Research status of vermicular graphite cast iron machining abroad

In the research and application of vermicular cast iron, Europe is in the leading position in the world. In the 1990s, vermicular cast iron was widely used in automobile engines. However, due to the difficulty in processing vermicular cast iron, the tool life was greatly shortened. After six years of research in cooperation with foundry, manufacturer and material scientists, Abele clarified the wear mechanism of vermicular cast iron. The sulfur in vermicular cast iron directly affects the formation of MNS layer, which can protect the cutting edge from abrasive wear, and proposed that the lack of MNS layer must be considered when designing and processing vermicular cast iron tools. Dawson also found in his research that the reason for the low tool life during high-speed continuous cutting of vermicular cast iron is that there is no MNS lubrication layer on the tool surface during cutting, while gray cast iron is on the contrary. By comparing the processing of gray cast iron, Gastel found that the oxidation wear and diffusion wear of the tool are roughly the same as that of gray cast iron, and the main difference in tool life is the lack of MNS lubricating layer when processing vermicular cast iron. Vamnnayyartm studied different grades of cast iron under different continuous machining conditions from the aspects of cutting temperature, cutting force, tool life, deformed chip thickness and contact length. The results show that there is no significant difference in flank temperature when machining different CGI materials with hardness from 140 to 236 HBW.

In order to solve the difficult problem of machining vermicular cast iron, Guo found that when the cutting speed is greater than 500m / min, mam (modulation assisted machining) can reduce the wear degree of CBN tool in high-speed cutting of vermicular cast iron, and the service life of CBN tool is 20 times longer than that of ordinary machining tool, Mam assisted machining seems feasible for industrial applications involving high-speed machining of vermicular cast iron. Skvareniiw is assisted by Lam (laser assisted machining). It is found that when the material removal temperature is 400 ° C, the feed rate is 0.150mm/rev and the cutting speed is 1.7m/s, The tool life is 60% longer than that under the condition of traditional feed rate of 0.1mm/rev. After machining, the material is sliced and polished, and it is found that the microstructure of CGI does not change. The economic analysis shows that Lam can save about 20% of the cost for the processing of engine cylinder liner.

By comparing the high-speed milling of gray cast iron and vermicular cast iron, Silva found that when the cutting speed reached 600m / min, the wear of the flank when milling vermicular cast iron was twice that when milling gray cast iron, and the main wear forms of the tool under this condition were flank friction wear and bonding wear. Dlamini found that when cutting vermicular cast iron at high speed, due to the rapid wear of crescent pits on the front face of the cutting tool, the cutting tool failed before reaching the pure grinding standard of the rear face.

Sander gabaldo studied the processing of vermicular cast iron with cemented carbide tools. It was found that the tool life did not decrease with the increase of cutting speed. Only when the cutting speed reached 650m / min, the tool life showed a downward trend with the increase of cutting speed.

In addition, suhaimi compared various cooling and lubrication conditions of uncoated cemented carbide tools in CGI high-speed machining. Compared with conventional cooling conditions, the combination of indirect low-temperature cooling and minimum lubrication can increase the service life of cutting tools by 26%. Varghesew carried out turning experiments with four different tools under dry cutting and micro lubrication conditions respectively. It was found that the cutting force of cermet tools was significantly reduced at low speed compared with other tools. In high-speed cutting, the cutting force increases with the increase of micro lubrication, which shows that the cutting fluid has a negative effect on the machinability of vermicular cast iron.

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