Application and Adaptation of Arc-Based Welding Processes to Wire Arc Additive Manufacturing: A Review

Wire Arc Additive Manufacturing (WAAM) has emerged as one of the most industrially scalable arc-based metal additive manufacturing (AM) technologies, using established Gas Metal Arc Welding (GMAW), Gas Tungsten Arc Welding (GTAW), and Plasma Arc Welding (PAW) processes to deposit metallic material layer-by-layer into near-net-shape components. This review presents a physics-based examination of the adaptation of traditional welding processes for AM applications, with emphasis on: (i) the thermodynamic and metallurgical principles governing melt pool formation, solidification, and solid-state transformations; (ii) the thermal and solidification features that WAAM shares with multi-pass welding and those that are distinctive to WAAM, with particular attention to the temperature gradient-to-solidification-rate ratio (G/R) and its role in controlling grain morphology; (iii) deposition path strategies and their influence on heat distribution and microstructural homogeneity; (iv) arc metal transfer modes and their thermal implications for AM; and (v) mechanisms of defect formation including porosity, solidification cracking, residual stress, and geometric deviation. Unlike general WAAM reviews, this article specifically positions conventional arc welding processes as the metallurgical and thermal foundation of WAAM and critically examines how their operating principles are transformed under repeated layer-by-layer deposition. Key governing equations linking process parameters to microstructure and properties are presented. Among GMAW variants, Cold Metal Transfer (CMT) provides low heat input, controlled droplet transfer, and low spatter, whereas GTAW and PAW allow wire feed and arc power to be set independently; the preferred process therefore depends on the alloy, required deposition rate, geometry, and surface quality. A synthesis of findings across ferrous and non-ferrous alloy systems is presented, together with knowledge gaps and future directions toward closed-loop adaptive WAAM systems.