Metal cutting is the use of tools to remove excess metal material from the workpiece surface, thereby obtaining a processing method that meets the requirements in terms of geometry, dimensional accuracy, surface roughness and surface layer quality. The core problem is the interaction between the cutting part of the tool and the surface layer of the workpiece, that is, the cutting action of the tool and the reverse cutting action of the workpiece. This is the main contradiction in the cutting process, and the cutting action of the tool is the main aspect of the contradiction. The use of new tools to achieve efficient, high-quality, low-cost production is an important way for modern companies to increase economic efficiency. The improvement of tool materials is the main line of development of cutting tool technology. On the basis of the existing tool materials, it is also an effective method in the production practice to improve the cutting status through tool geometry design. A study published by the CIRP stated: “With the improvement of tool materials, the allowable cutting speed of the tool has been doubled every 10 years. With the improvement of tool structure and geometric parameters, the tool life has almost doubled every 10 years. "The use of new tool materials can improve the cutting performance of the tool, while optimizing the geometry of the cutting part of the tool can give full play to the power of new materials. Modern tools should not only meet the needs of advanced cutting technologies such as high-speed cutting, dry cutting, hard cutting, and composite cutting, but also have a higher level of versatility, rationalization of the structure, aesthetic appearance, and appearance. Claim. However, it is regrettable that the tool design has mainly depended on experience and tried-and-error methods for a long time. This method is inefficient and has a long development cycle. Obviously, it has hindered the development and use of new tools, and it cannot meet advanced requirements. The demand for cutting technology urgently requires advanced tool design techniques. The innovations in tool structure, tool material, and coating technology are driving the rapid development of cutting technology. This article introduced the new progress of tool structure design, tool materials and tool coating technology, pointed out the direction of advanced tool development, in order to promote the development and rational use of advanced tools, to play a due role in improving the processing efficiency of the manufacturing industry. Tool Structure Design Technology Tool structure design features difficult spatial calculations, complex shapes and difficult drawings, and the same shape and size. With the high development of powder metallurgy technology, mold manufacturing technology, and 5-axis linkage CNC grinding technology, the cutting part of modern metal cutting tools can be processed into very complex shapes. Therefore, the tool manufacturers continue to innovate, use advanced design techniques and professional application software for tool design.
Many of the complex shapes of knives are encountered in large quantities in production. For chip breaking, the cutting portion of the indexable insert is also designed to have a complex shape of the cutting edge and the chip breaker. In order to create a three-dimensional model of a complex-shaped tool, researchers have adopted two modeling methods: one is the synthesis method, that is, the equivalent blade method; the other is the decomposition method, that is, the differential blade method, and computer-aided design (CAD) technology Applied to the design of the tool. At present, the most widely used CAD software is UG, Pro/E, I-DEAS, etc. Some CAD software has undergone secondary development of the enterprise, and its applicability has been further improved. These software integrate three-dimensional solid modeling, plane drawing, engineering analysis, numerical control processing, component assembly and other modules to form a complete tool design software system, with strong solid modeling and programming functions. Computer-aided design makes the design and calculation of the tool simple, eliminating the need for drawing complicated drawings of the tool, and it can parametrically design the tool quickly, which is beneficial to improving the design level of the tool. Application of engineering analysis technology (such as finite element) to numerical simulation analysis of tool strength, can accurately grasp the force of each point on the tool, understand the internal stress, strain and temperature distribution of the tool, obtain stress, strain and temperature distribution Map and easily find out the danger points. The method can provide theoretical basis for improving the force condition of the tool, designing the tool structure reasonably and failure analysis of the tool, and providing a new method for the analysis and calculation of the tool strength and life. With the rapid development of the manufacturing industry, the high-tech industry sectors such as the automotive industry, aerospace industry, and mold and die industries have constantly put forward higher requirements for cutting and processing, and have promoted continuous innovation in the tool structure. The special tool sets developed for the automotive industry assembly line have become an important process factor that revolutionizes the processing technology, increases the processing efficiency, and reduces the processing cost, playing an important role. The development of the mold industry has promoted the continuous emergence of highly efficient machining tools such as multi-function face milling cutters, various ball-end milling cutters, modular end mill systems, plunge milling cutters, and large-feed milling cutters. In order to meet the needs of the aerospace industry to efficiently process large-scale aluminum alloy components, advanced tools such as aluminum alloy high-speed machining face milling cutters and end mills with novel structures have been developed. At the same time, a variety of new indexable blade structures have emerged, such as multi-function, multi-disc, multi-station variable angle, quick-change fine-tuning machine tool plum knife, efficient scraping blade for turning, complex shape With front-end milling cutter blades, ball end milling cutter blades, high-speed milling cutter blades to prevent flutter. The realization of the five-axis linkage CNC tool grinding machine function further diversified the geometric parameters of end mills, drills and other general-purpose tools, changed the traditional pattern of standard tool parameters and can adapt to different processed materials and processing conditions, and corresponding cutting performance. improve. Some innovative tool structures can also produce new cutting effects, such as unequal helix angle end mills, as compared with standard end mills, can effectively curb the tool vibration, reduce the surface roughness, and increase the cutting depth of the tool. Feed rate. The development of tungsten carbide taps and hard alloy thread milling cutters improves the threading efficiency to the level of high speed cutting, especially carbide thread milling cutters, which not only has high machining efficiency, but also has good generality, which can significantly reduce tooling costs. In addition, professional tool manufacturers continue to develop composite or special tools, innovative processing technology, give full play to the function of the machine. The application of microelectronics, sensing technology and the development of intelligent tools have enabled active control and optimization of the process. It can be seen that the advantages of tool materials and coatings can only be fully exerted through advanced tool structures. The innovative tool structure represents the direction of the current development of tool structures. The tool material currently used is a wide variety of tool materials, mainly diamond, cubic boron nitride, ceramics, metal ceramics, hard alloys and high-speed steel. Different tool materials have different properties and have their specific application range. 1 There are four types of diamond that diamond can use as a tool material: natural diamond, synthetic single crystal diamond, polycrystalline diamond and diamond coating. Natural diamond is the most expensive tool material. Since natural diamond can be sharpened into the sharpest cutting edge, it is mainly used in the field of ultra-precision machining, such as navigation gyro and computer hard disk chips in micro-machined parts, optical mirrors, missiles and rockets. Wait. Synthetic single crystal diamond knives have good size, shape and chemical stability and are mainly used to process wood, such as processing highly wear-resistant Al2O3 coated wood flooring. Polycrystalline diamond is made of cobalt as a binder and is pressed with diamond powder at high temperature and high pressure (about 507 MPa, several thousand degrees Celsius). Polycrystalline diamond tools have excellent wear resistance, can be used to cut non-ferrous metals and non-metallic materials, finishing difficult-to-machine materials, such as silicon aluminum alloy and hard alloy.
Cubic Boron Nitride Cubic Boron Nitride (CBN), like polycrystalline diamond, is also artificially synthesized at high temperatures and pressures. Its polycrystalline structure and properties are similar to that of diamond. It has high hardness and Young's modulus, which is very good. Thermal conductivity, small thermal expansion, low density, low fracture toughness. In addition, cubic boron nitride has excellent chemical and thermal stability and hardly reacts with iron group elements, which is superior to diamond. Therefore, cubic boron nitride is often used instead of diamond when processing ferrous metals. Polycrystalline cubic boron nitride (PCBN) is particularly suitable for machining cast iron, heat-resistant alloys, and ferrous metals with hardness exceeding HRC45 (such as engine parts, gears, shafts, bearings, and other automotive parts). The PCBN tool is suitable for high-speed dry cutting and can process high-speed grey cast iron at a speed of up to 20,000 m/min. The application of PCBN tools in high-speed hard cutting is also extensive, especially for alloy steel parts on precision-finished automotive engines, such as gears, shafts, and bearings with a hardness of between 65 HRC6O to 65, and these parts were used in the past. Cut to ensure dimensional accuracy and surface quality. The mechanical and thermal properties of CBN are affected by the type and amount of binder phase. The binder phase is cobalt, nickel or titanium carbide, titanium nitride, aluminum oxide, etc. The particle size of CBN and the type of binder phase affect the cutting performance. PCBN tools with low CBN content (mass fraction, the same, 50% to 65%) are mainly used for finishing steels (HRC45-65), while PCBN tools with high CBN content (80%-90%) are used for high-speed roughing. Semi-finished nickel-chromium cast iron, interrupted machining of hardened steel, sintered metal, hard alloy, heavy alloy, etc. CBN without binder phase is under development. By controlling the synthesis conditions, the CBN particles are made finer, and the fine-grained CBN has high thermal conductivity, high thermal stability, high hardness, and high strength even at high temperatures. CBN without binder phase is expected to be the next generation tool material. According to the chemical composition of ceramics, ceramic cutting tool materials can be divided into three major categories: alumina-based ceramics, silicon nitride-based ceramics, and Sailong (composite silicon nitride-alumina) ceramics. Alumina-based ceramics have good chemical stability and have a very small affinity with iron-based metals, and thus are less susceptible to cohesive wear. The solubility of alumina in iron is only 1/5 of the solubility of WC in iron. Therefore, alumina-based ceramics have less diffusion wear, and at the same time, its oxidation resistance is strong. However, alumina-based ceramics have lower strength, fracture toughness, thermal conductivity, and thermal shock resistance. Alumina-based ceramic tools offer superior cutting performance over silicon nitride ceramic tools in high-speed cutting of steel. Compared with alumina ceramics, silicon nitride-based ceramics have higher strength, fracture toughness and thermal shock resistance, lower coefficient of thermal expansion, Young's modulus and chemical stability, and do not easily bond with cast iron. Therefore, silicon nitride-based ceramic tools are mainly used for high-speed machining of cast iron. Sialon ceramic tools have high strength, fracture toughness, oxidation resistance, thermal conductivity, thermal shock resistance and high temperature creep resistance. However, it has a low thermal expansion coefficient and is not suitable for processing steel. It is mainly used for rough machining of cast iron and nickel-based alloys. In order to further improve the cutting performance and wear resistance of ceramic cutters when machining new materials, the researchers developed silicon carbide whisker toughened ceramic materials (including silicon nitride-based ceramics and alumina-based ceramic materials), and toughened ceramic cutting tools. High-speed cutting of composite materials and aerospace heat-resistant alloys (nickel-based alloys, etc.) is very effective, but it is not suitable for machining cast iron and steel. There are two types of methods for manufacturing ceramic cutting tools: hot pressing and cold pressing. The hot pressing method is to press a powdered raw material into a cake shape under high temperature and high pressure, and then cut into a blade; the cold pressing method is to press raw material powder into a blank at room temperature and then sinter into a blade. The hot-pressing ceramic tool is of good quality and is currently the main manufacturing method of the ceramic tool. The cold-pressing method can produce a ceramic tool with a complex surface shape or a hole. TiC(N)-based hard alloy TiC(N)-based hard alloy (ie, cermet) has low density, high hardness, good chemical stability, low coefficient of friction to steel, anti-rude and anti-diffusion wear during cutting. Strong ability, good wear resistance. The cermet tool is suitable for high-speed finishing of carbon steel, stainless steel, malleable cast iron, and can obtain better surface roughness. Commonly used cermets are: (1) TiC+Ni or Mo with high wear resistance of titanium carbide, TiC+WC+TaC+Co with high fracture toughness; (2) Toughened titanium nitride-based cermets; (3) ) TiCN+NbC with high wear and thermal shock resistance based on titanium carbonitride. Carbide hard alloys are high-hardness, refractory metal compound powders (WC, TiC, etc.), and powdered metallurgy products obtained by compacting and sintering binders using metals such as cobalt or nickel. The advent of carbide cutting tool materials has made a leap in the level of machining. Carbide cutting tools can achieve high speed cutting and hard cutting. In order to meet the cutting requirements for various difficult-to-machine materials, a number of carbide processing technologies have been developed to develop a variety of new types of hard alloys by using high-purity raw materials, such as low-impurity tungsten concentrates and high purity. Tungsten trioxide etc. Advanced processes such as vacuum sintering instead of hydrogen sintering, paraffin processing instead of rubber processing, and spray drying or vacuum drying instead of steam drying; changing the chemical composition of the alloy. Adjust the structure of the alloy; use surface coating technology. The new cemented carbides have been developed with the addition of tantalum, niobium carbides, fine grain and ultrafine grain cemented carbides, and the addition of rare earth elements such as cemented carbide. In the grain size of 0.2 ~ 1μm tungsten carbide grain added to the higher hardness (HRA90 ~ 93) and strength (2000 ~ 3500MPa, the highest 5000MPa) of TaC, NbC and other particles, can be made into an overall ultra-fine Grain carbide tools or indexable inserts. After grain refinement, the size of the hard phase becomes smaller and the binder phase is more evenly distributed around the hard phase, which can improve the hardness and wear resistance of the hard alloy and can significantly improve the tool life. If you increase the cobalt content appropriately, you can also increase the bending strength. The cutter can cut iron group materials, nickel-based and cobalt-based superalloys, titanium-based alloys, heat-resistant stainless steels, welding materials, and superhard materials at high speeds. High-speed steel ordinary high-speed steel is manufactured by the fusion method. In the advanced cutting processing, where machining efficiency and processing quality requirements are increasingly improved, the performance of ordinary high-speed steel is already insufficient. In the late 20th century, many high-performance high-speed steels gradually appeared. New high-speed steels on the basis of ordinary high-speed steels have been significantly improved in their normal and high-temperature mechanical properties by adjusting basic chemical components and adding other alloying elements. The high-performance high-speed steels used as tool materials include high-carbon high-speed steel, high-cobalt high-speed steel, high vanadium high-speed steel, and aluminum-containing high-speed steel. Powder metallurgy high-speed steel is melted by high-frequency induction furnace and sprayed with high-pressure helium or pure nitrogen to atomize, and then quenched to obtain fine uniform crystalline powder, or sprayed with high-pressure water to form powder. The obtained powder is at high temperature. High-pressure hot isostatic pressing made of powder metallurgy high-speed steel cutting tools. Compared with traditional high-speed steel, powder metallurgy high-speed steel has no defects of carbide segregation, and the grain size is small, so the bending strength and toughness is high, the hardness is high, the applicable cutting speed is high, the tool life is longer, and can be processed. Harder workpiece material. The tool coating technology and coating material cutting require high performance of the tool material. The tool cutting edge withstands high temperature (300-1200°C), high pressure (100-10000N/mm2), high speed (1-30m/s) and large Strain rate (103 ~ 107 / s), it is required that the tool must have high hardness and anti-wear properties, but also have high strength and toughness, and coating tool is one of the best solution to this contradiction. Coated cutters are coated with a high temperature and wear resistant material on a base material with high strength and toughness. The adhesion between the coating material and the base material is required to be firm and difficult to fall off. The coating technology, with its remarkable effects, good adaptability and quick response, will play an important role in promoting the improvement of tool performance and the advancement of cutting technology in the future. Currently, commonly used tool coating methods include chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma chemical vapor deposition (PCVD), salt bath immersion plating, plasma spray coating, pyrolytic deposition coating, and chemical coating. Law, etc. Among them, CVD and PVD are the most widely used. The chemical vapor deposition method is to deposit the coating material on the surface of the tool substrate by vacuum coating or arc evaporation in a vacuum furnace at a high temperature of 1000° C. It takes approximately 4 hours to deposit a 15 μm thick coating. In current cutting tools, 40-50% of the blades are coated with chemical vapor deposition and reinforced with cobalt.
Cutting tool material
The physical vapor deposition method is similar to the chemical vapor deposition method except that the physical vapor deposition is performed at about 500°C. The physical vapor deposition method was first applied to high-speed steel and later also applied to cemented carbide tools. The chemical vapor deposition method is mostly a multi-layer coating, and the physical vapor deposition method can be a single coating and a multi-layer coating. The PVD method includes arc plasma vapor deposition, plasma gun electron beam ionization, hollow cathode electron beam ionization, and e-beam electron beam ion plating. Each has its own characteristics, advantages and disadvantages. Recently, the progress of PVD has been particularly noticeable. A variety of processes have been competing to introduce various multi-layer, multi-layer, and composite coatings with different functions, which has greatly expanded the scope of application of coatings, and the speed of development of new coating varieties has accelerated significantly, with gradients. The development of structures and nanostructured coatings has made new breakthroughs in the performance of coatings. The coated cemented carbide tool has the following advantages: (1) The coating material of the surface layer has extremely high hardness and wear resistance. If compared with the uncoated hard alloy, the coated cemented carbide allows higher The cutting speed increases the machining efficiency, or it can significantly increase the tool life at the same cutting speed. (2) The friction coefficient between the coating material and the material being processed is small. If compared with the uncoated hard alloy, the cutting force of the coated hard alloy is reduced to a certain extent, and the surface quality of the processed surface is good. (3) Due to the good overall performance, coated carbide cutters have better versatility and a wider range of application. The most commonly used method for cemented carbide coatings is high-temperature chemical vapor deposition (HTCVD). The process of coating the surface of cemented carbide with plasma chemical vapor deposition (PCVD) has also been applied.
Multi-layer coating tool
Because the application temperature of the CVD method is above 1000°C, it is not suitable for the coating of high-speed steel tools. The HSS tool body is coated with PVD, and TiC, TiN, etc. are generally used for the coating material, but TiN is often used. The coated high-speed steel tool surface has a hard layer, good wear resistance, and a small coefficient of friction with the material being processed, and the toughness of the matrix material does not decrease. Compared to uncoated high-speed steel tools, coated high-speed steel tools can reduce cutting forces by 5% to 10% under the same cutting conditions. Due to the thermal barrier effect of the coating material, the cutting temperature of the cutting part of the tool base is reduced, the surface roughness value of the workpiece has been reduced, and the service life of the tool has been significantly improved. The three most common coating materials are TiN, TiCN, and TiAIN. Among them, the titanium nitride coating that appeared in the 1980s was the most widely used, and its coating color was golden yellow and it was easy to identify. The titanium nitride coating can increase the hardness and wear resistance of the tool surface, reduce the friction coefficient, reduce the build-up of the built-up edge, and prolong the tool life. Titanium nitride coated tools are suitable for machining low alloy steels and stainless steels. The surface of the titanium carbonitride coating is gray, the hardness is higher than that of the titanium nitride coating, and the abrasion resistance is better. Compared to titanium nitride coatings, titanium carbonitride-coated tools can be machined at higher feed rates and cutting speeds (40% and 60% higher than titanium nitride coatings, respectively), and workpiece material removal rates. higher. Titanium carbonitride coated tools can process a variety of workpiece materials. The titanium aluminum aluminide coating is gray or black and it is mainly coated on the surface of cemented carbide cutting tools. When the cutting temperature reaches 800 °C, it can still be processed and is suitable for high speed dry cutting. Chips in the cutting area during dry cutting can be removed with compressed air. Titanium aluminum nitride is suitable for processing brittle materials such as hardened steels, titanium alloys, nickel-base alloys, cast irons, and high-silicon aluminum alloys. Chemical vapor deposition diamond-coated tools are suitable for high-speed machining of aluminum and other non-ferrous metals such as copper, brass, and bronze; they can also be used to process graphite and composite materials (such as carbon-carbon reinforced plastics, glass fiber reinforced plastics, phenolic resins) Wait). CVD diamond thin film coated tools are often used for complex shaped tools such as inserts with chip formers, integral end mills, planers, and drills. Diamond thick-film coating tools are often used to cut high-eutectic aluminum alloys at high speeds. The diamond-coated end mill uses an ultra-fine particle cemented carbide substrate and CVD diamond coating for high-speed machining of non-metallic materials such as aluminum alloys and graphite. Ceramics have good physicochemical properties: high wear resistance, high temperature resistance, and corrosion resistance. Therefore, the coating tool made of the combination of the advantages of the base material and the excellent properties of the ceramic material can be better. Compared with the conventional coated tool, the friction coefficient is reduced, so that it is more wear-resistant and the tool life is prolonged. Newly developed hard coatings include carbon nitride coatings (CNx), diamond-like coatings (DLC), AlCrN coatings, etc.; TiSiN coatings for hard cutting, lubricated CrSiN coatings, and superior resistance AlCrSiN coatings with oxidizing power; other nitride coatings (TiN/NbN, TiN/VN, TiBoN), boride coatings (TiB2, CBN), etc. These coated knives have good high temperature stability and are suitable for Used for high speed cutting. Physical vapor deposition combined with chemical vapor deposition can be used to develop new coating tools. The inner layer can be coated with a chemical vapor deposition coating to form a high bond with the substrate, and the outer layer can be reduced by physical vapor deposition. The cutting force makes the tool suitable for high speed cutting. The progress of tool coating technology is also reflected in the practical application of nano-coatings. The application of hundreds of nanometers thick materials on each layer of the substrate material is called nano coating. The nano coating material has a very small particle size, so the grain boundaries are very long and thus have a high high temperature hardness. , strength and fracture toughness. The Vickers hardness of the nano-coatings can reach HV2800-3000, and the wear-resistance of Bi-micron materials can be increased by 5%-50%. It has been reported that titanium carbide and titanium carbonitride alternate coatings have been developed to reach 62 layers of coated tools and 400 layers of TiAlN-TiAlN/Al2O3 nanocoating tools. Compared with the above hard coatings, vulcanizates (MoS2, WS2) on high-speed steels are called soft coatings and are mainly used for the cutting of high-strength aluminum alloys, titanium alloys, and some rare metals. Conclusion Tool design is a harmonious combination of tool geometry, cutting material and coating. Only by continuously introducing advanced tool design techniques and promoting the development and use of new types of cutting tools, can we meet the development needs of advanced cutting technology. At present, the world's manufacturing industry is undergoing a profound strategic insurance restructuring. Europe and the United States, as well as Japan and South Korea and other developed countries and regions in the global scope for a new round of optimal allocation of manufacturing resources, China has become a developed country and regional manufacturing Large-scale transfer of industries and landing of important markets. However, China's manufacturing technology, especially the level of cutting processing, has a large gap compared with foreign countries. The development of advanced cutting technology, especially tool design technology, and improvement of processing efficiency, and the responsibility of building a strong manufacturing country are the responsibility of cutting technology. The shoulders of researchers and workers. As long as we attach great importance to the development and innovation of advanced cutting technology, and make unremitting efforts, the goal of a strong manufacturing country will certainly be realized!
Author: Liu Zhanqiang: engaged in machinery manufacturing and automation, the main research directions for the efficient machining, virtual manufacturing technology. He received a Ph.D. from the City University of Hong Kong in 1999 and a postdoctoral station at the Shandong University Mechanical Engineering in 2001. He was promoted to a professor in 2002. In 2003 he was hired as a doctoral tutor.
He is currently a communication review expert of the Materials Engineering Department of the National Natural Science Foundation of China and a senior member of the China Mechanical Engineering Society. He is a member of the China Machinery Industry Metal Cutting Tool Technology Association, Vice Chairman of the Expert Committee of the Replacing Tools, a member of the China University Cutting and Advanced Manufacturing Technology Research Association, and an AMS reviewer of international scientific journals. He has published more than 80 papers and won 3 scientific research awards.
