Selecting the correct GMAW (MIG) transfer mode—short‑circuiting, globular, spray, or pulsed‑spray—directly affects fusion reliability, spatter, heat input, position capability, and throughput. Mode selection depends on current/voltage, wire diameter, shielding gas composition, contact tip‑to‑work distance (CTWD), and power‑source characteristics.
High‑argon shielding (≥ ~80% Ar) is fundamental to axial spray on steels; CO₂‑rich gases shift operation toward globular or short‑circuiting at similar volt/amp settings. Pulsed‑spray uses waveform control (peak/background current) to achieve spray transfer at lower average heat input, enabling out‑of‑position work with Ar rich gases.
1) Short‑Circuiting Transfer (GMAW‑S)
Where it excels
Thin sheet/light plate, open‑root passes with gaps, and all‑position work due to a small, fast‑freezing puddle and repeated short cycles (≈20–200+ per second).
Typical settings & gases (carbon steel)
- Voltage/Current: ~16–22 V and ~80–200 A with 0.030–0.045 in (0.8–1.2 mm) wire; DCEP.
- Shielding gas: 75/25 Ar/CO₂ (C25) for a smoother arc; 100% CO₂ is common but harsher.
Equipment/setup notes
- Power source: CV. Adjust inductance to slow current rise during the short, reduces spatter and flattens the bead; too much causes stubbing.
- CTWD: keep short and consistent (≈3/8–1/2 in / 10–13 mm); longer stickout drops amperage and jeopardizes fusion.
Pros
Low heat input (limits distortion/burn‑through); strong positional control; tolerant of fit‑up gaps.
Cons / QA flags
More spatter than spray; lack‑of‑fusion risk on thicker sections when run cold, with long CTWD, or on mill scale. Not prequalified in AWS D1.1 (requires WPS/PQR); prequalified in AWS D1.3 for sheet ≤3/16 in.
2) Globular Transfer
Where it’s used
Transitional mode often seen with 100% CO₂ or low‑argon mixes on carbon steel, typically flat/horizontal. It offers penetration and low gas cost but produces large, irregular droplets.
Typical settings & gases
- Voltage/Current: Higher than short‑arc until droplets exceed wire diameter (gravity‑dominated transfer).
- Shielding gas: 100% CO₂ or Ar/CO₂ with < ~80% Ar keeps operation in globular rather than spray.
Pros
Higher deposition than short‑arc; good penetration; inexpensive gas.
Cons / QA flags
Most spatter, less stable arc, and limited positional capability; bead quality and HAZ cleanliness are typically inferior to spray.
3) Spray Transfer (Axial Spray)
Where it excels
Flat/horizontal fillets and grooves on medium‑to‑thick sections requiring high deposition and low spatter with consistent, smooth bead shape.
Gas requirement
Argon‑rich gases are mandatory for axial spray on steels; generally ≥ ~80% Ar, such as 90/10 Ar/CO₂ or 98/2 Ar/O₂; for aluminum, 100% Ar.
Typical settings & setup (ER70S‑6 steel)
- Voltage/Current: ~24–32 V and ~220–350+ A with 0.035–0.045 in wire; DCEP. CTWD: ~1/2–3/4 in (13–19 mm); too short spikes amperage/heat, too long destabilizes spray and reduces penetration.
Pros
Very low spatter, high travel speeds, and deep, finger‑like penetration (excellent for production).
Cons / QA flags
High heat input; largely limited to flat/horizontal; less suitable for thin gauges or heat‑sensitive alloys unless mitigated.
4) Pulsed‑Spray (GMAW‑P)
Where it excels
Situations needing spray‑quality fusion with lower average heat and better out‑of‑position control across carbon steel, stainless, and aluminum (manual or robotic).
Mechanism & requirements
The power source alternates peak current (detaches a single spray droplet) with background current (maintains the arc), achieving spray transfer at reduced average current and a calmer puddle; requires a pulsed‑capable inverter with waveform control. Shielding gases are Ar‑rich, as for spray.
Pros
Lower heat input and spatter than conventional spray; improved positional capability; particularly effective on aluminum and stainless.
Cons / QA flags
Higher equipment cost and parameter sensitivity; incorrect waveform or balance can yield ropey beads or cold lap.
Shielding Gas Strategy
- Ar/O₂ (1–5%) stabilizes spray and improves wetting/flat bead profiles on steels; Ar/CO₂ (5–15%) balances penetration and bead shape, but excessive CO₂ suppresses axial spray.
- Helium additions (Ar‑He or Ar‑CO₂‑He) increase arc voltage/heat flux and change droplet size/frequency; useful on thick aluminum and some steels, but they alter transfer dynamics and often require higher voltage.
Setup Levers That Strongly Influence Results
- CTWD is a production‑critical variable. At fixed wire‑feed speed, changing CTWD can swing amperage by 50+ A, shifting penetration and risking WPS violations; maintain consistent CTWD for repeatable results.
- Inductance (short‑arc) tunes current rise during the short; increasing inductance reduces spatter and flattens the bead, while excessive inductance causes stubbing.
- Travel speed influences penetration: faster travel tends to increase penetration by placing the arc at the leading edge of the pool; too slow lets droplets land on the pool and blunts penetration.
Quick Comparison (Carbon Steel, Solid Wire)
Ranges compiled from process/application sources and ER70S‑6 data sheets.
Practical Selection Guidance
- Thin sections, gap‑bridging, or all‑position: short‑circuit you must verify fusion and qualify per code as required.
- Economical CO₂ with acceptable cleanup, flat only: globular.
- High deposition and clean beads, flat/horizontal: spray with ≥80% Ar shielding.
- Spray‑quality fusion with lower heat and positional flexibility: pulsed‑spray with the correct waveform program.
Bottom line: The ACTIONABLE GUIDANCE
- Select mode to match joint, position, and heat budget.
- Thin sections, gap‑bridging, or all‑position → short‑circuit (verify fusion on thicker work).
- Flat/horizontal with planned cleanup and CO₂ economy → globular.
- High deposition, low spatter, flat/horizontal on medium‑to‑thick sections → spray with ≥~80% Ar.
- Spray‑quality fusion with lower average heat and positional flexibility → pulsed‑spray with the correct waveform.
- Lock in shielding gas first.
- Gas composition gates the transfer mode; no high‑argon, no axial spray.
- Set flow to achieve smooth coverage without turbulence.
- Standardize CTWD and teach it.
- CTWD drift is a primary cause of amperage/penetration variation at constant WFS.
- Use fixtures, nozzle/liner choices, and operator training to hold target CTWD by mode.
- Use inductance to tune short‑arc.
- Mild increases reduce spatter and improve bead shape; avoid over‑inductance.
- Start from credible windows, then optimize on coupons.
- Short‑arc with 0.035 in wire: ~18–23 V / ~80–175 A.
- Spray with 0.035–0.045 in wire: ~24–32 V / ~220–350+ A in Ar‑rich gas.
- Confirm travel speed and bead profile before releasing to production.
- Align procedures with code expectations.
- Short‑circuit on structural plate commonly requires WPS/PQR qualification.
- Spray/pulsed with solid wire may be prequalified when all prequalified conditions are satisfied (joint details, gas, filler, positions).
- Embed QA/QC in daily practice.
- For short‑arc on thicker work, prioritize joint cleanliness, fit‑up, and macro‑checks during setup.
- Monitor gas composition and flow, CTWD, and arc stability—the three levers most likely to drift and drive rework.
- Leverage pulsed‑spray for automation and mixed‑position production.
- Pulsed programs lower average heat and spatter, improve first‑pass yield, and expand positional capability in robotic cells.
Operational takeaway: choose the transfer mode for the position, thickness, and quality targets; set the gas to unlock that mode; standardize CTWD and (for short‑arc) inductance; launch from proven parameter windows; align with code requirements; validate on coupons—then scale to production.