Development and application of the hottest superha

2022-10-19
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Development and application of superhard tools

1 overview

superhard tools mainly include diamond tools and cubic boron nitride tools, of which artificial diamond composite (PCD) tools and cubic boron nitride composite (PCBN) tools are dominant. With the rapid development of modern manufacturing (especially automobile manufacturing), the production and application of superhard cutting tools are also growing rapidly year by year. By 1997, the annual sales of PCD tools had reached US $230million, and the annual sales of PCBN tools was US $170million

superhard tools are mostly used for cutting auto parts. Among them, 60% of PCD cutting tools are used in automobile manufacturing industry, and nearly 30% are used in woodworking cutting tools (by the end of 1990s, PCD woodworking cutting tools accounted for 40%); One half of PCBN cutters are used in automobile manufacturing, and about 20% are used in the processing of heavy equipment (such as rollers)

in recent years, with the rapid development of CNC machining technology and the widespread use of CNC machine tools, the application of superhard tools that can achieve high efficiency, high stability and long-life machining has become increasingly popular. At the same time, many advanced cutting concepts have been introduced, such as high-speed machining, hard machining, high stability machining, turning instead of grinding, dry cutting, etc. Superhard cutting tools have become an indispensable and important means in modern machining

2 main varieties and characteristics of superhard tools

(1) PCD metal cutting tools

pcd metal cutting tools can use the high hardness, high wear resistance, high thermal conductivity and low friction coefficient of PCD materials to achieve high precision, high efficiency, high stability and high surface finish machining of non-ferrous metals and wear-resistant non-metallic materials. This kind of cutting tools can be divided into welded PCD cutting tools and indexable PCD blades

in recent years, PCD tools with standard shanks have developed rapidly among welded PCD tools, such as PCD milling cutters with shanks, PCD boring cutters, PCD reamers, etc. the types of shanks are mainly cylindrical shanks, taper shanks and HSK shanks. This kind of tool (especially multi tooth tool) is characterized by small runout of the cutting edge to the shank (for example, the runout of the cutting edge of the HSK shank PCD milling cutter with a blade length of 30mm is only 0.002mm), which is especially suitable for large-scale high-speed processing of the formed surfaces, holes, step holes, etc. of various non-ferrous metal parts. For example, the PCD high-speed milling cutter with aluminum matrix cutter head (six edges, diameter 100mm) has a maximum speed of more than 20000r/min and a cutting speed of 7000m/min, which is suitable for the processing of formed surfaces of auto parts

the indexable PCD blade is made by embedding a PCD blank on the cemented carbide indexable blade and then grinding it. It can be clamped on the cutter bar, cutter holder or cutter head of various NC machine tools for high reliability mass processing. With the increasing popularity of CNC machine tools, machining centers and automatic production lines, indexable PCD blades are used more and more, and their tool durability can be dozens of times higher than that of cemented carbide tools

(2) PCD woodworking tools

PCD woodworking tools can be mainly divided into PCD saw blades and PCD formed woodworking milling tools. The PCD saw blade is formed by welding the PCD blank on the base of the saw blade and grinding it. Its structure is similar to that of the cemented carbide saw blade. The difference is that the front angle of the PCD saw blade is smaller than that of the cemented carbide saw blade, which is generally 5 ° ~ 10 °, the wedge angle is 65 ° ~ 75 °, the specification of the saw blade is generally mm, and the number of serrations can be up to 72 teeth

the main varieties of PCD formed woodworking milling cutters are trimming cutters for processing Al2O3 layers of laminate floors, PCD groove cutters, PCD furniture forming cutters, etc. their processing method is to copy (or combine) the shape of PCD cutters on the processed wood at one time. The cutting speed of PCD forming woodworking milling cutter can reach 3000m/min, the cutting amount can reach several meters per minute, and the tool durability is dozens or even hundreds of times that of cemented carbide tools. Because of its high efficiency and high durability, it is especially suitable for mass processing

(3) PCBN metal cutting tools

PCBN metal cutting tools can also be divided into welded PCBN tools and indexable PCBN blades

welded PCBN tools are made by welding PCBN tool blanks on steel substrates and grinding them, mainly including turning tools, boring tools, reamers, etc. PCBN tools are mostly used for the processing of wear-resistant ferrous metals, so the sharp angle of the tool cannot be too small. The front angle of the tool is generally -5 ° ~ 5 °, and the rear angle is generally 3 ° ~ 10 °. Negative chamfering is generally used in intermittent cutting

PCBN blades with indexable structure (mainly turning blades and milling blades) are generally formed by inserting and welding a PCBN blank on one corner of the indexable cemented carbide blade and grinding it. Considering that the tool blank is expensive and regrinding, it is generally made into one tip. With the improvement of welding quality, its shear strength can reach 0.78kg/m. As the size of PCBN tool blank becomes smaller and smaller, the price of non regrinding PCBN blade also decreases

3 development characteristics of superhard tool blank

the development of superhard tool blank materials is the basis for the development of superhard tools. One of the development characteristics of superhard tool blank materials is the serialization of products, and the specifications and varieties suitable for different processing objects are increasing. For example, the new brand cth025 (developed from syndite 025) of British DeBeers is a brand added for processing high wear-resistant materials, and its wear resistance is further improved; Compax1700 of General Electric Company (GE) is also a similar product, which is a kind of PCD composite with coarser particle size; Bzn6100 in PCBN tool blank is the replacement product of bzn6000, bzn8200 is the replacement product of bzn8100, and the newly launched bzn7000 is a pure CBN sintered body, which has excellent thermal conductivity and impact resistance, and is especially suitable for rough machining of high hardness materials and high-speed machining of cast iron; Similar products include cbn300 from seco in Sweden, kd420 from kenametal in the United States, kbn30s from Kyocera in Japan, etc; Mitsubishi mb835 PCBN tool blank is suitable for intermittent cutting of hardened steel. It disperses the cutting force by refining the CBN particle size (≤ 1 m) and enhances the adhesion between CBN particles and the molecular structure of PLA material at first; Bnx25 of Sumitomo Electric in Japan and dbc45 of DeBeers in Britain belong to this variety

Another development feature of superhard tool blanks is the increasing size of tool blanks. At present, the supply specification of superhard tool blanks abroad is generally more than 50mm, and 74mm composite sheets can also be supplied in batches. The maximum specification of PCBN tool blanks can reach 101mm, and small-size tool blanks are cut from large tool blanks. The cost of large-scale superhard tool blank is lower, which is more suitable for mass use. At present, only tool blanks below 20mm are available in China (such specification tool blanks were available abroad in the 1970s), which is due to the difference in the cavity size of two kinds of ultra-high pressure and high temperature equipment, namely, double top and six top

The third characteristic of the development of superhard tool blank materials is that CVD diamond film has entered the commercial supply stage from the development stage. Typical CVD diamond film cutting tools include kd100 coated blade of kenametal company in the United States, kdf300 brand CVD diamond film cemented carbide end milling cutter, etc. CVD diamond thick film cutters of Beijing Tiandi diamond company can also be supplied in batches. It is reported that British DeBeers company has successfully launched 250mm CVD diamond thick film, and has a series of products such as knife blank thick film, optical thick film, WEDM thick film, curved surface thick film, transparent thick film, etc

4 types and characteristics of special machine tools for superhard tools

special machine tools for machining superhard tools mainly fall into the following three categories:

(1) PCD tool grinding machine tools. These machine tools are represented by RS series tool grinding machines of EWAG company in Switzerland. This grinding machine tool can use the sharpness of ceramic bonded diamond wheels and a certain grinding pressure to realize the grinding of PCD, PCBN and natural diamond tools, which is characterized by good machine tool rigidity, With projection measuring device, it is the most widely used special grinding equipment for superhard tools abroad. Similar products include PCD tool grinding machines manufactured by Osaka diamond company in Japan and COBOM company in Britain. At present, PCD tool grinding technology is constantly improved, such as changing the constant pressure generated by the spring into pneumatic pressure, which can be adjusted within the range of 0 ~ 300N to adapt to different grinding objects. In order to control the grinding size, the scales on the grinding machine are equipped with digital display devices. Taiwan Yuanshan company changed the projection screen and other optical devices on the original edge grinder into a high-precision camera system, equipped with a precise measurement scale, which can display and control the grinding size on the monitor, and can realize non-stop measurement. The magnification of the camera is adjustable from 15 to 120 times, and can grind r0.05mm edge arc

(2) CNC EDM PCB tool forming machine such equipment is represented by QWD series machine tools of Vollmer company in Germany. This machine tool uses WEDM to process PCD and PCBN tools. Due to the advanced numerical control system, the runout of the multi edge tools can be controlled at 0.001mm, and the surface roughness of the tools can reach Ra0. New materials are widely used in high-tech fields 4 m。 The machine tool has six numerical control axes and two manual axes, which is especially suitable for the processing of multi edge tools such as step drills with handles, milling cutters, saw blades, etc. the geometric shapes of the edge, back, inner fold line and so on of step tools and curve tools can be cut out by inputting the program once, and the degree of automation and processing accuracy are very high. The disadvantage is that the roughness of cutting surface is slightly inferior to that of grinding surface, and the price of machine tool is relatively expensive

(3) ultra precision diamond tool grinder this equipment can grind the ultra precision machining straight-line diamond tools used in aerospace, military industry and other industries, which arouse the enthusiasm of many industries. The surface roughness of the tool RA ≤ 0.01 M, and the cutting edge radius R ≤ 0.1 M. The equipment adopts an aerostatic spindle, with an accuracy of 0.1 ~ 0.2 m, and the end face runout of the grinding disc is 0.1 ~ 0.2 m/300mm

5 typical application of superhard tools

(1) hard machining, turning instead of grinding

due to the extremely high hardness and red hardness of PCBN tools, the machined high hardness parts can obtain good surface roughness, so Turning Hardened Steel with PCBN tools can achieve "turning instead of grinding". Application examples include the machining of gear holes for automobiles and motorcycles. The materials of such parts are generally 20CrMnTi, carburized and quenched, with a surface hardness of 60 ~ 62Hrc, a gear hole accuracy of IT6, and a surface roughness of RA ≤ 0.8 M. The traditional processing technology is: Machining -> heat treatment -> grinding. The machining process of "turning instead of grinding" with superhard tools is: rough machining -> heat treatment -> finish machining. The new process can greatly improve the processing efficiency and reduce the processing cost. The original grinding process can only process 100 pinions per shift, but now PCBN tool is used for turning (cutting parameters v=60 ~ 120m/min, f ≤ 0.12mm/r, AP ≤ 0.1mm, and a shift can process 400 pinions. In addition, the processing cost allocated to each gear is also reduced.

(2) high speed cutting, high stability processing

in the automotive engine production line, The cylinder hole finishing of gray cast iron cylinder block is one of the key processes, which requires high dimensional accuracy, small surface roughness value and good stability; Due to the fast processing pace of the production line, it is required to have high cutting speed (usually V ≥ 500m/min), long tool life (number of machining holes ≥ 1000), and the blade life of chamfering, lip stop, rough and fine boring and other stations should meet the durability requirements. High speed cutting and high stability machining of engine cylinder bore can be realized by using PCBN tool. Its typical cutting parameters are: v=500m/min, f=0.2 ~ 0.4mm/r, ap=0.2 ~ 0.7mm; Machined surface roughness Ra ≤ 1.6 m, tool life>1000 pieces

(3) high speed, high stability, low roughness processing and mirror processing of non-ferrous metals

when using PCD tools to process non-ferrous metals, due to the high hardness of diamond, the affinity between the surface and metal is small, and the tools are generally polished into mirrors

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