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I know it's hard to quantify, but are rocket designers and astronauts more happy about the possibility of cold welding, or more negative about it?

I mean: two "bare metal" surfaces in vacuum weld together in the ambient temperature of space when they come in contact. In one hand, it could be invaluable in construction work, saving the whole bother with welding equipment - a good smack of a hammer will take care of bringing the elements in contact firm enough to form a weld. On the other hand, everything that isn't supposed to weld itself to anything else (like the aforementioned hammer) must be coated with, or made of non-welding substances. And if the protective layer is scratched, that still can "catch". It must add quite a bit of headaches.

So - in the absolutely subjective opinion of space equipment makers - do the headaches outweigh the benefits or vice versa?

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    $\begingroup$ This ESA study should shed some light. Contact data of different materials is included, and may be accessed online. $\endgroup$ Apr 8, 2016 at 22:15
  • $\begingroup$ To get a good cold weld, the surfaces should be aligned very well before contact. A good snack of a hammer may result in a bad alignment and only a small fraction of the surfaces areas being welded. $\endgroup$
    – Uwe
    Jun 29, 2017 at 21:11
  • $\begingroup$ "A good smack of a hammer" - is not a simple thing in zero gravity. You need a special hammer with absorption of inertia. $\endgroup$ Aug 30, 2020 at 13:16

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Virtually everything that goes into space is assembled on earth first. Nothing (to my knowledge) is 'assembled later' in orbit using cold welding, as there's no guarantee the weld will be of sufficient strength.

In space exploration, as it is currently undertaken, cold welding is only ever a bad thing. It usually disables some mission-critical piece of moving hardware, such as a reaction wheel.

However, I can imagine in the future, when humanity's presence in space is much more established, and complex products are manufactured in space, cold welding may indeed be a technique for the joining together of different parts. I doubt it would make as strong a weld as other pre-existing techniques, but then again, high join strength isn't always strictly necessary for something to be useful (for example, the adhesive on post-it notes).

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    $\begingroup$ +1, I've never heard of it being a good thing. $\endgroup$ Feb 11, 2019 at 23:30
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    $\begingroup$ @OrganicMarble perhaps there's an SF plot somewhere... $\endgroup$
    – uhoh
    Feb 11, 2019 at 23:51
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    $\begingroup$ @uhoh: Yeah, you caught me. $\endgroup$
    – SF.
    Feb 12, 2019 at 9:07
  • $\begingroup$ If two parts should be cold welded, the surfaces need some preparation first. Remove any oxide layers, dust and other contamination to get a clean, level and scratch free surface. Align the parts perfectly before welding them, but avoid any accidental premature contact. No correction of alignment is possible after the first contact. But how to get a gas tight cold weld without using ultimate fit tolerances? $\endgroup$
    – Uwe
    Feb 12, 2019 at 10:37
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    $\begingroup$ would a hammer work? Some sources indicate that vacuum cold welding requires either massive pressures between the surfaces an basically zero time, or good contact lasting several seconds, sometimes minutes. A hammer blow would impart moderate pressure for a microscopically short duration only. $\endgroup$ Aug 28, 2021 at 7:17

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