Controlling Waviness in Additive Manufacturing of Thin Walls by Laser-Directed Energy Deposition Process

Abstract

Laser-directed energy deposition is a powerful and promising metal-based additive manufacturing technique. This is becoming a prominent approach for the freeform production of thin-wall structures. However, its diffusion into the industry is still limited due to the challenges in controlling the geometry. One of the main causes for this is heat accumulation during multi-layer deposition. Therefore, the present study focuses on the real-time monitoring of molten pool thermal cycles using an IR pyrometer for a deep understanding of the spatiotemporal variations of it with layer number. From the experimental observations, the monitored molten pool cycles were found to clearly identify/indicate the heat accumulation with layer number. Based on this, the variation in laser scanning speed and interpass delay was systematically introduced during the deposition process to control the heat accumulation, which is once again monitored through the recorded thermal cycles. Further, a method to mitigate the existing waviness through adjusting the relative position between the powder focusing point, peak, and valley was demonstrated. Waviness was found to mitigate by carrying out the depositions keeping the powder focusing point aligned with the valleys of the undulated surface.