Process innovations in wire arc additive manufacturing systems: progress, challenges and future opportunities

Wire Arc Additive Manufacturing (WAAM) has emerged as one of the most practical and scalable technologies for fabricating large metal components. With high deposition rate and cost efficiency, WAAM is increasingly used in aerospace, marine, and other high-value industries. Conventional WAAM systems, based on commercial welding equipment and industrial robots, are limited in controlling material microstructure, mechanical properties, and geometric accuracy. As the demands for higher performance in fabricated parts continue to rise, process-oriented system innovations have become a key development trend. These modifications directly manipulate arc behaviour, wire feeding, thermal fields, and in-situ deformation, providing more effective regulation of molten pool dynamics and solidification patterns. Approaches such as multi-wire feeding, hybrid arc-laser configurations, external field assistance, and in-situ thermal or mechanical treatments have achieved improved structural uniformity, reduced defects, and higher deposition efficiency. Despite this rapid progress, the diversity and complexity of independently developed systems have led to a fragmented research landscape. This review synthesizes these innovations, evaluates their mechanisms and effectiveness, and maps them to key research objectives. It then provides critical insights of current research, discusses existing issues and highlights future opportunities to guide the development of high-performance, structurally reliable, and industrially deployable WAAM systems.