applications have been successful in cast iron materials, but their range is not yet extensive. Dry cutting of steel and difficult-to-machine materials is also being studied.
MQL technology combines compressed gas with a very small amount of lubricating fluid and then ejects it into the processing area to effectively lubricate the processed part between the tool and the workpiece. In Germany, there are still differences of opinion on whether it has a cooling function at the same time, and it is called micro-lubrication and micro-lubrication cooling, respectively.
MQL can greatly reduce the friction between “tool-workpiece†and “tool-chipâ€, which can suppress temperature rise, reduce tool wear, prevent sticking and improve the quality of workpiece processing. The lubricating fluid used is rare, but the effect is small. It is very remarkable, which not only improves the work efficiency, but also does not pollute the environment.
The amount of lubricating fluid used in the MQL method is very small, typically 0.03 to 0.2 L/h, and the amount of cutting fluid used in a typical machining center is as high as 20 to 100 L/min. Moreover, as long as the MQL technology is used properly, the processed tools, workpieces and chips are dry, avoiding the later processing. The clean and clean chips can be recycled after being compressed and completely polluted, so it is called quasi-dry. Cutting. 2 Research Status of MQL
Experiments show that MQL technology has different processing performance under different types and amounts of cutting fluid, different processing materials, different tools, different processing methods and different processing parameters.
The experimental results of drilling aluminum alloy with the amount of vegetable oil of 20ml/h show that under low speed and low feed, MQL has less cutting effect than casting; at higher cutting speed and higher feed, the effect of MQL It is better than casting.
When milling ASSAB 718 HH steel with 8.5ml/h BP CILORA 128 (high viscosity) cutting fluid, MQL technology greatly reduces cutting force at low speed, low feed, and low depth of cut compared to conventional cast cutting. The flank wear is reduced, the quality of the machined surface is improved, the concentrated thermal stress in the chip is avoided, and the weight and length of the burr are reduced.
When the S45C steel is turned at a normal speed of 9.6 ml/h of a certain water-soluble oil, the MQL achieves the same level of conventional cast cutting in suppressing tool wear, improving surface roughness, and controlling built-up edge formation. If a cutting fluid containing an extreme pressure agent is used, the tool wear can be more effectively extended.
When the medium carbon steel was turned at a normal speed of 200 ml/h, the results showed that MQL was better than cast cutting at low speed and high feed. It not only reduces the cutting force and feed force, but also reduces the variation of the cutting force, thus reducing the wear of the tool due to vibration during cutting. The quality of the machined surface has been improved and the thickness of the chips is also greater than the thickness of the chips under cast cutting.
The combination of MQL technology and coated tools enables the best results. When X90GrMoV18 alloy steel was processed using a high speed steel coated drill, a through hole having a diameter of 8.5 mm and a length of 25 mm was machined at a cutting speed of 30 m/min and a feed rate of 0.1 mm/r. When using pure TiAlN coated high speed steel Drill Bits for pure dry drilling, the drill bit is damaged after drilling a cutting length of 3.5 m; with a (TiAlN+MoS 2 ) composite coated drill bit and minimal lubrication, the drilling length is increased to 115 m.
The experimental results of cutting high-silicon aluminum alloy parts and stainless steel by MQL combined with low-temperature air-cooling technology show that this method can prolong the service life of the tool, inhibit the formation of built-up edge, improve the surface precision, and eliminate waste liquid and Waste treatment system to reduce production costs and prevent environmental pollution.
The experimental results of continuous turning stainless steel with MQL combined with water mist (cooling) composite spray lubrication cooling method show that this method can effectively play a role in the continuous cutting of difficult lubrication in the cutting zone, which can improve the quality of the machined surface and reduce tool wear. Moreover, the lubrication and cooling effects can be adjusted at any time by changing the amount of oil mist and water mist in the spray. 3 Practical application of MQL
At present, MQL technology is mainly used for drilling, reaming and tapping on cast iron, steel and aluminum alloy, as well as deep hole drilling and face milling of aluminum alloy.
Tbyssen in the United States integrates the lubrication system into the main shaft. The flow rate is controlled by the CNC program. The unit can drill 10 holes with a diameter of 8mm and a center distance of 20mm in 6.5s, using a cup of lubricating oil per hour. Part of it is evaporated, and the amount of cutting fluid in the chips is greatly reduced, so the processing cost is greatly reduced.
a. automobile manufacturing b. auto parts industry c. machine tool manufacturing d. handicraft industry e. other industries f. high speed machining milling machine g. machining center h. special plane i. universal machine tool k. other machine tools
Figure 1 Application status of micro-lubrication
In Germany, the MQL plant has 15,000 sets of markets per year in recent years (see Figure 1) and will increase further. The combination of MQL and new tools is also in the ascendant. It can be predicted that in the next two or three years, 5% of the German-made machining centers will use MQL combined with lubricated coated tools to replace cast cooling. 4 MQL environmental and economic performance evaluation
In many metal processing, oil lubricants are strongly agitated to form contaminated oil and gas mist in the air of the workshop. The additives, microorganisms and other components in the lubricant may also be inhaled by the operator after atomization. Respiratory system, digestive system cause harm, and may even cause cancer; in addition, oil mist will form a layer of adhesive on the upper part of the plant, causing trouble for daily maintenance. Therefore, it is necessary to study the concentration of air oil mist particles caused by different processing methods.
The traditional pouring method is different from the concentration of oil mist particles in the air caused by MQL. A joint research project between the University of Cicinati and Techsolve. Inc. in the United States conducted a comparison of the concentration of airborne oil mist particles produced by MQL and cast cutting, at 11 ml/min and 6.5 l/min respectively at the Tongil TNV-80CNC vertical machining center. The amount of AISI/SAE 4340 steel was drilled and milled. The results show that the oil mist particle generation rate (the amount of particles produced per minute) caused by the MQL method at lower cutting speed and metal removal rate is 340 to 3300 times that of the conventional casting method at the time of drilling; It is 100 to 140 times. At higher speeds and metal removal rates, this ratio will be greater.
In addition, the oil mist particle formation rate of different cutting fluids is also different. Under the same conditions, the production rate of oil mist particles of pure synthetic liquid is much higher than that of water-soluble cutting fluid, and even the concentration of airborne oil mist in the workshop exceeds the current OSHA (Occupational Safety and Health Administration) and NIOSH (National Institute for Occupational Safety and Health) regulations. Standard.
Compared with the traditional casting cutting method, MQL can greatly reduce the amount of cutting fluid, avoid the disposal of waste liquid, reduce the processing cost (including the purchase cost of cutting fluid, storage cost and waste disposal cost, etc.), and under certain conditions. Can achieve equal or even better processing performance. It marks a crucial step in getting rid of traditional cast machining. However, it also faces its own inherent challenge of eliminating the odor, bacteria and enzymes caused by traditional cutting fluids, while at the same time causing a rapid increase in the concentration of oil mist particles in the processing area. The environment and health have adversely affected. In addition, due to the high amount of oil mist particles generated, the machine tool using MQL processing method must have closed, suction ventilation and air freshening facilities, which brings additional cost to MQL processing. 5 MQL issues to be further studied
6 Summary
Many of the technologies emerging during the green cutting research process are a major innovation in traditional production methods. As one of the important branches of these technologies, MQL can greatly reduce friction, suppress temperature rise, reduce tool wear, prevent adhesion and improve the quality of workpiece processing. The use of lubricating fluid is rare, the effect is very significant, which not only improves the work efficiency, but also It will pollute the environment. MQL will be more widely valued and promoted due to its own superiority.
In the field of mechanical manufacturing, cutting fluids used in cutting (grinding) are important for improving machining efficiency and processing quality, but cutting fluids cause serious pollution to the environment during various periods of manufacture, use, handling and discharge. After the completion of the machining process, so-called "secondary effect" contamination occurs when the cutting fluid deposits on the surface of the part are removed.