Research on wear of PCBN tool cutting different cast iron materials

Polycrystalline cubic boron nitride (PCBN) superhard material tool has high hardness, good wear resistance and chemical stability, Its application in the field of automobile manufacturing is becoming more and more extensive. This paper summarizes and analyzes the research status of domestic and foreign scholars using PCBN superhard material tools to process gray cast iron, ductile iron and vermicular graphite iron. Mainly from tool material, process parameters, workpiece material, The wear mechanism of PCBN superhard material tool when cutting three kinds of cast iron is analyzed from the aspects of cutting environment and processing method. Finally, the wear situation of the tool when cutting different kinds of cast iron materials is summarized.

1. Common cast iron classification

At present, the commonly used cast irons in the field of automobile engine manufacturing mainly include gray cast iron, ductile iron and vermicular graphite iron. The microstructure, properties and application characteristics are shown in Table 1. The difference in graphite shape, matrix composition and content of various chemical elements in various cast iron materials determines their different uses and also affects the processing performance of castings made of this material.

Table 1 Properties and uses of various cast iron materials

2. Wear of PCBN tool cutting cast iron materials

PCBN tools are suitable for high-speed dry cutting of gray cast iron. The main factors affecting the wear of PCBN tools are the CBN content of the tool, the type of binder, the cutting parameters and geometric parameters of the tool, and the workpiece material.

Machining gray cast iron and ductile iron, studies have shown that high content (>90%) PCBN tools wear less than low content (<75%) PCBN tools when machining the same area of ​​gray cast iron, this is because CBN The tool with high content has higher hardness, better wear resistance and longer life; it is found that the cutting speed has a great influence on the wear mechanism of the tool. When it is greater than 150m/min, diffusion wear and chemical wear are dominant. The vermicular graphite cast iron is a difficult-to-machine material. The main reason is that the temperature of the tool tip when cutting vermicular graphite iron is higher than that of gray cast iron, and the loss of sulfur element in the production process of vermicular graphite iron is serious, so it cannot be protected when machining gray cast iron. The MnS layer of the PCBN tool causes severe chemical wear during cutting and reduces tool life. In addition, the high Ti content in vermicular graphite cast iron is also the cause of serious tool wear. The high hardness of Ti or its compounds in the workpiece will aggravate the abrasive wear of the tool.

Although the tool wear mechanisms when cutting different cast iron materials are roughly the same, such as adhesive wear, diffusion wear and chemical wear, the wear conditions of the tools are quite different. When the PCBN tool cuts gray cast iron with high ferrite content, crescent craters are easily formed on the rake face, and many thermal stress cracks appear at the cutting edge; when cutting ductile iron, the tool is prone to occur under the action of impact force. When cutting vermicular graphite cast iron, due to the influence of Ti element in cast iron and the difficulty of forming MnS lubricating film, the tool wear is more serious, and chemical wear such as oxidation and diffusion wear is the most serious. host. At present, PCBN cutting of vermicular graphite cast iron is not ideal, and in-depth research on tool materials, cutting process and wear mechanism is required.