MIG Welding: Mild Steel Basics

MIG welding (Metal Inert Gas, also known as gas metal arc welding or GMAW) is the most commonly used metal welding technique in the world – it’s fast, inexpensive, and even amateur welders can quickly learn to produce quality work.

Simply put, MIG welding is an arc welding process in which a continuous solid wire electrode is fed through a welding gun and into the weld pool, joining the two base materials together (think of it as a more advanced version of a hot glue gun, but for metal).

The MIG process enables a DIY welder to make, maintain and repair welds on material ranging from 24-gauge up to 1/2-inch thick. With a little practice and some good advice, you can become a competent MIG welder, able to do everything from repairing furniture to building an outdoor fireplace.

Here are some MIG welding basics to get you started.

Safety first 

• Always wear proper welding safety apparel and supplies, which includes leather shoes or boots, full-length pants, a flame-resistant long-sleeve jacket, leather gloves, a welding helmet, safety glasses and a bandana or skull cap to protect your head from sparks.
• Remove any potential fire hazards from the welding area.

Preparing the metal

• Use a metal brush or grinder to remove rust and surface contaminants from the metal prior to welding; get clean down to bare metal
• Make sure your work clamp connects to clean metal; any electrical impedance will affect wire feeding performance.
• On thicker metal – and especially on butt joints – bevel the joint to ensure the weld fully penetrates to the base metal.

Preparing your equipment

• Thorough check of your power source, gun and gas cylinders prior to starting any MIG welding project. 
• Make sure all cable connections are secure and free of damage.
• MIG welding requires DC electrode positive, or reverse polarity. Set your equipment accordingly.
• Set the shielding gas flow rate to 20 to 25 cubic feet per hour. If you spot a leak in your hose, replace it immediately.
• Adjust tension in the drive rolls and wire spool hub; inadequate tension can lead to poor wire feeding performance.
• Remove excess spatter from contact tubes, replace worn contact tips and liners and discard the wire if they are rusty.

Choosing wire

• Use ER70S-3 for all-purpose welding; use ER70S-6 wire when welding on dirty or rusty steel.
• .030-inch diameter wire is good for a range of metal thicknesses and applications; for thinner material, use a .023-inch wire to reduce heat input. For thicker material, use .035 or .045 inch.

Choosing a shielding gas mix

• A 75 percent argon/25 percent carbon dioxide blend (75/25 or C25) works well as an all-purpose shielding gas for carbon steel. A 100 percent CO2 gas provides deeper penetration, but also increases spatter and makes for a rougher bead.

Select voltage and amperage

• The electrical settings a weld requires depend on a range of variables, including metal thicknesses and type, type of joint, welding position, shielding gas and wire diameter and speed (among others). Do your research and fine-tune the welding arc to your personal preferences.

Wire stick-out

• The proper wire stick-out for most solid wire MIG applications is about 3/8”; try to maintain this length while welding. Tip: listen for a sound like sizzling bacon – if the arc sounds irregular, your stick-out is probably too long.

Push vs. pull

• When MIG welding mild steel, you can use either the push or pull technique, but remember that pushing usually offers a better view and enables you to better direct wire into the joint.

Travel angle

• Normal welding conditions in all positions call for a travel angle of five to 15 degrees. Greater angles tend to lead to more spatter, less penetration and arc instability.

Work angle and position

• Work angle and gun position varies with each welding position and joint configuration. For a helpful primer on flat, horizontal, horizontal, vertical and overhead welding tips, check out this video.

Practice!

• Most people can create good looking, high-quality MIG welds with a little practice. When you’re learning how to weld, take note of what you did right and what looks wrong.

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