On-Machine Optical System for Accurate Workpiece Hole Centering in Microdrilling

This study presents an on-machine optical noncontact procedure for centering cylindrical workpieces before microdrilling. The method was developed to replace touch-probe centering when drilling 0.20 mm and 0.35 mm blind holes in 0.5 mm diameter pure magnesium wires, for which mechanical probing produced local surface deformation and alignment errors. The optical setup combines a CMOS camera, a telecentric lens, and image processing to estimate the center of the wire cross section and align it with the machine coordinate system after a camera-to-spindle offset determination. In this work, the measurand is the 2D eccentricity at the inspected plane, defined as the distance between the center of the hole profile and the center of the external wire profile. Compared with touch-probe centering, the optical procedure yielded lower mean eccentricity and lower dispersion in the drilled specimens. For the data reported in the paper, the mean eccentricity decreased from about 14 μm to about 8 μm, while the standard deviation decreased from about 6 μm to about 3 μm. The proposed approach therefore provides a practical noncontact alternative for centering miniaturized ductile components in a micromachining environment. The present study is limited to planar eccentricity at the inspected section, which is an important aspect for the final accuracy of the workpiece, and does not address full 3D hole-to-wire coaxiality that strongly depends on the drilling process itself.