A Study on the Effect of Deposition Strategies on the Resulting Residual Stress During Laser Powder Directed Energy Deposition

In the present study, one of the key influencing parameters of the directed energy deposition (DED), i.e. the deposition strategy, is investigated to determine its influence on the residual stress (RS). Five deposition strategies, viz. linear raster, spiral out, spiral in, radial raster and fractal, are deposited via laser powder (LP) DED, and in situ melt pool temperatures are recorded via infra-red (IR) pyrometer. The thermal histories at specified measurement points obtained via computational fluid dynamics (CFD) simulations are validated via experimentally measured RS. The on-bead RS is measured via the non-destructive X-ray diffraction (XRD) technique. The radial raster and the spiral out strategies exhibited the RS of 190.3 MPa (Minimum) and 458.6 MPa (Maximum), respectively. Additionally, the quantitative evaluation of the geometrical attributes, viz. ‘travel length’ and the ‘number of turns’ that affect RS, is performed. The ‘number of turns’ is the dominant factor affecting the RS.