Practical MIG Welding: Stainless Steel

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Stainless Steel

06.45

00:00	Although 95% of us will only ever MIG weld mild steel, there can be real advantages to welding other materials like stainless steel with this fast and efficient method.
00:09	Stainless steel is often used in motorsports because it offers increased corrosion resistance and is available in many different configurations to construct parts like exhausts and fluid transfer plumbing for cooling and fuel systems.
00:21	It should be said that TIG welding is a better match than MIG welding for stainless steel.
00:25	This is something that you can learn about in detail inside of our practical TIG welding course but that doesn't mean it's not possible so let's get into it.
00:33	Starting with part prep, although stainless steel's chemical composition fends off corrosion, we still need to give the material some external preparation to get the best results.
00:43	We need to always buff back our material until we see the shiny steel beneath using a buffing disc on a grinder, a wire brush, scotch brite pad or sandpaper.
00:52	It's extremely important that the tools used to perform these tasks have not been used to abrasively clean mild steel.
00:58	If they have, we'll be embedding contaminants into the stainless steel and affecting its corrosion resistance.
01:05	Having a bright and shiny weld surface will increase the strength and improve the look of the weld while keeping our work area and MIG torch clean and free of spatter.
01:13	By buffing off any of the coatings with some dedicated stainless steel abrasives and cleaning our shiny steel down with acetone, we stand the best chance of producing a strong high quality weld.
01:24	Setting our machine up to weld stainless steel is fairly straightforward.
01:28	First we need to select and use the right consumables, being the gas and the filler wire.
01:33	If we're setting up a MIG welder from new to weld stainless steel, then we're already eliminating a source of contamination that we'd expect if we were to change from a mild steel spool in an old machine.
01:44	This is because the mild steel wire runs inside of the MIG lead liner and this can introduce contaminants to the weld.
01:51	To combat this, many serious fabricators have a second torch and lead that's dedicated to the use of welding stainless steel.
01:58	Although a cheaper option is just to buy a new liner to go inside your existing torch.
02:03	After understanding the weight of the wire spool that fits inside our machine, we need to look at the different types available for stainless steel.
02:10	Make sure to refer back to the earlier wire spool module if you need to refresh your understanding on this.
02:16	The three most common grades of stainless wire are 308, 309 and 316.
02:22	These wire grades may also have an L designator which indicates that the wire's carbon level falls at the low end of the carbon range.
02:30	It may also be common to see the SI designator, indicating a higher silicon content.
02:36	This provides more fluidity to the weld puddle and is recommended.
02:40	Again, the majority of material used in motorsport fabrication will suit either 0.8 or 0 .9mm filler wire.
02:47	One thing to note here is that shielding gas requirements differ between MIG welding stainless steel and mild steel.
02:54	Higher levels of carbon and oxygen in the shielding gas react with the stainless steel arc, resulting in some oxidation and reduction in the corrosion resistance.
03:03	This means that the maximum level of oxygen or carbon dioxide that should be used in a shielding gas mix for stainless steel is 3% oxygen and 5% carbon dioxide.
03:13	Now, if we refer back to our earlier shielding gas module, you'll see that Argo shield light falls within this range but Argo shield universal has 16% carbon dioxide, making it possible but not ideal to weld stainless steel with.
03:27	After opening up the shielding gas bottle tap and depressing the trigger on the hand piece of the MIG gun, we can now set the gas flow to around 10 litres per minute.
03:36	As the machine would have begun to roll out the wire, while setting gas flow, we need to trim it back to a stick out length of 10mm from the end of the gas nozzle.
03:44	Doing this will give us the correct stick out length as well as giving us a nice clean wire tip to begin our first weld.
03:51	When it comes to the settings, most machines will come with a setup guide to get us into the ballpark by referencing our material thickness, wire diameter, gas type and amperage or voltage needed for a specific application.
04:02	With that said, if you have a modern machine, there's a good chance it has a synergic function which you can simply input your stainless parameters and your machine will adjust its settings accordingly.
04:12	If you have the option then it's also advisable to dial in a little pre and post flow of shielding gas because stainless steel needs to be shielded after the arc is terminated for the period of time that it's glowing red.
04:24	This protects the metal in its molten state from atmospheric air.
04:28	The actual technique of welding stainless steel with a MIG is realistically very similar to that of mild steel.
04:34	We want to always use a pushing motion with our torch and that motion should see the torch leant over at a 15 to 30 degree angle to point the nozzle in the direction of travel and shield the arc with the gas exiting the nozzle.
04:49	We need to be mindful that we're keeping our wire stick out length close to the required 10mm and not allowing this to fluctuate too much.
04:56	We also need to consider inputting even amounts of heat into each edge of the material that we're welding together.
05:02	This will call for any weld joint to have an even amount of torch angle on each half.
05:08	As we weld our stainless steel, we need to consider the sound it's making and visually inspect the weld as it's forming.
05:14	As with mild steel, for nearly all jobs, we'll be using the short circuit method of welding.
05:19	This emits a fast crackling sound as the wire contacts the weld puddle and shorts out, sounding a lot like frying bacon.
05:26	Diagnosing a weld should be done during and after our weld session.
05:30	Any air bubbles, craters or discolouring will indicate a lack of shielding gas and will require you to make sure that your bottle's flow is adequate for the task that you're completing.
05:39	A good looking weld is usually a strong one while a small ropey looking weld sitting on the surface of the material will indicate a lack of heat and wire feed.
05:48	On the flip side, a wide sunken weld will indicate too much heat and may cause problems with stainless steel due to its lack of backside shielding gas and its propensity to react with the atmosphere more than we will see with mild steel.
06:01	We can always double check our welds with some destructive tests too as we covered in the practical skills section of the course.
06:08	In summary, stainless steel isn't a common material to MIG weld but having the ability to swap a roll of stainless wire into your machine and get your project welded up can certainly come in handy.
06:18	Remember to make sure that your part is clean and get that nice crispy bacon crackling sound coming from your torch, concentrating on keeping your wire sticker even, favouring both halves of the material equally.
06:30	Setup wise, make sure that you check out our stainless steel reference sheet for baseline settings to get you started or alternatively, if you've got access to a synergic welder, let it do the hard work for you.