WAAM of structural components—building strategies for varying wall thicknesses

Additive manufacturing with steel opens up new manufacturing possibilities for individual parts or complex supply chains. The direct energy deposition process DED-arc, also known as wire arc additive manufacturing (WAAM), is particularly suited for manufacturing large structures with a high degree of geometrical freedom. The design freedom makes WAAM ideal for creating force-flow-optimized steel nodes and spaceframes for use in the construction industry. Thick-walled parts can be manufactured with manifold strategies and a variety of infill patterns, like hachure, spiral, or meander as well as with and without a contour path. For parts with varying thicknesses, not all of them apply. If the wall thickness changes in increments smaller than the width of a weld bead, the desired shape cannot be made by selecting one of the available deposition strategies but the distance (overlap) between the individual weld beads needs to be varied. A variation of the weld bead overlap can often lead to compromised build quality due to the presence of voids. Thus, utilizing variable bead overlap requires the development of a deposition parameter set that allows deviation from the defined overlap values without running the risk of introducing voids between beads or between layers. In this study, four parameter sets were analyzed regarding their weld bead geometry, and tolerance ranges for the weld bead overlap were identified for each parameter set. They were found to vary between 15 and 50% overlap, depending on the parameter set and its corresponding weld bead geometry. The geometry of the surface of the last deposited layer was evaluated regarding the height difference. It can be stated that, with decreasing wire feed, the surface of the last welded layer becomes smoother. The findings obtained are transferred to the manufacturing of complex parts. As a result, parts with variable wall thickness in building direction were manufactured by variation of weld bead distances.