Coaxial Laser Metal Wire Deposition of stainless steel: process characterization

Laser Metal Wire Deposition (LMWD) is an additive manufacturing process which is based on melting a metallic wire to build metal structures in a layer by layer strategy. The process belongs to the directed energy deposition (DED) family, where more commonly powder feedstock is employed, blown by a carrier gas. Deriving from welding and brazing applications with a filler wire, the LMWD process has been most commonly applied with lateral wire feeding. This arrangement is intrinsically limiting for additive manufacturing, since deposition symmetry is absent and the head has to be realigned to maintain the correct deposition direction. The use of coaxial wire feeding would allow higher flexibility in deposited geometries with a better behavior in continuous processing, ensuring full independence to the travel direction and therefore encouraging the generation of three-dimensional structures. This work presents the LMWD of AISI 308L stainless steel applied with an industrial coaxial wire deposition head (CoaxCladder by Precitec GmbH & Co. KG) and a multi-mode fiber laser. In particular, the process feasibility is investigated in single layer deposition studying the main process parameters. Hollow cylindrical components with high aspect-ratio are demonstrated. The work also discusses the differences between wire and powder based DED processes by benchmarking surface roughness, build rate, and porosity. Under optimized conditions high aspect-ratio structures with good surface finish can be obtained. Furthermore, LMWD allows high build rates and components free of porosity. The process shows to be highly promising especially for applications requiring large build volumes. The use of wire feedstock also provides advantages in terms of safety, ease of handling, and high efficiency of material use, which are all beneficial for additive manufacturing of large components.