Welding Processes and Variables
Welding Processes and Variables
Candidates must understand the common arc welding processes used in Canada, especially shielded metal arc welding (SMAW), gas metal arc welding (GMAW), flux-cored arc welding (FCAW), gas tungsten arc welding (GTAW), and submerged arc welding (SAW). For each process, know the essential variables that affect weld quality: current type and polarity, amperage, voltage, travel speed, electrode angle, shielding gas composition and flow rate, and electrode classification. In SMAW, electrode type (e.g., E4310 vs. E7018) dictates storage and re-drying requirements; low-hydrogen electrodes must be kept in holding ovens. In GMAW, the transfer mode (short-circuit, globular, spray) depends on current density, gas, and wire diameter. FCAW uses either self-shielded or gas-shielded wires, each with distinct parameter windows. SAW requires granular flux and is typically used for straight seams.
A common trap is confusing welding variables with procedure qualification variables. For example, changing from DCEN to DCEP in GMAW is a change in current type, which may require requalification. Another trap is misidentifying the effect of electrode angle or travel speed on penetration and bead shape. Remember that increasing travel speed too much can cause undercut, while too slow can cause excessive reinforcement. Also, shielding gas flow rates that are too high can cause turbulence and porosity.
Worked example: A welder using SMAW with E7018 on DCEN (electrode negative) experiences arc blow. The solution is to switch to DCEP (electrode positive) or use a shorter arc. However, switching polarity is a change to an essential variable in many WPSs, so the WPS must be checked. If the WPS specifies DCEP only, the welder cannot simply switch to DCEN without a new WPS.
Rule of thumb: For SMAW, electrode positive (DCEP) provides deeper penetration, while electrode negative (DCEN) gives faster deposition but shallower penetration. Always verify polarity against the WPS.