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Laser welding porosity

Jewelry Discussion
#1

Many times fixing a crack or filling porosity pits in new and old
rings can add to the problem. While fusing the metal in an area
around a repair, more holes and pits appear. The only solution is to
continue to “beat” the metal in the same area until smooth of all
defects, sometimes requiring adding wire and extending the work area
3 to 4 times the original size. I have two questions:

1.) Is this a problem with the original casting being porous or a
problem with the alloy in the metal?

2.) Anyone have a better solution to prevent or cure the problem?

Gary L. Mills

#2 
Is this a problem with the original casting being porous or a
problem with the alloy in the metal?

Both can be factors. Some metals don’t like laser welding as much,
and are more prone to cracking as the welds cool/shrink. The porisity
itself might be caused by voids in the weld, or too high power
settings. Try using smaller wire and lower voltage settings. But from
what I’ve seen, most of the problems originate with the casting
itself. Melting a bit of porous metal sometimes fixes a pit, and
other times, the bubble or imperfection just floats around and
remains in the metal. And cracking of a weld often seems to be an
indication that there are still voids or other imperfections in the
metal below the weld which were not reached and fixed by the weld.

 Anyone have a better solution to prevent or cure the problem?

Different power settings. Sometimes a gentler, lower power setting
with smaller weld spots can forstall cracking. Other times, you need
to punch deeper into the metal to reach the deeper problem spots that
are causing the surface cracks. Argon shielding helps a good deal
with white golds in particular too. And sometimes I find that
smoothing a weld over by using low power settings as well as holding
the work so the beam hits the metal surface at a very shallow angle,
which produces a weld spot that’s a long narrow oval rather than a
round spot, can change stresses in the weld so as to reduce cracking,
as well as giving a smoother weld surface with less of the dimples
one often sees. If your laser has pulse shaping, that can go a looong
way to reducing problems too.

And another approach I sometimes find necessary is to use a filler
wire that’s not an exact match for the weld metal. Palladium white
gold or a yellower, lower nickle white gold when welding white gold
can give a more ductile weld that doesn’t crack as much. With some
higher zinc 14K yellow golds, I use a 14K that has no zinc. Higher
melting point, but welds better. Sometimes, I even find I need to use
an 18K yellow gold to weld especially problematic 14K, since the
much more ductile 18K simply isn’t likely to crack. Wire made from
hard silver solder, or IT silver solder, works better than sterling
silver for welding sterling. And so it goes…

Peter

#3

If you’re running gas it is definitely, to the best of my knowledge,
a casting porosity issue. Keep filling!

Gerry Aubin

#4

So far, I’ve found that when dealing with porosity its better to
first open up the hole with a suitable bur and then zap it. This
gives a more ‘solid’ wall to the hole on which to add your filler
wire. usually porosity is larger than what is apparent, keep zapping
it and the hole just gets bigger because the thin ‘overhangs’ just
blow away, creating excess amounts of soot which further exacerbate
the unwillingness of the metal to cooperate. Thinner gauge laser
wire is helpful here, you can use lower power and build the fill up
with less anxiety.

If you’ve got a large area of fine porosity you might try a margin
roller or even a hammer handpiece to smoosh the tiny holes flat. This
does cause a ‘sink hole’ that you have to fill but at least you’ve
got a more solid foundation to work on.

Is this a problem with the original casting being porous or a
problem with the alloy in the metal?

Yup, bad casting. Garbage in garbage out.

#5

Like so many things, there are so many variables involved in the
formation of pits that it’s exhausting just to think about it. But a
few pit avoidance and pit remedy laser welding tips are;

  1. With white gold, use 14K palladium white gold wire. It lasers MUCH
    bet ter than 14K nickel white gold. Keep your settings as low as you
    can while still getting a good weld.

  2. If you are generating a lot of carbon, you settings are too high
    (not suggesting settings because it depends on which machine you’re
    using). The creating carbon thing applies to any metal, the cleaner
    your weld the fewer pits you’ll have.

  3. Create a little depression over the pits with the laser or a bur,
    fill the depression with nice clean welds and then compress the weld
    with a hammer handpiece or the like. When compressing the weld you’re
    also compressing the pits, hopefully driving them a bit below the
    surface. To keep the pits from showing themselves, cleaning up the
    lasered/compressed area is tricky.

I have found that lapping the area and then high polishing with a
little rouge only works. The key is to remove the minimum amount of
material possible yet get it high polished. If you rubber wheel the
area, you’ll have pits, if you emery, then tripoli, then high polish
with rouge…you’ll have cut into the pits. Sometimes you’ll need to
compress, lap and high polish a couple of times to get them all. But
at least it works. Hey, if you wanted aneasy job you wouldn’t be a
metalsmith. It’s all about crappy career choices my friends.

Mark

#6

Just some thoughts.

For porosity, the typical technique is to use a narrow beam, medium
heat, and high hertz to “cave in” or collapse of the area around the
porosity area to insure you have seen it all. Then add the same wire
as the material you are working on. Sometimes balling up the end of
the wire first speeds up the process for larger holes. Argon will
flow the metal nicer, but this is an added cost. Also, UHP Argon
which is 99.999% pure will provide the best results and is a must for
titanium and eyeglasses.

Note for some metals such as white gold, you should build up the
heat in the part by using your pulse shaping technology. Too many
people forget their machines may have this feature. The LaserStar for
example has a porosity setting for each metal preloaded into the
memory setting making it easier, but many other manufacturers also
have the ability to change or modulate the temperature, you just have
to program them yourselves.

Again Voltage is depth and MS is heat. Too much voltage and not
enough heat will not produce the best results. Practice, Practice,
Practice…

Andre F.
www.LaserStar.net