The Comprehensive Guide to MIG Welding and CO2 Welding: A Hands-On Approach

MIG (Metal Inert Gas) welding, also known as Gas Metal Arc Welding (GMAW), is a popular welding process that uses a continuous solid wire electrode fed through a welding gun and into the joining of two base materials together. A shielding gas is also sent through the welding gun and protects the weld pool from contamination. The most common shielding gases used in MIG welding are 100% CO2, 75% Argon/25% CO2, and 98% Argon/2% Oxygen.

Understanding the Differences: MIG Welding with CO2 vs. Other Shielding Gases

When it comes to using CO2 as a shielding gas in MIG welding, it provides deeper penetration but also increases spatter and results in a rougher bead compared to 75/25 mixture. The deeper penetration is achieved due to the higher heat input of the CO2 gas, which can be beneficial for certain applications, such as welding thicker materials. However, the increased spatter and rougher bead can make the weld more difficult to clean up and may require more post-weld finishing.

It is also worth noting that MIG welders can be used with or without CO2, but when using CO2, a flux-coated or cored wire that generates the gas as it burns is required. This is because the CO2 gas does not provide the same level of shielding and protection as the 75/25 or 98/2 Argon/Oxygen mixtures.

Choosing the Right Wire for MIG Welding

mig welding and co2 weldingImage source: Mig weld example

For those who are new to MIG welding, it is recommended to use an AWS classification ER70S-3 wire for all-purpose welding and ER70S-6 wire when more deoxidizers are needed for welding on dirty or rusty steel. The wire diameter should be chosen based on the thickness of the metal being welded, with a 0.030-inch diameter being suitable for most DIY projects.

Wire Diameter Recommended Metal Thickness
0.023 inch (0.6 mm) 18 gauge (1.2 mm) to 16 gauge (1.6 mm)
0.030 inch (0.8 mm) 14 gauge (1.9 mm) to 10 gauge (3.4 mm)
0.035 inch (0.9 mm) 10 gauge (3.4 mm) to 1/4 inch (6.4 mm)
0.045 inch (1.1 mm) 1/4 inch (6.4 mm) to 3/8 inch (9.5 mm)

It’s important to note that the wire diameter should be selected based on the thickness of the metal being welded, the desired weld penetration, and the amperage output of the welding machine.

Preparing the Workpiece and Setting Up the MIG Welding Machine

When setting up the machine, it is crucial to clean the metal down to bare metal before striking an arc and ensure that the work clamp connects to clean metal. This helps to ensure a strong and consistent weld by removing any contaminants, such as rust, paint, or grease, that could interfere with the welding process.

The travel angle of the gun should be a 5 to 15 degree drop from the perpendicular position, and a slight weaving motion can help control the size, shape, and cooling effects of the weld puddle. This weaving motion can also help to create a more uniform and aesthetically pleasing weld bead.

It is also important to adjust the wire feed speed, voltage, and amperage settings on the welding machine to match the thickness of the metal being welded and the desired weld characteristics. Typically, thicker metals will require higher wire feed speeds, voltages, and amperages, while thinner metals will require lower settings.

Troubleshooting Common MIG Welding Issues

One common issue with MIG welding, especially when using CO2 as a shielding gas, is excessive spatter. This can be caused by a variety of factors, including:

  • Incorrect shielding gas flow rate
  • Improper wire feed speed
  • Incorrect voltage or amperage settings
  • Dirty or contaminated base metal

To address this issue, you can try the following:

  1. Adjust the shielding gas flow rate to the recommended range, typically between 25-35 CFH (cubic feet per hour).
  2. Ensure the wire feed speed is appropriate for the thickness of the metal being welded.
  3. Adjust the voltage and amperage settings to the recommended range for the wire diameter and metal thickness.
  4. Thoroughly clean the base metal to remove any contaminants before welding.

Another common issue is porosity, which can be caused by:

  • Insufficient shielding gas coverage
  • Contaminated base metal or filler wire
  • Incorrect gas flow rate
  • Drafts or wind disrupting the shielding gas

To address porosity, you can try the following:

  1. Increase the shielding gas flow rate and ensure the gas coverage is adequate.
  2. Thoroughly clean the base metal and filler wire to remove any contaminants.
  3. Protect the weld area from drafts or wind to maintain the shielding gas coverage.

By understanding and addressing these common issues, you can improve the quality and consistency of your MIG welds, whether using CO2 or other shielding gas mixtures.

Resources for Learning MIG Welding and CO2 Welding

For those who are just starting out with MIG welding, there are many resources available online to help learn the basics. Online welding courses, for example, provide step-by-step guidance and videos to help you learn faster. Additionally, there are many helpful videos on YouTube that cover topics such as tools to start welding, how to buy gas cylinders, and common MIG welding mistakes.

By following the guidance and techniques outlined in this comprehensive guide, you can become proficient in both MIG welding and CO2 welding, and tackle a wide range of DIY and professional projects with confidence.

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