Residual stress simulation and process optimization for brazing stainless steel heat exchanger components with novel copper-based filler alloy

Brazing technology is extensively utilized in heat exchanger fabrication owing to its advantages of minimal heat-affected zones, high joint strength, and process flexibility. To address the demand for high-performance (high-strength, high-thermal-conductivity, low-residual-stress), low-cost brazed joints in household water heater plate-fin heat exchangers, this study overcomes challenges in copper-based filler design and process optimization for stainless steel brazing. We innovatively developed a copper-based brazing paste (68Cu) and established a high-precision ANSYS thermo-mechanical model simulating brazing cooling processes in header-tube joints. Simulations revealed that 68Cu achieves residual stress control comparable to nickel-based (BNi-2) and silver-based (Ag-Cu-Ti) fillers while reducing costs. Single-factor analyses quantified effects of overlap width, heat exchange tube thickness, and brazing gap on residual stresses. Subsequently, orthogonal experimental design (three-factor, four-level) optimized these parameters, identifying the optimal combination: overlap width 3.1 mm, heat exchange tube thickness 0.30 mm, and brazing gap 0.05 mm. This configuration reduced the maximum compressive stress (σABxmax) to be reduced to 89 MPa, with σCDxmax of 147 MPa and σEFxmax of 244 MPa. The integrated approach provides systematic solutions for high-performance, low-cost stainless steel heat exchanger joints.