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only when good processing equipment cooperates with cnc tools can it exert its due efficiency and achieve good economic benefits. with the development of tool materials, the physical, mechanical properties and cutting performance of various new tool materials have been greatly improved, and the scope of application has been continuously expanded.

first, the tool material should have basic properties

the choice of tool material has a great influence on tool life, machining efficiency, machining quality and machining cost. cutting tools are subject to high pressure, high temperature, friction, shock 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, generally above 60hrc. the higher the hardness of the tool material, the better the wear resistance.

(2) strength and toughness. the tool material should have high strength and toughness to withstand cutting forces, shocks and vibrations, and prevent brittle fracture and chipping of the tool.

(3) heat resistance. the tool material has better heat resistance, can withstand high cutting temperatures, and has good oxidation resistance.

(4) process performance and economy. the tool material should have good forging performance, heat treatment performance, welding performance, grinding performance, etc., and should pursue a high cost performance.

2. types, properties, characteristics and applications of tool materials

1. types, properties and characteristics of diamond tool materials and tool applications

diamond is an allotrope of carbon, which is a relatively hard material that has been found in nature. diamond tools have high hardness, high wear resistance and high thermal conductivity, and are widely used in the processing of non-ferrous and non-metallic materials. especially in the high-speed cutting of aluminum and silicon-aluminum alloys, diamond tools are the main types of cutting tools that are difficult to replace. diamond tools that can achieve high efficiency, high stability and long life are an indispensable tool in modern cnc machining.

⑴ types of diamond tools

① natural diamond tool: natural diamond has been used as a cutting tool for hundreds of years. the natural single crystal diamond tool has been finely ground, and the cutting edge can be extremely sharp. the cutting edge radius can reach 0.002μm, which can realize ultra-thin cutting and can it produces extremely high workpiece accuracy and extremely low surface roughness, and is a recognized, ideal and irreplaceable ultra-precision machining tool.

② pcd diamond cutting tools: natural diamonds are expensive, and polycrystalline diamond (pcd) is widely used in cutting. after the success, natural diamond tools have been replaced by synthetic polycrystalline diamond in many occasions. pcd is rich in raw materials, and its price is only one tenth to one tenth of natural diamond.

pcd tools cannot grind extremely sharp edges, and the surface quality of the processed workpieces is not as good as that of natural diamonds. at present, pcd inserts with chipbreakers cannot be easily manufactured in the industry. therefore, pcd can only be used for fine cutting of non-ferrous metals and non-metals, and it is difficult to achieve ultra-precision mirror cutting.

③ cvd diamond tools: since the late 1970s and early 1980s, cvd diamond technology has appeared in japan. cvd diamond refers to the synthesis of a diamond film on a heterogeneous substrate (such as cemented carbide, ceramics, etc.) by chemical vapor deposition (cvd). cvd diamond has the exact same structure and characteristics as natural diamond.

the performance of cvd diamond is very close to that of natural diamond. it has the advantages of natural single crystal diamond and polycrystalline diamond (pcd), and overcomes their shortcomings to a certain extent.

(2) performance characteristics of diamond tools:

① extremely high hardness and wear resistance: natural diamond is the hardest substance that has been found in nature. diamond has extremely high wear resistance. when machining high-hardness materials, the life of diamond tools is 10 to 100 times that of cemented carbide tools, or even hundreds of times.

② low friction coefficient: the friction coefficient between diamond and some non-ferrous metals is lower than other tools, the friction coefficient is low, the deformation during processing is small, and the cutting force can be reduced.

③ the cutting edge is very sharp: the cutting edge of the diamond tool can be very sharp, and the natural single crystal diamond tool can be as high as 0.002 ~ 0.008μm, which can perform 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 easily dissipated, and the temperature of the cutting part of the tool is low.

⑤ has a low thermal expansion coefficient: the thermal expansion coefficient of diamond is several times smaller than that of cemented carbide, and the change in tool size caused by cutting heat is small, which is particularly important for precision and ultra-precision machining that require high dimensional accuracy.

(3) application of diamond tools.

diamond tools are mostly used for fine cutting and boring of non-ferrous and non-metallic materials at high speed. it is suitable for processing various wear-resistant non-metals, such as glass fiber reinforced plastic powder metallurgy blanks, ceramic materials, etc.; various wear-resistant non-ferrous metals, such as various silicon aluminum alloys; various non-ferrous metals finishing.

the disadvantage of diamond tools is that the thermal stability is poor. when the cutting temperature exceeds 700 ° c ~ 800 ° c, it will completely lose its hardness; in addition, it is not suitable for cutting ferrous metals, because diamond (carbon) is easy to mix with iron at high temperatures. the atomic action converts the carbon atoms into a graphite structure, and the tool is easily damaged.

2. types, properties and characteristics of cubic boron nitride tool materials and tool applications

the second superhard material, cubic boron nitride (cbn), synthesized by a method similar to the diamond manufacturing method, is second only to diamond in terms of hardness and thermal conductivity, and has excellent thermal stability. it can also be heated to 10000c in the atmosphere. oxidation does not occur. cbn has extremely stable chemical properties for ferrous metals and can be widely used in the processing of steel products.

(1) types of cubic boron nitride tools

cubic boron nitride (cbn) is a substance that does not exist in nature, and can be divided into single crystal and polycrystalline, namely cbn single crystal and polycrystalline cubic boron nitride (polycrystalline cubic bornnitride, referred to as pcbn). cbn is one of the allotropes of boron nitride (bn) with a structure similar to diamond.

pcbn (polycrystalline cubic boron nitride) is a polycrystalline material that sinters fine cbn materials together through bonding phases (tic, tin, al, ti, etc.) under high temperature and high pressure. diamond tool material, it and diamond are collectively referred to as superhard tool material. pcbn is mainly used to make knives or other tools.

pcbn tools 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 pcbn with a thickness of 0.5 to 1.0 mm on cemented carbide with good strength and toughness. its properties have good toughness, high hardness and wear resistance. it solves the problems of low bending strength and difficult welding of cbn inserts.

⑵ the main properties and characteristics of cubic boron nitride

although the hardness of cubic boron nitride is slightly lower than that of diamond, it is much higher than other high hardness materials. the outstanding advantage of cbn is that its thermal stability is much higher than that of diamond, which can reach above 1200°c (diamond is 700-800°c). reaction. the main performance characteristics of cubic boron nitride are as follows.

① high hardness and wear resistance: cbn crystal structure is similar to diamond, with hardness and strength similar to diamond. pcbn is especially suitable for processing high hardness materials that can only be ground before, and can obtain better surface quality of workpiece.

② it has high thermal stability: the heat resistance of cbn can reach 1400~1500℃, which is almost l times higher than that of diamond (700~800℃). pcbn tools can be used for high-speed cutting of superalloys and hardened steels at a speed 3 to 5 times higher than that of carbide tools.

③ excellent chemical stability: it does not have chemical effects with iron-based materials at 1200-1300 ° c, and will not wear as sharply 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, can be widely used in high-speed cutting of cast iron.

④ it has good thermal conductivity: although the thermal conductivity of cbn is not as good as that of diamond, the thermal conductivity of pcbn is second only to diamond among various tool materials, much higher than that of high-speed steel and cemented carbide.

⑤ has a lower coefficient of friction: a low coefficient of friction can reduce the cutting force during cutting, reduce the cutting temperature, and improve the quality of the machined surface.

(3) application of cubic boron nitride tool:

cubic boron nitride is suitable for finishing all kinds of hardened steel, hard cast iron, superalloy, cemented carbide, surface sprayed materials and other difficult-to-cut materials. the machining accuracy can reach it5 (the hole is it6), and the surface roughness value can be as small as ra1.25～0.20μm.

cbn tool material has poor toughness and flexural strength. therefore, cubic boron nitride turning tools are not suitable for rough machining at low speed and large impact load; at the same time, it is not suitable for cutting materials with high plasticity (such as aluminum alloys, copper alloys, nickel-based alloys, steels with high plasticity, etc.), because cutting these severe built-up edge occurs when metal is used, which deteriorates the machined surface.

3. types, properties and characteristics of ceramic tool materials and tool applications

ceramic tools have the characteristics of high hardness, good wear resistance, excellent heat resistance and chemical stability, and are not easy to bond with metals. ceramic tools occupy a very important position in cnc machining, and ceramic tools have become one of the main tools for high-speed cutting and difficult-to-machine materials processing. ceramic tools are widely used in high-speed cutting, dry cutting, hard cutting and cutting of difficult-to-machine materials. ceramic tools can efficiently process high-hard materials that traditional tools can't process at all, and realize "grinding by car"; the cutting speed of ceramic tools can be 2 to 10 times higher than that of carbide tools, thus greatly improving cutting production efficiency; ceramic tools the main raw materials used in tool materials are the most abundant elements in the earth's crust. therefore, the popularization and application of ceramic tools is of great significance to improve productivity, reduce processing costs, and save strategic precious metals, and will also greatly promote the advancement of cutting technology.

(1) types of ceramic tool materials

the types of ceramic tool materials can be generally 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 the most widely used. the performance of silicon nitride-based ceramics is better than that of alumina-based ceramics.

(2) 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 carbide and high-speed steel tools, reaching 93-95hra. ceramic tools can process high-hard materials that are difficult to process with traditional tools, and are suitable for high-speed cutting and hard cutting.

② high temperature resistance and good heat resistance: ceramic tools can still be cut at high temperatures above 1200 °c. ceramic tools have good high-temperature mechanical properties, and a12o3 ceramic tools have particularly good oxidation resistance, and the cutting edge can be used continuously even if it is in a red hot state. therefore, ceramic tools can achieve dry cutting, which can save cutting fluid.

③ good chemical stability: the ceramic tool is not easy to bond with metal, and has good corrosion resistance and chemical stability, which can reduce the bonding wear of the tool.

④ low friction coefficient: the affinity between ceramic tools and metal is small, and the friction coefficient is low, which can reduce the cutting force and cutting temperature.

(3) ceramic knives have applications

ceramic is one of the tool materials mainly used for high-speed finishing and semi-finishing. ceramic tools are suitable for machining all kinds of cast iron (gray cast iron, ductile iron, malleable cast iron, chilled cast iron, high alloy wear-resistant cast iron) and steel (carbon structural steel, alloy structural steel, high strength steel, high manganese steel, hardened steel etc.), can also be used to cut copper alloys, graphite, engineering plastics and composite materials.

the performance of ceramic tool materials has the problems of low bending strength and poor impact toughness, and it is not suitable for cutting at low speed and impact load.

4. properties and characteristics of coated tool materials and application of tools

coating the tool is one of the important ways to improve the tool performance. the emergence of coated tools has made a major breakthrough in the cutting performance of tools. the coated tool is coated with one or more layers of refractory compound with good wear resistance on the tool body with good toughness, which combines the tool matrix with the hard coating, thereby greatly improving the performance of the tool. coated tools can improve machining efficiency, improve machining accuracy, extend tool life and reduce machining costs.

about 80% of the cutting tools used in new cnc machine tools use coated tools. coated tools will be the most important tool varieties in the field of cnc machining in the future.

(1) types of coated tools

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 cemented carbide tools generally use chemical vapor deposition, and the deposition temperature is around 1000 °c. coated high-speed steel tools generally use physical vapor deposition, and the deposition temperature is around 500 °c;

according to the different substrate materials of coated tools, coated tools can be divided into carbide-coated tools, high-speed steel-coated tools, and coated tools on ceramics and superhard materials (diamond and cubic boron nitride).

according to the nature of the coating material, 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. the main advantages are high hardness and good wear resistance, typically tic and tin coatings. the goal of "soft" coating tools is a low coefficient of friction, also known as self-lubricating tools, which have friction with the workpiece material. the coefficient is very low, only about 0.1, which can reduce bonding, reduce friction, and reduce cutting force and cutting temperature.

nanoeoating tools have recently been developed. this coated tool is available in various combinations of coating materials (such as metal/metal, metal/ceramic, ceramic/ceramic, etc.) to meet different functional and performance requirements. reasonably designed nano-coating can make the tool material have excellent anti-friction, anti-wear and self-lubricating properties, which is suitable for high-speed dry cutting.

(2) characteristics of coated tools

the performance characteristics of coated tools are as follows:

① good mechanical and cutting performance: 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, but also has the high hardness, high wear resistance and low hardness of the coating. friction coefficient. therefore, the cutting speed of the coated tool can be more than 2 times higher than that of the uncoated tool, and a higher feed rate is allowed. the life of the coated tool is also improved.

② strong versatility: coated tools have a wide range of versatility, and the processing range is significantly expanded. one coated tool can be used instead of several non-coated tools.

③ coating thickness: with the increase of coating thickness, the tool life will also increase, but when the coating thickness reaches saturation, the tool life will no longer increase. when the coating is too thick, it is easy to cause peeling; when the coating is too thin, the wear resistance is poor.

④ regrindability: the regrindability of the coated blade is poor, the coating equipment is complex, the process requirements are high, and the coating time is long.

⑤ coating material: tools with different coating materials have different cutting performance. for example: when cutting at low speed, tic coating has an advantage;tin is more suitable for high-speed cutting.

(3) application of coated tools

coated tools have great potential in the field of cnc machining, and will be the most important tool variety in the field of cnc machining in the future. coating technology has been applied to end mills, reamers, drills, compound hole machining tools, gear hobs, gear shapers, shaving cutters, forming broaches and various machine-clamped indexable inserts to meet the needs of high-speed cutting machining. the needs of materials such as steel and cast iron, heat-resistant alloys and non-ferrous metals.

5. types, properties, characteristics and applications of carbide tool materials

carbide tools, especially indexable carbide tools, are the leading products of cnc machining tools. since the 1980s, the variety of solid and indexable carbide tools or inserts has been expanded to various in the field of cutting tools, indexable carbide tools have expanded from simple turning tools and face milling tools to various precision, complex and forming tools.

(1) types of carbide tools

according to the main chemical composition, cemented carbide can be divided into tungsten carbide-based cemented carbide and carbon (nitride) titanium (tic(n))-based cemented carbide.

tungsten carbide-based cemented carbides include tungsten-cobalt (yg), tungsten-cobalt-titanium (yt), and rare carbides (yw), each of which has its own advantages and disadvantages. the main components are tungsten carbide (wc) and titanium carbide. (tic), tantalum carbide (tac), niobium carbide (nbc), etc., the commonly used metal bonding phase is co.

carbon (nitride) titanium-based cemented carbide is a cemented carbide with tic as the main component (some added other carbides or nitrides). the commonly used metal bonding phases are mo and ni.

iso (international organization for standardization) divides cutting carbides into three categories:

k class, including kl0 ~ k40, is equivalent to my country's yg class (the main component is wc.co).

class p, including p01 to p50, is equivalent to class yt in my country (the main component is wc.tic.co).

the m type, including m10 to m40, is equivalent to the yw type in my country (the main component is wc-tic-tac(nbc)-co).

each grade represents a series of alloys from high hardness to maximum toughness with numbers between 01 and 50. (2) performance characteristics of cemented carbide tools

the performance characteristics of carbide cutting tools are as follows:

① high hardness: cemented carbide cutting tools are made of carbide with high hardness and melting point (called hard phase) and metal binder (called bonding phase) by powder metallurgy method, and its hardness is 89~93hra , much higher than that of high-speed steel. at 5400c, the hardness can still reach 82-87hra, which is the same as the hardness of high-speed steel at room temperature (83-86hra). the hardness value of cemented carbide varies with the nature, quantity, particle size and content of metal bonding phase of carbide, and generally decreases with the increase of bonding metal phase content. when the binder phase content is the same, the hardness of yt alloy is higher than that of yg alloy, and the alloy with tac (nbc) addition has higher high temperature hardness.

② bending strength and toughness: the bending strength of commonly used cemented carbide is in the range of 900-1500mpa. the higher the metal binder phase content, the higher the flexural strength. when the binder content is the same, the strength of yg-based (wc-co) alloys is higher than that of yt-based (wc-tic-co) alloys, and the strength decreases with the increase of tic content. cemented carbide is a brittle material, and its impact toughness at room temperature is only 1/30 to 1/8 of that of high-speed steel.

(3) application of commonly used carbide cutting tools

yg alloys are mainly used for machining cast iron, non-ferrous metals and non-metallic materials. fine-grained cemented carbide (such as yg3x, yg6x) has higher hardness and wear resistance than medium-grained carbide when the cobalt content is the same, and is suitable for processing some special hard cast iron, austenitic stainless steel, heat-resistant alloy, titanium alloy, hard bronze and wear-resistant insulating materials, etc.

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 higher heat resistance and wear resistance, the brand with higher tic content should be selected. yt alloys are suitable for processing plastic materials such as steel, but not suitable for processing titanium alloys and silicon-aluminum alloys.

yw alloy has both the properties of yg and yt alloys, and has good comprehensive performance. it can be used for processing steel, cast iron and non-ferrous metals. such alloys can have high strength if the cobalt content is appropriately increased, and can be used for roughing and interrupted 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 high alloy tool steel with more alloying elements such as w, mo, cr, and v added. high-speed steel tools have excellent comprehensive performance in terms of strength, toughness and manufacturability. in complex tools, especially for hole-making tools, milling cutters, threading tools, broaches, gear cutting tools and other complex cutting tools, high-speed steel is still occupy a major position. high-speed steel knives are easy to sharpen cutting edges.

according to different uses, high-speed steel can be divided into general-purpose high-speed steel and high-performance high-speed steel.

⑴ universal high-speed steel tool

general purpose high speed steel. generally, it can be divided into two types: tungsten steel and tungsten-molybdenum steel. this type of high-speed steel contains 0.7% to 0.9% (c). according to the different tungsten content in steel, it can be divided into tungsten steel with w content of 12% or 18%, tungsten-molybdenum steel with w content of 6% or 8%, and molybdenum steel with w content of 2% or without w. . general-purpose high-speed steel has a certain hardness (63-66hrc) and wear resistance, high strength and toughness, good plasticity and processability, so it is used to manufacture various complex tools.

① tungsten steel: the typical grade of general-purpose high-speed steel tungsten steel is w18cr4v (w18 for short), which has good comprehensive performance. the high temperature hardness at 6000c is 48.5hrc, which can be used to manufacture various complex tools. it has the advantages of good grindability and low decarburization sensitivity, but due to the high carbide content, the distribution is less uniform, the particles are large, and the strength and toughness are not high.

② tungsten-molybdenum steel: refers to a high-speed steel obtained by replacing part of tungsten in tungsten steel with molybdenum. the typical grade of tungsten-molybdenum steel is w6mo5cr4v2 (referred to as m2). the carbide particles of m2 are fine and uniform, and the strength, toughness and high temperature plasticity are better than those of w18cr4v. another tungsten-molybdenum steel is w9mo3cr4v (w9 for short), its thermal stability is slightly higher than that of m2 steel, its bending strength and toughness are better than w6m05cr4v2, and it has good machinability.

⑵ high-performance high-speed steel cutting tools

high-performance high-speed steel refers to a new type of steel with carbon content, vanadium content, and alloying elements such as co and al added to the general-purpose high-speed steel composition, thereby improving 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, suitable for manufacturing and processing ordinary steel and cast iron, drills, reamers, taps and milling cutters with high wear resistance requirements or tools for processing harder materials, should not withstand large shocks.

② high vanadium high speed steel. typical grades, such as w12cr4v4mo, (ev4 for short), with v content increased to 3% to 5%, good wear resistance, suitable for cutting materials with great tool wear, such as fiber, hard rubber, plastic, etc., can also be used for processing materials such as stainless steel, high strength steel and superalloys.

③ cobalt high speed steel. it is a cobalt-containing super-hard high-speed steel. typical grades, such as w2mo9cr4vco8 (referred to as m42), have high hardness, and its hardness can reach 69-70hrc. it is suitable for processing high-strength heat-resistant steel, high-temperature alloys, titanium alloys, etc. machining material, m42 has good grindability and is suitable for making sophisticated and complex tools, but it is not suitable for working under impact cutting conditions.

④ aluminum high speed steel. it belongs to aluminum-containing superhard high-speed steel, typical grades, such as w6mo5cr4v2al, (501 for short), high temperature hardness at 6000c also reaches 54hrc, cutting performance is equivalent to m42, suitable for manufacturing milling cutters, drills, reamers, gear cutters, broaches etc., for processing alloy steel, stainless steel, high-strength steel and superalloy and other materials.

⑤ nitrogen superhard high-speed steel. typical grades, such as w12m03cr4v3n, referred to as (v3n), are nitrogen-containing super-hard high-speed steels, with hardness, strength, and toughness equivalent to m42. they can be used as substitutes for cobalt-containing high-speed steels for low-speed cutting of difficult-to-machine materials and low-speed high-precision machining. processing.

(3) melting 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 manufactured by melting method. they are made into knives through processes such as smelting, ingot casting and plating. the serious problem that is prone to occur in smelting high-speed steel is carbide segregation. hard and brittle carbides are unevenly distributed in high-speed steel, and the grains are coarse (up to several tens of microns), which affects the wear resistance and toughness of high-speed steel tools. and adversely affect cutting performance.

② powder metallurgy high-speed steel (pm hss): powder metallurgy high-speed steel (pm hss) is a molten steel smelted in a high-frequency induction furnace, atomized with high-pressure argon or pure nitrogen, and then quenched to obtain fine and uniform crystals structure (high-speed steel powder), and then the obtained powder is pressed into a knife billet under high temperature and high pressure, or a billet is first made into a billet and then forged and rolled into a knife shape. compared with the high-speed steel produced by the melting method, pm hss has the advantages that the carbide grains are fine and uniform, and the strength, toughness and wear resistance are much improved compared to the melting high-speed steel. in the field of complex cnc tools, pm hss tools will further develop and occupy an important position. typical grades, such as f15, fr71, gfl, gf2, gf3, pt1, pvn, etc., can be used to manufacture large-size, heavy-duty, high-impact tools, as well as precision tools.

3. selection principles of cnc tool materials

at present, the widely used cnc tool materials mainly include diamond tools, cubic boron nitride tools, ceramic tools, coated tools, carbide tools and high-speed steel tools. there are many total grades of tool materials, and their performance varies greatly. the following table

the main performance indicators of various tool materials.