Machinability of Compacted Graphite Iron (CGI) and Flake Graphite Iron (FGI) with coated carbide

Compacted Graphite Iron (CGI) has an important role in manufacturing of new generation engines. Better strength of CGI, as compared to flake graphite iron (FGI), allows CGI engine to perform at higher peak pressure. This can give higher fuel efficiency and lower emission rate. However, the machinability of CGI is poor as compared to FGI. The machinability of CGI is an area that needs to be studied in a better way to cut the production cost of the engine. It is a well known fact that the as-cast engine block has varying microstructure and mechanical properties due to different cooling rates at different locations of such a geometrically complex component. This has highlighted the need for studying machinability as a function of microstructural and mechanical properties so that the machining process could be optimized. For this reason, machinability of 18 different types of CGI materials along with two FGI materials has been studied in turning operation. The criteria used for comparison of machinability were tool life and cutting forces. A model for relating tool life to the mechanical properties of CGI has been developed and the machinability of the different CGIs has also been compared with flake graphite iron (FGI). A model for resultant cutting force as a function of mechanical properties and cutting parameters has been developed. It has been seen that, while machining CGI and FGI, the tool life is found to decrease drastically with increase in hardness, ultimate tensile strength and pearlite content. The highest tool life is almost 6 times of the least tool life noticed out for the 18 different types of CGI. The best tool life given by CGI is still almost half of that for the FGI materials used for comparison, although the force value measured for FGI was comparatively higher than from the ferritic CGI materials