Basic properties of tool materials

The material of the tool must have high high temperature hardness and wear resistance, the necessary bending strength, impact toughness and chemical inertness, good process (cutting, forging and heat treatment, etc.), and not easy to deform. Usually when the material hardness is high, the wear resistance is also high; the bending strength is high, the impact toughness is also high. However, the higher the hardness of the material, the lower the flexural strength and impact toughness.

Due to the high temperature, high pressure, high speed, and in the corrosive fluid medium work parts, the application of more and more difficult to process materials, cutting the level of automation and machining accuracy requirements are getting higher and higher. In order to adapt to this situation, the development direction of cutting tools will be to develop and apply new cutting tool materials. Further develop the vapor deposition coating technology of cutting tools, deposit higher hardness coating on high toughness and high strength substrate, and better solve the contradiction between hardness and strength of cutting tool materials. Further develop the structure of indexable cutting tools; Improve the manufacturing accuracy of cutting tools, reduce the difference of product quality, and optimize the use of cutting tools.

The following materials are commonly used in general processing tools: carbon tool steel, alloy tool steel, high-speed steel, hard alloy, superhard materials.

Carbon tool steel is a high-quality high-carbon steel with a carbon mass fraction of 0.65-1.35. The grades used as tools are generally T10A and T12A, and the normal temperature hardness is 60-64HRC. When the cutting edge is heated to 200-250 degrees, its hardness and wear resistance will drop rapidly, thus losing cutting performance.

In order to improve the performance of carbon tool steel, often in which the right amount of alloying elements such as manganese, chromium, tungsten, silicon and vanadium, so as to form the alloy tool steel, commonly used grades are 9sicr,GCr15,CrWMn and so on. Compared with carbon tool steel, the hardness of alloy tool steel after heat treatment is similar, while the heat resistance and wear resistance are slightly higher, and the heat treatment is also better. However, compared with high-speed steel, the cutting speed and service life of alloy tool steel are far inferior to high-speed steel, so that its application is greatly restricted. Therefore, alloy tool steel is generally only used to replace carbon tool steel.

High speed steel is a kind of high alloy tool steel containing tungsten, aluminum, chromium, vanadium and other alloying elements. The main advantages of high-speed steel are high hardness, strength and wear resistance, good heat resistance and quenching, and its allowable cutting speed is more than twice that of carbon tool steel and alloy tool steel. The cutting edge of high-speed steel is sharp after grinding, so it is also called front steel and white steel. High-speed steel is a kind of tool material with good comprehensive performance and wide application range. It is often used to manufacture tools with complex structure, such as forming tools, milling cutters, drill bits, reamersBroach, gear cutter, etc.

Cemented carbide is an alloy material manufactured by powder metallurgy method. It is made of high hardness, high melting point metal carbide WC, TiC and other powders, sintered at high temperature with cobalt and other metal binders. Cemented carbide has high hardness, up to 89-93HRA at room temperature, wear resistance and heat resistance are higher than that of tool steel, and it can still cut normally at 800-1000 degrees. Its cutting speed is several times that of high-speed steel. The tool life is also increased by dozens of times, and it can process materials that are difficult to cut with high-speed steel tools, so it is widely used. But it also has bending strength and impact toughness than high-speed steel is low, cutting edge can not be as sharp as high-speed steel tools and other shortcomings.

Superhard materials are mainly diamond, cubic boron nitride and ceramics. Diamond is the hardest material in nature, its hardness can reach 10000HV. Natural diamonds are expensive. Rarely used. Synthetic diamond is sintered with graphite as raw material at high temperature. Mainly used for high-speed fine turning, boring non-ferrous metals and their alloys and non-metallic materials. When cutting copper alloy or aluminum alloy, the cutting speed can reach 800-3800 M/MIN. Due to the high wear resistance of diamond, the processing size and tool life are long. Therefore, it is often used in CNC machine tools, combined machine tools and automatic machine tools, and the roughness after processing can reach 0.1-0.025um. However, the heat resistance of diamond tools is poor, and the cutting temperature should not exceed 700-800 degrees. Low strength, brittleness, sensitive to vibration, only micro cutting. Mainly to mention the ceramic, ceramic cutting tool for the time than the carbide earlier, but because of its brittleness, the development is very slow. However, since the 1970 s, it has developed relatively quickly. There are two main ceramic tool materials, namely, alumina and silicon nitride. As a cutting tool, ceramics have the advantages of low cost, high hardness and good high temperature resistance, and have a good prospect.

Tool material selection

High-speed steel has high bending strength and impact toughness, as well as good machinability, modern is still the most widely used tool material, followed by cemented carbide.

Polycrystalline cubic boron nitride is suitable for cutting high hardness hardened steel and hard cast iron. Polycrystalline diamond is suitable for cutting non-ferrous metals, alloys, plastics and glass fiber reinforced plastics. Carbon tool steel and alloy tool steel are now only used as files, die and taps and other tools.

Cemented carbide indexable inserts have been coated with titanium carbide, titanium nitride, alumina hard layers or composite hard layers by chemical vapor deposition. The physical vapor deposition method being developed can be used not only for carbide cutting tools, but also for high-speed steel cutting tools, such as drills, hobs, taps and milling cutters. The hard coating acts as a barrier to chemical diffusion and heat conduction, which slows down the wear rate of the tool during cutting, and the life of the coated blade is about 1 to 3 times higher than that of the uncoated blade.