"Tom Del Rosso" wrote in message
...

Tim Williams wrote:
Spot welded? (I'll watch later)

But what temperature would that be at?

Well.. welding is welding, yes, but you get very different results between
highly localized and loosely generalized heating methods. In order of HAZ
(heat affected zone) size, smallest to largest: e-beam, laser, spot, arc,
torch, friction, induction, forge. (Give or take various considerations
for each process, but I think this is a pretty typical ordering.)

E-beam and laser do highly localized heating (down to the micron), with
e-beam having more penetration I would think (an electron beam as high as
~1MeV can shoot, I think, a milimeter or so into solid metal?).

Spot welding is a traditional thermal method, but it's heatsinked with
solid copper electrodes, and done in a relatively short pulse (100ms for
the better ones, though you may spend seconds with a cheap unit;
obviously, YMMV). So the HAZ is small (ay from the weld, heating drops
off rapidly). Precedent: vacuum tubes are all spot welded construction;
generalized heating wouldn't go over so well on a precision grid (can you
say warpage?) or chemically treated cathode.

Arc welding, again varying by type, is still fairly sharp, but I wouldn't
guess it would be good enough for most electrical purposes. MIG (GMAW) is
generally the fastest (splat some metal on, then run), while TIG (GTAW) is
the slowest (you can sit there cooking the workpiece with the arc if you
want). (Oxyacetylene is slower still, obviously because the flame has
lower temperature than an arc, plus all the gas blowing by heats up a lot
more work than just the weld zone.)

Friction and induction welding are pretty specialized, being useful on
shapes with continuous symmetry (e.g., butt-welding circular pipes with
friction spin welding; long seam welds with friction stir, or induction,
which is common for seamed pipe).

Forge welding I suppose is the silly case of "100% HAZ", because you
generally have to put the entire workpiece into the fire to get it hot
enough (somewhere around spitting white hot) before it'll mash together
when you whack it with the hammer. Friction and induction welding really
are examples of forge welding (the metal is not melted), but because they
involve localized rather than bulk heating, and apply to specialized
processes (you can't spin-weld just anything..), they can be separately
identified.

So, when it comes to electronics, spot welding is a great way to go, if
available -- it doesn't make much EMF (yet another concern!), since
current is applied across the wire; it doesn't heat things up, and it's
fast and cheap, great for production.

Ultrasonic welding and wedge bonding are pertinent examples also from the
electronics industry, being used for very small joints of course (where
heating cannot be tolerated, so spot welding is out).

Tim "spent years on RCM"

--
Seven Transistor Labs
Electrical Engineering Consultation
Website: http://seventransistorlabs.com