Vacuum based automatic depowdering

Powder and inkjet printing
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ezrec
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Vacuum based automatic depowdering

Post by ezrec »

So, here's an idea:

Assume the part build area is 100mm x 100mm x 100mm.

Assume the piston range in Z is 150mm.

Assume a hole, suitable for a shop vacuum (with filter bag for powder) hose is at Z=0mm-20mm

At Z=50mm, there is a 5mm ledge on the inside of the part chamber, and a freely movable mesh plate of 99mm x 99mm sits on top. The mesh plate has 2mm - 5mm holes, and a 7mm border.

The piston itself is 89mm x 89mm, just clearing the ledge at Z=50mm, then, on the rising phase, pushes the mesh plate to the top of the part bin.

As the part is built, Z decreases, and the piston, mesh plate, and part volume drop.

When the build is completed, the piston descends to Z=50mm, and the vacuum is enabled.

The piston then descends to Z=25mm, and the powder is sucked out of the build chamber, while the mesh plate holds the part at Z=50mm.

In theory, this should allow rapid (and recoverable) depowdering of most objects.

Thoughts? Concerns?
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dragonator
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Re: Vacuum based automatic depowdering

Post by dragonator »

The basics I have had in my mind as well, but I like how detailed you thought of it here. The ledge thing is something I like in particular. It fixes quite a few problems I had with my design.

In a way, this is how Z-corp printers unload themselves. They claim they can get rid of 70% of the powder this way. Lets start of with the notion that this idea will most likely work.

a few concerns that wouldn't be disastrous or should be fixable.

I dislike additional Z-movement because it takes up a lot of space. If you design tabletop printer (which I prefer to do) you want to make a printer as low as possible. With a conventional system, you'd need 2mm of printer height for every 1mm of build area height, plus an additional 50-100mm for mechanisms. This adds up quickly. I do think whoever that it can be done in less (maybe even way less) than 50mm, so this does not have to be a deal breaker if the depowdering properly works. Also if the printer is standing on the floor, the Z-argument is no longer relevant.

The vacuum cleaner part is simple in theory, but harder in practice, because you want to recover the powder. You'll need a way to capture the powder, but also not introduce contaminants (such as dust). Fine filters in the vacuum are needed to capture the dust, because gypsum is ridiculously fine. Cyclone filters are hard to use here because the gypsum is too fine. Having said that, Z-corp does it this way, and so it should be possible with the right equipment.

The vacuum should not be too high, or it will damage the part by forcing it against the mesh, but this should be easy to overcome.

The only issue I would have is if you want to have a 3DP printer to test a lot of materials. All these channels, hoses, corners and meshes are hard to clean, and if you want to change powders, you'd need to do a cleaning of the entire system and the filter bag of the vacuum. This system would not be very practical on a prototype printer designed for powder testing, but for a usable click and print printer, this system would make it a lot easier.

As long as the powder is properly recovered, this is not a bad idea at all. All you need is to have decent filters and it should be possible.
ezrec
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Re: Vacuum based automatic depowdering

Post by ezrec »

Agreed on all your points.

As I am focusing on granular sugar, the filter issue isn't a problem for recovery.

I'm willing to continue to sacrifice resolution for the advantages of quick prototyping (thick layers).

There are many ways to make the 50mm smaller - a FFM built plastic air guide could adapt a standard shop vac hose port to a 4-channel 5mm high "vacuum insert" that would go into the bottom of the powder box, providing both the ledge and the vacuum inlets beneath it.

The design of that is a bit beyond my immediate skills, but so long as the cross sectional area of the vacuum inlets of the insert match the area of the shop vac port, there should be no loss of suction.

Stuff to think about later for my design (I have no FFM printer - yet), but I'll pick it up again when I start working on my next printer design.
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dragonator
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Re: Vacuum based automatic depowdering

Post by dragonator »

Depending on the powder, efficient recovery is necessary. Zcorp powder (the original) costs around $100/kg. It is ridiculously expensive. Granted that if you make it yourself, it could be cheaper, decent filtering is still a preferred thing.

I think that you can make the 5cm gap as little as 1cm without too much problems. Adding vibration motors might also help, since it loosens the powder. Air guides would indeed be a good way of reducing the gap.

Software and electronics are necessary evil for me. Design is kind of my area (it being my job and such). If you have a mighty need of a design, hit me up and I will draw it for you.
ezrec
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Re: Vacuum based automatic depowdering

Post by ezrec »

Sugar is highly hydroscopic, and tends to clump, which is why I'm leaning towards the 4-5cm range.

Regardless, than you for your offer of design assistance - I'll let you know if I need it for the vacuum insert.
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