So I put a new door skin (or the bottom 3" of a door skin) on my truck's driver's door, and it's all caved in along the weld. I had it fit with about a 1/16" gap, tacked it in place every 2" or so, then skipped around as I welded it (all this with a MIG). It still pulled in, and I didn't realize how bad until I was almost done. I can't get to the back side of it with a hammer to knock it back out, and I really don't want to cut it out and start over. It's about 3/16" or 1/4" down at it's worst point, and I don't want to slop it full of filler without trying everything else first. Could somebody explain to me the torch/wet rag method for this kind of thing? I tried searching for an explanantion, and couldn't find anything. I took a shot at it last night with my propane torch and wet paper towels, and got scared I'd screw something up worse and stopped. I've got a slide hammer, but I always think of those things as a last resort... I don't have any finished pics, but here's about halfway through the tacking process:
cut away the inner structure to get a hammer/dolly in there and weld it back in when done, or build a dolly to get behind it. because you migged it and the welds are hard, i would consider using a gas torch to heat the welds to red hot, then you can use your homemade dolly behind, and hammer on the face to bring the welds up, by putting pressure on the dolly as you hammer. what you need to do is STRETCH because the weld shrunk when it cooled, don't shrink, that's what got you where you are now.
Ray has a good point. With mig welds they are very hard and it may take some heat. If it was me I would grind your welds pretty smooth otherwise you will just drive the high parts of the weld in. You may be able to get a curved spoon (a body dolly in a curved shape with a handle) or I have used a piece of leaf spring and heated them up and bent them into the shape I need and get them in small areas. Your welds are kind of grabbing all of the surrounding sheetmetal and you have to hammer and dolly and relax the area of the weld and the surrounding areas where the metal is under tension. If you cannot get anything in there you may have to try to open up the inner panel as suggested by Ray-good luck -Jim
I can get to the back of the welds with a dolly--they aren't buried too bad, they're just behind enough of the structure that I can't swing a hammer at them. I've got a curved dolly that'll go in there, and if that won't, I've got leaf springs I just took out. I've already ground the welds down on the face of the door. So, just to review for my thick head: 1. Grind the welds down on the outside of the door (also get what I can of the penetration on the inside? I might be able to sneak a 7" grinder in there with some 40 grit...). 2. Heat the welds up to red hot--an area of 6-8 inches at a time good enough? I don't have an oxy torch, but I can get MAPP gas for my handheld, and that should be enough. 3. Hold the dolly on the inside of the door, and hammer on the weld. How hard do I swing? 4. Repeat. Repeat. Repeat. I assume I work my way down the door, maybe do it in several passes? Thanks for the advice, guys--this sheet metal welding business is new to me.
Mostly right---Don't be to concerned about grinding down the welds on the "don't show" side. Do not heat 6" at a time though. Heat a section not more then 1 1/2" long to a cherry red. You would be well advised to have a helper either to hand the torch to or to do the actual hammering and dollying. Sheet metal cools so quickly that by the time you shut the torch off, lay it down, pick up the hammer and pick up the dolly, the "hot spot" will be cooled off. A series of good firm raps with the hammer directly on the "hot-spot" backed up with good firm pressure from the dolly are what you are trying to achieve-not a crushing blow that damages things even more. I am not sure that you will be able to reach the temperature range you need to if you don't have oxy acetylene.
Metalwork is something that I have not mastered in spite of a pretty good amount of time doing it, but I may be able to help you a bit. I also do not believe Mapp will do the job. OA is needed to bring the weld up to red in a quicker amount of time. I have never used Mapp but I would assume it would take too long and during that time you would be putting a lot of heat in the whole panel which is not going to help you. Make a little torch stand out of metal. You can make one out of a 5" long piece of angle iron at a 45 degree angle so the torch handle lies in it with the end hanging over the end of angle clamped to a metal brace. You need something that you can set the torch down quickly, hammer the weld while it is still very hot and pick up the torch still lit and go on to the next small area and repeat the hammering process. An area 1 1/2 to 2" at a time is fine. Most sheetmetal fabricators use OA welding because the weld stays softer and many use Tig because you can get in quick and get out and the weld bead with Tig is very controllable and you can keep the weld bead small. Mig welds tend to be quite hard and do not respond to hammering in quite the same way as OA and Tig. They can be brittle and crack the weld so don't go too hard. You want to use the dolly on technique for the weld bead which means back up the weld with the dolly (or spoon or piece of steel or whatever you are using as a dolly). By using red heat you are forging the weld or trying to make the weld and the surrounding metal become one. I have never been successful doing that with mig welds but with a dolly on technique you can improve the panel by hammering the weld and immediate are with red heat. You never want to hammer too hard or you will just stretch the area and/or crack the weld. Set a goal to plannish or smooth the area. Use red heat on the weld bead and then after you have done that you can use off dolly technique without heat. There is a pretty good chance there may be some remaining high and low spots in the areas surrounding the repair. Place the dolly or spoon on the low spot and put some light at a angle to the panel so you can watch the movement as you push up the low spot with the spoon or dolly. As you push up that spot gently tap down the high spot just next to the low spot (so you are not coming into contact with the dolly)with a body hammer with a low crown (pretty flat). Patience is the key. Good luck-Jim
I agree with ray. Heat the weld and stretch it. Each weld bead has shrunk down and pulled metal with it. !/16 gap may have been too much. Funny, I was just doing this today on a prototype display buck that the fab dept basically said " screw it, let the body guys fix it" as they built. Fuckers. Anyways, stretch the welds. To avoid this in the future with a mig/sheetmetal weld, tighten the gap to 1/2 of what you had, get some beer for a helper (when yer done!), and gently tap/stretch each weld as it cools...just as the red is going away. The helper can hold the dolly under each weld for you since you can't really change tools that quick. The result is no pull and a pretty flat panel. Good luck. It's really not that bad.
it shouldn't really be necessary to hammer the welds when they are still red hot, but it will help. what you are doing is basically annealing the weld. the only reason a mig weld is hard, is because of the rapid cooling of a mig weld. there is no difference in filler rod, so once you heat it red and allow it to slowly cool, it should be as soft as if you gas welded it to begin with.
Your weld shrunk the area. You need to stretch. The only reason to reheat the weld would be if you can not get enough force between the hammer and dolly to stretch. Use a high crowned hammer and a high crowned dolly so that the contact area is small. You will be able to stretch using less force. Push out with the dolly while hammering. Then use a dolly that matches the curves of the door skin to smooth the area out, and repeat as often as necessary. I would not reheat...especially not to red hot...unless you want to shrink and harden the metal some more. Here is an article that might help for the next time: http://metalshapers.org/101/jkelly/index.html John www.ghiaspecialties.com
Ok I am a little confused. If it is sunk in or shrunk in, you heat it up and put the dolly on the BACK of the panel and hammer on the low area?it seems like this is backwards, that you should be hammering on the high spot. So if there is a high spot on a panel, you should heat that area up, place the dolly on the high side, and hammer on the low area to get the high spot back down? Maybe that is why I have a hard time doing hammer and dolly work. I wish one of the Metalworking gurus would do a tech on this.
be careful with heat... you'll oil can the rest of the door. Looks like a good spot to learn how to use lead...
This use to confuse me also. I think the hammer blow actually smash's the metal thinner thus stretching it.
The idea behind hammering on the low area with a dolly backing it up is that you are stretching to make more surface area. If you have more surface area it will want to grow outwards if you put pressure on the dolly from the back. Use heat only as a last resort! If you use heat, heat the metal only a little bit. Do not let it turn blue or red. Heating the metal to red hot and cooling it does not soften the metal, it makes it harder. You can stretch the metal more easly with heat, but it becomes even harder to work with a hammer and dolly after it has cooled. Leadsled01 and Leadsled51, click on the link in my post above and read the article and the linked articles to get a better grasp of what is happening. John www.ghiaspecialties.com
If someone brought me this door and said, "Hey I screwed up, can you fix it?" I would start by fabbing a new replacement panel that goes 3/4 of an inch higher on the original skin (to unaffected metal). I would loosely crimp 2 of the three edges and scribe a line on the door. I'd cut the bad repair off 3/4 of an inch below my scribed line and cleco my new panel into place, with clecos every six inches or so. Scribe again, because the panel will have better fit now with the other piece gone. Remove clecos and panel, leaving little tabs where the cleco holes are, cut on the new scribed line. Re-cleco the panel to the door to check fit and contour. At this point I probably have the panel on and off the door a dozen times to sneak up on the best fit. When you're happy with the fit begin to tack weld. HERE'S WHERE YOU MADE YOUR MISTAKE... every tack weld needs one firm smack from a flat faced body hammer with firm backing from the right shaped dolly. As you said, skip around to avoid getting too much heat in any one area. Zip cut off the tabs as soon as the panel has sufficient tacks to keep it in place. I don't use water to squench or compressed air to cool. I let the heat work for me, watch each tack as it cools if it pulls, smack it again.... if it bulges, go light pressure with the dolly (let it bounce) and give light taps with the hammer to pull the metal in. You absolutely have to control each tack or the whole panel will get away on you , as you have found. Tighten up the 2 crimped edges and crimp the 3 edge and viola, door bottom patch, no warpage!!
I've got a some of this work to do and was wondering about hammering the welds and what that was all about. What you just said just helped my thinking process a ton! Thanks for commenting on this task. I like the idea of using the clecos also. One question for you. If you're using clecos then are you implying you're running an overlap behind the upper, original door skin?
No, he's telling you to only overlap the panels where the clecos are holding it. Butt weld inbetween the clecos. Once you have the panel tacked in good, use a zip wheel and remove the tabs that the clecos went through. Then you just have a few holes to fill and a nice butt welded panel.
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