Adoom

Backing a butt weld with copper?

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So I have seen this technique where you put a bit of copper or brass hard against the back side of where you are welding some thin metal. It's good for butt welds and filling holes because it absorbs the heat and stops you blowing holes in the metal. And the copper doesn't stick to the steel you are welding.

I've just tried this for the first time today, using a bit of flattened copper pipe. It seems to work well if you can get the copper to sit flat against the metal you are welding.

But some of the stuff I an trying to weld is NOT flat and the weld blows through until it reaches the copper. I have one weld where 3 panels come together in a Y shape, so making a bit of copper fit nicely is hard.

I've heard you can also use aluminium instead of copper...

What about aluminium foil.... if I hammer a bunch of it into the back of the join it should conform to the shape nicely? Yeh, nah?

Has anyone tried this?

 

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Ali foil may melt and contaminate the weld.

If you cant get the copper in there dont rely on it. blow throughs means too hot for the context - turn down the power a bit or change techniques?

Maybe try get some 'cold' bridging tacks in to hold it together. They will soak a bit of heat and allow the pool to get going when you go over it (slowly) with another pick and peck stack of hotter tacks (instead of a bead)

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You could also use some self tappers to hold in a backing strip Behind the join, depending on the application

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The weld join I am trying to make looks like this. The top is the patch I am welding in. The left is the remains of the inner guard. The right is the inner wheel arch(front).

 

weld.jpg.e55aad541a6e580680e511f8daf0597f.jpg

It's the left side of this patch, where the burn mark is.

patch.thumb.jpg.3c26c38518f4e736eb26d34fae4bf071.jpg

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I'm very reluctant to offer welding advise, as I'm so terrible at it myself. So take from this what you want.

But for welding really thin metal with a mig, I basically lay a bunch of overlapping track welds. I get nice and comfortable, support my hand, pull the the trigger...watch the metal change colour (red), then release the trigger but remain in position, watch the red glow fade out of the weld (takes about a second)....repeat....IMG_20161020_141458.thumb.jpg.b469f3aefc6878bb0503fc7d1cdaf1ec.jpg

Doing it like this stops you from blowing big holes through your work.

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@Adoom

Now it could be the photo tricking me, but have you ground the metal back you're trying to weld? If you have, apologies, but from where i'm sitting it looks like you're trying to weld painted metal to your guard. That is never going to end well, bare metal or nothing. Just looks white to me, and the burn mark indicates shit getting messy. Also with metal that thin, you pretty much want no gap. Is your welder on its lowest setting? 

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Yeah, metal is ground back either side on the top flat surface. It's a T shaped join and I couldn't get right down into it to get the vertical surface totally clean. That's what is burning up and covering everything else in soot.

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My post was aimed at Adoom sorry (edited to suit), I should have quoted. But yeah, not prepping a weld area is just making life harder on yourself.

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Ok so your welds look too big, and possibly too hot @Adoom.

What wire size are you using? .6 is the standard for body repairs in the auto industry.

Also, your gaps look far too big! They need to be hair sized 

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9 hours ago, Bling said:

@Adoom

Now it could be the photo tricking me, but have you ground the metal back you're trying to weld? If you have, apologies, but from where i'm sitting it looks like you're trying to weld painted metal to your guard. That is never going to end well, bare metal or nothing. Just looks white to me, and the burn mark indicates shit getting messy. Also with metal that thin, you pretty much want no gap. Is your welder on its lowest setting? 

The photo, it tricks you. The metal is new, with that grey/zinc whatever coating on it, looks white in the camera flash.

The burn mark is because I burnt through into the guard where I hadn't completely removed all the underseal from the seam. I have removed the paint all around the weld area on both sides. 

The gap is the best I could do, most of it is 0-1mm, some parts might be 2mm.

I do have the welder turned up quite high to get enough penetration on the plug welds I was doing. I'll have to try experiment with a lower setting without having the weld just sit on top of the metal.

 

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Seeing the photo it looks like a similar patch to the ones I recently did on my truck. Shouldn't need any copper behind it, looks like it needs some fiddling with settings/technique

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Yeah, as small a gap as possible the better, try less heat and another trick I found is to have the wire sticking out of the gun more, this changes the voltage/whatever at the weld just enough sometime to make it work, are you grinding that zinc coating off the new metal? that shits nasty and fucked my welds up.

 

 

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28 minutes ago, flyingbrick said:

Ok so your welds look too big, and possibly too hot @Adoom.

What wire size are you using? .6 is the standard for body repairs in the auto industry.

Also, your gaps look far too big! They need to be hair sized 

I am using 0.6

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I agree as most of the above, need to work in hot tacks that sit flat (they should almost look the same on both sides of the job). If you cant achieve this you need to ask why, its probably a combination of the big gaps and maybe how you are doing it. Get two of your clean new steel patches and practice big-fat hot tacks on it and get them perfect, then if these setting don't transfer to the job you need to think about why and make changes.

Also I recommend using normal cold rolled sheet over zinc coated, its at least 1 million times easier to work with and welds nicer. If you need corrosion resistance on the back paint it with epoxy primer before welding. I was told to use cold rolled by a guy who does restorations for a living and would never go back.

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Grind any coating off, it will just make it harder to weld. And if it's grabbing crap from the underside that won't help either. The fresher the steel is and the cleaner the better. Even with settings right, crap in the weld will ruin it. Have you seen the thin metal technique video in migwelding UK forum? Its a good guide. Not bagging your attempt BTW, I have been there before, so just passing on what I found works. Set the settings on some scrap before starting on the job too. Plug weld settings will be miles different to welding that area. What sort of settings does the welder have? Leas wire speed could be worth trying with less amps. 

 

/beaten by Speeno

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24 minutes ago, Spencer said:

I agree as most of the above, need to work in hot tacks that sit flat (they should almost look the same on both sides of the job). If you cant achieve this you need to ask why, its probably a combination of the big gaps and maybe how you are doing it. Get two of your clean new steel patches and practice big-fat hot tacks on it and get them perfect, then if these setting don't transfer to the job you need to think about why and make changes.

Also I recommend using normal cold rolled sheet over zinc coated, its at least 1 million times easier to work with and welds nicer. If you need corrosion resistance on the back paint it with epoxy primer before welding. I was told to use cold rolled by a guy who does restorations for a living and would never go back.

Where would I get cold rolled sheet from? In manageable sizes.

19 minutes ago, Bling said:

Grind any coating off, it will just make it harder to weld. And if it's grabbing crap from the underside that won't help either. The fresher the steel is and the cleaner the better. Even with settings right, crap in the weld will ruin it. Have you seen the thin metal technique video in migwelding UK forum? Its a good guide. Not bagging your attempt BTW, I have been there before, so just passing on what I found works. Set the settings on some scrap before starting on the job too. Plug weld settings will be miles different to welding that area. What sort of settings does the welder have? Leas wire speed could be worth trying with less amps. 

 

/beaten by Speeno

I have a boc mig 170P. I have 6 settings for power and variable wirespeed.

I am using 0.6mm wire.

I did set it up with a couple scrap bits of the patch metal butted together. I set it as high as I could for tacking without blowing through. I suspect the original steel I am welding the patches to might be a bit thin in places. 

I'll try it on a lower setting this weekend.

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Hmmm 6 settings sounds not so good, I had a inverter mig and the fine tuning of settings made a real difference. A whole sheet of cold rolled here was around $100 so just bought the whole sheet, used around 1/6th of it then gave it away, was handy to have around.

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