1.6 Other Welding, Cutting Processes, and Process Variables

Beyond the Five Arc Processes

The CWI exam also covers oxyfuel, brazing/soldering, resistance, electroslag, stud welding, thermal cutting, and the process variables that tie them all together.

Oxyfuel Welding and Cutting (OFW / OFC)

Oxyfuel burns a fuel gas (usually acetylene) with oxygen to weld or cut. A neutral oxy-acetylene flame reaches about 5,600–6,300°F (≈3,100–3,480°C). The flame setting is exam-tested:

Oxyfuel cutting (OFC) does not melt steel — it oxidizes (burns) preheated metal and blows the iron-oxide slag out of the kerf. It works only on metals that oxidize readily, i.e., carbon and low-alloy steels. It will not cut stainless, aluminum, or copper because their oxides melt higher than the base metal (chromium oxide on stainless; Al₂O₃ at ~3,700°F vs. aluminum at ~1,220°F), so the reaction self-extinguishes. OFC requires: ignition temperature below melting point, oxide melting point below base-metal melting point, an exothermic reaction, and fluid slag.

Brazing and Soldering

Both join metal without melting the base metal, using a filler that wets the joint by capillary action. The dividing line is 840°F (450°C): brazing uses filler that melts above 840°F; soldering uses filler that melts below 840°F. Both rely on flux to clean oxides and proper joint clearance (typ. 006") for capillary flow. Because the base metal never melts, brazed and soldered joints are inspected differently from fusion welds — the inspector looks for full capillary fill, wetting, and the absence of voids rather than fusion-line indications.

Common brazing fillers include silver (BAg), copper-phosphorus (BCuP, self-fluxing on copper), and brass (RBCuZn); common solders are tin-based alloys. A frequent exam distinction: braze welding deposits filler into a groove or fillet like fusion welding (no capillary action) yet still keeps the base metal below its melting point — it is not the same as capillary brazing.

Other Processes and Thermal Cutting

ESW and CAC-A matter most to inspectors: ESW's extreme heat input drives grain growth and usually mandates PWHT; CAC-A is the primary method for back-gouging a groove root and for removing defective welds before repair. One CAC-A caution the CWI enforces: gouging leaves a carbon-enriched, hardened layer on the cut surface, so the groove must be ground clean before rewelding to avoid carbon pickup and cracking.

Choosing a Process — Comparative Summary

The inspector is often asked why a given process was specified. The quick mental map below ties the chapter together:

Each choice trades deposition rate, position capability, portability, and quality against one another — exactly the factors a WPS balances.

Process Variables and Heat Input

The three master arc variables are current (amperage), arc voltage, and travel speed:

• Current drives penetration and deposition — raise it for deeper, hotter welds.
• Voltage controls arc length and bead width — higher voltage widens and flattens the bead.
• Travel speed is inversely related to heat — faster travel = less heat per inch, narrower bead, but too fast causes undercut/incomplete fusion.

These combine in the heat input formula that WPSs and codes (e.g., AWS D1.1) limit to control HAZ properties:

Heat Input (J/in) = (Volts × Amps × 60) ÷ Travel Speed (in/min)

The 60 converts seconds to minutes so the answer comes out in joules per inch (divide by 1,000 for kJ/in). Worked example: a weld run at 26 V, 200 A, traveling 10 ipm:

Heat Input = (26 × 200 × 60) ÷ 10 = 312,000 ÷ 10 = 31,200 J/in = 31.2 kJ/in

If travel speed doubles to 20 ipm at the same volts and amps, heat input halves to 15.6 kJ/in — faster travel cools the joint, raising the cooling rate and hardness in the HAZ. This inverse relationship is a favorite Part A calculation.

Exam trap: OFC cuts carbon steel only, not stainless/aluminum/copper; PAC cuts all metals; CAC-A is for back-gouging and defect removal; the brazing/soldering line is 840°F.