The tool material is the fundamental factor that determines the cutting performance of the tool, and has a great influence on the machining efficiency, processing cost, processing quality, and tool life. When using carbon tool steel as the cutting tool material, the cutting speed is only about 10m/min; at the beginning of the 20th century, high-speed steel tool materials appeared, the cutting speed was increased to several tens of meters per minute; in the 1930s, carbides appeared and the cutting speed was increased to each The minute is more than 100 meters to several hundred meters; the emergence of current ceramic cutting tools and superhard cutting tools has increased the cutting speed to more than one kilometer per minute; the development of processed materials has also greatly promoted the development of cutting tool materials.
First, the tool material should have the performance
The excellent tool material is the basic condition for the efficient operation of the tool. The cutting part of the tool works under strong friction, high pressure, and high temperature and should have the following basic requirements.
High hardness and high wear resistance
The hardness of the tool material must be higher than the hardness of the material being processed to cut the metal. This is an essential requirement for the tool material. The hardness of the existing tool material is above 60HRC. The harder the tool material, the better the wear resistance, but due to the more complex cutting conditions, the wear resistance of the material is also determined by its chemical composition and the stability of the metallographic structure.
Sufficient strength and impact toughness
Strength refers to the resistance to cutting forces and does not cause the blade to disintegrate and the tool bar should have the performance. It is generally expressed in flexural strength.
Impact toughness refers to the ability of the tool material to ensure no chipping under intermittent cutting or impact working conditions. Generally, the higher the hardness, the lower the impact toughness and the more brittle the material. Hardness and toughness are a contradiction, and it is also a key to overcome the tool material.
High heat resistance
Heat resistance, also known as red hardness, is a measure of the performance of tool materials. It comprehensively reflects the ability of the tool material to maintain hardness, wear resistance, strength, oxidation resistance, anti-adhesion and resistance to diffusion at high temperatures.
Good craftsmanship and economy
In order to facilitate the manufacture, the tool material should have good craftsmanship, such as forging, heat treatment and grinding processing performance. Of course, economy should be considered comprehensively when manufacturing and selecting. Current superhard materials and coated tool materials are more expensive, but their service life is very long. In bulk mass production, the cost allocated to each part is reduced. Therefore, it must be comprehensively considered when choosing.
Second, commonly used tool materials
The commonly used tool materials are tool steel, high-speed steel, carbide, ceramics, and super-hard tool materials. Currently, the most widely used materials are high-speed steel and carbide.
High speed steel
High-speed steel is a kind of high-alloy tool steel with more tungsten, chromium, vanadium and other alloying elements, and it has good comprehensive performance. Its strength and toughness are the highest among existing tool materials. High-speed steel manufacturing process is simple, easy to sharpen into a sharp cutting edge; forging, heat deformation is small, currently in the complex tool, such as twist drills, taps, broaches, gear cutters and forming tool manufacturing, still plays a major role.
High-speed steel can be divided into ordinary high-speed steel and high-performance high-speed steel.
Ordinary high-speed steels, such as W18Cr4V, are widely used to make all kinds of complex tools. The cutting speed is generally not too high, 40-60m/min when cutting ordinary steel.
High-performance high-speed steel, such as W12Cr4V4Mo is smelted by adding some carbon, vanadium, and cobalt and aluminum elements to ordinary high-speed steel. Its durability is 1.5-3 times that of ordinary HSS.
Powder metallurgy high-speed steel is a high-speed steel put into the market in the 1970s, its strength and toughness were increased by 30% -40% and 80% -90% respectively. The durability can be increased by 2-3 times. At present, China is still in the stage of experimental research and production and use are still small.
Carbide
According to GB2075-87 (refer to the use of 190 standards) can be divided into P, M, K three categories, P-type hard alloy is mainly used to process long-cut ferrous metal, marked with blue; M is mainly used for processing black metal And non-ferrous metals, marked with yellow, also known as general-purpose carbide, K is mainly used for processing short-cut ferrous metal, non-ferrous metals and non-metallic materials, marked with red.
P, M, and K (the following Arabic numerals indicate the performance and the conditions under which the load is handled or the processing conditions. The smaller the number, the higher the hardness and the lower the toughness.
P class is equivalent to China's original tungsten-titanium drilling, the main component is WC + TiC + Co, code-named YT.
K class is equivalent to China's original tungsten drills, the main component is WC + Co, code-named YG.
M class is equivalent to China's original tungsten-tungsten-bismuth-cobalt generic alloy, the main component is WC + TiC + TaC (NbC) + Co, code-named YW.
Third, the coating tool outlined
Coated cutters are a new type of tool material that has appeared in the past 20 years. It is an important breakthrough in tool development and an effective measure to solve the contradiction between hardness, wear resistance, strength and toughness of tool materials. Coated cutters are obtained by coating a hard-wearing hard alloy or high-speed steel tool substrate with a hard-wearing refractory metal compound. Commonly used coating materials include TiC, TiN and Al2O3. After a layer of titanium carbide (TiC) was coated on a cemented carbide substrate for the first time in the early 1970s, the cutting speed of ordinary hard alloys was increased from 80 m/min to 180 m/min. In 1976, a titanium carbide-alumina double-coated cemented carbide appeared again, increasing the cutting speed to 250 m/min. In 1981, titanium carbide-aluminum oxide-cobalt nitride triple coated cemented carbides appeared, which increased the cutting speed to 300m/min.
In the high-speed steel substrate tool coating mostly TiN, commonly used physical vapor deposition (PVD method) coating, commonly used in drills, taps, milling cutters, hobs and other complex tools, coating thickness of several microns, coating The hardness can reach 80HRC, which is equivalent to the hardness of the general hard alloy, the durability can be increased by 2-5 times, and the cutting speed can be increased by 20%-40%.
Carbide is coated on a tough cemented carbide substrate and coated with a layer of highly wear-resistant, hard-to-melt metal compounds ranging from a few microns to a few dozen microns thick. Chemical Vapor Deposition (CVD) is generally used. . The coating thickness of coated cemented carbide produced by Zhuzhou Cemented Carbide Factory in China can reach 9μm and the surface hardness can reach 2500-4200HV.
At present, various industrialized countries have developed very rapidly in the research and application of coated tools. Leading Sweden, the use of coated cemented carbide inserts has accounted for 70%-80% in turning, and has reached more than 50% in milling. However, coated cutters are not suitable for processing high-temperature alloys, titanium alloys, and non-metallic materials, and are also not suitable for rough machining of forged castings with sand or crust.
Fourth, diamond tools
Diamond tools are divided into natural diamond and synthetic diamond tools. Natural diamond has the highest hardness and thermal conductivity coefficient in nature. However, due to its high price, processing and welding are very difficult. Except for a few special applications (such as watch precision parts, lighting accessories and jewelry engraving and other processing), rarely as cutting Tools are used in industry. With the development of high-tech and ultra-precision machining. For example, miniature parts of micro-machinery, various reflectors in nuclear reactors and other high-tech fields, navigation gyros in ** or rockets, processing of ultra-precision parts such as computer hard disk chips and accelerator electronics*, single-crystal brilliant diamonds can satisfy The above requirements. In recent years, a variety of chemical methods have been developed for grinding diamond cutters and brazing diamonds with protective atmospheres. The manufacturing process for natural diamond cutters has become relatively simple. Therefore, in the field of high-tech applications for ultra-precision mirror cutting, natural diamonds have played a role. Important role.
In the 1950s, diamond-based cutting tools, namely polycrystalline diamond (PCD), were manufactured in the 1970s using artificial high-temperature high-pressure technology to synthesize diamond powder. The PCD grains are in no order. They have no directionality and therefore have uniform hardness. It has high hardness and thermal conductivity, low coefficient of thermal expansion. With high elastic modulus and low friction coefficient, the cutting edge is very sharp. It can add a variety of non-ferrous metals and wear-resistant high-performance non-metallic materials, such as aluminum, copper, magnesium and its alloys, carbide, fiber plastic materials, metal matrix composites, wood composite materials.
The performance characteristics of PCD, CVD thick film, and synthetic single crystal diamond for the three main diamond tool materials are: PCD weldability, mechanical grinding ability and fracture toughness are the highest, abrasion resistance and edge quality are centered, and corrosion resistance Worst. CVD thick film has the best corrosion resistance, mechanical grinding, cutting edge quality, fracture toughness and wear resistance centered, and poor weldability. Synthetic single crystal diamond has the best edge quality, wear resistance and corrosion resistance. Sex, mechanical grinding and fracture toughness are the worst.
Diamond cutting tools are the ideal tool materials for high speed cutting (2500-5000m/min) aluminum alloys. However, due to the affinity of carbon for iron, especially at high temperatures, diamonds can react with iron, so it is not suitable for cutting. Iron and its alloy workpieces.
Fifth, cubic boron nitride
Cubic boron nitride (CBN) is a purely synthetic material. It is a second superhard material, CBN micropowder, synthesized in the late 1950's using a diamond-like method. Due to the poor sintering properties of CBN, it was not until the 1970s that cubic boron nitride agglomerates (polycrystalline cubic boron nitride PCBN) were produced, which consisted of CBN fines with a small amount of binder phase (Co, Ni or TiN, TiC or Al2O3). ) Sintered at high temperature and pressure. CBN is a dense phase of boron nitride, with high hardness (second only to diamond) and heat resistance (1300, 1500 degrees), excellent chemical stability (much better than diamond) and thermal conductivity, low coefficient of friction . The affinity between PCBN and Fe elements is very low, so it is an ideal tool material for high-speed cutting of ferrous metals.