Regulation strategy for Directed Energy Deposition-Laser Powder process based on working distance modulation: Modelling and application to thin wall configurations

Abstract

Additive manufacturing introduces a new paradigm for the manufacture of metal parts. Many parameters are involved in the Directed Energy Deposition-Laser Powder (DED-LP) process. However, two related parameters, working distance and z-increment, remain largely unstudied despite having a major role in the part final geometry. In order to better understand the evolution of these parameters during the multi-layer deposition, a semi-analytical model is developed to evaluate the final height of the part with a moderate calculation time. The powder spray is modelled and calibrated using high-speed imaging. The first part of the experimental campaign consists in the deposition of 12 single-bead walls with an identical number of layers, but varying manufacturing configurations. The final heights of these walls range from 2.96 mm to 5.79 mm depending on the parameters values. The modelled and experimental results are reasonably matched except for an initial working distance of 2.5 mm where the carrier gas is unstable. For the second part of the experiment, an instrumented thin wall is manufactured while clamped only at one end in order to obtain a nozzle-to-workpiece distance variation over time. The last layer of this wall is almost horizontal thanks to a self-regulation phenomenon in accordance with the semi-analytical model. These two experiments and the model show that the DED-LP process exhibits either a self-regulating or diverging regime function of the manufacturing configuration. These phenomena are responsible for the non-uniformity of the layer heights. The working distance and the z-increment are parameters that allow to optimise the manufacturing process by increasing the powder capture efficiency leading to a reduction in the number of deposited layers and manufacturing time.