[Jewelry making - Article 00113] - Re: [Orchid] Experience with PUK welder

[Peter W . Rowe]

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>     .... The welds are brittle and the tips break away fairly easily.
>     If you weld near a stone, the stone will likely be damaged by the
>     arc. Diamonds are the exception. It is usless for repairing most
>     glasses frames. It works on titanium but again the weld breaks
>     easily if twisted. I've never used it successfully on 18k yellow
>     gold. I do a lot of jewellery assembly and the machine is excellent
>     for that purpose but if you think you're buying a cheap alternative
>     to a laser welder you will be disappointed. 

    If it makes you feel any better, laser welders too, have their
    limits, especially those, like older machines or some of the less
    costly ones available now, that don't offer pulse shaping abilities.
    Laser welds are generally inherantly 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 equally quickly, cools. As it cools, it shrinks.
    Unlike a cooling solder joint where everything got hot, in this
    instance, the weld alone is cooling, thus stretching it. Some metals
    just get a bit harder. Others downright crack. Pulse shaping allows
    the weld to be cooled a bit slower, allowing just a tad of annealing
    to happen as it cools, thus avoiding some of the cracking problems.
    But lasers can blast stones, give cracky brittle welds, and otherwise
    not always live up to the promises of sales people who may not always
    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
    paramaters to adjust and alter. Retipped prongs don't crack off, for
    example, in most cases I've seen. But they ARE harder than a torch
    retipped prong, which may be a good thing for wearing properties. On
    the other hand, a laser repaired whole prong which now needs to bend
    at the weld for setting a stone? In white gold that will often be a
    cracky problem. 

    Platinum though, is a dream to weld. And if your laser has the
    power, the usual 18K yellow golds work very nicely too. I have more
    trouble with 14K yellow. Tends to crack. So do many of the nickel
    white golds, especially when you're working on a casting... 

    And I too 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, flow solder in, and the seam is then 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. 

Peter
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