Dual-loop proportional control for high-precision induction brazing of thin-walled aluminum waveguides

This study presents an automated induction brazing system for thin-walled aluminum waveguide assemblies, integrating dual-loop control with real-time positional feedback. Two proportional control strategies were evaluated: a baseline single-loop heating-rate controller and an enhanced dual-loop configuration incorporating active inductor realignment based on thermal asymmetry. The single-loop system, operating at 20 Hz, achieved an average absolute temperature error of 3.4 °C with a 92% success rate, but exhibited sensitivity to workpiece-inductor gap variations, leading to inter-element temperature deviations exceeding 15 °C under moderate misalignments. To address this, a secondary feedback loop was introduced to dynamically correct flange-to-tube temperature differentials, improving thermal uniformity across the brazing zone. Full-scale validation on 120 assemblies across four geometric classes demonstrated that the dual-loop system reduced average temperature error to 2.1 °C, limited peak temperature spread to 8 °C, and increased yield to 97%. The control architecture features distinct bandwidth separation for power and positional loops, minimizing cross-coupling. A modular C++ software environment synchronizes multi-source data streams-including pyrometry, manipulator kinematics, power metrics, and video analytics-with real-time KPI tracking and long-term logging to an SQL-based historian. These results highlight the potential of feedback-driven control architectures in precision thermal joining, and suggest pathways for future enhancements using adaptive or fractional-order control algorithms.