Equipment and process windows for laser metal deposition with coaxial wire feeding

For some materials and applications, it is advantageous to use a wire instead of powder additives for laser metal deposition (LMD). By utilizing a wire as an additive material, major disadvantages of powder-based LMD processes can be eliminated. Contamination of the process cell with metal powder, significant material losses during the process, health and safety issues, and insufficient powder quality are just some of the problems avoided by this approach. A continuous ring-shaped laser beam surrounding the wire is one of the distinguishing features of the presented LMD processing head. The laser beam and wire are arranged coaxially to each other, with the wire being fed through the inside of the hollow, ring-shaped laser beam. The coaxial supply of inert gas avoids exposure of the melt pool to atmospheric oxygen. Through this design, the wire LMD process is independent of the feed direction. A very high degree of material utilization paired with the aforementioned advantages promises the potential for efficient and precise buildup of two- and three-dimensional geometries. The reduced mass of the head through advanced design makes highly dynamic LMD processes feasible. By allowing the use of thin additive wires, even intricate geometries can be built up in near-net-shape. To evaluate the potential of this novel approach for wire-based laser material deposition, a prototype processing head was designed, built, and tested. First, results and measurements regarding beam shaping, process behavior, and resulting deposits are shown and discussed. Material samples from both Inconel 718 and Titanium Ti-6Al-4V were built and evaluated metallographically. An outlook toward future research and possible applications is given.