Online melt pool depth estimation in laser metal deposition using a coaxial thermography system

One of the most important parameters influencing the quality of laser metal deposition (LMD) parts is the melt pool depth, which is defined as the distance from the top surface of the substrate to the deepest point of the melt pool. In this study, an online melt pool depth estimation technique is developed using a coaxial thermography system integrated into the LMD process. First, using an infrared camera and a charge-coupled device camera, the melt pool width and length as well as the layer height were measured in real time. The surface melt pool profile was then defined, and the temperature distribution within the deposited layer was calculated by solving a laser-induced heat conduction equation. Finally, the melt pool depth is estimated online. Variations in the laser power, printing speed, build temperature, and material were used in validation tests of the proposed technique, and the results were compared with microscopic inspections. The results showed that the proposed technique can accurately estimate the melt pool depth to within 2%.