A good horse needs to be equipped with a good saddle and uses advanced CNC processing equipment. Choosing the right tool material has a great influence on tool life, processing efficiency, processing quality and processing cost. This article provides dry goods about tool knowledge, collect and forward, and learn together.

01
Tool materials should have basic properties

The choice of tool material has a great influence on tool life, processing efficiency, processing quality and processing cost. The tool must withstand high pressure, high temperature, friction, impact and vibration during 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, 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 in order to withstand cutting forces, impacts and vibrations, to prevent tool brittle fracture and chipping.
(3) Heat resistance. The tool material has better heat resistance, can withstand high cutting temperatures, and has good oxidation resistance.
(4) Process performance and economy. Tool materials should have good forging performance, heat treatment performance, welding performance; grinding processing performance, etc., and should pursue a high performance-price ratio.

02
Type, performance, characteristics and application of tool materials

1. Diamond tool material

Diamond is an isomer of carbon. It is 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 metals and non-metallic materials. Especially in the high-speed machining of aluminum and silicon-aluminum alloys, diamond tools are the main cutting tool varieties that are difficult to replace. Diamond tools that can realize high-efficiency, high-stability and long-life machining are indispensable and important tools in modern CNC machining.

⑴ Types of diamond tools

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

② PCD diamond tool: natural diamond is expensive, and the diamond is widely used in cutting or polycrystalline diamond (PCD). Since the early 1970s, polycrystalline diamond (Polycrystauine diamond, PCD blade for short) developed by high temperature and high pressure synthesis technology After the success, natural diamond tools have been replaced by artificial polycrystalline diamond in many occasions. PCD raw materials are rich in source, and its price is only a few tenths to one tenth of natural diamonds. PCD tools cannot grind extremely sharp The cutting edge and the surface of the processed workpiece are not as good as natural diamond. At present, it is not easy to manufacture PCD inserts with chip breakers in the industry. Therefore, PCD can only be used for non-ferrous and non-metallic precision cutting, it is difficult to achieve ultra Precision mirror cutting.

③ CVD diamond tools: From the late 1970s to the early 1980s, CVD diamond technology appeared in Japan. CVD diamond refers to the synthesis of diamond films on heterogeneous substrates (such as cemented carbide, ceramics, etc.) by chemical vapor deposition (CVD). 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 combines the advantages of natural single crystal diamond and polycrystalline diamond (PCD), and overcomes their deficiencies to a certain extent.

⑵ Performance characteristics of diamond cutter

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, and even up to several hundred times.
② Has a very low friction coefficient: the friction coefficient between diamond and some non-ferrous metals is lower than other tools, the friction coefficient is low, the deformation during processing is small, and the cutting force can be reduced.
③ The cutting edge is very sharp: the cutting edge of the diamond tool can be sharply sharpened, and the natural single crystal diamond tool can be as high as 0.002 to 0.008 μm, which can perform ultra-thin cutting and ultra-precision machining.
④ Has high thermal conductivity: diamond has high thermal conductivity and thermal diffusivity, cutting heat is easily dissipated, and the temperature of the cutting part of the tool is low.
⑤ Has a low thermal expansion coefficient: The thermal expansion coefficient of diamond is several times smaller than that of cemented carbide, and the change in tool size caused by cutting heat is very small, which is particularly important for precision and ultra-precision machining that requires high dimensional accuracy.

⑶ Application of diamond cutter

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

The disadvantage of diamond tools is poor thermal stability. When the cutting temperature exceeds 700 ℃ ~ 800 ℃, it will completely lose its hardness; in addition, it is not suitable for cutting ferrous metals, because diamond (carbon) is easy to contact iron at high temperatures The action of atoms converts carbon atoms into graphite structures, and the cutter is easily damaged.

2. Cubic boron nitride tool material

Cubic boron nitride (CBN), the second superhard material synthesized by a method similar to the diamond manufacturing method, is second only to diamond in terms of hardness and thermal conductivity. It has excellent thermal stability and is heated to 10000C 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 tools

Cubic boron nitride (CBN) is a substance that does not exist in nature, and 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 its structure is similar to diamond.

PCBN (polycrystalline cubic boron nitride) is a polycrystalline material that sinters fine CBN materials through a combined phase (TiC, TiN, Al, Ti, etc.) under high temperature and high pressure. It is currently second only to artificial hardness Diamond tool material, it and diamond are collectively called superhard tool material. PCBN is mainly used to make knives or other tools.

PCBN tools can be divided into integral PCBN blades and PCBN composite blades sintered with carbide.

The PCBN composite blade is made by sintering a layer of PCBN with a thickness of 0.5-1.0mm on a hard alloy with good strength and toughness. Its performance has good toughness and high hardness and wear resistance. Solve the problems of low bending strength and welding difficulties of CBN blades.

⑵ The main performance and characteristics of cubic boron nitride

Although the hardness of cubic boron nitride is slightly inferior to 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 more than 1200 ℃ (diamond is 700-800 ℃). Another outstanding advantage is that it is chemically inert and does not play a chemical role with iron at 1200-1300 ℃ reaction. The main performance characteristics of cubic boron nitride are as follows.

① High hardness and wear resistance: CBN crystal structure is similar to diamond, with hardness and strength similar to diamond. PCBN is particularly suitable for processing high-hardness materials that could only be ground before, and can obtain better workpiece surface quality.

② Has high thermal stability: CBN's heat resistance can reach 1400 ~ 1500 ℃, almost l times higher than the heat resistance of diamond (700 ~ 800 ℃). PCBN tools can cut high-temperature alloys and hardened steels at high speeds 3 to 5 times higher than cemented carbide tools.

③ Excellent chemical stability: it does not play a chemical role with iron-based materials up to 1200-1300℃, and will not wear like diamonds. At this time, it can still maintain the hardness of cemented carbide; PCBN tools are suitable for cutting hardened steel Parts and chilled cast iron can be widely used for high-speed cutting of cast iron.

④ Has good thermal conductivity: Although the thermal conductivity of CBN can not catch up with diamond, PCBN is second only to diamond in thermal conductivity of various tool materials, which is much higher than that of high-speed steel and cemented carbide.

⑤ Has a low coefficient of friction: a low coefficient of friction 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 cubic boron nitride tool application

Cubic boron nitride is suitable for finishing various hardened materials such as hardened steel, hard cast iron, high temperature alloy, cemented carbide, surface sprayed 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.

The toughness and bending strength of cubic boron nitride tool materials are poor. Therefore, cubic boron nitride turning tools are not suitable for roughing at low speeds and large 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 Metal will produce serious built-up edge, which will deteriorate the processed surface.

3. Ceramic tool material

Ceramic tools have the characteristics of high hardness, good wear resistance, excellent heat resistance and chemical stability, and are not easy to bond with metals. Ceramic tools occupy a very important position in CNC machining. Ceramic tools have become one of the main tools for high-speed cutting and machining of difficult-to-machine materials. Ceramic tools are widely used in high-speed cutting, dry cutting, hard cutting and cutting of difficult-to-machine materials. Ceramic tools can efficiently process high-hard materials that traditional tools can't process at all, and realize "turning instead of grinding"; the optimal cutting speed of ceramic tools can be 2 to 10 times higher than cemented carbide tools, which greatly improves the cutting production efficiency ; The main raw material used in ceramic tool materials is the most abundant element in the earth's crust. Therefore, the promotion and application of ceramic tools is very important for improving productivity, reducing processing costs, and saving strategic precious metals, and will also greatly promote the cutting technology. progress.
⑴ Types of ceramic cutter materials

The types of ceramic cutter 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 superior to that of alumina-based ceramics.

⑵ Performance and characteristics of ceramic cutter

① 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 carbide and high-speed steel tools, reaching 93-95HRA. Ceramic tools can process high-hard materials that are difficult to process with traditional tools, and are suitable for high-speed cutting and hard cutting.
② High temperature resistance and good heat resistance: ceramic tools can still 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 when it is in a red hot state. Therefore, ceramic cutting tools can achieve dry cutting, which can save cutting fluid.
③ Good chemical stability: ceramic cutters are not easy to bond with metal, and have good corrosion resistance and good chemical stability, which can reduce the bonding wear of cutters.
④ Low friction coefficient: The affinity of ceramic tools and metal is small, and the friction coefficient is low, which can reduce the cutting force and cutting temperature.

⑶ Ceramic knife has application

Ceramic is one of the cutting tool materials mainly used for high-speed finishing and semi-finishing. Ceramic cutters 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 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 performance of ceramic tool materials has the problems of low bending strength and poor impact toughness, which is not suitable for cutting under low speed and impact load.

4. Coated tool material

Coating the tool is one of the important ways to improve the performance of the tool. The emergence of coated tools has made a major breakthrough in cutting performance. Coated cutters are coated with one or more layers of refractory compounds with good wear resistance on the cutter body with good toughness. It combines the cutter base with a hard coating, thereby greatly improving the performance of the cutter. Coated tools can improve processing efficiency, improve processing accuracy, extend tool life and reduce processing costs.

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

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 cemented carbide tools generally use chemical vapor deposition method, the deposition temperature is about 1000 ℃. Coated high-speed steel tools generally use physical vapor deposition method, the deposition temperature is about 500 ℃;

According to the different base materials of coated cutters, coated cutters can be divided into cemented carbide coated cutters, high-speed steel coated cutters, and coated cutters on ceramics and superhard materials (diamond and cubic boron nitride).

According to the nature of the coating material, coated tools can be divided into two categories, namely "hard" coated tools and "soft" coated tools. The main goals pursued by "hard" coated tools are high hardness and wear resistance The main advantages are high hardness and good wear resistance, typically TiC and TiN coatings. The goal of "soft" coated tools is a low friction coefficient, also known as self-lubricating tools, which rubs against the workpiece material The coefficient is very low, only about 0.1, which can reduce bonding, reduce friction, and reduce cutting force and cutting temperature.

Recently developed a nano-coated (Nanoeoating) tool. This coating tool can use different combinations of multiple coating materials (such as metal/metal, metal/ceramic, ceramic/ceramic, etc.) to meet different functional and performance requirements. The well-designed nano coating can make the cutting tool material have excellent anti-friction and anti-wear functions and self-lubricating properties, which is suitable for high-speed dry cutting.

⑵ Features of coated tools

① Good mechanics and cutting performance: the coating tool combines the excellent performance of the base material and the coating material, which not only maintains the good toughness and high strength of the base, but also has the high hardness, high wear resistance and low resistance of the coating Coefficient of friction. Therefore, the cutting speed of coated tools can be increased by more than 2 times than uncoated tools, and a higher feed rate is allowed. The life of coated tools has also been improved.

② Strong versatility: Coated tools have wide versatility, and the processing range is significantly expanded. A coated tool can replace several uncoated 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 is easy to cause peeling; when the coating is too thin, the wear resistance is poor.

④ Regrindability: Coated blades have poor regrindability, complex coating equipment, high process requirements and long coating time.

⑤ Coating material: The cutting performance of cutting tools with different coating materials is different. For example, when cutting at low speed, TiC coating has an advantage; when cutting at high speed, TiN is more suitable.

⑶ Application of coated tools

Coated tools have great potential in the field of CNC machining, and will be the most important tool variety in the field of CNC machining in the future. Coating technology has been applied to end mills, reamers, drills