Design, fabrication and mechanical characterization studies on Wire and Arc Additively Manufactured (WAAM) diagrid elements

The design approach changed in the last decades with the innovation offered by software for Computer-Aided Design (CAD), three-dimensional computer modelling and digital fabrication methods enabling new forms. The development in digital fabrication techniques led to the application of automatic processes in the structural engineering sector through Additive Manufacturing (AM) based technologies. It offers numerous benefits over conventional manufacturing methods, such as design of more complex and optimized components due to greater freedoms in shape and geometry, therefore bringing to a reduced material usage and shortened build times. The focus of this research is on the metal additive manufacturing methods, in particular, the adopted technique is the Wire-and-Arc Additive Manufacturing (WAAM), which best suits the possibility to realize large-scale metal structures and to allow new geometric forms. WAAM advantages compared to the other processes are fast large-scale production, freedoms in shape and geometry, structural efficiency with reduced material usage. The current research comprises the overarching process from the computational design to the mechanical characterization of the WAAM-produced elements, through the fabrication step. The computational design and fabrication stages were carried out at Technische Universität Braunschweig. There is still limited research focused on the characterization of WAAM-produced metal elements for structural engineering applications, therefore the research carried out at University of Bologna was focused on the establishment of 3D-outcome mechanical properties, pointing up the influence of surface roughness and imperfections on the mechanical response, together with the study on how the intersection between WAAM-produced bars influences the overall behavior of the specimen

Wire-and-Arc Additive Manufacturing for lattice steel structures: overview of the experimental characterization on dot-by-dot rods

With the advent of a new arc-based additive manufacturing (AM) process, referred to as Wire-and-Arc Additive Manufacturing (WAAM), the scale of the metal printed parts increased up to several meters, thus becoming suitable for large-scale applications in marine, aerospace and construction sectors. However, specific considerations in terms of geometrical and mechanical properties ought to be made in order to effectively use the printed outcomes for structural engineering purposes. The introduction of the novel printing strategy referred to as “dot-by-dot”, consisting in successive drops of molten metal, enabled the use of WAAM to realize complex lattice structures, made by continuous grids of WAAM rods. Nevertheless, their proper design requires an accurate evaluation of the influence of the non-negligible inherent geometrical irregularities on the mechanical response of the rods. Hence, extensive experimental work is needed in order to evaluate the mechanical response of “dot-by-dot” WAAM rods with geometrical imperfections. The present study focuses on the mechanical characterization of dot-by-dot WAAM-produced 304L stainless steel intersected rods, constituting the basic units of grid and lattice structures. The mechanical response of the specimens is assessed through tensile experimental tests conducted on two-ways planar nodes obtained from the intersection of two rods with different angles, hereafter also refereed to as crossed rods. The experimental results are then compared with tensile tests on single rods, to quantify the influence of the intersection angle in the structural response of the lattice structures

Combined Additive Manufacturing Techniques for Adaptive Coastline Protection Structures

Traditional reinforcement cages are manufactured in a handicraft manner and do not use the full potential of the material, nor can they map from optimised geometries. The shown research is focused on robotically-manufactured, structurally-optimised reinforcement structures which are prefabricated and can be encased by concrete through SC3DP in a combined process. Based on the reinforcement concept of “reinforcement supports concrete,” the prefabricated cages support the concrete during application in a combined AM process. To demonstrate the huge potential of combined AM processes based on the SC3DP and WAAM techniques (for example, the manufacturing of individualized CPS), the so-called FLOWall is presented here. First, the form-finding process for the FLOWall concept based on fluid dynamic simulation is explained. For this, a three-step strategy is presented, which consists of (i) the 3D modelling of the element, (ii) the force-flow analysis, and (iii) the structural validation in a computational fluid dynamics software. From the finalized design, the printing phase is divided into two steps, one for the WAAM reinforcement and one for the SC3DP wall. The final result provides a good example of efficient integration of two different printing techniques to create a new generation of freeform coastline protection structures