Beginner’s Guide to MIG Welding Steel

MIG welding is one of the easiest and most accessible welding methods for beginners, making it a great choice for metalworking projects at Tharwa Valley Forge. Whether you're repairing tools, fabricating equipment, or just starting out, understanding the basics will help you achieve strong, clean welds.

In this FAQ, we cover essential tips on choosing the right welder, setting up your machine, and troubleshooting common issues. If you're new to welding or looking to refine your skills, this guide will set you on the right path.

Happy welding! ⚒️

1. What is MIG welding?

MIG (Metal Inert Gas) welding, also known as Gas Metal Arc Welding (GMAW), is a process that uses a continuously fed wire electrode to join metal while being shielded by an inert or semi-inert gas to prevent contamination.

Why is MIG welding good for beginners?

• Ease of use – Unlike stick welding, which requires striking an arc manually, MIG uses a trigger-fed wire for a smooth process.
• Speed – MIG welding is much faster than other processes like TIG or stick welding.
• Clean welds – With proper shielding gas, it produces minimal slag and spatter.

2. What type of steel can I weld with a MIG welder?

MIG welding is most commonly used for welding mild steel, but it can also handle:

• Stainless steel (requires special wire and gas).
• Aluminum (requires a spool gun and pure argon gas).
• Galvanized steel (but the zinc coating must be ground off first).

For thicker steel, MIG welding works best when using multiple passes or higher amperage welders (220V machines).

3. Do I need shielding gas for MIG welding?

Yes, shielding gas is required unless you’re using flux-cored wire (which has a built-in flux to protect the weld). The most common gases for steel are:

• 75% Argon / 25% CO₂ (C25 mix) – Produces cleaner welds with minimal spatter.
• 100% CO₂ – Provides deeper penetration but creates more spatter.
• 100% Argon – Not suitable for welding steel (used for aluminum).

Make sure the gas flows at 20-25 CFH (cubic feet per hour) for proper shielding. If you weld outdoors, use flux-cored wire since the wind can blow away the shielding gas.

4. What size wire should I use?

Choosing the right wire size depends on the thickness of the steel:

• 0.023" (0.6mm) – Best for thin materials like automotive panels and sheet metal.
• 0.030" (0.8mm) – Great for general-purpose welding of materials up to 3/16" thick.
• 0.035" (0.9mm) – Good for thicker materials up to 1/4".
• 0.045" (1.2mm) – Used for industrial applications and heavy steel.

For most beginner projects, ER70S-6 wire (which contains deoxidizers to handle dirtier steel) is a solid choice.

5. What voltage and wire speed settings should I use?

Each welder has a chart (usually inside the lid) that provides recommended voltage and wire speed settings based on material thickness and wire diameter. A general guide:

Adjust settings as needed for penetration and bead quality.

6. How do I prepare the steel before welding?

Proper steel preparation is essential for a strong weld. Steps to follow:

1. Remove contaminants – Grind off rust, paint, and grease using a wire brush, flap disc, or grinder.
2. Ensure a good fit – Use clamps to hold pieces tightly together. A small gap (about 1/16") may help penetration on thicker materials.
3. Check for moisture – Moisture can lead to porosity in the weld. Keep metal dry before welding.

For thicker steel, beveling the edges before welding helps improve penetration.

7. How should I position the MIG gun?

• Hold the gun at a 10-15° angle, with the wire pushing the weld pool forward.
• Keep the wire tip 3/8" to 1/2" (10-12mm) from the metal for a stable arc.
• Move the gun at a steady speed – too fast results in weak, shallow welds, while too slow can cause excessive buildup (cold lap).

Push vs. Pull Technique

• Push (forehand welding) – Produces a smoother, cleaner weld with less penetration.
• Pull (backhand welding) – Increases penetration but may produce more spatter.

For MIG welding steel, pushing is generally preferred for flat and horizontal positions.

8. Why is my weld full of spatter or inconsistent?

Common causes of spatter and poor weld quality:

• Wrong voltage/wire speed settings – Too high or too low can cause inconsistency.
• Dirty metal – Rust, paint, or oil can lead to weak welds.
• Poor gas coverage – Ensure gas is flowing properly at 20-25 CFH and there are no leaks.
• Wrong wire stick-out – Keep the wire tip at the correct distance (3/8" to 1/2").

Quick Fixes

• Increase gas flow if you notice porosity (tiny holes in the weld).
• Reduce voltage if you experience excessive spatter.
• Adjust wire speed to match travel speed.

9. How do I know if I have a strong weld?

A good weld should have:
✅ Smooth, consistent bead (no excessive ripples or undercut).
✅ Good penetration – The back of the joint should show some weld fusion.
✅ No porosity or cracks – Holes or cracks mean a weak weld.

To test strength, try bending the welded piece – a solid weld should hold without cracking.

10. What safety gear do I need for MIG welding?

Welding produces high heat, bright UV light, and sparks, so proper safety gear is crucial:

• Auto-darkening welding helmet – Should have a shade range of 10-13 to protect your eyes.
• Flame-resistant clothing – Cotton or leather (avoid synthetic materials that melt).
• Welding gloves – Protect hands from heat and sparks.
• Steel-toe boots – Keep feet safe from falling metal.
• Respirator or good ventilation – Welding fumes contain harmful particles, especially from galvanized steel (which produces toxic zinc fumes).

11. What MIG Welder Should I Buy for a 10A Socket?

If you're limited to a standard 10A (240V) household power socket, you need to choose a low-amperage MIG welder that operates efficiently within that power constraint.

What to Look For:

✅ Input Power: The welder should be designed for 10A plugs (typically 140A or lower output).
✅ Duty Cycle: A higher duty cycle means you can weld longer before the machine overheats. Look for at least 30% at 100A.
✅ Multi-Process Capability: Some welders also allow Stick (MMA) and TIG welding, adding flexibility.
✅ Gas vs. Gasless: If you plan to weld outside, a welder with flux-cored (gasless) capability is useful.

Recommended Options:

• Unimig Viper 120A or 140A – Compact, reliable, and runs on a standard 10A socket.
• Bossweld 140 MIG – Affordable and capable of welding mild steel up to 4mm thick.
• Lincoln Electric Power MIG 140MP – A solid option for small workshops.

Important Tip: If you need more power (e.g., welding steel over 4mm thick), you may need a welder that requires 15A or 20A sockets. Always check your home's circuit capacity before upgrading!

Extra Safety Tips

• Never weld near flammable materials (keep a fire extinguisher nearby).
• Keep your workspace well-ventilated (fume extraction or an open area helps).
• Avoid touching freshly welded metal – It stays hot for a while!