I. Types of Cubic Boron Nitride Cutting Tools: Intertwining Microstructure and Macro Performance

Cubic boron nitride (CBN), as a kind of magical substance that does not exist in nature, occupies an important position in the field of cutting tool materials with its unique microstructure and excellent macroscopic performance.CBN has two forms of monocrystalline and polycrystalline, which corresponds to CBN monocrystalline and polycrystalline cubic boron nitride (PCBN), respectively.The preparation process of PCBN is just like an elaborate construction of the microcosm, and the micro CBN material is treated like a microcosmic world through combining phases (TiC, TiN, Al, Ti, etc.) under the extreme conditions of high temperature and high pressure. Under the extreme conditions of high temperature and high pressure, the fine CBN materials are sintered together to form a polycrystalline material through the bonding phases (TiC, TiN, Al, Ti, etc.) as if they were strung together by delicate silk threads. This polycrystalline structure gives PCBN unique properties, making it the hardness of the current synthetic cutting tool materials second only to diamond, and diamond is jointly known as the twin star of super-hard cutting tool materials.

PCBN cutter can be further subdivided into whole PCBN blade and PCBN composite blade sintered with cemented carbide. the design of PCBN composite blade is exquisite, it cleverly utilizes the better strength and toughness of cemented carbide, and sintered a layer of 0.5-1.0mm thick PCBN on its surface. this composite structure makes the PCBN composite blade combine the advantages of both materials, both with cemented carbide and diamond, and the advantages of both materials. This composite structure makes PCBN composite inserts combine the advantages of both materials, not only the toughness of cemented carbide, but also the high hardness and wear resistance of PCBN, which perfectly solves the two long-standing problems in the field of cutting tool manufacturing of low bending strength and welding difficulties of CBN inserts, and opens the door to a wider range of applications for PCBN cutters in machining scenarios.

Second, the main performance of cubic boron nitride, characteristics: excellent performance of the multi-dimensional analysis

High hardness and abrasion resistance: the sharp edge of cutting processing

The crystal structure of CBN is similar to that of diamond, and this similarity is like a genetic code, which gives CBN hardness and strength similar to that of diamond. In the microcosm of cutting, PCBN is like an incredibly sharp edge, especially suited for machining high hardness materials that could only be handled by grinding before. When PCBN cutters are in contact with high hardness workpieces, their high hardness and wear resistance are fully demonstrated, just like chipping iron like mud, leaving smooth and precise machining traces on the surface of the workpieces, and obtaining excellent surface quality of the workpieces, which is irreplaceable in the modern manufacturing industry where machining precision is required to be extremely high.

High thermal stability: a stable guarantee for high-temperature cutting

In the cutting process, the rise of temperature is an inevitable challenge, and the thermal stability of CBN is like a layer of high-temperature resistant armor for PCBN tools.CBN's heat resistance can reach 1400 - 1500 ℃, which is almost twice as much as that of diamond (700 - 800 ℃), which means that PCBN tools can be used in the face of high-temperature machining. This means that PCBN tools are at home in high-temperature environments, cutting difficult-to-machine materials such as high-temperature alloys and hardened steels at speeds that are 3-5 times higher than those of cemented carbide tools. Under these high-temperature and high-speed cutting conditions, PCBN tools still maintain stable performance and do not soften or deform due to high temperatures, thus ensuring machining accuracy and efficiency.

Excellent chemical stability: a shield against chemical attack

The chemical interaction between the tool and the workpiece material is a complex and critical factor in cutting, and PCBN tools have excellent chemical stability, especially when in contact with ferrous materials, even at temperatures as high as 1200 - 1300°C. This characteristic is in contrast to diamond, which has the same chemical stability as diamond. This characteristic contrasts with diamond, which, when interacting with iron atoms at similarly high temperatures, converts the carbon atoms into a graphite structure, resulting in rapid damage to the tool. PCBN tools, on the other hand, maintain carbide-like hardness at these high temperatures. This chemical stability makes them ideal for cutting hardened steel parts and cold-hardened cast iron, and they are widely used in the high-speed cutting of cast iron.

Better thermal conductivity: efficient channel for heat transfer

Thermal conductivity plays an important role in tool performance, it is like a highway hidden inside the tool, responsible for the rapid transfer of heat generated during the cutting process. the thermal conductivity of CBN, although slightly inferior to diamond, is still one of the highest among all types of tool materials, second only to diamond, and much higher than high-speed steel and cemented carbide. This good thermal conductivity makes PCBN tools in the cutting process can be timely heat emitted, effectively reducing the temperature of the cutting part of the tool, reducing the high temperature caused by tool wear and workpiece thermal deformation, for high-precision machining to provide strong support.

Low coefficient of friction: optimized lubricant for the cutting process

On the microscopic contact surfaces of the cutting process, the size of the coefficient of friction has a profound effect on the cutting process. PCBN tools have a low coefficient of friction, which acts as a highly effective lubricant between the tool and the workpiece. A low coefficient of friction significantly reduces cutting forces, resulting in a smoother cutting process, lower cutting temperatures and less wear between the tool and the workpiece. This optimized cutting process helps to improve the machined surface quality, resulting in a smoother, flatter surface of the machined workpiece, which meets the stringent requirements of modern manufacturing for high-precision machining.

Third, the application of cubic boron nitride tools: precision positioning in the field of CNC machining

Cubic boron nitride tool in the field of CNC machining has a clear and unique application positioning, it is like a professional craftsman, good at dealing with specific types of materials and processing tasks. Cubic boron nitride tools show excellent performance in the finish machining of hardened steels, hard cast irons, high-temperature alloys, cemented carbides, surface coated materials and other difficult-to-cut materials. It is able to raise machining accuracy to a high level of IT5 (IT6 for holes) while controlling the surface roughness value to a very small range of Ra1.25 - 0.20μm, providing a precise and efficient solution for machining these high-performance materials.

However, just as every tool has its own range of applications, Cubic Boron Nitride tools are not all-purpose. Due to the nature of the material itself, Cubic Boron Nitride tool material has relatively poor toughness and flexural strength. This limits its use in certain machining scenarios, such as in low-speed, impact-loaded roughing environments, where the use of Cubic Boron Nitride turning tools may lead to premature tool damage. In addition, for cutting materials with high plasticity (such as aluminum alloys, copper alloys, nickel-based alloys, and steel with high plasticity), Cubic Boron Nitride tools are not suitable. Because when cutting these materials, it will produce serious chip tumors, these chip tumors will be attached to the surface of the tool, destroying the quality of the machined surface, so that the surface of the workpiece after machining becomes rough and uneven, unable to meet the machining accuracy requirements.

Fourth, the principle of selection of CNC tool materials: scientific matching to achieve the best machining results

Mechanical performance matching: find the strength and hardness of the tool and workpiece balance point

In CNC machining, the mechanical properties of the tool and workpiece material matching is essential. Tool material hardness, flexural strength and toughness and other mechanical properties of parameters and workpiece materials need to achieve a delicate balance between the two ends of the scale, either side of the imbalance may affect the machining effect.

In terms of hardness, the order of tool material hardness is: diamond tools > cubic boron nitride tools > ceramic tools > carbide > high-speed steel. This difference in hardness determines the range of workpiece materials they can machine. Workpiece materials with high hardness, such as hardened steel and cemented carbide, must be machined with tools of higher hardness, and the hardness of the tool material is generally required to be above 60 HRC. Hardness and wear resistance are closely related, the higher the hardness, the better the wear resistance, but may also affect the toughness of the tool. For example, the change of cobalt content in cemented carbide is a good reflection of this balanced relationship. When the cobalt content increases, the strength and toughness of cemented carbide increases, but the hardness will be reduced accordingly, this characteristic makes it more suitable for rough machining, able to withstand larger cutting force and impact; and when the cobalt content decreases, the hardness and wear resistance increases, more suitable for finishing, able to ensure machining accuracy while extending tool life.

In addition, tools with excellent high-temperature mechanical properties have obvious advantages in high-speed cutting. Ceramic tool is a typical example, its excellent high-temperature performance makes it able to maintain stability in high-speed cutting, allowing the cutting speed can be 2 - 10 times higher than the carbide, greatly improving the processing efficiency.

Matching physical properties: Selecting the right tool for the thermal conductivity of the workpiece

Different tool materials have different physical properties, which interact with the workpiece material during machining and affect the machining results. When machining workpieces with poor thermal conductivity, a tool material with better thermal conductivity should be used in order to avoid heat build-up in the cutting zone, resulting in high tool and workpiece temperatures. This choice is like opening up a fast evacuation channel for heat, so that the cutting heat can be rapidly transmitted, thus effectively reducing the cutting temperature.

Diamond tools, for example, it has a high thermal conductivity and thermal diffusivity, cutting heat can be quickly dispersed out, will not produce a large thermal deformation in the tool and workpiece. This feature for the high dimensional accuracy requirements of precision machining tools is critical, because a small thermal deformation may lead to processing size deviation, affecting product quality.

Various cutting tool materials have different physical performance indicators such as heat resistance temperature, thermal conductivity, thermal expansion coefficient and thermal shock resistance. For example, the heat-resistant temperature of diamond tools is 700 - 800 ℃, PCBN tools are 1300 - 1500 ℃, ceramic tools are 1100 - 1200 ℃, TiC (N) based cemented carbide is 900 - 1100 ℃, WC based ultra-fine grain cemented carbide is 800 - 900 ℃, HSS is 600 - 700 ℃. The order of thermal conductivity is PCD>PCBN>WC-based Cemented Carbide>TiC (N)-based Cemented Carbide>HSS>Si3N4-based Ceramic>A1203-based Ceramic. The thermal expansion coefficients are in the order HSS>WC-based Cemented Carbide>TiC (N)>A1203-based ceramics>PCBN>Si3N4-based ceramics>PCD, and the thermal shock resistance is in the order HSS>WC-based Cemented Carbide>Si3N4-based ceramics>PCBN>PCD>TiC (N)-based Cemented Carbide>A1203-based ceramics. These differences in physical properties provide an important basis for choosing the right tool material for different machining scenarios.

Chemical matching: Considering the chemical affinity of the tool to the workpiece

The problem of matching the chemical properties of cutting tool materials with those of the machining object involves the chemical affinity between the tool material and the workpiece material, chemical reactions, diffusion and dissolution and other aspects. Different materials of cutting tools in contact with different workpiece materials, will show different chemical stability.

For example, the anti-adhesion temperature of various tool materials (with steel) in the following order: PCBN > ceramics > carbide > HSS; the anti-oxidation temperature in the following order: ceramics > PCBN > carbide > diamond > HSS; the diffusion strength of the tool varies with different workpiece materials, and the diffusion strength of the tool is in the following order for steel: diamond > Si3N4 ceramic > PCBN > A1203 ceramic; the diffusion strength of the tool varies with different workpiece materials; the diffusion strength of the tool varies with different workpiece materials; the diffusion strength of the tool varies with different workpiece materials. For steel, the order of diffusion strength is Diamond > Si3N4-based ceramics > PCBN > A1203-based ceramics; for titanium, the order of diffusion strength is A1203-based ceramics > PCBN > SiC > Si3N4 > Diamond. These differences in chemical properties determine the adaptability of the tool in the processing of specific materials, only the choice of chemical properties of the tool and workpiece materials to match, in order to avoid premature failure of the tool due to chemical action, to ensure that the machining process is carried out smoothly.

Reasonable choice: according to the workpiece material to determine the best tool

In the practice of CNC machining, the correct choice of tool material is the key to achieving efficient, high-quality machining. Generally speaking, PCBN, ceramic tools, coated carbide and TiCN-based carbide tools are suitable for CNC machining of ferrous metals such as steel due to their specific performance advantages. These tools are able to fully utilize their advantages of hardness, heat resistance and chemical stability when processing ferrous materials, and effectively meet the various challenges of ferrous metal machining.

PCD tools, on the other hand, excel in the machining of non-ferrous materials such as Al, Mg, Cu and their alloys and non-metallic materials. Their high hardness, high wear resistance and low coefficient of friction enable them to cut non-ferrous and non-metallic materials with high precision and efficiency. Cubic boron nitride tools have an irreplaceable position in the field of ferrous metal finishing by virtue of their excellent hardness, thermal and chemical stability, becoming an important tool choice for processing specific materials in CNC machining and providing strong support for the high-quality development of modern manufacturing industry.