nightmare mig welding stainless :(

[alessio-malta]

Hi, been reading on this forum alot since I bought my mig welder as this forum is full with useful information. I have been welding mild steel for some time now and have achieved good results, but now I'm trying to weld stainless steel for the first time and I cannot understand what am I doing wrong.

I'm fabricating an exhaust for my car using 76mm polished 304 stainless, 2mm wall tickness and I'm using my mig to tack the pieces together and afterwards get it tig welded. the problem is that when I start the weld the puddle wont fuse with the base metal and dribble like it was water, and on the mig gun, I'm left with a molten bead on the tip of the welding wire. I'm tacking the pipes together successfully , but it seems that they are tacked by the base metal melting into each other, rather than the welding wire fusing them.

To give you more information I'm using a telwin mig 30-220amp, 85%argon/15 Co2 gas (everyone uses this here for stainless), and I'm using 316 stainless welding wire. According to the welding calculator I'm using power setting 3 (my welder has 6 settings). tried to use setting 4, more powerful but still no weld. on setting 5 it just blows through when I press the gun.

in what ways is stainless welded compared to mild steel?? faster/slower/push/etcc....??

hope I explained the problem clearly.

Thanks

Alessio

 

[madkayaker]

I think its your gas. I have always used pure argon for stainless

 

[Jim_gsxr1000]

I had heard that pure argon for stainless

 

[chunkolini]

This one has been discussed here several times.
Pure argon leaves a very raised weld with little penetration.
I had a custom mix made using argon and 5%CO2 and still got a better result with regular Mig mix.
Somewhere there is a thread I did years ago with samples using pure argon the mix I was supplied and regular mix with photos of all three.
Alessio try speeding up the wire feed, do it a small amount at a time, and keep an eye on what is happening. Mig welding stainless is harder than mild steel.

Photo's on page two of this thread http://www.mig-welding.co.uk/forum/showthread.php?t=19083&page=2
My main problem was with spatter sticking to the metal. Hope it helps.
Look for Technical Al's response. He does know his onions on this subject.

 

[alessio-malta]

forgot to mention that on the welding wire spool ther is written arg/co2 mix, so I'm sure I should get some decent welding with this type of gas. I've alredy tried to speed up the feed but still same result, no penetration.

Does stainless make the same sound as mild steel.??

even when welding I can see clearly that there is a bead forming on the tip of the welding wire and it just won't weld in, and then when the bead gets bigger like 3-4mm in diameter is just falls off.

 

[the repair man]

Sounds like your not getting enough heat into the stainless, you need more power for stainless. Can you up your voltage and slow your wire feed on your welder? I have a Tig for stainless so haven't mig'd it for a while, but defo remember you need more power.

 

[matt1978]

Tig welding for stainless is 100% Ar

Mig welding stainless is either

97Ar 2.5 % Co2 (2% is also a available)depending in which gas company you use

Or 98% Ar 2% O

Or a Ar/He/Co2

Any other gas for mig welding Stainless is a compromise and is not correct regardless of what you read or hear.

But in saying that its all dependant on how critical the job is

 

[Lawnmowerboy]

No you need less heat for stainless but that's not helping the OP

It would help if you did a few set up pieces and the correct gas is BOC Stainshield or similar but we only tig stainless with pure argon.

 

[dannyp]

sounds to me te OP is tacking not seaming things together, the gas isn't ideal but it'll weld

sounds like insufficent wire speed to me.

i'd defantly increase the wire speed as for power if it starts blowing holes turn it down if it dosent and welds that'll do just fine

 

[the repair man]

No you need less heat for stainless but that's not helping the OP

It would help if you did a few set up pieces and the correct gas is BOC Stainshield or similar but we only tig stainless with pure argon.

Stainless needs more power than mild steel for the weld. The only reason you try to keep heat down is to stop the metal deforming, as stainless is more prone to deformation. At least that's how I've always understood it.

 

[langy]

I get lots of customers doing this, I just tell them to tack with normal mig wire and when I tig the parts I just clean off the tacks, much easier for the customer

 

[Lawnmowerboy]

I'm pretty sure it conducts less heat than mild steel so you need less heat. It deforms more because it can't dissipate the heat as well...

 

[Llama]

I'm pretty sure it conducts less heat than mild steel so you need less heat. It deforms more because it can't dissipate the heat as well...

I should think this is the case. Stainless and mild steel have pretty much the same specific heat capacity, but the conductivity of stainless is ~3 times less conductive than mild.