by makeme

Time and Resolution

In Uncategorized on 22, Nov, 2011 at 19:36

I was discussing ways of making better prints with a guy in my office. What follows is the result of that discussion.

A big problem for 3D printing is that you have to trade resolution and time. If you want a cleaner and more accurate part you have to wait longer for it. This is because the printers can’t cover a large area at once. Whatever method is used for the smallest areas has to be used for the largest ones. Maybe you can change tools, but that’s got issues.

Wouldn’t it be nice to be able to form an entire layer at once? Yes. Yes it would. Here is a theoretical method for doing that.

Start with a build surface. Fill that build surface with a grid of tiny holes and in between those holes put tiny electromagnets. Next, flip that surface upside down so that the electromagnets are on the bottom. Now when you inject ferrofluid through the holes you can move it around on the underside of the build surface with the electromagnets. By turning the electromagnets on in a controlled order you can arrange the ferrofluid so that it outlines the exact shape of your first layer.

magnetic fluid 3d printing

Now put that into a tank so that the bottom of the ferrofluid, which is hanging off of the build surface, is just touching the bottom of the tank.

magnetic fluid 3d printing 2

Inject the printing substance through the build surface into the cavities formed by the ferrofluid. Even if the substance is liquid, it will be constrained by the floor of the tank and the ferrofluid.

magnetic fluid 3d printing 3

Harden the printing substance in some way. Heat, UV light, catalyst…kind words. Whatever works. Then raise the build surface by one layer height. Fill the tank with enough of a support substance to just reach the depth of one layer height. This support substance needs to be denser than the printing substance.

magnetic fluid 3d printing 4

Inject more printing substance through the build surface surface to fill the cavity formed by the ferrofluid and the previously hardened printing substance. Any overhangs will rest on the support substance.

magnetic fluid 3d printing 5

Repeat this procedure for each layer, rearranging the ferrofluid when necessary.

magnetic fluid 3d printing 6

This process, or something similar, could open up a paradigm in which you don’t have to trade time and resolution. Each area of detail can be resolved at the same time by just controlling all the relevant electromagnets, then the open space can simply be filled with whatever it is you’re using to print. It doesn’t seem like the control electronics would be all that complicated, either. Basically you’re just drawing on an LCD readout. The complicated part of this idea is the various substances. It’s more of a chemistry problem than an electrical problem.

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  1. Printing a full layer at once could speed things up, assuming that the layers set and are ready to be printed-upon faster than it would take to plot the layer with an FDM machine. This is how LCD/DLP projector resin printers, inkjet-binding powder printers, and probably some others I can’t think of at the moment work, though with the exception of an LCD, these are limited to printing in progressive scan lines rather than being truly simultaneous. There’s a reason 2D printers work this way instead of using plotters, and I’d like to see a reprap designed using this type of technology. I even played with the idea once of using a laser printer build objects out of successive layers to toner (which would probably be more impractical in terms of material costs than resin printers, but would have amazing resolution).

    Your idea, if I understand it correctly, would require hugely intricate custom-machined parts to even begin to approach the resolution of current repraps that can be built with hand tools and off-the-shelf parts, and could not increase its quality without custom-machining even more intricate versions of the same parts. It’s an interesting idea, but I’m not sure I see the upside.

  2. Yeah…it’s not a great idea, but it is theoretically possible. The concept evolved when we put the goal of not having to trade off time for resolution front and center, rather than putting just time or just resolution first.

    It’s not intended as a call for anyone to prototype the thing, but more as a thought experiment. For example, maybe the same sort of idea could be applied to SLA. If you got a UV transparent LCD and a big UV light you could expose the entire photopolymer layer at once.

    I like your idea of progressive scan lines. I even worked out an idea for stacking extruders next to each other to accomplish it. However, the math just didn’t work. Because the current approach involves jamming plastic into the nozzle, you have to ensure there’s enough surface area to get the plastic melting in time to come out of the nozzle. That means, if you want a lot of extruders, you need a lot of plastic surface area (either tons of rolls or a giant roll of a flat sheet). While the multi-extruder head could be small enough for a desktop, the sheer volume of plastic necessary to feed it would take up the space of a mini-fridge or worse. That’s not even getting into the issue of building the head strong enough to resist that much internal pressure.

    Basically, to answer the “it couldn’t be built at home” question…I think a whole lot of good ideas are going to HAVE to be commercially produced. The best toys just can’t be built in a garage.

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