Research status of machining of mite graphite cast iron in China

In the 1960s, China began to study vermicular cast iron, but the production and processing of vermicular cast iron is much more difficult than gray cast iron and nodular cast iron. Many universities and scientific research institutes have carried out a large number of cutting experiments on vermicular cast iron, including the research on the cutting tools, surface integrity, chips and burrs used in machining. In view of the difficult machinability of vermicular cast iron, there are many studies on the tool wear in the process of machining vermicular cast iron.

At present, the tools used in processing vermicular cast iron are coated cemented carbide tools, ceramic tools and PCBN tools, and uncoated cemented carbide tools are rarely used. In production practice, coated cemented carbide tools are mostly used to process vermicular cast iron at a small cutting speed under dry cutting conditions.

Zhang Yuling selected coated cemented carbide and uncoated cemented carbide tools to carry out the milling test of vermicular cast iron. It is found that there is a certain degree of hard spot wear on the back surface of uncoated tools, and coated tools can obtain better surface quality than uncoated tools. Niu Jiahui selected coated cemented carbide tools and silicon nitride ceramic tools to carry out the milling experiment of vermicular graphite cast iron. It is found that the milling force of ceramic tools is greater than that of coated cemented carbide tools under the same conditions. In the study of Yang Jianfeng 151 cutting vermicular graphite cast iron rut450, it is found that the most suitable tool is coated cemented carbide tool. This result is consistent with the tool matching model established by Niu Jiahui for vermicular graphite cast iron, and the main wear mechanisms of the four tools are abrasive wear and adhesion wear. Similar conclusions have been reached in the study of Ni Gaoming M. Liu Hongtao and Li Panlai% both carried out experiments on machining vermicular cast iron with PCBN tool. It was found that high cutting efficiency and tool wear resistance could be obtained when machining vermicular cast iron with PCBN tool, and crescent depression wear was common on the rake face.

In the research of Niu Jiahui m, it is found that the surface machined by coated cemented carbide tools can reach RA < 0.35gm and ceramic tools can reach RA < 0.3gm. No matter which tool is selected, smaller surface roughness can be obtained in the appropriate cutting speed range. In Zhang Yuling’s research, it is found that too low cutting speed will promote vibration, and too high cutting speed will cause edge collapse. In Yang Jianfeng’s research, it is found that coated cemented carbide tools and coated ceramic tools can obtain better machining quality, and the surface roughness of coated cemented carbide tools is the best. Suruil studied the effects of different workpiece material removal on the machined surface roughness at normal cutting speed and high speed. It was found that with the increase of workpiece removal, the surface roughness Ra and RZ at normal cutting speed increased, and decreased first and then increased at high speed.

The research of various scholars shows a certain degree of similarity. Coated cemented carbide tools are an ideal choice for processing vermicular cast iron at present. In addition, Lu Juan and others compared the SVM model optimized by differential evolution algorithm (de-svm) and the SVM model optimized by common optimization algorithms (ant colony algorithm and genetic algorithm). When predicting the accuracy of machined surface roughness of vermicular cast iron, they found that de-svm was better than the SVM model optimized by common optimization algorithms. Lu Juan also showed in subsequent publications that the prediction performance of GPR without cross validation is similar to that of GPR with cross validation, which is better than back propagation neural network and SVM.

Surui studied the vermicular cast iron chips obtained by coated cemented carbide tools at various cutting speeds and feed rates. The chips are serrated as a whole, but with the increase of cutting speed, the cutting shoulder changes from serrated to needle. Continuous cutting cannot be obtained at all cutting speeds, and no adiabatic shear zone can be found on the serrated chips, It is similar to Li Panlai’s conclusion in the study of vermicular graphite cast iron chip. In Xiong Feifei’s research, with the increase of milling speed, the formation mode of chip changes from plastic deformation to brittle fracture. In the shoulder grinding of vermicular cast iron, Zhang Yuling found that the material stratification phenomenon is serious and the chip deformation is large in the cutting process at low speed. Under this condition, the cutting force fluctuates greatly, which is easy to cause cutting vibration and poor machining surface quality. Therefore, higher cutting speed should be adopted as far as possible.

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