Numerical evaluation of the cryogenic cooling effect on compacted graphite iron during end-milling

Compacted graphite iron (CGI) is a metal that exhibits remarkable mechanical properties based on the adhesion of graphite and iron particles. CGI has attracted considerable attention from the automobile industry and has been used as a substitute for gray iron. However, CGI is hard to machine because of high strength and toughness. In this study, a cryogenic machining process was applied to CGI, and numerical studies were performed. Cryogenic machining uses liquid nitrogen (LN2) as a coolant, as this improves machinability. In the numerical study, cutting force and temperature were simulated, and machining characteristics were analyzed according to the cutting condition during cryogenic end-milling. The cutting force was predicted using a model of material plastic behavior, and the tool geometry and machining conditions were the input parameters. The contact mechanism between LN2 and the work material was studied, and the cutting temperature was simulated according to the rotation angle of the cutting tool. The numerical modeling was experimentally validated. The simulation and experimental machining data were in good agreement; the maximum and minimum errors were 31.5% and 2.6% for the cutting force and 17.6% and 10.3% for the temperature, respectively. The effects of cryogenic cooling were further studied experimentally. The sprayed LN2 increased the cutting force and decreased the temperature and tool surface friction. The friction decreased slightly with the insignificant influence on cutting force.