Optimization of hole quality produced by novel drill geometries using the Taguchi S/N approach

Reportedly, the drill geometry influences the drilling operation. In fact, the performance of the drill bit is strongly associated with productivity, thus with economy of production. Moreover, the typical performance indicators, i.e., deviation from diameter, cylindricity, perpendicularity, and concentricity, are altered by drill geometry. This fact stresses the need for a novel design of drills with further optimization of performance indicators of hole quality. In that perspective, herein, new drill geometries were designed and fabricated. Afterward, those drills were employed to create holes on AISI 4140 steel, and their performances were investigated and optimized to suggest cutting parameters of best interest. For performance tests, four different drill geometries, four different cutting speeds (90, 100, 110, 120 m/min), and four different feeds (0.15, 0.20, 0.25, 0.30 mm/rev) were practiced. To measure the performance of the drills, the quality of the drilled holes was studied in terms of the deviation from diameter, cylindricity, perpendicularity, and concentricity. During the experiment, geometry 3 that was developed as the original drill geometry exhibited poor chip evacuation. As such, geometry 4 was developed by considering these negativities, and it was found to demonstrate superior performance compared to other geometries in terms of hole quality. Furthermore, ANOVA revealed that the drill bit flute geometry is the most influential factor. Lastly, the Taguchi S/N approach disclosed that drilling with geometry 4 at the cutting speed of 90 m/min and feed rate of 0.15 mm/rev produced optimum machining performance.