The development and application of cutting technology is determined by the advancement of machine tool technology, and its tool material development plays a decisive role. Studies have shown that at high speed cutting, as the cutting speed increases, the cutting force decreases, and the cutting temperature rises very high. After reaching a certain value, the rise gradually slows down. The main cause of tool damage is the wear and tear of mechanical friction, bonding, chemical wear, chipping, crushing and plastic deformation under the cutting force cutting temperature. Therefore, the high-speed cutting tool material mainly requires mechanical properties at high temperature, thermal physical properties, and resistance. Bonding properties, chemical stability (oxidation, diffusibility, solubility, etc.) resistance to thermal shock resistance and coating crack resistance.
Based on this requirement, in the past 20 years, a number of materials suitable for high-speed cutting tools have been developed, and various workpiece materials can be machined under different cutting conditions.
Although we always hope to obtain high hardness to ensure the wear resistance of the tool and high toughness to prevent the chip from breaking, the current technological development has not found such a superior performance tool material, and the fish can not have both. Therefore, we will actually select a more suitable tool material according to the needs: the roughness of the tool material is prioritized during roughing, and the hardness of the tool material is prioritized during finishing. Of course, people are also looking forward to processing at ultra-high cutting speeds for better results. The following is a brief introduction to common workpiece materials and tool related conditions.
First, aluminum alloy:
1, free cutting aluminum alloy
The material is widely used in the aerospace industry. The applicable knife has K10, K20 and PCD, the cutting speed is 2000~4000m/min, the feed rate is 3~12m/min, and the tool rake angle is 12°~18°. The angle is from 10° to 18° and the edge angle is up to 25°.
2, cast aluminum alloy
Casting aluminum alloys vary according to their Si content. K10 and Si3N4 tools can be used for cast aluminum alloys with Si content less than 12%. When Si content is greater than 12%, PKD (synthetic diamond) and PCD can be used. (Polycrystalline diamond) and CVD diamond coated tools. For silicon-on-silicon alloys with a Si content of 16% to 18%, PCD or CVD diamond coated tools are preferred, with a cutting speed of 1100 m/min and a feed rate of 0.125 mm/r.
Second, cast iron:
For castings, when the cutting speed is greater than 350m/min, it is called high-speed machining, and the cutting speed has a great influence on the selection of the tool. When the cutting speed is lower than 750m/min, coated hard alloy and cermet can be used; when cutting speed is 510~2000m/min, Si3N4 ceramic cutter can be used; when cutting speed is 2000~4500m/min, CBN can be used. Tool.
The metallographic structure of the casting has a certain influence on the selection of high-speed cutting tools. When the cutting speed is more than 500m/min, the castings with pearlite can use CBN or Si3N4. When ferrite is mainly used, due to diffusion wear The reason for the serious wear of the tool is that CBN should not be used, but ceramic tools should be used. If the binder phase is metal Co, the grain size is 3 μm on average, and the BZN6000 with CBN content greater than 90% to 95% is suitable for processing gray cast iron with high ferrite content at V=700 m/min. The binder phase is ceramic (AlN+AlB2), Amborite insert with an average grain size of 10μm and a CBN content of 90%-95%. When processing high gray pearlite content, the cutting speed is less than 1100m/min. As the speed increases, the tool life also increases.
Ordinary steel
The cutting speed has a great influence on the surface quality of steel. According to the research of PTW Institute of Darmstadt University, the best cutting speed is 500-800m/min.
At present, coated hard alloys, cermets, non-cermets, and CBN tools can be used as tool materials for high-speed cutting of steel parts. Among them, the coated cemented carbide can be used as a cutting fluid. The wear resistance of TiN coated tools produced by PVD coating method is better than that of coated tools produced by CVD coating method, because the former can well maintain the shape of the cutting edge and achieve high precision and surface quality of the machined parts. .
Cermet tools account for 30% of the Japanese tool market. TiC-Ni-Mo-based cermets have good chemical stability, but have poor flexural strength and thermal conductivity, and are suitable for small feed rates of 400-800 m/min. Finishing with small depth of cut; Carboly uses TiCN as the matrix, and the cermet with less molybdenum and more tungsten in the bond combines strength and wear resistance. Kyocera uses TiN to increase the toughness of the cermet, and its processed steel or Cast iron can be cut to a depth of 2 to 3 mm. CBN can be used to mill bearing steel or hardened steel with little or no ferritic structure.
Third, high hardness steel:
High-speed cutting tools for high-hardness steel (HRC40-70) are available in cermet, ceramic, TiC coated carbide, PCBN, etc.
The cermet can be made of TiN-added cermet with basic composition of TiC. Its hardness and fracture toughness are roughly equivalent to those of cemented carbide, and the thermal conductivity is less than 1/10 of that of cemented carbide, and it has excellent oxidation resistance and adhesion resistance. And wear resistance. In addition, it has good mechanical properties at high temperatures and low affinity with steel, and is suitable for SKD processing of medium and high speed (around 200m/min). Cermets are especially suitable for grooving.
The ceramic tool can cut the workpiece material with hardness up to HRC63, such as quenching the workpiece and then cutting it to achieve “cutting and grindingâ€. When the quenching hardness is 45 steel with HRC 48-58, the cutting speed can be 150-180 m/min, the feed rate is 0.3-0.4 min/r, and the cutting depth can be 2~4 mm. Al2O3-TiC ceramic tools with a particle size of 1μm and a TiC content of 20% to 30% can be used to process high-hardness steels with high anti-flaking properties at a cutting speed of about 100m/min.
When the cutting speed is higher than 1000m/min, PCBN is the best tool material, and the PCBN tool with CBN content greater than 90% is suitable for processing hardened tool steel (such as H13 tool steel of HRC55).
Fourth, high temperature nickel base alloy:
Inconel718 nickel-based alloy is a typical difficult-to-machine material with high high-temperature strength, dynamic shear strength, small thermal diffusivity, and work hardening during cutting, which will result in high temperature and wear speed in the cutting area of ​​the tool. When cutting the alloy at high speed, ceramic and CBN tools are mainly used.
Silicon carbide whisker reinforced alumina ceramics can achieve long tool life at 100-300 m/min. When the cutting speed is higher than 500 m/min, the TiC alumina ceramic tool is less worn, and at 100-300 m/min. The gap wear is large. Silicon nitride ceramics (Si3N4) can also be used for the processing of Inconel718 alloys.
Canadian scholar MAElbestawi believes that the optimal cutting conditions for SiC whisker-reinforced ceramic processing Inconel718 are: cutting speed 700m/min, depth of cut 1~2mm, feed rate 0.1-0.18mm/z.
Sialon ceramics have high toughness and are suitable for cutting in solution treated Inconel 718 (HRC45) alloy. Al2O3-SiC whisker reinforced ceramic is suitable for processing nickel base alloy with low hardness.
5. Titanium alloy: (Ti6Al6V2Sn)
Titanium alloy has high strength and impact toughness, and its hardness is slightly lower than that of Inconel 718. However, its work hardening is very serious, so high temperature and severe tool wear occur during cutting. Japanese scholar T. Kitagawa et al. have obtained a large number of experiments and found that the high-speed milling of titanium alloy with a carbide 1010 diameter double-edge spiral milling cutter (30° helix angle) can achieve satisfactory tool life and cutting speed up to 628m. /min, the feed rate per tooth can be 0.06~0.12mm/z, and the cutting speed of continuous high-speed turning titanium alloy should not exceed 200m/min.
Sixth, composite materials:
Advanced composite materials for aerospace applications (such as Kevlar and graphite composites). Previously, carbides and PCDs were used. The cutting speed of cemented carbide was limited, while PCD inserts and carbide or high speed steel knives were used at temperatures above 900 °C. The body weld is melted, and a high-speed cutting of about 300 m/min can be achieved with a ceramic cutter.
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Label: How to choose high speed cutting tool materials
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