## 5 Conclusions  
In laser metal deposition processes, oxidation is a major challenge, as it negatively affects the resulting mechanical properties of the built-up components. To reduce oxidation, either a complete inert gas atmosphere can be used or only the hot process zone can be shielded locally, with the latter approach offering considerable advantages in terms of gas consumption, equipment complexity, and setup time. The nozzle concepts studied in the literature are for powder-based LMD and cannot be directly applied to the wire-based process due to the lack of the carrier gas flow. In addition, geometric constraints resulting from the conical shape of the laser beam have to be considered. Therefore, in this work, a novel local shielding gas concept for laser metal deposition with coaxial wire feeding was developed and evaluated thoroughly for its effectiveness. First, a nozzle geometry was designed based on established concepts from fluid mechanics. For this, an iterative approach utilizing CFD simulations was pursued. For the final design, the flow rate was varied simulatively to obtain a sufficiently protected area at an economical gas consumption. Subsequently, the concept was investigated based on deposition experiments with stainless steel. The effects of the flow rate on the weld bead geometry as well as the melt pool temperature were examined. Finally, a fully dense solid cuboid without existing oxide inclusions was successfully built up. The following conclusions are drawn:  
* Using the developed shielding gas concept, an oxide-free deposition was possible for individual weld beads as well as for a solid cuboid. * The nozzle geometry enables a direction-independent shielding gas coverage with minimal turbulence, thus preventing mixing with the atmosphere. * Increasing the shielding gas flow rate from 10 1/min to 70 1/min resulted in a 15 K lower melt pool temperature as well as a drop in the weld bead width by approximately 110 \(\upmu\)m. This could be attributed to the convective cooling effect of the shielding gas. * The concept is applicable to many commercially available coaxial wire deposition heads. In the investigations conducted, the shielding gas concept proved to be highly effective for the deposition of stainless steel. In future studies, the application of the concept for the deposition of further materials, in particular, highly reactive alloys, should be investigated. Since oxidation is highly influenced by the cooling rate of the deposited weld bead as well as the traverse speed when using a local shielding gas concept, these factors should be  
Figure 13: Microhardness distribution of the built-up cuboid along the z-direction at the center and the lateral regions. Additionally considered. Furthermore, it should be analyzed to which extent more complex part geometries affect the flow condition and, thus, the effective protection region. Another subject worth investigating is the effect of the shielding gas flow on the surface tension-based Marangoni flow within the melt pool and the resulting weld bead characteristics. Conceptualization, C.B. ; Methodology, C.B., L.M. and A.Z. ; Software, L.M. ; Validation, C.B. and L.M. ; Formal analysis, C.B. and X.F.Z. ; Investigation, C.B. and L.M. ; Resources, M.F.Z. ; Data curation, C.B. and L.M. ; Writing--original draft, C.B. ; Writing--review & editing, A.Z., X.F.Z., S.B. and M.F.Z. ; Visualization, C.B. and L.M. ; Supervision, M.F.Z. ; Project administration, C.B., X.F.Z. and M.F.Z. ; Funding acquisition, C.B., X.F.Z. and M.F.Z. All authors have read and agreed to the published version of the manuscript. The results presented were achieved within the AdDEDValue project, which is supported by the German Federal Ministry for Economic Affairs and Climate Action (BMWK) within the funding program \"Digitalization of Vehicle Manufacturers and the Supplier Industry\" (grant number 13 IK002L) and supervised by the VDI Technology Center (VDI TZ).