On-machine chromatic confocal measurement for micro-EDM drilling and milling

On-machine surface measurement of micro-scale components after micromachining becomes crucial to satisfy the increasing quality requirements. It implements a seamless measurement activity without interrupting manufacturing actions and hence facilitates the closed-loop quality control inline. Chromatic confocal probe sensing is a promising technique for on-machine integration thanks to its capability of assessing the surface with high accuracy and high speed. This paper presents the development of an on-machine measuring system using a chromatic confocal sensor, integrated in a micro-electrical discharge machining (micro-EDM) machine. The effects of scanning speed are qualitatively investigated in relation to outliers and quantitatively reflected through surface height parameters. In addition, the effects of surface gradient and surface contamination upon the measurement quality are studied. Two study cases, i.e. an array of micro-dimples and a micro-gear which are drilled and milled by micro-EDM, respectively, have been implemented to evaluate the developed system and to compare with off-line commercial confocal microscope. This comparative study demonstrates the system capability for on-machine areal measurement with sub-μm accuracy and reduced inspection time of 64%.