Optimization of Accuracy and Surface Finish of Drilled Holes in 350 Mild Steel

This chapter presents analysis and optimization of machinability of Mild steel grade 350 while high speed drilling operation. Taguchi design of experiments (DoEs), analysis of variance (ANOVA) and other traditional methods were applied to optimize the input variables in order to minimise the circularity, cylindricity, diameter error and surface roughness of drilled holes. It was found that point angle was the highest contributor for the circularity, cylindricity and surface roughness of drilled holes. The circularity error was minimum at the low speed (584 rpm), low feed (0.15 mm/rev) and moderate point angle (125°). The cylindricity error of holes was minimised at the high speed (849 rpm), moderate feed (0.2 mm/rev) and moderate point angle (125°). The moderate speed, low feed and moderate point angle minimised surface roughness considerably. The interaction between speed and point angle had the maximum contribution to the diameter error of drilled holes. The diameter error was minimum at the moderate speed, low feed and moderate point angle.