Quote from: john smith 19 on 03/02/2015 09:52 amNote that although "3D printing" is fairly new you should keep in mind that additive techniques are at least half a century old. Quite a lot of Aerojet designs used a combination of photoetched foils diffusion bonded into stacks.The technology is also used by Velocisys and Meggit to build "printed circuit" heat exchangers and chemical reactors to deliver so called "process intensification."Personally I always thought Aerojet could have pushed it much harder. They tended to do the stuff flat and then press (or use high pressure gas) to get it to shape. Obvious extensions that came to mind were :-Constructing parts as blocks but with either the final part inside the block, or internal cavities, defined by "perforations" around the outline. The little segments left holding parts inside the block would be quick to etch away, freeing the component.Stretching or bending the unbonded foils should be much easier than doing it to the finished product, provided layer alignment can be preserved. It would mean that once the layers were bonded together they would need to have their edges trimmed to give the right size.A technique in MEMS mfg is the use of "sacrificial" layers that can be preferentially etched to release objects. Making structures that are curved as you go down the layers smoothly is probably too difficult. However by using a smaller number of masks could give a more viable "stepped" structure. Those steps should be preferentially etched, giving a (relatively) smooth result. OTOH curves in the plane are relatively simple. Generally curves give smoother fluid flow.It should be possible to fabricate in situ sensors based on fluids effects on the resonance frequencies of various structures, being driven and read by various acoustic transducers. Embedded electrical sensors are likely to more difficult due to the need to create insulating and encapsulating layers inside the structures. By combining sub units split along different planes it would be possible to make more complex structures. this is relevant because of the difficulty of putting curves through layers. Layer thickness can also be varied. Historically they have been foils the same thickness, but they could be substantially thicker, from a few 0.002" up to say 1 or 2 mm thick. It should be possible to dispense with a photo resistant and go with a "direct write" exposure of the foils in a liquid, with the laser activating the liquid to etch the foil. While these methods don't have the total flexibility of metal deposition of 3D printing they are likely to be much faster to produce a large unit quickly (or many small units as a block). Just some possibilities which are also additive but not 3D printing. I got the chance to try "platelet" fabrication technology in 1998-99 when we built this engine, which was LOX cooled, 2400 psia Pc design pressure, 6.6K-lbf. As can be seen from the photos, individual copper foils were assembled in a stack and then diffusion bonded together. It wasn't cheap at the time costing about $80K, but we fired it 40 times and it worked well.Edit: spelling
Note that although "3D printing" is fairly new you should keep in mind that additive techniques are at least half a century old. Quite a lot of Aerojet designs used a combination of photoetched foils diffusion bonded into stacks.The technology is also used by Velocisys and Meggit to build "printed circuit" heat exchangers and chemical reactors to deliver so called "process intensification."Personally I always thought Aerojet could have pushed it much harder. They tended to do the stuff flat and then press (or use high pressure gas) to get it to shape. Obvious extensions that came to mind were :-Constructing parts as blocks but with either the final part inside the block, or internal cavities, defined by "perforations" around the outline. The little segments left holding parts inside the block would be quick to etch away, freeing the component.Stretching or bending the unbonded foils should be much easier than doing it to the finished product, provided layer alignment can be preserved. It would mean that once the layers were bonded together they would need to have their edges trimmed to give the right size.A technique in MEMS mfg is the use of "sacrificial" layers that can be preferentially etched to release objects. Making structures that are curved as you go down the layers smoothly is probably too difficult. However by using a smaller number of masks could give a more viable "stepped" structure. Those steps should be preferentially etched, giving a (relatively) smooth result. OTOH curves in the plane are relatively simple. Generally curves give smoother fluid flow.It should be possible to fabricate in situ sensors based on fluids effects on the resonance frequencies of various structures, being driven and read by various acoustic transducers. Embedded electrical sensors are likely to more difficult due to the need to create insulating and encapsulating layers inside the structures. By combining sub units split along different planes it would be possible to make more complex structures. this is relevant because of the difficulty of putting curves through layers. Layer thickness can also be varied. Historically they have been foils the same thickness, but they could be substantially thicker, from a few 0.002" up to say 1 or 2 mm thick. It should be possible to dispense with a photo resistant and go with a "direct write" exposure of the foils in a liquid, with the laser activating the liquid to etch the foil. While these methods don't have the total flexibility of metal deposition of 3D printing they are likely to be much faster to produce a large unit quickly (or many small units as a block). Just some possibilities which are also additive but not 3D printing.
The article that Prober linked to above has been moved to here:http://3dprintingindustry.com/news/rocket-engine-completely-3d-printed-79813/
