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[wierd]

You will have to retool anyway.  The assembly robots will still need new programs to properly pick and place bolts, apply welds, etc.

Industrial robots are..... Very stupid. They run very literal, very exacting programs. Not much fuzzy logic in manufacturing.

Sintered metal (what aluminum 3D printing really is) also has structural limitations that solid machined metal does not have.

1) It has an amorphous/irregular/unpredictable grain direction
2) It has small voids in the resulting material
3) resulting metal grain structure has unpredictable grain size/orientation.

Combined, this makes the material have unpredictable strain and stress characteristics, making it less ideal for load bearing or structural components. The void problem makes the material more prone to stress fracture, especially from accoustic vibrations.

There's a reason why milled parts are milled.  The designer of the part needed at least one of the following characteristics of milled metal:

1) Predictable grain direction (To mitigate internal stresses)
2) Uniform material composition
3) Controlled metal grain size and orientation.

Most CNC machines on a factory floor will have a tool carousel that has stock tools in it. (End mills, spot drills, face mills, etc.) The NC programmer will try to stick to these stock tools as much as is inhumanly possible, because the loading and unloading of custom tools into the tool carousel is where the infamous "Retooling" time comes in. As long as the actual tool numbers and tools remain constant between jobs, there is no retooling, even when making radically different parts.

If your assembly line keeps certain metal types in fixed work cells to maximize/economize workflow, then even having dissimilar metals in the production flow wont result in retooling. (Tools made for cutting aluminum are NOT the same as tools made for cutting steel, inconel, or other hard metals!! The cutting methodologies that are most efficient are VERY different! Tools made for steel will gum up when cutting aluminum, and tools made for aluminum will burn up/snap off when cutting steel. For this reason (as well as keeping waste streams seperate for recycling) dissimilar metals need to stay in different work cells, then converge at the assembly stage.

Other than producing shapes that physically cannot be either formed, or machined, (and castings are too inconsistent/inaccurate), I dont see a real niche for 3D printed metals.  To me, the place they would shine would be in very novel shaped items that no tool in the universe can produce with subtractive manufacturing.

Say, things that purposefully have a large void inside them, or have some complex internal structure. (think corrugated cardboard, only made from aluminum)

[Bumber]

You could print a car with golf ball dimples on the outside to make it more aerodynamic.

[wierd]

Or, you can use a hammer die in the hydropress, and get the same result, cheaper, with stronger metal.

Where 3D printed metal shines, is for novel metal parts that make use of internal structures not attainable any other way.

[Sheb]

And for generating internet noise.

[Osmosis Jones]

Or, you can use a hammer die in the hydropress, and get the same result, cheaper, with stronger metal.

Where 3D printed metal shines, is for novel metal parts that make use of internal structures not attainable any other way.

Internal structures yes, but there are other situations as well; implant materials will be huge. My background is orthopaedic biomaterials, and honestly, laser-sintered Ti-based implants are the future. Aside from being able to make them porous, 3D printed medical implants are a perfect example of a situation where the customisation possibilities (e.g. larger/smaller/longer stem/wider head/etc) is far and away more valuable than the cost savings of casting, and as long as the material is sufficiently corrosion resistant and bio-inert, an implant can easily and rapidly be sintered  together with mechanical properties far in excess of what is necessary.

Plus, since Ti is already an utter bitch to work with, people use powder metallurgy a lot anyway; it's rapid-manufacturing rather than press-and-sinter, but it's an easier migration.

[Dutrius]

How good would 3D printing be for nanoscale engineering? Can we make structures that precisely yet?

[i2amroy]

AFAIK "printing" is something you can do with nanostructures (and it's a viable method), but the ways that you "print" a nanoscale structure and the ways that you print larger ones are two totally different things due to the structure sizes that you are dealing with.

[alway]

How good would 3D printing be for nanoscale engineering? Can we make structures that precisely yet?

That's what a computer is. Though they typically only do a few layers since the process is hella expensive. Basically you print a layer at a time with some sort of vapor deposition technique.

[Dutrius]

Fair enough.

[Cryxis, Prince of Doom]

Random metallurgy/materials science question. How hard would it be to put a metal jacket around a hollow glass spheroid that is filled with fluid? 

[forsaken1111]

Random metallurgy/materials science question. How hard would it be to put a metal jacket around a hollow glass spheroid that is filled with fluid?

I'd imagine that would depend on what metal, and what fluid. And what kind of glass. I doubt it would be too hard to tack weld 2 halves of a steel shell around a glass ball full of water.

[Cryxis, Prince of Doom]

Hydrochloric acid would be the fluid, not exactly sure what glass so let's just assume something optimal for this (I don't know my glasses very well), and the metal would be copper.

Preferably a smooth jacket around the glass spheroid.

[Helgoland]

Shouldn't be that much of a problem. Why the glass though? And for what purpose would you need such a contraception?

[forsaken1111]

Before he specified copper I was imagining a glass capsule full of liquid nitrogen being submerged in mercury, forming a solid mercury shell.

[Bauglir]

Freezing mercury bullets - for when you absolutely must kill that fucking werewolf fire elemental.