Hi all,
I'm a novice welder trying to mig braze some copper sheet metal together for an art project. I'm using .023 silicon bronze wire on a Lincoln 140HD with Argon gas. The problem is that the braze doesn't stick to the copper and creates little globules that fall right off. I've tried varying power and speed and don't notice much difference in the outcome. Anybody have any ideas why this might be happening? Thank you!
This sounds typical of not having enough volts/amperage to get the copper hot enough to melt/fuse the SilBr. Realize that copper conducts heat very, very well. Thus it takes a lot more voltage to “weld” it. If you used a formula of voltage for material thickness (based upon carbon steel) you’re too low.
Try again but raise the voltage 1 full volt. Try a short sample. If not right, raise the voltage again. You will also need to raise the WFS accordingly.
Try again but raise the voltage 1 full volt. Try a short sample. If not right, raise the voltage again. You will also need to raise the WFS accordingly.
As was mentioned the copper is not getting hot enough, can you use another process. Tig braze and especially gas brazing are better if you can. You might even get away with using the mapp gas torch, I do. just use flux with gas torch. Both of those are easier too. If you can do it with the tig it would be a handy skill for an artist to learn as well. Pics of art projects are appreciated too 
SIlicon Bronze brazing copper honestly sounds like an absolute nightmare let alone with mig. Copper is the king of heat conductivity and silicon bronze melts at very close to the same temperature pure copper does, so you'll basically be melting copper by the time you've heated it up enough to stick.
Precisely.sbaker56 wrote: ↑Mon Nov 01, 2021 9:24 pm SIlicon Bronze brazing copper honestly sounds like an absolute nightmare let alone with mig. Copper is the king of heat conductivity and silicon bronze melts at very close to the same temperature pure copper does, so you'll basically be melting copper by the time you've heated it up enough to stick.
Which is why it works. It doesn’t look great on paper though I admit. If in serious doubt and having no need for adventure, silver solder. But if you have a roll of it then it seems like a wasted opportunity to not even have a crack, assuming you have the gear too.
Gdarc21 wrote: ↑Tue Nov 02, 2021 12:23 pmPrecisely.sbaker56 wrote: ↑Mon Nov 01, 2021 9:24 pm SIlicon Bronze brazing copper honestly sounds like an absolute nightmare let alone with mig. Copper is the king of heat conductivity and silicon bronze melts at very close to the same temperature pure copper does, so you'll basically be melting copper by the time you've heated it up enough to stick.
Which is why it works. It doesn’t look great on paper though I admit. If in serious doubt and having no need for adventure, silver solder. But if you have a roll of it then it seems like a wasted opportunity to not even have a crack, assuming you have the gear too.
I'm all for giving it a try, In fact I have a piece of copper and some silcon bronze, I might experiment some with trying to tig braze it to some steel or cut it in half and try brazing it back together. I just have faint memories of trying it before and it going terribly, and I'd have to imagine trying to do it with mig would go worse. But I'll admit my experience actually trying it is slim at best.
It is a bit of fun and handy skill to have. I find for me anyway, compared to tig welding tigbrazing is a bit low and slow and gets a bit quicker as filler melts.
1.6mm filler at 57 amps is ballpark for my welder on steel. If you have a pulse it comes up sweet. You will have to go hotter for copper and if the copper is a bit on the thick side its possible to preheat with gas torch a bit just so you dont have to hang around too long with tig torch.
I focus on just melting the filler in puddle, if it wets then it works. This is not so much a how to, just what I do, hope it helps.
1.6mm filler at 57 amps is ballpark for my welder on steel. If you have a pulse it comes up sweet. You will have to go hotter for copper and if the copper is a bit on the thick side its possible to preheat with gas torch a bit just so you dont have to hang around too long with tig torch.
I focus on just melting the filler in puddle, if it wets then it works. This is not so much a how to, just what I do, hope it helps.
I’ve used copper wire for tig brazing copper sheet. For my purpose it works the same as silicone bronze and about the same cost. The wire I have is labeled 16 ga. dead soft pure copper. But I think it is really about 18 ga. It matches my copper sheet thickness, pretty close. I’m not good enough to lay a consistent bead, but a few tacks work fine. Usually sanding and acetone cleaning allows it to stick.
The great thing about copper sheet is it’s so easy to shape. I soften it with Bernzomatic propane torch to red color. Then hit water to cool, shape, clean and tack away.
The great thing about copper sheet is it’s so easy to shape. I soften it with Bernzomatic propane torch to red color. Then hit water to cool, shape, clean and tack away.