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1 Introduction
With the development of manufacturing technology, cutting processing, as the main basic process of manufacturing technology, has entered a new stage of development characterized by the development of high-speed cutting, the development of new cutting processes and processing methods, and the provision of complete sets of technologies. At the same time, tool technology is also developing in the direction of high hardness, high speed, high precision and dry machining, playing an important role in the automotive, aerospace, energy, military, mold and other fields.
PCBN tools, ceramic tools, coated tools, etc. all have high hardness, wear resistance and chemical stability, suitable for high-speed cutting, dry cutting, hard cutting and other green manufacturing requirements. Due to the unparalleled superiority of PCBN tools in machining precision, cutting efficiency and tool life, the promotion and application of PCBN tools can create huge economic benefits.
2.PCBN tool performance
Cubic boron nitride (CBN) is one of the isomers of boron nitride (BN). Its structure is similar to that of diamond. It has the same chemical bond type and similar lattice constant, so it has hardness and strength similar to diamond.
Polycrystalline cubic boron nitride (PCBN) is a polycrystalline crystal formed by sintering CBN as a main component and a binder at high temperature and high pressure. The binder is mainly composed of metal type (represented by Co and Ni) or ceramic type (TiC, TiN, Al2O3 is representative).
2.1 Characteristics of PCBN tools
(1) has high hardness and wear resistance
The microhardness of CBN fine powder is 8000-9000 HV, and the hardness of sintered body PCBN is generally 3000-5000 HV. When cutting wear-resistant materials, its wear resistance is 50 times that of cemented carbide tools, 30 times that of coated carbide tools, and 25 times that of ceramic tools.
(2) has high thermal stability
The heat resistance of PCBN can reach 1400 ° C ~ 1500 ° C, the hardness of PCBN at 800 ° C is higher than the normal temperature hardness of ceramic and cemented carbide. Therefore, the PCBN tool is suitable for processing high hardness and wear resistant materials such as hardened steel, cast iron and high temperature alloy steel.
(3) has excellent chemical stability
PCBN is particularly chemically inert. It does not react with iron-based materials at temperatures between 1200 °C and 1300 °C. It reacts with carbon at 2000 °C. In neutral and reducing gases, both acid and alkali are Stable; its bonding and diffusion effects on various materials are much smaller than that of hard alloys, so PCBN tools are particularly suitable for processing steel materials.
(4) has good thermal conductivity
Among all kinds of tool materials, the thermal conductivity of PCBN is second only to diamond, the thermal conductivity is 1300W/(m °C), and the thermal conductivity of PCBN increases with increasing temperature.
(4) has a lower coefficient of friction
The coefficient of friction of CBN is 0.1 to 0.3, and the friction coefficient decreases as the cutting speed increases. This characteristic leads to a reduction in friction between the chips during cutting, a reduction in cutting deformation, a reduction in cutting force, and an improvement in the quality of the machined surface.
2.2 Application of PCBN tool
The development of manufacturing technology and difficult-to-machine materials is driving the development of tool technology. The red hardness and wear resistance of PCBN tools have great advantages in hard dry-cutting difficult-to-machine materials. PCBN tools have higher impact strength and crush resistance than ceramic knives. They are usually used to process materials with hardness higher than 50HRC. They still have high hardness at cutting temperatures up to 2000°C, and diamonds may dissolve under the same conditions. And converted into graphite. Therefore, the rigidity of the machine tool can be slightly inferior when cutting hardened metal. In addition, some special PCBN tools are resistant to high power roughing cutting loads, intermittent cutting impacts, and wear and cutting heat during finishing.
Early PCBN tools were hard but lacked sufficient toughness. With the development of tool material technology and the increasingly advanced manufacturing process, the material and toughness of PCBN tools have changed a lot. At present, PCBN tools can meet the requirements of special workpiece material processing processes more widely, and have been widely used in machining fields such as turning, milling and boring. For example, the automobile industry replaces the original grinding process with the new large-particle whole PCBN blade for efficient cutting of difficult-to-machine alloy cast iron; the mold industry adopts PCBN tool for high-speed finishing and hardening steel die to complete the surface finishing process, which has become a new process in the mold manufacturing industry. .
3.PCBN tool design
As a new tool material that has been updated in the 21st century, PCBN tools have shown great economic benefits and have attracted close attention from various industrial countries around the world. PCBN tools have made great strides in design and manufacturing.
3.1 Wiper Technology
Since the wiper technology changes the corner radius of the tool tip and doubles the feed rate, high feed cutting can be achieved; if the cutting parameters are constant, the surface quality is doubled. As a result, Sandvik Coromant has introduced Wiper technology into the range of PCBN inserts for high productivity and high surface quality in the outer and inner circular cutting processes, with great success in finishing and semi-finishing and roughing turning. In the processing of more and more hardened materials, turning with Wiper technology has enhanced the competitive advantage of grinding. Toshiba has developed four new PCBN inserts using the Wiper technology. The BX310 and BX330 inserts are suitable for continuous or intermittent cutting of hardened steel with a hardness of 50-60HRC. The blade is sintered from medium CBN particles and heat-resistant ceramic binder to improve the surface quality of the tool and enhance the wear resistance of the tool. The BX930 and BX950 blades are suitable for high-speed finishing of heat-resistant alloy steel, cast iron and iron. A substance. The blade is sintered from a high content of CBN particles with Co and carbide to enhance the transverse fracture resistance of the tool.
3.2 PCBN blade chipbreaker design
The chipbreaker design for the overall PCBN insert is a new development in cutting tool design. The chipbreaker increases the rake angle of the cutting edge and improves the flow of chips on the insert, reducing cutting forces and cutting zone temperatures, thus extending tool life. Lower cutting forces also increase tool accuracy and optimize chip outflow for better surface finish. The Secomax CBN300 blade developed by Seco is shown in Figure 2. It is sintered on the basis of CBN30 with coarse particle powder and a new process. It has high impact resistance and can be economically cut by using special technology. The combination of the blade's integral PCBN insert and the increased cutting edge of the cutting edge combines to create a cutting edge with chipbreaker, enabling the PCBN tool to be machined from conventional hard materials such as hardened steel and chilled cast iron. The processing field has entered the field of milling applications. The tool has been used in a new engine flexible production line built by Shanghai General Motors Co., Ltd., and has achieved good results. It is used to mill the engine block plane with a cutting speed of up to 2000m/min and a tool life of four times that of a typical PCBN tool. The PCBN chipbreaker is an ideal insert for finishing pearlite grey cast iron, especially for boring. Tests using these blades for boring of automotive engine blocks have shown that tool life is 50% higher than equivalent negative rake angle inserts. In April 2004, Kyocera Corporation of Japan developed a three-dimensional groove type BB type PCBN insert suitable for processing hardened steel. As shown in Figure 3, the BB type is compared with the chips in the normal blade processing. The insert adopts a new three-dimensional groove design. Through the entire process, the parts can be processed in one part without the need to change the tool during the cutting process. It can effectively control the chip breaking of hardened steel of different hardness, thus improving the processing efficiency and obtaining better surface quality.
3.3 PCBN blade coating
Tool surface coating is an effective means to improve tool life, improve the accuracy and surface quality of the machined parts, and reduce cutting costs.
Coated PCBN inserts offer significant advantages when turning hard materials. Seco has developed the Secomax CBN100 PVD coated insert. These new coatings are designed to ensure excellent adhesion between the coating and the PCBN substrate interface. It consists of Ti(C, N)+(Ti, Al)N+TiN with a total thickness of 2~4μm. It is suitable for rough finishing of pearlitic gray cast iron and hard steel and hard cast iron. In the comparison of the Secomax CBN100 blade and the Secomax CBN100 PVD coated blade hard car 62HRC bearing steel finishing test, it was found that when the cutting speed reached 130m/min, the tool life increased from 24min of the uncoated blade to 33min of the coated blade; A similar increase was observed at higher speeds (see Figure 4). In industrialized countries, coated tools account for more than 80% of all tools used. It is expected that the market for super-hard coated tools will reach US$2 billion per year in recent years, and the application fields are mainly concentrated in the automotive industry, while the proportion in China is still not as good. 20%. Therefore, it is of great significance to promote the application of coated tools and to develop new coated tool materials. Another research trend is to use CBN film as the wear-resistant coating of the tool, which can increase the service life of the tool by several times or even several times. Since the CBN coating is always accompanied by a large internal stress, the CBN coating is easily peeled off from the substrate. The biggest problem at present is to solve the bonding force between the CBN coating and the cemented carbide substrate. A more effective method is to add a transition layer between the substrate and the coating, such as titanium nitride, silicon nitride, boron-rich gradient layer and the like. Industrial developed countries have invested heavily in this area to fully exploit the potential advantages of CBN materials, and it is not too far to prepare practical CBN tool coatings.
3.4 New Self-Lock (Structure) Blade
Figure 5 shows the CB7015 insert with the new Safe-Lock structure from Sandvik Coromant. This series of inserts is primarily developed for high quality surfaces and high productivity machining of hardened steel parts. The Safe-Lock multi-angle technology mechanically locks the PCBN insert away from the high temperature cutting area, thus providing strength and safety superior to conventional tip structures. Finishing in continuous and slightly intermittent conditions allows for high-speed cutting; larger cutting edges provide better cutting performance in cutting steps, undercuts, and other profiling. 4. Conclusion
PCBN tools offer significant advantages in terms of resource savings, environmental pollution reduction, and reduced manufacturing costs. The design and use of PCBN tools provides new productivity drivers for different manufacturing industries. In industrialized countries, PCBN tools have been widely used. Although Shanghai Volkswagen Automotive Co., Ltd., Changchun FAW Group Corporation and Dongfeng Motor Group Co., Ltd. have widely used PCBN tools in production, the manufacture and use of PCBN tools in China is still in the development stage. Therefore, it is necessary to strengthen the research of PCBN tool manufacturing technology and application technology, strengthen the promotion and promotion of PCBN tools, guide users to correctly and rationally use PCBN tools, and make the cutting processing technology of difficult-to-machine materials enter a new stage.
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Tag: PCBN Tool material High speed cutting Cutting speed Cutting force
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