h a l f b a k e r yIdea vs. Ego
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3D printers are receiving a lot of attention in the news these days, because they are seen to be a potential disruptive technology. However, most devices of this type are very limited in the materials they can work with, mainly fabricating models in plastics like PLA or ABS. Advanced high-end models
which do work with metal (eg. Selective Laser Sintering or Electron Beam Melting) require a build chamber to either be under vacuum or else filled with an inert gas, in order to prevent oxidation of the metal being used to form the part/model.
Could laser-accelerated electroplating or electroforming be used as the basis for a 3D printing aproach which additively fabricates macroscopic parts or models from metal? I emphasize macroscopic, because the method already seems to have been investigated for fabricating metal microstructures - but I'd like to know why it couldn't be used in conjunction with stereolithography to make larger metal structures on the order of many centimeters in length width and height?
Consider for a moment the much-heralded FormLabs Form1 3D stereolithography printer, which can manufacture plastic models using a UV-laser to solidify a UV-curable liquid polymer. A thin layer of liquid polymer is hit from below by the lasers, causing it to solidify wherever hit, and the resulting shape is slowly pulled out of that liquid layer from above.
It seems to me that a similar approach could be taken by using the method of laser-enhanced electroplating, and substituting the UV-curable liquid polymer for a solution of metal ions. By controlling where the lasers hit, an electroformed metal shape could be created and slowly pulled from the liquid layer from above.
Now take a look at something I looked up in a book called Modern Electroplating:
"The development of laser-enhanced electroplating process offers a promising technique for high-speed and mask-less selective plating and/or as a repair and engineering design change scheme for microcircuits [300, 325-28]. For this, temperature is used to modify the position of the equilibrium potential in a localized region so that electro-deposition is driven by the potential difference between this region and the non-irradiated regions. Use of a focused argon laser beam (488nm) in an acid copper solution provided plating rates as high as 25µm/s [300]. Bindra et al [327, 328] discussed the mechanism of laser-enhanced acid copper plating and Paatsch et al [329] reported on laser-induced deposition of copper on p-type silicon. It was demonstrated that the increase in the plating rate under laser illumination results principally from photo-induced heating of the electrode surface [328]."
I think a 3D printer based on electroplating/electroforming would be cheaper than existing metal 3D printers using SLS or EBM, because it doesn't require your build chamber to be under vacuum, or filled with an inert gas. And a theoretical build speed of 25µm/s is nothing to sneeze at - that's 1mm every 40 seconds, or 1cm every 400 seconds. Theoretically, you could print a 30cm tall model made of metal in 200 minutes - put all those old pennies to good use. Even if your real-world speed was only half that, it would still be quite competitive with existing 3D printing systems.
It seems to me that a 3D electroplating approach could bring 3D printing of metal parts into the home consumer market. After all, there are plenty of consumer-level home-electroplating kits sold to for people who plate their own jewelry, etc. So electroplating is not some exotic technology, and electroforming is just electroplating taken to greater heights/thicknesses.
FormLabs Form1
http://www.youtube....watch?v=PZrMRYWFORY
FormLabs Form1 Stereolithography Printer [sanman, Mar 02 2013]
Laser-Enhanced Electroplating
http://books.google...ctroforming&f=false
Laser-Enhanced Electroplating [sanman, Mar 02 2013]
3D microfabrication
http://www.google.com/patents/US5641391
[piluso, Mar 02 2013]
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Any device that inspires thought on 3D metal printing has my vote [+] |
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The laser in the device may not be legal for the average peasant, but if it were available for rent at a DIY machine shop (Google TechShop) it would be tops. |
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"The 448nm wavelength laser cited in the book I quoted from has less energy than a laser-diode in a blu-ray DVD burner which is 405nm wavelength." |
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The 448nm wavelength laser cited in the book I quoted from has less energy than a laser-diode in a blu-ray DVD burner which is 405nm wavelength. I think a suitably high-power laser can be found for acceleration of electroplating. Don't forget that electric current can also be used to determine the electroplating speed. Another factor would be the geometry of your sacrificial metal anode that's used to supply the metal ions into the aqueous solution, and its separation distance from the part/model being formed. |
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Remember that one of the weaknesses of 3D printers, including those for metal, is the bond strength between the build layers. But with electroplating/electroforming, the resultant ionic bonding is particularly strong, so you won't have to worry about the layers not being strongly bonded to each other. This and the high precision should make for good quality structural parts - perhaps even aerospace grade. |
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What do you find bad about my science? Again, regular electroplating may be slow, but laser-enhanced electroplating/electroforming with a strong electric current level could be quite rapid. The laser enhancement works through the Soret Effect, whereby heavy particles in a liquid solution will move towards a heat gradient (in this case, a hotspot produced by a laser) |
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I don't particularly see anything wrong with the fundamental science (other than the need to PREVENT electroplating where the laser is not shining), but I am aware that a number of significant metals, like iron and aluminum, can't be electroplated "cleanly" from a water solution. The IONS are OK, but the METAL reacts with the water and oxidizes. |
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It could therefore be worth looking into other liquids that support ion transport, perhaps ammonia. But note that this may require sealing and refrigerating the 3D printing chamber (ammonia is toxic and has a low boiling point) --it depends on the liquid chosen, of course. |
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I'm not sure that requiring a chemical bath is any
more practical than a vacuum/inert atmosphere,
in fact I would suggest it's somewhat less so, since
electroplating chemicals require special handling,
a nitrogen atmosphere can be dumped. |
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More importantly, however, electroplating is a
reactive process between the plating metal and
the substrate. Once your plating gets a certain
thickness away from that substrate, you aren't
going to get any more build-up, which limits your
part sizes rather drastically. |
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//electroplating is a reactive process between the
plating metal and the substrate. Once your plating
gets a certain thickness away from that substrate,
you aren't going to get any more build-up// |
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That's not true. You can plate gold onto gold,
chrome onto chrome... and you can continue
indefinitely. Plating is not a reaction between
the plating metal and the substrate - it is the
donation of electrons to the metal cations to
reduce them to metal. |
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I meant electrical, not chemical, reaction, but it's
possible I'm confusing my coatings. My
understanding was that you needed the substrate to
act as a cathode in order for electroplating to work,
and that it wasn't possible without a differential
substrate.
I know most applications do work that way. |
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No, you're thinking of chemical deposition, I
think. |
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For electrodeposition, the starting material
(which, if you wanted, could be the same as the
plated metal) acts as the cathode. But the
deposited metal then also acts as the cathode for
further deposition. The deposition doesn't
depend on a chemical reaction per se between
the cathode and the plated metal, but only on
the ability of the metal to pass electrons on to
the plating metal cations. |
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Were this not the case, (and if electroplating
depended on a special reaction between plating
metal and substrate) no plating would be more
than a few atomic layers thick. Yet many platings
are
tens of microns thick and can, in theory, be
indefinitely thick. |
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Laser-enhanced electroplating has been shown able to print electrical circuit patterns without any masking required. This is proof that such electroplating can be done in a selective manner guided by the laser, without indiscriminate coating buildup. It's simply a matter of repeating this process to scale in the Z-dimension. |
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I think a liquid bath is superior to inert gas or vacuum not just because of the simplicity, but also because a liquid medium permits ion transport, which is better for bonding purposes than mere melting and curing. Furthermore, both the laser intensity and the electric current level can be dynamically adjusted to obtain the best possible characteristics at each point during part formation. |
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Electroformed parts tend to be structurally strong, since the process expressly ensures strong bonding between the layers. Inter-layer bonding is a particular problem for additively manufactured parts, which could be addressed by this process. The ability to create structurally strong parts to high precision tolerances could help 3D printing to gain much stronger appeal and to really take off. |
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I almost started a new idea from this. The before-posting-googling showed me that some smart guys already patented it :-) [link] |
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What patent? Who's got it? |
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Regarding build restrictions, I'd suggest looking at the videoclip link I posted for the FormLabs Form1 printer. It doesn't have any build restrictions other than build volume. It actually prints in extra supports to keep the model supported and attached to the build platform. You just pull off those supports after printing is done, and then you've just got the model. I don't think the build platform has to move in anything other than Z-axis, because the laser can scan in X and Y. |
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I'm thinking that it might be possible to even have a metal powder as an anode, because that would give the most surface area from which metal ions could be leached to put into aqueous solution. The build speed is directly affected by the rate at which metal ions are replaced back into solution by the anode. Or imagine something like steel wool, or a bunch of metal filings. That kind of stuff would have a lot of surface area, and metal filings might even be cheapest, because they're a form of scrap. |
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In thinking about this a bit more, it seems to me that the way the laser beam becomes part of the system is related to the voltage applied between the electrodes. It takes a certain minimum voltage before any particular ion will begin to attach itself as a metal atom to an electrode. Well, what if the voltage was just a little less than the required amount? Then the energy of the laser photons can make up the difference (one of the properties of a photon is that it has an electric field). This would allow metal to be electroplated out ONLY where the laser shines, and nowhere else. |
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[MechE], one possibility that you might have been employing without thinking about it is the fact that, as ions are electroplated out of solution, there are fewer ions left in the solution, which means of course the plating action would eventually stop, unless more ions are somehow added to the solution. |
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Usually that is done by having one electrode of impure metal, and the other electrode acquires pure metal as the ions migrate through the solution between the electrodes. |
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Note that if we did that here (using purified metal as the source-of-ions, of course), then we would need TWO lasers, one for each electrode, to make sure that not only do ions electroplate out to form the desired part, but that at the other electrode, the metal is encouraged to go into the solution as ions. |
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So, as long as the source-material electrode is big enough, we should be able to construct just about any metal part with this process. |
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Also, one thing that I think someone missed in an earlier anno: Metal conducts electricity, so that even if the receiving electrode is pulled out of the solution with part of the metal part attached to it, the rest of the metal part is still in the solution, conducting electricity. All you need is appropriate gripping/supporting hardware to help lift the part, and again just about anything might be made by this method. |
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Vernon - yes, I too think that a system at or near some equilibrium tipping point could likewise be selectively manipulated by the laser to achieve the deposition. Anyway, that's already been proven by previous studies which can be Googled. I'd also recommend Googling for "Soret Effect" because that's the effect identified by Idaho National Laboratories as being responsible for the laser-enhanced electroplating effect. |
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As for the gripping/supporting part, you can again check that link I posted for the FormLabs Form1 printer, because it already operates that way. Actually, I'd already emailed my idea to them, because I think their printer could be adapted for this process through appropriate modifications. |
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For a x,y,z printer, the geometry restriction is vertical walls only - at best. More likely there will be a taper to the vertical walls. Reason being that the laser must have a surface to shine upon to create the heat to precipitate electroplating. So no undercuts whatsoever, for the 3 DOF version proposed. |
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Also, there is nothing to ensure that each layer will have a uniform thickness, unlike with laser sintering. |
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Also, the thermal conductivity of the part will blur the x,y spot size, much more than with quasi-2D printing on a low-thermal-conductivity substrate. |
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The use of laser stereolithography means that the spot size can be made small enough that even with blurring a high definition can still be achieved. |
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Thickness would be a function of solution concentration, laser power, and electric current level. |
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