[fredygump]

Hey, I'm hoping some experienced guys can help give me some advice?

I'm MIG welding 16ga ductwork, and the issue of weld color has come up. With TIG, yeah, we know we want "straw" color, but nobody at the shop seems to care about getting color when MIG welding. One experienced guy was impressed by the color I was getting, and another guy said color doesn't matter on this and I should be welding hotter.

I have been playing with the balance between volts, wire speed, travel speed, minimizing spatter, etc. I have been welding around 18v which is working the best for getting color, but most everybody else is welding the same material at 20v. I'm starting to get consistent color, and the other guys are getting smoke gray.

But I'm chasing this thing all around, and I'm not sure if I'm going in the right direction. When I travel fast, it looks like it is melting in. When I get in a jam and slow down, it piles up and looks like a cold weld. If I crank the volt up to 20, then it behaves more like black iron, and the color goes away.

I'm welding horizontal position, 18 to 18.5v, tri-mix gas, .030 308L wire. Does that sound right? What would you do?

[exnailpounder]

I don't Mig weld SS but I do my fair share of it in Tig and having color in SS is very important to the integrity of the chromium. If you gray it out and cook it, it will rust eventually. I think your welds look great...whoever told you to weld hotter needs to do more homework. Show us some pics of HIS welds and let us decide.

[fredygump]

I think I figured it out. I didn't know for sure that I had a problem, but I felt that something wasn't quite right. I started thinking that what I really need was to get more amps WITHOUT increasing voltage or wire speed...so I thought I should try .035" wire.


I don't understand why this is, but with the .030" wire, the base metal near the weld didn't heat up the way it should. All the heat seemed to stay in the weld bead, like it was insulated from the base metal. I guess it is because heat doesn't transfer through stainless very well? I tried everything, all different voltage and wire speed settings...by cranking up the wire speed I could get full penetration, but in the process I would get the weld metal too hot.

I was dealing with this problem by low wire speed and fast travel speed...it worked okay, but I was concerned I wasn't getting very good penetration.


When I switched to .035" wire, suddenly the base metal got hot, and the puddle wetted out perfectly. The difference was night and day! I kept using the same voltage, but with a slightly lower wire speed. Now I'm getting good penetration, decent color, and a much more consistent looking weld.

Now, if only I would have figured this out two weeks ago....



In case anybody is curious, here is what I've learned is important for MIG welding stainless:

Higher gas flow than normal--40 to 45 CFH & Recessed Contact Tip.

(This gas flow probably seems way too high, but Tri-Gas is 90% helium, so it tries to float away. No gas or not enough gas = "popping" wire and trouble starting a weld, damaged contact tops, etc. Having a recessed contact tip also helps prevent this "popping", because being recessed means more of the wire is shielded.)

Short stick out--I think this also has a lot to do with gas coverage. I think it is more about the distance between the nozzle and the work, rather than the distance from the contact tip to the work. So a recessed tip doesn't mean the nozzle has to be that much closer. But as close as possible while still being able to see what you're doing...

If you put the gun down for awhile, you can be sure the shielding gas has escaped. So hit the trigger quick to let some gas flow through, trim your wire, and then resume tacking or welding. This will prevent "popping".


This is what I learned while working with .030" SS wire. The .035" has been a lot easier to work with, but I thought I'd put it down in writing in case someone else is experiencing the same kind of issues.

[Otto Nobedder]

You are dealing with several misconceptions. They sound logical, but...

Helium does not float away. It goes where you point it, like any other gas that's flowing. Turn your gas down to 20-25 (Helium does not lift the ball as much because of it's lower density, so your actual flow is higher than indicated).

Weld current in MIG/MAG is a function of voltage (set/fixed) versus current (adjusted by wire speed). This is irrespective of wire size. True, you will not use the same wire speed for different wire sizes, but your weld amperage is a direct function of your set voltage relative to your wire speed.

If you were having a challenge you could not solve with .030 wire, you were (like with stick welding) using too small an electrode (wire) for the job at hand.

Steve S

[jmiller451]

Can someone explain to me the reasoning for the difference in shielding gases for MIG welding stainless. I am curious why for TIG welding stainless requires 100% insert and anything from 50 ppm to 2% oxygen causes discoloration; however, MIG welding stainless requires inert plus some amount of oxygen.

Also, can I get discolored welds by changing the oxygen amount in MIG welds? How do metal artists change the color of MIG welds for stainless?

[fredygump]

You are dealing with several misconceptions. They sound logical, but...

Helium does not float away. It goes where you point it, like any other gas that's flowing. Turn your gas down to 20-25 (Helium does not lift the ball as much because of it's lower density, so your actual flow is higher than indicated).

Weld current in MIG/MAG is a function of voltage (set/fixed) versus current (adjusted by wire speed). This is irrespective of wire size. True, you will not use the same wire speed for different wire sizes, but your weld amperage is a direct function of your set voltage relative to your wire speed.

If you were having a challenge you could not solve with .030 wire, you were (like with stick welding) using too small an electrode (wire) for the job at hand.

Steve S

You should have chimed in with your advice when I posted initially, instead of waiting and then telling me that I am doing it all wrong.


What I am writing here is the result of 60+ hours (continuous) and counting, welding the same material (16ga 2B SS), the whole time trying to get a weld with specific characteristics:

1) good color
2) good penetration
3) consistent bead

The reason I chose to experiment with higher gas flow is because of this video:

https://www.youtube.com/watch?v=-TnytUigGfI


Before watching this video, I did not know it is possible to MIG weld stainless and have color. I have seen plenty of people MIG weld SS, but they are all overheating the weld material, which compromises the composition of the metal leading to corrosion (carbide precipitation).


What I described are the things I have done that made progressive improvements, and now I am to the point where I am consistently getting the kind of weld I want. I got it dialed, and I'm just sharing what I did that gave me good results. ...Because maybe someone else will search the internet to find out about getting color, and this might be helpful.


Current is directly affected by wire size (cross sectional area of wire). Bigger wire carries more current @ a given voltage. With .035 wire, I am getting nearly double the Amps as I did with .030 wire. But my voltage, bead size, and travel speed are almost exactly the same. The difference is that now I'm getting much better penetration along with a weld that has good color.

[Otto Nobedder]

...You should have chimed in with your advice when I posted initially, instead of waiting and then telling me that I am doing it all wrong...

Perhaps it would have helped, but as a moderator I read every post every day. That's often in the 100's, and that limits my time to reply to individual posts. I'm glad you seem to have it sorted out.

Steve S