Application of a novel automatic filler delivery method in induction brazing of copper pipes in heat pump manufacturing: A comparative study with pre-placed ring method

Induction brazing offers localized heating and short brazing cycle, but joint quality is strongly influenced by filler metal delivery method. In industrial practice, filler metal is commonly applied as pre-placed rings; however, this approach is prone to defects. This study investigates a novel automatic wire-feeding method as an alternative to the conventional approach. Comparative experiments were conducted at brazing temperature ranging from 710 to 800°C using copper pipes with outer diameters of 9.6 mm and 9.8 mm and BCuP-Ag filler alloy. Joint quality was assessed through macrographic imaging and analyzed using a defect segmentation and classification algorithm built on YOLOv11. Mechanical properties and microstructure characteristics were evaluated through tensile testing, microhardness measurement, and SEM/EDS analysis. Results showed that defect area decreased with increasing temperature for both methods, with lower defect formation consistently observed in automatic wire feeding methods. Defect formation was also influenced by the gap size, with automatic method showing optimal performance in 0.045–0.140 mm clearance range. Higher temperatures enhanced filler spread and joint integrity; however, microhardness measurements and SEM/EDS results indicated that excessive brazing temperature promoted formation of intermetallic phases and microstructural degradation, whereas 750 °C provided an optimal balance of diffusion, bonding, and stability. Although tensile strengths were slightly higher in ring brazed joints, all fractures occurred in base metal, confirming joints integrity. The automatic wire feeding method demonstrated improved processes control, reduced defect formation, and consistent performance, making it a promising alternative for high-quality, repeatable joints in automated copper-brazing applications, particularly in HVAC and heat-pump systems.