UV curing photopolymer for rapid prototyping

Hi Alan,

... my hand is something better now, so i'm continuing with the curing setup.

Actually i'm reprogramming a MySmartControl-brick as adjustable 'low-power'-driver for the 445nm@1Watt-diodelaser.

With a poti and an enable input it will convert the value of the poti in a PWM-signal with signal durations from 1ms to 1s in ms-steps, what's roughly a possible power adjustment from 1mW to 1Watt effective (averaged) power.

With such a type of PWM-driver and a higher resolution you can adjust your 10W-laser too.

For the 50Watt IR-fiber-laser I'll use an AOM, that reduces the max. possible power to maybe 20 Watts, but can modulate this with 40MHz from zero to max. energy by applying an analoque signal from 0 to 5 Volts ...

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Viktor
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Hi Viktor,

Hope your hand is better.

I've emailed suscomp so hopefully I'll be able to get hold of some material to play with! I have the laser up an running coupled to the reprap prusa - video here and blog post here. For now its a sortof reprap laser cutter so I've been doing some quick/simple cutting tests with it using fan on/off to turn the laser on/off (laser power parameters are set on the laser). How are you planning to generate g-code to control your laser instead of an extruder?

mmm.... an AOM would be a nice toy to have!

Alan.

Hi Alan,

my CNC-software can generate layered paths and G-code, but it's meant as subtractive fabbing in the original way, so i had to do some tweaking in the postprocessor for an additive process ... but it's working.

Better use any common programm for the normal reprap and optimize the resulting G-code, so it's controlling the laser and layer-changer instead of the extruder motor and the Z-axis only ...

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Viktor
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Hi Fernando,

i've managed to test the three polymer probes (SR 499, SR 601E, CN2302/2305) with different light sources - they behave nearly identical, but SR 601 is more viscouse.

UV-LED's with 405nm: nearly instant curing/hardening - 1s exposure time hardens nearly 1mm from the surface in depth.
(It's nearly the same with Bondic: [www.bondic.de] )

BluRay-diodelaser with 405nm and 50mW: - instant curing/hardening

Blue Diodelaser with 445nm and 200mW: - nearly no effekt!
- with higher intensities and longer curing times hardening occurs, but not from surface down, but from the bottom of the droplet (contact area to black eloxated aluminium surface) upwards - the surface of the droplet stays fluid!

Superbright Blue and White (blue LED with yellow fluorescent) LED's: - no effekt after some ten minutes

Fluorescent bulbs: - no effekt after some ten minutes.

So it seems, the polymers don't react with 445nm and above, but cure instantly with 405nm.

With more of the SR 601E (most viscouse) i'll try with my Paste-extruder and atached curing UV-LED's: [reprap.org]

The SR 499 or CN2302/2305 could be great for the reworked SLA-printer with a BluRay-laserdiode, but here we'll need some litres of polymer to fill the building box ...

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Viktor
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Excellent work and very interesting results!

It is interesting that the photoinitiators I have will not work at 445nm. This is a wavelength that will be very difficult to cover with PIs that have an acceptable price... The effect you see "curing from the bottom up but never at the surface" is what we mean by "Oxygen inhibition". The interface layers of the resin with air is saturated with Oxygen that inhibits the free radical curing reaction. This is a nuisance that can be worked around chemically, but if the 405nm does not have this problem, we should go with that setup, as the other would be adding complexity.

As for the 405nm that is excellent news! I have 2 PIs that will readily work and some of the resins I have to mix curing systems are all well suited for this setup.

The next step would be to send you samples with the other PI I have that should work even better at 405nm with less tack and very good polymerization. Also, I would be sending resins that have been tuned to have very nice physical properties, closer to ABS. I'm sure you would like to toy around with those.

As for a large vat test, how much do you think would be needed?

And I forgot: another series of tests would be to try an pinpoint what is the cure time/resolution boundaries that one can achieve with the 405nm system. What is the minimum voxel you can get and how long do you have to irradiate for curing it?

Adding dyes may become necessary for having a better control of voxel dimentions. There are some succesful tests that have been made using Castin' Craft Amber and Yellow resin dyes. We have achieved 0.025 -0.045mm resolution with those on a DLP printer setup:

[3dlprint.com]
[3dlprint.com]

Hi Fernando,

I think the best way for me is to work with the 200mW BluRay-laserdiode - the spot can be as small as 0.03mm, or maybe even smaller, but then only with powers below 50mW as i have to cut away all the beam irregularities with a small aperture.

With a simple Arduino-based PWM-driver/controller the curing time is selectable as single pulse or series with some microseconds to milliseconds durations, so the average power is easy adjustable from zero to max CW power.

For tests with larger volumes a litre schould be enough - the SLA setup has a square size of maybe 400x300x300mm, but i can use smaller boxes and reduce the building area.

Can you give me the estimated prices for larger volumes?

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Viktor
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spota Wrote:
-------------------------------------------------------
...
> Adding dyes may become necessary for having a
> better control of voxel dimentions. There are some
> succesful tests that have been made using Castin'
> Craft Amber and Yellow resin dyes. We have
> achieved 0.025 -0.045mm resolution with those on a
> DLP printer setup:
...

Spota, have you actually been able to significantly decrease the cure depth using the Castin' Craft dyes?

While I've seen some small depth reduction using Castin' Craft yellow/red with Loctite 3105 and a 405nm laser, the depth reduction was not nearly enough to be useful. I'm just about to do some tests with FD&C Yellow #5, which in a preliminary test worked much better than the Castin' Craft dye.

Does this means you will go with 445 or 405nm? This I need to know too on top of the power, as it tells me what photoinitiator to use. 445nm would mean I have to get myself a very expensive PI as Camphoroquinone, that is also quite slower than BAPO.

1kg should be no problem for this test. There are still some test to be done and questions to be answered (dyes) and I think I will share the cost of this with you. Let's PM and we'll arrange a shipping of the resin just to cover some of my expenditures, shipping costs, base materials etc...

Only condition: it will have to wait a week as I am expecting the delivery of more base materials. There has been a terrible bottleneck and I am almost completely depleted! Is this OK?

...
>
> Spota, have you actually been able to
> significantly decrease the cure depth using the
> Castin' Craft dyes?

We had somebody achieve 0.025mm resolution by twaking exposure times and playing with Castin'Craft Yellow clear and opaque dyes. But you are right about the 405nm inefficiency.

I have measured the absorption spectra of CC's clear amber dye and the peak is around 460nm. At 405nm there is a kick in in absorbance, but it's not ideal. So you would have to add uite a lot of it to make a difference.

I also have Tartrazine (E102, FD&C Yellow #5) available and will eventually measure its spectra too, but I don't think it is a very good compound either as it is notoriously difficult to dilute in hydrophobic (non-water based) media.

The ideal dye for 405nm is still Sudan I. It's right there where it needs to be. So much so that you need minute concetrations to completely extinguish the light.

Hi Fernando,

the 200mW BluRay-diodelaser has 405nm - the 445nm-diodelaser has 1W max, but is only interesting (if you find a cheap mixture) for highspeed-scanning with two accurate (and expensive) XY-galvos.

I've seen 405nm-modules (complete with lens) from 20mW to 700mW and prices between 20 and 80 Euros at ebay ...

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Viktor
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Wow, excellent!
I would actually love to have a machine that uses the 405nm 200mW laser for printing large objects. I may get one built for me at a later stage. Will you be using a CNC or RepRap machine together with the Laser instead of 2 galvo mirrors?

Be it as it may, I will get you the 1kg resin, I may add some mineral filler to the mix to help you deal with any heat peaks, add some thermal inertia. Do you have a blog where you document your designs?

Hi Fernando,

... no blog - if it's worth to document, i'll set it in the RepRap-laser-Wiki or create a new page ...

The first setup will be on my CNC-mill, a preassembled wood-mendel is waiting here too, but for accurate laser-fabbing I'll assemble a special 3-axis stage with 1 micron accuracy.

But I have a complete XY-scanner with laser-optics from an old SLA-machine, that will fit perfectly for the 405nm-laser, so 3 options, I have to buildup over time ...

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Viktor
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madscifi Wrote:

> Spota, have you actually been able to
> significantly decrease the cure depth using the
> Castin' Craft dyes?
>
> While I've seen some small depth reduction using
> Castin' Craft yellow/red with Loctite 3105 and a
> 405nm laser, the depth reduction was not nearly
> enough to be useful. I'm just about to do some
> tests with FD&C Yellow #5, which in a preliminary
> test worked much better than the Castin' Craft
> dye.

@Madscifi - Hi, I'm Peter from the [www.3dlprint.com].

The reduction seen is very noticeable in my setup. I have exposures of 0.5 seconds to cure ~0.043 mm layer. Fernando sent me small samples of a few resins and the end results can be seen in the gallery. I have cured with the Castin' Craft transparent Amber, but the results were about 1/2 to 1/3 cure depth reduction. I have not tried the Red opaque ( although I have and also have the "blue, green and yellow" transparent kit ), but the opaque yellow is by far the best. I would guess that your saturation was not enough to limit the cure depth. A layer of 0.2mm is cured in 8 seconds and that is using the slower resins.

Peter
3DLPrint.com

P.S. Hi Fernando!

Peter, Thanks.

I'm getting much better results with the opaque yellow. One thing that is curious is that even with 0.2 mm layers the surface of the objects show very little stair-stepping. I'm assuming that means that I have not cured the resin sufficiently, but that is just a guess at this point.




I have also learned that resin containing pigmented dyes needs to be stirred just before printing.

... you seem to have a more diffuse curing characteristic - then the vertical edges will 'blurr' and react a bit with the next layer too, so you'll receive a sort of averaging or 'antialiasing' over the layer height.

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Viktor
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Quote

I'm assuming that means that I have not cured the resin sufficiently

This curing process takes some time, that's perfectly normal. After lighting UV-curable resin it gets into some glibberish state very quickly, but complete curing can take several hours. Stereolithography machines usually came with an UV-"oven", a box with a lot of UV lamps inside. You'd but your fresh parts in there to fully complete the photo-inition. After washing them, of course.

So, as long as you can keep the geometry, there's no need to increase the UV energy you put into the part.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

This proces is called post cure and can take different forms, using a range of UV or visible sources.
My resins will only need a cuple of standard fluo bulbs and a final black-light fluo bulb to do the post-curing.
There will be no to very little tackyness left and the object achieves final hardness withing 30 minutes.
Post curing in the sun is also very effective.

If you ar elosing some reolution it may also be due to diffusion inside the resin. This may be caused by a flat distribution of filler particle sizes.

Traumflug Wrote:
-------------------------------------------------------
> I'm assuming that means that I have not cured the
> resin sufficiently
>
> This curing process takes some time, that's
> perfectly normal. After lighting UV-curable resin
> it gets into some glibberish state very quickly,
> but complete curing can take several hours.
> Stereolithography machines usually came with an
> UV-"oven", a box with a lot of UV lamps inside.
> You'd but your fresh parts in there to fully
> complete the photo-inition. After washing them, of
> course.
>
> So, as long as you can keep the geometry, there's
> no need to increase the UV energy you put into the
> part.

... received 1.5kg of new photopolymer from Fernando - the next evenings/weekends could be interesting

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Viktor
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Hi VDX. From memory, you're in NZ?

I personally work with the latest and greatest in SLA every day, but I'm always interested in where the community takes the idea in the hacker realm. I'm switching over materials in a vat from one of our machines in the next few days, and will have a couple hundred kg's of Somos NeXt that I'm not entirely sure what I'll do with. I can swing a couple kg's your way if you think you could do anything with it. Might be worth your time just to see if some of the commercial SLA resins are of any use. Shoot me a PM if you're interested.

proto Wrote:
-------------------------------------------------------
> Hi VDX. From memory, you're in NZ?

... this was Vik from NZ, i'm in 'old Germany'

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Viktor
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... made first test with manually dispensing and UV-curing - it works, but not as desired, the resin is so low-viscous, that it flow down from higher structures before it cures to solid ... maybe Fernando has to mix a resin with paste-like consistency/viscosity ...

For beamer- or laser-curing in a vat it should be perfect, but this will need some more time, until I've reassembled the setup for laser-curing again (have to mill some parts, so the CNC-mill is actually reconfigured and the scanning SLA-printer isn't operable until now) ...

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Viktor
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Hello Viktor,

I wasn't aware you were going to try dispensing the resin. I have made some mixes with the resin you have with fumed silica. This very effectively adds thixotropy to the mix, achieving ranges of rheology from thick liquid to paste.
The resin you have now has specifically been formulated to achieve a very low viscosity without having any volatiles.

If you are interested in dispensing the current resin, we could try with some additives.

Cheers

Hi Fernando,

the resin you sent me is perfect suited for lasercuring, what's the main target to achieve

Dispensing is a sidepath I'm working on occasionally ... maybe you can send me a probe of thixotropic/paste-like resin or an additive so i can mix small quantities on my own for testing with the dispenser?

Last week a friend sent me two LED's with 405nm and 9Watts of power (with watercooling!), and yesterday I've ordered two LED's with 380nm and 1W power for testing with ambient UV-light for postcuring.

The 380nm-LED's are single-emitters, so could maybe be used for spot-curing too for high-speed/high-volume-fabbing, but the 405nm-types are array-emitters with a footprint of maybe 5x5mm, so more for aerial curing ...

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Viktor
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Quote

Last week a friend sent me two LED's with 405nm and 9Watts of power

Wow! Stereolithography machines come with lasers in the range from 10 to 100 Milliwatts and are pretty fast already.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

... yes, my old SLA-printer had a 30mW HeCd-laser, but the laser was outweared and removed, so we're changing to a diodelaser with 405nm and max. 200mW of power. With beamshaping to receive a better spot-quality the max. power will reduce to something like 100 to 150mW, but this should be enough for the start.

The 9W@405nm-LED's are meant for post-curing the printed object.

The 1W@380nm-LED's are interesting for postcuring too, but as single-emitter they could be small enough, so i can produce a spot of maybe 0.5mm size, what should be a good test-candidate for high-volume-fabbing for bigger/coarser objects with UV-polymers ...

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Viktor
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Massive power!!!

OK, I will try and send you some thixotropic paste or fumed silica so that you can play around with paste like resins.
The light under which it will be active remains the same, so everything between 365 to 425nm is good.
Add your current resin to small amounts, little by little, and homogenise. This fumed silica is powerfull stuff and makes resin become extremely thick in low dosages.

... sounds promising

In the meantime I'll try to assemble a second 3-axis machine and hack the galvo-scanner-driver of the SLA-printer ... could be a good idea to have all three fabbing methods working ...

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Viktor
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guys this is amazin' 3d printer - they have used a cheap pico projector. check this [www.miicraft.com]
i can't wait to see your result guy... i buy resin from you guys..

more power.

... should have done more with the UV-printer, but had some more urgent work to do.

Actually I'm job-changing, so closing/transferring the current projects is in the main focus.

The next projects on my private list are a 'comercial' CNC-toolhead with diode lasers ... rework/reuse dental-3D-scanners to bigger scan voluminas ... and then again 3D-printing with spota's UV-resin and different curing methodes ...

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Viktor
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