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Laser: Does cover gas make for stronger join?


#1

After much consultation and experiment to find a delicate yet
springy wire for an open-work neck piece, I have decided to use full
hard X1 White gold from Stuller. The joins of the wire and small
stone settings need to be strong but retain flexibility and memory.
For this reason, a torch is out and a laser is the choice for
joining elements.

The problem at first was lack of strength of the laser welds. Butt
joints are definitely useless. Joining was changed to overlapping
wires and mechanical attachment for the stone settings.

All preliminary welds have been done without a cover gas(the
business has yet to invest in the argon). My real question is this:
Will cover gas create a stronger welded join in fine gauge white
gold wire? Will the weld with and without cover gas be substantially
different or the same for this metal being welded?

Any suggestions from your experience will be greatly appreciated.

Tom.


#2
My real question is this: Will cover gas create a stronger welded
join in fine gauge white gold wire? Will the weld with and without
cover gas be substantially different or the same for this metal
being welded? 

Nickel white golds seem to benefit more from argon shielding than
any other metal, at least in my experience. Welds have much less
tendacy to brittleness or cracking, and much less porosity. If you
work with white golds in the laser, get argon. It’s not that costly
to add. Mostly, the cost is a decent regulator for the argon. Argon
itself isn’t cheap, but you can start with a smaller sized tank if
budget is a problem. And with what you already spent to get a laser,
the argon is a minor cost in comparison. The other comment that
occurs to me is to be careful not to use too high power settings. Use
finer filler wire, shorter millisecond settings, lower voltages, if
you can, and the welds may significantly improve. Also, be sure to
tell Stuller, when deciding on which alloy to buy, that you’re using
a laser with it. Some of their alloys work better with a laser than
others.

Peter


#3

Why would they spring for a Laser & not the UHP gas. Does not make
since, that is like driving your car with the parking brake on. The
UHP Argon will make a definite stronger laser joint, provided the
joint is not placed where it has to fail do to poor layout & design.


#4

I have been using a laser for 6 years. I love what it enables me to
do but experience makes me very skeptical of some of the persistent
claims about weld strength. The claim that a laser weld is "stronger"
than solder just does not seem to be true in my experience. Neither
does the claim that cover gas makes a critical difference.

The most practical real life situation that tests a joint’s strength
is when that joint is distorted. Laser welds just don’t seem to take
stretching, twisting or forging very well at all. With or without
cover gas. In the same situation a soldered joint is also at risk,
but it does not fail nearly as soon. Whenever I have joined a ring
and then tried to stretch it even a wee bit larger, it cracks! Solder
the same joint in silver or gold and it will stretch several sizes.
Weld it and it cracks at 1/8 size stretch.

The only scientific study I have seen on laser weld strength was on
platinum test pieces. My limited experience with platinum is that it
welds beautifully with a laser. Better than any other material I have
tried. But I do not think it is honest to project test results from
one material to another. Silver is not very laser friendly. There are
tricks to make it better, but I do not think anyone with actual
workshop experience is going to claim that laser welding silver is
going to give you as reliably strong a joint as silver soldering.
Gold is better. Palladium white gold, better yet. Red gold, not much
better than silver. Copper? Forget it!

Maybe in a laboratory situation where you can fine tune the variable
factors to an ideal, you can document superior results. But
generally in real life we are dealing with a variety of thicknesses,
alloys and limited time that do not give us the opportunity to arrive
at the optimum pulse combination for each job. In a situation like
chain manufacturing, where the same joint will be repeated millions
of times by a robot I can see that you could fine tune that to a much
better setting. But when you are dealing with repairs or custom work,
each situation is unique, so your trial-and-error is more a matter of
your past experience than something you have multiple chances to find
the right combination of settings for this one job. Or the next.

I would love to see someone with solid material science engineering
experience do a series of unbiased tests to measure the strength of
welds on the various materials that jewelers use. If someone has done
such tests, please, let’s have a look. My suspicion is that jewelers
are generally reluctant to admit that their laser welding results are
not measuring up to what the salesman and manufacturer’s reps said
their results should be. There are a lot of factors. Cover gas is
only one variable. It is somewhat embarrassing to admit that the
most expensive tool you own isn’t working out as well as everyone
says it should. If the welds are good enough for 95% of the
applications, the claim that a laser weld is actually stronger
doesn’t really have to face verification most of the time.

I am going to be using my laser for most of the day today making
something that I couldn’t possibly make any other way. It is an
amazing tool and I love it. But I think the claims about joint
strength are greatly exaggerated. I would be glad to be proven wrong.

Stephen Walker


Andover, NY


#5

Thank you, Stephan. Your candid response says a lot of what I have
experienced and it is not easy for my employer to accept that his
costly machine has a wonderful place in the work but may not do what
the hype has painted.

Perhaps the machine will do a lot better with improved approaches to
the tool and materials. However, with my somewhat limited experience
with the laser I honestly cannot claim expert knowledge enough to
always distinguish between device limits and operator miscues.

We will most surely be adding cover gas and I do believe it will
help with the quality of welds, more with some metals than others.
And, we realize there is more to it than a simple zap of heat
considering the parameters which can and should be applied to that
zap to meet the situation. In that, my knowledge lacks sufficiently
enough to be frustrating at times.

I have a quite involved custom piece which essentially requires the
laser for assembly. In that and successful repairs done thus far,
the machine proves its worth in our shop, even if not exactly as
billed.

Yes, I imagine several of us would like to see a technically accurate
study on effectiveness of jewelry scale laser welding in different
situations and perhaps with work-a-rounds for difficult combinations
of ingredients. Comments appreciated. Tom.


#6
But I think the claims about joint strength are greatly
exaggerated. I would be glad to be proven wrong. 

A while back I and others got into just that debate following
Leonids assertion that laser welds are never as good as solder
joints, or more precisely, that HIS solder joints, ie meaning solder
joints done well/correctly with a high level of craftsmanship, were
ALWAYS stronger than laser welds.

It turned into a bit of a heated thread, and I know I may have
gotten a bit overly “enthousiastic” in defending laser welds.

But the truth is that laser welds, right off the machine, MIGHT be
very strong, or might not, depending on the metal, the joint
geometry, the technique used, etc. In many cases, laser welds tend to
be brittle and work hardened. The reason is that each little weld
spot is a bit of molten metal on an otherwise much cooler solid
surface, and as that solidifies and cools, it shrinks, with the
surrounding metal not also shrinking to match, as happens with
solder joints or torch work. So the weld metal is stretched. Each
little weld spot gets stretched and tensioned and work hardened
before the next spot goes over it, then doing the same. This can, on
some metals, leave a network of tiny almost invisible cracks which
show up the moment you try to stretch or flex the metal. Not good at
all. With some metals, if they’ve formed these micro cracks (and yes,
argon shielding seems to help with this on some metals, not with
others), then you’re not going to have a strong weld, no matter what
you do.

However, with other metals, especially platinum and higher karat
yellow golds, there isn’t this problem with cracking, at least not
commonly. These welds still form an area with rather chaotic crystal
structure, and are often distinctly work hardened, so if that differs
too much from the parent metal, this can also create a likelyhood of
breaking when stretched. But with this situation, you have a
solution. You can, of course, actually anneal the metal. That causes
recrystalization, and if the weld was solid without porosity, the
result can be a pretty uniform structure as strong as the original
metal, which can outperform many solder joints (which are also pretty
much always annealed by the soldering process.) If you don’t want the
metal fully annealed, you can also go half way. Heating to a
distincly lower temperature can allow the work hardened metal to
partially anneal. Properly, this is called normalization or stress
relieving the metal. If the weld was originally too different in
hardness from the parent metal, this process can greatly improve the
situation. It ends up not that much softer than before, but more
uniform without the brittleness. With platinum, this is of use since
the temperatures needed to do this to platinum are much lower than
annealing. In particular, the temps are still within the range of
what properly protected (boric acid, flux, etc) diamonds can still
withistand, and the result will be a strong durable weld. It’s not
normally required to go this extra step with many platinum welds, but
it’s possible.

And some welds simply don’t have the problem. For example, with thin
ring shanks in a sizing joint, or wires being joined as butt joints,
in some metals, especially platinum, it’s possible to set the laser
at a high enough voltage setting, and long enough "millisecond"
settings, that one can use a single laser pulse to fully penetrate
alll the way through the entire joint. What that means is that the
entire weld area, all the way through the wire or shank (usually
this is the thin ladies shanks), was molten simultaniously, just as
it would have been had you fused it with a torch. Although metal next
to the weld remaind fairly cool, the geometry of this weld is such
that the metal is not restricted from shrinking as it cools, so then
there is not the work hardening stretching of the weld that can occur
in other weld geometries. These welds come off the machine pretty
much ductile and almost as soft as annealed, even after you’ve used
smaller additional pulses to clean up around the weld. Shape it just
a little with a hammer on a mandrel, and you’ll have a weld that is
as likely to withstand stretching and deformation as any solder
joint, and most solid unwelded metal too.

But I admit that these are a special situation, and most welds are
not quite this good, even if they are still quite good enough.

And back to that prior discussion with Leonid and others, my
objection to his statement regarding strength of laser welds was
mostly his assertion that they were NEVER as strong as solder. I
simply don’t like that kind of absolute statement. “Never”, and
"Always", are descriptors that are all too often just too strong and
exaggerated, even if they are close to the truth. Now, if he’d said
his solder joints were “usually” stronger, or “often” stronger, than
laser welds, I’d not have argued.

The same applies here.

Lasers are wonderful tools, allowing us to do many things difficult
or impossible to do other ways. They don’t do it all, and don’t do
everything they do all that well. But sometimes their results are
better than any other way, and other times their results are
acceptable and faster or more economical than other ways. And then
there are the times when proper use of the laser amounts to remain
sitting at your workbench, doing the job as you’d have done before
buying the laser. Knowing when they are the right choice for a job,
and when other methods are the right choice, is all part of the skill
needed to use a laser welder.

Peter Rowe


#7

Dear Mike and Peter,

Your responses are what I expected and are just in time to help get
cover gas for our laser work. A man from the welding supply we use
for gases came by and is sending a quote for cylinder, regulator and
hose. Get that, get the stuff delivered and a little rearrangement
of the work area and it will be ready.

I certainly have enough experience with weak bonds to see what
difference the cover may make with other factors the same. And yes,
after that I do plan to change parameters a bit to find the best
weld for the material at hand.

Your responses are very appreciated. Tom.


#8
each little weld spot is a bit of molten metal on an otherwise much
cooler solid surface, and as that solidifies and cools, it shrinks,
with the surrounding metal not also shrinking to match, as happens
with solder joints or torch work. So the weld metal is stretched.
Each little weld spot gets stretched and tensioned and work
hardened before the next spot goes over it, then doing the same.
This can, on some metals, leave a network of tiny almost invisible
cracks 

Thank you Peter! I guess it is better later than never. I can
contribute to this discussion by saying that laser welding is an
industrial process, which can be done well if industrial quality
control measures are used. These measures are next to impossible or
let’s us say very expensive to employ in jewellery shops, so in
practice laser welds produced in everyday practice are of inferior
quality compared to well fitted and well executed soldered joints.

Leonid Surpin
www.studioarete.com


#9
I certainly have enough experience with weak bonds to see what
difference the cover may make with other factors the same. And
yes, after that I do plan to change parameters a bit to find the
best weld for the material at hand. 

By the way, regarding weld strength, and especially weld cracking,
if you happen to have one of the newer lasers (the newer Rofins, for
example) that allow you to play with pulse shaping, this can have a
big effect on weld strength. Sometimes these machines come
pre-programmed with various pulse shapes that have been found most
useful for different purposes, but usually you can also define your
own. Play with it. Things like a slow cool down ramp at the end of
the main welding pulse can help a lot with brittle welds, as it
allows the metal just a little bit of time, cooling just a little bit
more slowly, to stress relieve or partially anneal. If you don’t have
a machine with programmable pulse shapes, then this isn’t an option,
and the newer lasers without specific pulse shaping settings usually
try to simply give you an optimum pulse shape automatically. That’s
simpler to use, of course. But personally, I prefer the option of
defining pulse shapes if I want. Unfortunately, I only got to play
with that for a while with the laser we’ve got at work. That newer
upgraded control board fritzed, and now we’re back to the older one
without pulse shaping. And my own shop’s laser is simply too old for
such fancy bells and whistles. But it sure was useful while it was
available, and if I were shopping for a new laser, I’d insist on
that feature.

cheers
Peter


#10
Thank you Peter! I guess it is better later than never. I can
contribute to this discussion by saying that laser welding is an
industrial process, which can be done well if industrial quality
control measures are used. These measures are next to impossible
or let's us say very expensive to employ in jewellery shops, so in
practice laser welds produced in everyday practice are of inferior
quality compared to well fitted and well executed soldered joints. 

You’re welcome, Leonid.

However, do note that I said that such cracking can SOMETIMES occur,
and not always. It’s much more common on some alloys than others, and
virtually non-existant on some. I don’t think I’ve ever seen it
happen, for example, on the iridium platinum alloys I most commonly
use, nor on 18K yellow gold. for both these, I find that properly
done laser welds can often be superior to solder joints.

I disagree with you about “industrial measures” needing to always be
done. In industry, of course, where a single type of operation may be
done over and over, samples can be tested, methods refined, until the
result is predictable over and over. In jewelry weldind, this may not
seem to be the case, but in practice, experience with the laser, as
to what works and what does not, teaches the user which instances are
better soldered, and which are better welded. And with the laser,
working under a microscope does have the advantage that it’s not so
easy to overlook problems during the welding. The machines themselves
offer a repeatability and degree of control that in and of itself is
already much of what your “industrial measures” implies, and the
experience and skill of the operator supplies much of the rest. One
keeps track of the laser settings and methods that work best for
given tasks, just as the industrial setups would do (laser welders
even have multiple memory setups for just this type of info storage)

One big hurdle to be overcome is that beginning (or lazy, or
overworked, etc) laser owners tend to find the laser so easy to use
that it becomes sort of the default method, used not because it’s
better, but because it’s easier. In this instance, what you once said
about it being for people who don’t want to bother removing stones,
is perhaps applicable. But as people get used to the laser, it
teaches you what it does well. If you think you’re getting good
welds on a sizing seam, and then find, as you hammer or stretch that
seam, that it fails, then you’ll be more careful about making that
choice the next time. Likewise, having seen many fine platinum and
diamond rings repaired, or prongs rebuilt, using gold solders because
diamonds could not be removed for the work, and having also done many
of these jobs over the last number of years with the laser, I can
tell you that the laser retipped platinum prongs and other parts,
are even after a number of years, clearly superior. The retipped
prongs are a little harder and more durable, sometimes even more so
than newly set prongs (which might be still fully annealed) It’s a
balance between available methods, and each needs to be chosen based
on what will work best, not just on what is easier or quicker.

As I said, the bit problem I had with your statement in the last
round of this discussion was that you claimed solder was always
superior. It’s not. It CAN be superior in some, maybe many instances,
and the laser CAN be superior in others. There are many variables,
and no single “blanket” statement covers all of them. It IS, perhaps
true, that the use of solder is a bit more predictable. Like you, I
know beforehand pretty much what the result of a well done solder
joint will be. The same is true of many other traditional processes.
The laser is a little less predictable when doing something new, or
with new or unfamilier metals, etc. But this is all part of the
process. I use both my torches and my laser on a daily basis,
sometimes both on a single job. When I’m done, I want to be able to
look at the job and know that it’s done the best way, will give long
and proper service, and should it ever need repair or service by some
other jeweler, I want to know that it does not contain any traps for
the unwary. And before starting, I also want to consider whether a
given choice of method has risks I should avoid. All these factors
come into play, and I choose my method for a given task accordingly.
In the end, this is not much different from the same sort of process
one uses in choosing among various traditional methods and tools.
The laser is merely a new tool, capable of some things, and not of
others. It’s a powerful tool, but neither magic, nor does it do
everything. But SOME of the things it does, it does exceptionally
well, sometimes that means better than any solder seam.

Peter


#11

Hi Peter,

The reason is that each little weld spot is a bit of molten metal
on an otherwise much cooler solid surface, and as that solidifies
and cools, it shrinks, with the surrounding metal not also
shrinking to match, as happens with solder joints or torch work. So
the weld metal is stretched. Each little weld spot gets stretched
and tensioned and work hardened before the next spot goes over it,
then doing the same. This can, on some metals, leave a network of
tiny almost invisible cracks which > show up the moment you try to
stretch or flex the metal. Not good at all. With some metals, if
they've formed these micro cracks (and yes, argon shielding seems
to help with this on some metals, not with others), then you're not
going to have a strong weld, no matter what you do.

I think you are correct in most of your post but I think your
analysis is a little off as to the work hardening bit.

The metal shrinks and is stressed by this shrinkage but it is not
work hardened. The cracking is most often hot tearing, the cooling
metal is stressed beyond its tensile strength and the matrix splits
as it shrinks. You cannot anneal the weld to recrystallize it because
there has not been any cold work to strain the crystals in the weld,
rather it is the bulk metal in the areas adjacent to the weld that
can be stress relived to and if heated hot enough for long enough and
they have had enough cold work then they can recrystallize. But the
crystal structure in the weld will basically remain unchanged as it
is in an as solidified state with crystals that can only be reduced
in size by enough cold work followed by recrystallization annealing.

In any form of fusion (Laser, TIG, stick, MIG etc) welding there is
a issue with the significant change in crystal structure between the
solidified molten metal in the fusion zone and the bulk metal of the
weldment. There is an area called the Heat Affected Zone (HAZ) that
lies between the fused metal and the bulk metal. This area is under
quite a bit of strain as the molten metal cools and is often the
area that gives way when stressed after welding. The HAZ can actually
anneal and recrystallize during the cooling period after welding as
the intense heat from the molten metal next to it provides enough
energy for the crystal transformation.

In both the laser and the pulse arc welds the HAZ tends to be small
due to the very brief period of heat application and I think this
may act to concentrate the stress.

Another problem with with Laser and Pulse Arc welds in jewelry
applications is that they are not full penetration welds. With
brazing as long as the seam is clean, well fluxed and tight enough
the filler metal will flow across the full face of the joint. With
welding often the operator just fuses the outer surface of the weld
and leaves an inner area or backside of the weld un-joined

James Binnion
James Binnion Metal Arts


#12
Another problem with with Laser and Pulse Arc welds in jewelry
applications is that they are not full penetration welds. With
brazing as long as the seam is clean, well fluxed and tight enough
the filler metal will flow across the full face of the joint. With
welding often the operator just fuses the outer surface of the
weld and leaves an inner area or backside of the weld un-joined 

If this is so, then the operator has not truly welded his seam. This
is not how welding is performed, as total penetration of the weld is
required.

Instead of the “tight” joint required for correct brazing, with
welding. a tapered "gap is required, to begin the weld.

On thicker seams, a “V” gap, or an “X” shaped gap are the welder’s
starting points (joints), and it as the narrow point, where the
metal touches that his first “full penetration” weld must start.

The metal at the point where they touch is first welded thoroughly,
and then the “gap” is back filled, by welding new metal into the
metal on either side of this joint, gradually overfilling and until
the two pieces are completely joined, as in the arc welding process
on steel. On thinner metal, a pulse strong enough to fully penetrate
is all that is required, to begin the welding process.

It is not at all unusual to change you settings throughout the
welding process, on heavier pieces, to achieve a good weld, as the
parameters of the process are changing from penetration, to good
flow into the surrounding metal.


#13
I think you are correct in most of your post but I think your
analysis is a little off as to the work hardening bit. 

probably. It’s based simply on observation, not any formal research
by me, or anything I’ve read. I likewise sometimes use the word
anneal, when it’s really just stress relieving without any
recrystalization.

The metal shrinks and is stressed by this shrinkage but it is not
work hardened. The cracking is most often hot tearing, the cooling
metal is stressed beyond its tensile strength and the matrix
splits as it shrinks. 

agreed. I think of this as being related to metals that are “hot
short”, ie those that don’t like to be forged hot. And it’s not hard
to figure that if the shrinkage stresses cracked the metal, then the
metal did not get stretched, so no hardening. Just a cracked useless
weld and a frustrated goldsmith.

You cannot anneal the weld to recrystallize it because there has
not been any cold work to strain the crystals in the weld, rather
it is the bulk metal in the areas adjacent to the weld that can be
stress relived to and if heated hot enough for long enough and they
have had enough cold work then they can recrystallize. But the
crystal structure in the weld will basically remain unchanged as
it is in an as solidified state with crystals that can only be
reduced in size by enough cold work followed by recrystallization
annealing. 

I imagine you know more of the formal metalurgy here than I do. But
are you sure of this? I know that if I’m welding things like a T
joint, and weld all one side and then the other, I will have a weld
that is not straight, as the weld shrinkage on the first side pulls
the piece out of position. That’s not the parent metal shrinking,
it’s the weld itself. If the weld geometry is such that the weld
cannot deform/pull the parent metal out of position to compensate
for the shrinkage, then it seems to me that the only metal that can
be shrinking is the weld itself and immediate slight surrounding
area. If it shrinks and cracks, you see this as a star shaped crack
radiating out from the center of the weld spot, or a longer linear
crack that runs down the middle of a weld bead. The cracks are always
on the weld itself, not the adjacent metal. If it does not crack,
however, then it either has to stretch as it cools, or pull the
parent metal out of shape.

Now, if I take a cold, fully annealed wire, put one end in a vise,
and give the other a good pull, I can stretch it a little. The result
is not only a nicely straightened wire, but a slightly stiffer one.
ie, it’s a little work hardened. In the laser weld, only the
shrinkage that occurs after the metal has solidified has any effect
of course, but that seems significant. And that shrinkage should be,
it seems to me, deforming crystals as it stretches.

If I take, for example, a nicly annealed piece of gold or platinum,
and get a good solid weld on a butt joint (like a ring sizing, for
example), I can easily feel simply by attempting to hammer, roll,
burnish, that weld, that the metal of the weld is distinctly harder
than the fully annealed wire next to the weld.

In any form of fusion (Laser, TIG, stick, MIG etc) welding there is
a issue with the significant change in crystal structure between
the solidified molten metal in the fusion zone and the bulk metal
of the weldment. There is an area called the Heat Affected Zone
(HAZ) that lies between the fused metal and the bulk metal. This
area is under quite a bit of strain as the molten metal cools and
is often the area that gives way when stressed after welding. The
HAZ can actually anneal and recrystallize during the cooling period
after welding as the intense heat from the molten metal next to it
provides enough energy for the crystal transformation. In both the
laser and the pulse arc welds the HAZ tends to be small due to the
very brief period of heat application and I think this may act to
concentrate the stress. 

I do see this, mostly with white golds, if I try and stretch a weld,
such as stretching a ring with a laser welded joint. Sometimes the
weld itself fails, but sometimes it seems lke the weld is tearing
away from the adjacent metal. That would be what you describe. The
first seems only somewhat helped by stress releaving the piece after
welding. The second seems helped quite a bit. Probably this is
because when the welds themsevles fail, it’s also partly due to
simply a bad weld with cracks or voids, or the like…

Another problem with with Laser and Pulse Arc welds in jewelry
applications is that they are not full penetration welds. With
brazing as long as the seam is clean, well fluxed and tight enough
the filler metal will flow across the full face of the joint. With
welding often the operator just fuses the outer surface of the
weld and leaves an inner area or backside of the weld un-joined 

Speak for yourself, Oh bearded one… (grin). I try not to get
surface-only welds. All too often they’re a waste of time. The trick
is to arrange the weld method so that you DO get full penetration.
Usually this means not welding a tight fitted joint, but rather, one
with a V groove on one or both sides, so you can comletely fill the
weld all the way through with successive passes. One does the same
with a stick arc welder sometimes… And on some welds, (platinum in
particular is good this way) you can get surprisingly deep
penetration with higher power levels. (I can get all the way through
a 2mm shank in a single pulse on platinum, for example.) Doing this
has advantages beyond speed in that full penetration welds like this
seldom if ever have cracks, since the whole weld is cooling and
shrinking uniformly, just as a torch fused joint could do. (well,
almost…)

cheers
Peter


#14
There is an area called the Heat Affected Zone (HAZ) that lies
between the fused metal and the bulk metal. This area is under quite
a bit of strain as the molten metal cools and is often the area
that gives way when stressed after welding. 

One of the easiest ways to deal with HAZ related issues is to
preheat the entire piece.

Reasons for not heating the entire piece are, final required
properties are adversely affected by heat, size and/or shape of
piece make preheating too difficult, high thermally conductive
materials require long heat times, and cost. In industry cost is the
most often cited reason.

Dan Culver


#15
I imagine you know more of the formal metalurgy here than I do. But
are you sure of this? I know that if I'm welding things like a T
joint, and weld all one side and then the other, I will have a weld
that is not straight, as the weld shrinkage on the first side pulls
the piece out of position. That's not the parent metal shrinking,
it's the weld itself. If the weld geometry is such that the weld
cannot deform/pull the parent metal out of position to compensate
for the shrinkage, then it seems to me that the only metal that can
be shrinking is the weld itself and immediate slight surrounding
area. If it shrinks and cracks, you see this as a star shaped crack
radiating out from the center of the weld spot, or a longer linear
crack that runs down the middle of a weld bead. The cracks are
always on the weld itself, not the adjacent metal.

This is hot tearing from a what is called a highly restrained weld.
If you look at how many structural welds are done the metals to be
joined are separated by a gap. That gap allows the weld metal to
shrink without being restrained by the parent metals. If there is no
gap the things like pre heating of the metal before welding are done
to reduce the cooling rate and reduce the stress on the cooling weld.

If it does not crack, however, then it either has to stretch as it
cools, or pull the parent metal out of shape.

Yes, there is nowhere enough change in section to develop any cold
work that could be recrystalized. You are just stress reliving it if
you heat it or worst case growing the crystal size if you heat hot
and long enough. If cracks are in the weld then it is hot tearing, it
is not just hot short metals that do this.

Now, if I take a cold, fully annealed wire, put one end in a vise,
and give the other a good pull, I can stretch it a little. The
result is not only a nicely straightened wire, but a slightly
stiffer one. ie, it's a little work hardened. In the laser weld,
only the shrinkage that occurs after the metal has solidified has
any effect of course, but that seems significant. And that
shrinkage should be, it seems to me, deforming crystals as it
stretches.

Yes you are doing some deformation but you have to do a lot of
deformation to get to the point of being able to recrystallize when
annealing like 30-50 % reduction in section. Cooling metal will be
only a couple of percent at most. So you have some strain in the
lattice and if you anneal it you will relive that strain but it will
not recrystallize.

If I take, for example, a nicly annealed piece of gold or
platinum, and get a good solid weld on a butt joint (like a ring
sizing, for example), I can easily feel simply by attempting to
hammer, roll, burnish, that weld, that the metal of the weld is
distinctly harder than the fully annealed wire next to the weld.

Yes the metal is under stress and is harder, no argument there but
again heating it will relive the stress but not recrystallize it.
You do not need recrystallization to regain softness. What you will
not get is smaller equiaxed crystals in this case, the weld and
surrounding metal crystal size will remain basically unchanged
everything will shift a little to allow for the strain to leave the
matrix but that is it.

if I try and stretch a weld, such as stretching a ring with a laser
welded joint. Sometimes the weld itself fails, but sometimes it
seems lke the weld is tearing away from the adjacent metal. That
would be what you describe. The first seems only somewhat helped by
stress releaving the piece after welding. The second seems helped
quite a bit. Probably this is because when the welds themsevles
fail, it's also partly due to simply a bad weld with cracks or
voids, or the like...

Since we do not do any of the tests ( test coupons, x-ray,
magnaflux, ultrasound, etc) that are done to structural welds we
really have no idea how good or bad our welds are till they fail.
This is one of the biggest problems with using welding in jewelry,
the operators have virtually no feed back to train them in proper
welding technique. Brazing is so much easier to do well and gives a
lot more visual clues to how good the joint is.

Speak for yourself, Oh bearded one... (grin). I try not to get
surface-only welds. All too often they're a waste of time. The
trick is to arrange the weld method so that you DO get full
penetration. Usually this means not welding a tight fitted joint,
but rather, one with a V groove on one or both sides, so you can
comletely fill the weld all the way through with successive passes.
One does the same with a stick arc welder sometimes... And on some
welds, (platinum in particular is good this way) you can get
surprisingly deep penetration with higher power levels. (I can get
all the way through a 2mm shank in a single pulse on platinum, for
example.) Doing this has advantages beyond speed in that full
penetration welds like this seldom if ever have cracks, since the
whole weld is cooling and shrinking uniformly, just as a torch
fused joint could do. (well, almost...)

I know you do Peter but again this is the biggest area of problem
with these tools, they are sold as a miracle tool that will allow
anyone to do jobs that are impossible with a torch yadda, yadda,
yadda. But the truth is it takes a lot of training hands on time and
knowledge to become a good welder but almost any fool can make a
pretty weld that has no strength.

In the hands of a skilled tech the laser and pulse arc tools are
great but too many buy them without the understanding of how much
there is to learn about becoming a good welder.

Over the past couple of years I have been doing a lot of welding
both small jewelry scale and much larger stuff. I have learned a
great deal about it and mostly learned how much I don’t know about it
but I am getting better :slight_smile:

One of the things I have learned is that there is a lot to be
gleaned from structural welding texts that will make your jewelry
scale work a lot better. One good book is The Procedure Handbook of
Arc Welding published by Lincoln. It has a huge amount of information
(750 pages) and is sold very inexpensively ($25) directly from
Lincoln

https://ssl.lincolnelectric.com/lincoln/apdirect/item.asp?prodnum=PH

Jim

James Binnion
James Binnion Metal Arts


#16
One of the easiest ways to deal with HAZ related issues is to
preheat the entire piece.

Yes it is quite effective also weld preparation with a gap helps a
lot.

James Binnion
James Binnion Metal Arts


#17

Another problem with with Laser and Pulse Arc welds in jewelry
brazing as long as the seam is clean, well fluxed and tight enough
the filler metal will flow across the full face of the joint. With
welding often the operator just fuses the outer surface of the weld
and leaves an inner area or backside of the weld un-joined

If this is so, then the operator has not truly welded his seam.
This is not how welding is performed, as total penetration of the
weld is required.

I was a little tired when I wrote this and should have started that
paragraph with something to the effect that most operators are using
the laser and pulse arc welder in in a fashion that does not create
a full penetration weld.

I am in agreement with you on the weld prep The biggest
problem I see with the use of welding in jewelry is that jewelers
have not been trained to be welders.

James Binnion
James Binnion Metal Arts


#18
I am in agreement with you on the weld prep The
biggest problem I see with the use of welding in jewelry is that
jewelers have not been trained to be welders.

When it comes to using the laser, a bit of training in arc and gas
welding steel is a big help. Laser welding jewelry is a LOT more
like those processes, than torch brazing jewelery, because of the
"non traditional" joint preparations required for a good weld. 30+
years at the bench, was less a prepration for the laser, than the 6
week of evening tech school classes I took on welding steel, and
aluminum, as a hobby/home repair class.

20-25 years ago, or so, I became convinced that gold should be
weldable, even though we were being taught then that it could not. A
platinum specialist I trained in ‘75 with showed me very effective
ways of torch fusing gold and platinum, which only conviced me even
more that welding should be possible. I started reading about laser
applications for precious metals in the late 70’ or very early 80’s,
and then, the night school welding classes I took, only convince me
even more that welding should be possible for gold, silver and
platinum.

After ten years now, of using a laser, I find working without it is
like working without my left hand, it is now so much a part of my
techniques. My torch is on the right side of my bench, and the laser
is adjacent to the left side of the bench. Each tool works best at
specific applications, and neither is a replacement for the other.
Some jobs, I can do with either, but there are specific applications
that each excels at, and the six months I had to work without access
to a laser a few years ago were areal trial.

I am no scientist, nor researcher, or teacher. Just a bench jeweler,
always trying to find the most effective way to produce the results
I am seeking. I am not going to be deliberately stress testing welds
in a lab, but I do have to personally face any displeased customers,
and ten years with the laser has showed me that this tool is
extremely effective at producing reliable welds, that hold up over
years of normal use, by my customers. When a weld has failed, which
occasionally they have, it has led me to find ways to do improve the
process.


#19

Dear Gentlemen, my local brothers-in-law are welders and good enough
at that work to be sent to several foreign locations to instruct,
troubleshoot and service water desalination products. I should ask
them about critical joins of metal difficult to weld and some of what
is mentioned in these excellent posts to Orchid. I remember the great
laser debate but now we are getting into some nitty gritty of
"welding realities 101" or perhaps a second level course. Much of
what full scale professional welders take for gran= ted and assume
as essential part of the process is new to me and likely
to many jewelers who have little knowledge of welding.

With a full penetration and need to fill there is more actual work
than the beginners simple fusing of surface areas on both sides. The
time to do the work increases when the weld is made sound(er).

Even with limited laser experience, I have discovered it is a
marvelous tool but as with all tools has limitations. I am fortunate
that our model allows changing of parameters including the “ramp” of
the shot, something I have found useful even if not fully understood
considering how it all takes place is such a short nip of time.

I say this to say thanks and please continue anytime to post useful
concerning laser operation, methods and limits. One of
these days I might actually get to the training sessions.

Tom


#20

Crafford LaserStar does offer a 2 day class at their RI facility. It
is a good class to take after you have used the laser a bit. They
really got into the Pulse-shaping technology, which was beyond my
needs at that time, because my employer then had an older pre
Pulse-shaping laser. My own machine now has this feature, just the
basic 3, and I use it all the time.

I would recommend this class, but there really is a need for a
higher level class, I think. Laser welding precious metals has now
been around longnenough that I am sure there are some highly
experienced operators, who have taken the technology well beyond
those basicly intro level courses.