Tool materials should have basic performance
The choice of tool materials has a great impact on tool life, machining efficiency, machining quality and machining costs. The tool must withstand high pressure, high temperature, friction, shock and vibration when cutting. Therefore, the tool material should have the following basic properties:
(1) Hardness and wear resistance. The hardness of the tool material must be higher than 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.
(2) Strength and toughness. Tool materials should have high strength and toughness to withstand cutting forces, shocks and vibrations, and prevent brittle fracture and chipping of the tool.
(3) Heat resistance. The tool material has good heat resistance, can withstand high cutting temperatures, and has good oxidation resistance.
(4) Process performance and economy. The tool material should have good forging performance, heat treatment performance, welding performance, grinding performance, etc., and pursue high performance and price ratio.
diamond tool materials
Types, properties and characteristics of diamond tool materials and tool applications
Diamond is an isomer of carbon, the hardest material ever 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 metals and non-metallic materials. Especially in the high-speed machining of aluminum and silicon-aluminum alloys, diamond tools are difficult to replace the main types of cutting tools. Diamond tools that can achieve high efficiency, high stability and long life processing are indispensable tools in modern CNC machining.
- Types of diamond tools
- Natural diamond cutter: Natural diamond has been used as a cutting tool for hundreds of years. The natural single crystal diamond cutter has been finely ground, and the edge can be sharply sharpened. The radius of the cutting edge can reach 0.002μm, which can achieve ultra-thin cutting. The extremely high precision of the workpiece and the extremely low surface roughness are recognized, ideal and irreplaceable ultra-precision machining tools.
- PCD diamond tool: natural diamond is expensive, diamond is widely used in cutting or polycrystalline diamond (PCD). Since the early 1970s, polycrystalline diamond (Polycrystauinediamond, PCD blade) has been successfully developed after high temperature and high pressure synthesis technology. In many cases, natural diamond tools have been replaced by synthetic polycrystalline diamond. PCD raw materials are abundant, and the price is only one-tenth to one-tenth of that of natural diamond.
PCD cutters are not able to grind extremely sharp edges, and the surface quality of the machined workpiece is not as good as natural diamond. It is not easy to manufacture PCD inserts with chipbreakers in the industry. Therefore, PCD can only be used for fine cutting of non-ferrous metals and non-metals, and it is difficult to achieve ultra-precision mirror cutting.
- CVD Diamond Tools: Since the late 1970s to the early 1980s, CVD diamond technology has appeared in Japan. CVD diamond refers to the synthesis of a diamond film on a heterogeneous substrate (such as cemented carbide, ceramics, etc.) by chemical vapor deposition (CVD). The 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, and it has the advantages of natural single crystal diamond and polycrystalline diamond (PCD), and to some extent overcome their shortcomings.
(2) Performance characteristics of diamond tools:
- Extremely high hardness and wear resistance: Natural diamond is the hardest substance found in nature. Diamond has a very high wear resistance. When machining high hardness materials, the life of diamond tools is 10 to 100 times, or even hundreds of times, that of cemented carbide tools.
- has a very low coefficient of friction: 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 very sharp: the cutting edge of the diamond tool can be sharply sharpened, and the natural single crystal diamond tool can be as high as 0.002~0.008μm for ultra-thin cutting and ultra-precision machining.
- It has high thermal conductivity: diamond has high thermal conductivity and thermal diffusivity, cutting heat is easy to dissipate, and the cutting temperature of the tool is low.
- has a low coefficient of thermal expansion: diamond has a thermal expansion coefficient several times smaller than that of cemented carbide, and the change in tool size caused by cutting heat is small, which is especially important for precision and ultra-precision machining with high dimensional accuracy.
(3) Application of diamond tools.
Diamond tools are used for fine cutting and boring of non-ferrous and non-metallic materials at high speeds. Suitable for processing all kinds of wear-resistant non-metal, such as FRP powder metallurgy blank, ceramic materials, etc.; various wear-resistant non-ferrous metals, such as various silicon-aluminum alloy; various non-ferrous metal finishing.
The disadvantage of diamond cutters is that the thermal stability is poor. When the cutting temperature exceeds 700 ° C ~ 800 ° C, it will completely lose its hardness; in addition, it is not suitable for cutting ferrous metals, because diamond (carbon) is easy to iron with at high temperatures The atom acts to convert carbon atoms into a graphite structure, and the tool is extremely fragile.
cubic boron nitride tool materials
The second superhard material, cubic boron nitride (CBN), synthesized by a method similar to the diamond manufacturing method, is second only to diamond in terms of hardness and thermal conductivity, and has excellent thermal stability. It is heated to 10,000 C 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.
(1) Types of cubic boron nitride tools
Cubic boron nitride (CBN) is a substance that does not exist in nature. It has a single crystal and a polycrystal, namely CBN single crystal and polycrystalline cubic boron nitride (PCBN). CBN is one of the isomers of boron nitride (BN) and has a structure similar to that of diamond.
PCBN (polycrystalline cubic boron nitride) is a polycrystalline material in which fine CBN materials are sintered together through a bonding phase (TiC, TiN, Al, Ti, etc.) under high temperature and high pressure. Diamond tool material, which is collectively referred to as a superhard tool material. PCBN is mainly used to make tools or other tools.
PCBN tools can be divided into integral PCBN inserts and PCBN composite inserts sintered with cemented carbide.
PCBN composite blade is made by sintering a layer of O.5~1.0mm thick PCBN on cemented carbide with good strength and toughness. Its performance has good toughness and high hardness and wear resistance. It solves the problems of low bending strength and difficult welding of CBN inserts.
(2) Main performance 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, up to 1200 °C (300-800 °C for diamond). Another outstanding advantage is that it is chemically inert and does not chemistry with iron at 1200-1300 °C. reaction. The main performance characteristics of cubic boron nitride are as follows.
- aHigh 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 can only be ground before, and can achieve better surface quality of the workpiece.
- Have a very high thermal stability: CBN heat resistance can reach 1400 ~ 1500 ° C, almost l times higher than the heat resistance of diamond (700 ~ 800 ° C). PCBN tools can cut high-temperature alloys and hardened steels at high speeds 3 to 5 times faster than cemented carbide tools.
- Excellent chemical stability: It does not play a chemical role with iron-based materials up to 1200-1300 °C. It does not wear sharply like diamond. At this time, it can still maintain the hardness of cemented carbide. PCBN cutter is suitable for cutting hardened steel. Parts and chilled cast iron for wide-speed cutting of cast iron.
- has good thermal conductivity: although the thermal conductivity of CBN cannot keep up with diamond, the thermal conductivity of PCBN in all kinds of tool materials is second only to diamond, which is much higher than that of high speed steel and hard alloy.
- Has a low coefficient of friction: a low coefficient of friction can result in reduced cutting forces during cutting, lower cutting temperatures, and improved surface quality.
(3) Cubic boron nitride tool application:
Cubic boron nitride is suitable for finishing difficult-to-cut materials such as hardened steel, hard cast iron, superalloy, hard alloy, and surface spray materials. The processing accuracy can reach IT5 (hole is IT6), and the surface roughness value can be as small as Ra1.25~0.20μm.
The cubic boron nitride tool material has poor toughness and bending strength. Therefore, cubic boron nitride turning tools are not suitable for rough machining with low speed and large impact load; at the same time, it is not suitable for cutting plastic materials (such as aluminum alloy, copper alloy, nickel-based alloy, plastic large steel, etc.) because of cutting these Metals can cause severe built-up edges and deteriorate the machined surface.
ceramic tool materials
Ceramic knives 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 play an important role in CNC machining. Ceramic tools have become one of the main tools for high-speed cutting and difficult machining of materials. Ceramic tools are widely used in high-speed cutting, dry cutting, hard cutting, and machining of difficult-to-machine materials. Ceramic tools can efficiently process high-hard materials that traditional tools can’t process at all, and achieve “car grinding”; the optimal cutting speed of ceramic tools can be 2~10 times higher than that of hard alloy tools, which greatly improves the efficiency of cutting processing. The main raw material used in ceramic tool materials is the most abundant elements in the earth’s crust. Therefore, the promotion and application of ceramic tools is of great significance for improving productivity, reducing processing costs, and saving strategic precious metals. It will also greatly promote cutting technology. progress.
(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. Silicon nitride-based ceramics are superior to alumina-based ceramics.
(2) Performance and characteristics of ceramic tools
The performance characteristics of ceramic tools are as follows:
- High hardness and good wear resistance: Although the hardness of ceramic tools is not as high as PCD and PCBN, it is much higher than that of hard alloy and high-speed steel tools, reaching 93-95HRA. Ceramic tools can process high-hard materials that are difficult to machine with traditional tools and are suitable for high-speed cutting and hard cutting.
- High temperature resistance and heat resistance: Ceramic tools can still cut at temperatures above 1200 °C. Ceramic tools have very good high temperature mechanical properties. A12O3 ceramic tools have excellent oxidation resistance, and the cutting edges can be used continuously even in a red hot state. Therefore, ceramic tools can achieve dry cutting, eliminating the need for cutting fluid.
- Good chemical stability: ceramic tools are not easy to bond with metal, and have good corrosion resistance and chemical stability, which can reduce the bonding wear of the tool.
- Low friction coefficient: ceramic tool has low affinity with metal and low friction coefficient, which can reduce cutting force and cutting temperature.
(3) Ceramic knives have applications
Ceramics are one of the tool materials primarily used for high speed finishing and semi-finishing. Ceramic cutters are suitable for cutting all kinds of cast iron (grey cast iron, ductile iron, malleable cast iron, chilled cast iron, high alloy wear resistant cast iron) and steel (carbon structural steel, alloy structural steel, high strength steel, high manganese steel, hardened steel). Etc.) can also be used to cut copper alloys, graphite, engineering plastics and composites.
The performance of ceramic tool materials has low bending strength and poor impact toughness, and is not suitable for cutting under low speed and impact load.
coated tool materials
Coating the tool is one of the important ways to improve tool performance. The emergence of coated tools has made a major breakthrough in tool cutting performance. The coated tool is coated on one or more layers of high-resistance refractory compound with good wear resistance. It combines the tool base with the hard coating to greatly improve the tool performance. Coated tools can increase machining efficiency, increase machining accuracy, extend tool life and reduce machining costs.
About 80% of the cutting tools used in the new CNC machine tools use coated tools. Coated tools will be the most important tool in the field of CNC machining in the future.
(1)Type of coated tool
Depending on the coating method, coated tools can be divided into chemical vapor deposition (CVD) coated tools and physical vapor deposition (PVD) coated tools. Coated cemented carbide tools are generally chemical vapor deposition with a deposition temperature of around 1000 °C. The coated high speed steel tool generally adopts physical vapor deposition method, and the deposition temperature is about 500 ° C;
Depending on the material of the coated tool, the coated tool can be divided into carbide coated tools, high speed steel coated tools, and coated tools on ceramic and superhard materials (diamond and cubic boron nitride).
Depending on the nature of the coating material, coated tools can be divided into two broad categories, namely “hard” coated tools and ‘soft” coated tools. The main goal pursued by “hard” coated tools is high hardness and wear resistance. Sex, its main advantages are high hardness and good wear resistance, typically TiC and TiN coatings. The goal of “soft” coating tools is low friction coefficient, also known as self-lubricating tool, which rubs against the workpiece material. The coefficient is very low, only about 0.1, which can reduce bonding, reduce friction, reduce cutting force and cutting temperature.
Nanoeoating tools have recently been developed. This coating tool can be used in different combinations of coating materials (such as metal/metal, metal/ceramic, ceramic/ceramic, etc.) to meet different functional and performance requirements. The well-designed nano-coating allows the tool material to have excellent anti-friction and anti-wear properties and is suitable for high-speed dry cutting.
(2)Characteristics of coated tools
The performance characteristics of coated tools are as follows:
- Mechanical and cutting performance:
The coating 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 substrate, but also has high hardness, high wear resistance and low coating. Coefficient of friction. As a result, coated tools can be cut more than twice as fast as uncoated tools and allow for higher feed rates. The life of coated tools is also improved.
The coating tool has a wide versatility and a wide range of processing. A coated tool can replace several non-coated tools.
- Coating thickness:
The tool life will increase with the increase of coating thickness, but when the coating thickness reaches saturation, the tool life will no longer increase significantly. When the coating is too thick, peeling is likely to occur; when the coating is too thin, the abrasion resistance is poor.
The coating blade has poor regrind, complex coating equipment, high process requirements and long coating time.
- Coating material:
The tool with different coating materials has different cutting performance. For example, TiC coatings have an advantage when cutting at low speeds; TiN is suitable for high-speed cutting.
(3)Application of coated tools
Coated tools have great potential in the field of CNC machining and will be the most important tool in the field of CNC machining in the future. Coating technology has been applied to end mills, reamers, drills, composite hole machining tools, gear hobs, gear shaping cutters, shaving cutters, forming broaches and various machine clip indexable inserts to meet high-speed cutting operations. The need for steel and cast iron, heat resistant alloys and non-ferrous metals.
cemented carbide tool materials
Carbide 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 inserts have been extended to In the field of cutting tools, the indexable carbide tools are expanded from simple turning tools and face milling cutters to various precision, complex and forming tools.
(1) Types of cemented carbide tools
According to the main chemical composition, cemented carbide can be divided into tungsten carbide based hard alloy and carbon (titanium nitride) (TiC (N)) based hard alloy.
Tungsten carbide-based hard alloys include tungsten-cobalt (YG), tungsten-cobalt-titanium (YT), and rare-type carbides (YW), each of which has 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.
The carbon (nitrogen) titanium-based cemented carbide is a hard alloy containing TiC as a main component (some of which are added with other carbides or nitrides), and the commonly used metal bonding phases are Mo and Ni.
ISO (International Organization for Standardization) classifies cutting carbides into three categories:
K class, including Kl0 ~ K40, is equivalent to China’s YG class (the main component is WC.Co).
Class P, including P01 to P50, is equivalent to YT in China (the main component is WC.TiC.Co).
Class M, including M10 to M40, is equivalent to YW in China (the main component is WC-TiC-TaC(NbC)-Co).
Each grade represents a series of alloys from high hardness to maximum toughness, with numbers between 01 and 50, respectively.
(2) Performance characteristics of cemented carbide tools
The performance characteristics of cemented carbide tools are as follows:
- High hardness:
Carbide tools are made of carbides (called hard phase) and metal binder (called bonded phase) with high hardness and melting point by powder metallurgy method, and their hardness is 89-93 HRA. It 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 the cemented carbide varies with the nature, quantity, particle size and content of the metal binder phase of the carbide, and generally decreases as the content of the binder metal phase increases. When the content of the binder phase is the same, the hardness of the YT-based alloy is higher than that of the YG-based alloy, and the alloy to which TaC (NbC) is added has a high high-temperature hardness.
- Bending strength and toughness:
The bending strength of commonly used cemented carbides is in the range of 900-1500 MPa. The higher the metal bond phase content, the higher the flexural strength. When the content of the binder is the same, the strength of the YG-based (WC-Co) alloy is higher than that of the YT-based (WC-TiC-Co) alloy, and the strength decreases as the TiC content increases. Cemented carbide is a brittle material, and its impact toughness is only 1/30 to 1/8 of that of high speed steel at room temperature.
- Application of commonly used cemented carbide tools
YG alloys are mainly used to process cast iron, non-ferrous metals and non-metallic materials. Fine-grained hard alloys (such as YG3X, YG6X) have higher hardness and wear resistance than the medium grains when the cobalt content is the same. It is suitable for processing some special hard cast iron, austenitic stainless steel, heat-resistant alloy, Titanium alloy, hard bronze and wear-resistant insulation materials.
The outstanding advantages of YT-based cemented carbides are high hardness, good heat resistance, high hardness and compressive strength at high temperatures, and higher resistance to YG and better oxidation resistance. Therefore, when the knife is required to have high heat resistance and wear resistance, a grade with a high TiC content should be selected. YT alloys are suitable for processing plastic materials such as steel, but it is not suitable for processing titanium alloys and silicon aluminum alloys.
YW alloy has the properties of YG and YT alloys and has good comprehensive performance. It can be used for processing steel and for processing cast iron and non-ferrous metals. Such alloys, if properly added to the cobalt content, can be used at high strength and can be used for roughing and interrupted cutting of various difficult-to-machine materials.
In general, PCBN, ceramic tools, coated carbide and TiCN-based carbide tools are suitable for CNC machining of ferrous metals such as steel; PCD tools are suitable for non-ferrous materials such as Al, Mg, Cu and their alloys. Processing of non-metallic materials. Table 3-3-2 lists some of the workpiece materials that are suitable for machining the above tool materials.