Machinability of Compacted Graphite Iron (CGI), a Microstructural and Mechanical Properties Comparison Approach

Paper in proceeding, 2009

Compacted Graphite Iron (CGI) has an important role in manufacturing of new generation engines. Better strength of CGI allows engines to perform at higher pressure and also to have better efficiency with lower emission rate. 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 know 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 Gray Cast Iron (GCI) materials has been studied in turning operation. 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 grey cast iron (GCI) for reference. The criteria used for comparison of machinability are tool life and cutting forces. When machining CGI, 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 GCI reference material, although the force value measured for GCI was comparatively higher than for some of the CGI materials.