---
title: "Arc welding: SMAW, TIG and MIG"
subject: "Workshop Technology"
chapter: 10
key: "semester_2/workshop_technology:arc-welding-smaw-tig-mig"
source: https://www.bctengineer.com/q/semester_2/workshop_technology/arc-welding-smaw-tig-mig
site: BCT Engineering
---

# Arc welding: SMAW, TIG and MIG

Workshop Technology · Chapter 10: Metal Joining Process

- Asked in: year not given, 4+4 marks
- Video: [4 Types of Welding Explained: MIG vs TIG vs Stick vs Flux Core](https://www.youtube.com/watch?v=y-OKi8oSNQ4) — TimWelds
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/workshop_technology/arc-welding-smaw-tig-mig
- Whole chapter: https://www.bctengineer.com/md/semester_2/workshop_technology/chapter-10

## Question

Explain shielded metal arc welding (SMAW) and the functions of the electrode coating. Differentiate between TIG and MIG welding.

## 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.

## Answer

#### 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.

```text
   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 |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. In SMAW, where is the arc struck?
   A. Between a tungsten electrode and a separate filler rod
   B. Between a coated consumable electrode and the work
   C. Between two copper electrodes
   D. Between wire and gas nozzle only
   Answer: B. The arc melts the electrode tip and base metal into a weld pool. (Key point: SMAW principle)

2. Which is NOT a function of the electrode coating?
   A. Gives shielding gas
   B. Forms slag that slows cooling
   C. Stabilises the arc
   D. Raises the current supplied by the machine
   Answer: D. The coating shields, forms slag, stabilises the arc, adds alloy and deoxidises; it does not raise the current. (Key point: Functions of the coating)

3. With DC straight polarity (electrode negative), what happens?
   A. More heat goes to the work, giving deeper penetration for thick plates
   B. More heat goes to the electrode, suiting thin sheets
   C. No heat reaches the work
   D. Arc cannot be struck
   Answer: A. Straight polarity puts more heat in the work; reverse polarity suits thin sheet and non-ferrous. (Key point: Polarity)

4. How do TIG and MIG differ?
   A. TIG uses consumable wire; MIG uses tungsten
   B. TIG uses a non-consumable tungsten electrode with hand-fed filler; MIG feeds consumable wire continuously
   C. Both use consumable wire
   D. TIG is fast; MIG is slow
   Answer: B. TIG is slow, precise and clean; MIG is fast and easily automated. (Key point: TIG vs MIG)

## Related in Workshop Technology

- [Temporary and permanent joints; soldering, brazing, welding](https://www.bctengineer.com/question.md?key=semester_2%2Fworkshop_technology%3Ajoints-soldering-brazing-welding-compare) — Workshop Technology, chapter 10
- [Sheet metal cutting and forming operations](https://www.bctengineer.com/question.md?key=semester_2%2Fworkshop_technology%3Asheet-metal-operations-explained) — Workshop Technology, chapter 8

## Related in other subjects

- [Gas flames, arc welding and heat input](https://www.bctengineer.com/question.md?key=semester_4%2Fmanufacturing_and_production_processes%3Aoxyacetylene-flames-smaw-heat-input-numerical) — Manufacturing and Production Processes, chapter 12