Shielding gases by process
Summary
Section titled “Summary”In gas-shielded arc welding processes (GMAW and GTAW) typical flow rates range from 5 to 25 L/min (0.18 to 0.88 cfm), depending on the base material, gas mixture, and welding position. Shielding gases serve to displace oxygen and water vapor from the fusion zone, preventing oxidation, porosity, and excessive spatter. They are classified as inert —argon (Ar) and helium (He)— and active —carbon dioxide (CO₂), oxygen (O₂), nitrogen (N₂), and hydrogen (H₂)— the latter used only in GMAW on ferrous metals. The correct choice of gas determines penetration, arc stability, welding speed, and mechanical properties of the weld bead.
Operating Parameters
Section titled “Operating Parameters”| Process | Material thickness (mm / in) | Typical mixture | Flow rate (L/min / cfm) | Transfer mode |
|---|---|---|---|---|
| MIG (GMAW) | 0.5–6.3 mm / 0.020–0.250 in | Ar 75% + CO₂ 25% | 12–18 L/min / 0.42–0.64 cfm | Short circuit, spray |
| MAG (GMAW) | 1.0–12.0 mm / 0.039–0.472 in | CO₂ 100% | 10–15 L/min / 0.35–0.53 cfm | Short circuit, globular |
| TIG (GTAW) | 0.125–6.0 mm / 0.005–0.236 in | Ar 100% | 6–12 L/min / 0.21–0.42 cfm | Pulsed arc, continuous |
| MIG aluminum | 1.5–8.0 mm / 0.059–0.315 in | Ar 100% or Ar+He 50% | 15–25 L/min / 0.53–0.88 cfm | Pulsed spray |
| TIG aluminum | 0.5–6.0 mm / 0.020–0.236 in | Ar 100% | 8–14 L/min / 0.28–0.49 cfm | AC/DC |
Applicable Materials
Section titled “Applicable Materials”| Base material | Recommended GMAW gas | Recommended GTAW gas | Observations |
|---|---|---|---|
| Carbon steel | Ar+CO₂ (90/10 to 75/25), pure CO₂ | Pure Ar, Ar+He (75/25) | Pure CO₂ gives greater penetration but more spatter |
| Stainless steel | Ar+O₂ (98/2), Ar+CO₂ (98/2), tri‑mix (Ar+He+CO₂) | Pure Ar, Ar+H₂ (95/5) | H₂ only in austenitic TIG; improves fluidity |
| Aluminum and alloys | Pure Ar, Ar+He (75/25 to 50/50) | Pure Ar, Ar+He | Higher flow rates due to low density of helium |
| Copper and alloys | Pure Ar, Ar+He | Pure Ar, Ar+He | Helium to compensate for high thermal conductivity |
| Magnesium and alloys | Pure Ar | Pure Ar | Strictly inert gas; no active components |
| Low-alloy steels | Ar+CO₂ (90/10 to 80/20) | Pure Ar | Control of diffusible hydrogen |
| Dissimilar materials | Specific mixture according to combination | Pure Ar or Ar+He | Possible with TIG; with GMAW use compatible consumable |
Parameters by Material
Section titled “Parameters by Material”Carbon Steel – GMAW (MIG/MAG)
Section titled “Carbon Steel – GMAW (MIG/MAG)”| Mixture | Typical flow rate (L/min / cfm) | Penetration | Arc stability | Spatter |
|---|---|---|---|---|
| CO₂ 100% | 10–15 L/min / 0.35–0.53 cfm | High (+25%) | Low | Abundant |
| Ar 75% + CO₂ 25% | 12–18 L/min / 0.42–0.64 cfm | Medium | High | Moderate |
| Ar 90% + CO₂ 10% | 12–18 L/min / 0.42–0.64 cfm | Medium | Very high | Few |
| Ar 98% + O₂ 2% | 12–16 L/min / 0.42–0.57 cfm | Low | Excellent | Minimal |
Stainless Steel – GTAW (TIG)
Section titled “Stainless Steel – GTAW (TIG)”| Mixture | Typical flow rate (L/min / cfm) | Penetration | Surface finish | Porosity risk |
|---|---|---|---|---|
| Ar 100% | 6–10 L/min / 0.21–0.35 cfm | Medium | Good | Low |
| Ar 95% + H₂ 5% | 7–10 L/min / 0.25–0.35 cfm | High | Excellent | Very low |
| Ar 75% + He 25% | 8–12 L/min / 0.28–0.42 cfm | High | Very good | Low |
Aluminum – GMAW and GTAW
Section titled “Aluminum – GMAW and GTAW”| Process | Mixture | Typical flow rate (L/min / cfm) | Advantages | Application |
|---|---|---|---|---|
| MIG | Ar 100% | 15–22 L/min / 0.53–0.78 cfm | Smooth arc, good surface cleaning | Thicknesses < 3 mm / 0.12 in |
| MIG | Ar 50% + He 50% | 18–25 L/min / 0.64–0.88 cfm | Greater penetration, more fluid weld pool | Thicknesses > 3 mm / 0.12 in |
| TIG | Ar 100% | 8–12 L/min / 0.28–0.42 cfm | Bright finish, narrow bead | General use |
| TIG | Ar 70% + He 30% | 10–14 L/min / 0.35–0.49 cfm | Better wetting, deep penetration | Thick parts, heat sinks |
Advantages and Limitations
Section titled “Advantages and Limitations”| Mixture | Advantages | Limitations |
|---|---|---|
| Ar 100% (GTAW) | Smooth arc, easy ignition, heavy gas protects with low flow rate (6–12 L/min / 0.21–0.42 cfm) | Low penetration in high thermal conductivity materials |
| He 100% (GTAW) | High arc energy (ionization at higher voltage), penetration 40–60% greater than argon | Light gas, requires 2–3 times higher flow (15–25 L/min / 0.53–0.88 cfm) and is more expensive |
| Ar/CO₂ 75/25 (GMAW) | Good balance of penetration and stability, generates few spatter with spray transfer | Not suitable for non-ferrous materials |
| CO₂ 100% (GMAW) | Maximum penetration, low cost | Unstable arc, heavy spatter, high surface oxidation |
| Ar/O₂ 98/2 (GMAW) | Excellent stability and wetting, ideal for stainless steel | Do not use on aluminum or titanium |
| Tri-mix (Ar/He/CO₂) | Hot arc, uniform penetration, good fluidity in stainless steels | High cost, supply complexity |
Selection Guide
Section titled “Selection Guide”- GMAW process on carbon steel: Select Ar/CO₂ 75/25 for general use with good appearance and low spatter. If deep penetration and economy are priorities, use pure CO₂ (10–15 L/min / 0.35–0.53 cfm).
- GMAW process on stainless steel: Ar/O₂ 98/2 or Ar/CO₂ 90/10 for spray transfer; for thicknesses greater than 5 mm / 0.20 in consider tri-mix Ar/He/CO₂ with 5-10% helium.
- GTAW process on stainless steel: Pure Ar (6–10 L/min / 0.21–0.35 cfm) for standard work; add up to 5% H₂ in austenitic for improved fluidity and penetration.
- Aluminum GMAW: Thicknesses < 3 mm / 0.12 in → Ar 100% (15–20 L/min / 0.53–0.71 cfm); thicknesses > 3 mm / 0.12 in → Ar+He 50/50 (18–25 L/min / 0.64–0.88 cfm).
- Aluminum GTAW: Ar 100% (8–12 L/min / 0.28–0.42 cfm) sufficient in most cases; use Ar 70/He 30 for wider beads and extra penetration.
- Dissimilar materials: TIG with pure Ar or Ar/He (70/30) is the most versatile option; GMAW only if the metallurgical combination is favorable with the proper filler metal.
- Always verify gas purity: Ar ≥ 99.995%, He ≥ 99.996%, CO₂ ≥ 99.8%.
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What gas flow rate is recommended for MIG welding of carbon steel with 75% Ar / 25% CO₂ mixture?
Section titled “What gas flow rate is recommended for MIG welding of carbon steel with 75% Ar / 25% CO₂ mixture?”For carbon steel with solid wire and 75/25 mixture, a flow rate of 12 to 18 L/min (0.42–0.64 cfm) is recommended, adjusting within that range according to welding position and wind speed in the environment.
Can pure CO₂ be used in TIG welding?
Section titled “Can pure CO₂ be used in TIG welding?”No. In TIG, the tungsten electrode requires a strictly inert gas; any presence of CO₂ causes immediate oxidation. Argon must have a minimum purity of 99.995% (grade 4.5) to ensure arc stability.
Which gas provides the greatest penetration in MIG on steel?
Section titled “Which gas provides the greatest penetration in MIG on steel?”Pure CO₂ produces up to 30% greater penetration than the 75/25 Ar/CO₂ mixture, although at the cost of a more unstable arc and more spatter.
What shielding mixture is recommended for welding aluminum with MIG?
Section titled “What shielding mixture is recommended for welding aluminum with MIG?”For aluminum with MIG, pure argon or a mixture of argon with 25–50% helium is used, with a flow rate of 15–25 L/min (0.53–0.88 cfm) to ensure effective coverage and prevent oxidation.
What is the minimum thickness that can be welded with TIG?
Section titled “What is the minimum thickness that can be welded with TIG?”The TIG process can weld thicknesses from 0.125 mm (0.005 in), making it the preferred choice for very thin sheets and high-precision applications.
Why are small amounts of O₂ or CO₂ added to argon in GMAW?
Section titled “Why are small amounts of O₂ or CO₂ added to argon in GMAW?”The addition of 2–5% O₂ or 5–25% CO₂ to argon improves arc stability, reduces surface tension of the molten pool, and increases wetting. These mixtures are typically used with flow rates of 12–18 L/min (0.42–0.64 cfm).
References
Section titled “References”- engineeringtoolbox.com: https://www.engineeringtoolbox.com/gas-mixture-properties-d_586.html
- efunda.com: https://www.efunda.com/processes/metal_processing/welding_inertgas.cfm