7 ms·

Making 3D printing truly 3D

35 points by samizdis 5y ago

zbrozek 5y ago
arxiv link https://arxiv.org/abs/2109.02780 https://arxiv.org/abs/2109.02780
SiempreViernes 5y ago
They show pictures of Benchy here: https://www.nature.com/articles/s41586-022-04485-8/figures/4 https://www.nature.com/articles/s41586-022-04485-8/figures/4 No visible layering, though I've just looked at the picture and not read to check if they post process. Ironically it seems to have trouble making holes in the print.
Ancapistani 5y ago
This seems like a variant on something that I've been interested in for quite some time, but haven't had the time/motivation/focus to really play with it. I call it "non-parallel slicing" in my head, but I think there is another term for it. I use almost exclusively FDM printers. Slicers take a 3D model and "slice" it into a series of horizontal profiles that are laid down one-by-one on top of another to create the 3D output. This results in the print head moving in the X and Y axes pretty much constantly, but the Z axis moving only once per layer, and moving only in one direction (+Z). There's no physical reason the Z axis couldn't be more mobile. Yes, you'd have to be careful to ensure that the print head doesn't impact the print in areas where material has already been placed, but that can be represented by a virtual model of the print head in software - or even by a handful of standard measurements: * nozzle inner diameter: 0.4mm * nozzle outer diameter: 0.7mm * nozzle angle of approach: 30º * Z-offset between nozzle and lowest part of the hot end: 5mm The above would mean that instead of layers being all parallel to one another and to the bed, layer height could change dynamically throughout the print process. If you're printing a wing section flat on the bed, the center will bulge - so the first layer height at the leading edge of the wing would be as small as possible (say, 0.05mm). At the thickest point the layer height could be larger (say, 0.3mm). The next layer would then be laid on top of the layer below, compounding the differences in layer height. With traditional, parallel slicing, to get that resolution you'd have to set your layer height to 0.05mm throughout the print. The top surface of the wing would be a series of "stairsteps" much like the "jaggies" seen when upscaling a raster image. With a well-designed non-parallel slicer and an appropriate model, the top surface would be a single layer, laid down in a complex three dimensional curve. The nozzle's "angle of approach" and the "Z-offset between nozzle and hot end" would place fairly restrictive limits on how much any given layer could diverge from horizontal and from the prevous layer. That said, this approach would allow today's commodity printers to be used in this way. A more capable approach would be to design printer hardware to directly take advantage of non-parallel layers, by adding additional axes: A, B, and C, which would represent rotation around the X, Y, and Z axes respectively. This would allow full movement of the print head relative to the work piece (subject to the physical constraints of having the print bed supported on a plane, which the hot end may not impact). The best part of all of the above is that the language used to encode instructions for 3D printing - Gcode - is literally designed for this use case. Gcode was originally intended to control milling machines, and 5- and 6-axis CNC are fairly common (albeit expensive). I came across someone's university project a couple of years ago that implemented something similar to this concept, but never investigated it deeply and have since lost the link.
- Ancapistani 5y ago
  If you're familiar with work being done in support of the above, or even if you're just intrigued by it like I am... please feel free to reply or connect with me. Maybe you'll "light the fire" for me to spend some real time working on this :)
  - pikewood 5y ago
    Non-planar slicing? https://all3dp.com/2/non-planar-3d-printing-simply-explained/ https://all3dp.com/2/non-planar-3d-printing-simply-explained...
- rkagerer 5y ago
  Formlabs SLA printers can do "adaptive layer height" where they adjust the layer thickness of the print as you go, using thin layers where there's more detail and thick, faster printing ones where there isn't. The build still only progresses in one direction, though.
  - birdman3131 5y ago
    I recall cura doing this as well for fdm.
- ncmncm 5y ago
  Any additive 3D printer can do variable layer thickness. It just needs the software to adjust the amount of plastic fed to the print head, according to how thick the layer should be, and lower the bed less for thinner layers. Layers that vary in thickness are trickier. It seems like any additive printer should be able to do them given slightly smarter software and a pointy nozzle, but controlling temperature in a pointy nozzle at varying flow rate is not simple. The heating element is far away from the pointy end, and heat arrives at the tip both by conduction in the metal and also by physical motion of the melted filament medium. You need to vary the current to the heater so that the tip stays at the right temperature at all the different filament flow rates. Changes to the current have to happen well ahead so the right amount of heat actually reaches the tip, by the two routes, sometime later. You are also changing the feed rate of the filament, so it is carrying heat down at varying speed. The point is cooling by radiation and convection, the latter which varies by how fast the tip is moving, and the ambient temperature.
bawolff 5y ago
That's cool and all, but i don't see how you can justify this as being more "3d" than traditional 3d printing.
- amelius 5y ago
  Because you can print things like a table in its normal orientation.
  - gweinberg 5y ago
    That's kind of a non-sequitur though. A 3D printed table is no less 3D if you had to print it upside down. And who even has a table they haven't flipped over at least once?
    - ncmncm 5y ago
      Not all shapes are flat on one side and have no hollows. Most shapes do not match that criterion. So, on most 3D printers, they have to add sacrificial support structures. Also, most 3D printers add material a layer at a time, which is very slow. This one starts out with all the resin at its final position, so only the light moves.
    - deleted 5y ago
      [deleted]
- blenderdt 5y ago
  Almost all 3D printer print 2D layers on top of eachother. Maybe Carbon is the only exception because the continuously morph the layers in the Z-direction. The end result is a 3D model, but it is printed in 2D. This method is more 3D because you can print at any point in space.
  - typhonic 5y ago
    To break it down further, the 2D layers are laid down as a bunch of 1D structures when using the popular filament extruders.
rkagerer 5y ago
This is more like how I first assumed 3D printing worked, before I knew better. (Then again, when I was young I assumed all four wheels on a car were powered). Anyone know more about how those nano capsules work to prevent curing before the focal point? In 3D printing, resin hardens in a flat and straight line along the path of the light. Here, the researchers use nano capsules to add chemicals so that it only reacts to a certain kind of light—a blue light at the focal point of the laser that's created by the upconversion process.
- ryanmcbride 5y ago
  Unless I'm misreading it looks like the light isn't the correct wavelength, or possibly concentration, to cure the resin except for at the focal point. I'm not sure exactly how they're doing it but picture the adjustable lens of a flashlight, that lets you move the focal point (the point at which the beam crosses over itself). The resin would only cure where that crossover happens. I'm not sure if that's exactly what's going on but from the article that's what it seems to be.
- impossiblefork 5y ago
  Photon upconversion is highly nonlinear, with basically no upconversion at low intensity, because if it weren't, then you don't have energy balance (at least two red photons are needed to make a blue photon).
  - rkagerer 5y ago
    Does the light actually react with the resin near the focal point to trigger the shift to blue?
    - impossiblefork 5y ago
      No, definitely not. It's some kind of nonlinear optical effect happening in a medium which ends up as it was from the start. Two photons somehow excite the medium together, and a higher energy photon comes out, but the medium is not changed chemically. I found this referred to as 'upconverting fluorescence' on one website, but I don't actually know anything about nonlinear optics, so I don't know how it works.
blenderdt 5y ago
So this is voxel printing. But after reading the article I still don't get why the resin only cures at the focal point and not in the beam. To me it's also unclear what the red laser has to do with it.
- wrthfl 5y ago
  As I understand the red laser hits the beam and then creates the focalpoint/ blue dot.
  - blenderdt 5y ago
    Ah yes. Zbrozek posted a better link in this thread. Two lasers cross and at that point the nanoparticles in the resin help to focus the light and cure the resin at that point.
    - ncmncm 5y ago
      No. They have a single laser source that converges at the point. It doesn't seem to say whether they move the laser source in 3D near the tank, or just in 2D and vary its focal distance.
ncmncm 5y ago
The article doesn't really make any sense. They seem to be talking about a sort of non-linear absorption of the laser light, so that above some critical intensity that is found only close enough to the focal point of a converging laser beam, something suspended in the resin is triggered to absorb the red and ?? emit blue light, the which causes a chemical reaction in the surrounding resin at just that point, curing it. Looking at the paper, they talk about red light producing excitons in one material that become triplets of "annihilator excitons" in another bit attached to it, and, with enough intensity, a pair of such triplets that will "fuse" to make a single "hot" exciton, which decays emitting a blue photon. Presumably at lower intensity you get only one triplet at a time which hasn't enough energy to emit the critical blue photon. The suspended particles must be much smaller than the 637 nm red wavelength. You would still need to build up the object from the inside out, or conventionally bottom up, unless the cured bits pass light exactly the same as the uncured resin. They also seem to suggest that if the resin is especially gelatinous, a cured bit does not move while other bits are being cured, so you don't need the sacrificial support structures. Presumably, since nothing in the system moves except the light source, you should be able to make this work faster than one that has to add layers of resin. The bit that catches the red photons seems to be a porphyrin cage around a palladium ion. So you trap some amount of palladium in each article produced. Getting suspended particles to hold together (in a silica shell) but disperse without clumping was its own challenge.
- q845712 5y ago
  it's possible that you're missing the trick of "two photon excitation" which the paper sort of breezes past, but is the solution for "i only want the effect to happen right where i've created a tiny focal sphere of this laser." see e.g. https://en.wikipedia.org/wiki/Two-photon_excitation_microscopy https://en.wikipedia.org/wiki/Two-photon_excitation_microsco... The triplets described in this paper seem to build on the "standard" 2P effect.
  - ncmncm 5y ago
    The "two photon excitation" they talk about seems to refer to a different, altogether slower process that requires many orders of magnitude higher intensity light, and has to go very, very slowly so as not to vaporize the resin by putting energy in too fast for it to diffuse away.
daemonk 5y ago
I guess the viscosity of the resin prevents structures of certain size from sinking? I assume you would still need to try to print it in a way where "heavier" structures are done first on the bottom and work your way up?
- petermcneeley 5y ago
  What is the density of the hardened resin vs the stock?
  - ncmncm 5y ago
    It had better be exactly identical to the unhardened, or stuff will warp according to how much nearby is hardened.
- ncmncm 5y ago
  Unless the fused bits transmit light exactly the same as the unfused bits, you would need to build up from the bottom, or anyway starting farther away from the light source, regardless.
tomlin 5y ago
I believe this has already been done, and you can actually make out origins in 3D engraving (example: https://res.cloudinary.com/forallpromos/image/fetch/f_auto/https://www.forallgifts.com/sites/default/files/imagecache/585x585/images/products/736457/wedding-tower_1_2_3_1.jpg https://res.cloudinary.com/forallpromos/image/fetch/f_auto/h...)
zwieback 5y ago
Cool, but what's the advantage of this process? All the downsides of SLS plus more complex optics and chemistry so there must be some reason they are working on this.

35 points by samizdis 5y ago

arxiv link https://arxiv.org/abs/2109.02780 https://arxiv.org/abs/2109.02780

They show pictures of Benchy here: https://www.nature.com/articles/s41586-022-04485-8/figures/4 https://www.nature.com/articles/s41586-022-04485-8/figures/4 No visible layering, though I've just looked at the picture and not read to check if they post process. Ironically it seems to have trouble making holes in the print.

Ancapistani 5y ago

This seems like a variant on something that I've been interested in for quite some time, but haven't had the time/motivation/focus to really play with it. I call it "non-parallel slicing" in my head, but I think there is another term for it. I use almost exclusively FDM printers. Slicers take a 3D model and "slice" it into a series of horizontal profiles that are laid down one-by-one on top of another to create the 3D output. This results in the print head moving in the X and Y axes pretty much constantly, but the Z axis moving only once per layer, and moving only in one direction (+Z). There's no physical reason the Z axis couldn't be more mobile. Yes, you'd have to be careful to ensure that the print head doesn't impact the print in areas where material has already been placed, but that can be represented by a virtual model of the print head in software - or even by a handful of standard measurements: * nozzle inner diameter: 0.4mm * nozzle outer diameter: 0.7mm * nozzle angle of approach: 30º * Z-offset between nozzle and lowest part of the hot end: 5mm The above would mean that instead of layers being all parallel to one another and to the bed, layer height could change dynamically throughout the print process. If you're printing a wing section flat on the bed, the center will bulge - so the first layer height at the leading edge of the wing would be as small as possible (say, 0.05mm). At the thickest point the layer height could be larger (say, 0.3mm). The next layer would then be laid on top of the layer below, compounding the differences in layer height. With traditional, parallel slicing, to get that resolution you'd have to set your layer height to 0.05mm throughout the print. The top surface of the wing would be a series of "stairsteps" much like the "jaggies" seen when upscaling a raster image. With a well-designed non-parallel slicer and an appropriate model, the top surface would be a single layer, laid down in a complex three dimensional curve. The nozzle's "angle of approach" and the "Z-offset between nozzle and hot end" would place fairly restrictive limits on how much any given layer could diverge from horizontal and from the prevous layer. That said, this approach would allow today's commodity printers to be used in this way. A more capable approach would be to design printer hardware to directly take advantage of non-parallel layers, by adding additional axes: A, B, and C, which would represent rotation around the X, Y, and Z axes respectively. This would allow full movement of the print head relative to the work piece (subject to the physical constraints of having the print bed supported on a plane, which the hot end may not impact). The best part of all of the above is that the language used to encode instructions for 3D printing - Gcode - is literally designed for this use case. Gcode was originally intended to control milling machines, and 5- and 6-axis CNC are fairly common (albeit expensive). I came across someone's university project a couple of years ago that implemented something similar to this concept, but never investigated it deeply and have since lost the link.

Ancapistani 5y ago
If you're familiar with work being done in support of the above, or even if you're just intrigued by it like I am... please feel free to reply or connect with me. Maybe you'll "light the fire" for me to spend some real time working on this :)
- pikewood 5y ago
  Non-planar slicing? https://all3dp.com/2/non-planar-3d-printing-simply-explained/ https://all3dp.com/2/non-planar-3d-printing-simply-explained...
rkagerer 5y ago
Formlabs SLA printers can do "adaptive layer height" where they adjust the layer thickness of the print as you go, using thin layers where there's more detail and thick, faster printing ones where there isn't. The build still only progresses in one direction, though.
- birdman3131 5y ago
  I recall cura doing this as well for fdm.
ncmncm 5y ago
Any additive 3D printer can do variable layer thickness. It just needs the software to adjust the amount of plastic fed to the print head, according to how thick the layer should be, and lower the bed less for thinner layers. Layers that vary in thickness are trickier. It seems like any additive printer should be able to do them given slightly smarter software and a pointy nozzle, but controlling temperature in a pointy nozzle at varying flow rate is not simple. The heating element is far away from the pointy end, and heat arrives at the tip both by conduction in the metal and also by physical motion of the melted filament medium. You need to vary the current to the heater so that the tip stays at the right temperature at all the different filament flow rates. Changes to the current have to happen well ahead so the right amount of heat actually reaches the tip, by the two routes, sometime later. You are also changing the feed rate of the filament, so it is carrying heat down at varying speed. The point is cooling by radiation and convection, the latter which varies by how fast the tip is moving, and the ambient temperature.

bawolff 5y ago

That's cool and all, but i don't see how you can justify this as being more "3d" than traditional 3d printing.

amelius 5y ago
Because you can print things like a table in its normal orientation.
- gweinberg 5y ago
  That's kind of a non-sequitur though. A 3D printed table is no less 3D if you had to print it upside down. And who even has a table they haven't flipped over at least once?
  - ncmncm 5y ago
    Not all shapes are flat on one side and have no hollows. Most shapes do not match that criterion. So, on most 3D printers, they have to add sacrificial support structures. Also, most 3D printers add material a layer at a time, which is very slow. This one starts out with all the resin at its final position, so only the light moves.
  - deleted 5y ago
    [deleted]
blenderdt 5y ago
Almost all 3D printer print 2D layers on top of eachother. Maybe Carbon is the only exception because the continuously morph the layers in the Z-direction. The end result is a 3D model, but it is printed in 2D. This method is more 3D because you can print at any point in space.
- typhonic 5y ago
  To break it down further, the 2D layers are laid down as a bunch of 1D structures when using the popular filament extruders.

rkagerer 5y ago

This is more like how I first assumed 3D printing worked, before I knew better. (Then again, when I was young I assumed all four wheels on a car were powered). Anyone know more about how those nano capsules work to prevent curing before the focal point? In 3D printing, resin hardens in a flat and straight line along the path of the light. Here, the researchers use nano capsules to add chemicals so that it only reacts to a certain kind of light—a blue light at the focal point of the laser that's created by the upconversion process.

ryanmcbride 5y ago
Unless I'm misreading it looks like the light isn't the correct wavelength, or possibly concentration, to cure the resin except for at the focal point. I'm not sure exactly how they're doing it but picture the adjustable lens of a flashlight, that lets you move the focal point (the point at which the beam crosses over itself). The resin would only cure where that crossover happens. I'm not sure if that's exactly what's going on but from the article that's what it seems to be.
impossiblefork 5y ago
Photon upconversion is highly nonlinear, with basically no upconversion at low intensity, because if it weren't, then you don't have energy balance (at least two red photons are needed to make a blue photon).
- rkagerer 5y ago
  Does the light actually react with the resin near the focal point to trigger the shift to blue?
  - impossiblefork 5y ago
    No, definitely not. It's some kind of nonlinear optical effect happening in a medium which ends up as it was from the start. Two photons somehow excite the medium together, and a higher energy photon comes out, but the medium is not changed chemically. I found this referred to as 'upconverting fluorescence' on one website, but I don't actually know anything about nonlinear optics, so I don't know how it works.

blenderdt 5y ago

So this is voxel printing. But after reading the article I still don't get why the resin only cures at the focal point and not in the beam. To me it's also unclear what the red laser has to do with it.

wrthfl 5y ago
As I understand the red laser hits the beam and then creates the focalpoint/ blue dot.
- blenderdt 5y ago
  Ah yes. Zbrozek posted a better link in this thread. Two lasers cross and at that point the nanoparticles in the resin help to focus the light and cure the resin at that point.
  - ncmncm 5y ago
    No. They have a single laser source that converges at the point. It doesn't seem to say whether they move the laser source in 3D near the tank, or just in 2D and vary its focal distance.

ncmncm 5y ago

The article doesn't really make any sense. They seem to be talking about a sort of non-linear absorption of the laser light, so that above some critical intensity that is found only close enough to the focal point of a converging laser beam, something suspended in the resin is triggered to absorb the red and ?? emit blue light, the which causes a chemical reaction in the surrounding resin at just that point, curing it. Looking at the paper, they talk about red light producing excitons in one material that become triplets of "annihilator excitons" in another bit attached to it, and, with enough intensity, a pair of such triplets that will "fuse" to make a single "hot" exciton, which decays emitting a blue photon. Presumably at lower intensity you get only one triplet at a time which hasn't enough energy to emit the critical blue photon. The suspended particles must be much smaller than the 637 nm red wavelength. You would still need to build up the object from the inside out, or conventionally bottom up, unless the cured bits pass light exactly the same as the uncured resin. They also seem to suggest that if the resin is especially gelatinous, a cured bit does not move while other bits are being cured, so you don't need the sacrificial support structures. Presumably, since nothing in the system moves except the light source, you should be able to make this work faster than one that has to add layers of resin. The bit that catches the red photons seems to be a porphyrin cage around a palladium ion. So you trap some amount of palladium in each article produced. Getting suspended particles to hold together (in a silica shell) but disperse without clumping was its own challenge.

q845712 5y ago
it's possible that you're missing the trick of "two photon excitation" which the paper sort of breezes past, but is the solution for "i only want the effect to happen right where i've created a tiny focal sphere of this laser." see e.g. https://en.wikipedia.org/wiki/Two-photon_excitation_microscopy https://en.wikipedia.org/wiki/Two-photon_excitation_microsco... The triplets described in this paper seem to build on the "standard" 2P effect.
- ncmncm 5y ago
  The "two photon excitation" they talk about seems to refer to a different, altogether slower process that requires many orders of magnitude higher intensity light, and has to go very, very slowly so as not to vaporize the resin by putting energy in too fast for it to diffuse away.

daemonk 5y ago

I guess the viscosity of the resin prevents structures of certain size from sinking? I assume you would still need to try to print it in a way where "heavier" structures are done first on the bottom and work your way up?

petermcneeley 5y ago
What is the density of the hardened resin vs the stock?
- ncmncm 5y ago
  It had better be exactly identical to the unhardened, or stuff will warp according to how much nearby is hardened.
ncmncm 5y ago
Unless the fused bits transmit light exactly the same as the unfused bits, you would need to build up from the bottom, or anyway starting farther away from the light source, regardless.

tomlin 5y ago

I believe this has already been done, and you can actually make out origins in 3D engraving (example: https://res.cloudinary.com/forallpromos/image/fetch/f_auto/https://www.forallgifts.com/sites/default/files/imagecache/585x585/images/products/736457/wedding-tower_1_2_3_1.jpg https://res.cloudinary.com/forallpromos/image/fetch/f_auto/h...)

zwieback 5y ago

Cool, but what's the advantage of this process? All the downsides of SLS plus more complex optics and chemistry so there must be some reason they are working on this.