Level 4 welding moves you from the stick electrode to wire-fed and tungsten arcs. These notes follow the two Level 4 units and the industrial attachment, so you can check what you know before your CDACC assessment.
Units and hours
| Unit | Hours | What you must be able to do |
|---|---|---|
| Metal Inert Gas Welding | 200 | Draft working drawings, MIG/MAG weld plates and pipes up to 10 mm in the flat, horizontal and vertical positions, and maintain the MIG set. |
| Tungsten Inert Gas Welding | 200 | Read and draft weld symbols, assembly drawings and procedures, TIG weld steel, stainless, aluminium and copper alloys, and maintain the TIG set. |
| Industrial Training | 320 | Work under a workplace mentor, keep a logbook and portfolio, and meet every critical item in the mentoring tool. |
Key notes by unit
Metal Inert Gas Welding
- A MIG set is constant voltage: you set the voltage, and the wire feed speed sets the current.
- Pure CO2 digs deep but cannot give true spray; an argon-rich mix such as M21 gives a smoother arc and spray at high current.
- Short-circuit transfer suits thin sheet and vertical work; spray suits thicker plate in the flat position.
- Keep stick-out steady, about 10–15 mm for short circuit. Too long a stick-out lowers the current and invites lack of fusion.
- Check a frame for square by comparing its diagonals, tack in a balanced order and avoid over-welding.
Tungsten Inert Gas Welding
- A TIG set is constant current. Use DCEN for steel, stainless and copper alloys, and AC for aluminium so the reverse half-cycle breaks up the oxide.
- ISO 6848 tungsten colours: grey ceriated, gold or blue lanthanated, red thoriated, green pure. Thoriated dust is slightly radioactive.
- Stainless pipe needs an argon back purge. Silver to light straw tint means good cover; dark blue to grey means it failed.
- Do not use ER4043 on high-magnesium 5000-series aluminium; ER5356 is the usual choice there.
- A WPS sets the ranges you must stay inside. A run can fail on current or travel speed even when its heat input looks fine.
Industrial Training
- Agree your training plan with the workplace mentor in the first week.
- Fill the logbook daily and get it signed weekly.
- Build the portfolio as you go: drawings, weld records, test results and maintenance reports.
- Every critical item must be met to be found competent.
Practice questions
1. On a MIG set, which control mainly sets the current?
Answer: The wire feed speed.
2. Why can 100% CO2 not give true spray transfer?
Answer: It gives globular, spattery transfer at high current; an argon-rich mix such as M21 is needed for spray.
3. A trainee holds 25 mm stick-out instead of about 12 mm. What happens?
Answer: The current drops, the bead runs cold and narrow, fusion suffers and gas cover gets worse.
4. Find the arc energy for a MAG run at 22 V, 180 A and 300 mm/min.
Answer: E = 22 × 180 × 60 ÷ (1,000 × 300) = 0.79 kJ/mm, before the process efficiency factor.
5. Which polarity is used for TIG on stainless, and why?
Answer: DCEN: about 70 percent of the heat goes into the work and the tungsten stays sharp.
6. Why is AC used for TIG on aluminium?
Answer: The electrode-positive half-cycle cleans off the oxide; the electrode-negative half supplies most of the heat.
7. What is a red-banded tungsten and what care does it need?
Answer: 2% thoriated (WT20). Grind it on a dedicated grinder with extraction, or use a ceriated or lanthanated type instead.
8. The root of a stainless milk-line weld is dark grey and crusty. Why?
Answer: The back purge was missing or poor (sugaring). Cut out and reweld with a proper purge.
9. A frame’s diagonals measure 2,236 mm and 2,241 mm, with a 2 mm limit. Is it square?
Answer: No. The 5 mm difference exceeds the limit.
10. Using about 1 s of post-flow per 10 A, how long is post-flow at 120 A?
Answer: About 12 seconds, unless the WPS or manual says otherwise.
Common mistakes in the assessment
- Neglecting drawings, which carry a large share of the marks in both units.
- Mixing up arrow side and other side between the ISO 2553 and AWS systems.
- Welding before checking gas flow, polarity and drive rolls.
- Grinding a tungsten across the point instead of along it, so the arc wanders.
- Leaving out the maintenance record.
Safety essentials
- Match the filter shade to the current: about 10 at low MIG current, up to 12–13 at high current.
- Use extraction always, especially on stainless and galvanised steel.
- Argon is heavier than air and gives no warning: never use it in tanks or pits without ventilation and an oxygen check.
- Clamp the earth on the job, close to the weld.
- Get a hot-work permit and clear flammables outside the booth.
Get the full guide
The Welding Level 4 Study Guide covers every learning outcome with illustrated chapters, costings, practical tasks and mock assessments. Start with the free sample PDF.
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