Hardness is the basic characteristic of special blade material. Tool to cut from the workpiece chip, its hardness must be greater than the hardness of the workpiece material. The cutting edge hardness of cutting tools used in metal cutting is generally above 60HRC. Wear resistance is the ability of a material to resist wear. Generally speaking, the higher the hardness of the tool material, the better its wear resistance. The hardness of hard points (carbides, nitrides, etc.) in the structure is higher, the quantity is more, the particle is smaller, the distribution is more uniform, the wear resistance is better. Wear resistance is also related to the chemical composition, strength, microstructure and temperature of the friction zone. Formula can be used to express the wear resistance of materials: WR: WR= kic0.5e-0.8h1.43 where: H -- material hardness (GPa). The higher the hardness, the better the wear resistance. KIC -- fracture toughness of material (MPa·m?) . The larger the KIC, the smaller the fracture caused by stress and the better the wear resistance. E -- GPa of material. When E is very small, the microstrain caused by abrasive particles is helpful to generate lower stress and improve the wear resistance.
The profiled blade has sufficient strength and toughness
In order to make the tool under great pressure, as well as in the cutting process often occurs in the impact and vibration of the working conditions, without breaking blade and fracture, tool materials must have enough strength and toughness.
High heat resistance (thermal stability)
Heat resistance is the main index to measure the cutting performance of tool materials. It refers to the tool material in high temperature conditions to maintain a certain degree of hardness, wear resistance, strength and toughness performance.
Tool materials should also have the ability to resist oxidation at high temperature and good anti-bonding and anti-diffusion ability, that is, tool materials should have good chemical stability.
Good thermophysical properties and thermal shock resistance
The better the thermal conductivity of the tool material, the easier the cutting heat from the cutting area, which is conducive to reducing the cutting temperature.
Cutting tool in the intermittent cutting or use of cutting fluid, often by a lot of thermal impact (temperature change is violent), so the tool will produce cracks and lead to fracture. The ability of tool materials to resist thermal shock is expressed by the heat shock coefficient R, defined as R= lambda (1-) /E in form: lambda -- thermal conductivity coefficient; Sigma b -- tensile strength. -- poisson ratio; E -- elastic modulus; -- thermal expansion coefficient.
High thermal conductivity makes the heat easily dissipated and reduces the temperature gradient on the tool surface. Small thermal expansion coefficient can reduce thermal deformation; Small modulus of elasticity can reduce the amplitude of alternating stress caused by thermal deformation. It is beneficial to improve the thermal shock resistance of the material. Special-shaped blade
Cutting fluid can be used in cutting materials with good thermal shock resistance.
Good process performance
In order to facilitate the manufacture of tools, tool materials are required to have good process performance, such as forging performance, heat treatment performance, high temperature plastic deformation performance, grinding processing performance.
economy
Economy is one of the important indicators of cutting tool materials. Although the cost of a single piece of high-quality cutting tool material is very high, the cost of each part is not necessarily very high due to its long service life. Therefore, the economic effect should be considered comprehensively when choosing tool materials.
Tool material: high speed steel
High speed steel is a kind of high alloy tool steel with more alloy elements such as tungsten, molybdenum, chromium and vanadium. High speed steel has high strength and toughness, and has certain hardness and wear resistance. Suitable for all kinds of cutting tools. HSS cutters are easy to make and easy to grind into sharp cutting edges. Therefore, despite the emergence of various new cutting materials, HSS cutters still account for a large proportion in metal cutting. Can process non - ferrous metals and high - temperature alloys. Due to the above properties of high speed steel, the tools used in piston machining such as milling sprue, milling cross groove, milling expansion groove and drilling bit for oil hole are all made of high speed steel. carbide
Cemented carbide is made by powder metallurgy of refractory metal carbides (such as WC, TiC, TaC, NbC, etc.) and metal binders (such as Co, Ni, etc.). As hard alloy contains a large number of metal carbides, these carbides have high melting point, high hardness, good chemical stability, good thermal stability and other characteristics, therefore, hard alloy material hardness, wear resistance, heat resistance are very high. Commonly used cemented carbide hardness is 89 ~ 93 HRA, than the hardness of high speed steel (83 ~ 86.6 HRA) high, in 800 ~ 1000 ℃ can perform cutting in fashion. At 540 ℃, the hardness of cemented carbide is 82 ~ 87 hra, at 760 ℃, hardness remained 77 ~ 85 hra. Therefore, the cutting performance of cemented carbide is much higher than that of high-speed steel, tool durability can be improved several times to dozens of times, in the same durability, cutting speed can be improved by 4 ~ 10 times.
At present, the cemented carbide cutting tools used by our company are mainly YG (wc-tic -Co) YG6 and YGX. Hard alloys such as YT15 in class YT (wc-tic -Co) are used in piston roughing, semi-finishing and partial finishing processes.
diamond
Diamond is the material with the highest hardness and the best thermal conductivity in the known mineral materials at present, and the friction and wear amount with various metal and non-metal materials is only 1/50 ~ 1/800 of that of hard alloy, which is the most ideal material for making cutting tools. However, natural monocrystalline diamonds are only used for ultra-precision machining of jewelry and some non-ferrous metals. Although De Beers and sumitomo electric have been industrialized, they have not yet entered into a large number of applications. The cutting edge of diamond cutter is very sharp (which is very important for cutting the chip with very small section), the roughness of the blade is very small, the friction coefficient is low, it is not easy to produce chip lump when cutting, and the surface quality is high. The surface roughness can be up to Ra0.012 m and the machining accuracy can be up to IT5 level.