I'm doing some sheetmetal work on my Truck. Im gonna resleeve the bottom half on my drivers door(cut the whole square bottom section out, and new section in) and some pieces on my fenders to replace.. What is the best way to run a bead on sheetmetal? I know with a Mig you can't really run a solid beam along the sheetmetal. I don't want to be there for hours using small tacks all around the whole section..Is Stick welding(Oxy-Acety) a possiblity? Any help on the Fastest way to do this and with the right application would be helpful..Than**x
If you have oxy-acetylene on hand, I've had good luck brazing panels long before the newer methods were available.
The reason that you tack weld back and forth is to reduce warpage due to the heat............Whatever method you use, if you in a big hurry, you will warp it all to hell.
x2 to that tack a spot move 6 or so inches inches away (depending on panel size) and tack again letting it cool between tacks to prevent warpage. I have done it with my MIG and had decent results but still practicing the technique because I tend to get rushed about things.
you want the fastest way or do you want minimal or no warping? when I have a big sheetmetal weld to do I make sure I have something else to fiddle with in between tacks. weld your tacks around the primeter...do something else while it cools, and come back and do the same thing lagain. I figure if you can't touch it with your bare hand it is still too hot to weld in that spot. watch your heat while grinding also.
To speed things up a little you can use Compressed Air-it will cool it quicker- And don't forget-the best Welders are the best Grinders-
[QUOTE=Nightshade;2542715 tack a spot move 6 or so inches inches away (depending on panel size) and tack again letting it cool between tacks to prevent warpage. Its not the only way,just the right way
Also hammer and dolly the tacks before welding more tacks. You MUST ALWAYS keep warps and bumps out. If you have a bump and keep welding, you are screwed. Wacking the tacks will straighten the panel.
In my somewhat limited experience, cooling a weld with compressed air serves to increase the warpage as it speeds the cooling. You want to make the temperature changes as gradual as possible. Of course, I pretty much only use an O/A for metal that's not a flloor or something else out of sight because you can pound the much less brittle weld bead flat on an O/A weld, so your mielage may vary with a MIG...
hijack alert (but related) so, for floor pans, let me know if this will work. I plan to punch holes on the outside edges of the pan to be welded in. One half inch overlap. The spot welds will be about 1 1/2 inches apart. When I spot all these in, I plan to hit the seams on the pan, to close it in, then grind smooth. Hit with some seam sealant, and KBS sealant. I thought about running a long bead along the seam, not sure if I should. Again, sorry about the hijack, but I'm sure others can get something out of this as well. Thanks JL
I was a little skeptical at first also. I work for a Company that has a GM Dealership (with a Body Shop), and was shown there that it was the way they do it. After they did, I satrted walking throught the Shop and watching the amount of Filler they used, and it was very little. I realize they are trying to make money at it (beating Flat Rate). I don't use this technique very often(I have the time to wait in between Welds), but whe I have done it I haven't noted any difference in warpage-if anything, it seems to make the HAZ area smaller-
Just bust out the mig, hold the trigger on the gun down and lay a nice long bead across that formerly flat door skin. I'm sure it'll work great, that's how i saw the guy on pimp my ride do it.
I will add to both questions here.. the floorpan weld technique you plan is perfect. Its easy to weld them that way too. Best Sheetmetal technique.... If I have a long seam to weld I do this for two reasons... It prevents warpage and helps prevent blow through... Tack your door piece in place. Cut a piece of the same thickness of material and as long as the weld you'll be making. The width of the material should be at least 1/8 wide. Clamp and Tack this long thin piece on the back side of your seam. This backing plate will help in alot of areas. It also allows you to run at a fast rate. You will still have to s***ch weld otherwise you will have warpage. After you weld the panel in place, you will notice most of the backing plate has actually fused in place. Be sure to grind and seal this area very well to prevent moisture from entering the seam from the back side.
In the amount of time it takes to read all these replies and wax poetic bout welding, you could have had both doors done properly using the tack and move (and have patience) method. .
I have alway's done the spot, move spot method with very good results. Yes, it takes time and you will be there for a little while doing it so you don't warp your panel.. But the way i look at it is, i can either spend the time in the beginning welding it slowly, or spend the time at the end ironing out all the warpage from being impatient.. I'd suggest just spot welding it with a mig.. Tony
All that follows I consider fact, but present as opinion. 1. Use smallest wire possible....023 if thinner than 18 gauge and .030 for 18 gauge and thicker and no flux core. 2. Use a C02/Argon mix 25/75% 3. Use AWS E70 wire. 4. S***ch weld. The only artificial cooling method (wet rag/compressed air) that really works is a backing bar of copper or aluminum.
Taking the time to tack it is the right way to do it, with a mig. Just jump back and forth from each panel, do them all at the same time.
I have heard that air/wet rag can cause the weld to become brittle. Once it's gound down there is a risk of cracking which tends to make paint look like ****.
The method I use on the sheet metal is something I call "dot" welding. Welding sheet metal is a different animal than welding up some thick steel in that the sheet metal is not as forgiving to excess heat. For example, when you start your weld bead with your mig welder set up properly for the gauge sheet metal you are using, if you were to actually do a weld p*** you would see the start of the weld had little to no penetration due to the metal still being cold, as you progress the metal is heating up and you get better flowout on the bead and penetration of the weld, and if you go much further you will blow a hole. To combat this problem, as well as minimize heat buildup and deformation of the sheet metal, most suggest using a tack weld process, sometimes combined with short weld p***es, skipping around to minimize heat buildup. When welding sheet metal, I will typically set my machine up for the next highest setting, for example, if welding 18 ga, I will use the machine heat and wire feed speed settings for 16 ga. When I weld the first tack, or "dot", you will see full weld penetration due to this higher setting. If we were doing a weld p*** it would blow a hole, but because it is only a single tack (dot) that chance is less likely. If you do tend to blow a hole while using this process, before reducing heat, try turning up the wire feed speed a bit. (If you have adequate heat to perform the weld process and the wire feed is not providing enough filler material, the machine is going to melt something-hence the blow hole. Speeding up the wire feed speed combats this) Skip around to minimize heat, or if you're in an area that has less chance of deforming (like next to a door jamb crease) you can do a few tacks in a row. In a case like this, I would let the first tack cool until the red glow starts to disappear, overlap about 1/3 to 1/2 of the last tack and do another. Repeat for about 1/4 to 1/2" p***, or as the metal will tolerate for the location. So actually you are still doing single tack welds, and allowing some cooling in between. Here's a lower fender repair I did, which may help to better show this process. The repair piece was made using a brake and Lancaster shrinker/stretchers. The first order of business is to clamp the lower edge flush with the bottom, align the side, and tack weld in place. As you can see I got a little too happy t******* and the long side has a bit too much gap there. When welding, much of the distortion you'll see in the metal comes from the heat stretching it out, and when it cools down, you'll get a bit more shrinkage than what actually stretched. It helps to planish out the weld tacks as you go (hammer and dolly), minimizing any shrinkage issues. Just don't overdo it. With any welding you are doing, check the back side to insure full penetration, or adjust your machine accordingly. If you need to weld it from both sides due to lack of weld penetration, you just doubled your chance of overly shrinking the area. I ground some welds off as I went. As the weld "dots" tend to fill in and get closer together, you'll run out of room for using the hammer and dolly, so this gets some of the excess out of the way for planishing the new weld dots. The rest of the welds are filled in, skipping around as usual to minimize heat buildup, and then ground smooth. One final note, you want to keep the metal as tight together as possible using this method. It will give you less chance of blowing a hole, and doesn't provide all that room for the metal to shrink even more. Ever use the Eastwood type sheet metal clamps and weld on either side, only to have them get real tight and hard to remove? This is a good example of the gap providing shrinkage room. One method to reduce this if you're real **** is to file a small relief for the clamps to fit in so the rest of the joint is tight. Here's the same process where I was less worried about planishing the welds: And the underside:
MP&C, Excellent response, but how long do you squeeze the trigger when doing the tacks? one second? two? BTW, where in MD are you? Thanks, Gary
Gary, about a second, maybe a little more on that joint where I had too much gap. I'll normally do a few to start and check the weld penetration and gauge the rest by how well that's doing. Leonardtown (St. Mary's County), about an hour SSE of DC
GREAT POST!!!! Im also getting ready to start welding sheetmetal.... We have covered mig so what about gas Oxy/Acet? I have been looking at a Meco Midget. http://www.tinmantech.com/html/meco_midget_torch.php Any tips or advise is one better that the other?
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