While welding process selection is crucial, even the most skilled techniques cannot compensate for an improper power source. This article demystifies welding power sources to help professionals match equipment with specific welding processes for optimal results.

Choosing a welding process primarily depends on weld characteristics, material types, shapes and thicknesses, and joint design. Production requirements—including welding speed and quality—must also be considered. Only after establishing the welding process should power sources and auxiliary equipment be selected. The welding process remains the primary factor in power source selection.

This guide focuses on power source selection for welding technologies that have matured over the past decade. Once considered specialized or limited to mass production, these methods now appear across virtually every metal fabrication sector. The growing manufacturing of previously difficult-to-weld metals, coupled with the economic and quality advantages of advanced processes, has made these technologies accessible even to small-scale metal fabrication shops.

These processes demand more complex power and control requirements than conventional shielded metal arc welding (SMAW). Since most metallurgists and welding engineers aren't electrical specialists, selecting appropriate power sources can prove challenging. This examination of power requirements for production welding processes aims to clarify these technical considerations.

Two fundamental power source types dominate welding applications: constant current (CC) and constant voltage (CV) systems, each suited to specific processes and applications.

• Constant Current (CC) Power Sources: Often called "drooper" machines due to their voltage drop as welding current increases, creating a characteristic drooping volt-ampere output curve.
  • When powered but not arcing (with no current flow), they maintain relatively high open-circuit voltage, typically 70-80 volts. Welding generally occurs on the steeper portion of the curve, making these ideal for manual electrode welding.
  • Arc voltage depends on the physical length between electrode and workpiece—impossible to maintain perfectly constant in manual welding. However, since current determines filler metal melting rate, consistent current ensures stable melting.
  • Variations exist based on power input (single-phase or three-phase), output (AC, DC, or AC/DC), and output control type (mechanical or electrical).
• Constant Voltage (CV) Power Sources: Current can range from zero to extremely high short-circuit levels at any voltage setting. Designed specifically for gas metal arc welding (GMAW), these machines generally aren't suitable for shielded metal arc welding.
  • No welding machine provides truly constant voltage—practical units show at least 1-volt drop per 100 amps output. Short-circuit currents may reach thousands of amperes.
  • CV machines typically feature lower open-circuit voltage (maximum 50 volts) compared to CC machines (80 volts). Operators set open-circuit voltage rather than current, with typical ranges from 10 to 48 volts.
  • Welding current self-adjusts during short-circuiting to maintain arc length at the set voltage, with electrode feed rate determining current magnitude.

All welding machines carry duty cycle ratings—a frequently misunderstood but critical specification. Based on a ten-minute period, a 100% duty cycle rating means the power source can operate continuously at or below its rated current. A 60% duty cycle doesn't indicate indefinite operation at 60% capacity, but rather six minutes of operation at rated current and voltage per ten-minute cycle, requiring four minutes of idle cooling time. Machines with sub-100% duty cycles can operate continuously by reducing current output.

Key advanced welding processes and their power requirements include:

• Gas Tungsten Arc Welding (GTAW/TIG): While not new, TIG welding merits inclusion for its effectiveness with challenging materials—including stainless steel, aluminum, magnesium, copper, beryllium copper, Hastelloy, Inconel, Invar, and Kovar—particularly in thin cross-sections.
  • TIG requires power sources similar to SMAW—those with drooping volt-ampere curves. However, process-specific considerations make dedicated machines preferable.
  • Standard AC power sources not designed for TIG require derating for AC TIG service due to partial rectification introducing DC components that can overheat transformers. Additional TIG-specific challenges include arc initiation, stability, and precise variable control for delicate work.
• Gas Metal Arc Welding (GMAW/MIG): GMAW's continuous wire feed has replaced tungsten inert gas (TIG) and SMAW in many applications primarily due to speed—often multiple times faster than alternative processes.
  • Additional advantages include cleaner welds (reduced oxide formation from shielding gas), minimized electrode waste, superior metallurgical properties, and operational simplicity improving quality consistency while reducing human variables.
• Arc Spot Welding: Gaining popularity for single-sided spot welding capability and rapid, repeatable production of multiple spot welds.
  • Performed via TIG or GMAW processes. TIG spot welding uses standard TIG power sources but requires specialized spot welding guns and controls, typically fusing base materials without filler wire—common for cold-rolled steel and stainless steel.
  • GMAW spot welding employs high currents (500-750 amps) with smaller diameter wires, requiring higher-voltage machines and specialized wire feeders and control units.
• Plasma Arc Welding: An extension of plasma cutting technology, sharing similarities with TIG but offering advantages over electron beam, laser, and ultrasonic welding regarding limitations and initial cost.
  • Like TIG, plasma welding typically fuses materials (though cold filler wire may be used). Water-cooled thoriated tungsten electrodes withstand extreme temperatures from focused plasma flames capable of deep, narrow penetration.