Starship Polaris said:You use microscopic machines to form molecular bonds turning the two pieces of metal into a single piece.
Dennis, you just used terms that have real meaning in a way that demonstrates you're not sufficiently conversant in what they actually mean.
"Molecular bonds" are also known, more commonly, as covalent bonds. This is the way that chemical compounds are created... two or more atoms of materials share an electron orbit, and the associated electron... ie, they share a "valence level"... and that creates a very strong bond between these two atoms. Molecules that are linear in nature can bend... ones that have a structure (hexagonal planar structures are reasonably common, for instance) form much more rigid materials.
Ionic bonds, on the other hand, involve no physical electron sharing. Rather, an electron is TRANSFERRED from a low-electron-affinity atom to a high-affinity one. The charged atoms (or "ions") are then drawn together by their opposing charges. This is, for example how salt is formed... and the lack of any unbound electrons is why these materials, in pure form and without crystalline flaws and crystal boundaries throughout, tend to be very hard and very transparent. No loose electrons to bounce photons back...
Metallic bonds involve the sharing of electrons. That is what makes them METALS. That's why the metals in the periodic table all fall largely together. They have a lot of electrons that are loosely held, and some of them "float away" when you have a lot of metal atoms together.
REACT a metal with something else... say, iron with oxygen... you no longer have a metal. AT ALL. You have (in the case I just gave)... ferrous oxide, aka RUST. It no longer has any of the characteristics that make it a metal. Further, the rust MOLECULES (there is no such thing as a "metal molecule") are held together by very light bonds... it's remarkably fragile.
The only way to get a strong bond out of that sort of material is to use IONIC bonds. For instance... sodium is a metal. Sodium chloride (table salt) is not a metal, it's what's referred to as a salt (there are MANY salts, by the way). But it's held together because the sodium transfers electrons to the chlorine, and the charges between the two ions hold them together.
My point? THERE ARE NO MOLECULAR BONDS... EVER... IN METALS. There cannot be. To create such a bond causes it to cease to BE a metal. It becomes something else... a salt.
Theoretically, if you put two perfectly smooth, planar piece of the same metal against each other, they would literally become a single piece of metal. The "electron sea" in each part would merge with that in the other part.
Unfortunately, there are no pure monocrystaline, perfectly clean and perfectly planar surfaces in the universe, as far as we know. So you can't REALLY check that. But if there WERE, we could "weld" without any tools, without any heat, without any pressure.
Which WOULD be pretty damned impressive as a construction technique.
This is why there are no joints or specular variations on the TOS Enterprise - the entire hull is manufactured to microscopically precise tolerances by nanonic devices programmed to do so. It's created that in a few large pieces in "vats" of the raw material (perhaps not the finaly alloy, but in fact the basic elements of it are themselves assembled into the final material by the microbots) - whether on Earth or in orbit is irrelevant - and then fused into a single unbroken shell by more nanomachines in orbital space.
That's all purely speculative. It's just as valid to say "the TOS enterprise had variations, we just couldn't see them on 1966 TV sets), or "the TOS Enterprise had a protective coating applied over the hull."
Nanomachines might "fuse" things together... but all you'd really be talking about would be little robots performing welding. And in order to do so, they'd need to be in between the parts being welded, and would have to weld in material to fill in the gaps as they "backed out."
This would actually be a lot LESS acceptable than a resistance weld or a "stir weld" using conventional technologies. Gap-filling welds result in not one, but TWO boundaries... and two possible regions for flaws to creap in. And flaws ALWAYS creep in... it's entropy at work.