How to mig weld part 4: Mig wire

This is an obvious choice here. If you're going to weld aluminium you would use an aluminium mig wire.

For welding stainless steel you would use stainless steel mig wire. And for mild steel you would use mild steel welding wire.

Aluminum mig wire

Let me start by saying that aluminum is a very soft metal to begin with. One of the biggest problems people face with mig welding aluminium is the wire feed ability. Nine times out of ten most people who need to weld aluminium will use 1.2 mm diameter wire ("0.045). By using a larger diameter wire it offers slightly better wire feeding as it is more rigid than the 0.9 mm diameter wire ("0.035). The grade of aluminium mig wire that you will also need to use will be 5356. This is the stuff that is used to make toolboxes, bull bars, boats etc.  You can go to this page which is about mig welding aluminum.

Stainless steel mig wire

Probably the most common grade of stainless mig welding wire would have to be 316. It seems to be used for a lot of general-purpose stainless steel welding applications. If you need to weld stainless steel to mild steel you are better off using a 309 grade as this has better crack resistant properties than using 316 when welding mild to stainless.

There are also other grades such as 307, 308, 309 and more. You will find that there will be a letter after the numbers, for example. You can get 316L, 316 LSi or 316Si. All these letters at the end of the numbers will mean each wire has a slightly different chemical composition. Some will have more silicon content and some will have less silicon content. The silicon content helps with the wetting in action when you are welding. Check with the manufacturer's specification sheet for the exact chemical compositions.

Mild steel mig wire

For mild steel mig welding wire we can break it down into about three or four categories. And they are:

Solid mig wire

Solid wire is the most commonly used welding wire through the world. Everyone from home DIY welders to welding shops and fabrication workshops will be using solid wire. The most common wire used is a Co2 / mixed gas ER70S-6 grade mild steel mig wire which is all positional welding. These wires are solid all the way through.

Gasless mig wire

Gasless mig wire can be used without the normally required bottle of shielding gas. It is most often used for people at home who do not want to spend money on renting and buying the welding gas bottles that would be needed if using the solid mig wire.

Fabricators who need to do some onsite work will often have a few spools of this stuff in the truck so that they do not have to cart around the welding gas bottle. And because it has a flux in it, welding outdoors in the wind will not affect it's performance. The flux burns and creates it's own shielding gas which the wind can't blow away. This wire is also called self shielded mig wire, and a common one is E71T-GS. This is a general purpose wire good for all general purpose welding projects and is an all positional welding wire.

Flux cored mig wire

Flux cored wire (FCW) is designed for heavy welding applications where you need to put down as much weld as fast as possible. We talk about the deposition rate when welding, this is how many kilograms per hour or pounds per hour you can put down. Flux core wire is really good at this and has much higher deposition rates than that of solid wire.

Don't confuse the gasless mig wire with the flux cored wires though. Yes, they are both flux cored but this flux cored wire does require a shielding gas. A very common wire is E71-T which can use straight Co2 gas or a mixed gas. This wire has way less spatter than a solid wire, but it will have a thin layer of slag over the top. This will self peel off it the welding conditions are right.

There are many more other compositions of FCW. You can get stainless steel flux cored wire, hard facing wires and wires for welding armor plate /bisalloy/wear plate etc. Flux cored welding wires are very popular in ship building yards. One of the best wires is the Kobe DW-100 (Kobelco Welding).

Metal cored mig wire

Metal cored wire is a very nice wire to use. It is different from the flux cored wires and leaves a very, very nice weld. With hardly any spatter left over, the finished welded beads are smooth as! There is no slag covering left either. The wires are hollow like the flux cored wires but the main ingredient inside the wire is iron. The iron in the center is in a powdered form. Because it is already broken down into a smaller particle sizes the welding arc is less violent and is much easier to enter spray transfer mode.

One engineering firm I know of was using the standard solid mig wire for their work and have since changed over to metal cored wire. The initial purchase price of the metal cored wire is much higher than the solid wire, but. It puts it down faster with more filler metal, which means less labor time on a job. Labor is the biggest cost in welding. And there is no clean up needed on the parts that this company are making. Before, they had to first weld the job, and then use chipping hammers, cold chisels and flap discs to get all the spatter off. Now it is just welded, picked up and put on the pallet ready to go to the galvanizers. The amount of time this welding business saved in time just by not having to do these extra jobs normally associated with the solid wire has really made a big difference to their wallets.

Metal cored mig welding wire uses mixed gases for shielding the welding arc. This wire has fast travel speeds and high welding wire deposition rates.

Mig wire conclusion

Mild steel, stainless and aluminum welding wires are the three most common for wires for mig welding.

There are literally hundreds if not thousands of different possible chemical compositions for welding wires. Other wires would be for special applications such as hard facing wires for bulldozer blades, grinding and cutting machines. Cast iron mig wires, for welding cast iron (very expensive), wires for welding exotic metals etc.

Fore more detailed information you can go to this page called mig welding wire.

Follow on now to how to mig weld part 5 where we show you how to put the mig wire on the machine and load it up.

How to mig weld.  Part 5. Mig wire installation.