MIG Welding Stainless Steel
MIG welding stainless steel is a very practical process for fabricators that need to use stainless components in their projects. It is much faster than TIG welding, inch per inch. It will also take fabricators less time to piece together a MIG project, because there is less prep work in terms of removing surface contaminants. However, it is less common than stainless TIG welding for several reasons.
MIG vs TIG
A lot of projects involving stainless are very high end, with nice finishing and polishing required. MIG isn’t always the best choice for this due to its spatter and wider bead profile. Also, good TIG beads are much easier on the eyes than most MIG beads. Some nice TIG dimes can actually add to a projects look and feel, without having to grind them or sand them away for the customer. Sometimes stainless projects are smaller scaled, often with much thinner metal gauges than normal jobs. TIG is a great process for tackling lighter gauge steel due its low amperage options. However, if you are fabricating with thicker stainless and making bigger projects, then stainless MIG can be a great option.
What You Need For Stainless MIG
MIG welding stainless steel is quite similar to hardwire in terms of the actual process. You can use the same machine and the same gun as you normally would. One difference is the gas mixture selections for stainless. With hardwire and dual shield, we generally run a 75/25 percent mix of argon and CO2, respectively. Sometimes we even run straight CO2.
With stainless MIG, there are several gas options. The least expensive being carbon dioxide/argon mixes. These range from 98% argon/2% CO2 all the way to 75% argon/25% CO2. These mixes work well for stainless, but they aren’t the best for puddle control. The best gas is what’s called a tri-mix. Our favorite mixture contains 90 % helium, 7.5 % argon and 2.5 % CO2.
Helium helps a lot with the stainless MIG bead because it allows for deeper penetration and a better puddle. The problem with stainless MIG is that it is more sluggish than a hardwire or flux core bead. The high levels of nickel and chromium make the welding process move slower on stainless. These elements are added for corrosion resistance (giving stainless its name), but they also act as a barrier for welds to penetrate through the surface.
316L wire is the most popular wire for stainless to stainless welding applications. 309L wire is most popular for joining mild steels to stainless steels.
Welders new to stainless MIG will notice that the puddle isn’t nearly as easy to push or control. Helium shielding aids with these effects, and helps the welder to manipulate their puddle better. The lower levels of argon and CO2 help with arc characteristics and arc starts. However, too much of these gases can weaken the stainless steels ability to resist corrosion. Too much CO2 will start to oxidize the stainless and make it prone to rust and darkening, which ruins the point of using stainless in the first place.
Costs Of Stainless MIG
One downside to this process is the cost of material. Not only is stainless more expensive than mild steel, but helium mixes and stainless wire are as well. This heavily contrasts regular mild steel processes – with hardwire MIG, we can get away with straight CO2 gas and some ER-70 wire. This is about as cheap as it gets for MIG, besides straight flux core (which has no external gas). For these differences in operating prices, shops and independent welders will need to up their rates for doing stainless work – or else they could end up losing money.
Stainless is a much tougher and harder material than mild steel. It wears down bandsaw blades and cut off wheels super quickly. Unless you you have a CNC machine or a handheld plasma cutter, you’ll need to budget for extra saw blades or cutoff wheels. If you are having the stainless pre-cut from your supplier, they will very likely be up-charging you for each cut. However, this can be a good option if you want to save time and not deal with cutting it yourself.
Weight Of Stainless
Stainless is roughly 6% heavier than mild steel. This isn’t a big issue, but you should keep it in mind for your projects. It will add weight to your final product, and it can be troublesome to transport it in larger quantities. This weight difference can cause issues if your client has weight requirements for the project you are building; especially if you are used to mild steel. This issue is small, but when you pick up a piece of stainless you will definitely feel that extra weight.
Stainless is known to warp more rapidly than mild steel. You’ll want to make sure to clamp properly and control your heat input. Due to stainless retaining heat for longer periods, the likelihood of warping can be frustrating for novice welders. It is best to tack it well, let it cool, and make sure to wait longer periods in between your actual weld beads.
Thinner stainless is known for extreme warpage. So, it will require tons of practice if you plan on welding stainless sheet metal – or thinner stainless in general.