Brazing is a precision joining process that employs a lower-melting-point filler metal than the base components. Brazing does not melt the workpieces, permitting the joining of dissimilar metals with very little distortion. Brazing is suitable for intricate assemblies in HVAC, aerospace, and electronics applications.

Capabilities

Advantages: Excellent for dissimilar metals, uniform joints, minimal distortion, good joint strength.

Disadvantages: Joint strength less than welding, potential for flux contamination, not ideal for high-temp service.

Applications: Heat exchangers, precision instruments, turbine blades, electrical connectors.

Process Cycle

• Preparation of the joint surface and cleaning
• Application of protective atmosphere or flux
• Positioning of filler metal (wire, rod, foil, or paste)
• Filler melting to its temperature (around 450°C+)
• Capillary action draws filler into the joint
• Controlled cooling
• After cleaning, remove flux residue (if used)

Equipment

• Torch brazing units (fuel-gas)
• Induction brazing units
• Furnace brazing units (continuous or batch)
• Dip/salt bath brazing units
• Vacuum brazing systems for high-purity service

Tooling

Primary:

• Aligning fixtures and clamps
• Graphite or ceramic furnace brazing support

Secondary:

• Pre-forming filler pastes or rings
• Flux applicators
• Cooling racks and post-cleaning stations

Materials

Possible Defects

• Incompletely filled capillary flow
• Voids and porosity
• Flux entrapment or contamination
• Poor adhesion resulting from poor wetting
• Differential cooling joint cracking

Design Rules

• Confirming to close joint clearances (typical practice is 0.001–0.005 in.)
• Design for uniform capillary paths
• Avoid large thermal gradients
• Use self-locating joints for repeatability
• Minimize exposure of joints to corrosive environments

Cost Drivers

• Joint volume and filler metal space
• Heating process and cycle time
• Fixturing complexity and reuseability
• Flux or shielding gas usage
• Clean-up and inspection processes after brazing

Brazing enables assembling of complex parts with high accuracy and compatibility among a broad range of metals; thus it is a key process in modern manufacturing if tolerance, integrity, and cosmetic finish are imperative.