3D Printing with WAAM to Form and Stiffen Lightweight Steel Panels for Freeform Façades (2024-09)¶

A growing trend in architecture that has impacted building technology, and the architectural landscape is the use of freeform metal panels in façades. However, these cladding panels are mostly handmade, costly, and require high thickness due to structural requirements [1]. To date, architects and engineers are now challenged to integrate aesthetics, strength, sustainability, and circularity into building processes. To overcome these challenges additive manufacture and robotic fabrication can improve sustainability and reduce manual labor. Wire Arc Additive Manufacturing (WAAM) is layer-based, material and process specific, metal 3D printing that is attracting attention in the construction industry due to its cost-effectiveness and efficiency [2]. WAAM can produce single components and rein-forced parts reducing material waste and manufacturing time, providing design flexibility and productivity advantages [3]. Although a limited number of projects have addressed the reinforcement of metal plates [4][5][6], there is still a gap in research on lightweight free form steel panels for the Construction Industry, either because the uniqueness of the scanning process to capture and reconstruct the geometry of the metal substrate; the support systems needed across the whole manufacture process or the deformation that thin plates experience in welding. A novel workflow that combines the deformation induced by WAAM and the effect of an elastically pre-bending plate over curved frames is here presented, improving the performance of existing materials and traditional structural elements used in the construction industry. The laboratory setup includes a Comau 6-axis Robotic Arm NM 16-3.1, a Fronius CMT welding device, 0.8 mm steel wire, C18 shielding gas (82%Ar, 18%CO2), and specific welding process and parameters [7]. The computational workflow was based on Grasshopper, Open CV, depth cameras and 3D scanners to build a digital model of the lab setup. This model provided the extraction of spatial coordinates and features of the plates, defining the position, direction and layer height of the welded lines and producing robot motion code. Generating a motion path for applying WAAM reinforcement to a steel plate involves a precise reconstruction of the target non-planar geometry. Given the challenges related to steel's reflectivity, two methods were employed to capture and reconstruct the geometry quickly and accurately. Initially, a depth camera Intel RealSense D405 was used over a white-coated surface of the steel plate to read the coordinates of points digitally projected onto it. An OpenCV-based script was then used to extract a grid of three-dimensional coordinates, enabling surface re-construction and digital generation of the printing path for the robotic system. Subsequently, during the welding process, a 3D Revopoint Range scanner captured the surface in greater detail. This approach allowed for the monitoring of deformations in the steel plate after each welding layer interpass. Thus, the welding path could be adjusted based on this detailed data to maintain the optimal distance between the welding gun and the metal surface throughout the process. An initial experiment was carried out on a series of 1000x200x1 mm steel strips welded with a longitudinal centerline, with a different number of layers (1 to 10 x 0.95mm) using a flat support over a welding table or a 5mts radius curved ribs as a support frame. The result showed that all the deformed strips followed a curved fashion ranged from 1 to 4 mt radius in the direction of the welded side for more than 2 layers and on a non-stable state for 1 and 2 layers showing a bending behavior in both sides. The next step was based on a combination of welded lines (distributed transversally every 150mm over plates of 940 x 500 x 1 mm) and a longitudinally elastically pre-bending deformation applied through the use of a concave or convex frame of 5 mts radius with mechanical fasteners every 10 to 15 cm and on the short sides with 30 mm flanges folded at 90° as a self-reinforcement of the short edges to avoid deformation. The result shows that a double curved plate is possible to fabricate using the deformation inherent to the welding process with WAAM using transversal lines of reinforcement (2 and 6 layer height) plus a mechanical pre-bending deformation applied to the long sides of the plate with a concave and convex curve. Here the behavior of the long side keeps the shape applied with the pre-bending process. In terms of structural behavior, a FEM analysis using Karamba3D shows clear differences between three steel plates under the same applied loads, zero degrees of freedom (DOF) and deformation conditions. The reinforced plate C with 6 layers of welding (1 x 6 mm), with a thickness of 0.1 cm and a mass of 3.91 kg, stands out as the most efficient option compared to plates A and B. In terms of mass, plate C represents only 17.65% of the mass of plate A, and 85% of the mass of plate B. In addition, its thickness of 16.67% compared to plate A, and 81.97% compared to plate B makes it an optimal choice in terms of material used. In summary, Plate C achieves the same deformation with less material, making it highly efficient in terms of both material and CO2 emissions.