Textile Auxiliary, Plastics Additives, Coating Additives Dynasty Chemicals (NingBo) Co., Ltd. , http://www.dychemco.com 1 Factors affecting dry machining
Dry cutting refers to a process in which cutting fluid is not used in machining. It eliminates a series of environmental negative effects caused by cutting fluid from the source, and has the following characteristics: (1) the formed chips are clean, non-polluting, easy to recycle and handle; (2) the supply related to cutting fluid is omitted. The purchase and maintenance costs of the relevant equipment such as recycling and filtration, as well as the costs associated with the processing of chips and cutting fluids, simplify the production system and save production costs; (3) The plant does not need to bear the pollution of cutting waste liquid without polluting the environment. Responsibility, there will be no safety and quality accidents associated with cutting fluids. 
However, if the cutting fluid is not used during machining, the cutting state will be further deteriorated, that is, the cutting temperature will increase, the friction between the tool/chip and the tool/work surface will be further aggravated, the chip removal will be poor, the tool life will be reduced, and The surface quality of the machined surface deteriorates. Therefore, in order for the dry cutting process to proceed smoothly, it is necessary to seek a technical solution that can make up for the main function of the cutting fluid. This requires careful analysis of various specific boundary conditions and complex factors affecting dry machining (drawings). 2 Measures to achieve dry machining
Developing tool materials for dry machining is one of the keys to its successful application. In dry machining, the cutting speed is higher than that of ordinary machining, which can accelerate chip evacuation and heat dissipation, thereby improving tool life and increasing the heat resistance of the tool. However, in high-speed cutting, a large amount of heat is generated in the cutting zone. The larger the amount of cutting, the higher the temperature in the cutting zone. Conventional methods generally require coolant cooling. However, using new tool materials and selecting reasonable cutting parameters, It can withstand high temperatures during cutting, perform high-speed cutting, and transfer most of the heat generated to the chips for dry cutting.
Dry cutting tool materials must have excellent thermal properties. Commonly used are bonded hard alloys with high hardness and good wear resistance, coated cemented carbide, ceramics, coated HSS, diamond and cubic boron nitride ( CBN) and so on. In recent years, 20% to 30% of SiC whiskers have been added to the Al 2 O 3 matrix to form a "whisker toughened ceramic". SiC whisker acts like a steel bar in reinforced concrete. It can be an obstacle to block or change the direction of crack development, and greatly improve the toughness of the tool. It is a promising dry cutting tool material.
Appropriate tool coating not only enhances the heat resistance of the tool, reduces the friction coefficient between the tool/chip and the tool/work surface, reduces tool wear, but also reduces cutting force and cutting temperature, improves tool life, and improves machining. Surface Quality. Therefore, the development of tool coating technology is also one of the keys to achieving dry machining.
At present, the main development trend of dry cutting tool coating technology: First, the use of "soft" coating, such as the "MOVIC" soft coating process developed by Guhring in Germany, is to apply a layer of solid lubricant - MoS 2 on the surface of the tool The surface of the coated tool has a lubricating function, which can reduce the friction between the chip and the tool during processing, avoid the formation of built-up edge and improve the tool life. Tests have shown that dry tapping is performed on aluminum alloys containing 9% Si. Uncoated taps can only process 20 holes, TiAlN coated taps can process 1000 holes, and MOVIC coated taps can process 4000 holes. The second is to use a soft/hard combination coating, that is, first apply a "hard" coating (such as TiN) on the tool, and then apply a "soft" coating (such as MoS 2 ). For example, a drill with a (Ti, Al)N+MoS 2 coating is used to drill deep holes in the gray cast iron engine block, the tool life is up to 1600 min, and the life of the drill coated with TiN or TiCN only is 19.6min and 44min.
The optimization of the tool geometry is very important in dry machining. Dry cutting is not recommended for standard tools. For this dry machining, the optimum tool geometry should be selected to reduce the friction between the tool and the chips during machining. Tool geometry optimization should be done: first, reduce the contact area between the tool/work surface, such as the drill should reduce the reverse cone and helix angle; second, consider the maximum lubricity of the tool surface to prevent the formation of built-up edge.
In addition, in the dry cutting process, the cutting edge of the fine-grained high-quality carbide tool and the diamond tool can be slightly lightly passivated, and the sharpness of the cutting edge is maintained by the strength of its own base body, thereby achieving the purpose of reducing the cutting temperature. This not only maintains the high performance of the tool, but also maintains the optimum service life of the tool.
In the case where dry cutting cannot be fully realized, the "Minimal Quantities of Lubricant (MQL)" technique can be used to minimize the amount of cutting fluid used. MQL is also called Near Dry Cutting. Here, the "minimum amount of cutting fluid" refers to the supply of cutting fluid with a small amount of cutting fluid (when the machine is working under optimal conditions, the cutting fluid consumption should be below 50mL / h, and the cutting fluid is cooled by normal jet cooling) Consumption may exceed 6L/min).
MQL technology mainly has two modes: aerosol external lubrication and internal cooling: the external lubrication method of the aerosol is to send the coolant into the jet cooling system to mix with the gas, and atomize to a nanometer gas through a multi-head nozzle under high pressure. The mist is continuously sprayed onto the surface of the tool to cool and lubricate the tool. The internal cooling method is to directly cool the cooling mist through the spindle and the tool into the cutting area to cool and lubricate it. According to the processing needs, the internal and external aerosols can be used together with two cooling and lubrication methods, and the effect will be better.
The biggest benefit of MQL technology is that if the tool is properly used, the tools, workpieces and chips can be kept dry, which avoids the hassle of waste disposal, so it is reasonable to call this technique “dry cuttingâ€. 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.
Dry cutting Because hot cutting fluid is not used, hot chips tend to stay in the cutting zone, increasing the heat of the workpiece, tool and machine tool. If the heat is too large, it will cause the workpiece to harden and the tool to deform, causing cracks on the surface of the workpiece. Therefore, chip evacuation becomes a major problem. However, with the development of processing technology, the use of reasonable processing methods can also solve the problem of chip removal. For example, the conventional drilling method from top to bottom can be carried out by drilling from the bottom to the top, and the cutting fluid can be used to assist the chip removal without a certain pressure. In addition, the suction system can be used to absorb lubricating aerosols, gases and chips in the cutting zone; the use of a jet system can also improve the chip evacuation conditions. In some cases where it is not possible to completely remove chips, an automatic and manual combination of chip removal methods can also be used.
In addition to the above methods, other measures can be taken: such as selecting reasonable cutting parameters; improving the design and manufacturing capabilities of the tool, because the complex tool geometry can solve the problem of chip removal in the closed space and reduce the cutting force; The use of new machines with fast and efficient chip evacuation, as well as the development of machine tools dedicated to dry machining. 3 Application of dry cutting technology
Dry cutting used to be a controversial method of processing, but with the development of tool materials, coating technology, tool structure and process equipment, and legal and market requirements, the United States, Germany, and Japan have conducted extensive research and Applied to actual production, it has achieved obvious economic and social benefits.
The "Red Crescent" cast iron dry cutting technology developed by LeBLond Makino in the United States is a high-speed machining using ceramic or CBN tools. Due to the high cutting speed and feed rate, the generated heat is quickly collected at the front end of the tool, so that the workpiece material at that place reaches a red hot state, and the yield strength is lowered, which can greatly improve the cutting efficiency. Generally, the metal removal rate (turning) of cast iron is 16 cm 3 /min, and the dry cutting of the red crescent can increase it to 149 cm 3 /min. The company also invented a patented process for dry turning of hardened steel (>50HRC) and titanium alloys with a carbide cutting tool at a cutting speed of 305 m/min. The cutting heat is carried away by the high-pressure cooling gas passing through the main shaft. The cutting temperature can be minimized and the tool-to-work contact can be limited to 25% per revolution.
Japan's Syun-ichi Yamagata has developed a dry extrusion tap for steel that significantly improves tap life compared to conventional wet extrusion taps. If the M4×0.7 through-hole thread on the cold-rolled steel plate is processed by ordinary extrusion tap, when the machining is about 7,000 holes, the cutting part of the tap will wear and bond, so that the cutting cannot be continued; and the dry extrusion tap processing is used. More than 50,000 holes will not cause bonding and significant wear, and the taps will continue to be used. The results show that the dry extrusion tap can increase the tool life by several times or ten times compared with the conventional extrusion tap.
Germany Guhring has carried out high-speed dry drilling processing on aluminum parts in engines, which has achieved remarkable economic benefits and established a good corporate environmental image. In addition, Germany, Finland, the United Kingdom and other high-speed gear dry hobbing, dry boring and other processing methods have also been studied, and have been applied in production, and achieved good results.
At present, the dry cutting in China is mainly the traditional cast iron milling process, and the research and application of the dry machining methods for other cutting processes are still very small.
Dry cutting and its measures
The use of cutting fluids must comply with environmental requirements. For this reason, a lot of exploration and research have been carried out, such as developing new cutting fluids, strengthening cutting fluid management, using cutting waste treatment technology and improving cooling methods, in an attempt to reduce the use of cutting fluids. The adverse effects brought about, but failed to achieve very satisfactory results. Dry Cutting (Dry Cutting) is a feasible method to fundamentally eliminate the disadvantages caused by traditional cutting fluids. Based on the current domestic and international experience in dry machining technology, this Paper analyzes the factors affecting dry machining. On this basis, it discusses some measures to achieve dry machining. Finally, it briefly introduces the research on dry machining at home and abroad. Application.