I need to weld stainless steel.
I have a Millermatic 135 wire welder.
What type of gas is recommended?
The welder tag recommends trimix - 90% he/7.5% ar/2.5co2
can I use this gas for mildsteel too? or will I have to buy different type of gas also.
I plan to buy a TIG set up, will I have to buy an argon bottle for this too?

 

You can use trimix, but it's expensive with the high helium content. I tig stainless with pure argon, you can get away with mig welding on pure argon, but the puddle behaves poorly, cooling too fast. I would use C5 (Argon with 5% CO2) for the mig welding, and pure argon for tig. You can use the C5 gas for tig welding stainless, but it makes the finished weld look dirty, and can cause heat warpage issues.
For tig on steel, straight argon is best, for mig you should use C5 or C25.
Generally, with the argon/CO2 mixes, the CO2 is used to control heat dissipation- the more CO2, the hotter the puddle will stay. Steel doesn't mind too much, but stainless is pretty picky. It's hard to control the puddle, since it holds heat in place for a long time.
Aluminum is a totally different class, you need either straight argon or a helium mix to keep the weld clean. If you use C5 on aluminum, the results will be poor, and on C25 the weld will fail before it's cooled.

 

so i can use c5 to mig stainless steel and use the c5 to tig mildsteel.
i will use argon when i tig aluminum.
i am trying to keep cost down, and trying to avoid having 4 or 5 gas bottles around.
thanks for the info.
what wire do you suggest? i will fuse up to 1/8 stainless flat stock to 1 in od tube.

 

You can use straight argon for steel, stainless, and aluminum with mig and tig welders no problem.

FordSix is right in that straight argon with mig welding stainless makes for interesting puddle problems, but I've found turning the gas flow down a little bit reduces that significantly. Not to the point that you do not have enough shielding gas, which you can tell by looking at the weld. Practice on some scrap first, similar in thickness to the materials you want to weld, to adjust the settings of the welder and the gas flow, then write them down in a book.

Every time I set things up for different type, or thickness material, or a different type of joint, I write down the settings of the ***** and the gas regulator. This way if I have to do that type of work again, I don't have to guess or remember anything. Look it up, set it, and weld away.

Argon is okay for just about everything, and that reduces the number of bottles you have to have lying around.

Since the regulator is on the bottle, and the pressure post-regulator isn't very much, I installed a short hose between the regulator, and a quick disconnect, which I installed the mating halfs on my plasma cutter as well as on my mig welder. This way I can just pop the connector off one unit, and install on the other unit easily enough, with the one bottle of argon on the welding cart. Here is the cart, without the bottle installed:



Since argon is an inert, noble gas, a little tiny bit seeping out when I disconnect the hose to move to the other machine isn't a big deal - totally harmless. I wouldn't do this with oxygen or acetylene of course.

 

How much stainless welding are you gonna do? If you need to get by without a TIG for now. Why not try SS flux core wire? If you are going to use a wire feed machine, you will not have the same apperance as you would with a TIG. So why not use some wire that will not require a bottle until you can get your hands on a TIG? An .035 1# roll of wire is not really expensive at all, and with some practice, can be made to look decent.

 

You don't need to have "4 or 5 bottles" hanging around.
I have Argon for Tig, C-25 for Mig plus a bottle of Trimix for stainless. Tig is the only way with stainless steel food grade tanks and home brew equipment.
Better in the long run to purchase owner owned 250/280 cu/ft bottles unless your only welding a small amount then smaller tanks would work.

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