This applies to all types of weapons, from simple knives to handguns to assault rifles to even military gear, such as night vision goggles. How far into the future do we have to go in order to see a future where one can effectively print and use weapons on the battlefield? How long would it take? Is it ever going to be feasible? How about printing food and ammunition for the soldiers, along with the aforementioned equipment?
We'll almost certainly never see 3d printing of weapons on the battlefield, but printing replacement parts are a possibility.
3d printing isn't magical. You need raw materials to do it. To poke at your example in the comments, there is no "orange/lemon stock" which can be printed with. There's efforts to be able to 3d print some foods, but they're rare. The real issue is finding a situation where you would want a lemon, rather than an orange, and have time to create a lemon from stock. Right now, the military solution is to send out MRE's, which quickly demonstrate that you really wouldn't care which citrus you got, so long as it was an actual fresh citrus!
To make 3d printing valuable you need to make those options valuable. It's far easier, right now, to issue everyone the same caliber rifle ammo than it is to ship printers to the front lines. The value in specializing things enough to warrant such 3d printing is limited. It's just too easy to actually ship the stuff you need along the supply lines.
One place I do see potential for, however, is the production of replacement parts. Our tools of war are terribly complex, and parts do break. Right now, the process for keeping our stuff in repair is actually kind of complicated. If I could have "gun steel" as a feedstock, and produce whichever gun part broke on me, then that could be a huge advantage.
I remember hearing a while back that they were very interested in being able to 3d print things on submarines. The idea was that they can't bring all the spare parts they need with them, but they could bring a 3d printer and feed stock. That would save a ton of space and mass.
On the battlefield?
Feasible? Never. It's a slow process, speeding it up means more parts that print at the same time. Which makes it more complex, complexity leads to greater chance of failure and harder to repair. Two things the military hates on the battlefield.
3D Printing also has issues with printing multiple materials at once. Especially things like night-vision goggles are rather complex pieces of technology. Something that's hard to print.
Printing food seems equally unfeasible. For food to come out food needs to go in. Until we have fusion and can create new matter the raw materials we print need to contain all the resources. So all we're doing it changing their shape. Unlike MRE's who only require water and heat these would require powered equipment. There is no benefit here.
What will work then?
Now that doesn't mean the military won't adopt 3D printing. If the technology matures I expect them to fully embrace it. But unlikely on the frontline. But the engineers will love 3D printing. No reason to carry specific spare parts, just print one. It's much quicker them ordering it from a depot.
As for speed, anything of size will take hours. A printing head can only move so fast before simple things like heat become an issue. Again multiple printing nozzles can alleviate this but that's added complexity.
See there is one way this could somehow work. If you had small 'portable' nuclear fusion. In a way that's safe enough to carry into a war zone. Now I'm not sure we ever even get there, but we might. But I think that's at least a Thousand years into the future, even if we find fusion in the next two hundred years.
But with that, you can easily convert printing materials into what you need. But by that time I doubt we'll be fighting battles anything remotely close to what we do now.
The advantage of the 3D printing that you can create anything (ok... any forms from the compatible raw materials, within the parameters of the 3D printer). You need only a descriptor file for that.
Its disadvantage is that you can't optimize the manufacturing for your goal. It is particularly visible in gun barrels. They wear out fast, and to avoid it, you need to have various technologies (specific fiber structure, hardened steel, etc).
A 3D printer can create any type of forms, while a rolling mill can only create a very selected set of the possible forms. This set has to be specified while you build the rolling mill, and not while you build the gun barrels with it.
In exchange, the rolling mill produces very properly tuned output, while the 3D printer produces essentially cast iron.
Furthermore, once the rolling mill is build, it can create a lot of very high quality gun barrels (or other parts), while the 3D printer is slow. Yes, also the 3D printer can be built to be fast. But if you want to build a factory capable to produce X guns / hour, then you will need have many, many, many times more \$ for the same X with 3D printers as with rolling mills (and with other metal processing machines). It is because a more general machine needs more parts as a specialized one.
On these reasons, a 3D printer based weapon factory, in mass production setting, won't ever stay the race with a chain of more specialized machines.
And if we are talking about battlefield, it also means mass production.
Note, 3D printers can be more advantageous if we eliminate the mass production capability requirement. For example:
- if the law doesn't protect you
- but it punishes you very hardly if you try to buy a weapon to defend yourself
- and you are in a life-threatening danger which makes (2) an acceptable risk.
Of course it could be useful also for terrorists.
3D printers can be also used to produce the non-critical parts of the weapon (in a not very complex one, only the barrel is critical). The barrel should come from a more specialized mass-source.
In a low-tech environment there is also a possibility to produce the specialized machines with 3D printers (i.e. you don't create the guns with the printers, instead you created the non-3D-printer factory what produces them).
I'm going to go the other way and say it would take something like 20 years for viable 3d printing on the battlefield. Now these won't be portable 3d printers individual soldiers carry, but much larger bulkier 3d printers which would be stationed nearby and manned by a team and maybe placed on a moving vehicle.
Having a quick search, I would imagine something similar to the powder bed fusion method, where multiple heads deposit a layer of metal powder and a high power laser melts the powder to form the metal structure. Multiplying the number of heads that deposit metal powder and the laser increases printing speed.
This would be much better than your traditional 3d printing where the printer head has to deposit the material. You can print the entire layer much faster, and you can start printing the next layer while the previous layer is still printing. The speed limitations would come from the laying down the metal powder, and the time taken for the melted metal to become stable enough for the next layer of powder to sit on it and retain the shape you want.
You would also 3d print multiple parts together. Utilizing the whole printing bed rather than a single section, since the printer head always has to traverse the entire bed each time you make an additional layer.