Clear prints with seamless joints on multi-part prints- UV glue/laser curing


#1

I am trying to print a multi-part, clear item. (Too large to print as 1 piece)

I want to try and optimize clarity of the glue joints that hold the printed pieces together. My first inclination is to use liquid resin as a glue, and use a handheld laser of the same power and 405 nm wavelength as the form to cure the clear resin.
Ideally you join with the same materials and processes used to create the pieces in the first place for consistent clarity.

However, I am questioning if this method will work because if the ‘spectral inhibitors/blockers’ in the resins that limit light penetration (even in clear).

Any help would be greatly appreciated!

I


#2

I’ve done this before with success for parts with small cross sectional areas that required bonding. Worked perfectly fine for me. I haven’t tried on bigger sections so unsure how that would work if the area you need to cure is very far from your laser.

I’ve also done this on opaque parts, but mostly to hide the seam after glueing with epoxy.


#3

It’s just a question of wattage.

We used a UV curable adhesive to glue bearing cartridges in to the actuators for HDDs (when I made HDDs). The fit of the bearing to the bore was almost line-to-line, so only a really thin layer of adhesive could make it down the bore with the cartridge. At first, we weren’t convinced the adhesive deeper down the bore would cure, since we could only light it up from the ends, and the gap the light had to travel was virtually nonexistent. But it did cure. We cut some early prototypes apart to confirm it. But we needed a lot of UV light, safety-goggle levels of light…

I’ve been using a small UV “spotlight” (basically a LED in a fixture with a lens that gave it a beam of about 15mm diameter) for this with my Formlabs prints for years. I tack the joint with the handheld light. But I always expose it to direct sunlight for a few minutes before I put any stress on the joint. Done properly, the joint becomes as strong as the surrounding resin and subsequent breaks might fracture through but they won’t fracture along the seam.

Note also, in a pinch you can use resin to glue stuff together that isn’t printed out of more resin.


#4

Yeah that makes sense. At some point it becomes impractical or potentially a safety hazard if you need a very high power UV source like you indicated.

These are some parts that I’ve bonded. One is high temp resin and the other is standard black. I used a UV laser pointer from Amazon for both. The black parts were bonded with epoxy and then the seams were filled afterwards with black resin and the laser pointer. The high temp part was done purely with the same resin.

https://photos.app.goo.gl/CJCmFJKR96Ty9e4XA


#5

Sorry maybe this has been answered, but has anyone tried this specifically on clear resin? For me it will all be about hiding the seams in places where it will be very obvious is there is a change in clarity. Another consideration will be the total elimination of any bubbles… but curing/clarity are the primary concerns at the moment.

If we did try and join 2 walls with let’s say 12mm thickness, what do you think is the exposure time needed for curing? I tried shining my 200mW 405nm green laser at a pool of tough resin (probably the worse to test given it’s high cure times), and there was no evidence of curing. I’m interested in the fact it seems like SLA and MSLA printers all seem to use 405nm curing wavelength, yet the lasers tend to be green and the LED’s tend to be purple. Maybe the LED’s emit a more pure version of the light whereas the laser has a lot of visual-spectrum light that is wasted? or vice versa?

Thanks!!


#6

200mW at 405nm should have been more than enough to cure your resin. 405nm is 405nm. If your light source isn’t blue (well, a bit purple/blue), it’s not emitting 405nm. Go hold your parts in the sun for a minute, or pour a little resin in to a cup, and see if it cures. It will. Pretty quick, too (though as it cures, the stuff deeper down takes longer).

When you glue clear parts together, you’ll see a seam if the adhesive (assuming it’s clear) has a different index of refraction than what’s being glued. If you glue two pieces of clear resin together with clear resin, the index of refraction is the same and the seam should be mostly invisible.


#7

The laser on the Form3 is green though? (same colour as the laser pointer)


#8

You’re viewing the laser through the orange acrylic light shield. The color you see isn’t the color it is. :slight_smile:


#9

Ah true, so the green is just the residual light whose wavelengths aren’t blocked by the shield.
Makes sense!


#10

Open the shield, hold your laser pointer inside pointed out and turn it on and see what color comes through… if it’s pretty bright compared to how it looks when it’s outside the shield, then it isn’t outputting a lot of UV.

The yellow/orange shield is colored that way because that’s the color that blocks the laser.

Don’t shine any laser in your eyes, of course…


#11

The green light isn’t residual light, the laser diode in the printer only emits 405nm, which would appear violet if you were to see any. The green light coming through the shield is light produced by the fluorescence of chemicals in the resin, so it’s more ‘new’ light than residual.

Your green laser pointer is almost certainly 532nm unless it’s a semi-fancy new direct-diode green laser pointer and it’s more like 520nm or something. At any rate, I wouldn’t expect any photochemical activity to happen to Formlabs resin exposed to wavelengths anywhere in the green part of the spectrum and longer.

To look at a more practical question, 12mm is probably just too thick to get a full cure in the middle, but as a super vague unofficial estimate, I’d suggest exposing the a joint like that at least 10 times as long as it takes your light source (whatever it is) to fully cure a really thin layer or <1mm droplet of resin. As Randy says, you may be able to tell whether you have uncured resin in the middle of the joint by the subtle difference in index of refraction between solid and liquid resin.


#12

Yeah I used my voilet laser and BOOM! curing! The fluorescence makes sense. Got some clear resin on order and will try it. Much appreciate the help all!