A good horse needs a good saddle and uses advanced CNC machining equipment. If the wrong tools are used, it will be useless! Selecting the appropriate tool material has a great impact on tool service life, processing efficiency, processing quality and processing cost. This article provides useful information about knife knowledge, collect it and forward it, let’s learn together.
Tool materials should have basic properties
The selection of tool materials has a great impact on tool life, processing efficiency, processing quality and processing cost. Tools must withstand high pressure, high temperature, friction, impact and vibration when cutting. Therefore, tool materials should have the following basic properties:
(1) Hardness and wear resistance. The hardness of the tool material must be higher than the hardness 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. Tool materials should have high strength and toughness to withstand cutting forces, impact and vibration, and prevent brittle fracture and chipping of the tool.
(3) Heat resistance. The tool material has good heat resistance, can withstand high cutting temperatures, and has good oxidation resistance.
(4) Process performance and economy. Tool materials should have good forging performance, heat treatment performance, welding performance; grinding performance, etc., and should pursue high performance-price ratio.
Types, properties, characteristics, and applications of tool materials
1. Diamond tool materials
Diamond is an allotrope of carbon and is the hardest material found in nature. Diamond cutting tools have high hardness, high wear resistance and high thermal conductivity, and are widely used in the processing of non-ferrous metals and non-metallic materials. Especially in high-speed cutting of aluminum and silicon-aluminum alloys, diamond tools are the main type of cutting tools that are difficult to replace. Diamond tools that can achieve high efficiency, high stability, and long service life are indispensable and important tools in modern CNC machining.
⑴ Types of diamond tools
① Natural diamond tools: Natural diamonds have been used as cutting tools for hundreds of years. Natural single crystal diamond tools have been finely ground to make the cutting edge extremely sharp. The cutting edge radius can reach 0.002μm, which can achieve ultra-thin cutting. It can process extremely high workpiece precision and extremely low surface roughness. It is a recognized, ideal and irreplaceable ultra-precision machining tool.
② PCD diamond cutting tools: Natural diamonds are expensive. The most widely used diamond in cutting processing is polycrystalline diamond (PCD). Since the early 1970s, polycrystalline diamond (Polycrystauine diamond, referred to as PCD blades) prepared using high-temperature and high-pressure synthesis technology has been developed. After its success, natural diamond cutting tools have been replaced by artificial polycrystalline diamond on many occasions. PCD raw materials are rich in sources, and their price is only a few to one-tenth of that of natural diamond. PCD cutting tools cannot be ground to produce extremely sharp cutting tools. The surface quality of the cutting edge and the processed workpiece is not as good as that of natural diamond. It is not yet convenient to manufacture PCD blades with chip breakers in the industry. Therefore, PCD can only be used for precision cutting of non-ferrous metals and non-metals, and it is difficult to achieve ultra-high precision cutting. Precision mirror cutting.
③ CVD diamond cutting tools: Since the late 1970s to the early 1980s, CVD diamond technology appeared in Japan. CVD diamond refers to the use of chemical vapor deposition (CVD) to synthesize a diamond film on a heterogeneous matrix (such as cemented carbide, ceramics, etc.). CVD diamond has exactly the 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.
⑵ Performance characteristics of diamond tools
① Extremely high hardness and wear resistance: Natural diamond is the hardest substance found in nature. Diamond has extremely high wear resistance. When processing high-hardness materials, the life of diamond tools is 10 to 100 times that of carbide tools, or even hundreds of times.
② Has a very low friction coefficient: The friction coefficient between diamond and some non-ferrous metals is lower than other cutting 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 ground very sharp. The natural single crystal diamond tool can be as high as 0.002~0.008μm, which can carry out ultra-thin cutting and ultra-precision processing.
④ High thermal conductivity: Diamond has high thermal conductivity and thermal diffusivity, so cutting heat is easily dissipated and the temperature of the cutting part of the tool is low.
⑤ Has a lower 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 very small, which is particularly important for precision and ultra-precision machining that requires high dimensional accuracy.
⑶ Application of diamond tools
Diamond tools are mostly used for fine cutting and boring of non-ferrous metals and non-metallic materials at high speeds. Suitable for processing various wear-resistant non-metals, such as fiberglass powder metallurgy blanks, ceramic materials, etc.; various wear-resistant non-ferrous metals, such as various silicon-aluminum alloys; and finishing processing of various non-ferrous metals.
The disadvantage of diamond tools is that they have poor thermal stability. When the cutting temperature exceeds 700℃~800℃, they will completely lose their hardness. In addition, they are not suitable for cutting ferrous metals because diamond (carbon) easily reacts with iron at high temperatures. Atomic action converts carbon atoms into graphite structure, and the tool is easily damaged.
2. Cubic boron nitride tool material
Cubic boron nitride (CBN), the second superhard material synthesized using a method similar to diamond manufacturing, is second only to diamond in terms of hardness and thermal conductivity. It has excellent thermal stability and can be heated to 10,000C in the atmosphere. No oxidation occurs. CBN has extremely stable chemical properties for ferrous metals and can be widely used in the processing of steel products.
⑴ Types of cubic boron nitride cutting tools
Cubic boron nitride (CBN) is a substance that does not exist in nature. It is divided into single crystal and polycrystalline, namely CBN single crystal and polycrystalline cubic boron nitride (Polycrystalline cubic bornnitride, PCBN for short). CBN is one of the allotropes of boron nitride (BN) and has a structure similar to diamond.
PCBN (polycrystalline cubic boron nitride) is a polycrystalline material in which fine CBN materials are sintered together through binding phases (TiC, TiN, Al, Ti, etc.) under high temperature and pressure. It is currently the second-hardest artificially synthesized material. Diamond tool material, together with diamond, is collectively called superhard tool material. PCBN is mainly used to make knives or other tools.
PCBN cutting tools can be divided into solid PCBN blades and PCBN composite blades sintered with carbide.
PCBN composite blades are made by sintering a layer of PCBN with a thickness of 0.5 to 1.0mm on a cemented carbide with good strength and toughness. Its performance combines good toughness with high hardness and wear resistance. It It solves the problems of low bending strength and difficult welding of CBN blades.
⑵ Main properties and characteristics of cubic boron nitride
Although the hardness of cubic boron nitride is slightly lower than 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, reaching temperatures above 1200°C (diamond is 700-800°C). Another outstanding advantage is that it is chemically inert and does not react with iron at 1200-1300°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, and has similar hardness and strength to diamond. PCBN is particularly suitable for processing high-hardness materials that could only be ground before, and can obtain better surface quality of the workpiece.
② High thermal stability: The heat resistance of CBN can reach 1400~1500℃, which is almost 1 times higher than the heat resistance of diamond (700~800℃). PCBN tools can cut high-temperature alloys and hardened steel at high speeds 3 to 5 times higher than carbide tools.
③ Excellent chemical stability: It has no chemical interaction with iron-based materials up to 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 quenched steel Parts and chilled cast iron, can be widely used in high-speed cutting of cast iron.
④ Good thermal conductivity: Although the thermal conductivity of CBN cannot keep up with diamond, the thermal conductivity of PCBN among various tool materials is second only to diamond, and much higher than high-speed steel and cemented carbide.
⑤ Has a lower friction coefficient: A low friction coefficient can lead to a reduction in cutting force during cutting, a reduction in cutting temperature, and an improvement in the quality of the machined surface.
⑶ Application of cubic boron nitride cutting tools
Cubic boron nitride is suitable for finishing various difficult-to-cut materials such as quenched steel, hard cast iron, high-temperature alloys, cemented carbide, and surface spray materials. The processing accuracy can reach IT5 (the hole is IT6), and the surface roughness value can be as small as Ra1.25~0.20μm.
Cubic boron nitride tool material has poor toughness and bending strength. Therefore, cubic boron nitride turning tools are not suitable for rough machining at low speeds and high impact loads; at the same time, they are 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 Serious built-up edges will occur when working with metal, deteriorating the machined surface.
3. ceramic tool materials
Ceramic cutting tools have the characteristics of high hardness, good wear resistance, excellent heat resistance and chemical stability, and are not easy to bond with metal. Ceramic tools play a very important role in CNC machining. Ceramic tools have become one of the main tools for high-speed cutting and processing of difficult-to-machine materials. Ceramic cutting 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 cannot process at all, realizing “turning instead of grinding”; the optimal cutting speed of ceramic tools can be 2 to 10 times higher than that of carbide tools, thus greatly improving cutting production efficiency. ; The main raw materials used in ceramic tool materials are the most abundant elements in the earth’s crust. Therefore, the promotion and application of ceramic tools are of great significance for improving productivity, reducing processing costs, and saving strategic precious metals. It will also greatly promote the development of cutting technology. progress.
⑴ Types of ceramic tool materials
Ceramic tool material types 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 the most widely used. The performance of silicon nitride-based ceramics is superior to that of alumina-based ceramics.
⑵ Performance and characteristics of ceramic cutting tools
① High hardness and good wear resistance: Although the hardness of ceramic cutting tools is not as high as PCD and PCBN, it is much higher than that of carbide and high-speed steel cutting tools, reaching 93-95HRA. Ceramic cutting tools can process high-hard materials that are difficult to process with traditional cutting tools and are suitable for high-speed cutting and hard cutting.
② High temperature resistance and good heat resistance: Ceramic cutting tools can still cut at high temperatures above 1200°C. Ceramic cutting tools have good high-temperature mechanical properties. A12O3 ceramic cutting tools have particularly good oxidation resistance. Even if the cutting edge is in a red-hot state, it can be used continuously. Therefore, ceramic tools can achieve dry cutting, thus eliminating the need for cutting fluid.
③ Good chemical stability: Ceramic cutting tools are not easy to bond with metal, and are corrosion-resistant and have good chemical stability, which can reduce the bonding wear of cutting tools.
④ Low friction coefficient: The affinity between ceramic tools and metal is small, and the friction coefficient is low, which can reduce cutting force and cutting temperature.
⑶ Ceramic knives have applications
Ceramics are one of the tool materials mainly used for high-speed finishing and semi-finishing. Ceramic cutting tools are suitable for cutting various cast irons (grey cast iron, ductile iron, malleable cast iron, chilled cast iron, high alloy wear-resistant cast iron) and steel materials (carbon structural steel, alloy structural steel, high strength steel, high manganese steel, quenched steel etc.), can also be used to cut copper alloys, graphite, engineering plastics and composite materials.
The material properties of ceramic cutting tools have the problems of low bending strength and poor impact toughness, making them unsuitable for cutting at low speeds and under impact loads.
4. Coated tool materials
Coating cutting tools is one of the important ways to improve tool performance. The emergence of coated tools has brought about a major breakthrough in the cutting performance of cutting 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, thereby greatly improving the tool performance. Coated tools can improve processing efficiency, improve processing accuracy, extend tool service life, and reduce processing costs.
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 CNC machining in the future.
⑴ 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 carbide cutting tools generally use chemical vapor deposition method, and the deposition temperature is around 1000°C. Coated high-speed steel cutting tools generally use physical vapor deposition method, 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 properties of the coating material, coated tools can be divided into two categories, namely “hard” coated tools and ‘soft’ coated tools. The main goals pursued by “hard” coated tools are high hardness and wear resistance Its main advantages are high hardness and good wear resistance, typically TiC and TiN coatings. The goal pursued by “soft” coating tools is a low friction coefficient, also known as self-lubricating tools, which friction with the workpiece material The coefficient is very low, only about 0.1, which can reduce adhesion, reduce friction, and reduce cutting force and cutting temperature.
Nanocoating (Nanoeoating) cutting tools have recently been developed. Such coated tools can use different combinations of coating materials (such as metal/metal, metal/ceramic, ceramic/ceramic, etc.) to meet different functional and performance requirements. Properly designed nano-coatings can make tool materials have excellent friction-reducing and anti-wear functions and self-lubricating properties, making them suitable for high-speed dry cutting.
⑵ Characteristics of coated cutting tools
① Good mechanical and cutting performance: Coated tools combine the excellent properties of the base material and the coating material. They not only maintain the good toughness and high strength of the base material, but also have the high hardness, high wear resistance and low Friction coefficient. Therefore, the cutting speed of coated tools can be increased by more than 2 times than that of uncoated tools, and higher feed rates are allowed. The life of coated tools is also improved.
② Strong versatility: Coated tools have wide versatility and significantly expand the processing range. One coated tool can replace several non-coated tools.
③ Coating thickness: As the coating thickness increases, the tool life will also increase, but when the coating thickness reaches saturation, the tool life will no longer increase significantly. When the coating is too thick, it will easily cause peeling; when the coating is too thin, the wear resistance will be poor.
④ Regrindability: Coated blades have poor regrindability, complex coating equipment, high process requirements, and long coating time.
⑤ Coating material: Tools with different coating materials have different cutting performance. For example: when cutting at low speed, TiC coating has advantages; when cutting at high speed, TiN is more suitable.
⑶Application of coated cutting 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, drill bits, composite hole processing tools, gear hobs, gear shaper cutters, gear shaving cutters, forming broaches and various machine-clamped indexable inserts to meet various requirements of high-speed cutting processing. The needs of materials such as steel and cast iron, heat-resistant alloys and non-ferrous metals.
5. Carbide tool materials
Carbide cutting tools, especially indexable carbide cutting tools, are the leading products of CNC machining tools. Since the 1980s, the varieties of various integral and indexable carbide cutting tools or inserts have been expanded to various types. A variety of cutting tool fields, in which indexable carbide tools have expanded from simple turning tools and face milling cutters to various precision, complex, and forming tool fields.
⑴ Types of carbide cutting tools
According to the main chemical composition, cemented carbide can be divided into tungsten carbide-based cemented carbide and titanium carbon (nitride) (TiC(N))-based cemented carbide.
Tungsten carbide-based cemented carbide includes three types: tungsten cobalt (YG), tungsten cobalt titanium (YT), and rare carbide added (YW). Each 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.
Titanium carbon (nitride)-based cemented carbide is a cemented carbide with TiC as the main component (some add other carbides or nitrides). The commonly used metal bonding phases are Mo and Ni.
ISO (International Organization for Standardization) divides cutting carbide into three categories:
Class K, including Kl0 ~ K40, is equivalent to my country’s YG class (the main component is WC.Co).
P category, including P01 ~ P50, is equivalent to my country’s YT category (the main component is WC.TiC.Co).
Class M, including M10~M40, is equivalent to my country’s YW class (main component is WC-TiC-TaC(NbC)-Co).
Each grade represents a series of alloys ranging from high hardness to maximum toughness with a number between 01 and 50.
⑵ Performance characteristics of carbide cutting tools
① High hardness: Carbide cutting tools are made of carbides with high hardness and melting point (called hard phase) and metal binders (called bonding phase) through powder metallurgy, with a hardness of 89 to 93HRA. , much higher than 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 changes with the nature, quantity, particle size of carbides and the content of the metal bonding phase, and generally decreases with the increase in the content of the bonding metal phase. When the binder phase content is the same, the hardness of YT alloys is higher than that of YG alloys, and alloys added with TaC (NbC) have higher high temperature hardness.
② Bending strength and toughness: The bending strength of commonly used cemented carbide is in the range of 900 to 1500MPa. The higher the metal binder phase content, the higher the flexural strength. When the binder content is the same, the strength of YG type (WC-Co) alloy is higher than that of YT type (WC-TiC-Co) alloy, and as the TiC content increases, the strength decreases. Cemented carbide is a brittle material, and its impact toughness at room temperature is only 1/30 to 1/8 that of high-speed steel.
⑶ Application of commonly used carbide cutting tools
YG alloys are mainly used for processing 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 with the same cobalt content. It 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 temperatures than YG type, and good oxidation resistance. Therefore, when the knife is required to have higher heat resistance and wear resistance, a grade with a higher TiC content should be selected. YT alloys are suitable for processing plastic materials such as steel, but are not suitable for processing titanium alloys and silicon-aluminum alloys.
YW alloy has the properties of YG and YT alloys, and has good comprehensive properties. It can be used to process steel, cast iron and non-ferrous metals. If the cobalt content of this type of alloy is appropriately increased, the strength can be very high and can be used for rough machining and interrupted cutting of various difficult-to-machine materials.
6． High speed steel cutting tools
High Speed Steel (HSS) is a high-alloy tool steel that adds more alloying elements such as W, Mo, Cr, and V. High-speed steel cutting tools have excellent comprehensive performance in terms of strength, toughness and processability. In complex cutting tools, especially those with complex blade shapes such as hole processing tools, milling cutters, threading tools, broaching tools, gear cutting tools, etc., high-speed steel is still used. occupy a dominant position. High-speed steel knives are easy to sharpen to produce sharp 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 General-purpose high-speed steel cutting tools
General purpose high speed steel. Generally, it can be divided into two categories: 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 the steel, it can be divided into tungsten steel with a W content of 12% or 18%, tungsten-molybdenum steel with a W content of 6% or 8%, and molybdenum steel with a W content of 2% or no W. . General-purpose high-speed steel has a certain hardness (63-66HRC) and wear resistance, high strength and toughness, good plasticity and processing technology, so it is widely used in manufacturing various complex tools.
① Tungsten steel: The typical grade of general-purpose high-speed steel tungsten steel is W18Cr4V, (referred to as W18). It has good overall performance. The high-temperature hardness at 6000C is 48.5HRC, and can be used to manufacture various complex tools. It has the advantages of good grindability and low decarburization sensitivity, but due to its high carbide content, uneven distribution, large particles, and low strength and toughness.
② Tungsten-molybdenum steel: refers to a high-speed steel obtained by replacing part of the 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 its strength, toughness and high-temperature plasticity are better than those of W18Cr4V. Another type 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 processability.
⑵ High-performance high-speed steel cutting tools
High-performance high-speed steel refers to a new steel type that adds some carbon content, vanadium content, and alloying elements such as Co and Al to the composition of general-purpose high-speed steel, 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) has high hardness at room temperature and high temperature. It is suitable for manufacturing and processing ordinary steel and cast iron, drill bits, reamers, taps and milling cutters with high wear resistance requirements, or tools for processing harder materials. It is not suitable to withstand large impacts.
② High vanadium high speed steel. Typical grades, such as W12Cr4V4Mo, (referred to as EV4), have V content increased to 3% to 5%, have good wear resistance, and are suitable for cutting materials that cause great tool wear, such as fibers, hard rubber, plastics, etc., and can also be used for processing Materials such as stainless steel, high-strength steel and high-temperature alloys.
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 very high hardness. Its hardness can reach 69-70HRC. It is suitable for processing difficult-to-use high-strength heat-resistant steels, high-temperature alloys, titanium alloys, etc. Processing 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 super-hard high-speed steel. Typical grades are, for example, W6Mo5Cr4V2Al, (referred to as 501). The high-temperature hardness at 6000C also reaches 54HRC. The cutting performance is equivalent to M42. It is suitable for manufacturing milling cutters, drill bits, reamers, gear cutters, and broaches. etc., used for processing materials such as alloy steel, stainless steel, high-strength steel and high-temperature alloys.
⑤ Nitrogen super-hard high-speed steel. Typical grades, such as W12M03Cr4V3N, referred to as (V3N), are nitrogen-containing super-hard high-speed steels. The hardness, strength, and toughness are equivalent to M42. They can be used as a substitute for cobalt-containing high-speed steels and are used for low-speed cutting of difficult-to-machine materials and low-speed, high-precision steels. processing.
⑶ Smelting 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 Smelting high-speed steel: Both ordinary high-speed steel and high-performance high-speed steel are made by smelting methods. They are made into knives through processes such as smelting, ingot casting, and plating and rolling. A serious problem that easily occurs when 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 dozens 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 liquid 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 press the resulting powder into a knife blank under high temperature and high pressure, or first make a steel billet and then forge and roll it into a knife shape. Compared with high-speed steel manufactured 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 melted 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-sized, heavy-loaded, high-impact cutting tools, as well as precision cutting tools.
Principles for Selection of CNC Tool Materials
Currently, the widely used CNC tool materials mainly include diamond tools, cubic boron nitride tools, ceramic tools, coated tools, carbide tools, high-speed steel tools, etc. There are many grades of tool materials, and their properties vary greatly. The following table shows the main performance indicators of various tool materials.
Tool materials for CNC machining must be selected according to the workpiece being processed and the nature of the processing. The selection of tool materials should be reasonably matched with the processing object. The matching of cutting tool materials and processing objects mainly refers to matching the mechanical properties, physical properties and chemical properties of the two to obtain the longest tool life and maximum cutting productivity.
1. Matching the mechanical properties of cutting tool materials and processing objects
The problem of matching the mechanical properties of the cutting tool and the processing object mainly refers to the matching of mechanical property parameters such as strength, toughness and hardness of the tool and the workpiece material. 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>tungsten 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 toughness of tool materials is: high-speed steel>tungsten carbide>cubic boron nitride, diamond and ceramic tools.
High-hardness workpiece materials must be processed with higher-hardness tools. The hardness of the tool material must be higher than the hardness 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 and its hardness decreases, making it suitable for rough machining; when the cobalt content decreases, its hardness and wear resistance increase, making it suitable for finishing.
Tools with excellent high-temperature mechanical properties are especially suitable for high-speed cutting. The excellent high-temperature performance of ceramic cutting tools enables them to cut at high speeds, and the allowed cutting speed can be 2 to 10 times higher than that of cemented carbide.
2. Matching the physical properties of the cutting tool material to the machined object
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, etc., are suitable for processing different workpiece materials. When processing workpieces with poor thermal conductivity, tool materials with better thermal conductivity should be used so that the cutting heat can be quickly transferred out and the cutting temperature can be reduced. Due to its high thermal conductivity and thermal diffusivity, diamond can easily dissipate cutting heat without causing large thermal deformation, which is particularly important for precision machining tools that require high dimensional accuracy.
① The heat resistance temperature of various tool materials: diamond tools are 700~8000C, PCBN tools are 13000~15000C, ceramic tools are 1100~12000C, TiC(N)-based cemented carbide is 900~11000C, WC-based ultra-fine grains Carbide is 800~9000C, HSS is 600~7000C.
② The order of thermal conductivity of various tool materials: PCD>PCBN>WC-based cemented carbide>TiC(N)-based cemented carbide>HSS>Si3N4-based ceramics>A1203-based ceramics.
③ The order of thermal expansion coefficients of various tool materials is: HSS>WC-based cemented carbide>TiC(N)>A1203-based ceramic>PCBN>Si3N4-based ceramic>PCD.
④ The order of thermal shock resistance of various tool materials is: HSS>WC-based cemented carbide>Si3N4-based ceramics>PCBN>PCD>TiC(N)-based cemented carbide>A1203-based ceramics.
3. Matching the chemical properties of the cutting tool material to the machined object
The problem of matching the chemical properties of cutting tool materials and processing objects mainly refers to the matching of chemical performance parameters such as chemical affinity, chemical reaction, diffusion and dissolution of tool materials and workpiece materials. Tools with different materials are suitable for processing different workpiece materials.
① The bonding temperature resistance of various tool materials (with steel) is: PCBN>ceramic>tungsten carbide>HSS.
② The oxidation resistance temperature of various tool materials is: ceramic>PCBN>tungsten carbide>diamond>HSS.
③ The diffusion strength of the tool materials (for steel) is: diamond>Si3N4-based ceramics>PCBN>A1203-based ceramics. The diffusion intensity (for titanium) is: A1203-based ceramic>PCBN>SiC>Si3N4>diamond.
4. Reasonable selection of CNC tool materials
Generally speaking, PCBN, ceramic tools, coated carbide and TiCN-based carbide tools are suitable for CNC processing of ferrous metals such as steel; while PCD tools are suitable for non-ferrous metal materials such as Al, Mg, Cu and their alloys and Processing of non-metallic materials. The table below lists some of the workpiece materials that the above tool materials are suitable for processing.
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Post time: Nov-01-2023
