The resin 3D printer is a relatively simple beast. There is a plate above a screen with a small (~0.2mm) gap between the two. Into this gap flows a resin. The screen displays an image and where the image is light, the resin polymerizes into a solid. The plate moves up one step and the whole process is repeated until a 3D part is constructed layer by layer.

Attempts to reinforce parts by incorporating short glass fibers in the liquid resin have been made, however, due to the small gap under the build plate, these fibers line up only in the x-y planes and the part gains no strength in the z axis.

To address this, let's incorporate magnetically sensitive reinforcement particles. The obvious candidate would be short steel fibers, but magnetically functionalized antibodies exist so it's clearly possible to make other things react to magnetic fields, e.g. small carbon fibers.

Now, our first layer is about to start, the build plate is 0.2mm off the screen, steel particle laden resin fills the gap. At this point an electromagnet mounted on the build plate switches on and all the steel particles stick to it in a vertical orientation. We turn on the screen/UV and the resin polymerizes around the particles. Now we have vertical reinforcement.

More sophistication could be added by having electromagnet pairs in various positions so that several particle orientations could be achieved.

The main problem will be ensuring the steel particles don't settle out or accumulate quickly in the first few layers.
-- bs0u0155, May 05 2022

Have them shaped such that they're structurally linked together. https://www.amazon....id=pla-812529524153
Maybe more hook shaped than the straight ones in this example. [doctorremulac3, May 06 2022]

Cold Welding https://en.wikipedi...g/wiki/Cold_welding
Possible solution to the "melting plastic" problem. Not sure how plastic behaves under very low air pressure... [neutrinos_shadow, May 12 2022]

I'll have to give this some thought.
-- doctorremulac3, May 05 2022


[+]
-- Voice, May 05 2022


What if you have the very tiny metal pieces shaped like jacks so they sort of interlace with each other? Not sure how you'd shape them being as small as they'd need to be but there's probably a way. Interesting idea. [+]
-- doctorremulac3, May 06 2022


I heartily endorse this.
-- 2 fries shy of a happy meal, May 06 2022


Wait. The whole process is still done in non-overlapping 0.2mm layers, right? So, supposing that the steel particles in a given layer coalesce into vertical filaments, all those filaments still stop abruptly at the edge of the layer, and there's nothing joining them on to the filaments in the next layer. So, surely, the resulting structure will simply shear apart at the layer boundaries, won't it?

Or is there some clever stuff about field lines that I'm not visualizing properly?
-- pertinax, May 06 2022


I was thinking that they'd be attached magnetically so they're hang between the solidified and liquid portions of the progressively hardening piece linking the layers like that.

Maybe I misunderstood. If not that's the way it should be done.
-- doctorremulac3, May 06 2022


I thought it's ferrous microparticles aligned in a resin.
-- Voice, May 06 2022


//The whole process is still done in non-overlapping 0.2mm layers,//

I'm aware of this, I'm in an odd situation where my brain thinks it's a solved problem, but it's not letting me know exactly how yet.

The solution is something to do with either recesses in the build plate or longer than 0.2mm particles.
-- bs0u0155, May 06 2022


//I'm in an odd situation where my brain thinks it's a solved problem//

[marked-for-tagline]
-- pertinax, May 06 2022


From what I read I thought that the ferrous particles would be aligned to alternate polarity with the layers above and below adding magnetic attraction to the bond.
-- 2 fries shy of a happy meal, May 07 2022


hmmm, if the particles are conductive then a very tiny current would heat a 3d print from the inside to solidify it into a single piece after printing.
-- 2 fries shy of a happy meal, May 07 2022


I thought of that but couldn't think of any binding material surrounding it that wouldn't melt. You're welding and melting metal after all.

What about having a metal matrix that the shape is built around that you then use corrosive chemicals to remove? The plastic object shaping material could be impervious to the chemical that would remove the metal.
-- doctorremulac3, May 07 2022


The heat of the metal particles might be the different enough that that it allows these particles to melt further into the previous layer making a deeper zig zag join. Especially, if they are being pulled to the previous layer ones by an attractive magnetic field. There would be no complete sheer line.

They will probably rust out over time.
-- wjt, May 07 2022


What about dropping the temperature of the whole thing down to -300 or 400 degrees Fahrenheit then just blast the welding current in just long enough to weld the touching metal parts?
-- doctorremulac3, May 07 2022


You wouldn't need to weld them, thermoplastic melts at a fairly low temperature. If you heat the metal up enough to weld you will just Swiss-cheese your print.

Just the right amount of heat on the other hand would cause roughly half of the magnetized particles to be drawn slightly towards one layer or the other depending on proximity. They would grip each layer after the print and solidify acting as vertical re-bar.
-- 2 fries shy of a happy meal, May 07 2022


//you will just Swiss-cheese your print.//

What I'm saying is get the whole thing down to -200 degrees or so so when you put the current through to weld the metal pieces you turn it off before it gets to the plastic which is so cold it'll take a measure of time to heat up. The metal will too, but before the heat expands outwards to the plastic you turn it off.

Electrical welding of metal happens very quickly. Zap it, bond the piece, continue freezing everything, zap it again till all the metal connected.
-- doctorremulac3, May 08 2022


Well sure you could be left with a welded scaffolding afterwards but any plastic around the welds would melt leaving hollows. If you want the 3d print to structurally strengthen between layers then you just want the particles to heat to a specific temp. just enough to barely melt between layers and anchor each one to the next.
Any more heat and the thermoplastic will just bubble where you don't want it to.

On a side note this procedure would be a very cool way to create an intricately formed single piece of metal using negative space to create that which could not be formed without using negative-space removal.
-- 2 fries shy of a happy meal, May 08 2022


Well that's my question, to what extent can the forming of those hollows be mitigated by split second welds happening in plastic that's frozen at -200 degrees or more? It takes some measure of time for the plastic to absorb that heat and change state from solid to liquid.

Does latent heat enter into the calculation?

Again, this is where 8th would roll his eyes and say "Stand back amateurs, here's the formula." and we'd both watch with our fingers crossed to see of whose take 8th's evaluation confirmed. Very weird, you'd think for him being such a smartass know-it-all who was less than subtle in pointing out he knew more than most people here, we'd have hated the guy, but we all loved him.

Maybe it's because he was funny as hell. Everybody loves a person with a sense of humor, especially a sick one like 8th's.
-- doctorremulac3, May 08 2022


//thermoplastic melts at a fairly low temperature//

You're in two different worlds here. Once cured resins, acrylates in this case, aren't thermoplastics. They won't melt/re solidify, if you heat them, they'll just eventually start to thermally degrade.
-- bs0u0155, May 09 2022


But can whatever material we're talking about be frozen enough to stem the effects of the heat from fusing of the metal grid inside when you're essentially welding them together? Just zap it long enough to weld the metal part without hurting the surrounding material because it's so cold?
-- doctorremulac3, May 10 2022


//stem the effects of the heat from fusing of the metal grid//

I think size is critical here. My idea was all about short, iron filing-sized particles. I don't think it's practical to weld anything that small. Or, beyond practicality, is it even possible? If you're thinking about a spot-welding type technique, then that requires relatively high current. Steel is a poor conductor and you'd get a lot of heating when moving current to the center of a part. That, and like lightning, there will be a more conductive path and that's where all the current will go.

Laser welding might be possible, but how many are we doing? Getting that right deep in a resin will be tough. Easier to make a mold and cast the damned thing in metal in the 1st place.
-- bs0u0155, May 12 2022



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