1.6 Other Welding and Cutting Processes
Key Takeaways
- Resistance welding (RSW, RSEW, FW) uses electrical resistance heat — no filler metal or gas needed
- Electroslag welding (ESW) welds thick plates in a single vertical pass with very high heat input — usually requires PWHT
- Stud welding is covered by AWS D1.1 Clause 9 and is common for shear connectors in composite construction
- Oxyfuel cutting (OFC) works only on carbon steel — not stainless, aluminum, or copper (oxide layer issues)
- Air carbon arc gouging (CAC-A) is essential for back-gouging, defect removal, and weld repair preparation
- Plasma arc cutting (PAC) cuts all metals including stainless and aluminum
1.6 Other Welding and Cutting Processes
Beyond the five major arc welding processes (SMAW, GMAW, FCAW, GTAW, SAW), the CWI exam covers several additional welding and thermal cutting processes.
Resistance Welding (RW)
Resistance welding generates heat through electrical resistance at the interface of two parts being joined. No filler metal, flux, or shielding gas is needed.
| Process | Description | Application |
|---|---|---|
| RSW (Resistance Spot Welding) | Electrodes clamp and pass current through overlapping sheets | Automotive body panels, sheet metal assemblies |
| RSEW (Resistance Seam Welding) | Rotating wheel electrodes create continuous weld seam | Fuel tanks, pipe, can manufacture |
| FW (Flash Welding) | Parts are brought together, flashed, and forged | Railroad rails, chain links, band saw blades |
| PW (Projection Welding) | Current concentrated at designed projections | Nuts/bolts to plates, cross-wire mesh |
Electroslag Welding (ESW)
- Welds thick plates (typically 1" to 12"+) in a single pass
- The arc starts, then is extinguished as slag becomes conductive and provides all heat
- Welding is performed vertically upward with copper shoes (dams) containing the weld pool
- Produces very high heat input — PWHT almost always required
- Very high deposition rates but limited to vertical butt joints in thick plate
Stud Welding (SW)
- Welds threaded or unthreaded studs to a base plate using an arc
- Two types: arc stud welding (drawn arc) and capacitor discharge (CD) stud welding
- AWS D1.1 Clause 9 covers stud welding requirements
- Common in structural steel for shear connectors (composite steel/concrete decks)
Thermal Cutting Processes
| Process | Principle | Applications |
|---|---|---|
| OFC (Oxyfuel Cutting) | Oxygen jet oxidizes preheated metal; iron oxide is blown away | Carbon steel plate cutting, beveling |
| PAC (Plasma Arc Cutting) | Constricted arc ionizes gas to create high-velocity plasma jet | All metals, stainless, aluminum, thinner carbon steel |
| CAC-A (Air Carbon Arc Gouging) | Carbon electrode melts metal; compressed air blows it away | Weld removal, back-gouging, defect removal |
Oxyfuel Cutting (OFC) — Key Details
OFC works only on metals that oxidize (primarily carbon and low-alloy steels). It does not work on stainless steel, aluminum, or copper alloys because:
- Stainless steel: chromium oxide has a higher melting point than the base metal
- Aluminum: aluminum oxide melting point (~3,700°F) is far above the base metal (~1,220°F)
OFC Requirements:
- Metal must have an ignition temperature below its melting point
- The oxide melting point must be below the metal's melting point
- The reaction must be sufficiently exothermic to sustain cutting
- Metal oxide must be fluid enough to be blown from the kerf
Air Carbon Arc Gouging (CAC-A)
This process is critically important for welding inspectors because it is the primary method for:
- Back-gouging groove welds to ensure complete joint penetration
- Removing defective welds for repair
- Preparing weld joints when mechanical methods aren't practical
CAC-A uses: carbon or graphite electrode + compressed air (80–100 psi)
For the Exam: Know that OFC only works on carbon steel (not stainless, aluminum, or copper). Know that CAC-A (air carbon arc gouging) is used for back-gouging and defect removal. Know that ESW produces very high heat input and usually requires PWHT.
Why does oxyfuel cutting (OFC) NOT work on stainless steel?
What is air carbon arc gouging (CAC-A) primarily used for in welding inspection?