Heat input-based feedback control for enhanced repeatability in Wire Arc Additive Manufacturing

In Gas Metal Arc Welding (GMAW)-based Additive Manufacturing, namely Wire Arc Additive Manufacturing (WAAM), process repeatability is strongly affected by fluctuations in heat input occurring during layer deposition. Even when nominal parameters are fixed, variations in the previously deposited geometry modify the contact-tip-to-workpiece distance (CTWD), causing changes in welding current and voltage and, consequently, in the actual heat input. These deviations propagate through the build, leading to geometric inconsistencies, arc instability and defects that compromise both part quality and compliance with qualification procedures. Moreover, heat input consistency throughout the build represents a key parameter to be monitored and controlled in additive manufacturing to ensure that the final component meets industrial qualification requirements. However, despite its relevance, feedback control strategies for real-time regulation of the heat input remain limited in the literature. This work introduces a control strategy, named CCHR (CTWD Control for Heat-input Regulation), in which heat input is explicitly regulated as the primary controlled variable, rather than indirectly influenced through geometric control. Heat input is computed online from measured current, voltage and welding speed, while CTWD is used as the actuation variable. A dynamic model relating CTWD variations to process power is identified and used to design a combined feedforward-feedback controller that maintains the desired heat-input level throughout the build. Experimental validation performed on Invar 36 walls produced in short-circuit transfer mode shows that the proposed strategy improves process predictability and part quality across different operating conditions. The controller, developed as a variant of standard short circuit process, reduces heat-input variability, stabilises arc behaviour and leads to more consistent layer geometry, demonstrating that CTWD-based heat-input regulation provides a practical solution for robust and repeatable WAAM production, enabling also a more reliable compliance with qualified deposition procedures. The implementation of the proposed controller on a full-scale component demonstrates its scalability and industrial relevance, satisfying the deployment robustness and stability requirements for practical industrial adoption.