01
Tool materials should have basic properties
The choice of tool material has great influence on tool life, machining efficiency, machining quality and machining cost.Cutting tools to withstand high pressure, high temperature, friction, impact and vibration.Therefore, the tool material should have the following basic properties:
(1) hardness and wear resistance.The hardness of tool material must be higher than that of workpiece material, generally more than 60HRC.The higher the hardness of the tool material, the better the wear resistance.
(2) strength and toughness.The cutting tool material should have high strength and toughness, so as to withstand cutting force, impact and vibration, and prevent brittle fracture and edge collapse of the tool.
(3) heat resistance.The tool material's heat resistance is good, can bear the high cutting temperature, has the good anti-oxidation ability.
(4) process performance and economy.Tool material should have good forging performance, heat treatment performance, welding performance;Grinding performance, and the pursuit of high performance ratio.
02
Tool material types, properties, characteristics, applications
1.Diamond tool material
Diamond, an isomer of carbon, is one of the hardest materials found in nature.Diamond tools have high hardness, high wear resistance and high thermal conductivity, and are widely used in the processing of nonferrous and nonmetallic materials.Especially in the high speed machining of aluminum and silicon alloy, diamond cutting tools are the main cutting tools that are difficult to be replaced.Diamond cutting tools with high efficiency, high stability and long life are indispensable tools in CNC machining.
Type of diamond tools
(1) natural diamond cutting tools: natural diamond as a cutting tool for hundreds of years of history, natural single crystal diamond tool after fine grinding, can grinding extremely sharp blade, blade radius of 0.002 mu m, can realize the ultra-thin cutting, can work out high precision and low surface roughness of workpiece, is accepted, the ideal and does not take the place of ultra-precision machining tools.
(2) the PCD diamond tool: natural diamond is expensive, diamond is widely used in machining or polycrystalline diamond (PCD), since the early 1970 s, the use of high temperature and high pressure synthesis technology of the preparation of polycrystalline diamond (Polycrystauine diamond, hereinafter referred to as PCD blade after successful development, on many occasions, natural diamond cutting tool has been replaced by artificial polycrystalline diamond.PCD is rich in raw materials and its price is only a few to a tenth of that of natural diamond.PCD tools cannot grind out extremely sharp edges, and the surface quality of processed workpiece is not as good as that of natural diamond, so it is not easy to manufacture PCD blades with broken chip slots in the industry.Therefore, PCD can only be used for fine cutting of nonferrous metals and nonmetals, and it is difficult to achieve ultra-precision mirror cutting.
CVD diamond tools: since the late 1970s to the early 1980s, CVD diamond technology in Japan.CVD diamond refers to the synthesis of diamond film on heterogeneous matrix (such as cemented carbide, ceramics, etc.) by chemical vapor deposition (CVD). CVD diamond has exactly the same structure and characteristics as natural diamond.Compared with natural diamond, the properties of CVD diamond are very close to that of natural diamond.
The diamond tool performance characteristics
High hardness and wear resistance: natural diamond is the hardest substance that has been found in nature.Diamond has a very high wear resistance, when processing high hardness materials, the diamond tool life of the carbide tool is lO ~ 100 times, even up to hundreds of times.
Has very low friction coefficient: the friction coefficient between diamond and some nonferrous metals is lower than other tools, low friction coefficient, processing deformation is small, can reduce the cutting force.
Cutting edge is very sharp: the cutting edge of the diamond tool can be sharpened very sharp, natural single crystal diamond tool can be up to 0.002 ~ 0.008 m, can carry out ultra-thin cutting and ultra-precision processing.
(4) has a high thermal conductivity: diamond thermal conductivity and thermal diffusion rate is high, cutting heat is easy to spread out, cutting tool part temperature is low.
(5) has a lower thermal expansion coefficient: the thermal expansion coefficient of diamond is several times smaller than the cemented carbide, by the cutting heat caused by the small change in tool size, which is particularly important for precision and ultra-precision machining with high dimensional accuracy requirements.
Application of diamond tools
Diamond tools are used for fine cutting and boring of nonferrous metals and nonmetallic materials at high speed.Suitable for processing various wear-resisting non-metal, such as glass steel powder metallurgy blank, ceramic materials;Various wear resistant non-ferrous metals, such as all kinds of silicon aluminum alloy;All kinds of non - ferrous metal finishing.
The disadvantage of diamond tools is that their thermal stability is poor. When the cutting temperature exceeds 700℃ ~ 800℃, they will completely lose their hardness.In addition, it is not suitable for cutting ferrous metals, because diamond (carbon) at high temperature is easy to interact with iron atoms, carbon atoms into graphite structure, the tool is very easy to damage.
2.Cubic boron nitride tool material
The second superhard material, cubic boron nitride (CBN), synthesized by a method similar to that used in diamond fabrication, is second only to diamond in hardness and thermal conductivity, with excellent thermal stability and no oxidation when heated to 10000C in the atmosphere.CBN has very stable chemical properties for ferrous metals and can be widely used in the processing of iron and steel products.
Type of cubic boron nitride cutter
Cubic boron nitride (CBN) is a substance that does not exist in nature and can be divided into single crystals and polycrystals, namely, CBN single crystals and Polycrystalline cubic boron nitride (PCBN).CBN is one of the isomers of boron nitride (BN).
PCBN (polycrystalline cubic boron nitride) is a polycrystalline material sintered together by the combination phase (TiC, TiN, Al, Ti, etc.) of the fine CBN material under high temperature and high pressure. At present, it is the tool material second only to diamond in hardness by artificial synthesis.PCBN is mainly used to make tools or other tools.
PCBN cutter can be divided into integral PCBN blade and carbide composite sintered PCBN composite blade.
The PCBN composite blade is made of a sintered layer of o-5 ~ 1.0mm thick PCBN on a hard alloy with good strength and toughness. Its performance has both good toughness and high hardness and abrasion resistance. It solves the problems of low bending strength and welding difficulty of CBN blade.
The main performance of cubic boron nitride, characteristics
The hardness of cubic boron nitride is slightly lower than that of diamond, but it is much higher than other high hardness materials.The outstanding advantage of CBN is that the thermal stability is much higher than diamond, can reach more than 1200℃ (diamond is 700 ~ 800℃), another outstanding advantage is the chemical inertia, and iron at 1200 ~ 1300℃ is not chemical reaction.The main properties of cubic boron nitride are as follows.
(1) high hardness and wear resistance: CBN crystal structure and diamond similar, with diamond and similar hardness and strength.PCBN is especially suitable for machining high hardness materials which can only be ground before, and can obtain better surface quality of workpiece.
Has very high thermal stability: the heat resistance of CBN can reach 1400 ~ 1500℃, almost l times higher than that of diamond (700 ~ 800℃).PCBN tools can be used to cut high temperature alloy and hardened steel at 3 ~ 5 times the speed of carbide tools.
Excellent chemical stability: and iron materials to 1200 -- 1300℃ also do not have a chemical effect, will not be as sharp as diamond wear, then it can still maintain the hardness of cemented carbide;PCBN tool is suitable for cutting hardened steel parts and chilled cast iron, can be widely used in high-speed cutting of cast iron.
(4) has a good thermal conductivity: although the thermal conductivity of CBN is not as good as diamond, but in all kinds of tool materials PCBN thermal conductivity is next to diamond, much higher than high-speed steel and cemented carbide.
With a lower coefficient of friction: low coefficient of friction can lead to the reduction of cutting force, cutting temperature, machining surface quality.
Cubic boron nitride tool application
Cubic boron nitride is suitable for finishing all kinds of hardened steel, hard cast iron, high temperature alloy, hard alloy, surface spraying material and other difficult cutting materials.The machining precision can reach IT5(hole is IT6), and the surface roughness value can be as small as Ra1.25 ~ 0.20 m.
Cubic boron nitride tool material toughness and bending strength is poor.Therefore, cubic boron nitride turning tool is not suitable for rough machining with low speed and large impact load.At the same time is not suitable for cutting plastic materials (such as aluminum alloy, copper alloy, nickel base alloy, plastic large steel, etc.), because the cutting of these metals will produce a serious chip tumor, and make the processing surface deterioration.
3.Ceramic tool material
Ceramic tool has the characteristics of high hardness, good wear resistance, good heat resistance and chemical stability, and is not easy to bond with metal.Ceramic cutting tools play a very important role in CNC machining. Ceramic cutting tools have become one of the main cutting tools for high speed cutting and difficult to process materials.Ceramic cutting tools are widely used in high speed cutting, dry cutting, hard cutting and difficult to process materials.Ceramic cutting tools can efficiently process the high hard materials that traditional cutting tools can't process at all, so as to realize "using car instead of grinding".The optimum cutting speed of ceramic tool can be 2 ~ lO times higher than that of cemented carbide tool, thus greatly improving the production efficiency of machining;The main raw materials used in ceramic cutting tool materials are the most abundant elements in the earth's crust. Therefore, the popularization and application of ceramic cutting tools is of great significance to improve productivity, reduce processing costs, and save strategic precious metals. It will also greatly promote the progress of cutting technology.
Type of ceramic tool materials
Ceramic cutting tool materials generally can be divided into three categories: alumina - based ceramics, silicon nitride - based ceramics, composite silicon nitride - alumina - based ceramics.Alumina - based and silicon nitride - based ceramic tool materials are the most widely used.The performance of si3n4 - based ceramics is superior to that of alumina - based ceramics.
The ceramic tool performance, characteristics
(1) high hardness, good wear resistance: although the hardness of ceramic tools is not as high as PCD and PCBN, but much higher than the carbide and high-speed steel tools, up to 93-95hra.Ceramic tools can be used to process hard materials which are difficult to be processed by traditional tools, and are suitable for high speed cutting and hard cutting.
High temperature resistance, good heat resistance: ceramic tool in 1200℃ above the high temperature can still be cut.Ceramic cutting tools have good high temperature mechanical properties, A12O3 ceramic cutting tools have particularly good antioxidant properties, cutting edge even in the red heat state, but also continuous use.Therefore, ceramic cutting tools can achieve dry cutting, thus eliminating cutting fluid.
(3) good chemical stability: ceramic tool is not easy to bond with metal, and corrosion resistance, chemical stability is good, can reduce the tool bonding wear.
Low friction coefficient: ceramic tool and metal affinity is small, low friction coefficient, can reduce the cutting force and cutting temperature.
Ceramic knife has applications
Ceramic is one of the tool materials mainly used for high - speed finishing and semi - finishing.Ceramic tool is suitable for cutting all kinds of cast iron (gray cast iron, ductile cast iron, malleable cast iron, cold cast iron, high alloy wear resistant cast iron) and steel (carbon structural steel, alloy structural steel, high strength steel, high manganese steel, quenched steel, etc.), also can be used for cutting copper alloy, graphite, engineering plastics and composite materials.
The ceramic cutting tool has the problems of low bending strength and poor impact toughness, which are not suitable for cutting under low speed and impact load.