On reliable measurement of micro drilling forces and identification of different phases

• Reliable measurement of thrust and torque in micro-drilling.
• Use of separate force dynamometer and torque sensor.
• Application of cross-correlation to thrust and torque signals.
• Synchronization of thrust and torque signals in time domain.
• Unique identification different phases in micro-drilling.

Mechanical micro-drilling process is often used in the manufacture of miniature components and molds. Frequent breakage of micro-drill is a major problem necessitating a thorough investigation into the process. One of the important responses measured during micro-drilling process is variation of thrust force and torque. Since the values of thrust force and torque are very low in micro-drilling, reliable measurements have to be carried out using high-resolution dynamometer. In the present work, micro-drilling is carried out using 0.5 mm diameter drill on Al 6061-T6 sheet of 3 mm thickness. The measurement results obtained from multi-component dynamometer are discussed first. Subsequently, a torque sensor mounted on the multi-component dynamometer is used to measure the torque, while the thrust force is acquired from latter. Since it is practically impossible to start acquiring the signals at a given time instant, the signals have to be synchronized in time domain using a novel signal processing technique. Different phases in micro-drilling, namely entry, full penetration and dwell are identified uniquely.