Closed-loop control of alternating dual-electron beams for molten pool regulation during in-situ additive manufacturing

In-situ additive manufacturing (AM) is well known for integrating of material synthesis and near-shaping fabrication. However, the insufficient metallurgy has become a widespread challenge owing to the molten pool's short lifetime. Our previous research proved that employing alternating dual-electron beams can effectively manipulate the molten pool length, thereby prolonging its duration time. However, it is difficult for the preset alternating dual-heat source parameters under current open-loop operations to guarantee the desired molten pool length for the time-variation of the AM process. Therefore, this study further proposes a closed-loop control of alternating dual-electron beams to maintain a stable molten length, thereby ensuring internal metallurgical quality and external forming morphology. Specifically, based on a self-developed atmospheric-pressure vapor-prevention visual sensor, a machine-vision closed-loop control system for the molten pool length was established. The influence of the alternating dual-beam parameters on the molten pool length was studied and modeled, and the deflection voltage was selected as the controlled variable owing to its good dynamic performance and wide manipulation range. Given the nonlinearity and time variance of the AM process, a Fuzzy-PID controller with the ability to adjust control parameters in real-time was designed. The experimental verification results indicated that the developed controller could effectively control the molten pool to the expected length and exhibited good robustness in the disturbance test. Finally, a multi-layer multi-pass component was successfully fabricated with a closed-loop-controlled molten pool length of 24 mm. This study significant for promoting the industrial application and intelligent development of in-situ AM technology.