Vacuum Chamber

Anybody heard of this? Could this help to improve the quality of the vacuum? If it's good enough for vacuum tubes, then why couldn't it be good enough for a RepRap?

[en.wikipedia.org]

[tubecrafter.com]

[tubecrafter.com]


Our main enemy is oxygen - am I correct? Do we care as much if there is an other harmless gas inside the build chamber?

Edited 2 time(s). Last edit at 02/10/2013 04:52PM by sanman.

... for electrons any gas is a 'blocker' ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Is this the better answer then?

[en.wikipedia.org]

[www.gammavacuum.com]

Edited 1 time(s). Last edit at 02/11/2013 09:24AM by sanman.

I was going over the schematics you guys put up on the wiki page for the build chamber, and I noticed something... there's no door. How do you get the parts out once printed? Forgive me if I misunderstood and you're not going with the design on the wiki page, but that struck me as pretty odd. Having to dismantle the chamber every time you print something seems pretty... dumb.

hi
Yeah we have moved on,

We hopefully have found a way of removing any need for TIG welding equipment, reducing costs and allowing mother printer to self print build platform piston/powder cylinder in sections by having an outer main chamber made of glass. So that any welding that is needed can fit within the mother machine.

This may be achieved by using a 6inch 4 way reducer as filament/ anode chamber connected to the small diameter electron gun beam tube, (surrounded by focusing and deflection coils acting through the non magnetic 304L tube ), which connects ( via O rings) to the aluminium top plate of the main chamber. This main chamber is based around a large diameter borosilicate thick glass cylinder (positioned vertically), with an aluminium plate top and bottom, ( glass cylinder main chamber is surrounded with a removable concrete pipe for shielding when running) , with L gaskets ( vacuum bell jars sealing method) to seal glass to top and bottom plates. The build platform, motors and hopper are all contained within this main glass chamber hanging off the top plate. For access the whole assembly will be lifted out of the glass tube vertically.

Thanks for your feedback
Kind regards
MetalicaRap team.

great, thanks for the response!

I was trying to sketch out your description, could you elaborate on how the build plate, piston and motor all "hang" from the top plate? As far as I can tell, for them to hang there would have to be bars placed vertically in the chamber for them to hang from. but wouldn't these bars get in the way of the build plate? If so, how do you plan to maintain a powder-tight seal between the build plate and the bars/glass wall?

Also, you didn't mention a powder spreading mechanism at all.. could you elaborate a bit more on that please? I'm really interested to know how you plan to spread powder over the build area using only the space inside the tube.

Thanks!

hi
Think of the large diameter glass outside the whole existing design, so that all the parts need not create a vacuum seal as the glass has already achieved this, this means that all the piston hoopper etc can be printed within the same diamter build chamber on the mother machine through splitting parts in to smaller parts and then assemble them. The bars they would hang off therefore fit outside the existing mechanism/piston piston wall. And so would the end of the hopper.
I hope that helps
kind regards
MetalicaRap team



ps.The other option is to suspend the large diameter glass cylinder 90cm above ground and open the chamber by lowering the bottom plate which has the build platform on top of it.

Edited 1 time(s). Last edit at 03/29/2013 07:49AM by rapatan.

Yes, thanks that's much clearer! Thanks

Also, how is the design of the power supply coming along? I was sourcing parts the other day and it seems like the power supply is by far the most expensive part.

The rest (motors, electronics, vacuum pump, etc.) can be bought fairly cheaply from places like ebay. and even the prefab steel is reasonable from somewhere like mfgquote.com.

That is not entirely correct. Arcam's 3D EBM printer has a partial helium build atmosphere of .001 torr and last I checked it worked rather well!

Edited 1 time(s). Last edit at 10/12/2013 05:10AM by ShayneBrown.

VDX Wrote:
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> ... for electrons any gas is a 'blocker' ...


What kind of blocker? Wireless blocker?

ShayneBrown Wrote:
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> VDX Wrote:
> --------------------------------------------------
> -----
> > ... for electrons any gas is a 'blocker' ...
>
>
> What kind of blocker? Wireless blocker?

For a electron beam to work there needs to be a vacuum. a vacuum is created by sucking out all the gas inside the chamber. If there is gas in the chamber the electrons aren't going to travel very far as they would have to push the gas molecules out of the way first. If it was air for instance it would arc through the air to the nearest metal object, e.g. the chamber and not behave like a beam

So creating a non-vacuum chamber big enough that the nearest metal/conductive object is the metal powder can also work?

Do you plan to use the double vacuum now - just like you stated: high vacuum at the electron beam source/gun and low vacuum in the main chamber?

I heard that a laser 3D printer needs vacuum too so it's good we chose the electron beam path. Couldn't we create a moving electron source, no or hardly vacuum, such that the gun is positioned as near as possible to the metal powder that we want to melt or the metal structure we want to mill away?

A laser sls printer does not need a vacuum but an inert atmosphere to sinter most metals. The inert gas prevent oxidisation which prevents proper bonding.

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Make your Mendel twice as accurate.
[www.thingiverse.com]

Quote
pyrotronics
For a electron beam to work there needs to be a vacuum. a vacuum is created by sucking out all the gas inside the chamber. If there is gas in the chamber the electrons aren't going to travel very far as they would have to push the gas molecules out of the way first. If it was air for instance it would arc through the air to the nearest metal object, e.g. the chamber and not behave like a beam

What if the electron beam did not have to travel very far? Could this allow for a reduction in the quality of the vacuum?

Does anyone have a graph of acceptable beam distance vs required vacuum quality?

Furthermore, what if you could ionize the gas in your chamber, and then use an electric field to repel it away from the electron beam's path?

For example, suppose your electron beam was operating in a pulsed fashion, and you could likewise operate your electric field in a synchronized short-sharp-pulsed manner to push gaseous ions out of the way just as the electron beam pulse came through. Would that be possible?


[link.springer.com]

Look at that link - is that something that can be made to work here?

Edited 2 time(s). Last edit at 07/13/2014 02:57PM by sanman.

Sorry but i Didn't really think that through.

For the chamber - have seen a bell jar (http://en.wikipedia.org/wiki/Bell_jar) used in the electron microscope at Uni. A bloke I see occasionally has a vacuum chamber for metallizing telescope mirrors. IIRC it can do up to 14" and he uses a bell jar with a Refrigeration Vaccum Pump and an oil diffusion pump.

If you don't need to see inside steel would do (cut off LPG/Propane cylinder?) and for 10^-4 something like this:
[www.ebay.com.au]
is claimed to get close/do the job depending on what they meant by the claim "3 x 10 -1 Pa, 25 Microns"

I have worked with high vacuum in the past, and I have to say that I think this concept is unfortunately a non-starter. To get a good electron beam, you need a very good vacuum indeed. Any residual gas will ionize and form a discharge between the electrodes of the electron gun.

Getting a good enough vacuum generally takes several hours of pumping using a diffusion pump. One of the main problems is outgassing. Gases from the air are absorbed by surfaces within the vacuum chamber, and when you evacuate the chamber, these gases gets slowly released. So you have to keep pumping until this outgassing reduces to a low enough value, and only then can you start up the electron beam.

In this case, the chamber will include a large amount of metallic power, and the total surface area of all the particles will be very high. Therefore, unless the powder is comprised of something that absorbs very little gas, outgassing from the powder will be a huge problem. Heating the powder may speed up outgassing, but I suspect it would still take many hours if not days to reduce to a low enough value.

Add to that the problems of building a power supply providing high voltage (I think 60kV was mentioned) at a significant current, and providing X-ray shielding. I think laser sintering would be a more practical way to go.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

hi

Their are electron beam 3D printers working to day at the same specifications as this printer, as well as electron beam welders (using tungsten cathode filaments at 10-4 torr ). Though the top end printers use a LaB6 cathode's that are longer lasting and brighter but is too costly as it requires better vacuum 10-7 Torr.

Standard practise for solving the out gassing chamber wall issue is through baking out the chamber. The out-gassing powder issue is solved by heating the powder in a special oven over night prior to use.

The Xray shielding is done with concrete pipe or brick lined apparatus bay or using leaded glass rather than plane glass for vacuum chamber wall, (all stainless steel vacuum chamber walls require no extra X ray shielding).

These above findings have been confirmed by electron gun specialists who spent their career designing electron guns at international physics facilities.


The a 60kV voltage 5KW power supply already exists commercially, but with microprocessor control, our FPGA control version does create software challenges but also provides some advantages.

The laser route is unlikely ever to create a practicable largely self printing printer when limited to a normal domestic kitchen mains power outlet, laser printing poor energy inefficiency will mean impracticable long build times ( in the order of months) for all but jewelry sized items , unfortunately this is precisely why it is often proposed by some ( other problematic issues discussed include; KW laser costs , barrier gas bubbles in printed metal, non steel materials printing efficiency (7 times lower see below), massive size of KW laser printers due to long KW laser focal lengths, and lasers inability to; create thin metal solar cells, refine titanium sponge or make titanium powder.

thanks for your ideas.


kind regards
Rapatan

ref
Wall plug to metal efficiency of laser eg; Yag in iron 10%, Yag in aluminium 2.1% , Yag in titanium 1.5% metal absorption of laser page 27
wall plug to laser efficiency

ref
Wall plug to metal efficiency of Electron beam is 70% (88% for power supply wall plug to electron beam and 80% for electron beam to metals)

Edited 4 time(s). Last edit at 04/11/2015 04:53PM by rapatan.

Thanks for your considered reply. As a software engineer, I don't see why you would need an FPGA solution for controlling the PSU when a software solution could be easier and more flexible , but I guess you may have folks on your team with more experience with FPGAs than with embedded software. I do hope you can get this project up and running, although I fear the high vacuum requirements will be the stumbling block that prevents a domestic 3D printer of this type becoming a reality.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Hi All,

I think this project is a really interesting one, and not completely hopeless to do under a budget. Here are my thoughts, for what they're worth. (And I apologize in advance if anything has already been said).

-Regarding pumping to <1E10-4 Torr:
You should be able to do this with a two-stage rotary vane pump (~2E-3 Torr) plus a diffusion pump -- each which are relatively inexpensive. Titanium sublimation pumps were also mentioned, and would work surprisingly well to get below that final bit of pressure. At the minimum pressure in question, molecular flow begins to take over. Flashing titanium onto the large internal surface area of the chamber would be a great way to get there.

-Vacuum Motors
Although sealed vacuum-rated motors are available, these can get expensive rather quickly. Not only do the motors cost more, you will also require many more electrical feedthrus, increasing cost quite a bit and making it difficult to work on. Probably the best/cheapest way for a Z axis would be to buy a bellows and translate by expanding/contracting the bellows. This way, the only vacuum-specific piece of equipment you need is the bellows, and everything is easily accessible from outside of the chamber.

-Focus/Deflection
Another method for focus/deflection is the use of electrodes rather than coils. The electrodes are superior in my opinion because they can be precisely machined, and are therefore much easier to align. They also have a much faster response time, so precise beam positioning can be achieved almost instantaneously (versus coils, which are primarily useful for raster patterns only). Also, the electrostatic method uses almost no power because there is almost no current draw.

I hope this is useful.

Thanks,
Paul

hi
please could the above be removed as this is inappropriet and missleading as max vac for the above chamber is 29 torr, for any beam you need at least 0.001 Torr and for a focused beam on tungsten cathode 0.0001 to 0.00001 , LaB6 cathode 0.0000001 to 0.00000001 Torr
kind regards
Rapatan

Edited 1 time(s). Last edit at 11/19/2015 10:12AM by rapatan.