1. Advantages of PCBN tool materials
In the field of machining and manufacturing, cutting technology has entered a period of revolutionary innovation represented by high-speed milling, CNC multi-function cutting, and micro-shape/super-finishing. At the same time, the revolutionary innovation of cutting tools has also made new progress. At present, the tool material is dominated by coated cemented carbide, and the highest cutting speed range is 300-600m/min. It can be predicted that the development of high-speed cutting will be more rapid in the future. When the era of ultra-high-speed cutting above 1000m/min comes, PCBN will have the most powerful tool material.
(1) Comparative advantage with diamond
CBN (cubic boron nitride) is second only to diamond at room temperature, and its thermal conductivity and thermochemical stability to iron-based metals are superior to diamond. Diamond tools are only suitable for the cutting of non-ferrous metals and their alloys, while PCBN tools are also suitable for the machining of ferrous metals and their alloys. 
(2) Comparative advantages with cemented carbide
PCBN (Polycrystalline Cubic Boron Nitride) is superior to cemented carbide in high temperature chemical stability and red hardness. It is the best tool material for high speed cutting of high hardness materials. The cutting characteristics of PCBN tools vary with the amount of CBN, the particle size, and the type of binder. Recently, a single-phase PCBN without bonding agent has been successfully developed, and it is expected to obtain more remarkable effects in terms of cutting speed and improving tool life. The higher the CBN content in PCBN, the higher the wear resistance, but the toughness is reduced, especially in the case of intermittent cutting such as end milling, in terms of cutting edge shape, cutting conditions (especially the depth of cut) Special measures should be taken to ensure the strength of the cutting edge and give full play to the advantages of the PCBN tool. For example, when PCBN and carbide ball end mills are used to mill self-hardening steel at high speed, it is known from the comparison of cutting speed and tool life that PCBN tools have superior life characteristics. When high-hardness steel of HRC60 or higher is milled at high speed with PCBN end mill, ultra-high-speed high-precision cutting of over 2000m/min can be realized. Although the cutting speed of the rapid wear of the flank surface has not been confirmed, the PCBN tool can be used for dry cutting because of its high temperature hardness. Within the cutting speed limit range, it can be found that the higher the cutting speed, the more the PCBN tool life is, and the unique performance that other tools such as cemented carbide do not have. PCBN tools also exhibit high tool life in the machining of cast iron, and good machining results are available from lower cutting speeds to high speed cutting speeds. In the boring of automotive parts (such as engine blocks, etc.), PCBN tools exhibit high precision, high efficiency and long life. From the example of the tool wear characteristics of high-speed milling gray cast iron, it is known that 500 to 2000 m/min is a cutting speed range that is advantageous for the life characteristics of the tool. 
Nowadays, the cutting process is rapidly developing in the direction of miniaturization and precision, especially in the aspects of finishing tools and long-life tools, and the technical trends of PCBN tools are of concern. In addition, the high-efficiency and high-precision turning of high-hardness steel with PCBN turning tools has been recognized again. It can be said that PCBN tools are promising tools both now and in the future.
2. PCBN tool application and precautions
In the processing of mold parts, the high-efficiency of high-hardness steel milling with ball end mills has attracted much attention. In the field of milling, the era of machining centers with spindle speeds of tens of thousands of revolutions per minute has been ushered in. High-speed milling tools have ceramic-coated carbide tools, and it can be said that the conditions for extensive high-speed milling have matured. In recent years, the precision pursued by cutting machining is getting higher and higher, which inevitably requires the criterion of tool change - the flank wear width value is reduced (the tool change cycle time is shortened); at the same time, the cutting speed and feed rate are continuously increased to further Improve the efficiency of cutting; high-speed milling machining centers with spindle speeds exceeding 4 to 50,000 rpm are used in large quantities. As a result, PCBN ball end mills with excellent heat resistance and wear resistance and are most suitable for high-speed milling must be used. And the amount of use continues to increase.
However, the material cost and grinding cost of the PCBN ball end mill are higher than that of the hard alloy, and there is a disadvantage that the chipping is prone to occur during processing, so it is necessary to develop a new applicable technology. One of the new technical measures is to use PCBN tools with CBN content of 50-60 vol% in order to improve the toughness and suppress the occurrence of chipping when milling high-hardness steel. From the example of the flank wear pattern of the PCBN tool with low CBN content, the crater wear pattern of the rake face and the corresponding wear pattern when the cutting edge portion is chipped, it is known that this wear pattern generates high temperature during high-speed cutting and is here. Thermal expansion occurs under high temperature conditions, resulting in deterioration of the binder. 
As a technical measure to solve the problem of binder degradation, it is conceivable to reduce the binder and increase the CBN content to obtain a PCBN tool material which is excellent in heat resistance and wear resistance and is suitable for tool requirements. However, previous practice has shown that increasing the CBN content means that the toughness of the tool is lowered, and the edge of the blade is prone to occur. The best solution to prevent the cutting edge of the tool tip is to use a negative rake angle and passivation treatment on the cutting edge arc. This solution can effectively suppress the chipping during cutting, and is one of the key technical measures to give full play to the characteristics of the PCBN tool. 
3. PCBN tool design and application examples
In the finishing of mold parts, PCBN tools perform exceptionally well in terms of machining efficiency, machining accuracy and tool life. There are two types of commercially available ball end mill cutting edges, one is a cutting edge with an axial rake angle and a radial rake angle of 0°, and a negative chamfering of the tip portion; the other is unique. The negative chamfered shape cutting edge. 
The cutting edge of the cutting edge of the PCBN tool with high CBN content is chamfered, and the edge portion is passivated into an R arc shape, which is an important measure to solve the chipping during cutting. In the case of face milling, the negative rake angle, centerless cutting edge ball end mill for ultra-high speed milling can improve the surface roughness compared to ball end mills with a central cutting edge. Therefore, when designing the cutting edge of a PCBN tool, it is necessary to use a tool shape that can fully utilize the material characteristics of the tool. When milling high-toughness special cast iron, even PCBN tools with lower CBN content have much longer life than coated carbide ball end mills, and the wear-resistant PCBN tools remain the highest. The precision of the machined surface.
In the fine-shape, sub-micron ultra-precision machining, the management of tool life is one of the important key technologies, requiring the use of tools with high life characteristics. It can be asserted that in this field of processing, it is not the most suitable tool for PCBN tools.
The machine tool that can perform high-hardness steel micro-machining is a machining center with ultra-high-speed precision cutting function. It has a new spindle structure different from the original machining center. For example, two linear motors are arranged on the drive shaft. Sensitive, vibration-free cutting feed action; the spindle uses an air turbine/hydrostatic bearing that minimizes thermal effects and can carry spindles with rotational speeds up to 120,000 revolutions per minute.
The results of high-speed milling of high-hardness steel with a binderless PCBN tool show that the tool is used in the best machining conditions (cutting edge shape, cutting conditions, tool clamping method, etc.) compared with the PCBN tool with bonding agent. Shows superior tool life characteristics. 
4. More and more attention to PCBN tool technology
In the field of machining, high-speed milling technology has achieved high added value, and technological advances aimed at higher targets are continuing. PCBN tools have evolved from being suitable for special machining to one of the mainstream tools. However, as mentioned above, it must be clearly realized that there are still many problems that need to be overcome in terms of technology. In order to truly arrive in the era of PCBN tools, it is necessary to solve the existing technical problems as early as possible.
In the field of machining and manufacturing, cutting technology has entered a period of revolutionary innovation represented by high-speed milling, CNC multi-function cutting, and micro-shape/super-finishing. At the same time, the revolutionary innovation of cutting tools has also made new progress. At present, the tool material is dominated by coated cemented carbide, and the highest cutting speed range is 300-600m/min. It can be predicted that the development of high-speed cutting will be more rapid in the future. When the era of ultra-high-speed cutting above 1000m/min comes, PCBN will have the most powerful tool material.
(1) Comparative advantage with diamond
CBN (cubic boron nitride) is second only to diamond at room temperature, and its thermal conductivity and thermochemical stability to iron-based metals are superior to diamond. Diamond tools are only suitable for the cutting of non-ferrous metals and their alloys, while PCBN tools are also suitable for the machining of ferrous metals and their alloys. 
(2) Comparative advantages with cemented carbide
PCBN (Polycrystalline Cubic Boron Nitride) is superior to cemented carbide in high temperature chemical stability and red hardness. It is the best tool material for high speed cutting of high hardness materials. The cutting characteristics of PCBN tools vary with the amount of CBN, the particle size, and the type of binder. Recently, a single-phase PCBN without bonding agent has been successfully developed, and it is expected to obtain more remarkable effects in terms of cutting speed and improving tool life. The higher the CBN content in PCBN, the higher the wear resistance, but the toughness is reduced, especially in the case of intermittent cutting such as end milling, in terms of cutting edge shape, cutting conditions (especially the depth of cut) Special measures should be taken to ensure the strength of the cutting edge and give full play to the advantages of the PCBN tool. For example, when PCBN and carbide ball end mills are used to mill self-hardening steel at high speed, it is known from the comparison of cutting speed and tool life that PCBN tools have superior life characteristics. When high-hardness steel of HRC60 or higher is milled at high speed with PCBN end mill, ultra-high-speed high-precision cutting of over 2000m/min can be realized. Although the cutting speed of the rapid wear of the flank surface has not been confirmed, the PCBN tool can be used for dry cutting because of its high temperature hardness. Within the cutting speed limit range, it can be found that the higher the cutting speed, the more the PCBN tool life is, and the unique performance that other tools such as cemented carbide do not have. PCBN tools also exhibit high tool life in the machining of cast iron, and good machining results are available from lower cutting speeds to high speed cutting speeds. In the boring of automotive parts (such as engine blocks, etc.), PCBN tools exhibit high precision, high efficiency and long life. From the example of the tool wear characteristics of high-speed milling gray cast iron, it is known that 500 to 2000 m/min is a cutting speed range that is advantageous for the life characteristics of the tool. 
Nowadays, the cutting process is rapidly developing in the direction of miniaturization and precision, especially in the aspects of finishing tools and long-life tools, and the technical trends of PCBN tools are of concern. In addition, the high-efficiency and high-precision turning of high-hardness steel with PCBN turning tools has been recognized again. It can be said that PCBN tools are promising tools both now and in the future.
2. PCBN tool application and precautions
In the processing of mold parts, the high-efficiency of high-hardness steel milling with ball end mills has attracted much attention. In the field of milling, the era of machining centers with spindle speeds of tens of thousands of revolutions per minute has been ushered in. High-speed milling tools have ceramic-coated carbide tools, and it can be said that the conditions for extensive high-speed milling have matured. In recent years, the precision pursued by cutting machining is getting higher and higher, which inevitably requires the criterion of tool change - the flank wear width value is reduced (the tool change cycle time is shortened); at the same time, the cutting speed and feed rate are continuously increased to further Improve the efficiency of cutting; high-speed milling machining centers with spindle speeds exceeding 4 to 50,000 rpm are used in large quantities. As a result, PCBN ball end mills with excellent heat resistance and wear resistance and are most suitable for high-speed milling must be used. And the amount of use continues to increase.
However, the material cost and grinding cost of the PCBN ball end mill are higher than that of the hard alloy, and there is a disadvantage that the chipping is prone to occur during processing, so it is necessary to develop a new applicable technology. One of the new technical measures is to use PCBN tools with CBN content of 50-60 vol% in order to improve the toughness and suppress the occurrence of chipping when milling high-hardness steel. From the example of the flank wear pattern of the PCBN tool with low CBN content, the crater wear pattern of the rake face and the corresponding wear pattern when the cutting edge portion is chipped, it is known that this wear pattern generates high temperature during high-speed cutting and is here. Thermal expansion occurs under high temperature conditions, resulting in deterioration of the binder. 
As a technical measure to solve the problem of binder degradation, it is conceivable to reduce the binder and increase the CBN content to obtain a PCBN tool material which is excellent in heat resistance and wear resistance and is suitable for tool requirements. However, previous practice has shown that increasing the CBN content means that the toughness of the tool is lowered, and the edge of the blade is prone to occur. The best solution to prevent the cutting edge of the tool tip is to use a negative rake angle and passivation treatment on the cutting edge arc. This solution can effectively suppress the chipping during cutting, and is one of the key technical measures to give full play to the characteristics of the PCBN tool. 
3. PCBN tool design and application examples
In the finishing of mold parts, PCBN tools perform exceptionally well in terms of machining efficiency, machining accuracy and tool life. There are two types of commercially available ball end mill cutting edges, one is a cutting edge with an axial rake angle and a radial rake angle of 0°, and a negative chamfering of the tip portion; the other is unique. The negative chamfered shape cutting edge. 
The cutting edge of the cutting edge of the PCBN tool with high CBN content is chamfered, and the edge portion is passivated into an R arc shape, which is an important measure to solve the chipping during cutting. In the case of face milling, the negative rake angle, centerless cutting edge ball end mill for ultra-high speed milling can improve the surface roughness compared to ball end mills with a central cutting edge. Therefore, when designing the cutting edge of a PCBN tool, it is necessary to use a tool shape that can fully utilize the material characteristics of the tool. When milling high-toughness special cast iron, even PCBN tools with lower CBN content have much longer life than coated carbide ball end mills, and the wear-resistant PCBN tools remain the highest. The precision of the machined surface.
In the fine-shape, sub-micron ultra-precision machining, the management of tool life is one of the important key technologies, requiring the use of tools with high life characteristics. It can be asserted that in this field of processing, it is not the most suitable tool for PCBN tools.
The machine tool that can perform high-hardness steel micro-machining is a machining center with ultra-high-speed precision cutting function. It has a new spindle structure different from the original machining center. For example, two linear motors are arranged on the drive shaft. Sensitive, vibration-free cutting feed action; the spindle uses an air turbine/hydrostatic bearing that minimizes thermal effects and can carry spindles with rotational speeds up to 120,000 revolutions per minute.
The results of high-speed milling of high-hardness steel with a binderless PCBN tool show that the tool is used in the best machining conditions (cutting edge shape, cutting conditions, tool clamping method, etc.) compared with the PCBN tool with bonding agent. Shows superior tool life characteristics. 
4. More and more attention to PCBN tool technology
In the field of machining, high-speed milling technology has achieved high added value, and technological advances aimed at higher targets are continuing. PCBN tools have evolved from being suitable for special machining to one of the mainstream tools. However, as mentioned above, it must be clearly realized that there are still many problems that need to be overcome in terms of technology. In order to truly arrive in the era of PCBN tools, it is necessary to solve the existing technical problems as early as possible.