Brazing and Soldering Guide

Brazing and soldering join metals using filler material that melts below the base metal’s melting point. The base metals never melt. Instead, the filler flows into the joint by capillary action, wetting the surfaces and forming a metallurgical bond when it solidifies. These processes fill a critical gap where welding would cause distortion, damage heat-sensitive components, or fail because the metals can’t be fusion welded together.

When to Braze Instead of Weld

Brazing is the right choice in several specific situations. Joining dissimilar metals (copper to steel, carbide to tool steel) is the most common. Brazing also works for thin-walled assemblies that would burn through or distort under welding heat, for joints that need to be leak-tight without post-weld machining, and for production runs where furnace brazing hundreds of parts at once beats welding them individually.

HVAC copper pipe work is almost entirely brazed with BCuP (copper-phosphorus) filler alloys. These alloys are self-fluxing on copper-to-copper joints, making the process fast and reliable. Plumbing transitions from copper to brass or steel fittings use silver braze alloys (BAg series) with flux.

Brazing Methods

Torch brazing is the most common method in small shops. An oxy-fuel or air-acetylene torch heats the joint, flux prevents oxidation, and filler is hand-fed or pre-placed. Temperature control matters. Heat the base metal, not the filler rod, and let capillary action draw the filler into the joint.

Furnace brazing runs parts through a controlled-atmosphere or vacuum furnace. Used in production for carbide tools, heat exchangers, and aerospace assemblies where consistent joint quality across hundreds or thousands of parts is required.

Induction brazing uses electromagnetic coils to heat the joint area rapidly and precisely. Fast cycle times make it ideal for repetitive production work like brazing fittings onto tubes.

Soldering Basics

Soldering works at lower temperatures with tin-based filler alloys. Electrical connections, electronics, plumbing (potable water uses lead-free solder), and jewelry are the primary applications. Soldering irons, torches, and wave soldering machines apply the heat depending on the application.

Articles in This Section

The guides below cover filler metal selection, joint design principles, torch brazing technique, HVAC brazing procedures, and common brazing defects with fixes.