Measurement and analysis of radial force, radial torque and surface integrity in micro-drilling of an Al7075-T6 alloy

Drill tip wandering during the entrance in the workpiece is a significant issue in micro-drilling because it directly affects hole quality, drill bit and dynamic stability. Although radial force and radial torque significantly influence drill tip wandering, measuring these characteristics has always been challenging, particularly due to their extremely low values. Therefore, the current research work aimed at measuring and analysing radial force and radial torque and correlating them with hole quality characteristics for the first time. Micro-holes are drilled on Al7075-T6 workpiece material using the pilot hole drilling technique under a wide range of spindle speeds and feeds. Radial force and radial torque exhibit increasing and decreasing behaviour with spindle speed, indicating the ‘size effect’. The oversize error shows an increasing trend with spindle speed and is closely related to radial force and radial torque. The deformation layer displays an increasing and decreasing pattern with spindle speed, clearly separating size effect regions. Furthermore, under a field-emission scanning electron microscope (FESEM), the deformation layer shows a higher possibility of cracks in the shearing region. However, due to the size effect, material accumulation with lesser or no cracks are obtained in the ploughing and transition regions. Hence, this research work clearly shows evidence of the ‘size effect’ and correlates it with radial force and radial torque for the first time. In addition, the impact of radial force and radial torque on hole oversize error and deformation layer in micro-drilling is being reported for the first time.