Properties oriented WAAM—microstructural and geometrical control in WAAM of low-alloy steel

Abstract

Today, arc-based additive manufacturing has great potential for industrial application due to new developments in robotics, welding technology, and computer-aided manufacturing. Two issues are currently the focus of research. One is the accurate generation of geometry with respect to the design, e.g., geometry fidelity, defined roughness, and shape deviations within the tolerances. Here, there are still open questions, particularly with regard to path planning and the dependence of the geometry on the selected process variables. The second topic is the adjustment or determination of the achievable mechanical and microstructural properties, as these are of crucial importance for the use of the technology in industry. The combination of both areas into a geometry- and property-oriented approach to additive manufacturing has been little discussed in the literature for arc-based welding processes. The correlations between cooling conditions and emerging properties can serve as a starting point for such a consideration. The temperature history depends on three key factors: the energy input, the interpass temperature (which in additive manufacturing is determined by the time to over-weld), and the heat transfer conditions, which are determined by the part geometry. The melt pool size or volume also depends on these three constraints. In this study, an approach is presented to realize property-oriented additive manufacturing from the interaction of property-oriented path planning and a melt pool size control system. By controlling the melt pool size, the cooling of the material can be adjusted within certain limits, and consequently, a local adjustment of the microstructure can be achieved, which greatly influences the local mechanical properties. This work demonstrates this approach for a low-alloy filler metal (DIN EN ISO 14341-A G 50 7 M21 4Mo/A5.28 ER80S-D2). Gas metal arc welding was carried out using an M21 shielding gas (82% Ar, 18% CO2). Finally, microstructural characterization will show that different microstructural morphologies and properties can be achieved in a component by combining property-oriented path planning and the use of a control loop to regulate the melt pool size.