PUK Arc Welders vs. Laser Welders

Q: I bought a PUK arc welder as a cheap alternative to a laser welder. It’s good for jewelry assembly, but I’ve been mostly disappointed with it for other common tasks. Unless the stone I’m welding next to is a diamond, it’s likely to get damaged by the arc. It’s useless for repairing glasses frames, and doesn’t seem to work well for 18K yellow gold. Will a laser welder do the rest of these things better?

A: If it makes you feel any better, laser welders too, have their limits, especially those, like the older machines or some of the less costly ones available now, that don’t offer pulse-shaping abilities. Laser welds are inherently work-hardened, and perhaps for the same reason you can get brittleness in a PUK weld. Here you’ve just generated a little molten pool of metal in what amounts to a larger, rigid, mass of cold metal. The molten metal solidifies quickly and then cools equally quickly. As it cools, it shrinks. Unlike a cooling solder joint where everything got hot, in this instance, the weld alone is cooling, so it has to stretch. Some metals just get a bit harder, others crack. Pulse-shaping allows the weld to be cooled a bit slower, allowing just a little bit of annealing to happen as it cools, thus avoiding some of the cracking problems. But lasers can blast stones, give crack-prone brittle welds, and otherwise fail to always live up to the promises of sales people who may not themselves be expert laser welder operators.

With that said, lasers seem to have fewer of these problems than do the PUK welders, perhaps just because you’ve got a few more parameters to adjust and alter. Retipped prongs don’t crack off, for example, in most cases I’ve seen. But they will be harder than a torch-retipped prong, which may be a good thing for its wearing properties. On the other hand, a laser-repaired whole prong in white gold which needs to bend at the weld for setting a stone will often be crack-prone. Platinum though, is a dream to weld with the laser. And if your laser has the power, the usual 18K yellow golds work very nicely too. I have more trouble with 14K yellow, which tends to crack. So do many of the nickel white golds, especially when you’re working on a casting.

I often use my laser not for the whole assembly, but as a way to attach and align and hold parts for subsequent soldering. Among other things, I can construct a tight capillary seam, tack it with the laser, then flow solder in, so that the seam is virtually invisible, as a good solder seam should be. Laser welds, and PUK welds, just don’t do that, since the weld bead has width, and the deeper the weld, the wider the weld zone ends up being. If you can clean up the weld, it can be an invisible seam. But for detailed precisely-fitted parts, sometimes it’s messier than solder.

by Peter W. Rowe M.F.A., G.G.