Development and Modeling of a Robotic Restoration System Based on Laser Directed Energy Deposition

Abstract

Laser-based directed energy deposition (DED) technique has the potential for precise restoration of localized damage in high value components. This paper describes the indigenous development and sub-systems integration of a robotic restoration system based on laser DED. This system comprises of four modules: a robot for imparting desired outcome; 3 kW fiber laser as the energy source; powder feeder; and a quartz block head connected deposition head with co-axial powder delivery nozzle. In addition, a damage detection technique using a laser line scanner has been developed. Experimental characterization of the developed system is also presented. Laser DED involves a complex interplay of several physical phenomena, such as powder particle injection, melt pools formation, deposition spreading, and coupled metallo-thermomechanical behavior which induces residual stresses in the deposition and the substrate. In order to understand the complete process, each of these vital mechanisms needs to be studied. Computational fluid dynamics models have been developed to predict the flow and injection of powder particles via coaxial annular nozzle, melt pool spreading and deposition geometry. The major challenge in restoration via DED is the compromised service life of the restored part due to unfavorable residual stresses originating from differential thermal expansion/contraction, volume dilation and transformation plasticity. A fully coupled metallo-thermomechanical model has been presented in this paper. The residual stresses obtained from the model have been validated using residual stress measurements from X-ray diffraction and neutron diffraction techniques. Finally, process maps have been developed based on these physics-based models to obtain optimal process parameters to ensure favorable residual stresses, dilution and geometry in DED.