SLA curing Light Intensity

[msizemore]

We've gotten into SLA printing at work via a Form2, and are on the cusp of creating a curing chamber. FormLabs has a good white paper on curing time and temperature, but I didn't find details on what light intensity a curing chamber should be designed for.

What has your experience been with UV curing SLA parts and can you point me to some resources on this?

[jimustanguitar]

I've been using a UV nail polish curing box. Mine looks a lot like this one: smile.amazon.com/Manicure-Machine-Polish-Curing-Acrylic/dp/B01NA8L9H2/ref=sr_1_81?ie=UTF8&qid=1486269416&sr=8-81&keywords=uv+nail+curing+box

I put the parts in that, on a rotating solar display stand, and it does a nice job. A few hours in the box, and things come out nice and solid. I've also seen people build them out of LED strips.

Shane would be the best guy to point you in a direction on intensity and time.

What wavelength of light do you need?

[msizemore]

Feb 4, 2017 23:39:05 GMT -5 jimustanguitar said:

I've been using a UV nail polish curing box. Mine looks a lot like this one: smile.amazon.com/Manicure-Machine-Polish-Curing-Acrylic/dp/B01NA8L9H2/ref=sr_1_81?ie=UTF8&qid=1486269416&sr=8-81&keywords=uv+nail+curing+box

I put the parts in that, on a rotating solar display stand, and it does a nice job. A few hours in the box, and things come out nice and solid. I've also seen people build them out of LED strips.

Shane would be the best guy to point you in a direction on intensity and time.

What wavelength of light do you need?

405 nm is what the man says. Though it looks like 395 to 405 will do just as well.

I did pick up some UV led strips that will be a good starting point. I would like to stick a little more science into this box though...

[sgraber]

Feb 4, 2017 15:16:58 GMT -5 msizemore said:

We've gotten into SLA printing at work via a Form2, and are on the cusp of creating a curing chamber. FormLabs has a good white paper on curing time and temperature, but I didn't find details on what light intensity a curing chamber should be designed for.

What has your experience been with UV curing SLA parts and can you point me to some resources on this?

Howdy!  Yeah it's a pretty good white paper and I was kind of surprised they haven't come out with their own cure chamber based on those results.  My guess is they will at some point.

For those reading this, here's the direct link to the white paper:  formlabs.com/media/upload/How-Mechanical-Properties-of-SLA-3D-Prints-Are-Affected-by-UV-Curing.pdf

I did find it disappointing that they did not report the total UV irradiance that the part was exposed to at ultimate physical properties in the paper.  This would have been reported in mJ/cm^2 but they only report mW/cm^2.  That said, mJ/cm^2 is just mW/cm^2 * time (sec) and I'm assuming they took the wattage reading at the same distance from the LEDs as the parts were cured.  That said, their reporting isn't standard in the UV curing industry and leads to confusion.

In the conclusions, they report optimum properties at 1.25 mW for different times and temperatures for their resins:

Standard:  1.25 mW/cm^2 * 60 min * 60 sec/min = 4500 mJ/cm^2
Castable: 1.25 mW/cm^2 * 120 min * 60 sec/min = 9000 mJ/cm^2
Tough:  1.25 mW/cm^2 * 30 min * 60 sec/min = 2250 mJ/cm^2
Flexible:  1.25 mW/cm^2 * 60 min * 60 sec/min = 4500 mJ/cm^2

All of that said:  if you look in their datasheets for each resin, they report the mW/cm^2 and time that the dogbones were subjected to before measuring their physical properties.  In a number of instances, their recommendations from their white paper and the settings at which they cured their dogbones do not match.  For example, their Tough resin physical properties (formlabs.com/media/upload/Tough-DataSheet.pdf) were tested after the part was under 2.5mW/cm^2 for 120 min @ 60°C (total irradiance of 18,000 mJ/cm^2).  I can't tell you why that is either.

Most of the people on the Formlabs forum seem to either use the UV fingernail lights or they build their own chambers.  We use the standard 36W / 365nm UV fingernail lights (power compact bulbs) in our lab at MakerJuice as that's what most of our customers have and can easily source.

FWIW if you do want to build it to their specs, they do list the UV LED arrays they used in that white paper.

There's also a number of people on the forum that have builds:

forum.formlabs.com/t/diy-cure-box-made-easy-thanks-ikea/10967
forum.formlabs.com/t/upgraded-uv-curing-chamber/9201
forum.formlabs.com/t/build-of-atlasbraces-ikea-uv-chamber/11139
forum.formlabs.com/t/budget-uv-cure-box-jar/3176

Not sure if this helps or not, but let me know!