Wire arc additive manufacturing of metals: A review on processes, materials and their behaviour

Metal additive manufacturing (MAM) techniques are continuously progressing since last decade and have marked a remarkable impact on the industry. Amongst the numerous MAM techniques, wire arc additive manufacturing (WAAM) exhibits high deposition rates, less production time, low raw material cost, flexibility with respect to the part size and high efficiency. WAAM is thus becoming one of the most promising AM techniques for metallic materials. Alloys of titanium, aluminium, nickel, steel and so on are predominantly utilized in WAAM and it has various applications in aerospace, marine and automotive industries. A lot of research has been put in and innovative practices have been developed to enhance the quality of the product by mitigating limitations such as corrosion, residual stresses, cracks, spatter, deformations, delamination, oxidation and porosity. In this review article, the effect of various process parameters and their optimization to counter the challenges in WAAM by using different methods of improvements like inter-pass cooling, heat treatment, inter-pass rolling, melt pool modifications and various optimization strategies are thoroughly discussed. Various trends and future aspects of WAAM are discussed to identify the challenges and research directions.