I just got a neew MIG welder (millermatic 175 w/argon .023"wire) and I had a few questions on mig welding sheet metal.

1. How do I know when I have the settings correct. I know its a combination of sound, weld thickness, and weld penetration but im not positive.

2. WIth sheet metal do you pull, push or hold the gun straing up? Pulling has given me the best luck so far and I hear that pulling gives the best penetration.

3.What should I look for in a sheet metal bead? I can make a good bead but the bead seems to be lacking that "fishscale" look. I havent seen many sheet metal MIG welds so I assume the fishscales arent as prominent?

4. How much penetration is enough. I can get it so I have very little to none or I can get a bead where the bead sticks out further on the backside of the weld then the side I welded from. I assume equal bead thicknesses would be the best?

5. Any special gun techniques for sheet metal. What distance should the gun be held at? Ive been holding the tip fairly close unless im welding an area that might get some blowby then I hold the tip furthur away. Do you guys have any special stitching patterns or do you just stick with the smooth and steady approach. I tried doing a stitch pattern and a loop pattern and both seemed to cause more spatter. The slower I move the tip the faster the tick sounds go.

Well I know thats a lot of questions but hopefully I can get some help. I might just give stick welding sheet another try as I heard its better for thinner stuff anyway. Most of the welding im doing is filling small holes and fully welding some seam welds. Basically just making all the lapped joints in the car look smooth. Oh and the car im doing this on is a tube chassied 67 ghia. Thanks

I dont have any problems setting up with thicker steel but getting a clean attractive mig weld in the sheet metal seems alot more difficult.

"I might just give stick welding sheet another try as I heard its better for thinner stuff anyway."

News to me, normally the other way round. By the sound of it your new to mig, but experianced on stick.

My advice is to get on a college course similare to lurn the basics of MIG first, its worked well for me. Failing that a good book on how to MIG weld is about the next best option.


"How do I know when I have the settings correct"

A lot of time, practice and weird looking welded shapes. Colleges tend to have large bins of off cuts to practice on and large bins of off cuts turned into potential Turner prize winners.

[Edited on 14/3/05 by clbarclay]

That's tig welding, like plates stacked up. I usually work away from myself on sheet more for visibility than anything. Get a book or video or some evening classes. Frost do some stuff or "Learning MIG Welding" by SIP. Watching someone who knows what they're doing is best though.

MIG is equal in sheet metal work with gas welding. Mig has the advantage of being a quick process not heating up the metal very much limiting warpage (very important on sheet metal). The only problem is mig welds are very strong much stronger then the surrounding metal. This can make it hard to form metal after its welded. Stick heats up the metal more but you can fusion weld with stick using very little filler metal leaving a welded joint that acts like the rest of the sheet. I plan on taking classes and ive read the books. Oh yea when I mig as stated earlier I always lean to the side of the weld so the tip dosent block the weld puddle.

Settings

(1) make sure the reel spins freely enough not to drag but has enough damping it so the wire dosen't uncoil ---- helps to clean off any stick label residue that you sometimes get on new reels of wire.
(2) Feed roller tension should be set so if you put your palm in front of the wire you feel a definite prodding/stabbing but the feed stalls.
(3) Gas flow should be such that the gas just shrouds the arc but not so high it blows the arc about.
(4) Normally working when welding steel is for a right handed person to push the nozzle right to left -- the nozzle angle should be about 30 degrees to the horizontal ---/---
(5) Usually for 1.5mm sheet metal set on most welder the power controls are set to a medium setting.
(6) The feed rate control is the main control you adjust for different welds as altering this increases the voltage/current and the feed rate at the same time.
(7) Cut back the wire with snips to abut 4 mm from the nozzle after every run.
(8) Eyeprotection v actually being able to see the weld -- For welding on thin sheet with low current/voltage setting use a 7 or 8 glass, 9 or 10 for thickermaterial where you use higher voltage/current settings.


[Edited on 14/3/05 by britishtrident]

[Edited on 14/3/05 by britishtrident]

This instruction document might help

A handy tip I picked up from a sheety mate:
When you're welding seams in sheet steel it's a good idea to shake your hands a bit to ensure that both sides are covered adequately. Apparently a decent drinking session the night before helps quite a lot......