- Practice · 4+4 marks
Arc welding: SMAW, TIG and MIG
Short answer
SMAW uses a coated consumable electrode; the arc melts electrode and base metal. Coating provides shielding gas, slag, arc stabilisation and deoxidation. TIG employs a non‑consumable tungsten electrode with separate filler; MIG uses a continuously fed consumable wire. TIG yields high quality on thin sections; MIG is faster and suits thicker production.
Explain shielded metal arc welding (SMAW) and the functions of the electrode coating. Differentiate between TIG and MIG welding.
Shielded metal arc welding (SMAW)
An electric arc (about 3500 to 5000 °C) is struck between a coated consumable electrode and the work. The arc melts the electrode tip and the base metal into a weld pool, which solidifies as the electrode moves.
electrode holder
|\ coated electrode
| \
~~~~~~~|~~~~~ arc ~~~ slag over weld bead
===== work =================
transformer/rectifier: 20-40 V, 50-400 A
- Supply: AC transformer or DC rectifier. With DC straight polarity (electrode negative) more heat goes to the work, giving deeper penetration for thick plates; with reverse polarity (electrode positive) less heat goes to the work, suiting thin sheets and non-ferrous metals.
Functions of the coating (flux):
- Gives a shielding gas to protect the pool from oxygen and nitrogen.
- Forms a slag that covers the weld and slows cooling.
- Stabilises the arc (ionising elements), and adds alloying elements.
- Cleans the molten metal (deoxidises).
TIG versus MIG
| Point | TIG (GTAW) | MIG (GMAW) |
|---|---|---|
| Electrode | Non-consumable tungsten | Consumable wire fed continuously |
| Filler | Separate rod (hand fed) | The electrode wire itself |
| Shielding gas | Argon or helium | Argon, CO2, or mixture |
| Weld quality | Very clean, precise, high quality | Good, high deposition |
| Speed | Slow | Fast, easily automated |
| Skill needed | High | Moderate |
| Uses | Thin sheets, stainless steel, aluminium, magnesium, titanium | Thicker sections of steel, aluminium; production welding |
✓ Answer checked by Claude Opus 5.5 (high effort)
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