Approach for advanced working distance monitoring and control capability in laser metal deposition processing for additive manufacturing

Abstract

The working distance is an essential parameter of the laser metal deposition (LMD) process which has to be kept at a constant level for successful applications. Especially when applying LMD in additive manufacturing (AM) to generate large-scale components, distance control is crucial as these parts can take multiple hours to complete. If over time the working distance runs out of the processing limits, the process efficiency will decrease, and this can lead to a process break down destroying the component build. The development approach is to integrate an enhanced distance measurement system based on optical coherence tomography (OCT) into a commercial LMD powder processing head. By deflecting an elliptic measuring track around the processing area, the OCT system can detect the working distance as well as topological information (2D + d) compared to a standard 1D distance measurement (1D + d). By continuously collecting data when moving the processing head, a 3D-scan of the surface can be recorded online. This technology is beneficial for AM as well as LMD repair applications as the system allows the scanning of unknown surfaces prior to LMD processing. In a next development step, the position data of the laser-cell (robot or CNC-Machine) is linked to the 2D + d data gaining full 3D information with high spatial and temporal resolution in real-time. Based on these monitoring capabilities, a closed loop control can be set up by implementing stabilization methods. By adapting LMD process parameters like the powder feed rate or the processing speed, a work distance and LMD track height control can be achieved.