What are the Types of Cutting Tool Materials and Their Applicable Occasions?

With the rapid 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.

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:

• 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.
• 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.
• Heat resistance: The tool material has better heat resistance, can withstand high cutting temperatures, and has 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-cost performance.

What Types of Tool Materials are there? Their Properties, Characteristics, and Applications.

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 tool material for CNC machining must be selected according to the workpiece to be machined and the nature of the machining. 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.

Diamond Tool:

Diamond is an allotrope of carbon, the hardest 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 types of cutting tools that are difficult to replace. Diamond tools that can achieve high efficiency, high stability, and long life are indispensable tools in modern CNC machining.

1. Types of diamond tools:
   • 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 produce extremely high workpiece accuracy and extremely low surface roughness, and is a recognized, ideal, and irreplaceable ultra-precision machining tool.
   • PCD diamond tools: Natural diamonds are expensive, and polycrystalline diamond (PCD) is widely used in cutting. Polycrystalline diamond prepared by high temperature and high-pressure synthesis technology has been replaced by synthetic polycrystalline diamond on many occasions. PCD is rich in raw materials, and its price is only one-tenth to one-tenth of that 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 chip breakers cannot be easily manufactured in the industry. Therefore, PCD can be used for fine cutting of non-ferrous metals and non-metals, and it is difficult to achieve ultra-precision mirror cutting.
   • CVD diamond tools: CVD diamond technology has appeared in Japan. CVD diamond refers to the synthesis of a diamond film on a heterogeneous substrate by chemical vapor deposition (CVD). CVD diamond has the same structure and characteristics as natural diamond. The performance of CVD diamond is close to that of natural diamond, and it has the advantages of natural single crystal diamond and polycrystalline diamond (PCD).
2. Performance characteristics of diamond tools:
   • 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.
   • 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.
   • The cutting edge is sharp: The cutting edge of the diamond tool can be 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.
   • 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.
   • Has a lower thermal expansion coefficient: The thermal expansion coefficient of a 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 requires high dimensional accuracy.
3. Application of diamond tools:

   Diamond tools are mostly used for fine cutting and boring 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. All kinds of wear-resistant non-ferrous metals, all kinds of 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. It is not suitable for cutting ferrous metals, because diamond (carbon) easily interacts with iron atoms at high temperatures. In action, the carbon atoms are converted into a graphite structure, and the tool is easily damaged.

Cubic Boron Nitride Tool:

The second super hard material, cubic boron nitride (CBN), synthesized by a method like the diamond manufacturing method, is second only to diamond in terms of hardness and thermal conductivity and has excellent thermal stability. It can 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 the single crystal and polycrystalline, namely CBN single crystal and Polycrystalline cubic boron nitride (PCBN). CBN is one of the allotropes of boron nitride (BN) with a structure like diamond. PCBN is a polycrystalline material that sinters fine CBN materials together through bonding phases (TiC, TiN, Al, Ti, etc.) under high temperature and high pressure. Collectively referred to as super hard tool materials. PCBN is used to make knives or other tools.

   PCBN tools can be divided into integral PCBN inserts and PCBN composite inserts sintered with cemented carbide. The PCBN composite insert is made by sintering a layer of PCBN with a thickness of 0.5 to 1.0 mm on a cemented carbide with good strength and toughness. Its properties have both good toughness and high hardness and wear resistance. Problems such as low bending strength and difficult welding of CBN inserts.

2. The 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 the thermal stability is much higher than that of diamond, which can reach above 1200°C (diamond is 700-800°C) reaction. The performance characteristics of cubic boron nitride are as follows.

   • High hardness and wear resistance: CBN crystal structure is like diamond, with hardness and strength like diamond. PCBN is especially suitable for processing high hardness materials that can be ground before and can obtain a better surface quality of the workpiece.
   • 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.
   • Excellent chemical stability: It does not have a chemical effect with iron-based materials at 1200-1300 ℃, and will not wear as sharply as diamond, and 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 the high-speed cutting of cast iron.
   • 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, and higher than that of high-speed steel and cemented carbide.
   • Has a low friction coefficient: A low friction coefficient 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. The cubic boron nitride turning tool is not suitable for rough machining with low speed and large impact load. 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 when cutting these metals, serious built-up edges will occur, which will deteriorate the machined surface.

Ceramic Tool:

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 an important position in CNC machining, and ceramic tools have become one of the 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. The optimal cutting speed of the ceramic tool can be 2 to 10 times higher than that of the carbide tool, thus improving the cutting production efficiency. The raw materials used in ceramic tool materials are the most abundant elements in the earth's crust. The popularization and application of ceramic tools can improve productivity, reduce processing costs, and 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:
   • High hardness and good wear resistance: Although the hardness of ceramic tools is not as high as that of PCD and PCBN, it is higher than that of cemented 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.
   • 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.
   • 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.
   • 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 used for high-speed finishing and semi-finishing. Ceramic tools are suitable for cutting various cast irons and steels, as well as 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.

Coated Tools:

Coating the tool is one of the important ways to improve the tool's performance. The emergence of coated tools has made a breakthrough in the cutting performance of tools. The coated tool is coated with one or more layers of the refractory compound with good wear resistance on the tool body with good toughness, which combines the tool matrix with the hard coating so that the performance of the tool is improved. Coated tools can improve machining efficiency, improve machining accuracy, extend tool life, and reduce machining costs. About 80% of the cutting tools used in CNC machine tools use coated tools.

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 into ceramics and super hard materials.

   According to the nature of the coating material, coated tools can be divided into hard-coated tools and soft-coated tools. The goal pursued by hard-coated tools is high hardness and wear resistance, and its main advantages are high hardness and good wear resistance, typically TiC and TiN coatings. The goal pursued by soft-coated tools is low friction coefficient, also known as self-lubricating tools. Its friction coefficient with the workpiece material is low, about 0.1, which can reduce adhesion, reduce friction, and reduce the cutting force, and cutting temperature.

   Nano-coating tools can use different combinations of various 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:
   • 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 has the high hardness, high wear resistance, and low strength of the coating friction coefficient. 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 improved.
   • 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.
   • 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 significantly. When the coating is too thick, it is easy to cause peeling. When the coating is too thin, the wear resistance is poor.
   • Regrind ability: The refundability of the coated blade is poor, the coating equipment is complex, the process requirements are high, and the coating time is long.
   • Coating material: Tools with different coating materials have different cutting performances. When cutting at low speed, TiC coating is dominant. When cutting at high speed, TiN is more suitable.
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. 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 high-speed machining of various steels. And the need for materials such as cast iron, heat-resistant alloys, and non-ferrous metals.

Carbide Tool:

Carbide tools, especially indexable carbide tools, are the leading products of CNC machining tools. The varieties of integral and indexable carbide tools or inserts have been extended to various cutting tool fields, among which indexable carbide tools have been expanded from simple turning tools and face milling cutters to various precision, complex and forming tools.

1. Types of carbide tools:

   According to the chemical composition, cemented carbide can be divided into tungsten carbide-based cemented carbide and carbon (nitride) titanium (TiCN)-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 advantages and disadvantages. The components are tungsten carbide (WC), 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 component, and the commonly used metal bonding phases are Mo and Ni.

   ISO (International Organization for Standardization) divides cutting carbides into three categories:

   • Class K, including Kl0-K40 (the component is WC.Co).
   • Class P, including P01 to P50 (the components are WC.TiC.Co).
   • Class M, including M10 to M40 (the component is WC-TiC-TaC(NbC)-Co).
2. Performance characteristics of cemented carbide tools:
   • High hardness: Cemented carbide cutting tools are made of carbide with high hardness and melting point and metal binder by powder metallurgy method. 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 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.
   • 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 1/30 to 1/8 of that of high-speed steel.
3. Application of commonly used carbide cutting tools:

   YG alloys are used for machining cast iron, non-ferrous metals, and non-metallic materials. Fine-grained cemented carbide (such as YG3X, and YG6X) has higher hardness and wear resistance than medium-grained cemented carbide when the cobalt content is suitable for processing some special hard cast iron, austenitic stainless steel, heat-resistant alloys, titanium alloys, 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 difficult to machine materials.

High-Speed Steel Tool:

High-Speed Steel (HSS) 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 hole-making tools, milling cutters, threading tools, broaches, gear cutting tools, and other complex cutting tools, high-speed steel 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.

1. Universal high-speed steel tool:

   General-purpose high-speed steel. 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). The content of tungsten in steel 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 without W. General-purpose high-speed steel has a certain hardness (63-66HRC) and wears resistance, high strength and toughness, good plasticity, and processability, so it is widely used in the manufacture of various complex tools.

   • Tungsten steel: The typical grade of general-purpose high-speed steel tungsten steel is W18Cr4V (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, the distribution is less uniform, the particles are large, and the strength and toughness are not high.
   • Tungsten-molybdenum steel: Refers to high-speed steel obtained by replacing part of tungsten in tungsten steel with molybdenum. The typical grade of tungsten-molybdenum steel is W6Mo5Cr4V2 (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, whose thermal stability is slightly higher than that of M2 steel, its bending strength and toughness are better than W6M05Cr4V2, and it has good machinability.
2. High-performance high-speed steel cutting tools:

   High-performance high-speed steel refers to a 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.

   • 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.
   • High vanadium high-speed steel: Typical grades, such as W12Cr4V4Mo (EV4), 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 be used for processing stainless steel, high Materials such as strength steels and superalloys.
   • Cobalt high-speed steel: It is a cobalt-containing super-hard high-speed steel. Typical grades, such as W2Mo9Cr4VCo8 (M42), have high hardness, and their hardness can reach 69-70HRC. It is suitable for processing high-strength heat-resistant steel, high-temperature alloys, titanium alloys, and other difficult-to-machine materials. M42 has good grindability and is suitable for making sophisticated and complex tools, but it is not suitable for working under impact cutting conditions.
   • Aluminum high-speed steel: It is super-hard high-speed steel containing aluminum. Typical grades, such as W6Mo5Cr4V2Al (501), have a high-temperature hardness of 54HRC at 6000C, and the cutting performance is equivalent to M42. It is 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.
   • Nitrogen super hard high-speed steel: Typical grades, such as W12M03Cr4V3N (V3N), are nitrogen-containing super-hard high-speed steels with comparable hardness, strength, and toughness 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.
3. Melting chain high-speed steel and powder metallurgy high-speed steel:

   According to different manufacturing processes, high-speed steel can be divided into melting chain high-speed steel and powder metallurgy high-speed steel.

   • Melting chain high-speed steel: Ordinary high-speed steel and high-performance high-speed steel are manufactured by the melting chain method. They are made into knives through processes such as smelting, ingot casting, and plating. The problem that is prone to occur in melt chain high-speed steel is carbide segregation. Hard and brittle carbides are unevenly distributed in high-speed steel, and the grains are coarse, which adversely affects the wear resistance, toughness, and cutting performance of high-speed steel tools.
   • Powder metallurgy high-speed steel (PM HSS): Powder metallurgy high-speed steel (PM HSS) is the molten steel melted from a high-frequency induction furnace, atomized with high-pressure argon or pure nitrogen, and then quenched to obtain fine and uniform steel. The crystalline structure (high-speed steel powder), and then the obtained powder is pressed into a blade blank under high temperature and high pressure, or a steel blank is first made into a blade shape by forging and rolling. Compared with the high-speed steel produced by the melting method, PM HSS has the advantage that the carbide grains are fine and uniform, and the strength, toughness, and wear resistance are much improved compared to the melt-chain 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, and can be used to manufacture precision tools.