An Experimental Investigation of the Influence of Cutting-Edge Geometry on the Machinability of Compacted Graphite Iron

Background

The increasing environmental demands to reduce emissions and fuel consumption are placing continuous pressure on the automotive industry to search for a new material for engine block and other structural parts in place of Flake Graphite Iron (FGI), which is also known as Lamellar Graphite Iron (LGI) or Gray Cast Iron (GCI) . An economic way to reduce the fuel consumption and hence emission is to increase the peak pressure by using a stronger material, like CGI, in the manufacturing of engine, which can withstand the higher pressure and has all other satisfactory material properties for engine applications. This can even decrease the weight of the engine and hence the material used because of its higher strength. Mohrdieck, (2003) mentioned that in case of heavy duty truck diesel engine the peak pressure can reach up to 200 bar for maintaining an efficient combustion with lower emission. This high pressure will surely increase the forces on all components in the engine. Thus, the engine material must have higher strength to withstand the increased forces in addition to all the other engineering and environmental requirements. Compacted graphite iron (CGI) has around 75 percent higher tensile strength, 45 percent higher stiffness than FGI, mentioned by Dawson, S. (2008). The wear resistance of CGI is approximately double of that of FGI. Although, the thermal conductivity and damping capacity of the CGI are comparatively less than that of the FGI, these properties are still good enough to use the material in engine components (Dawson et al., 1998). Nayyar et al. (2009) have showed that the mechanical properties of CGI material can be controlled by appropriate choice of chemical composition and cooling rate. Later, Nayyar et al., (2012) have seen almost 8 times difference of tool life between pearlitic CGI and ferritic CGI, at a cutting speed of 300 m/min with coated carbides. CGI was first commercially used to manufacture the disk brakes of high speed rail trains in 1999 (Buchholz, 2003). Today automobile companies are investigating the possibilities of using CGI to manufacture future truck engines. But these companies are facing a true problem in using CGI because of the potentially high cost involvement in the machining. Tool life is considerably lower for machining CGI as compared to FGI. It was seen by Nayyar et al. (2009) that the tool life, when machining pearlitic CGI, could decrease by 15 times than when machining pearlitic FGI in continuous operation at a cutting speed of 300 m/min with coated carbides tools.