Laser beam joint welding of complex powder bed based additive manufactured components
Final Report Abstract
The aim of the project is to investigate the ability of laser beam welding to join metallic additive manufactured parts using PBF-LB/M technology to other identical AM parts and to wrought parts of the same material. Despite the apparent simplicity of the idea, very little research has been devoted to studying the laser welding of PBF-LB/M parts and the influence of factors on the joining process. Two materials have been included in this research: the nickel-based precipitation hardened alloy Inconel 718 and the austenitic stainless steel AISI 316L. The study focuses on butt-welded joints without using any filler. The part geometry is predetermined by the proposal. The specimens comprise plates and sheets measuring 80.0 mm x 25.0 mm with thicknesses of 7.0 mm and 2.0 mm, respectively. Although not originally outlined in the proposal, the significance of heat treatments as an intermediate stage after additively manufacturing the parts and before welding is considered. Thermal treatment is essential to dissolve residual stresses induced during the build-up process, before separating the parts from the build plate and proceeding with further manufacturing steps. Stress-relieving heat treatments mostly but not entirely eliminate the typical columnar grain microstructure in the as-built state. The existence of inherent AM imperfections, like localized lack-of-fusion and porosity, does not aggravate welding imperfections such as liquation cracking. However, these flaws, when combined, detract from the mechanical performance of the joints. Furthermore, while there are no differences in welded geometry among identical pairs of samples welded in different directions, two welded samples have varying mechanical properties, such as tensile performance and hardness. It has been observed that differences in build direction between 0° and 90°, i.e. when layers are oriented parallel or perpendicular to the seam, are irrelevant. When oriented diagonally at 45°, the ultimate tensile strength and hardness of these materials decrease. PBF-LB/M parts made from these materials can be welded with a continuous wave (cw) laser. Nonetheless, recommended stress-relieving heat treatment temperatures and times for Inconel 718 do not bring the material to its optimal weldable microstructural condition, as liquation cracking seems to worsen. Welding lattice structures with a laser is challenging due to the presence of cavities and filigrees nearby. These voids have a negative impact on the dissipation of weld heat input, causing distortion and solidification cracking. While this is not an issue for thick plates, it does become problematic for sheets, leading to asymmetry in the seam when welding a wrought part to a thin lattice structure due to significant hindrance in heat dissipation rates on the PBF-LB/M side.
Publications
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Laser welding of L-PBF AM components out of Inconel 718. Procedia CIRP, 111, 92-96.
Brunner-Schwer, Christian; Simón-Muzás, Juan; Biegler, Max; Hilgenberg, Kai & Rethmeier, Michael
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Mitigation of liquation cracking in laser welding of pairs of L-PBF processed and wrought parts of Inconel 718. IIW 2022 International Conference on Welding and Joining, Tokyo, Japan
Simón-Muzás, J.; Brunner-Schwer, C.; Rethmeier, M. & Hilgenberg, K.
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Mechanical properties of laser welded joints of wrought and heat-treated PBF-LB/M Inconel 718 parts depending on build direction. Lasers in Manufacturing Conference LiM 2023, Munich, Germany
Simón-Muzás, J.; Brunner-Schwer, C.; Hilgenberg, K. & Rethmeier, M.
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Weldability of PBF-LB/M Inconel 718 lattice structures by laser beam. IIW 2023 International Conference on Welding and Joining, Singapore
Simón-Muzás, J.; Brunner-Schwer, C.; Hilgenberg, K. & Rethmeier, M.
