3D printing with steel

Abstract

Extended keynote paper of Eurosteel 2021 Automated production is finding its way into the fabrication of structural steel. One robot holds attachments (stiffeners, end plates, etc.) on a steel beam or column and another robot produces weld seams. However, welding robots can also be used for Additive Manufacturing (Wire and Arc Additive Manufacturing, WAAM). The wire electrode serves as a printing material. The Institute of Steel Construction and Materials Mechanics in Darmstadt is investigating how typical connecting elements for steel structures can be printed directly on steel beams using Additive Manufacturing with arc welding and robots. Furthermore, structural elements such as nodes for space frames can be printed and even complete structures, e.g. columns and a little bridge, have already been manufactured additively. The main focus is on determining suitable welding and process parameters. In addition, topology optimization is necessary in order to achieve good structures using a small amount of material. This is possible due to the free design prospects of WAAM, which opens up new design and production strategies.

Topology Optimisation in Structural Steel Design for Additive Manufacturing

“…As steel design and detailing is deeply affected by fabrication and erection procedures, which usually constrain engineering options in a more extensive manner compared to construction with other common materials, a further investigation into recent research papers devoted to considering such aspects into TO is due. For such an end, and regardless of a deeper review on Additive Manufacturing for TO in Section 7, one shall refer to recent reviews [420,421], and keynote [422] on employing welding robotics in the so-called Wire and Arc Additive Manufacturing (WAAM) of topology optimised steel members and connections. However, the most common methods of creating steel in AM use powder as a feedstock and laser or electron beams as binding mechanisms [423].…”

“…Some recent examples of topologically optimised and additively manufactured joints can be found in Figure 11. Herein, new concepts and interesting solutions for space structures can be found [422], yet the significant predominance of applications for lattice, reticulated, and generally tensegrity structures is evident. Such shortcoming is mostly due to the limited quantity of load combinations which can reasonably be considered for the optimisation process.…”

“…Problems with the optimisation process have an outstanding issue in the incapacity of some algorithms for accounting non-linearity [422]. This is critical in several connection types, including the bolted ones, where plasticity plays a major role.…”

“…As such, the nature-inspired structural concept is particularly prone to TO, in which a solution for optimising and manufacturing its joints is paramount. Other interesting developments in the TO of joints among tubular elements can be found in the [422] (reproduced under the Creative Commons Attribution-NonCommercial-NoDerivs License); (e) joint specimens topologically optimized with the bi-directional evolutionary structural optimisation (BESO) method for axial loads and bending in the RMIT University [427].…”

“…Examples of topologically optimised and additively manufactured metallic connections for civil engineering structures. Left to right and top to down: (a) Non-TO and TO joint specimens by ARUP[355]; (b) several joints designed in the University of Leeds[139]; (c) wire and arc additive manufacturing (WAAM) printed bolted joint in the Technical University of Darmstadt[422] (reproduced under the Creative Commons Attribution-NonCommercial-NoDerivs License); (d) WAAM printed node in the Technical University of Darmstadt[422] (reproduced under the Creative Commons Attribution-NonCommercial-NoDerivs License); (e) joint specimens topologically optimized with the bi-directional evolutionary structural optimisation (BESO) method for axial loads and bending in the RMIT University[427].…”