Welding processes for the CWI exam: SMAW to SAW

The two questions that sort every process

Ask these about any process:

1. How does filler get into the joint? Through a hand-fed stick, a wire pushed by a feeder, a separate rod, or a wire buried under a blanket of flux.
2. What protects the pool? A slag from a flux covering, a shielding gas, or both.

Once those two are fixed, the strengths, limits and typical flaws follow. A process that depends on gas is sensitive to wind. A process that makes slag needs cleaning between passes, and trapped slag is a possible flaw. A process that feeds wire automatically deposits faster than one that needs you to stop and change electrodes.

The five processes in plain words

SMAW (shielded metal arc welding, "stick"). A flux-covered electrode is consumed as you weld. The covering burns to make a gas shield and a slag. It's portable, needs no gas bottle and works outdoors and out of position, which is why it's common in field repair. Speed is limited because you stop to change electrodes. Some electrode types, the low-hydrogen ones, pick up moisture from the air and need controlled storage. Expect questions on that.

GMAW (gas metal arc welding, "MIG"). A solid wire feeds continuously and an external gas protects the pool. It's fast, clean and easy to learn, and it's semi-automatic: the machine feeds the wire and the welder controls travel. The gas shield is easily blown away, so drafts cause porosity. Some ways of running it put in little heat, which can leave lack of fusion on thick sections.

FCAW (flux cored arc welding). The wire is a hollow tube filled with flux. It comes in two flavors: self-shielded, where the core makes its own protection, and gas-shielded, where an external gas does part of the job. It deposits a lot of metal, works well in the field and makes slag you must remove. The self-shielded version suits wind. Both make plenty of fume.

GTAW (gas tungsten arc welding, "TIG"). A tungsten electrode that doesn't melt makes the arc, an inert gas protects the pool and filler is added by hand as a separate rod when needed. You get precise control and very clean welds on thin and critical material, including stainless steel and aluminum. It's slow and demands skill. A typical flaw is a tungsten inclusion if the electrode touches the pool.

SAW (submerged arc welding). A bare wire feeds into a mound of granular flux that buries the arc. Nothing is visible while you weld. It deposits metal very fast with deep penetration, which suits thick plate and long straight seams in the shop, mostly flat or horizontal. It's usually mechanized. Unfused flux is recycled and the slag has to come off.

Side-by-side comparison

This table is our summary for study. Your course notes and your own reading of AWS's published exam outline should confirm the exact list of processes in scope.

Which discontinuities belong to which process

Part A likes to connect a flaw to its likely cause. Start from the shielding and the filler:

• Porosity points to shielding trouble in gas-protected processes (a draft, a clogged nozzle, a dirty joint) or to moisture and contamination in any of them.
• Slag inclusions can only come from processes that make slag: SMAW, FCAW, SAW.
• Tungsten inclusions belong to GTAW alone.
• Lack of fusion shows up where heat input or technique is too low to melt the joint faces, a known risk in some GMAW setups.
• Hydrogen cracking ties to hydrogen sources such as damp low-hydrogen electrodes and to hard, restrained joints. The full chain from heat-affected zone to preheat is in welding metallurgy for the CWI exam.

For the definitions and appearance of each flaw, read weld discontinuities explained. To see which NDE method finds each one, use the NDE methods guide.

How Part A asks about processes

Part A is closed book, 165 questions in 135 minutes, so you can't look anything up. Process questions tend to take three shapes:

• Identify: a description of the filler and shielding, and you name the process.
• Select: a job (thin stainless tube, outdoor structural repair, thick plate seams) and you pick the best fit.
• Troubleshoot: a flaw and a likely cause, and you pick the process or the fix.

Heat input questions pair with the process material. The CWI math calculator works heat input step by step, so practice it alongside the process notes. For the whole exam layout, see the Part A guide.

Turn the table into memory

Rewrite the comparison table from memory once a day for a week. Then invent three jobs and decide which process fits and why. To test yourself on drawings, take the welding process quiz: 20 explained questions on naming each process, the GMAW transfer modes, polarity and the flaws each process leaves. Where you hesitate is where you study next. The free 10-question Part A check is scored by area and shows exactly which topics to study first, so you can take it here and see whether processes are a strength or a gap.

FAQ

What's the difference between SMAW and GMAW?

SMAW uses a flux-covered stick that makes its own shielding and slag, so it needs no gas and handles wind and field work. GMAW feeds a solid wire continuously under an external shielding gas, which is faster and cleaner but sensitive to drafts.

Which process is best for thin metal?

GTAW gives the finest control of heat and puddle, so it's the usual pick for thin and critical material. GMAW can also work on thin sections with the right settings and is much faster.

What does shielding gas do?

It keeps oxygen, nitrogen and moisture in the air away from the molten pool, where they would cause porosity and a weaker weld. Some gases also change arc behavior and penetration.

Which processes are semi-automatic?

GMAW and FCAW. The machine feeds wire continuously and the welder controls the gun position and travel. SAW is usually fully mechanized.