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RepRap machine for UV-curable resins

Posted by spota 
RepRap machine for UV-curable resins
February 11, 2008 05:29AM
I have lately devised a couple of resins that cure very well with UV light (see builders blog: [builders.reprap.org] on Monday, February 11, 2008)
The price of a kg of this resin would be around 10 to 13
VDX
Re: RepRap machine for UV-curable resins
February 11, 2008 05:42AM
Hi Fernando,

... it seems i have all the needed parts without not the resins winking smiley

With my old CNC-system i already have a very good cartesian robot, capable of highspeed-moving with 12,5 microns accuracy in the area of 500x500x100 mm.

For the UV-sources i found an Eprom-eraser with a second lamp and from my PCB-etching-era i have a big doublesided UV-curer with 10 bigger UV-tubes, so i'm able to cure smaller areas with the Eprom-eraser or until DIN-A3 with the big device.

For my other tasks with paste-dispensing i'm on developing and milling the parts needed for a steppermotor-driven dispenser, so this should work in the next months too.

For diode-lasers: - maybe you can find capable UV-diode-lasers in the BluRay-drives in actual consoles?

Some of them should already be worn out, so maybe you can grab some cheap at ebay or somewhere else?

Viktor
Re: RepRap machine for UV-curable resins
February 11, 2008 06:04AM
Ok, Viktor. I'll PM you for your address.
Maybe we can figure out how to get you some samples. Your equipment would be areal boost for the advancement of this device!
Re: RepRap machine for UV-curable resins
February 12, 2008 06:00AM
aka47 Wrote:
-------------------------------------------------------
> Clever stuff
>
> I had originally suggested LED's because I was envisaging a ring of leds around the deposition type nozzel/needle.
> The tool head can then Deposit, Deposit & Cure or Cure only and can be selective about which areas get cured and for how long.
>
> Whilst a syringe is an option, providing the tubing needles etc were screened to prevent UV penetration a feed line could be used instead giving much more volume without pausing to refill.
>
> Reading your thoughts etc though, I think a closed box (polished aluminum maybe so it reflects) with lamps over head but angled might give best results.
>
> The deposition tool head will cast shadows but if it is pretty much always on the move or is withdrawn periodically this might work.
>
> Other thoughts ideas are perhaps making a hollow object with the usual FDM technology then filling and UV curing with the resin mix on a dual head system.
>
> Thoughts for what they are worth...
>
> aka47

Edited 2 time(s). Last edit at 02/12/2008 06:04AM by Fernando.
Re: RepRap machine for UV-curable resins
February 20, 2008 08:21AM
This might be my most stupid question ever.

Is it possible to pour a layer of this liquid into a bassin and then use a UV-source to harden only the parts that are to be solid, leaving everything else liquid?

Then add another layer and put the UV-lamp on the places where you want solid.

After doing this with the whole object, just pour the remaining (unexposed) liquid away?

If I'm not already sent to the corner of the classroom, maybe the UV-source needn't go around on a CNC-rig at all, how about using a set of mirrors to reflect the beam and draw in the liquid, pretty much like when making laser patterns on a wall?
VDX
Re: RepRap machine for UV-curable resins
February 20, 2008 08:30AM
Hi mimarob,

... this is exactly the 3D-printing strategy of common stereolitho-machines.

As UV-source they use an UV-laser for a spot-size of around 100 microns.

With this layer-stepping the printed object dives in the epoxy-bath and only the topmost slice is processed.

When ready, you pull the object out of the bath - when printing hollow honeycomb-structures in the inner volumes and a thicker wall on the outside, the fabbing is much faster and you can harden the fluid epoxy between the honeycomb-walls in an UV-oven, or you have holes at the bottom, so the fluid epoxy went out and you receive very leightweight objects or perfect positive-forms for cast-molding or so.

Viktor
Re: RepRap machine for UV-curable resins
February 20, 2008 01:20PM
I think Viktor has answered there quite exhaustively.
I would add that I have no idea what an optical robot with precision mirror parts means as a development challenge, and if it's manageable, what the price tag would be.
I would rather carry an optical fiber with a lens at the end on a cartesian robot arm, which would make things easier to implement.
Also, I wager the UV laser needed for these resins I make are non-trivial ones. They need high output at 256 and 365nm wavelengths, exactly. I know cheap lamps for doing this, maybe some LEDs, but lasers.... I invite anybody who is more laser savvy than me to answer this questions, which I think is crucial: what would be the final price tag and complexity for an UV-laser operated stereolithography machine.
VDX
Re: RepRap machine for UV-curable resins
February 20, 2008 01:50PM
Hi Fernando,

... i recently found the specs of the bluray-laser - it has 405nm wavelength ...

So maybe it's not so a bad idea to salvage a (old/broken) PS3-drive and searh some UV-curable epoxies at 400nm for high-accuracy fabbing?

Viktor
Re: RepRap machine for UV-curable resins
February 20, 2008 02:21PM
Well, I know the products needed for visible (blue light) radiation curing and they are all very expesive, sadly.

This application, for now, is out of our reach, unless I manage to get fulltime in a research-lab with all the means necessary to find out some cheap chemical that would do this. This means if I win the lottery or some philanthropist to pay for my bills smiling smiley
Re: RepRap machine for UV-curable resins
February 20, 2008 02:28PM
well, i'd say the resins you found look great. now we need to get you a machine to use as a test bed, as well as a syringe based extruder. i'm working on a lasercut design for a syringe based extruder. it probably will be a month or two before i even get the first pieces cut though. its just an idea in my head right now.
Re: RepRap machine for UV-curable resins
February 20, 2008 03:26PM
Ah, if you could get me plans for a syringe based RepRap I'd rush in and start buying and building myself one. I am confident enough on the resins I found to start printing some very neat stuff as soon as I have a robot for it. Maybe you could tell me what are the modules I can start with and that will support your newly designed syringe head. I will probably not have finished the building before you design you syringe head anyway.

As for the UV curing, I'll first try with the aluminum sheet covered box mentioned above and 2 lamps sitting on the top corners. It is by far the cheapest and easiest construction I can think of and as such needs to be investigated.
Re: RepRap machine for UV-curable resins
February 20, 2008 04:29PM
okay, i'll post my design when i get a bit of time. it will be easily attachable to a Darwin or McWire bot. Either will suffice, it just depends on which you'd rather build. Of course you are free to build your own machine as well, its just that I imagine you'd rather get straight to printing rather than mess with cartesian bots winking smiley
Re: RepRap machine for UV-curable resins
February 20, 2008 04:57PM
The [email protected] machine has a laser cut syringe extruder you could pinch.


[www.hydraraptor.blogspot.com]
VDX
Re: RepRap machine for UV-curable resins
February 20, 2008 04:59PM
Hi Fernando,

... actually i'm fully occupied with other problems and havent't searched for the resins.

But it shouldn't be a long job to atach a motorized dispenser and the small UV-lamp to my CNC, so maybe you can send me some probes for testing?

I'll send you my adress ...

Viktor
Re: RepRap machine for UV-curable resins
February 20, 2008 05:12PM
the [email protected] design is cool, but unfortunately their MIT style includes using special linear actuators (aka stepper motors with a screw embedded) that cost $150

For a syringe extruder, thats the majority of the cost. Hell, it should cost less than $50 for the whole kit, using a cheap NEMA 17 and/or one our our $6 dc motors and some threaded rod.

perhaps we could take theirs and modify it... that would be nice.
Re: RepRap machine for UV-curable resins
February 20, 2008 05:21PM
You can linear steppers a lot cheaper than that. This is the first hit on Google [www.motioncontrolproducts.com]


[www.hydraraptor.blogspot.com]
VDX
Re: RepRap machine for UV-curable resins
February 21, 2008 01:27AM
Hi Zach,

nanotec sells cheap linear actuators for 25 Euros ( [en.nanotec.com] )

Or look at the images in the Thread "Easy to assemble linear drives" ( [forums.reprap.org] ) - here i built linear drives by fixing a threaded rod with the same diameter to the motor-axis and a nut or PTFE-block with threading as mover. When you atach a tube to the nut, which is longer then the threaded rod, and a fitting for the plunger, then you can use common syringe-cartouches for the dispenser ...

Viktor
Re: RepRap machine for UV-curable resins
February 21, 2008 05:39AM
why do you need to move the syringe around? I though it would just act as a tap in a bath tub to fill more resin, then you would move around the laser/diode or whatever to harden the object where desired?

/Erik
VDX
Re: RepRap machine for UV-curable resins
February 21, 2008 05:48AM
Hi Erik,

it's for testing reprap-fabbing with UV-resins - i want to atach the syringe to the toolhead beside the millhead and output some test-trays.

Then i'll saturate the complete layer with the UV-lamp to cure it.

Then output next layer ontop of the hardened trays, and so on ...

It's testing for adhesion of the actual layer to the already hardened/cured sheet.

Viktor

Edited 1 time(s). Last edit at 02/21/2008 05:55AM by Viktor.
Re: RepRap machine for UV-curable resins
February 21, 2008 09:19AM
Ok, so the resin has a rather low viscosity that makes it stay on top of the previous layer? I was imagining something more like milk, floating out evenly everywhere...
Re: RepRap machine for UV-curable resins
February 21, 2008 10:54AM
It has more of a honey like viscosity, yes.
Probably acrylic resins could be made less viscous. But those resins remains to be tested yet as I have only tried out Polyester for now.
Re: RepRap machine for UV-curable resins
February 21, 2008 04:55PM
Hey guys, what about his for an idea. To gain the accuracy of a normal reprap and the ability to create nearly any shape, why not have the resin be in a sort of basin? The laser head could then dive into the resin and progress form there. This seems like it would provide accuracy, an near infinite number of shape possibilities, and a very cheap way to create the complicated designs people seem to be looking for. Food for thought.


Jay
$20 Syringe extruder: [www.evilmadscientist.com]
How I modified it for my repstrap: [www.instructables.com]

Its basically a syringe hooked up to an air-pump.

Works great and can easily extrude something with the viscosity of honey, given that the something is not nasty enough to dissolve it.

So, how can I obtain some of this UV curing epoxy?
VDX
Re: RepRap machine for UV-curable resins
February 22, 2008 01:35AM
Hi Gene Hacker,

i've tried with a pneumatic powered dispenser too with extruding a heat-curing epoxy-glue of honey-like viscosity at room-temp, 'working' viscosity at 60
I don't have that problem, I use a valve that lets the pressure off to prevent extruding.

Anyway, how nasty is this stuff, will it dissolve any plastics?
VDX
Re: RepRap machine for UV-curable resins
February 22, 2008 04:09AM
Hi Gene Hacker,

... if you wish a bit more accuracy at start and end, then a simple valve for releasing the pressure isn't enough - even the much expensiver vacuum-supported dispensers have problems forming a homogenous thread, so the aren't used in 3D-printers and the [email protected] decided to go the mechanical way ...

The paste-flow isn't "switch-n-run", but has a bad hysteresis, which is heavy depandant of viscosity, which changes highly when temperature shifts some centigrades over the extruding process.

So when dispensing a simple circle, you often didn't close it (because of paste-delay at start) or you have a blob at the start/stop, because of post-flow after releasing the pressure ...

I questioned some vendors and distributors of pneumatic dispensers and all tell me, it's a big problem to get homogenity - the best mis-rates were at 20% of the tray-diameter, some feared until 50% fluctuation over dispensing-time.

For cake-icing it's no problem, but when you want to build a layered object, then the errors can accumulate to ugly misshapings ...

Viktor
Re: RepRap machine for UV-curable resins
February 22, 2008 05:35AM
I made some tests with pressure pots a while ago and I can confirm that the repeatability of these devices is very tricky to achieve.
But if you want to use that simple and cheap device for testing UV-resin extrusion, you can go ahead. The Polyester resin is OK with polyethylene plstic this pump syringe seems to be made of. There are some plastics that do not respond well to PE resins. These are mostely polystyrene compound plastics. PE resins contain Styrene monomer as a solvent and thsi will attach Polysteyrene plastics and weaken them pretty fast, eventuelly dissolving them completely.

As for where you can get the UV resin, I wanted to post the recipy on the wiki but I didn't find the old Metrials page there was a time ago. Frankly, I do not know anymore where to post the recipy in a way to make it stick. I'll see if I can find those pages I did back and post it there.
I'd also like to post the links to website where you can get the chemicals needed. They are all mostly harmless chemicals as long as you don't ingest them or rinse your eyes with them winking smiley. Wear gloves (and goggles if you are of the clumsy kind) so that you won't get any of the stycky resin on your hands. Also, mix everything close to an open window, as styrene is not very healthy to inhale. These are the usal recommendatios as for any commercial glue or resin, really.
VDX
Re: RepRap machine for UV-curable resins
February 22, 2008 02:52PM
... today i borrowed from one of my previous boss an old pressure/vacuum-dispenser-system with a heated syringe-head and will try to bring this to work again.

Then i can test with time<->pressure-dispensing and look if it's capable of some accuracy in thread-geometry ...

Viktor
Re: RepRap machine for UV-curable resins
February 24, 2008 06:14PM
On the circle closing and the start and stop look, that was due to air bubbles in syringe. Some of the first layers actually turned out to be remarkably smooth. The blob is where I lifted the extruder off. The indentation on the side of one of the extrusions was due a "bump" when I was taking the picture.

But I do see your point on pneumatic extruders.

As for syringe extruders, it also might be possible to make crude linear actuator by using a glue stick hooked up to a stepper motor.
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