Research status and development of cutting perform

2022-09-23
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Research status and development ideas of abrasive cutting performance of cemented carbide tool materials

machining is one of the most widely used machining technologies in modern manufacturing industry. According to statistics, the proportion of cutting processing in the whole manufacturing process abroad is about 80% - 85%, while in China, the proportion is as high as 90%

tools are indispensable and important tools in cutting. Whether ordinary machine tools, advanced numerical control machine tools (NC), machining centers (MC) and flexible manufacturing systems (FMC), they must rely on tools to complete cutting. The development of cutting tools has a direct impact on improving productivity and processing quality. Material, structure and geometry are the three elements that determine the cutting performance of the tool, in which the performance of the tool material plays a key role. The international society of production engineering (CIRP) pointed out in a research report: "due to the improvement of tool materials, the allowable cutting new material industry is the basic industry, and the cutting speed is almost doubled every 10 years". Cutting tool materials have developed from high-speed steel and cemented carbide at the beginning of the 20th century to high-performance ceramics and superhard materials. The heat-resistant temperature has increased from 500 ~ 600 ℃ to more than 1200 ℃, and the allowable cutting speed has exceeded 1000m/min, which has increased the cutting productivity by more than 100 times in less than 100 years. Therefore, it can be said that the development history of tool materials actually reflects the development history of cutting technology

this paper reviews the basic properties of conventional tool materials, comprehensively reviews the research status of cemented carbide tool materials, and puts forward the research and development ideas of preparing high-performance cemented carbide materials by whisker toughening and strengthening and nano composite strengthening technology

basic properties of conventional tool materials

(1) high speed steel

high speed steel invented by American mechanical engineer F. W. Taylor and metallurgical engineer m.white in 1898 is still a common tool material. High speed steel is a kind of high alloy tool steel with more alloying elements such as W, Mo, Cr and V. its carbon content is 0.7% - 1.05%. High speed steel has high heat resistance, and its cutting temperature can reach 6000 ℃. Compared with carbon tool steel and alloy tool steel, its cutting speed can be doubled. High speed steel has good toughness and formability, and can be used to manufacture almost all kinds of cutting tools, such as tap, fried dough twist drill, gear cutting tool, broach, small diameter milling cutter, etc. However, high-speed steel also has defects such as poor wear resistance and heat resistance, which has been difficult to meet the increasingly high requirements of modern cutting tools; In addition, the storage resources of some main elements (such as tungsten) in high-speed steel materials are increasingly exhausted in the world. It is estimated that their reserves are only enough to be mined for 40 ~ 60 years. Therefore, high-speed steel materials are facing a severe development crisis

(2) ceramics

compared with cemented carbide, ceramic materials have higher hardness, red hardness and wear resistance. Therefore, when processing steel, the durability of ceramic tools is 10 ~ 20 times that of cemented carbide tools, its red hardness is 2 ~ 6 times higher than that of cemented carbide, and its chemical stability and oxidation resistance are better than cemented carbide. The disadvantages of ceramic materials are high brittleness, low transverse fracture strength and poor ability to withstand impact load, which is also the focus of continuous improvement in recent decades

ceramic tool materials can be divided into three categories: ① alumina based ceramics. Usually, tic, WC, SiC, TAC, ZrO2 and other components are added to the Al2O3 matrix material, and the composite ceramic tool is formed by hot pressing. Its hardness can reach 93 ~ 95hra. In order to improve the toughness, a small amount of CO, Ni and other metals are often added. ② Silicon nitride based ceramics. The commonly used silicon nitride based ceramics are sin+tic+co composite ceramics, whose toughness is higher than that of alumina based ceramics, and its hardness is equivalent. ③ Silicon nitride alumina composite ceramics. Also known as Sialon ceramics, its chemical composition is 77%si3n4+13%a12o3+10%y2o3, its hardness can reach 1800hv, and its bending strength can reach 1.20gpa. It is most suitable for cutting high-temperature alloys and cast iron

(3) cermet

cermet is different from cemented carbide composed of WC, which is mainly composed of ceramic particles, tic and tin, adhesives Ni, Co, Mo, etc. Gold 2. The pendulum is not vertical: only hang a mound. The hardness and red hardness of ceramics are higher than that of cemented carbide and lower than that of ceramic materials; Its transverse fracture strength is greater than that of ceramic materials and less than that of cemented carbide; Good chemical stability and oxidation resistance, peel wear resistance, oxidation and diffusion resistance, low bonding tendency and high blade strength

the cutting efficiency and working life of cermet tools are higher than that of cemented carbide and coated cemented carbide tools, and the machined workpiece surface roughness is small; Due to the low adhesion between cermet and steel, when using cermet tools instead of coated carbide tools to process steel workpieces, the chip formation is relatively stable, and it is not easy to grow chip entanglement in automatic processing, and the edges of parts are basically free of burrs. The disadvantage of cermet is that it has poor thermal shock resistance and is fragile, so its application range is limited

hard alloy military aviation sales will increase by $45.7 billion. Research on gold tool materials is now for most of the use of high molecular polymers.

because the wear resistance and strength and toughness of hard alloy tool materials are not easy to take into account, users can only choose suitable tool materials among many hard alloy brands according to the specific processing objects and processing conditions, which brings a lot of inconvenience to the selection and management of hard alloy tools. In order to further improve the comprehensive cutting performance of cemented carbide tool materials, the current research hotspots mainly include the following aspects:

(1) grain refinement

the strength and wear resistance of cemented carbide tool materials can be improved by refining the grain size of hard phase, increasing the surface area between hard phases, and enhancing the adhesion between grains. When the grain size of WC decreases below submicron, the hardness, toughness, strength and wear resistance of the material can be improved, and the temperature required to achieve complete densification can also be reduced. The grain size of ordinary cemented carbide is 3 ~ 5 μ m. The grain size of fine grain cemented carbide is 1 ~ 1.5 μ M (micron level), ultrafine grain cemented carbide grain size up to 0.5 μ M or less (sub micron, nano scale). Compared with ordinary cemented carbide with the same composition, the hardness of Ultrafine Grain Cemented Carbide can be increased by more than 2hra, and the bending strength can be increased by 600 ~ 800MPa

the commonly used grain refinement process methods mainly include physical vapor deposition, chemical vapor deposition, plasma deposition, mechanical alloying, etc. Equal diameter lateral extrusion (ECAE) is a promising grain refinement process. This method is to put the powder in the mold and extrude it in a direction different from (nor opposite to) the extrusion direction, and the cross-sectional area during extrusion remains unchanged. The powder grains processed by ECAE process can be significantly refined

because the above grain refinement process is still not mature, nano grains are easy to grow into coarse grains during cemented carbide sintering, and the general growth of grains will lead to the decline of material strength, and a single coarse WC grain is often an important factor causing material fracture. On the other hand, the price of fine grain cemented carbide is relatively expensive, which also restricts its popularization and application

(2) coated cemented carbide

on the cemented carbide substrate with good toughness, a thin layer of wear-resistant metal compound is coated by CVD (chemical vapor deposition), PVD (physical vapor deposition), HVOF (high velocity oxy fuel thermal spraying) and other methods, which can combine the strength and toughness of the substrate with the wear resistance of the coating and improve the comprehensive performance of cemented carbide tools

coated cemented carbide tools have good wear resistance and heat resistance, especially suitable for high-speed cutting; Because of its high durability and good versatility, it can effectively reduce the number of tool changes and improve the processing efficiency when used in small batch and multi variety flexible automatic processing; Coated cemented carbide tools have strong anti crescent wear ability, stable cutting edge and groove shape, reliable chip breaking effect and other cutting performance, which is conducive to the automatic control of the machining process; After passivation and refinement, the matrix of coated cemented carbide tools has high dimensional accuracy, which can meet the requirements of automatic machining for tool change and positioning accuracy

the above characteristics determine that coated cemented carbide tools are particularly suitable for automatic processing equipment such as FMS and CIMS (Computer Integrated Manufacturing System). However, the coating method still fails to fundamentally solve the problem of poor toughness and impact resistance of cemented carbide matrix materials

(3) surface, integral heat treatment and cyclic heat treatment

nitriding, boriding and other treatments on the surface of cemented carbide with good strength and toughness can effectively improve its surface wear resistance. The overall heat treatment of cemented carbide with good wear resistance but poor strength and toughness can change the bonding composition and structure in the material, reduce the adjacency of WC hard phase, and improve the strength and toughness of cemented carbide. The comprehensive properties of cemented carbide materials can be comprehensively improved by using cyclic heat treatment to alleviate or eliminate the stress between grain boundaries

(4) adding rare metals

adding rare metal carbides such as TAC and NBC in cemented carbide materials can make the additives combine with the original hard phases WC and tic to form a complex solid solution structure, so as to further strengthen the hard phase structure. At the same time, it can inhibit the grain growth of hard phase and enhance the structural uniformity, which is of great benefit to improve the comprehensive properties of cemented carbide. In the grades of P, K and M cemented carbides in ISO standard, there are such cemented carbides with TA (NB) C added (especially in the grades of M)

(5) adding rare earth elements

adding a small amount of rare earth elements such as yttrium in cemented carbide materials can effectively improve the toughness and bending strength of the materials, and the wear resistance is also improved. This is because rare earth elements can strengthen the hard phase and bonding phase, purify the grain boundary, and improve the wettability of carbide solid solution to bonding phase. Cemented carbides with rare earth elements are most suitable for rough machining and semi finishing. In addition, this kind of cemented carbide also has broad application prospects in cemented carbide tools such as mining tools, anvils, wire drawing dies, etc. China is rich in rare earth resources, and the research on adding rare earth elements to cemented carbide also has a high level. (end)

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