Can You Mig Weld With Carbon Dioxide – And Should You?
Technically, yes, you can MIG weld using pure carbon dioxide (CO2) as a shielding gas, but it’s generally not recommended for most DIY applications and will likely result in a less-than-ideal weld.
While CO2 is cheap and readily available, it creates a deep, erratic arc, excessive spatter, and a wider heat-affected zone, making it unsuitable for many materials and projects where precision and weld quality are important.
Alright, let’s talk about MIG welding and shielding gases. You’ve probably seen those cylinders hooked up to your MIG welder, and maybe you’ve wondered about the different gas options. Specifically, the question often comes up: can you MIG weld with carbon dioxide? It’s a common query, especially for folks just getting their feet wet in metal fabrication or those looking for the most budget-friendly approach.
As a fellow DIYer who’s spent countless hours in the workshop, I understand the drive to explore every possibility, especially when it comes to saving a few bucks or making do with what you have. It’s tempting to think that any gas will do the job.
But here at The Jim BoSlice Workshop, we’re all about doing things right, safely, and with the best possible results. So, let’s dive deep into whether MIG welding with carbon dioxide is a viable option, what the consequences are, and what you should be considering for your projects.
The Role of Shielding Gas in MIG Welding
Before we get to the specifics of CO2, it’s crucial to understand why we use shielding gas in the first place during Metal Inert Gas (MIG) welding. Your MIG welder uses a continuously feeding wire electrode that also acts as the filler metal. As this wire melts, it forms the weld puddle.
The problem is, the atmosphere around us is full of oxygen and nitrogen. If these elements come into contact with your super-hot, molten metal, they can cause serious contamination. This contamination leads to brittle welds, porosity (tiny holes in the weld), and a generally weak joint.
The shielding gas, flowing from the welding gun, creates a protective bubble around the arc and the molten weld pool. This bubble displaces the atmospheric contaminants, allowing the molten metal to cool and solidify cleanly, forming a strong, sound weld.
Can You MIG Weld With Carbon Dioxide? The Technical Answer
So, to answer the primary question directly: can you MIG weld with carbon dioxide? Yes, your MIG welder can technically operate with pure CO2 as the shielding gas. The gas will flow, and you will be able to create a weld.
Many entry-level MIG welders, especially those designed for thinner materials like sheet metal found in automotive repair or hobbyist projects, are often advertised as “gas or gasless” and are compatible with pure CO2. It’s a readily available and inexpensive gas, which makes it appealing.
However, and this is a big “however,” the results you’ll get are far from ideal for most applications. Pure CO2 is not an inert gas; it’s an active or semi-inert gas. This means it actually participates in the welding process, and not in a good way.
The Consequences of Using Pure CO2 for MIG Welding
When you use pure carbon dioxide for MIG welding, you’re going to encounter several significant drawbacks that will affect your weld quality, your welding experience, and potentially the integrity of your project.
1. The Arc Characteristics: Erratic and Unstable
Pure CO2 creates what’s known as a “spray transfer” mode, but it’s a very aggressive and unstable version of it. The arc will be wide, spattery, and difficult to control.
Instead of a smooth, focused arc that melts the wire and base metal precisely, you’ll get a much broader, more turbulent arc. This makes it challenging to maintain a consistent weld puddle and can lead to poor bead appearance.
2. Excessive Spatter: A Messy Process
This is one of the most immediate and noticeable issues. Pure CO2 welding is notorious for producing an incredible amount of spatter. These are molten metal droplets that fly off the arc and stick to your workpiece, your welding machine, and everything nearby.
Cleaning up this spatter is a time-consuming and frustrating task. It can also embed itself into the weld, which is a form of contamination and weakens the joint. You’ll find yourself using anti-spatter spray and wire brushes far more often than you’d like.
3. Deeper Penetration and Wider Heat-Affected Zone (HAZ)
Because CO2 is an active gas, it causes the molten metal to become more fluid. This leads to deeper penetration into the base metal than you might get with inert gases. While deeper penetration can sometimes be desirable, with pure CO2, it’s often uncontrolled and can burn through thinner materials easily.
Furthermore, the aggressive arc and increased fluidity result in a much wider heat-affected zone (HAZ). This is the area of the base metal surrounding the weld that has been altered by heat. A wider HAZ can change the metal’s properties, making it softer, weaker, or more brittle, especially in alloys like certain steels.
4. Porosity and Weld Defects
Despite the deep penetration, pure CO2 welding is also prone to porosity. The active nature of the gas can lead to the absorption of oxygen and carbon into the molten weld pool. As the weld cools, these elements can be released, forming tiny gas pockets (pores) within the solidified metal.
Porosity is a major cause of weld weakness. It creates stress concentration points, making the weld susceptible to cracking under load. You might see a visually acceptable weld, but it could be riddled with internal defects.
5. Limited Material Compatibility
Pure CO2 is generally only suitable for welding mild steel, and even then, it’s not the preferred choice for quality results. It is absolutely not recommended for welding stainless steel or aluminum.
For stainless steel, using CO2 will lead to severe chromium depletion, resulting in a loss of corrosion resistance and a discolored, brittle weld. For aluminum, it’s a non-starter; you need a truly inert gas like Argon for aluminum welding.
When Might Pure CO2 Be Considered?
Given all these downsides, are there any situations where MIG welding with pure CO2 makes sense?
For the average DIYer working on projects that require even a moderate level of weld quality, the answer is almost always no. However, there are niche applications where its cheapness and availability might lead some to use it:
- Very Thin Sheet Metal Repairs: For quick, cosmetic repairs on thin mild steel where strength and appearance are secondary, and the primary goal is simply to hold pieces together. Think of very basic automotive body panel tacking where appearance isn’t paramount.
- Low-Stress Applications: If you’re welding something that will experience virtually no structural load and appearance is not a concern.
- Budget Constraints: In situations where cost is the absolute primary driver and the limitations are understood and accepted.
Even in these cases, the extra effort in cleanup and the potential for weaker welds often outweigh the initial cost savings.
Better Shielding Gas Options for MIG Welding
If you’re looking to get good results with your MIG welder, you’ll want to move beyond pure CO2. The most common and effective shielding gases for MIG welding are Argon and its mixtures with other gases like CO2 and Oxygen.
1. Pure Argon (100% Ar)
Argon is a truly inert gas, meaning it doesn’t react with the molten metal. This results in a stable arc, minimal spatter, and clean welds.
- Pros: Excellent for aluminum and magnesium. Good for thin stainless steel and some exotic metals. Provides a smooth arc and clean welds.
- Cons: Can be more expensive than CO2. May result in less penetration on thicker mild steel compared to gas mixtures.
2. Argon-CO2 Mixtures (e.g., 75% Ar / 25% CO2)
This is the workhorse gas for MIG welding mild steel. The combination of Argon and CO2 provides a good balance of properties. The Argon keeps the arc stable and reduces spatter, while the CO2 (being an active gas) helps with penetration and bead shape.
- Common Mixes: 75% Argon / 25% CO2 (often called “C25”) is very popular for general steel fabrication and repair. Other mixes like 80/20 or 90/10 are also used for specific applications.
- Pros: Excellent for mild steel, offering good penetration, a stable arc, and manageable spatter. Versatile for various thicknesses.
- Cons: Not suitable for aluminum or stainless steel (though low CO2 mixes can be used for some stainless applications).
3. Argon-CO2-Oxygen Mixtures (Tri-Mixes)
These are more specialized gas blends, often used for advanced applications, particularly with stainless steel and some nickel alloys. The addition of a small amount of oxygen can further refine the arc and bead characteristics.
- Pros: Can offer superior performance for specific materials and welding positions.
- Cons: More expensive and less common for general DIY use. Requires careful selection based on the material and application.
Understanding Your Welder’s Capabilities
Many hobbyist or entry-level MIG welders are designed to run on pure CO2 or an Argon/CO2 mix. When you purchase a welder, check its specifications to see what gases it’s rated for.
Some welders have a “gas/no-gas” switch. This switch often changes the polarity of the machine and can affect how it performs with different wire types and shielding gases. If you’re using a solid wire designed for gas welding, you’ll need to ensure your gas setup is correct. If you’re using a flux-cored wire, it produces its own shielding, and you may not need an external gas cylinder at all.
Best Practices for MIG Welding with CO2 Mixtures
If you’ve decided to use an Argon/CO2 mixture (like C25) for your mild steel projects, here are some tips to get the best results:
- Proper Gas Flow Rate: The correct gas flow is crucial. Too little, and you won’t get adequate shielding. Too much, and you’ll create turbulence that draws in air, defeating the purpose. A good starting point for most setups is 20-25 cubic feet per hour (CFH), but always check your gas regulator and welding machine recommendations.
- Correct Gas Pressure: Ensure your regulator is set correctly. A common mistake is having the pressure too high or too low.
- Check for Leaks: Regularly inspect your gas hose, connections, and regulator for any leaks. Even a small leak can significantly reduce the amount of shielding gas reaching your weld.
- Proper Stick-Out: This refers to the length of the welding wire that extends beyond the tip of the welding gun (the “contact tip”). For most steel welding with gas, a stick-out of about 1/4 to 1/2 inch is ideal. This is sometimes called the “wire extension.”
- Gun Angle: Maintain a slight drag angle (pushing the gun away from the direction of travel) or a neutral angle. A severe push angle can cause the shielding gas to be blown away.
- Cleanliness is Key: Always ensure your base metal is clean and free of rust, paint, oil, and grease. Contaminated metal will lead to a contaminated weld, regardless of your shielding gas.
Frequently Asked Questions About MIG Welding With Carbon Dioxide
Can I use a CO2 tank from a soda dispenser for welding?
Yes, in many cases, you can adapt a CO2 tank used for soda fountains for MIG welding. These tanks are essentially the same type of cylinder. You’ll need a specific CO2 regulator designed for welding gas pressures, as soda fountain regulators are often low-pressure. Make sure the tank is food-grade CO2 and that you use the correct regulator and fittings.
Will pure CO2 damage my MIG welder?
Pure CO2 will not directly damage your MIG welder itself, as the machine is designed to handle the electrical arc and wire feed. However, the results of welding with pure CO2, such as excessive spatter and potential weld defects, can be frustrating and may lead you to believe the machine isn’t performing correctly. It’s more about the weld quality than the machine’s hardware.
Is it safe to weld with pure CO2?
Welding with pure CO2 is generally safe from a fume perspective, as it doesn’t produce the same toxic fumes as some other welding processes. However, like all welding, it produces intense UV radiation and heat. Always wear appropriate personal protective equipment (PPE), including a welding helmet with the correct shade, flame-resistant clothing, gloves, and eye protection. Ensure good ventilation in your workspace.
What’s the cheapest shielding gas for MIG welding?
Pure carbon dioxide (CO2) is typically the cheapest shielding gas. However, as we’ve discussed, the cost savings often come at the expense of weld quality. For mild steel, a 75% Argon / 25% CO2 mix offers a much better balance of cost and performance.
How do I switch between gas and gasless welding on my MIG welder?
Many MIG welders have a physical switch on the machine labeled “Gas/No-Gas” or similar. When using flux-cored wire (gasless), you’ll typically flip this switch to “No-Gas” and ensure the machine is set to the correct polarity (usually DCEN – Direct Current Electrode Negative). When using solid wire with external shielding gas, you’ll flip the switch to “Gas” and connect your gas cylinder with the appropriate regulator and hose.
The Verdict: Quality Over Cost for Your Projects
When it comes to MIG welding, the shielding gas is a critical component that directly impacts the strength, appearance, and integrity of your welds. While the allure of cheap, readily available pure carbon dioxide is understandable, the reality is that it’s a poor choice for most DIY projects.
You’ll spend more time cleaning up spatter, wrestling with an unstable arc, and potentially dealing with weak or defective welds. For any project where durability and a clean finish matter – whether it’s building a sturdy workbench, repairing a trailer hitch, or fabricating custom metal art – investing in the right shielding gas is paramount.
For most DIYers working with mild steel, a 75% Argon / 25% CO2 mixture is your go-to. It offers a fantastic blend of affordability and performance, making your welding experience smoother and your finished projects stronger and better looking. So, while you can technically MIG weld with carbon dioxide, for the sake of your craft and the quality of your work, you really shouldn’t if you can avoid it. Happy welding!
