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Field Enhanced 3D Composite Printer

Customize the orientation of the reinforcement fibers with switchable electric fields during printing
  [vote for,

3D printers are now surprisingly cheap. I 3D printed a pencil holder while doing work experience at a nuclear engineering company back in the late 90's and was told it probably cost $30,000, if it weren't a "training/calibration exercise". Now, 3D printers cost about as much as 2D printers, and are hilariously cheaper to run.

I got one myself, it works like this: At the bottom there is an LCD screen, similar to the one you're looking at, only monochrome - black and white if you will. Instead of white however, the screen allows UV* light to pass through forming any image you like. Above the screen is a bath of goo. When exposed to the UV image, the goo stops being goo and starts being plastic. So far, you can make a 2D plastic shape.

The 3D part is where the build platform** comes in. The platform is a solid lump of flat aluminum that begins ~0.1mm from the screen with ~0.1mm of goo between it and the screen surface, then when the first UV image is formed, the goo polymerizes on the surface of the platform. The platform moves up 0.1mm and the process repeats until your shape emerges from the goo, upside down attached to the platform. Lovely. What more can we need? Well, the plastic formed is just plastic, it has great properties, like corrosion resistance, flexibility etc. but add in reinforcement like glass or carbon fiber and you create a composite material. These can be made with extraordinary properties, huge strength-to-weight ratios, complex shapes and the reinforcement material can be selectively arranged to provide rigidity/flexibility in specific directions & areas.

A common composite you might find in a typical power tool, usually nylon with ~30% glass fiber reinforcement. These parts are injection molded with short glass fibers randomly distributed in the molten plastic. There's no control of the fiber orientation, because the part is molded all in one go. More sophisticated components, like in F1 cars or aircraft, lay sheets of woven fiber, usually by hand, and carefully control orientation in that manner. But what can we do with the 3D printer?

So, take glass/carbon fibers and modify them to have a +ve end and a -ve end. In something like artificial spider's silk, this already an inherent property, one end is a carboxylic acid that loses a proton to become -ve, the other end is an amine that gains a proton to become +ve and the whole molecule is net 0 charge, but will happily align itself with an electric field.

Now, in our 3D printer we have goo, containing randomly arranged fibers with +ve/-ve ends. Now, just before we turn on the UV light to polymerize the plastic, we apply an electric field across say, the x axis. All the fibers line up and then you turn on the light. Now the reinforcement is aligned, and better yet, you get control of the orientation in 0.1mm steps. If you only align in the x axis, your part will be stiff in that direction, and as flexible as the base plastic in the y&z axes. Now you have complete control, you may even be able to "knit" the fibers, making a continuous x,y,z mesh.

Possible problems: I don't know how hard it is to make glass/carbon fibers with +ve/-ve ends with net 0 charge. It would be easy to purify them however, apply an electric field and the net -ve will migrate to one electrode and net +ve to the other. I'm not sure how electric fields work in relatively non-conductive hydrophobic resins, or if that could be modified.

*I say UV. 405nm, which is like diet UV.I mean, you can see it quite easily, so it isn't UV is it? No, we have a word for that. It's V. Ultimately, 405nm LEDs are cheap as chips and do the job just fine, so who cares.

**platform implies support, but with a feeling of "from below". This platform is at the top, the English language doesn't really have a word for something you build upon from below, and extend downward. Maybe it's just silly human bias, should we build houses from the roof down? It makes a lot of sense, it would keep the builders dry and you could crack on with the electrics practically from the start.

bs0u0155, Dec 30 2020

You've seen these printers right? https://www.youtube...watch?v=5w78TGggCig
[2 fries shy of a happy meal, Dec 30 2020]

270 nm solid sate light source https://www.alibaba...er.3.6c5a6baax5NLIu
[beanangel, Dec 31 2020]

Putting Y shapes and mesh shapes through a plastics nozzle Stringy_20injection...nsumption_205-10_25
[beanangel, Dec 31 2020]

The stonely wave is a kind of wave I had not heard of, decreases rapidly from source; useful for this https://en.wikipedi.../wiki/Stoneley_wave
A Stoneley wave is a boundary wave (or interface wave) that typically propagates along a solid-solid interface.[2] When found at a liquid-solid interface, this wave is also referred to as a Scholte wave.[3] The wave is of maximum intensity at the interface and decreases exponentially away from it. [beanangel, Jan 01 2021]

Lasers making stoneley waves at solid liquid interfaces https://www.spiedig...2.23974.short?SSO=1
[beanangel, Jan 01 2021]


       //mixed materials you''ll have to go with FDM instead of SLA. What make of printer did you get?//   

       Why? There are already resins with carbon/glass mixed in. I think the only challenge is to prevent settling out, even then, with tiny particles in viscous resin, the settling is only a concern with very long time periods, storage etc. Even if it was an issue during printing, you could rig a peristaltic pump to keep the mix recirculating.   

       I got one of the anycubic monos. Now I just need to learn fusion360 or similar.
bs0u0155, Dec 30 2020

       //How much flow can the process tolerate before it disrupts the surface being cured?//   

       You only need to get ahead of settling, and I really doubt that's a problem on the time scale of hours. Even if it was, you could pump between polymerization steps, while the platform is moving. Like I say, it's probably only a transport/storage issue.   

       //3D SLD process that used multiple, intersecting lasers//   

       Ugh. That's a heavy-handed expensive, engineering-heavy approach. The lasers will be operating at relatively long and varying distances. That means the error in control will be massively, and variably amplified in the 3D space. That means very high-precision control, stable mounting and so on, that's why laser-scanning microscopes cost millions. Also, if you think about it, say your resin polymerizes at the intersection of 3 beams, you still have 1/3 of the polymerizing intensity along the whole beam, so the bulk resin is going to slowly polymerize. The only solutions are to progressively replace the resin, use many more beams, which needs more control & precision, or to be focusing the laser at a point, which is VERY expensive to do with precision at long range.
bs0u0155, Dec 30 2020

       //should we build houses from the roof down?//
I have read about this being done, in Japan IIRC. Makes a lot of sense actually; no need for scaffolding etc, build one level then jack it up & build underneath. I recently suggested it at work for assembling a large project.
neutrinos_shadow, Dec 30 2020

       //should we build houses from the roof down?//   

       There's a construction technique for high-rise buildings where a central core is erected, and then individual floors are assembled at ground level and then raised to the top of the core, in succession.
8th of 7, Dec 30 2020

       With your new charge migrating fibers at 3D printing you can do a lot!   

       Primitively, imagine a cube made of ball grid array chip bottoms as the interior faces of your 3D printer. What if you 3d printed a dissolves in water or solvent polymer around your actual workpiece(nurse polymer), and the Nurse polymer had conductive traces in it and all the solder balls they made contact with; they could turn on and do something like 2D and even 3D electrophoresis of the actual workpiece as it sets-up.   

       Computer models, genetic algorithms, and machine learning could assist with modelling and planning an (up to) 6-axis of electrophoresis effect from the BGA-like conductors on the sides.   

       ...You could make Y shaped   

       - + Y   

       reinforcement fibers and arrange them in entirely new electric ways.   

       If you have the right viscosity of fiber pre-builds these fibers could look like Y or # (net), They could pass through the nozzle as well. [link] That adds more latitude to what the materials can do. I have never heard of Branched reinforcement fibers before, but I think they must have some use.   

       As to the UV Laser/LED, I saw .6W 308 nM and 270 nM Ones online [link] so you are right they are getting better.   

       A material I just read about at wikipedia is "amorphous metal glass". It holds strongest thing ever records from what I read, and you could include whiskers of that in your 3D print resin.
beanangel, Dec 31 2020

       //strongest thing ever//   

       Was that tensile- strongest, compressive- strongest, shear- strongest, strongest personality or strongest- smelling?
pertinax, Dec 31 2020

       [pertinax] you caused me to think of something funny. It might be well known and have a name. (let me know if ir does):   

       If a person is talking to an audience of people, all of whom are better in productivity, ethics, and conduct than they are, then each of the members comes up with it's own interpretation of "Strong". Often or usually, sort of (Hmmm. but not really) They will always pick a version for strong that exceeds the productivity, ethics, and conduct of the person who used the word strong.   

       I think its megapascals of squishing pressure prior to failure at some standard like an ASTM test.
beanangel, Dec 31 2020

       Thank you, that answers my question.
pertinax, Jan 01 2021

       [bs0u0155] noticed he could use a kind of wave with 200 nm area of decay (evanescent wave) caused me to notice the Stoneley wave, which could be used at a much faster, but lower resolution micrometer 3D printer (? not that I've calculated it or anything).   

       Almost all of the people that publish about stoneley waves are part of the petroleum industry, Someone who knows about stoneley waves there might be able to instantly say what they thought about using them for 3D printing. There are some references on how to make stoneley waves at interfaces with lasers [link].   

       Wikipedia says, "The wave is of maximum intensity at the interface and decreases exponentially away from it." so if there is somehow a way to get an activator of 3D printing fluid to respond to stoneley waves, (like say a laser) then you've got much tinier resolution than LCD pixels. Bigger than 200 nm evanescent waves possibly, which is great as [bs0u0155] points out that printing speed matters as well.   

       Something as exciting as a new kind of wave seems like it would be better known. It is also called a "tube wave" and sometimes causes chevrons. The way it will travel through rock suggests that some milder version would travel through the human body. I wonder if Stoneley waves could be used for ultrasound imaging, like medical imaging and industrial imaging. I found zero papers on that.   

       Also, Stoneley waves might only work on certain materials. It is possible making ultrasound contrast agents out of stoneley wave materials could improve ultrasound imaging. Stoneley waves only like to travel along "interfaces", which sounds great for differentiating tissues, noticing deep delaminations, and reading at depth how on-tolerance the interior of a manufactured thing is.
beanangel, Jan 01 2021


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