Effect of tool geometry on the wear of cemented carbide coated with TiAlN during drilling of compacted graphite iron

The improvement of machinability of compacted graphite iron (CGI) is a constant goal of automotive industry. The application of compacted graphite iron (CGI) in parts such as cylinder block to replace the traditional cast irons presents as advantages the higher mechanical strength and the resistance to thermal shock at the CGI. However, these characteristics represent much more problems in the manufacturing process due to the CGI poorer machinability. Metallurgical variables controlled from casting parameters have been studied, but the manufacturing aspects such as tool geometry are few explored yet. Among the machining operations drilling is the most common one in the automotive industry. This study investigated the effect of three tool geometries on the wear of cemented carbide coated with TiAlN during drilling of CGI, with eutectic composition (4.3% of equivalent carbon). The influence of the chisel edge of drills was studied. The wear of drills was monitored at five steps: set-up, 25%, 50%, 75% and at the end of the tool life monitored through the VBbmax flank tool wear on the tools cutting edge. Images from scanning electron microscope showed abrasion as a predominant wear mechanism. The results showed the importance of the drill geometry selection in order to achieve better productivity. The geometry with tip radius obtained the best results, double the life of the tool to grind into spiral point drill which is used as reference due to its application in the production of engine blocks. It was also observed that the tool geometry influences the surface roughness of holes, and these results can be related to shape of chips.