Multivariable QFT control of the direction flip problem in wire arc additive manufacturing

Additive metal manufacturing (AM), particularly Wire Arc Additive Manufacturing (WAAM), offers a compelling alternative to traditional machining methods. While AM presents advantages such as reduced material waste and lower production costs, challenges remain in effectively controlling the process to prevent defects and optimise material deposition. This article proposes a multivariable control system for WAAM utilising Quantitative Feedback Theory (QFT) to maintain the shape of the heat-affected zone (HAZ) during transitions in direction flips during layer deposition. By modelling these direction flips as predictable disturbances, the full potential of QFT to integrate feedback and feedforward actions is exploited. The resulting multivariable control laws seek to minimise temperature variation in two critical points around the welding pool by adequately manipulating the power and speed of the heat source. A benchmark system is established to evaluate the effectiveness of the proposed control system. The results demonstrate significant improvement in temperature control, leading to enhanced layer construction quality and reduced need for height corrections or cooling pauses.