Welding, Brazing, Soldering & Bonding
Distinguishing soldering, brazing and welding by temperature and fusion; welding methods; joint inspection and bonding for electrical continuity.
Welding, brazing & soldering — summary notes
Free- The joining processes differ by temperature and by whether the parent metal is melted. SOLDERING uses a filler melting below about 450 °C; the parent is not melted and the joint relies on the solder wetting clean, fluxed surfaces — mainly electrical connections.
- BRAZING uses a filler melting above about 450 °C but below the parent's melting point, drawn into the joint by capillary action; it gives a stronger joint than soldering without fusing the parent.
- WELDING melts the parent metals themselves, with or without filler, to form a fused joint of parent-metal strength — used for structural and high-load work.
- Common welding methods: oxy-acetylene (gas), and the electric-arc processes MMA, and the inert-gas processes TIG and MIG, which shield the weld pool with argon or helium so it does not oxidise. TIG is favoured for thin aircraft materials.
- Joint inspection is largely visual, backed by NDT. A soldered joint should be bright, smooth and fully wetted with no dry (grainy) joint. A brazed joint should show complete even fillets with full penetration and no voids.
- A welded joint is inspected for penetration and a uniform bead, and for freedom from cracks, porosity, undercut, inclusions and lack of fusion — confirmed by dye-penetrant, magnetic-particle or radiographic testing.
- Bonding (electrical) connects metal parts to a common low-resistance reference; flux residues from any process are corrosive and must be removed after the joint is made.
- ⚠ Exam trap: distinguish the three by temperature and by whether the parent melts — only welding fuses the parent metal.
- Temperature order
- solder < ~450 °C < braze < weld (weld fuses the parent)
- Inert-gas welding
- TIG / MIG shield the pool with argon or helium
- Weld defects
- cracks · porosity · undercut · inclusions · lack of fusion
A filler metal melts at 500 °C while the parent stays solid, and is drawn into the joint by capillary action. Which process is this?
Brazing — the filler melts above ~450 °C but below the parent's melting point, and capillary action pulls it into the fitted joint without fusing the parent metal.
Why is TIG welding preferred for thin aircraft alloy structure?
TIG gives a precisely controlled, clean weld with an inert-gas shield that prevents oxidation, and the heat input can be kept low — important on thin material where distortion and burn-through are risks. The result is a high-quality weld suitable for inspection to aircraft standards.
Welding, brazing & soldering concept map
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