Joining
Brazing vs Welding
Brazing joins metals by melting a filler alloy above 450 C that flows into a capillary gap while the base metals stay solid. Welding fuses the base metals themselves. The core trade: brazing gives low distortion, dissimilar-metal capability, and batch automation; welding gives maximum joint strength on thick structural sections.
| Brazing | Welding | |
|---|---|---|
| Process temperature | 620 to 900 C filler melt, base solid | Base metal melts, 1500 C+ for steel |
| Joint strength | 170 to 250 MPa shear with 0.05 to 0.1 mm gap | Matches base metal, 400 to 550 MPa mild steel |
| Dissimilar metals | Yes: copper to steel, carbide to steel | Limited, cracking and dilution issues |
| Distortion and HAZ | Minimal, tolerances hold within 0.1 mm | Significant, fixturing and post-weld straightening |
| Batch automation | Furnace brazes 100+ joints per cycle | Robot welds one seam at a time |
| Section thickness | Best under 3 mm, lap joints | 3 mm to 100+ mm, butt and fillet |
| Consumable cost | Silver alloy $80 to $150/lb, copper paste cheaper | Steel wire $2 to $5/lb plus gas |
Choose Brazing when
- Thin-wall or dissimilar joints: copper to steel, carbide inserts
- Hundreds of joints per assembly, as in heat exchanger cores
- Tight post-join tolerances where weld distortion is unacceptable
Choose Welding when
- Structural loads where the joint must match base metal strength
- Sections over 3 mm and full-penetration butt joints
- Field repair and one-off fabrication with portable equipment
The verdict
Weld structure, braze assemblies. If the joint carries primary structural load in sections over 3 mm, weld it. If the assembly is thin-wall, mixes metals, needs 100 joints sealed at once, or cannot tolerate distortion, braze it, ideally in a batch or continuous furnace.
Cost comparison
A manual TIG cell costs $5,000 to $15,000 and a skilled welder $30 to $45/hr, with each structural joint taking 2 to 10 minutes. Torch brazing hardware runs under $2,000, but silver filler at $80 to $150/lb stings on large joints. The crossover is batch furnace brazing: one $150,000 to $400,000 continuous furnace joins hundreds of assemblies per hour at pennies per joint, which is why radiator cores and carbide tooling get brazed while frames and weldments get welded.
Common questions
Is a brazed joint as strong as a welded joint?
Not in tension against base metal, but a properly designed brazed lap joint with a 0.05 to 0.1 mm gap develops 170 to 250 MPa shear, and with 3T to 4T overlap the assembly often fails in the parent metal before the joint. Welds win for butt joints and thick sections.
Why do heat exchangers get brazed instead of welded?
A radiator or plate exchanger has hundreds of joints on 0.1 to 0.5 mm foil. A controlled-atmosphere braze furnace seals every joint in one 30 to 60 minute cycle with almost no distortion. Welding each joint individually would burn through the foil and cost 50 to 100x more labor.