Multi-faceted monitoring of powder flow rate variability in directed energy deposition [preprint]

Powder flow rate is a key parameter in Directed Energy Deposition (DED) processes. At standard deposition rates, if powder flow rate drops for 1 second, 30 mm of melt track is affected. With such fast deposition speeds, even a very low-magnitude variation in the powder flow rate can affect build quality. In this work we quantify the powder flow rate stability for different types of 316L steel powders using a combination of weight measurement, flow imaging, build data and coaxial melt pool imaging. The flow rate variation was directly measured using both weight and side-on imaging. This was correlated with build height, showing that flow rate variation can affect build quality. Finally, the same behavior was observed in coaxial melt pool imaging, which has implications when using melt pool imaging for closed-loop control of build quality.