Thread: Welding sheet metal

Tweet

Hey Guys;
I’m getting ready to start patching some bad spots in the old Ranchero body.
Got a question about welding sheet metal
and keeping it from warping.
I’ve welded sheet metal before but it didn’t matter if it was warped.
I know that it can warp very easy.
I know after you get it lined up and clamped down you spot weld it in several spots then cool it off with a air hose.
After that can you run a strait bead or should you just keep spot welding the whole thing and cooling it down with the air hose. Thanks Kurt

Originally Posted by vara4

Hey Guys;
I’m getting ready to start patching some bad spots in the old Ranchero body.
Got a question about welding sheet metal
and keeping it from warping.
I’ve welded sheet metal before but it didn’t matter if it was warped.
I know that it can warp very easy.
I know after you get it lined up and clamped down you spot weld it in several spots then cool it off with a air hose.
After that can you run a strait bead or should you just keep spot welding the whole thing and cooling it down with the air hose. Thanks Kurt

just continue skipping around and spot welding, don't run any beads, it will warp. Takes a bit of time to do it right.

Thanks Dave. Kurt

Yep, what dave said!! I have not found a better way yet.

Thanks hotroddaddy; I had seen it done some years ago but could not remember.
Had a friend tell me just cut it out take some sheet metal and glue it to the back inside.
Then he said to bondo it in, he said that's the way all the body shops do it today.
I thought to myself not on this car, I want it done right or as close to right as I can
get it. Thats probably why when I look at alot of the old cars running around that I see so many bad spots and I'm not even close to being a body man.
At some of the car meetings I go to a few of the cars have fresh paint jobs, when you start looking close, you can see cracked bondo or rust spot bubbling up where the didn't treat the rust. It's crazy you pay these guys good money and they can't even treat a light rust. I had a buddy pay a guy 6 grand to do his car, all he had was a little rust and about 5 or 6 dings. The rust was not bad just some pitting, within one month he had bubbles under the paint because the guy didn't treat the rust like he said he would.
I was pissed and it was not even my car. Good body men are hard to find these days.
Kurt

vara4,

You will get lots of opinions on this subject, however I am in the opinion that butt welding the panels is the best way to go. The suggestion that was given regarding skipping around is a great one, however I am not known at times for being the most patient. I work for a Company that has GM/Jeep Dealerships, and I go to the body Shop and learn from those guys a lot. They all like to use an Air Gun to cool the weld (for flat rate), and when I have brought it up on Forums, people say it doesn't work-I think it does because the smaller the HAZ (Heat Affected Zone) the less shrinkage you will have, and therefore the least amount of warping. The only thing I see that is a potential downside is that your air had better be dry or you may force water into the joint.

The guys in the Body Shop also love panel bonding, but I think you may get "ghosting" (on a hot day see faint lines in the paint)-they tell me thats the standard in the Industry today, and I'm certain it's as strong or stronger than a weld.

If you really want it nice with minimal distortion, obviously hammer welding is the way to go. And don't for get about the Epoxy Paint inside and out so it won't rust!

In really depends on your situation, in a perfect world this is how I would do it. I would butt weld it but leave a gap of a 1/32" and put a alum. brass or copper plate behind it to pull the heat away from the metal. Tack it up all the way down the seam keeping the tacks as far apart from each other as possible. Stop when you feel things are getting to hot and let it cool off. If you dont have the patience to do it right then you might want let some one else do it.

I like to use a flanged seam, hammer welded all the way to keep things smooth and the seam tight. There is no quick way to do it....used to be a product called Moistbestos that you could use to soak up the heat, but the feds took that away. Bonding panels is probably fine if you're in a body shop working flat rate. I've yet to see a glued panel that doesn't ghost out a seam line after a few years. Think I'll stick to welding mine! Usually I use the Mig for the tacks then the Tig to fill in the blanks, but using a Mig for the whole process is just fine, too.

When I have a long weld to do joining a couple pieces together, I try to make that the secondary job for the day and spend the cooling time for the welds working on something else.

Ive always been told that a flanged seam collects moisture and starts rusting from inside out. I have no experience here, just what ive been told.

Originally Posted by hotroddaddy

Ive always been told that a flanged seam collects moisture and starts rusting from inside out. I have no experience here, just what ive been told.

I use seam sealer on the inside, a light coat of Evercoat Metal to Metal on the outside. Once the seam sealer is set up on the inside, and primed and painted the moisture is sealed away from the seam as well as it is sealed away from the metal on the outside..... I suppose if the welds aren't hammer welded to make them tight, or no seam sealer is applied, it could be a problem,,,,,but so is a butt weld with no protective coating applied to the inside.... Done it this way for years, no problems. Sure does make the fitting and welding go a lot better....

Good points Dave! That always seems to be a big dilema in some spots anyway. How do you get paint or sealer inside some spots? Im having that problem with the door repair, once i fix it i have no way of sealing the inside, so its just gonna rust from the inside out again.

Originally Posted by hotroddaddy

Good points Dave! That always seems to be a big dilema in some spots anyway. How do you get paint or sealer inside some spots? Im having that problem with the door repair, once i fix it i have no way of sealing the inside, so its just gonna rust from the inside out again.

I sand, grind, neutralize or whatever on the inside when the panel is off. I'll do something to finish and seal the inside of a repaired panel, even if I have to make an access panel to get at it. On the absolutely impossible places, I use the weld thru primer. If you can't get anything over it, doesn't really matter what kind of joint you have, it's gonna rust!!!!! When all else fails on the really impossible places, a can of spray on undercoating with a long plastic nozzle sprayed through an access hole is better then nothing.... Also, on my flange joints, I flange the topside of the joint in so that there is not an open lip facing up on the overlap to allow moisture to accumulate.... (Hope that makes sense, I could show you a whole lot better then I can write!!!!)

when you put a patch in you want to get all the rust out i first tap it with a body pick hammer too see how punky it is them cut out with a cut off wheel take bad part off flip over look at the rust on the back side if rust is past your cut take a hammer tap off the rust the part you cut off see how thin the metal is if thin your have to cut bigger repair if you do not do this the patch will fail by the time you grind and prep for paint your fix will be paper thin and any time you weld the metal is now super clean all junk has been boiled out where you welded it now will rust much faster . i was a flat rate body man for many years i have welded many panels on and made many i never used panel bond on any thing other then door skins .for me a butt weld work the best .if i had to a small over lap i never use a flange tool .i some times welded the panel from the back side if i could get in there like if cutting down running boads .on how to weld with out warping. one thing i used thicker sheet metal for the repair .i always welded just under a body line if there was one not to far from the patch like a door bottom or fender . fit up is a big deal . and very clean were you weld. i tack welded the panel down keep going till about every 1inch a part once tack you must not let it get very hot .i set the mig welder for low heat and not alot of bead more bead more grinding = more heat = wraping . i ground the heads off the tacks thru out the tacking job so i can work the steel if needed with a hammer and dolly if a low spot can not be work out cut the tack loose pull up and retack when all tacks are ground level to metal then i move up the tacks till they are less then a 3/4 apart then grind them flat and wire wheel then a go from tacks to welds and only weld about 1/2 to 3/4 between tacks no more .when cool grind weld flat. and hop around never start form one end and stop when done.i walk way till cool s down .it is still to hot if you can not keep your hand on it. get on and off the panel with out putting alot of heat in to it . i set welder or check wire speed for low bead . when the panel at this point it is harder to warp but still can hapen. i let it cool down by it self or a damp rag you have to watch this water or blowing can shrink the spot that can make it wrap to that may not be what you want. i never hit the weld any more then needed with a hammer and dolly this can make stretch the steel so you do not want that. i ether i used a hi speed angle grinder with a sharp 24 grit(new) or a grinding stone you want to get on and off the panel do not dwell on the weld. the way i did it there was not much grinding when done .as i did it along the way.i never used flap wheels they will not cut the hi s off the weld just blend and they make more heat = wraping if you want to seal coat the back side after welding there are things you can buy or make you can use firber glass reisn or a west epoxy put on with a brush then epoxy paint it then use a uncoating work in with a brush or amber wax bass under coating sprayed in with a under coating gun . before you get this far you many want to add a drain hole at the bottom of patch i used the word Tack less then a 5/16 to 3/8 spot weld ideal size was for a tack was 3/16to 1/4 of weld for me

Everyone who says to not run a bead is correct. Hope you are using a mig welder with sheilding gas, so much easier to clean up. A 110 V. with shielded wire is good also, be sure to wear your safety glasses when you hit the slag with your grinder. Skip weld is what you use, and until you are competely tacked up, spot abot 3" apart then "skip" around with 1/2" welds until you get it stitched completely. You can get your metal to pull tight by applying a cool damp cloth immediately after you finish your weld. If you ard using a stick, a cooler weld can be achieved by "pulling" the rod away from the work slightly after you strike your arc. I use that method on 20 gauge and lighter, and hold heat to 2 seconds or less. works well with cold galvenized, too.

I found this website in good old plain english that might be of help to all:www.weldingtipsandtricks.com:)