Effects of Tool Edge Preparation on Tool Life in Drilling of SAE4144M Steel

Tool edge preparation plays an important role in machining of hardened steels because the cutting edge has to withstand the large tool stresses produced during the process. Tool edge preparation has been a topic of considerable research for turning and milling. However, there are considerably less studies about tool edge preparation for drilling. This paper investigates the influence of twist drills cutting edge preparation (sharp, chamfered and honed geometry) on tool life in drilling process of SAE 4144 M quenched and tempered steel. The study involved the characterization of the cutting edge microgeometries and the analysis of the tool wear mechanisms. The results showed that sharp tools have higher surface roughness at the cutting edge and present surface defects resulting from the grinding process. These drills are more susceptible to chipping at the cutting edge leading to an unpredictable wear behavior. Tools with edge preparation are more reliable. However, manually chamfered tools present surface defects on the flank face near to the cutting edge, which affect negatively the adherence of the coating and may be sites for further chipping. Best results in terms of tool life were achieved with honed tools, which present less stress concentration on the cutting edge minimizing chipping. Moreover, honed cutting edges have better surface finish with less surface defects, resulting in a suitable tool-workpiece contact interface that decreases friction and adhesion forces during the drilling process.