Hacker News Reader

Hacker News

Comment by drabiega | Hacker News Reader

Full thread

drabiega

Unless I'm missing something, this is not exactly a new technology.

http://makezine.com/2014/07/26/droplit-the-low-cost-diy-resi...

http://www.instructables.com/id/DIY-high-resolution-3D-DLP-p...

http://www.3ders.org/articles/20120911-a-list-of-diy-high-re...

View on HN

You are. Using UV to cure photo-sensitive resin isn't the innovation, it's using the oxygen permeable membrane.

If you look at the Form 1 printer or the B9Creator, there's a mechanical step between every layer where it needs to actuate the platform in order to loosen the resin from the projection window, so it can build the next layer. In the Form 1, it peels the print off, and the B9Creator slides a window. (look for videos on youtube.)

In both instances, the amount of time spent actuating the mechanical part adds up, and results in a significant amount of time spent in the print actuating the plate. What the oxygen membrane allows us to do is to skip that step between every layer, and simply keep shining a continuous changing image slice of the object as we're pulling the object out of the resin.

Not only does this have the advantage of speeding up prints by orders of magnitude, in materials, the grain of the object influences the type of thing you can built. If you print a stress holding object with the grain orientated in the wrong direction, the part will fail very readily. This way, we have greater design freedom, without worrying about grain direction.

Thanks for clearing that up. I was going to ask how this differs from the form 1 which, at first glance, seemed like the same concept.

Is the oxygen permeability what keeps the printed object from adhering to the membrane?

The oxygen inhibits the curing, so it only begins to cure ~20um above the membrane, which means that it never sticks, since it never touches the window, and that can just continually pull it upwards.

Is this process really better than the one used in the Peachy printer? Peachy printer uses resin tank that is filled with salt water from the bottom (which raises the level continuously, resin floats on saltwater) and the UV curing is done from the top. One huge thing for the Peachy is that you can use any tank, and the size of the print isn't limited. Also, Peachy costs just $100.

Well here you only need a small tank relative to the finished print, also, you don't move the laser head, but only the parts of the item that has already been printed. Everything else stays still, meaning reduced vibration which seems to mean a really steady quality of print.

In Peachy, both the laser head and the print are fixed in place. So it doesn't have the usual moving parts at all (although it uses modulated laser mirrors instead of a projector for cost reasons).

>> What the oxygen membrane allows us to do is to skip that step between every layer, and simply keep shining a continuous changing image slice of the object as we're pulling the object out of the resin.

What keeps the oxygen at the bottom of the tank? Why doesn't it diffuse upward and prevent curing? Why doesn't it get sucked upward and prevent curing? Are there limitations on the geometry needed to prevent oxygen from moving up?

SLA is layered, each layer a knife sweeps over it and refills and smooths the uncured resin layer. This is submerged, so drawing the parts upwards pulls in more fluid automatically so everything can be run continuously. What I don't get is that, hydraulically most of the liquid pulled in is going to come from the oxygenated layer. But I'm guessing that reacts with the resin and neutralizes quickly when it is too far from the diffusion membrane that provides the source of new oxygen.

They're doing the "growing" on a membrane at the bottom of the tank, instead of layer by layer at the top of the tank.

That should let them print really quickly and precisely, even compared to the SLA printers you link.

The reason it hasn't been possible in the past is that the polymerization process requires oxygen, which has only previously been available from the air over the liquid resin. Their system has some "secret sauce" for getting it to the bottom of the vat.

You've got it backwards about the role of oxygen--it is being used to inhibit polymerization in this case. They are allowing oxygen to dissolve into a thin layer at the bottom of the vat so that the build doesn't stick to the membrane, and they can have a continuous draw.

The true build layer is actually within the liquid, near the bottom, but not on it.

You're totally right. Oxygen inhibits the polymerization process. Interestingly, oxygen inhibition is also what allows things to be printed in layers (or, in this case continuously) as it allows the newly cured material to bond to the partially-cured inhibited material below it.

In one of the images on their site they're claiming it's different from SLA and much faster.

do those also feature the oxygen aspect? I assume that increases their precision.

Reply on news.ycombinator.com