Influence of milling interventions on the geometry of wall-shaped structures in hybrid wire-arc direct energy deposition

The Hybrid Wire-Arc Direct Energy Deposition (Hybrid Wire-Arc DED) process integrates Wire-Arc Direct Energy Deposition (Wire-Arc DED) with machining (typically milling) interventions, offering the potential for creating intricate geometries and finished surfaces. However, if milling is employed as a hybrid intervention rather than as a final part-finishing process, the interplay between these processes remains under-investigated. This paper examines the influence of milling interventions on the geometry of a wall-shaped structure, quantified by the transverse cross-sectional width, built using a Hybrid Wire-Arc DED. Through experiments on mild steel, the underlying causes of observed wall-width variations are analyzed. Initial observations suggested that thermo-mechanical deformations from milling influence the width variations. However, evidence indicates the significant role of additional remelting cycles experienced by the milled surface layer during subsequent layer depositions. The study also reveals that the observed increase in wall width for each milling intervention occurs at approximately the same depth below the milled surface. A mechanistic explanation for this observation is given. Crucially, the findings suggest that unless milling is done at higher frequencies, like after each layer deposition, the resultant unevenness might render the Hybrid Wire-Arc DED process less efficient in terms of surface quality and dimensional accuracy than its non-hybrid counterpart.