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Superhard tools are mostly used for the machining of automotive parts. Figure 3 and Figure 4 show the sales share of global PCD tools and PCBN tools in various application fields in 1995. Among them, 60% of PCD tools are used in the automotive industry, nearly 30% are used in woodworking tools (up to 40% of PCD woodworking tools in the late 1990s); 1/2 of PCBN tools are used in the automotive industry. About 20% is used for processing heavy equipment such as rolls.
In recent years, with the rapid development of CNC machining technology and the widespread use of CNC machine tools, the application of super-hard tools that can achieve high efficiency, high stability and long-life processing has become more and more popular, and many advanced cutting concepts have been introduced. Such as high-speed cutting, hard processing, high-stability processing, grinding by car, dry cutting, etc. Superhard tools have become an indispensable tool in modern machining.
2 Main types and characteristics of superhard tools
(1) PCD metal cutting tool PCD metal cutting tool can achieve high precision, high efficiency and high stability of non-ferrous metals and wear-resistant non-metallic materials by using PCD materials with high hardness, high wear resistance, high thermal conductivity and low friction coefficient. And high surface finish processing. Such tools are mainly structurally divided into welded PCD cutters and indexable PCD inserts.
In recent years, the fastest-growing variety of welded PCD tools is PCD tools with standard tool holders, such as PCD cutters with handles, PCD files, PCD reamers, etc. The type of tool holder is mainly cylindrical handle, taper shank and HSK handle. . This kind of tool (especially multi-toothed tool) is characterized by small beating of the cutting edge (such as the cutting edge of the HSK shank PCD milling cutter with a blade length of 30mm is only 0.002mm), especially suitable for various colored Large-scale high-speed machining of forming surfaces, holes, stepped holes, etc. of metal parts. For example, the PCD high-speed milling cutter (six-blade, diameter 100mm) with aluminum base cutter has a maximum speed of 20,000R/MIN, and the cutting speed is up to 7,000M/MIN, which is suitable for forming surface of automotive parts.
The indexable PCD insert is made by inserting a PCD blank on the carbide indexable insert and then sharpening it. It can be clamped on the cutter bar, tool holder or cutter head of various CNC machine tools. High-reliability high-volume processing. With the increasing popularity of CNC machine tools, machining centers and automatic production lines, the use of indexable PCD inserts is increasing, and the tool durability can be increased by several times compared with cemented carbide tools.
(2) PCD woodworking tools PCD woodworking tools can be divided into two major categories: PCD saw blades and PCD forming woodworking cutters. The PCD saw blade is formed by welding the PCD tool blank to the saw blade base and then sharpening. The structure is similar to that of the carbide saw blade. The difference is that the front angle of the PCD saw blade is smaller than that of the hard alloy saw blade. It is 5°～10°, the wedge angle is 65°～75°, the saw blade size is generally ø100-450mm, and the number of saw teeth can be up to 72 teeth.
The main types of PCD forming woodworking cutters are trimming knives, PCD grooving knives, PCD furniture forming knives for processing laminate flooring Al2O3, etc. The processing method is to copy (or combine) the shape of the PCD cutter to the quilt at one time. Processing on wood. The cutting speed of PCD forming woodworking cutter can reach 3,000m/min, the cutting amount can reach several meters per minute, the tool durability is dozens or even hundreds of times of cemented carbide tools, due to high efficiency, high durability Features such as degree, especially suitable for high-volume processing.
(3) PCBN metal cutting tools PCBN metal cutting tools can also be divided into two types: welded PCBN tools and indexable PCBN blades.
The welded PCBN tool is obtained by welding the PCBN tool blank on the steel substrate, mainly including turning tools, boring tools and reamers. PCBN tools are mostly used for the processing of wear-resistant ferrous metals, so the tool nose angle should not be too small, the tool rake angle is generally -5° to 5°, the back angle is generally 3° to 10°, and the negative cutting is generally negative. Chamfer.
The PCBN inserts (mainly for the inserts and milling inserts) of the indexing structure are typically welded to a corner of the indexable carbide insert with a PCBN blank that is sharpened. Considering the expensive and re-grinding of the blank, it is generally only made into one tip. With the improvement of the quality of the welding process, the shear strength can reach 0.78kg/m2. As the size of the PCBN blank becomes smaller, the price of the non-reground PCBN insert is also reduced.
3 Development characteristics of super-hard knife blank
The development of superhard tool blanks is the basis for the development of superhard tools. One of the development characteristics of super-hard knife blank materials is the serialization of products, and the variety of specifications suitable for different processing objects is increasing. For example, the new CTH025 grade (developed by Syndite 025) from DeBeers in the UK is a new grade for the processing of highly wear-resistant materials, and its wear resistance is further improved; the General Electric Company (GE) Compax1700 also It is a similar product, which is a PCD composite sheet with a coarser grain size; BZN6100 in PCBN blank is a replacement product of BZN6000, BZN8200 is a replacement product of BZN8100, and the newly introduced BZN7000 is a pure CBN sintered body with excellent Thermal conductivity and impact resistance, especially suitable for high-hardness material roughing and high-speed cutting of cast iron; similar products include Sweden's Seco CBN300, Kenametal's KD420, Japan's Kyocera's KBN30S, etc.; Japan's Mitsubishi MB835 The PCBN blank is suitable for interrupted cutting of hardened steel. It refines the cutting force by refining the CBN particle size (≤1μm) and enhances the adhesion between CBN particles; BNX25 of Sumitomo Electric Co., Ltd. and DBC45 of DeBeers of the United Kingdom Such brands belong to this category.
Another development feature of superhard blanks is the ever increasing size of the blank. At present, the supply specifications of foreign superhard blanks are generally above ø50mm, and the composite sheets of ø74mm can also be supplied in batches. The maximum size of PCBN blanks can reach ø101mm, and the small size blanks are cut from the large blanks. Large-size super-hard tool blanks are cheaper and more suitable for high-volume use. At present, there are only stencil blanks of ø20mm or less in China (there are such knives in the 1970s), which is due to the difference in cavity size between the two-sided top and the six-sided top.
The third characteristic of the development of superhard blank material is that the CVD diamond film has entered the commercial supply stage from the development stage. More typical CVD diamond film tool products include KD100 coated blades from Kenametal, KDF300 grade CVD diamond film and carbide end mills. Beijing Tiandi Diamond's CVD diamond thick film cutters are also available in volume. According to reports, the British company Debeers has successfully introduced ø250mm CVD diamond thick film, and there are a series of thick film, optical thick film, wire-cut thick film, curved thick film, transparent thick film and other products.
4 Types and characteristics of special hard machine tools
There are three main types of special machine tools for machining superhard tools:
(1) PCD tool sharpening machine This type of machine tool is represented by RS series grinding machine of Ewag Company of Switzerland. This sharpening machine can realize the PCD, PCBN and the use of the sharpness of ceramic bond diamond grinding wheel and certain grinding pressure. The sharpening of natural diamond tools is characterized by the rigidity of the machine tool and the projection measuring device. It is the most widely used sharpening equipment for superhard tools. Similar products include PCD cutter sharpeners manufactured by Osaka Diamond Corporation of Japan and CoBom of the United Kingdom. At present, PCD tool sharpening technology is continuously improved, such as changing the constant pressure generated by the spring to pneumatic pressure, and can be adjusted in the range of 0 to 300N to adapt to different grinding objects. In order to control the grinding size, the scale on the sharpening machine is equipped with a digital display. Taiwan Yuanshan Company changed the optical device such as the projection screen on the original sharpening machine to a high-precision camera system, equipped with a precise measuring scale, which can display and control the grinding size on the monitor, which can realize online measurement without stopping the machine. The multiple is adjustable from 15 to 120 times, and the edge arc of R 0.05 mm can be ground.
(2) CNC EDM PCB tool forming machine This type of equipment is represented by the QWD series of machine tools from Vollmer, Germany. The machine tool uses PCG and PCBN tools for EDM. Thanks to the advanced CNC system, the multi-edge tool can be controlled to be 0.001mm, and the surface roughness of the tool can reach Ra0.4μm. The machine has six CNC axes and two manual axes. It is especially suitable for machining multi-edge tools such as shank step drills, milling cutters, saw blades, etc. The cutting edge, the edge of the curved tool, the back, and the inner can be cut by one input program. Geometric shapes such as broken lines, high degree of automation and machining accuracy are high. The downside is that the surface roughness of the cut surface is slightly lower than that of the ground surface, and the machine tool is more expensive.
(3) Super-precision diamond tool grinding machine This equipment can grind ultra-finished linear-edged diamond tools for aerospace, military and other industries. The surface roughness of the tool is Ra≤0.01μm, and the cutting edge radius r≤0.1μm. The equipment adopts an aerostatic main shaft with an accuracy of 0.1 to 0.2 μm, and the end face of the grinding disc is 0.1 to 0.2 μm/ø 300 mm.
5 Typical application of superhard tools
(1) Hard processing, grinding by car Due to the extremely high hardness and red hardness of PCBN tools, the high hardness parts can be processed to obtain good surface roughness, so the use of PCBN tools for turning hardened steel can achieve The car is worn." Application examples such as machining of gear holes of automobiles and motorcycles, such parts are generally 20CrMnTi, carburized and quenched, surface hardness is 60-62HRC, gear hole precision is IT6, surface roughness Ra≤0.8μm. The traditional processing technology is: machining -> heat treatment -> grinding. The processing technology of “hardening by car†with super-hard tools is: roughing->heat treatment->finishing. The new process can greatly improve the processing efficiency and reduce the processing cost. The original grinding process can only process 100 pinions, and now it is PCBN tool turning (cutting parameters V=60～120m/min, f≤0.12mm/r) , ap ≤ 0.1mm, a class can process 400 pinions, in addition, the processing cost allocated to each gear has also decreased.
(2) High-speed cutting, high-stability processing in the automobile engine production line, the cylinder hole finishing of the gray cast iron cylinder is one of the key processes, requiring high dimensional accuracy of the cylinder hole machining, small surface roughness value and good stability; The processing line of the production line is fast, requiring high cutting speed (usually V≥500m/min), long tool life (number of machining holes ≥1000), and the blade life of multiple stations such as chamfering, stop, and coarse boring should be satisfied. Durability requirements. High-speed cutting and high-stability machining of engine cylinder bore can be realized by PCBN tool. Typical cutting parameters are: V=500m/min, f=0.2～0.4mm/r, ap=0.2～0.7mm; machining surface roughness Ra≤1.6μm, tool life>1,000 pieces.
(3) High-speed, high-stability, low-roughness processing and mirror processing of non-ferrous metals When PCD tools are used to process non-ferrous metals, the hardness of the diamond is high, the surface and metal affinity are small, and the tool is generally polished into a mirror surface, which is not easy to produce chips. The tumor is therefore very good in dimensional stability and surface quality, and the tool life is also long.
For example, the copper commutator that uses the PCD tool to machine the motor commutator, the typical cutting parameters are: V=300m/min, f=0.08mm/r, ap≤0.15mm, the machined surface roughness Ra0.1～0.2μm, the tool The life is > 5,000 pieces, while the carbide tool can only process a few pieces.
Using PCD tools to process a variety of silicon-aluminum alloy parts, surface roughness Ra ≤ 0.1μm, tool life can reach several thousand to tens of thousands, especially suitable for large-scale production of automotive and motorcycle parts.
With single crystal diamond tools, mirror spherical processing can be realized on ultra-precision lathes. The machine tool adopts ultra-precision gas static pressure spindle and rotary table, the runout is ≤0.3μm, and the workpiece adopts high-precision pneumatic chuck, which can realize fast and high-precision positioning. When processing oxygen-free copper material, the surface roughness Ra≤0.025μm, roundness ≤0.3μm; when processing aluminum parts, the surface roughness Ra≤0.025μm.
(4) Dry cutting, cleaning process using PCBN tool to process boron-containing cast iron cylinder liner, cutting parameters: V=200m/min, f=0.1mm/r, ap=0.2～1mm, machining surface roughness Ra≤1.6μm , precision IT6, tool life between two sharpening > 100 pieces, can achieve "car grinding". Due to the dry cutting, the cutting (grinding) cutting liquid and the grinding wheel ash are avoided to pollute the environment, and the chips can be recycled and reused, which meets the requirements of clean production.
Development and application of superhard tools
Superhard tools mainly include diamond tools and cubic boron nitride tools, among which synthetic diamond composite (PCD) tools and cubic boron nitride composite (PCBN) tools dominate. With the rapid development of modern manufacturing (especially the automobile manufacturing industry), the production and application of super-hard tools are growing rapidly year by year. Figure 1 and Figure 2 show the growth of global sales of PCD tools and PCBN tools in the past decade.