Tech Post's? Heres one for the beginning welders....

Since Ryan wants Tech posts, and I know more about Fabrication and Welding than I do about Suspensions and Drivetrains, I’ll make my Tech post about Welding Sheetmetal.

Sheetmetal is obviously one of the hardest things to Weld without warpage. I can offer a few tips on controlling warpage for the non-professional welders on this board. It’s easier to keep warpage out in the first place, than it is to fix it later.

To start with, tacking correctly is one of the best ways to control a piece of sheet metal. Once you get a couple of tacks to hold the piece in place, you need to start worrying about keeping both sides of the joint even. If you can reach the backside of the Weld this is best done by Dollying each tack as you go because that also “stress relieves” the tacks. If it’s a blind joint, control the relationship between the two pieces with a scraper blade wedged into the gap. You can then manipulate the two pieces of metal by prying them up or down until they match. I tack about every half inch when warpage is an issue, and also cool as I go with a wet rag.

Fit of the joint is especially important too because you want an even gap all the way around. On most automotive sheet metal I will try for an even 1/16” gap on the joints. When a Weld cools, it draws the metal towards it. An even gap makes it easier to achieve full penetration, plus allows the weld to pull evenly all the way across the joint. Full penetration is important because as you grind the weld down flush with the surface, you are taking away the strength of the joint. Full penetration leaves you with a weld joint that’s the same thickness as the surrounding metal after it is finished.

If you are a beginner, it is also important to practice on a couple pieces of scrap that are the same thickness as your project. Keep both penetration, and travel speed in mind as you adjust your amperage. The quicker you travel while welding, the less heat gets into the surrounding metal, but you still need the full penetration. If the Welder is set too hot, you run the risk of blowing through the metal. If it is too cold, you will be grinding all the weld off when you finish it out because you lack penetration. If you use lower amperage, but a slower travel speed to achieve full penetration, you aren’t any better off because you are letting more heat get into the surrounding metal.

Keeping the heat from getting into the surrounding metal is the number one way to prevent warpage from happening in the first place. You have to remember that in a formed panel, like a car body, the metal is stressed into shape. Getting too much heat into that stressed metal will cause it to relax. That is why its also important to do all your welding at an even speed and fill rate, so the entire joint gets the same amount of heat.

After I have a panel tacked in place, I will start welding about an inch at a time, skipping around and cooling between each weld. Once the piece is entirely welded, it is again a good idea to stress relieve it with hammer and Dolly if possible and I do this before doing any grinding. That keeps the hammer strokes on the Bead instead of the panel, and this is also important because the Bead is what’s doing the pulling. As you smack the bead between the hammer and Dolly, it expands what the bead has pulled, if you get my drift. It is possible to over-do it though and make the joint grow, so take it easy.

When rough grinding the joint, I suggest doing it with a Flap Disc. This looks like a Grinding wheel, but is made up of sandpaper flaps. 60 Grit is what I use most of the time because it gives you a good removal rate without getting too aggressive. A finer grit could be used, but it will put more friction heat into the metal because it is spinning at the same rate, but not removing material as fast. Frequent cooling with that wet rag is important here too. If you end up with a low spot or two, go ahead and get that area a little hotter before you cool it and the wet rag will help to draw the low spot back up.

Another tip for keeping heat out of the surrounding metal is to use a “Heat Sink”. I use strips of 1/8” Copper. It is easy to make the soft Copper strips conform to the shape of the panel you are working on, and Copper conducts heat much faster than steel. Clamped to the backside of a weld joint, it also keeps you from blowing through, and acts as a Gas Trap, which keeps porosity out of the backside of the Weld and enhances the strength of the Bead. Copper will also allow you to fill holes much easier because on top of drawing away the excess heat, it will not stick to the filler metal. Just make damn sure you don’t touch the Copper right after welding. It transfers heat so fast that even a couple of spot welds will make the copper hot enough to burn you.

 

Good stuff......thanks!

Brian

 

Yeah, thanks from me too. All good helpful stuff.
Mart.

 

Nice start to a beautiful week of on topic tech!

TDC

 

So what is your opinion on the heat soak putty?

 

bftwcs, thanks for the info. i have some questions. i am a begginer at sheet metal welding. i get the job done, but it's not to pretty most of the time. first, on the wet rag, will this cause rust? i have a problem with my welds building up on the outside and i have to grind so much that i make the whole area to thin before i'm done, am i not welding hot enough? and this is the second time i've seen the copper come up this must be very important.

 

"So what is your opinion on the heat soak putty?"

I have only used the putty once. It seemed to work allright, but that was on a small machine part. I don't know how it would work on sheetmetal.

"i am a begginer at sheet metal welding. i get the job done, but it's not to pretty most of the time. first, on the wet rag, will this cause rust?"

The water evaporates quickly from the heat.You don't have to keep the metal totally cold, I keep the rag handy and as soon as I raise my hood I cool it enough to stop the high heat from traveling into the surrounding metal. You don't want to get it completely cool, just cool enough to touch.

"i have a problem with my welds building up on the outside and i have to grind so much that i make the whole area to thin"

Without seeing your Beads, its hard to tell. That sounds like either too much Wire speed, or not enough amperage. On sheetmetal I adjust my Welder and my Travel speed to end up with a bead that is nearly flat, and has full penetration.

For someone who does not have a lot of Welding experience, the copper will help a lot. You can run the Welder with less wire speed, which makes it easier to run a Flatter, full penetration bead without blowouts.

Just like everything else, practice helps more than anything. Butt pieces of Scrap sheetmetal together and start experimenting with Gap, Heat, Wire speed, and travel speed.

Where I work, there are three of us that do the Majority of the Welding. Each of us will operate with slightly different settings on the Welders whether its MIG, TIG, or Stick because we weld differently. Travel speed and personal technique are different with just about everyone. I have trained several Apprentices, and while most of them turned out to be good Welders, only one of them can pick up where I leave off, and weld with the same settings and travel speed that I do.

 

Great info, I am in the middle of it right now...

Thanks for taking the time to post this ON topic subject !

 

i'm definalty not doing something right. thanks for the great info. this should help tremndiously. whats the best gauge steel for car bodys? 20 or 22?

 

I spent the day yesterday welding up a side marker light hole on my Chevy pickup. I had alot of problems. It was mostly due to the filler piece of metal shifting around. It made it hard to tack into place. Any tips on how to hold a filler piece of metal in place when it is not accessible from the back? I usually use magnets, but in this situation they just didn't help at all.

BTW, thanks for the tips. What you have said so far makes alot of sense and I realize I'm doing a few things wrong. Practice, practice, practice.........................E

 

"Any tips on how to hold a filler piece of metal in place when it is not accessible from the back?"


Tack one corner, then push it down into the hole. Manipulate it with a Scraper Blade, or a thin screwdriver that will fit in the gap and Tack the other three corners.

Once all four corners are tacked with an even gap all around the Patch use your thin screwdriver or whatever, to pry the Patch panel up or down while making Tacks every 1" or so. After you make a full circuit around the patch panel and everything is fitting flush, go back through and put another small tack between each of the 1" gaps so you end up with 1/2" between tacks.

That should be close enough to keep the metal from warping/buckling between the tacks as you weld it up. I usually grind the Tacks down close to flush before welding so they dont make humps in the bead, but it probably doesn't really make any difference.

 

so this copper strip is held in the middle of the seam? How wide of strips do you use?

just to be sure, would it be better to weld the panel in COMPLETELY with tacks? Would that cause a problem other than time?

thanks for the great article

 

I generally use a strip about 2" wide, and use deep Vise grip C clamps to hold it in place. On a blind joint, it would depend on whether or not you can clamp it in place. Once or twice I have had to drill a few 3/16" holes through both pieces and Rivet the strip because I couldn't get a clamp on it. After welding you just drill out the Rivets and fill the holes. Those Kleko's or whatever they call them would work good in that case too.

Most of the time on a blind joint I won't bother with the Copper. Instead, I will concentrate on getting the patch panel or Joint gapped and prepped correctly, then use a wet rag to control the heat. The copper backing strip is handy if you can get it clamped in place easily, or if you are a beginner and have trouble welding without blow outs. But sometimes it is more trouble than its worth...

Tacking the panel in? I guess it would work but it would be time consuming and you run the risk of "cold lap" between each tack.

 

where can I get copper strips?

 

Briggs, most hardware stores sell 1/2" or so diameter copper pipe. I guess you could cut them down the middle and flatten them.

 

I work for an Industrial Sheetmetal outfit so I just shear strips off Scrap Copper. Check with Sheetmetal shops in your area. Architectural Sheetmetal uses a lot of Copper for Roofs, gutters, and Ornamental work. You don't necessarily need 1/8" either. Thinner Copper will work fine as a backer on Sheetmetal, but the heavier stuff will pull heat away more efficiently.

Aluminum works almost as well too, and is easier to find.

 

Here is another scan concerning Wirefeed and Amperage suggestions for MIG welding.

 

bttt (shameless promotion of this post)

 

BTTT