Definition Dry cutting is a method of cutting machining without cutting fluid and without cutting fluid in order to protect the environment and reduce costs. Dry cutting is not simply to stop using the cutting fluid, but to ensure high efficiency, high product quality, high tool durability and reliability of the cutting process while stopping the use of cutting fluid. This requires dry cutting with excellent performance. Tools, machine tools, and ancillary equipment replace the role of cutting fluid in traditional cutting to achieve true dry cutting.
Background of dry cutting technology First of all, to understand the role of cutting fluid in the traditional cutting process. Cutting fluid is usually one of the indispensable production factors in most machining, and plays an important role in ensuring machining accuracy, surface quality and production efficiency. As global environmental awareness increases and environmental regulations become more stringent, the negative effects of cutting fluids on the environment are becoming more apparent. According to statistics, 20 years ago, the cost of cutting fluid was less than 3% of the cost of the workpiece. At present, in high-productivity production enterprises, the cost of cutting fluid supply, maintenance and recycling costs together account for the manufacturing cost of the workpiece. 13%-17%, while tooling costs only 2%-5%. About 22% of the total cost associated with cutting fluids is the processing cost of cutting fluid. It is estimated that if 20% of the cutting process uses dry machining, the total manufacturing cost can be reduced by 1.6%. Green manufacturing that is environmentally friendly is considered a modern manufacturing model for sustainable development. Dry cutting without any cutting fluid in the process is a green manufacturing process to control the source of environmental pollution. It can obtain clean, non-polluting chips, eliminating the need for cutting fluid and its processing, etc., which can be further reduced. Production cost 3. Therefore, the direction of future machining is to use or use as little cutting fluid as possible. With the development of high temperature tool materials and coating technology, dry machining has become possible in the field of machine building. DryCutting technology came into being under such a historical background and has developed rapidly since the mid-1990s. Its development history is only ten years, and it is a frontier research topic of advanced manufacturing technology.
Generally, the cutting fluid has three main functions of cooling to remove the heat generated by cutting, reduce tool wear and prevent oxidation of the surface of the workpiece;
Lubrication reduces friction, reduces cutting force, and ensures smooth cutting;
The chip removal quickly removes the chips from the surface of the workpiece and prevents the chips from scratching the surface of the workpiece.
However, from the perspective of environmental protection, the negative effects of cutting fluid are becoming more and more obvious, mainly in the following aspects:
1) The high temperature generated during the process causes the cutting fluid to form a hazy volatilization, pollute the environment and threaten the health of the operator;
2) Certain cutting fluids and adhesive tapes The cutting chips of the cutting fluid must be treated as toxic and hazardous materials, and the processing cost is very high;
3) Leakage and overflow of cutting fluid have a great impact on safe production; 4) Additives of cutting fluid (such as sulfur, chlorine, etc.) will cause harm to the operator's health and affect the quality of processing.
In addition, a large number of studies on the cutting process have also shown that the traditional cooling, lubrication and chip evacuation of cutting fluids are not fully and effectively utilized in many machining processes, especially in high-speed cutting. Therefore, attempts have been made to change this condition with or without cutting fluids to accommodate clean production processes and reduced production costs. Dry machining technology is an advanced processing method produced in this case. The dry cutting technology not only reduces the environmental pollution of the cutting fluid, improves the working conditions of the operator, but also saves the cost associated with the cutting fluid and reduces the cost of the chip recycling process. Dry cutting technology places higher demands on machine tools and tooling technology. In recent years, industrialized countries have paid great attention to dry cutting research. Dry cutting This new processing method is one of the development trends of metal cutting in the future.
Dry cutting features
(1) Chips are clean, clean, non-polluting, easy to recycle and handle
(2) Eliminating the cutting fluid transfer, recovery, filtration and other equipment and corresponding costs, simplifying the production system and reducing production costs
(3) The separation device for cutting fluid and chips and the corresponding electrical equipment are omitted. Compact machine structure, reducing floor space
(4) No environmental pollution
(5) There will be no safety accidents or quality accidents related to the cutting fluid.
Dry cutting implements dry cutting tool technology (1) The tool should have excellent heat resistance (high temperature hardness) and wear resistance
(2) Minimize the friction coefficient between the tool and the chip
(3) Reducing the dependence on cutting fluid chip removal
The cutting machine technology of dry cutting has a rapid heat transfer and the discharge of chips and dust.
The dry cutting process technology should pay special attention to the reasonable matching between the tool material and the workpiece material.
With the new tool materials for more than a decade, the emergence of high-hardness materials has made it possible for dry cutting. Dry cutting requires not only high hardness and thermal toughness of the tool material, but also good wear resistance, thermal shock resistance and adhesion resistance. The tool materials currently used for dry cutting are mainly ultra-hard materials such as ultra-fine cemented carbide, ceramics, cubic boron nitride and polycrystalline diamond. Figure 1 shows the hardness versus temperature for several tool materials. Ultra-fine cemented carbide can improve the toughness of ordinary cemented carbide, has good wear resistance and high temperature resistance, and can produce deep hole drills and inserts with large rake angles for dry machining of milling and drilling. Ceramic knives (Al203, Si3N4, cermet (Cennet) and other materials have little hardness at high temperatures, that is, they have good red hardness, so they are suitable for general purpose dry cutting without coolant [1131. But this The materials are generally brittle, that is, the thermal toughness is not good, so it is not suitable for interrupted cutting. That is to say, ceramic tools are more suitable for dry turning and not for dry milling. Cubic boron nitride (CBN) materials High hardness, up to HV3200~HV4000, second only to diamond, good thermal conductivity, up to 1300W/MK, good high temperature chemical stability, good thermal stability at 1200 °C. Casting cast iron with CBN tool can greatly improve Cutting speed for machining hardened steel, which can be replaced by turning. Polycrystalline diamond (PCD) tool has very high hardness, up to HV7000~HV8000, thermal conductivity up to 2100 W/MK, and small linear expansion coefficient. The heat generated during cutting can be quickly transferred from the tool tip to the tool body, thus reducing the machining error caused by the thermal deformation of the tool. PCD tools are more suitable for dry machining of copper, aluminum and aluminum alloy workpieces.
Coating the tool with coating technology is an important way to improve tool performance. In the past decade, tool coating technology has developed very rapidly, with up to 15 coating materials and some tools with up to 13 layers on the body. The coating process is also becoming more and more mature. With the development of technology, the technical problem of low bonding strength between the coating and the base material has been solved. There are two main types of coated tools: one is “hard†coated tools such as TiN, TIC and Al203. These tools have high surface hardness and good wear resistance. Among them, the TIC coated tool is particularly resistant to flank wear, while the TiN coated tool has a higher resistance to "crater" wear. The other type is "soft" coated tools such as MOS2, WS and other coated tools. This kind of coated tool is also called “self-lubricating toolâ€, and its friction coefficient with the workpiece material is very low, only about 0.01, which can effectively reduce the cutting force and reduce the cutting temperature. For example, the "MOVIC" coated tap developed in Switzerland is coated with a layer of MOS2. Cutting experiments show that uncoated taps can only process 20 tapped holes; 1000 tapped holes can be machined with TiAlN coated taps, while MoS2 coated taps can process 4000 tapped holes. High speed steel and cemented carbide can be used for dry cutting after PVD coating. CBN tools that were originally only suitable for dry cast iron castings can also be used to process steel, aluminum alloys and other superhard alloys after coating.
In fact, the coating has a function similar to a coolant, which creates a protective layer that isolates the tool from the heat of cutting so that heat is rarely transferred to the tool, thus keeping the tip hard for a longer period of time. And sharp. Smooth surface coatings also reduce friction to reduce cutting heat and keep tool materials from chemical reactions, as high temperatures have a large catalytic effect on chemical reactions in most high-speed dry cutting. TiAlN coating and Mo2 soft coating can also be alternately coated to form a multi-coated tool, which has the characteristics of high hardness and good wear resistance, small friction coefficient and easy chip flow, and excellent alternative cooling. The function of the liquid. Tool coating plays a very important role in dry cutting technology.
Tool geometry design Dry-cutting tools typically have crater wear as the primary cause of failure because there is no cutting fluid in the process and the temperature of the tool and chip contact area increases. Therefore, it is usually necessary to have a large rake angle and a blade inclination angle, but the blade edge strength is affected after the rake angle is increased. In this case, a suitable negative chamfer or rake face reinforcement unit should be provided, so that the tool tip and The cutting edge will have sufficient volume of material and a reasonable way to withstand cutting heat and cutting forces, while reducing the adverse effects of impact and crater expansion on the tool, allowing the tool tip and cutting edge to remain adequate for longer cutting times. Structural strength. In recent years, many large-angle turning inserts have been developed abroad (such as the front angle of a ME-13 new carbide insert introduced by Carboloy in the United States up to 34°) and a spiral-edged milling insert with a positive rake angle ( The blade has a nearly constant rake angle along the cutting edge, and the back rake angle or side rake angle can be changed from negative to small or from small to large), aiming to reduce the driving power of the machine tool and reduce the cutting force by reducing the cutting force. Temperature to meet the tool requirements for dry cutting.
Mitsubishi Metal Corporation of Japan has developed a "slewing turning tool" for dry cutting. The tool uses a circular super-hard blade. The supporting part of the blade is equipped with a bearing. During machining, the blade can automatically rotate, so that the cutting edge is always maintained. Sharp, with high work efficiency, good processing quality, long tool life and so on.
There is also a heat pipe cutter that also achieves an ideal dry cut. Their structure is basically the same as that of a conventional turning tool, except that a heat pipe is formed inside the shank body. The working medium in the heat pipe is generally acetone, ethanol and distilled water. The heat pipe is a highly efficient heat transfer element that utilizes the two strongest heat transfer mechanisms, boiling heat absorption and condensation heat release. The heat conductivity of the heat pipe is several hundred times that of silver and copper rods. The heat pipe tool is a self-cooling tool, so there is no need to cast the cutting fluid from the outside, especially for CNC machine tools, machining centers and automatic production lines.
The role of dry cutting in the field of gear processing The key to dry cutting in gear machining is to find a way to replace cooling and lubrication. At present, there are two successful dry cutting methods: high speed dry cutting and low temperature cold cutting.
High-speed dry cutting method This processing method uses a high cutting speed for cutting without the action of cooling or lubricating oil. Dry cutting must use the appropriate cutting conditions. First, use a high cutting speed to minimize the contact time between the tool and the workpiece, and then use compressed air or other similar methods to remove the chips to control the temperature of the working area. With the extensive use of CNC technology, the rigidity and dynamic performance of machine tools are constantly improving, and it is not difficult to increase the cutting speed of machine tools. Practice has shown that when the cutting parameters are set correctly, 80% of the heat generated by cutting can be carried away by the chips.
The high-speed dry cutting method has the following advantages: First, because it eliminates the oil chip separation process, the cooling oil tank and the oil chip separation device, and the corresponding electrical equipment, the machine tool is compact. Secondly, this method greatly improves the processing environment; processing costs are also greatly reduced. In order to further extend the tool life and improve the quality of the workpiece, 10 to 1000ml of lubricating oil per hour can be used for minor lubrication during dry gear cutting. The chips produced by this method can be considered as dry chips. The accuracy, surface quality and internal stress of the workpiece are not adversely affected by the micro-lubrication. Process monitoring can also be carried out with automatic control equipment.
High-speed dry cutting has strict requirements for the knife: 1 The tool should have excellent high temperature resistance and can work without cutting fluid. New types of cutting materials such as cemented carbide, polycrystalline ceramics and CBN are the materials of choice for dry cutting tools; 2 the coefficient of friction between the chips and the tool should be as small as possible (the most effective method is the surface coating of the tool), supplemented by Good chip removal structure and reduced heat accumulation; 3 dry cutting tools should also have higher strength and impact toughness than wet cutting tools.
Low-temperature cold-air cutting This cutting method is a processing method in which cold air of -10 to -100 ° C and very small amount of vegetable oil are used instead of cooling and lubricating oil cooling. It was first proposed by Yokokawa Kazuhiko of Meiji University in Japan. It has been found that in the metal cutting process, if only a very small amount of vegetable oil with good lubricating effect and unoxidized is supplied to the processing point, the processing point will lose lubricity due to high temperature. If cold air is supplied to the processing point (-10 to -100 °C), the high temperature of the processing point can be prevented and the above situation can be avoided.
The cutting performance is greatly improved during cold air cutting. Tests have shown that cold air cutting and grinding are more than twice as efficient in performance as oil cutting and grinding. Comparison of cutting performance with and without vegetable oil cutting agent and cold air. It can be seen that the use of cold air cutting is better than the use of plants, and the cutting performance of the tool is further enhanced when cold air is used together with trace vegetable oil. Cutting conditions during the test: workpiece diameter: f92 ~ f98mm, cutting speed: 45.1 ~ 48.0m / min, feed: 0.5mm, cutting tool: tool nose radius R0.4, equivalent to SKH4 high speed steel, no re-grinding blade.
The new carbide coating method and the use of CNC machines have led to a new trend in the manufacture of cylindrical gears: high-speed cutting of carbide-free tools without cooling. If the process parameters are optimally set, the machining time is short and the tool life is longer. Japan's Mitsubishi Corporation, the US Gleason Corporation, etc. have carried out fruitful research in this regard. Japan's Mitsubishi Corporation introduced the world's first dry hobbing system. It uses a cutting speed that is twice the speed of conventional hobbing and can reach 200m/min. Dry hobbing has special requirements for hobs. Mitsubishi's special dry hobs are made of MACH7 high-speed steel. The surface is coated with a special coating to help dissipate heat and reduce tool loss. Its life can be extended to general wetness. 5 times the cutting method. This system is ideal for processing automotive final drive gears, large load gears, automotive pinions and planetary gears, reducing production costs by at least 40%.
Gleason uses a hard-metal hob to machine bevel gears on a Phoenix machine with dry-cutting. Compared to conventional high-speed steel tool wet cutting, the cutting time is reduced by 50% and the surface roughness of the gear is significantly reduced. And the geometric precision is also greatly improved, and the machining accuracy can reach AGMA 12-13. The company's GP series gear hobbing machine, with its unique design, makes its dry cutting quality comparable to wet cutting quality. The bed is designed as a large angled slope to facilitate chip flow. The inside of the bed is circulated and cooled to help maintain heat balance. In addition, the machine is equipped with a vacuum dedusting and dust removal system. This series of hobbing machines can achieve a rolling speed of up to 3000r/min.
LMT-Fette uses a carbide cutter to dry-roll the gears, which significantly reduces the processing time and cost of the gears. The KC250H dry hobbing machine developed by Japan's Kento Iron Works uses carbide carbide hob, cold air cooling and micro-lubrication to perform high-speed hobbing. Due to the supply of cold temperature with stable temperature, the thermal deformation of the workpiece is extremely small. Compared with the traditional high-speed steel hob KA220 wet hobbing machine, the processing speed is increased by 3.2 times and the gear precision is also significantly improved.
Current Status of Dry Cutting Technology Dry cutting technology is a green cutting technology developed to meet the world's rising environmental requirements and sustainable development strategies. The scientific significance of dry cutting was officially established in 1995. At the 1997 International Conference on Production Engineering (CIRP), Professor F. Klocke of the Aachen University of Technology in Germany gave a keynote report on “dry cuttingâ€; in January 1999, At the meeting of the recipients of the National Science Foundation's “Design and Manufacturing Disciplineâ€, Dr. BPErdel, President of the internationally renowned tool manufacturer MAPAL, also gave a keynote report on the development of dry cutting in the United States. Dry cutting technology has been in various industries and academics in various countries. The community has caused widespread concern. At present, industrial developed countries including Europe, the United States and Japan attach great importance to the research of dry cutting. Dry cutting technology has been successfully applied to the production field, which has a certain relationship with the strong industrial base and strict environmental regulations of these countries. Among them, German companies are particularly popular. In mass production, 10%-15% of the processing uses dry cutting technology and has achieved good economic benefits. Many well-known machine tool manufacturers in the world have dry cutting in their catalogue. Machine tool machining center. Japan has also conducted extensive research on dry cutting, and recently they have developed several dry machining centers that do not use cutting fluids. On one of the machines, a dry cutting system with liquid nitrogen cooling is used to extract high purity nitrogen from the air. The liquid nitrogen is sent to the cutting zone at a normal temperature of 5-6 atmospheres, and dry cutting can be smoothly performed. Research on dry cutting technology in China has also started. Chengdu Tool Research Institute, Shandong University of Technology and Tsinghua University have systematically studied superhard tool materials (such as ceramics, cubic boron nitride, diamond, etc.) and tool coating technology, and have achieved many research results. China's ceramic tools have formed a certain production capacity, which provides a preliminary technical basis for the research and application of dry cutting technology. The KT series machining center developed by Beijing Machine Tool Research Institute can realize high-speed dry cutting. However, in general, China still has a large gap in the research of dry cutting theory and abroad. The scale of application in industry is smaller, and we need to accelerate research and popularization and application in the future.
Dry cutting development prospect
The ISO and JIS14000 series of standards were established in 1996, respectively, which have strict regulations on environmental management and monitoring. Their implementation is undoubtedly another challenge to the export of China's machine tool products. In order to improve the technical content and technological innovation capability of our products, it is necessary and urgent to carry out research and development of dry cutting technology in the invincible position in the international market competition. Compared with wet processing, dry processing not only improves production efficiency, reduces production costs, but also contributes to environmental protection. It is an ideal and clean metal cutting method. Dry cutting technology has been in existence for less than a decade, and it is an emerging green manufacturing technology. In the 21st century, the manufacturing industry is increasingly demanding green environmental protection. Dry cutting technology as a green manufacturing process is of great significance for saving resources, protecting the environment and reducing costs. With the rapid development of machine tool technology and various super-hard and high-temperature tool materials and coating technology, as well as the deepening of related process research, dry cutting technology will be widely used in the field of metal cutting.
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