Development of micro torque measurement device using strain gauge

These days, more precise machining is needed because of the integration of semiconductor and electric products. Microdrill is a tool for delicate machining such as holes of PCB (Printed Circuit Board). Bad conditions of drill such as vibration caused by eccentricity or increase of thrust force by drill's tip abrasion have bad effects on the quality of PCB circuit or induce fracture of the drill. Therefore, to improve PCB circuit quality and lengthen drill life, checking drill condition is important. Drill condition is checked by mechanical categories. Torque is the most complex parameter to measure among the mechanical categories and it is much harder to measure when the drill flute diameter is smaller than mm scale. Therefore, this research focuses on development of torque measurement device for microdrill. This research shows how to obtain torque of φ 200 µm drill by strain gauge. Drilling creates torque on the workpiece. If the workpiece is attached to a long rod, the torsional force is transferred along the rod. Therefore, torque is evaluated from the torsional strain value of the rod. We know the strain and the torque have proportional relationship in small range. Therefore if we know strain-torque proportional constant, we can measure torque by measuring only strain. From the experiment, we obtained strain-torque relation of 3.82 (γ xy ) real ≈ T the torque value of φ 200 µm drill is evaluated as 10 −4 Nm scale. This method is useful to monitor the drilling phenomenon and apply simply in industrial environments.