Express Wire Coil Cladding as an Advanced Technology to Accelerate Additive Manufacturing and Coating

Abstract

Metal shafts are indispensable components in mobility, energy, and mechanical engineering. In such applications, the shafts need to withstand severe mechanical loads, friction, high temperature, or corrosive media. This is why shafts are often completely made of high-performance alloys. From a technical point of view, coating an inexpensive base shaft with a thin layer of high-performance material is mostly sufficient to ensure its functionality. Adding functional parts such as shoulders or bearing seats by additive manufacturing instead of creating them by subtractive manufacturing is an advantageous approach to increase flexibility and material efficiency. Reliable and economic Additive Manufacturing and coating processes need to be developed further, and laser-based processes such as wire-based laser metal deposition (LMD-w) offer high potential to accomplish this. They can generate a stable metallurgical bond between the base material and the cladding or the added feature without excessively heating the work piece. Due to their low build-up rate, however, LMD processes are not economically competitive with high-speed subtractive technologies such as drilling or turning, which are predominately used for shaft production. Motivated by this challenge, we present an alternative approach that increases the deposition rate for laser-based shaft cladding. Instead of adding the filler wire continuously, wire coils are wound and preplaced on the shaft. In a second step, laser processing while rotating the part generates a metallurgical bond between the wire and the substrate. In this study, several solid and flux-cored wires were analyzed regarding their suitability for this two-step coil winding and LMD process. The results from LMD experiments give an overview of the resulting surface state and of the welded joint quality after deposition. Metallographic cross-sections show low porosity of the deposited layers and small heat-affected zones in the base shaft. Thanks to its good scalability, this innovative two-step process can help strongly increase the build-up rate compared to classic LMD-w.