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 be the most powerful tool material, which has great advantages.
(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 longer the PCBN tool life, which is unique to other tools such as cemented carbide. 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, 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. 
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