The Most Common Gases Utilized in MIG Welding
In MIG (Metal Inert Gas) welding, the choice of shielding gas is crucial for achieving optimal weld quality. The most prevalent gases used include inert options like argon (Ar) and helium (He), alongside reactive gases such as oxygen (O2) and carbon dioxide (CO2). These gases are often combined to form blended shielding atmospheres tailored to specific metals and application requirements, offering a versatile approach to welding various materials.
Argon: The Versatile Inert Gas
Argon is a dense, inert gas that naturally settles over the weld pool, creating an effective barrier against atmospheric contamination. Its ease of ionization allows it to sustain stable, long-lasting arcs at lower voltage settings, making it ideal for many applications. While pure argon excels in welding non-ferrous metals such as aluminum, magnesium, titanium, copper, and nickel due to its cathodic cleaning properties via DCEP polarity, it is less suitable for steel welding where deeper penetration is desired.
Carbon Dioxide: The Economical Reactive Gas
CO2 stands out as the most economical shielding gas, often favored by hobbyists and small-scale welders. It can be used alone without blending, providing good penetration for thick steel sections, although it tends to produce more spatter and a less stable arc compared to inert gases. Pure CO2 is typically employed in short-circuit transfer modes and is ideal for high-speed, high-volume steel welding. However, it is not recommended for welding thin sheets or non-ferrous metals due to its aggressive oxidation properties.
Oxygen: Enhancing Arc Stability and Penetration
In small quantities—generally up to 9%—oxygen can be blended into argon or CO2 to improve arc stability, weld pool fluidity, and penetration depth when welding low alloy or mild steel. The addition of oxygen helps reduce arc irregularities caused by surface oxides, but it must be used cautiously, as excessive oxygen can lead to increased oxidation and defects. Importantly, oxygen should be avoided when welding non-ferrous metals like aluminum, copper, and magnesium, as it promotes undesirable oxidation reactions.
Helium: The High-Heat Inert Gas
Helium is a lighter, inert gas that produces a hotter, more energetic arc, resulting in increased penetration and faster welding speeds—particularly beneficial for thick aluminum, magnesium, or copper alloys. Because helium is more expensive and less dense than argon, it requires higher flow rates to prevent it from drifting away from the weld site. Blending helium with argon can strike a balance between cost and performance, allowing for enhanced weld quality on challenging materials.
Blended Gases and Their Applications
- 75% Argon + 25% CO2: Offers an excellent compromise between arc stability, spatter control, and deep penetration for steel welding.
- Argon with 1-3% Oxygen: Fine-tuned for smooth arc control, with 2-3% oxygen ideal for mild steel, and lower percentages suited for stainless steel to maintain corrosion resistance.
- 10% Argon + 85-90% Helium + 2-5% CO2: Commonly used for stainless steel, providing high travel speeds and superior bead quality.
- Argon with 25-75% Helium: Specifically designed for welding thick aluminum, magnesium, and other non-ferrous metals, where higher helium content yields deeper penetration.
- Argon + CO2 + O2: Suitable for low alloy steel and some stainless steel applications, balancing oxidation control with weld performance.
Choosing the Right Shielding Gas Based on Metal Type and Thickness
Steel and Stainless Steel
For carbon steel, a mixture of 75% argon and 25% CO2 delivers a balanced weld with good penetration and minimal spatter. Pure argon is less suitable due to surface oxidation issues, while pure CO2 offers maximum penetration but can cause excessive spatter and unstable arcs. When welding stainless steel, a mixture of argon with a small percentage of oxygen (up to 2%) or a specialized tri-mix (helium, argon, and CO2) provides better control, faster travel speeds, and superior weld bead appearance.
Aluminum and Non-Ferrous Metals
Pure argon or argon-helium blends are essential for aluminum welding. Helium enhances penetration and welding speed but increases globular transfer, so it should be used cautiously—preferably below 50% helium. Preheating aluminum thick sections can reduce the need for helium enrichment. For thinner sheets or delicate applications, straight argon remains the preferred choice.
Metal Thickness Considerations
Thicker metals benefit from higher heat input and consequently more energetic shielding gases like helium blends. Conversely, thin materials require lower heat input, favoring argon-rich mixtures to prevent burn-through and distortion. The selection of shielding gas should also consider the desired weld penetration, bead appearance, and process efficiency.
Cost and Practical Aspects of Shielding Gases
Acquiring and Managing Gas Tanks
When choosing a gas supply, you can opt to purchase or lease cylinders. Refillable tanks are more economical over time and come in various sizes—commonly 40, 80, and 125 cubic feet (CF). Hobbyists and occasional welders should consider smaller tanks, while professional shops benefit from larger ones to reduce refill frequency. Always verify the refill policies of your supplier, as some only refill tanks they own.
Cost Comparison and Selection
Argon is generally more expensive than CO2, but the overall cost depends on supplier pricing and tank size. For instance, refill prices range approximately from $45 to $85 per refill, varying by tank size and gas mixture. While 100% argon provides excellent weld quality, blending it with CO2 or helium can optimize costs while maintaining weld performance.
Summary Table for Shielding Gas Selection
Choosing the appropriate shielding gas hinges on the metal type, thickness, desired weld characteristics, and budget. The table below simplifies this selection process, providing quick guidance based on common welding scenarios.
Final Tips and Recommendations
Always consult with your local gas supplier before purchasing, as their refill policies and available mixtures may vary. It’s advisable to buy a tank that matches your typical usage to balance cost-efficiency and convenience. Investing in a larger tank can be more economical long-term and reduce downtime, especially for frequent welding operations.