The selection of milling cutter material is a crucial decision in cutting processing, which is directly related to processing efficiency, processing quality, processing cost, and tool life. Different cutting tool materials have different physical and chemical properties and are suitable for different processing conditions and materials. Therefore, choosing the right end mill tool material is the key to achieving efficient and high-quality processing.
End Mill Tool Materials Should Have Basic Properties
The selection of cutting tool materials has a great impact on tool life, processing efficiency, processing quality, and processing cost. End mill tools must withstand high pressure, high temperature, friction, impact, and vibration when cutting. Therefore, milling tool materials should have the following basic properties:
- Hardness and wear resistance. The hardness of the tool material must be higher than the hardness of the workpiece material, generally required to be above 60HRC. The higher the hardness of the tool material, the better the wear resistance.
- Strength and toughness. The tool material should have high strength and toughness to withstand cutting force, impact, and vibration, and prevent brittle fracture and chipping of the tool.
- Heat resistance. The tool material should have good heat resistance, be able to withstand high cutting temperatures, and have good oxidation resistance.
- 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 performance-price ratio.
End Mill Tool Performance
Diamond Cutting Tools
Diamond is an allotrope of carbon and is the hardest material found in nature. Diamond milling cutters 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 the high-speed cutting of aluminum and silicon aluminum alloys, diamond end mills are the main cutting tool variety that is difficult to replace. Diamond tools that can achieve high efficiency, high stability, and long-life processing are an indispensable and important tool in modern CNC processing.
Types of Diamond Cutting Tools
Natural diamond cutting tools: Natural diamond has been used as a cutting tool for hundreds of years. After fine grinding, the natural single-crystal diamond tool can be sharpened to an extremely sharp edge with a cutting-edge radius of up to 0.002μm. It can achieve ultra-thin cutting and can produce extremely high workpiece precision and extremely low surface roughness. It is a recognized, ideal, and irreplaceable ultra-precision machining tool.
PCD diamond cutting tools: Natural diamonds are expensive. Polycrystalline diamond (PCD) is widely used in cutting. Since the early 1970s, polycrystalline diamond (PCD) prepared by high-temperature and high-pressure synthesis technology has been widely used in cutting. After the successful development of diamonds, referred to as PCD blades, natural diamond tools have been replaced by artificial polycrystalline diamonds on many occasions. PCD raw materials are abundant, and their price is only a few tenths to a dozen tenths of natural diamonds. PCD end mills cannot grind extremely sharp edges, and the surface quality of the workpieces processed is not as good as natural diamonds. At present, it is not easy to manufacture PCD milling cutter 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-precision mirror cutting.
CVD diamond cutting tools: CVD diamond technology has appeared in Japan since the late 1970s and early 1980s. CVD diamond refers to the synthesis of diamond film on a heterogeneous substrate (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 diamonds. It has the advantages of natural single-crystal diamond and polycrystalline diamond (PCD), and overcomes their shortcomings to a certain extent.
Performance Characteristics of Diamond End Mills
- 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 up to several hundred times.
- It has a very low friction coefficient: The friction coefficient between diamond and some non-ferrous metals is lower than that of other tools. The low friction coefficient means less deformation during processing, which can reduce cutting force.
- The cutting edge is very sharp: The cutting edge of diamond milling cutters can be sharpened very sharply. Natural single-crystal diamond tools can be as high as 0.002 to 0.008μm, which can perform ultra-thin cutting and ultra-precision processing.
- It has high thermal conductivity: Diamond has high thermal conductivity and thermal diffusivity, cutting heat is easy to dissipate, and the temperature of the cutting part of the tool is low.
- It has a low thermal expansion coefficient: The thermal expansion coefficient of diamond is several times smaller than that of carbide, and the change in cutting tool size caused by cutting heat is very small, which is particularly important for precision and ultra-precision processing with high dimensional accuracy requirements.
Application of Diamond Milling Cutter
Diamond cutting tools are mostly used for fine cutting and boring of non-ferrous metals and non-metallic materials at high speed. 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; various non-ferrous metal finishing.
The disadvantage of diamond end mills 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 atoms at high temperatures, converting carbon atoms into graphite structures, and the tool is easily damaged.
Cubic Boron Nitride Cutting Tool Material
Cubic boron nitride (CBN), a second superhard material synthesized by a method similar to the manufacturing method of diamond, is second only to diamond in hardness and thermal conductivity. It has excellent thermal stability and does not oxidize even 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.
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 (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 that sintered fine CBN materials together through a binding phase (TiC, TiN, Al, Ti, etc.) under high temperature and high pressure. It is currently the tool material with artificial hardness second only to diamond. It and diamond are collectively referred to as superhard tool materials. PCBN is mainly used to make knives or other tools.
PCBN cutting tools can be divided into integral PCBN blades and PCBN composite blades sintered with cemented carbide.
PCBN composite blades are made by sintering a layer of 0.5-1.0mm thick PCBN on a cemented carbide with good strength and toughness. They have good toughness, high hardness and wear resistance, and they solve the problems of low bending strength and difficult welding of CBN blades.
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℃ (diamond is 700-800℃). Another outstanding advantage is that it is chemically inert and does not react chemically with iron at 1200-1300℃. The main performance characteristics of cubic boron nitride are as follows.
- High hardness and wear resistance: The crystal structure of CBN is similar to that of diamond, and it 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 workpiece surface quality.
- It has 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 a speed of 3-5 times higher than that of carbide tools.
- Excellent chemical stability: It does not react chemically with iron materials at 1200-1300℃, 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, and can be widely used in high-speed cutting of cast iron.
- Good thermal conductivity: Although the thermal conductivity of CBN cannot catch up with diamond, the thermal conductivity of PCBN is second only to diamond among all kinds of tool materials, and is much higher than high-speed steel and cemented carbide.
- Low friction coefficient: Low friction coefficient can lead to reduced cutting force, lower cutting temperature, and improved surface quality during cutting.
Application of Cubic Boron Nnitride Milling Cutter
Cubic boron nitride is suitable for finishing various hard-to-cut materials such as hardened steel, hard cast iron, high-temperature alloy, cemented carbide, surface spraying materials, etc. The machining accuracy can reach IT5 (IT6 for holes), and the surface roughness value can be as small as Ra1.25~0.20μm.
Cubic boron nitride cutting tool materials have poor toughness and bending strength. Therefore, cubic boron nitride turning tools are not suitable for rough machining at low speed and high impact load; at the same time, they are not suitable for cutting materials with high plasticity (such as aluminum alloy, copper alloy, nickel-based alloy, steel with high plasticity, etc.), because when cutting these metals, serious built-up edge will be generated, which will deteriorate the machined surface.
Ceramic Cutting Tool Materials
Ceramic milling cutters 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 end mills have become one of the main tools for high-speed cutting and 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 cemented carbide tools, thereby greatly improving the 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 is of great significance to improving productivity, reducing processing costs, and saving strategic precious metals, and will also greatly promote the advancement of cutting technology.
Types of Ceramic Cutting Tool Materials
Ceramic cutting 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 milling cutter materials are the most widely used. The performance of silicon nitride-based ceramics is superior to that of alumina-based ceramics.
Performance and Characteristics of Ceramic Cutting Tools
- High hardness and good wear resistance: Although the hardness of ceramic milling cutter 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 end mills can process high-hard materials that are difficult to process with traditional tools, and are suitable for high-speed cutting and hard cutting.
- High temperature resistance and good heat resistance: Ceramic cutting tools can still cut at high temperatures above 1200℃. Ceramic tools have good high-temperature mechanical properties. A12O3 ceramic tools have particularly good oxidation resistance, and the cutting edge can be used continuously even in a red-hot state. Therefore, ceramic tools can achieve dry cutting, thereby eliminating cutting fluid.
- Good chemical stability: Ceramic milling cutters are not easy to bond with metals, and are corrosion-resistant and chemically stable, which can reduce the bonding wear of tools.
- Low friction coefficient: Ceramic tools have a low affinity with metals and a low friction coefficient, which can reduce cutting force and cutting temperature.
Ceramic Cutting Tools have Applications
Ceramic is one of the tool materials mainly used for high-speed finishing and semi-finishing. Ceramic milling cutter tools are suitable for cutting various cast irons (gray cast iron, ductile 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, hardened steel, etc.), and can also be used to cut copper alloys, graphite, engineering plastics, and composite materials.
Ceramic milling cutter tool material performance has the problems of low bending strength and poor impact toughness, and is not suitable for cutting under low speed and impact load.
Coated End Mill Tool Materials
Coating the tool is one of the important ways to improve tool performance. The emergence of coated end mill tools has made a major breakthrough in tool-cutting performance. Coated milling cutters are coated with one or more layers of refractory compounds with good wear resistance to the toughness of the tool body. It combines the tool substrate with the hard coating, thereby greatly improving the tool’s performance. Coated tools can improve processing efficiency, improve processing accuracy, extend tool 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 processing in the future.
Types of Coated End Mills
Depending on the coating method, coated milling cutters can be divided into chemical vapor deposition (CVD) coated cutters and physical vapor deposition (PVD) coated cutters. Coated carbide cutters generally use chemical vapor deposition, and the deposition temperature is around 1000°C. Coated high-speed steel cutters generally use physical vapor deposition, and the deposition temperature is around 500°C.
Depending on the different base materials of coated end mills, coated cutters can be divided into carbide coated cutters, high-speed steel coated cutters, and coated cutters into ceramics and superhard materials (diamond and cubic boron nitride), etc.
According to the properties of the coating material, coated milling cutters can be divided into two categories, namely “hard” coated milling cutters and “soft” coated cutters. The main goal of “hard” coated cutters is high hardness and wear resistance. Its main advantages are high hardness and good wear resistance. Typical examples are TiC and TiN coatings. The goal of “soft” coated cutters is low friction coefficient, also known as self-lubricating cutters. Its friction coefficient with the workpiece material is very low, only about 0.1, which can reduce adhesion, reduce friction, and reduce cutting force and cutting temperature.
Nano-coated cutters have recently been developed. This type of coated cutter can use different combinations of various coating materials (such as metal/metal, metal/ceramic, ceramic/ceramic, etc.) to meet different functional and performance requirements. Reasonable design of nano-coating can make the tool material have excellent anti-friction and anti-wear functions and self-lubricating properties, suitable for high-speed dry cutting.
Characteristics of Coated End Mill Tools
- Good mechanics and cutting performance: Coated cutting 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 body, but also have the high hardness, high wear resistance, and low wear resistance of the coating. friction coefficient. Therefore, the cutting speed of coated milling cutter 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.
- Strong versatility: The coated milling cutter tool has wide versatility and the processing range is significantly expanded. One coated tool can replace several non-coated tools.
- 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.
- Regrindability: Coated blades have poor regrindability, complex coating equipment, high process requirements, and long coating time.
- 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.
Application of Coated Milling Cutters
Coated cutting 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 shaping cutters, gear shaving cutters, forming broaches, and various machine-mounted indexable inserts to meet the needs of high-speed cutting of various steels and cast irons, heat-resistant alloys and non-ferrous metals.
Carbide End Mill Tool Materials
Carbide end mill tools, especially indexable carbide tools, are the leading products of CNC machining tools. Since the 1980s, various types of integral and indexable carbide tools or blades have been expanded to various cutting tool fields, among which indexable carbide tools have expanded from simple turning tools and face milling cutters to various precision, complex, and forming tool fields.
Types of Cemented Carbide Milling Cutter Tools
According to the main chemical composition, cemented carbide can be divided into tungsten carbide-based cemented carbide and titanium carbide (TiC (N))-based cemented carbide.
Tungsten carbide-based cemented carbide includes three types: tungsten cobalt type (YG), tungsten cobalt titanium type (YT), and rare carbide added type (YW). They each have their own advantages and disadvantages. The main components are tungsten carbide (WC), titanium carbide (TiC), tantalum carbide (TaC), niobium carbide (NbC), etc. The commonly used metal bonding phase is Co.
Titanium carbide (nitride)-based cemented carbide is a cemented carbide with TiC as the main component (some have other carbides or nitrides added), and the commonly used metal bonding phases are Mo and Ni.
ISO (International Organization for Standardization) divides cutting cemented carbide into three categories:
- K type, including Kl0~K40, is equivalent to my country’s YG type (the main component is WC.Co).
- P class, including P01~P50, is equivalent to my country’s YT class (main components are WC, TiC, and Co).
- M class, including M10~M40, is equivalent to my country’s YW class (main components are WC-TiC-TaC(NbC)-Co).
Each grade is represented by a number between 01 and 50, representing a series of alloys from high hardness to maximum toughness.
Performance Characteristics of Cemented Carbide Milling Cutter Tools
High hardness: cemented carbide milling cutter tools are made of carbides (called hard phase) with high hardness and melting point and metal binder (called bonding phase) through powder metallurgy. Its hardness reaches 89-93HRA, which is 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 varies with the nature, quantity, particle size, and content of the metal bonding phase of carbides, and generally decreases with the increase of bonding metal phase content. When the bonding phase content is the same, the hardness of YT alloy is higher than that of YG alloy, and the alloy with TaC (NbC) added has higher high-temperature hardness.
Flexural strength and toughness: The flexural strength of commonly used cemented carbide is in the range of 900-1500MPa. The higher the content of the metal bonding phase, the higher the flexural 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. 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.
Application of Common Cemented Carbide Tools
YG alloys are mainly used for processing cast iron, nonferrous metals, and non-metallic materials. Fine-grained cemented carbide (such as YG3X, and 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 alloys, titanium alloys, hard bronze, and wear-resistant insulating materials.
The outstanding advantages of YT cemented carbide are high hardness, good heat resistance, higher hardness and compressive strength at higher temperatures than YG, and good oxidation resistance. Therefore, when the tool 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 not suitable for processing titanium alloys and silicon-aluminum alloys.
YW alloys have the properties of both YG and YT alloys, and have good comprehensive performance. They can be used for processing steel, cast iron, and nonferrous metals. If the cobalt content of this type of alloy is appropriately increased, the strength can be very high, and it can be used for rough processing and intermittent cutting of various difficult-to-process materials.
High-speed Steel Milling Cutter
High-speed steel (HSS) is a high-alloy tool steel with a large number of alloy 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 occupies a major position in complex tools, especially in the manufacture of hole-processing tools, milling cutters, threading tools, broaches, gear-cutting tools, and other complex blade-shaped tools. High-speed steel tools make it easy to sharpen the cutting edge.
According to different uses, high-speed steel can be divided into general-purpose high-speed steel and high-performance high-speed steel.
Universal High-speed Steel Tools
Universal 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% tungsten (C). According to the different tungsten content in the steel, it can be divided into tungsten steel containing 12% or 18% W, tungsten-molybdenum steel containing 6% or 8% W, and molybdenum steel containing 2% or no W. Universal 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 the manufacture of various complex tools.
Tungsten steel: The typical grade of universal high-speed steel tungsten steel is W18Cr4V (abbreviated as W18), 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, uneven distribution, large particles, low strength, and toughness.
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 (abbreviated as M2). The carbide particles of M2 are fine and uniform, and its strength, toughness, and high-temperature plasticity are better than W18Cr4V. Another tungsten-molybdenum steel is W9Mo3Cr4V (abbreviated as W9), which has slightly higher thermal stability than M2 steel, better-bending strength and toughness than W6M05Cr4V2, and has good machinability.
High-performance High-speed Steel Tools
High-performance high-speed steel refers to a new type of steel that adds some carbon content, vanadium content, and alloy elements such as Co and Al to the general high-speed steel composition, thereby improving its heat resistance and wear resistance. There are mainly the following categories:
- 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 tools for processing ordinary steel and cast iron, drills, reamers, taps, and milling cutters with high wear resistance requirements, or processing harder materials. It is not suitable for large impacts.
- High-vanadium high-speed steel. Typical grades, such as W12Cr4V4Mo (abbreviated as EV4), have V content increased to 3% to 5%, good wear resistance, and are suitable for cutting materials that are extremely wear-prone to tools, such as fibers, hard rubber, plastics, etc. It can also be used to process materials such as stainless steel, high-strength steel and high-temperature alloys.
- Cobalt high-speed steel. It is a cobalt-containing super-hard high-speed steel, with typical grades such as W2Mo9Cr4VCo8 (abbreviated as M42). It has a high hardness of 69-70HRC, which is suitable for processing difficult-to-process materials such as high-strength heat-resistant steel, high-temperature alloys, and titanium alloys. M42 has good grindability and is suitable for making precision and complex tools, but it is not suitable for working under impact-cutting conditions.
- Aluminum high-speed steel. It is an aluminum-containing super-hard high-speed steel, with typical grades such as W6Mo5Cr4V2Al (abbreviated as 501). 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 to process alloy steel, stainless steel, high-strength steel, and high-temperature alloys.
- Nitrogen super-hard 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-process materials and low-speed, high-precision machining.
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.
Smelting high-speed steel: Ordinary high-speed steel and high-performance high-speed steel are both manufactured by smelting. They are made into cutting tools through processes such as smelting, ingot casting and plating, and rolling. The serious problem that smelting high-speed steel is prone to is carbide segregation. Hard and brittle carbides are unevenly distributed in high-speed steel, and the grains are coarse (up to tens of microns), which hurts the wear resistance, toughness, and cutting performance of high-speed steel cutting tools.
Powder metallurgy high-speed steel (PM HSS): Powder metallurgy high-speed steel (PM HSS) is a steel liquid smelted in a high-frequency induction furnace, atomized with high-pressure argon or pure nitrogen, and then rapidly cooled to obtain a fine and uniform crystalline structure (high-speed steel powder), and then the obtained powder is pressed into a knife blank under high temperature and high pressure, or first made into a steel billet and then forged and rolled into a tool shape. Compared with high-speed steel manufactured by melting method, PM HSS has the following advantages: small and uniform carbide grains, much higher strength, toughness, and wear resistance than smelting high-speed steel. PM HSS tools will further develop and occupy an important position in the field of complex CNC tools. Typical grades, such as F15, FR71, GF1, GF2, GF3, PT1, PVN, etc., can be used to manufacture large-sized, heavy-loaded, and high-impact tools, and can also be used to manufacture precision tools.
Selection Principles of CNC Cutting Tool Materials
The cutting tool material for CNC machining must be selected according to the workpiece and processing properties. The selection of tool material should be reasonably matched with the processing object. The matching of cutting tool material and processing object mainly refers to the matching of mechanical properties, physical properties, and chemical properties of the two to obtain the longest tool life and maximum cutting productivity.
Matching the Mechanical Properties of Cutting Tool Materials and Processing Objects
The problem of matching the mechanical properties of cutting tools and processing objects mainly refers to the matching of mechanical properties parameters such as strength, toughness, and hardness of tools and workpiece materials. Tool materials with different mechanical properties are suitable for processing different workpiece materials.
- The order of hardness of cutting tool materials is diamond tool> cubic boron nitride tool> ceramic tool> cemented carbide> high-speed steel.
- The order of bending strength of cutting tool materials is high-speed steel> cemented carbide> ceramic tool> diamond and cubic boron nitride tools.
- The order of toughness of cutting tool materials is high-speed steel> cemented carbide> cubic boron nitride, diamond, and ceramic tools.
High-hardness workpiece materials must be processed with tools of higher hardness. The hardness of milling cutter tool materials must be higher than that of workpiece materials, generally requiring more than 60HRC. The higher the hardness of end mill tool materials, the better its wear resistance. For example, when the cobalt content in cemented carbide increases, its strength and toughness increase, and its hardness decreases, which is suitable for rough processing; when the cobalt content decreases, its hardness and wear resistance increase, which is suitable for fine processing.
Tools with excellent high-temperature mechanical properties are particularly suitable for high-speed cutting. The excellent high-temperature performance of ceramic tools enables them to cut at high speeds, and the allowable cutting speed can be increased by 2 to 10 times compared to cemented carbide.
Matching the Physical Properties of Cutting Tool Materials and Processing Objects
Tools with different physical properties, such as high-speed steel tools with high thermal conductivity and low melting points, ceramic tools with high melting points 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 good thermal conductivity should be used to allow cutting heat to be quickly transferred and reduce cutting temperature. Due to the high thermal conductivity and thermal diffusivity of diamond, cutting heat is easy to dissipate and will not cause large thermal deformation, which is especially important for precision machining tools with high dimensional accuracy requirements.
- Heat resistant temperature of various end mill 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 ultrafine grain cemented carbide, and 600-7000C for HSS.
- The order of thermal conductivity of various end mill tool materials: PCD>PCBN>WC based cemented carbide>TiC(N) based cemented carbide>HSS>Si3N4 based ceramics>A1203 based ceramics.
- The order of thermal expansion coefficient of various end mill tool materials is HSS> WC-based cemented carbide>TiC(N)> A1203-based ceramics>PCBN> Si3N4-based ceramics>PCD.
- The order of thermal shock resistance of various end mill tool materials is: HSS>WC-based cementedcarbide>Si3N4-based ceramics>PCBN>PCD>TiC(N)-based cemented carbide>A1203-based ceramics.
Chemical Property Matching Between Cutting Tool Materials and Processing Objects
The chemical property matching problem between cutting tool materials and processing objects mainly refers to the chemical property parameters such as chemical affinity, chemical reaction, diffusion, and dissolution between tool materials and workpiece materials. Different tools are suitable for processing different workpiece materials.
- The anti-adhesion temperature of various cutting tool materials (with steel) is PCBN>ceramics>carbide>HSS.
- The anti-oxidation temperature of various cutting tool materials is ceramics>PCBN>carbide>diamond>HSS.
- The diffusion strength of various cutting tool materials (for steel) is diamond>Si3N4-based ceramics>PCBN>A1203-based ceramics. The diffusion strength (for titanium) is A1203-based ceramics>PCBN>SiC>Si3N4>diamond.
