Monitoring concept for powder flow monitoring in Laser-Directed Energy Deposition (L-DED) process based on flexible piezoelectric sensors

Background: The quality of powder-blown Laser-Directed Energy Deposition (L-DED) is mainly governed by the energy density per unit of mass employed to melt the material. In most of the previous works, the focus in process monitoring and control was on the control of energy input, by controlling the properties of the melt pool. However, the powder mass input is as important to monitor as the energy input, in order to preserve the equilibrium of the process. Methods: In this paper, the authors present the first test results of the Pyzoflex® sensor for powder flow monitoring in L-DED using real powder feeding system in the robot-based laser-processing cell. The sensor was tested against the powder projected from the powder feeder under typical flow regimes and the real-time measurements were taken using a specifically designed software tool. Results: The graphical representation of the registered sensor signals are clearly correlated with the powder flow values set at the powder feeder, which demonstrates that the piezoelectric sensors can detect the powder flow with elevated precision in real time. Conclusions: The first laboratory tests of flexible printed piezoelectric sensors demonstrate that they are fast and precise in the powder flow measurement, but that more effort must be invested in the robustness of the measurement setup as well as in clearing and stabilization of the registered signal.