Furnace Brazing

Furnace brazing joins pre-assembled parts in a controlled atmosphere or vacuum, producing clean, consistent, low-distortion joints across many components in a single cycle.

Overview

Furnace brazing is a joining process where pre-assembled components and brazing filler are heated in a controlled atmosphere or vacuum furnace until the filler flows and forms metallurgical joints. The entire assembly heats uniformly, which minimizes distortion and produces clean, oxide-free joints, especially in stainless steels and high-temperature alloys. It supports complex multi-joint assemblies and can process many parts per run, making it efficient for batch and production work.

Choose furnace brazing when you need repeatable joint quality, good strength at elevated temperatures, and clean joints without post-braze flux removal. It is strong on stainless, nickel alloys, and hard-to-weld materials, and works well for capillary joints with tight, consistent clearances. Tradeoffs include limited part size to the furnace envelope, long cycle times, higher fixturing and setup cost, and relatively poor suitability for very low volumes or large, localized repairs. Joint design, cleanliness, and gap control are critical to avoid voids, incomplete flow, or joint movement during the braze cycle.

Common Materials

  • 304 stainless steel
  • 316 stainless steel
  • 1018 carbon steel
  • Inconel 625
  • Copper
  • Carbide inserts

Tolerances

±0.002" to ±0.005" after brazing, depending on part size and fixturing

Applications

  • Stainless steel heat exchangers
  • Carbide-tipped cutting tools
  • Aerospace vane and nozzle segments
  • Fuel rails and injector assemblies
  • Honeycomb seal and shroud assemblies
  • Medical instrument subassemblies

When to Choose Furnace Brazing

Use furnace brazing for multi-joint or complex assemblies that need clean, consistent, low-distortion joints and can be processed in batches. It fits best when you can design precise joint clearances, justify furnace setup cost with at least small-to-medium production volumes, and need good performance at elevated temperatures or in corrosive environments.

vs Torch Brazing

Choose furnace brazing when you need many identical joints, tight process control, and minimal operator variability across batches. It is better for stainless and high-temperature alloys, flux-free or low-residue joints, and assemblies that benefit from uniform heating, while torch brazing suits one-off work, repairs, or very large parts that won’t fit in a furnace.

vs Wave Soldering

Choose furnace brazing when you need structural strength, high-temperature service, and joints in bulk metal parts rather than on printed circuit boards. It handles thicker sections, dissimilar metals, and high-strength joints, whereas wave soldering is optimized for attaching electronic components and thin copper features with low-melting solder.

vs TIG Welding

Choose furnace brazing when distortion and residual stress must be minimized, or when joining thin or dissimilar metals that are difficult to weld. It also makes sense when you need multiple small joints made simultaneously in a fixture, while TIG is better for localized, high-strength fusion joints and large fabrications.

vs Induction Brazing

Choose furnace brazing when you have many parts or joints that can run as a batch, need very clean joints in vacuum or controlled atmosphere, or require uniform heating of complex assemblies. Induction brazing is more suitable for localized heating, faster cycle times on single joints, or when only a small region must reach brazing temperature.

vs Manual Soldering

Choose furnace brazing when joint strength, temperature capability, and structural integrity matter more than low-temperature processing. Furnace brazing supports higher service temperatures, stronger joints, and tougher alloys, while manual soldering is for lower-strength, low-temperature electrical or light mechanical connections.

Design Considerations

  • Design lap or socket joints with uniform gaps, typically around 0.001"–0.005" depending on alloy and part size, to promote capillary flow
  • Provide positive joint location features and stable fixturing surfaces to prevent parts from floating or shifting during the brazing cycle
  • Avoid massive section thickness changes near joints to reduce thermal gradients, distortion, and incomplete filler flow
  • Ensure all joint areas are accessible for filler placement (paste, preform, or shim) and cleaning before brazing
  • Specify which dimensions are critical after brazing and allow stock or features for any required post-braze machining
  • Include vent paths or reliefs in enclosed cavities to prevent trapped gases or flux from causing porosity or joint blowouts during heating