Thanks! (Although, it is nice to see a good old /. link - pretty rare to see that on HN!)

Not recently. Atmospheric EB has been around for a long time. Leybold started in the 60's and by the 70's a few companies had machines. Band saw blade welding is one of the big users of atmospheric EB.

The big problem with ATM EB is that the beam diffuses in the air rapidly so you have a few usable cm from the aperture to the work piece. The machines work by using a standard EB column with a turbo or diffusion pumped gun chamber firing down a baffled tube, each baffle having a small hole for the beam to pass and the space between the baffles is pumped by large vacuum pumps. PTR had a picture of such a machine and you can see a big umbilical of vacuum hoses snaking from the head to a battery of large Stokes piston vacuum pumps. Each baffle successively reduces the atmosphere leaking in until the isolation valve can be opened and the head can maintain enough vacuum to prevent flash over arcing.

A lot of that big stuff you see like pressure vessel welding uses reduced atmosphere welding where a small space is sealed as best as possible so the pressure can be reduced below 1 pascal (1E-2 Torr.) Then a standard pumped welding head can be used.

The more recent development was the plasma arc window stuff Brookhaven national labs did with Joining Tech (knew someone who worked for them when that project was active) though I know of no manufacturer using it.

The applications on Earth are already realized:

https://en.wikipedia.org/wiki/Laser_beam_welding#Equipment

https://rickyswelding.com/best-laser-welding-machine/

> I think the key reason that space-based research tends to be so technologically fruitful is that it imposes a discipline on the science done, through the constraints that space imposes on meeting ambitious mission objectives.

The enormous budget and the elite scientific and engineering talent also may help. On Earth, those resources don't usually go toward finding a new way to weld things.

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> but your heat affected zone is bound to be much larger because the only way heat leaves the part is radiation.

Which is the whole point of processes like laser and electron beam welding: minimum heat input to achieve the required penetration. Some parts can be held in your bare hand immediately after welding and they might be warm or hot to the touch. Sure there are parts that are glowing hot but those are usually big, deep welds.

> Also, laser welders (at least terrestrial ones) have a copper tip that you drag across the part which keeps the laser a consistent distance away from the weld.

You are thinking of a cutting head. Welding heads can completely omit a coaxial gas nozzle and use an air knife or nothing if the focal distance is long enough to prevent spatter from hitting the sacrificial cover glass in front of the focal lens.

> When welding thin material on Earth we use copper backing plates to suck heat out of the weld area, that could work in space.

There are methods of radiating heat into space which is likely what will be employed in the tooling and fixturing. Also, if the heat input in minimal and there is enough mass the part heat sinks itself.

I work in an e-beam and laser welding shop and I have built laser welding workstations.

If you get your two surfaces very very close, sure. The problem is most non-ground metal is going to have a surface finish that is too rough for this to work.

You could squeeze things together, but this depends on part geometry.

Sure but the surfaces have to be perfectly flat to where you measure the roughness in angstroms. Not something you can perform by hand or with mechanical polishing.

This is known as 'Cold Welding' https://en.wikipedia.org/wiki/Cold_welding

Not a metalurgist, but agree the oxide problem would go away. However I think you'd have a worse problem with heat. Aluminum in my limited experience gets really hot and soupy when welded, so that you have to go quite fast in many cases. Without an atmosphere to sync some of the heat, you might have very interesting thermal issues. You'd definitely need much bigger heat syncs. However depends likely on the scale of welding that's happening. Definitely will be interesting.

The kickass aluminum welding process doesn't melt aluminum at all. It's called friction stir welding. Invented in the UK in the 1990s, it involves moving a rotating tool through the aluminum. The rotation softens and mixes the solid metal, refining the grain structure and blending the two pieces together. It's what SpaceX uses to weld the tanks on the Falcon 9.

While you're correct about the oxide issue, there are welding processes which mitigate this. In particular, using alternating current instead of direct current causes a "cleaning" effect which knocks the oxide off of the weld area. Laser welding does a similar thing.

If you're welding aluminum with DC stick, DC TIG, or just an oxy-acetylene torch you can get good results by grinding the weld area with a flapper disk and brushing immediately before welding with a stainless wire brush that has never touched anything but aluminum. For DC TIG and oxy-acetylene I've used flux coated welding rods as filler material with some luck.

Also, you always need to keep oxygen away from weld, no matter what process or material you're welding. At welding temperatures metals will burn in the presence of oxygen. We do this by using shielding gasses, flux which burns and displaces the oxygen, using a slightly fuel-rich (or "reducing") flame, physically displacing all the oxygen (forge welding) etc.

> In a vacuum this problem wouldn't exist and aluminum should be no more difficult to weld than steel.

Aluminum is a PITA for more reasons than its oxide layer...

I was really interested in it but I'm very worried about my remaining eye.

Welding with current typically requires electrric arc. That typically requires some gas at high enough pressure. Welding in space would mean you need a lot of gas, which has to be shipped from earth and it's pretty hard to keep enough pressure near weld when you're in vacuum. Lasers have the smallest heat affected zone of all welding, so you need to get rid of smaller amount of heat after welding, pretty usable when you don't have atmosphere around you to cool your welds.

The current is the problem. Between the current flowing through the metal, and the resulting electromagnetic emissions, arc welding on an ungrounded spacecraft will no doubt cause all sorts of headaches. A laser does not require passing current through the object.

Fiber lasers can be quite efficient and the weld process itself is very efficient as less energy is delivered to the metal to perform the weld. Good beam control ensures a minimum of metal is melted to perform the weld and also doesn't get too hot to vaporize and sputter. I don't know about overall efficiency but laser welding continues to displace electrical welding due to a much higher level of process variable control.

Space has a vacuum which reduces heat convection. My understanding is that laser welding would apply less heat to the area around the weld point.

Cold welds have taken place in space.

https://en.m.wikipedia.org/wiki/Cold_welding