Illumination and image processing for real-time control of directed energy deposition additive manufacturing

This paper describes the optical setup and image processing required to estimate melt-pool width and build height for real-time control of melt-pool geometry in directed energy deposition additive manufacturing. To overcome optical interference from plasma emissions and laser interactions, the melt-zone is imaged using laser illumination. A single camera, fixed to the processing laser, views the laser interaction zone and provides images for estimating melt-zone width and build height. Using a bandpass filter and a single aspheric lens, the camera system provides sufficient magnification and depth of field to achieve a 1-mil (25.4 µm) resolution. Maintaining melt-zone geometry within desired tolerances requires an image acquisition and processing rate on the order of 100 frames per second. This bandwidth is achieved by a Camera Link camera and field-programmable gate array that implements algorithms for estimating melt-pool width and build height. The design and experimental verification of the camera, illumination, and processing systems are discussed.