Investigation of effects of different moving heat source scanning patterns on thermo-mechanical behavior in direct energy deposition manufacturing

One of the metallic (additive manufacturing) AM processes is directed energy deposition (DED), which utilizes a machine tool or robotic system for motion control. A laser heat source is used to melt the powder and substrate at the same time after the powder is fed through a powder feeder. Each layer of beads is deposited side by side, and then the layers are stacked over one another. During this process, parts are subjected to intense thermal cycles before reaching room temperature. This rapid heating and cooling, and subsequent expansion and contraction, leads to the generation of tensile and compressive residual stresses within the part. The accumulation of these thermal residual stresses has a detrimental effect on the final product quality. If the residual stresses exceed the yield strength of the material, this will lead to the non-uniform plastic deformation of the substrate as well as cracks, warping, and buckling. One of the influential factors on the amount and gradients of the residual stresses is the deposition or scanning pattern. Therefore, the depositions of the beads in each layer necessitate a careful analysis of the thermal history related to the scanning pattern in order to find the best path for bead deposition. It is desirable to minimize residual stresses and distortions. The purpose of this study was to investigate the thermo-mechanical characteristics for different scanning patterns for laser cladding-based additive manufacturing processes in three types of geometries. This study considered one-way, zigzag, spiral, and raster-angled pattern scans for various component configurations. The fabrication geometries are cross-type, a rectangular surface with a hole, and U-shape. These geometries account for different types of convection-conduction heat diffusion within the parts. The thermo-mechanical responses of the parts to different scanning patterns were assessed using an unsteady finite volume method with a one-way coupling with a finite element structural solver. The scanning patterns were derived from tool path geometry imported from commercial additive manufacturing software (APlus). According to the results, a high conduction zone during the last scan causes a non-uniform cooling rate while the latest scanning area experiences tensile stress. According to the study of different scanning patterns, geometry plays a role in determining which pattern performs best. Cross-type fabrication exhibits the best mechanical response to diffe