The combination of advanced processing equipment and high-performance CNC cutting tools is necessary to fully exert its due efficiency and achieve good economic benefits. With the rapid development of tool materials, various new types of tool materials have greatly improved their physical, mechanical, and cutting performance, and their application scope is also constantly expanding.

1、 The tool material should have basic properties

The selection of tool materials has a significant impact on tool life, processing efficiency, processing quality, and processing costs. Cutting tools must withstand high pressure, high temperature, friction, impact, and vibration during cutting. Therefore, tool materials should have the following basic properties:

(1) Hardness and wear resistance. The hardness of the tool material must be higher than that of the workpiece material, generally requiring a hardness of 60HRC or above. The higher the hardness of the tool material, the better its wear resistance.

(2) Strength and toughness. The tool material should have high strength and toughness to withstand cutting forces, impacts, and vibrations, and to prevent brittle fracture and edge collapse 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, and welding performance; Grinding performance, and the pursuit of high cost performance ratio.

2、 Types, properties, characteristics, and applications of cutting tool materials

1. Types, properties, characteristics, and tool applications of diamond cutting tool materials

Diamond is an allotrope of carbon, and it is the hardest material found in nature. Diamond cutting tools have high hardness, wear resistance, and thermal conductivity, and are widely used in the processing of non-ferrous and non-metallic materials. Especially in high-speed cutting of aluminum and silicon aluminum alloys, diamond cutting tools are the main type of cutting tools that are difficult to replace. Diamond cutting tools that can achieve high efficiency, high stability, and long service life are indispensable and important tools in modern CNC machining.

⑴ Types of diamond cutting tools

① Natural diamond cutting tools: Natural diamond has a history of over a hundred years as a cutting tool. After fine grinding, natural single crystal diamond cutting tools can have extremely sharp edges, with a cutting radius of up to 0.002 μ m. Being able to achieve ultra-thin cutting and achieve extremely high workpiece accuracy and low surface roughness, it is a recognized, ideal, and irreplaceable ultra precision machining tool.

② PCD diamond cutting tools: Natural diamond is expensive, and polycrystalline diamond (PCD) is widely used in cutting. Since the early 1970s, polycrystalline diamond (PCD) blades prepared by high-temperature and high-pressure synthesis technology have been successfully developed, and in many cases, natural diamond cutting tools have been replaced by artificial polycrystalline diamond. PCD raw materials are abundant, and their prices are only tens to tens of times that of natural diamond.

PCD tools cannot grind extremely sharp edges, and the surface quality of the processed workpiece is not as good as natural diamond. Currently, it is not convenient to manufacture PCD blades with chip grooves in industry. Therefore, PCD can only be used for precision cutting of non-ferrous metals and non-metals, making it difficult to achieve ultra precision mirror cutting.

③ CVD diamond cutting tools: Since the late 1970s to early 1980s, CVD diamond technology has emerged in Japan. CVD diamond refers to the synthesis of diamond films on heterogeneous substrates (such as hard alloys, ceramics, etc.) using chemical vapor deposition (CVD). CVD diamond has the same structure and characteristics as natural diamond.

The performance of CVD diamond is very similar to that of natural diamond, and it combines the advantages of natural single crystal diamond and polycrystalline diamond (PCD), which to some extent overcomes their shortcomings.

⑵ Performance characteristics of diamond cutting tools

① Extremely high hardness and wear resistance: Natural diamond is the hardest substance found in nature. Diamond has extremely high wear resistance. When processing high hardness materials, the lifespan of diamond cutting tools is 10-100 times that of hard alloy cutting tools, and even hundreds of times longer.

② Has a very low friction coefficient: The friction coefficient between diamond and some non-ferrous metals is lower than other cutting tools, with low friction coefficient and small deformation during machining, which can reduce cutting force.

③ The cutting edge is very sharp: the cutting edge of diamond tools can be ground very sharp, and natural single crystal diamond tools can reach as high as 0.002-0.008 μ m. Capable of ultra-thin cutting and ultra precision machining.

④ Has high thermal conductivity: Diamond has a high thermal conductivity and thermal diffusion rate, and cutting heat is easily dissipated. The cutting temperature of the tool is low.

⑤ Having a lower coefficient of thermal expansion: The thermal expansion coefficient of diamond is several times smaller than that of hard alloy, and the change in tool size caused by cutting heat is very small, which is particularly important for precision and ultra precision machining with high dimensional accuracy requirements.

⑶ Application of diamond cutting tools

Diamond cutting tools are commonly used for fine cutting and boring of non-ferrous and non-metallic materials at high speeds. Suitable for processing various wear-resistant non-metallic materials, 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 processes.

The disadvantage of diamond cutting tools is their poor thermal stability. When the cutting temperature exceeds 700 ℃ to 800 ℃, their hardness will be completely lost; In addition, it is not suitable for cutting black metals because diamond (carbon) easily interacts with iron atoms at high temperatures, converting carbon atoms into graphite structures, making the tool extremely susceptible to damage.

2. Types, properties, characteristics, and tool applications of cubic boron nitride tool materials

The second superhard material, cubic boron nitride (CBN), synthesized using a method similar to diamond manufacturing, is second only to diamond in terms of hardness and thermal conductivity. It has excellent thermal stability and does not oxidize when heated to 10000C in the atmosphere. CBN has extremely stable chemical properties for black metals and can be widely used in the processing of steel products.

⑴ Types of cubic boron nitride cutting tools

Cubic boron nitride (CBN) is a substance that does not exist in nature and can be divided into single crystal and polycrystalline, namely CBN single crystal and polycrystalline cubic boron nitride (PCBN). CBN is one of the isomers of boron nitride (BN), with a structure similar to diamond.

Cubic boron nitride (CBN) is a substance that does not exist in nature and can be divided into single crystal and polycrystalline, namely CBN single crystal and polycrystalline cubic boron nitride (PCBN). CBN is one of the isomers of boron nitride (BN), with a structure similar to diamond.

PCBN cutting tools can be divided into integral PCBN blades and PCBN composite blades sintered with hard alloy composites.

PCBN composite blades are made by sintering a layer of O.5-1.0mm thick PCBN on a hard alloy with good strength and toughness. Its performance combines good toughness, high hardness, and wear resistance, solving the problems of low bending strength and welding difficulties of CBN blades.

⑵The main properties and characteristics of cubic boron nitride

Although the hardness of cubic boron nitride is slightly lower than diamond, it is much higher than other high hardness materials. The outstanding advantage of CBN is that its thermal stability is much higher than that of diamond, reaching over 1200 ℃ (700-800 ℃ for diamond), and another outstanding advantage is its high chemical inertness, which does not react with iron elements at 1200-1300 ℃. 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 similar hardness and strength to diamond. PCBN is particularly suitable for processing high hardness materials that could only be ground before, and can achieve better surface quality of workpieces.

② 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 quenched steel at a speed 3-5 times higher than hard alloy tools.

③ Excellent chemical stability: It does not react chemically with iron based materials even at temperatures between 1200-1300 ℃, and does not wear sharply like diamond. At this time, it can still maintain the hardness of hard alloys; PCBN cutting tools are suitable for cutting quenched steel parts and cold hard cast iron, and can be widely used for high-speed cutting of cast iron.

④ Having good thermal conductivity: Although the thermal conductivity of CBN cannot match that of diamond, the thermal conductivity of PCBN is second only to diamond in various tool materials, much higher than that of high-speed steel and hard alloys.

⑤ Having a lower coefficient of friction: A lower coefficient of friction can lead to a decrease in cutting force, a decrease in cutting temperature, and an improvement in surface quality during machining.

⑶ Application of cubic boron nitride cutting tools

Cubic boron nitride is suitable for precision machining of various difficult to cut materials such as quenched steel, hard cast iron, high-temperature alloys, hard alloys, and surface spray materials. The machining accuracy can reach IT5 (hole IT6), and the surface roughness value can be as low as Ra1.25-0.20 μ M.

The toughness and bending strength of cubic boron nitride cutting tool materials are poor. Therefore, cubic boron nitride turning tools are not suitable for rough machining at low speeds and with high impact loads; It is not suitable for cutting materials with high plasticity, such as aluminum alloys, copper alloys, nickel based alloys, and steel with high plasticity, because cutting these metals will produce serious chip deposits, which will deteriorate the machining surface.

3. Types, properties, characteristics, and tool applications of ceramic tool materials

Ceramic cutting tools have the characteristics of high hardness, good wear resistance, excellent heat resistance and chemical stability, and are not easy to bond with metals. Ceramic cutting tools play a very important role in CNC machining, and have become one of the main cutting 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 cutting tools can efficiently process high hardness materials that cannot be processed by traditional cutting tools, achieving "turning instead of grinding"; The optimal cutting speed of ceramic cutting tools can be 2 to 10 times higher than that of hard alloy cutting tools, greatly improving the production efficiency of cutting; The main raw materials used for ceramic cutting tools are the most abundant elements in the earth's crust. Therefore, the promotion and application of ceramic cutting tools is of great significance for improving productivity, reducing processing costs, and saving strategic precious metals. It will also greatly promote the progress of cutting technology.

⑴ Types of ceramic tool materials

The types of ceramic 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 tool materials are the most widely used. The performance of silicon nitride based ceramics is superior to that of alumina based ceramics.

⑵ Performance and characteristics of ceramic cutting tools

① High hardness and good wear resistance: Although the hardness of ceramic cutting tools is not as high as PCD and PCBN, it is significantly higher than that of hard alloy and high-speed steel cutting tools, reaching 93-95HRA. Ceramic cutting tools can process high hard materials that are difficult to machine with traditional tools, making them suitable for high-speed cutting and hard cutting.

②High temperature resistance and good heat resistance: Ceramic cutting tools can still cut at high temperatures above 1200 ℃. Ceramic cutting tools have excellent high-temperature mechanical properties, and the oxidation resistance of A12O3 ceramic cutting tools is particularly good. Even when the cutting edge is in a red hot state, it can be used continuously. Therefore, ceramic cutting tools can achieve dry cutting, thereby saving cutting fluid.

③ Good chemical stability: Ceramic cutting tools are not easy to bond with metals, and are corrosion-resistant with good chemical stability, which can reduce the adhesive wear of cutting tools.

④ Low friction coefficient: Ceramic cutting tools have a low affinity with metals, resulting in a low friction coefficient that can reduce cutting force and cutting temperature.

⑶ Ceramic knives have applications

Ceramics are one of the tool materials mainly used for high-speed precision machining and semi precision machining. Ceramic cutting tools are suitable for cutting various cast iron (gray cast iron, ductile iron, malleable cast iron, cold hard cast iron, high alloy wear-resistant cast iron) and steel (carbon structural steel, alloy structural steel, high-strength steel, high manganese steel, quenched steel, etc.), and can also be used to cut copper alloys, graphite, engineering plastics, and composite materials.

Ceramic tool materials have problems with low bending strength and poor impact toughness, making them unsuitable for cutting at low speeds and under impact loads.

4．The properties and characteristics of coated tool materials and their applications in cutting tools

Coating the cutting tools is one of the important ways to improve their performance. The emergence of coated cutting tools has made significant breakthroughs in their cutting performance. Coated cutting tools are those that are coated with one or more layers of refractory compounds with good wear resistance on the tool body with good toughness. They combine the tool matrix with a hard coating, thereby greatly improving the tool performance. Coated cutting tools can improve machining efficiency, improve machining accuracy, extend tool life, and reduce machining costs.

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

⑴ Types of coated cutting 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 hard alloy cutting tools generally use chemical vapor deposition method, with a deposition temperature of around 1000 ℃. Coated high-speed steel cutting tools generally use physical vapor deposition method, with a deposition temperature of around 500 ℃;

According to the different substrate materials of coated tools, coated tools can be divided into hard alloy coated tools, high-speed steel coated tools, and coated tools on ceramics and superhard materials (diamond and cubic boron nitride).

According to the properties of coating materials, coated tools can be divided into two categories, namely "hard" coated tools and "soft" coated tools. The main goal pursued by "hard" coated cutting tools is high hardness and wear resistance, with the main advantages of high hardness and good wear resistance, typical of which are 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 very low, only about 0.1, which can reduce adhesion, reduce friction, and lower cutting force and cutting temperature.

Recently, nano coating tools have been developed. This coated tool can use different combinations of coating materials (such as metal/metal, metal/ceramic, ceramic/ceramic, etc.) to meet different functional and performance requirements. A well-designed nano coating can endow tool materials with excellent anti friction, anti-wear properties, and self-lubricating properties, making them suitable for high-speed dry cutting.

⑵ Characteristics of coated cutting tools

① Good mechanical and cutting performance: Coated cutting tools combine the excellent properties of the substrate and coating materials, maintaining good toughness and high strength of the substrate, as well as high hardness, wear resistance, and low friction coefficient of the coating. Therefore, the cutting speed of coated tools can be increased by more than twice compared to uncoated tools, and higher feed rates are allowed. The lifespan of coated cutting tools has also been improved.

② Strong versatility: Coated tools have a wide range of versatility and significantly expand the processing range. One coated tool can replace several non coated tools.

③ Coating thickness: As the coating thickness increases, the tool life also increases, but when the coating thickness reaches saturation, the tool life no longer increases 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 materials: Cutting tools with different coating materials have different cutting performance. For example, during low-speed cutting, TiC coating has an advantage; TiN is more suitable for high-speed cutting.

⑶ Application of coated cutting tools

Coated cutting tools have great potential in the field of CNC machining and will be the most important tool variety in the future. Coating technology has been applied to end mills, reamers, drill bits, composite hole processing tools, gear hobbing cutters, gear hobbing cutters, gear shaving cutters, forming broaches, and various machine clamp indexable inserts, meeting the needs of high-speed cutting of various materials such as steel and cast iron, heat-resistant alloys, and non-ferrous metals.