In-process height control during laser metal deposition based on structured light 3D scanning

Laser metal deposition is an additive manufacturing process capable of layer by layer construction of solid parts. An incorrect deposition distance between nozzle and substrate can result in height deviations from the ideal building path. The error can be propagated along layers, leading to an irreversible defect. Maintaining an optimal distance between the nozzle and the substrate is therefore a critical aspect. This paper introduces an off-line geometric control system for in-process measurement and build path correction. A structured light based 3D scanner measures the build height from an external, fixed position, providing more precise results than moving measuring systems. The deposition is stopped in certain stages of the process and the piece is scanned generating a three-dimensional point cloud. Processing of the collected data allows the build height determination. A control algorithm was developed to take corrective actions in accordance with the measured error. The system enables an accurate control of the generated geometry and permits the comparison with the original computer design. This approach reduces the required human supervision during the process and the occurrence of non-valid parts. The effectiveness of the method was proved through the contrast of parts built with and without control, showing a more accurate reproduction of the generated solid parts when corrections are applied. (C) 2018 The Authors. Published by Elsevier B.V.