This paper discusses a closed-loop control concept for laser machining. A key development in the proposed control scheme is an acoustic sensor for inferring hole, kerf, and groove geometry in real time during laser machining. By sensing the acoustic signal emitted from the impingement of a gas jet on the erosion front, correlations between resonant frequency and hole, kerf or groove geometry were found. A process model was developed from applying the wave equation to the case of an elliptically-expanding or a constant-area jet. Experiments showed an inverse relationship between depth of cut and resonant frequency for grooving, cutting, and drilling cases. The paper also includes preliminary simulation results of a closed-lop control scheme for laser grooving using acoustic sensing and a PID controller.

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