Extra layer printing problem


#1

I have observed some artefact on the part I have printed recently. I am using the Castable Wax.
Here is an example of the part that I want to print :

The part is easly printed and the aspect is good. The issue that I met is that I find extra material on the surface that I print with 90°. I know that printing at 90° is not recommended, but it work perfectly with my dimension. So in the end, I have around 0.5 mm of extra material :

I don’t want to add many support every time this happen for esthetic reason, I have tried and it does not really fix the issue. The only solution that would work at the moment would be to anticipate that extra support and take it out of my CAD, but I do not like that solution.
Anyone have met that problem? Is there any solution?


#2

turn it over . and use heavy support on bottom of the rounded part.


#3

Thank you for the reply.
Unfortunatly this is just one example. I have more complex parts with that problem, so this is not a suitable solution for me.
I guess there is no proper solution for that issue.


#4

I’d try raising it off the build platform and adding a couple smaller supports on center cylinder.


#5

There’s always going to be extra material on the underside of a print, it’s a result of SLA printing due to the light source (laser) going through the layer you’re currently printing.


#6

Yes, as Zachary said, printing with overhangs can cause this. When the first layers of an overhang are very thin, they cannot block 100% of the laser light transmission, so some light will transmit through the thin overhang into the liquid resin surrounding it, causing some extra resin to cure on the underside of that overhang as well.

The best way to fix this is to orient your parts so that there are as few/no overhangs as possible, or at least any critical dimensional surfaces are not downward (towards the build platform) facing.


#7

This is very insightful and disturbing at the same time.
So as a layer is cured a bit of the light passes thru that layer curing some resin behind it?!
That tells me no matter what way you have the part orientated some extra resin behind each layer will get cured. The part is submerged in resin each time when it cures a layer so I’m confused with the “drain off quickly” remark as its not curing layers when the part is lifted out of the vat during the peel process.
If it is curing the resin behind the layer that is being printed wouldn’t that be a laser power issue for that particular resin & not a orientation issue?


#8

It’s not related to parallel surfaces, when the layer is printed it is submerged several millimeters in resin so any surface on the bottom of the print whether it’s flat or angled will end up with extra resin cured there due to the laser going through the layer. It’s not an issue for surfaces facing upwards because there are existing layers on the other side of the layer so it’s just curing the existing print more.
That’s something I think would improve prints in future printers, if some kind of mechanism would be designed to where it leaves a thin layer of resin for the next layer to print, that way there’s a minimum amount of resin there.
Making the resin less viscous would also help so it doesn’t stay in one area as easily which will reduce the effects of indirect curing.


#9

Some Interesting thoughts about the mechanism of cure. Surely the resin only cures as far as the UV light source penetrates (that is penetrates with sufficient power to effect a cure in the exposed time) The cure stops when the UV energy is removed.

There are many different ways over penetration and the phenomenon often called “light bleed” can be cured, its a balance between exposure time, power, speed of the laser movement through the material. Simple things such as adding a colour will affect “light bleed” especially if the colour is from a material like titanium dioxide (white colours) alternatively a number of companies offer things such as “light blockers” that can be added to the resin.


#10

There’s no way to stop the laser from going through the current laser, but there’s ways to reduce the effect, for example like I was saying instead of submerging the print each time if you simply left a thin layer of resin on the bottom of the tray (as thin as you can make it) then that will help. Some of the resin on top would also not cure due to exposure to oxygen so to some degree you can stop it. It will still bounce around a bit within the resin itself (indirect curing), that will depend on what particles are in the resin so for example the clear resin won’t have that issue very much.