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Old 05-06-2009, 12:40 AM
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Default Mig welding sheet-metal**

This thread was originally posted on the old site. The original thread with photos can be found here:

http://allmetalshaping.forumsdot.com....php?f=11&t=23

Please make all new posts for this thread on the new site...that is HERE. We will be working to get the photos moved over.



I think learning how to weld sheet metal properly is one of the most important things to learn.

Until recently acquiring a tig welder, I had to mig weld my panels because the mig was the only welder I had. A mig weld is a much more brittle weld and over hammering will lead into a cracked weld. However it is possible to produce a nice piece using your mig welder.

Here is a fender I mig welded.


20080426_2.JPG



I think if you are using a mig it is key to have the panel fitting perfectly first, to reduce the need of extensive hammering. Don't ask me how I know .

I will show you the method I used for welding the fender,on some scrap pieces of metal.

I start off by tacking in 3/4 inch increments.


20081018_27.JPG



I start in the center of the panel and work outward alternating sides with each tack. After every two or three tacks,I grind down the proud of the weld,using a cut-off wheel.


20081018_28.JPG



Next I will re-stretch the HAZ of the weld (heat effected zone) This is the blued area around the weld. All I do is using the dolly on method I give each tack a few light hits with my body hammer. On dolly stretches metal off dolly shrinks metal.


20081018_30.JPG



Now that I have the panel all tacked in place, I start filling in between the 3/4 inch tacks.



20081018_39.JPG


After I fill in the weld I grind down the proud of the weld and re-stretch the Haz of the weld the same as I have shown with the tacks.When welding between the tacks I still start in the center and alternate sides.

When welding in I place a tack let off of the stinger then I lay another tack 1/2 on the previous tack and so on and so on.When placing each tack you have to almost burn through before letting off of the stinger.This is to insure a full penetration weld.This will take some getting used to.Here is a picture of the back side of the weld.



20081018_31.JPG


Here is a picture of the panel welded up.



20081018_42.JPG


I also welded a panel up using the same principals except I did not re-stretch the haz of the weld.Here is the result.


20081018_48.JPG



I think it is pretty obvious which method works better.

This is just the method I found to work the best for me, I would love to see other methods if you do it differently.

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Old 07-27-2009, 11:41 AM
chris@whiterhino chris@whiterhino is offline
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Nice post, I think I am going to test this out today. It is hard sometimes to take your time and just just run a large bead. I guess everyone is like that at some point, I know I used to be. You have the frame of mind, "It will not warp on me." Like you have some super human ability to control it warping or not!
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Old 07-27-2009, 06:03 PM
David Gardiner David Gardiner is offline
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I would be interested to know how much time it takes to weld and dress out an area like the one on the wing (fender) I know that it is a long drawn out process which will be worth while if a mig is all you possess but gas welding will give a much quicker and more workable result.
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Old 07-27-2009, 07:41 PM
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David

It is a slow process about an hour a foot.As you know If you hammer on a mig weld it will crack.So you have to keep up with it on every 3/4 of a inch of weld,there is hardly any hammering

If all you have is a mig welder it will work.Not the preferred method but sometime you have do what you have to do.

I have moved on to tig know but still use the same method.
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Old 07-27-2009, 07:42 PM
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Post your results Chris.
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Old 07-28-2009, 01:51 AM
chris@whiterhino chris@whiterhino is offline
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Quote:
Originally Posted by jhnarial View Post
Post your results Chris.

I'm sorry man, I have FAILED you again Lord Vader...(in my best Star Voice) I didn't get a chance to do that tonight, I was simply just to busy. I will try it tomorrow.
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Old 07-28-2009, 09:17 AM
David Gardiner David Gardiner is offline
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Quote:
Originally Posted by jhnarial View Post
David

It is a slow process about an hour a foot.As you know If you hammer on a mig weld it will crack.So you have to keep up with it on every 3/4 of a inch of weld,there is hardly any hammering

If all you have is a mig welder it will work.Not the preferred method but sometime you have do what you have to do.

I have moved on to tig know but still use the same method.
Dont get me wrong Johnny I have nothing against mig welding, and I said that if its all you have Ok. I do think you made an incredible job of this wing but I know how much effort went into the welding and finishing of the welds. I feel that mig welding is not the best or quickest method for butt welding edge to edge because it takes so much effort to dress out and because the weld is harder that the parent metal it can crack once you have groung and filed it and hammered it. (or even once it is on the car and painted) I use mig for some jobs because its ability to join the panels without putting much heat in is what I need (for example a corner butt weld on a panel or for plug welding)

Tig welding is fine and I know that contour autocraft use tig and teach this method. I also know that if you dont use filler rod there are some issues with tig welds cracking, if you do use filler rods and you can get a perfect weld with very little penetration and build up of bead you can get a result that is easy to metal finish. The problem I see is the amount of skill it takes to weld to this standard with tig on thin sheet. The gas welding method I show on my DVD takes very little skill and can be learned with a few hours of practice, the resulting weld has very little build and very little penetration so there is no grinding to do, the HAZ as you call it is very even so little distortion is caused. The weld has the same properties as the parent metal and is the same thickness so it is easy to dress out. I think for someone who only has a mig your wing will be an inspiration but for anyone starting out I would allways recommend getting gas equipment, it is the most versatile method of welding (for bodywork on old cars) it can also be used to heat things cut things and it costs no more (over here at least) to set up for gas than for mig. Having both is ideal though!

Regards

David
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Old 07-28-2009, 11:48 AM
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Quote:
Originally Posted by jhnarial View Post
David

As you know If you hammer on a mig weld it will crack.
Boy I wish I had paid more attention to that sentence a week ago..

I was hammering the crap out of my Mig welds and the haz, so when I ground them to finish, lo and behold- Cracks. I may have to redo the entire panel, because it'll nag at me, knowing it might crack..
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Old 07-28-2009, 02:11 PM
chris@whiterhino chris@whiterhino is offline
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Quote:
Originally Posted by David Gardiner View Post
Dont get me wrong Johnny I have nothing against mig welding, and I said that if its all you have Ok. I do think you made an incredible job of this wing but I know how much effort went into the welding and finishing of the welds. I feel that mig welding is not the best or quickest method for butt welding edge to edge because it takes so much effort to dress out and because the weld is harder that the parent metal it can crack once you have groung and filed it and hammered it. (or even once it is on the car and painted) I use mig for some jobs because its ability to join the panels without putting much heat in is what I need (for example a corner butt weld on a panel or for plug welding)

Tig welding is fine and I know that contour autocraft use tig and teach this method. I also know that if you dont use filler rod there are some issues with tig welds cracking, if you do use filler rods and you can get a perfect weld with very little penetration and build up of bead you can get a result that is easy to metal finish. The problem I see is the amount of skill it takes to weld to this standard with tig on thin sheet. The gas welding method I show on my DVD takes very little skill and can be learned with a few hours of practice, the resulting weld has very little build and very little penetration so there is no grinding to do, the HAZ as you call it is very even so little distortion is caused. The weld has the same properties as the parent metal and is the same thickness so it is easy to dress out. I think for someone who only has a mig your wing will be an inspiration but for anyone starting out I would allways recommend getting gas equipment, it is the most versatile method of welding (for bodywork on old cars) it can also be used to heat things cut things and it costs no more (over here at least) to set up for gas than for mig. Having both is ideal though!

Regards

David

David,

I have been looking high and low for the Gas welding Flux you used to weld the Alum. Where or what is it called? I found some flux for brazing aluminum and the guys at my local welding shop tell me that welding Alum with gas is not possible, I know it is BTW, so I am wanting to prove them wrong. Do I use the same flux?
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Old 07-28-2009, 03:44 PM
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Chris, go to Henrob Jims ad in the classifieds. He has it, is a good guy, and a supporter of the community.

Your welding supplier is clueless.
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