MIG Welding Wires

In Gas Metal Arc Welding (GMAW), you won’t be using a stick electrode or a filler rod.

Instead, everything you need to deposit a weld comes from a spool of metal wire.

In this welding process, more popularly known as MIG, a gas tank (typically CO2 or argon) provides the shielding while the wire melts into the base metal.

Nowadays, it is the most common process for structural welding and product fabrication.

When a welder pulls the trigger on his MIG gun (shown below), a wire feed machine advances the wire out through a brass nozzle. This allows for pinpoint accuracy and an unobstructed view of what’s happening inside the joint.

Welding out of position is a lot easier than with SMAW. And since the spool holds about a mile’s worth of wire, you don’t have to stop and reload very often. (The term MIG, incidentally, stands for “metal inert gas”.

However, since CO2 and O2 are reactive gases, it’s more accurate to say MAG – metal active gas – when these gases are used.)

Wire Classification

There are two consumables to consider in the GMAW process – the gas and the wire.

Like stick electrodes, there’s a classification system for the different choices of MIG wire available that’s managed by the American Welding Society.

The American Society of Mechanical Engineers also has a code, but it’s nearly identical.

The AWS code for solid steel wire is known as AWS A5.18.

Here’s what the classification number for a common wire for mild steel, ER70S-6, indicates:

• ER – Electric Rod

• 70 – This two or three-digit number represents the minimum tensile strength of the weld metal, measured in pounds per square inch (PSI) multiplied by 1,000.

• S – Solid wire.

• 6 – This number (with sometimes a letter added) indicates chemical additives used in the wire which may affect the polarity setting on the machine.

The 6, in this case, indicates more deoxidizers have been added to the wire, which is helpful when welding on dirty or rusty steel.

The other general-purpose carbon steel wire type is ER70S-3. This one doesn’t have the added chemicals, so is used primarily on new or clean steel.

The most commonly used aluminum MIG wires are ER5056, a soft wire with good ductility, and ER5356, which is harder and has high tensile strength.

Stainless steel MIG wire includes designations like ER308, ER316, and ER308–L. The L stands for low carbon, which provides extra corrosion resistance.

Wire Diameter

Once a wire type is determined for your welding equipment, two additional pieces of information are needed in order to purchase this consumable.

The first is the wire diameter, which is usually given in thousands of an inch. The most common sizes for welding on sheet metal are 0.35 and 0.45.