Only when advanced processing equipment is matched with high-performance NC tools can their due efficiency be fully exerted and good economic benefits be achieved. With the rapid development of tool materials, the physical, mechanical and cutting properties of various new tool materials have been greatly improved, and their application scope has also been expanding.
I The tool material shall have basic performance
The choice of tool material has a great influence on tool life, machining efficiency, machining quality and machining cost. The cutting tool must bear the effects of 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 the tool material must be higher than that of the workpiece material, which is generally required to be above 60HRC. The higher the hardness of the tool material, the better the wear resistance.
(2) Strength and toughness. The tool material shall have high strength and toughness to withstand cutting force, impact and vibration and prevent brittle fracture and blade breakage of the tool.
(3) Heat resistance. The tool material has good heat resistance, can withstand high cutting temperature, and has good oxidation resistance.
(4) Process performance and economy. The tool material shall have good forging performance, heat treatment performance and welding performance; Grinding processing performance, and the pursuit of high performance price ratio.
2、 Type, performance, characteristics and application of tool materials
1. Type, performance and characteristics of diamond tool materials and tool application
Diamond is the allotrope of carbon, which is the hardest material found in nature. Diamond tools have been widely used in the processing of non-ferrous and non-metallic materials because of their high hardness, high wear resistance and high thermal conductivity. Especially in high speed machining of aluminum and silicon aluminum alloys, diamond tools are the main cutting tools that are difficult to replace. The diamond tool which can realize high efficiency, high stability and long life machining is an indispensable tool in modern NC machining.
⑴ Type of diamond cutter
① Natural diamond tools: natural diamond has been used as cutting tools for hundreds of years. After fine grinding, natural single crystal diamond tools can be extremely sharp with a cutting edge radius of 0.002 μ m. It can realize ultra-thin cutting, and can process extremely high workpiece accuracy and extremely low surface roughness. It is recognized as an ideal and irreplaceable ultra precision machining tool.
② PCD diamond tools: natural diamonds are expensive, and polycrystalline diamond (PCD) is widely used for cutting. Since the early 1970s, After the PCD (Polycrystalline Diamond) blade prepared by high temperature and high pressure synthesis technology has been successfully developed, the natural diamond tool has been replaced by the artificial polycrystalline diamond in many occasions. The raw materials of PCD are rich in sources, and its price is only one tenth to one tenth of that of natural diamond.
PCD cutters cannot grind extremely sharp edges, and the surface quality of the machined workpiece is not as good as that of natural diamonds. Now, it is not convenient to manufacture PCD cutters with chip breaking grooves in industry. Therefore, PCD can only be used for fine cutting of non-ferrous metals and nonmetals, and it is difficult to achieve ultra precision mirror cutting.
③ CVD diamond tools: Since the late 1970s to the early 1980s, CVD diamond technology has appeared in Japan. CVD diamond refers to the synthesis of diamond films on heterogeneous substrates (such as cemented carbide, ceramics, etc.) by chemical vapor deposition (CVD). CVD diamond has the same structure and characteristics as natural diamond.
The performance of CVD diamond is very close to that of natural diamond, which has the advantages of natural single crystal diamond and polycrystalline diamond (PCD), and overcomes their shortcomings to a certain extent.
⑵ Performance characteristics of diamond tools
① Very high hardness and wear resistance: natural diamond is the hardest material found in nature. Diamond has very high wear resistance. When machining high hardness materials, the life of diamond tools is 10~100 times of that of cemented carbide tools, even hundreds of times.
② It has very low friction coefficient: the friction coefficient between diamond and some non-ferrous metals is lower than that of other tools. The friction coefficient is low, and the deformation during machining is small, which can reduce the cutting force.
③ The cutting edge is very sharp: the cutting edge of the diamond tool can be ground very sharp, and the natural single crystal diamond tool can reach 0.002 ～ 0.008 μ m. Capable of ultra-thin cutting and ultra precision machining.
④ It has high thermal conductivity: the thermal conductivity and thermal diffusivity of diamond are high, the cutting heat is easy to disperse, and the temperature of the cutting part of the tool is low.
⑤ Low thermal expansion coefficient: the thermal expansion coefficient of diamond is several times smaller than that of cemented carbide, and the tool size change caused by cutting heat is very small, which is particularly important for precision and ultra precision machining with high dimensional accuracy requirements.
⑶ Application of diamond tools
Diamond tools are mostly used for fine cutting and boring of non-ferrous and non-metallic materials at high speed. Suitable for processing various wear-resistant nonmetals, such as GRP powder metallurgy blanks, ceramic materials, etc; Various wear-resistant nonferrous metals, such as various silicon aluminum alloys; All kinds of non-ferrous metal finishing.
The disadvantage of diamond tools is their poor thermal stability. When the cutting temperature exceeds 700 ℃~800 ℃, they will lose their hardness completely; In addition, it is not suitable for cutting ferrous metals, because diamond (carbon) is easy to interact with iron atoms at high temperatures, so that carbon atoms can be converted into graphite structures, and the tool is extremely vulnerable to damage.
2. Types, properties and characteristics of cubic boron nitride tool materials and tool applications
The second kind of superhard material, cubic boron nitride (CBN), synthesized by a method similar to the diamond manufacturing method, is second only to diamond in hardness and thermal conductivity, and has excellent thermal stability. It does not oxidize when heated to 10000C in the atmosphere. CBN has extremely stable chemical properties for ferrous metals and can be widely used in the processing of steel products.
⑴ Type of cubic boron nitride tool
Cubic boron nitride (CBN) is a substance that does not exist in nature. It 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), and its structure is similar to diamond.
PCBN (Polycrystalline Cubic Boron Nitride) is a polycrystalline material sintered together by fine CBN materials through bonding phases (TiC, TiN, Al, Ti, etc.) under high temperature and high pressure. It is currently a tool material with artificial synthesis hardness second only to diamond. It and diamond are collectively referred to as superhard tool materials. PCBN is mainly used to make tools or other tools.
PCBN cutters can be divided into integral PCBN inserts and PCBN composite inserts sintered with cemented carbide.
PCBN composite inserts are made by sintering a layer of O.5~1.0mm thick PCBN on the cemented carbide with good strength and toughness. Its performance has both good toughness, high hardness and wear resistance. It solves the problems of low bending strength and welding difficulty of CBN inserts.
⑵ Main properties and characteristics of cubic boron nitride
Although the hardness of cubic boron nitride is slightly lower than that of diamond, it is far higher than that of other high hardness materials. The outstanding advantage of CBN is that its thermal stability is much higher than that of diamond, reaching above 1200 ℃ (700~800 ℃ for diamond). Another outstanding advantage is that CBN is chemically inert, and it can not react with iron at 1200~1300 ℃. The main performance characteristics of cubic boron nitride are as follows.
① High hardness and wear resistance: CBN crystal structure is similar to diamond, and has similar hardness and strength to diamond. PCBN is especially suitable for machining high hardness materials that can only be grinded before, and can obtain better workpiece surface quality.
② It has high thermal stability: the heat resistance of CBN can reach 1400~1500 ℃, which is almost 1 times higher than that of diamond (700~800 ℃). PCBN tool can be used to cut high temperature alloy and hardened steel at a speed 3~5 times higher than that of cemented carbide tool.
③ Excellent chemical stability: when the temperature reaches 1200-1300 ℃, it will not have chemical effect with iron based materials, and will not be worn as rapidly as diamond. At this time, it can still maintain the hardness of cemented carbide; PCBN tools are suitable for cutting hardened steel parts and chilled cast iron, and can be widely used in high-speed cutting of cast iron.
④ Good thermal conductivity: Although the thermal conductivity of CBN is not as good as that of diamond, the thermal conductivity of PCBN is only second to that of diamond in all kinds of tool materials, which is much higher than that of high-speed steel and cemented carbide.
⑤ Low friction coefficient: low friction coefficient can reduce the cutting force, reduce the cutting temperature and improve the quality of the machined surface.
(3) Application of cubic boron nitride tools
Cubic boron nitride is suitable for finishing various hard cutting materials such as quenched steel, hard cast iron, high temperature alloy, hard alloy and surface spraying materials. The machining accuracy can reach IT5 (IT6 for holes), and the surface roughness value can be as low as Ra1.25 ～ 0.20 μ m。
The toughness and bending strength of CBN tool material are poor. Therefore, cubic boron nitride turning tool is not suitable for rough machining with low speed and large impact load; At the same time, it is not suitable for cutting materials with large plasticity (such as aluminum alloy, copper alloy, nickel base alloy, steel with large plasticity, etc.), because serious chip buildup will occur when cutting these metals, which will deteriorate the machined surface.
3. Type, performance and characteristics of ceramic tool materials and tool application
Ceramic cutting tools have high hardness, good wear resistance, good heat resistance and chemical stability, and are not easy to bond with metal. Ceramic tools play a very important role in NC machining. Ceramic tools have become one of the main tools for high-speed cutting and difficult to machine materials. Ceramic tools are widely used in high-speed cutting, dry cutting, hard cutting and difficult to machine materials. Ceramic tools can efficiently process high hard materials that cannot be processed by traditional tools, realizing "turning instead of grinding"; The optimum cutting speed of ceramic tools can be 2~lO times higher than that of cemented carbide tools, thus greatly improving the cutting efficiency; The main raw materials used for ceramic tool materials are the most abundant elements in the crust. Therefore, the promotion and application of ceramic tools are of great significance for improving productivity, reducing processing costs and saving strategic precious metals, and will also greatly promote the progress of cutting technology.
⑴ Type of ceramic tool materials
Ceramic tool materials can generally be divided into three categories: alumina based ceramics, silicon nitride based ceramics, and composite silicon nitride alumina based ceramics. Among them, alumina based and silicon nitride based ceramic tool materials are most widely used. The performance of silicon nitride based ceramics is superior to that of alumina based ceramics.
⑵ Performance and characteristics of ceramic tools
The performance characteristics of ceramic tools are as follows:
① High hardness and good wear resistance: Although the hardness of ceramic tools is not as high as that of PCD and PCBN, it is much higher than that of cemented carbide and high-speed steel tools, reaching 93-95HRA. Ceramic tools can be used to machine high hard materials that are difficult to machine with traditional tools, and are suitable for high-speed cutting and hard cutting.
② High temperature resistance, good heat resistance: ceramic tools can still cut at a high temperature above 1200 ℃. Ceramic tools have good high temperature mechanical properties, and A12O3 ceramic tools have particularly good oxidation resistance. The cutting edge can be used continuously even in the hot state. Therefore, the ceramic tool can realize dry cutting, thereby saving cutting fluid.
③ Good chemical stability: ceramic tools are not easy to bond with metal, and have good corrosion resistance and chemical stability, which can reduce the adhesive wear of tools
④ Low friction coefficient: the affinity between ceramic tool and metal is small, and the friction coefficient is low, which can reduce the cutting force and cutting temperature.
(3) Ceramic knife has application
Ceramic is one of the tool materials mainly used in high-speed finishing and semi finishing. Ceramic tools are suitable for machining various cast irons (gray cast iron, nodular cast iron, malleable cast iron, chilled cast iron, high alloy wear-resistant cast iron) and steels (carbon structural steel, alloy structural steel, high-strength steel, high manganese steel, quenched steel, etc.), as well as copper alloys, graphite, engineering plastics and composite materials.
The ceramic tool material has the problems of low bending strength and poor impact toughness, so it is not suitable for cutting at low speed and under impact load.
4. Performance and characteristics of coated tool materials and application of tools
Coating treatment is one of the important ways to improve the tool performance. The appearance of coated tools has made a great breakthrough in the cutting performance of tools. Coated tools are coated with one or more layers of refractory compounds with good wear resistance on the tool body with good toughness. It combines the tool matrix with the hard coating, thus greatly improving the tool performance. Coated tools can improve machining efficiency, improve machining accuracy, prolong tool life and reduce machining cost.
About 80% of the cutting tools used in new CNC machine tools use coated tools. Coated tools will be the most important tool variety in the field of NC machining in the future.
⑴ Type of coated tool
According to different coating methods, coated tools can be divided into chemical vapor deposition (CVD) coated tools and physical vapor deposition (PVD) coated tools. Coated carbide tools are generally prepared by chemical vapor deposition at a temperature of about 1000 ℃. Coated high speed steel tools are generally deposited by physical vapor deposition at about 500 ℃;
According to the different substrate materials of coated tools, coated tools can be divided into cemented carbide coated tools, high-speed steel coated tools, and coated tools on ceramics and superhard materials (diamond and cubic boron nitride).
According to the properties of coating materials, coated tools can be divided into two categories, namely "hard" coated tools and "soft" coated tools. The main goal of "hard" coated tools is high hardness and wear resistance. Its main advantages are high hardness and good wear resistance, typically TiC and TiN coatings. The target of "soft" coated tools is low friction coefficient, also known as self-lubricating tools. Its friction coefficient with the workpiece material is very low, only about 0.1, which can reduce adhesion, friction, cutting force and cutting temperature.
Recently, nano coating tools have been developed. This coated tool can use different combinations of various coating materials (such as metal/metal, metal/ceramic, ceramic/ceramic, etc.) to meet different functional and performance requirements. The nano coating with reasonable design can make the tool material have excellent antifriction and antiwear functions and self-lubricating properties, which is suitable for high-speed dry cutting.
(2) Features of coated tools
The performance characteristics of coated tools are as follows:
① Good mechanical and cutting properties: the coated tool combines the excellent properties of the base material and the coating material, which not only maintains the good toughness and high strength of the base material, but also has the high hardness, high wear resistance and low friction coefficient of the coating. Therefore, the cutting speed of coated tools can be more than 2 times higher than that of uncoated tools, and a higher feed rate is allowed. The life of coated tools is also improved.
② Strong versatility: coated tools have wide versatility, and the processing range is significantly expanded. One coated tool can replace several non coated tools.
5. Types, properties, characteristics and applications of cemented carbide tool materials
Cemented carbide tools, especially indexable cemented carbide tools, are the leading products of CNC machining tools. Since the 1980s, various types of integral and indexable cemented carbide tools or inserts have been extended to various cutting tool fields, among which indexable cemented carbide tools have expanded from simple turning tools and face milling tools to various precision, complex and shaped tool fields.
⑴ Type of carbide tool
According to the main chemical composition, cemented carbides can be divided into tungsten carbide based cemented carbides and titanium carbide (TiC (N)) based cemented carbides.
Tungsten carbide based cemented carbides include Tungsten Cobalt (YG), Tungsten Cobalt Titanium (YT), and Rare Carbides (YW). They have their own advantages and disadvantages. The main components are tungsten carbide (WC), titanium carbide (TiC), tantalum carbide (TaC), niobium carbide (NbC), etc. The common metal bonding phase is Co.
Titanium carbide (nitrided) is a kind of cemented carbide with TiC as the main component (some have added other carbides or nitrides). The commonly used metal bonding phases are Mo and Ni.
ISO (International Organization for Standardization) divides cutting cemented carbides into three categories:
Category K, including Kl0 ～ K40, is equivalent to YG in China (mainly composed of WC. Co).
Category P, including P01 ～ P50, is equivalent to YT in China (mainly composed of WC. TiC. Co).
Category M, including M10 ～ M40, is equivalent to the YW category in China (mainly composed of WC TiC TaC (NbC) - Co).
Each grade represents a series of alloys from high hardness to maximum toughness with numbers between 01 and 50.
⑵ Performance characteristics of cemented carbide tools
The performance characteristics of cemented carbide tools are as follows:
① High hardness: The cemented carbide tool is made of carbide (called hard phase) and metal binder (called bonding phase) with high hardness and melting point by powder metallurgy. Its hardness is 89~93HRA, which is much higher than that of high-speed steel. At 5400C, the hardness can still reach 82~87HRA, which is the same as that of high-speed steel at room temperature (83~86HRA). The hardness of cemented carbide varies with the nature, quantity, particle size of carbide and the content of metal bonding phase, and generally decreases with the increase of the content of metal bonding phase. When the content of bonding phase is the same, the hardness of YT alloy is higher than that of YG alloy, and the alloy with TaC (NbC) has higher high temperature hardness.
② Bending strength and toughness: the bending strength of common cemented carbide is in the range of 900~1500MPa. The higher the content of metal bonding phase, the higher the bending strength. When the binder content is the same, the strength of YG (WC Co) alloy is higher than that of YT (WC TiC Co) alloy, and the strength decreases with the increase of TiC content. Carbide is a brittle material, and its impact toughness at room temperature is only 1/30-1/8 of that of high-speed steel.
⑶ Application of common cemented carbide tools
YG alloys are mainly used for processing cast iron, nonferrous metals and non-metallic materials. Fine grain cemented carbides (such as YG3X and YG6X) have higher hardness and wear resistance than medium grain cemented carbides when their cobalt content is the same. They are suitable for processing some special hard cast iron, austenitic stainless steel, heat-resistant alloy, titanium alloy, hard bronze and wear-resistant insulating materials.
The outstanding advantages of YT type cemented carbide are high hardness, good heat resistance, higher hardness and compressive strength at high temperature than YG type, and good oxidation resistance. Therefore, when the knife is required to have high heat resistance and wear resistance, the brand with high TiC content should be selected. YT alloy is suitable for processing plastic materials such as steel, but not titanium alloy and silicon aluminum alloy.
YW type alloy has the properties of YG and YT type alloys with good comprehensive properties. It can be used for processing steel, cast iron and non-ferrous metals. If the cobalt content is properly increased, this kind of alloy can have high strength and can be used for rough machining and intermittent cutting of various difficult to machine materials.
6. Types, characteristics and applications of high-speed steel tools
High Speed Steel (HSS for short) is a kind of high alloy tool steel with more alloying elements such as W, Mo, Cr and V. High speed steel tools have excellent comprehensive performance in terms of strength, toughness and processability. High speed steel still plays a major role in complex tools, especially in the manufacturing of hole processing tools, milling tools, thread cutting tools, broaches, gear cutting tools and other complex cutting tools. High speed steel tools are easy to grind sharp cutting edges.
High speed steel can be divided into general purpose high speed steel and high-performance high speed steel according to different uses.
⑴ Universal high-speed steel cutter
General purpose high speed steel. Generally, it can be divided into tungsten steel and tungsten molybdenum steel. This kind of high speed steel contains 0.7% ～ 0.9% additive (C). According to the different tungsten content in steel, it can be divided into 12% or 18% tungsten steel, 6% or 8% tungsten molybdenum steel, and 2% or no tungsten steel. General purpose high speed steel has certain hardness (63-66HRC) and wear resistance, high strength and toughness, good plasticity and processing technology, so it is widely used to manufacture various complex tools.
① Tungsten steel: the typical brand of universal high-speed steel tungsten steel is W18Cr4V (W18 for short), which has good comprehensive properties. The high temperature hardness at 6000C is 48.5HRC, and it can be used to manufacture various complex tools. It has the advantages of good grindability and low decarburization sensitivity, but due to the high content of carbide, uneven distribution, large particles, and low strength and toughness.
② Tungsten molybdenum steel: refers to a kind of high speed steel obtained by replacing part of tungsten in tungsten steel with molybdenum. The typical grade of tungsten molybdenum steel is W6Mo5Cr4V2 (M2 for short). The carbide particles of M2 are fine and uniform, and their strength, toughness and high-temperature plasticity are better than those of W18Cr4V. The other kind of tungsten molybdenum steel is W9Mo3Cr4V (W9 for short), its thermal stability is slightly higher than M2 steel, its bending strength and toughness are better than W6M05Cr4V2, and it has good machinability.
(2) High performance high-speed steel cutter
High performance high speed steel is a new type of steel that adds some carbon content, vanadium content and alloy elements such as Co, Al to the composition of general purpose high speed steel, so as to improve its heat resistance and wear resistance. There are mainly the following categories:
① High carbon high speed steel. High carbon high speed steel (such as 95W18Cr4V), with high hardness at room temperature and high temperature, is suitable for manufacturing and processing ordinary steel and cast iron, drills, reamers, taps and milling cutters with high wear resistance requirements or cutters for processing harder materials, and should not bear large impact.
② High Vanadium High Speed Steel. Typical brands, such as W12Cr4V4Mo, (EV4 for short), with the V content increased to 3% - 5%, have good wear resistance, and are suitable for cutting materials that greatly wear tools, such as fiber, hard rubber, plastic, etc., and can also be used for processing stainless steel, high-strength steel, high-temperature alloy and other materials.
③ Cobalt high speed steel. It is a cobalt containing superhard high speed steel with typical grades, such as W2Mo9Cr4VCo8 (M42 for short). It has very high hardness, and its hardness can reach 69-70HRC. It is suitable for machining high-strength heat-resistant steel, high-temperature alloy, titanium alloy and other difficult to machine materials. M42 has good grindability and is suitable for making precision and complex tools, but it is not suitable for working under impact cutting conditions.
④ Aluminum high-speed steel. It is an aluminum containing superhard high-speed steel with typical grades, such as W6Mo5Cr4V2Al (501 for short). The high temperature hardness at 6000C also reaches 54HRC, and the cutting performance is equivalent to M42. It is suitable for manufacturing milling cutters, drills, reamers, gear cutters, broaches, etc., and is used for processing alloy steel, stainless steel, high-strength steel, superalloys, and other materials.
⑤ Nitrogen superhard high speed steel. Typical grades, such as W12M03Cr4V3N (V3N for short), belong to nitrogen containing superhard high-speed steel. The hardness, strength and toughness are equivalent to M42. It can be used as a substitute for cobalt containing high-speed steel for low-speed cutting of difficult to machine materials and low-speed high precision machining.
(3) Melting of high-speed steel and powder metallurgy high-speed steel
According to different manufacturing processes, high speed steel can be divided into smelting high speed steel and powder metallurgy high speed steel.
① Melting high speed steel: both ordinary high speed steel and high-performance high speed steel are made by smelting. They are made into cutters through smelting, ingot casting, plating and rolling processes. Carbide segregation is a serious problem that is easy to occur in smelting high speed steel. Hard and brittle carbides are unevenly distributed in high speed steel, and the grain size is coarse (up to dozens of microns), which adversely affects the wear resistance, toughness and cutting performance of high speed steel tools.
② Powder metallurgy high speed steel (PM HSS): The powder metallurgy high speed steel (PM HSS) is a kind of steel melt from a high frequency induction furnace, atomized with high pressure argon or pure nitrogen, quenched to obtain fine and uniform crystalline structure (high-speed steel powder), and then pressed into a tool blank under high temperature and high pressure, or first made into a steel blank, then forged and rolled into a tool shape. Compared with the high speed steel made by melting method, PM HSS has the advantages that the carbide grains are fine and uniform, and the strength, toughness and wear resistance are much higher than those of the high speed steel made by melting. PM HSS tools will further develop and occupy an important position in the field of complex NC tools. Typical brands, such as F15, FR71, GFl, GF2, GF3, PT1, PVN, etc., can be used to manufacture tools with large size, heavy load and high impact, and can also be used to manufacture precision tools.
III Selection principle of NC tool materials
At present, the widely used NC tool materials mainly include diamond tools, cubic boron nitride tools, ceramic tools, coated tools, cemented carbide tools and high-speed steel tools. There are many general brands of tool materials, and their performance varies greatly. The following table shows the main performance indicators of various tool materials.
Tool materials for NC machining must be selected according to the workpiece and processing properties. The selection of tool materials shall be reasonably matched with the machining objects. The matching of cutting tool materials with the machining objects mainly refers to the matching of their mechanical properties, physical properties and chemical properties to obtain the longest tool life and maximum cutting productivity.
1. Mechanical property matching between cutting tool material and machining object
The matching of mechanical properties between cutting tools and machining objects mainly refers to the matching of mechanical properties such as strength, toughness and hardness of tools and workpiece materials. Tool materials with different mechanical properties are suitable for processing different workpiece materials.
① The order of tool material hardness is: diamond tool>cubic boron nitride tool>ceramic tool>cemented carbide>high speed steel.
② The order of bending strength of tool materials is: high speed steel>cemented carbide>ceramic tools>diamond and cubic boron nitride tools.
③ The order of tool material toughness is: high speed steel>cemented carbide>cubic boron nitride, diamond and ceramic tools.
The workpiece material with high hardness must be processed with a tool with higher hardness. The hardness of the tool material must be higher than that of the workpiece material, which is generally required to be above 60HRC. The higher the hardness of the tool material, the better its wear resistance. For example, when the cobalt content in cemented carbide increases, its strength and toughness increase, but its hardness decreases, which is suitable for rough machining; When the cobalt content decreases, its hardness and wear resistance increase, which is suitable for finishing.
Tools with excellent high temperature mechanical properties are especially suitable for high-speed machining. The excellent high-temperature performance of ceramic tools enables them to cut at a high speed, and the allowable cutting speed can be 2~10 times higher than that of cemented carbide.
2. Matching of physical properties of cutting tool materials and machining objects
Tools with different physical properties, such as high-speed steel tools with high thermal conductivity and low melting point, ceramic tools with high melting point and low thermal expansion, diamond tools with high thermal conductivity and low thermal expansion, are suitable for machining different workpiece materials. When machining workpieces with poor thermal conductivity, tool materials with good thermal conductivity should be used to make the cutting heat transfer quickly and reduce the cutting temperature. Because of the high thermal conductivity and thermal diffusivity of diamond, the cutting heat is easy to dissipate and will not produce great thermal deformation, which is particularly important for precision machining tools with high dimensional accuracy requirements.
① The heat resistance temperature of various tool materials: 700 ～ 8000C for diamond tools, 13000 ～ 15000C for PCBN tools, 1100 ～ 12000C for ceramic tools, 900 ～ 11000C for TiC (N) based cemented carbide, 800 ～ 9000C for WC based ultra-fine grain cemented carbide, and 600 ～ 7000C for HSS.
② The order of thermal conductivity of various tool materials is: PCD>PCBN>WC based carbide>TiC (N) based carbide>HSS>Si3N4 based ceramics>A1203 based ceramics.
③ The order of thermal expansion coefficient of various tool materials is HSS>WC based carbide>TiC (N)>A1203 based ceramics>PCBN>Si3N4 based ceramics>PCD.
④ The order of thermal shock resistance of various tool materials is HSS>WC based carbide>Si3N4 based ceramics>PCBN>PCD>TiC (N) based carbide>A1203 based ceramics.
3. Chemical property matching between cutting tool material and machining object
The matching problem of chemical properties between cutting tool materials and machining objects mainly refers to the matching of chemical properties such as chemical affinity, chemical reaction, diffusion and dissolution of tool materials and workpiece materials. The material of the workpiece is different for different cutters.
① The anti bonding temperature of various tool materials (with steel) is: PCBN>ceramics>cemented carbide>HSS.
② The oxidation resistance temperature of various tool materials is: ceramic>PCBN>cemented carbide>diamond>HSS.
③ The diffusion strength of the tool materials (for steel) is diamond>Si3N4 based ceramics>PCBN>A1203 based ceramics. The diffusion strength (for titanium) is A1203 based ceramic>PCBN>SiC>Si3N4>diamond.
4. Reasonable selection of NC tool materials
Generally speaking, PCBN, ceramic tools, coated cemented carbide and TiCN based cemented carbide tools are suitable for NC machining of ferrous metals such as steel; PCD tools are suitable for processing nonferrous materials such as Al, Mg, Cu and their alloys and non-metallic materials. Table 3-3-2 lists some work-piece materials suitable for machining the above tool materials.