I have been troubleshooting this issue on my own, as Formlabs support advised that it may be a faulty tank, which does not appear to be the case. They then said that models printed directly on the build plate may have this “skirting,” as they called it. Buy why?
My working hypothesis is that the additional laser power applied to the first layer, combined with reflections on the build plate surface, can work together to create an uneven perimeter.
To test my hypothesis, I modeled a circle with a chamfered bottom which was sliced in 0.1 mm increments and arrayed 14 times on the build plate, as illustrated below (the first 3 layers are not chamfered):
I then printed this file on several different substrates, each with the intention of testing the hypothesis that excess laser energy is being reflected around the perimeter of the first layer:
- Direct to standard build plate
- On shiny 3M aluminum tape
- On green polyester tape (used for powder coating)
- On amber-colored Kapton tape
As expected, the more reflective the surface, the more likely and worse the flashing/skirting. I also want to add that it is ONLY the first layer that is affected.
Printing directly to the build plate produced some skirting, as the surface is roughened. Yet, being aluminum, there were still some reflections.
Printing directly onto shiny aluminum tape produced the worst skirting, jagged, non-uniform, and extending > 1 mm from the first layer model perimeter. In fact, the first layer of the circles were not perfectly circular. Because the surface is shiny, more energy is reflected and distortions occur to the laser dot. Printing on shiny aluminum results in a first layer like this:
Printing on green polyester tape produced a small amount of smooth and uniform skirting. Because it is green in color, some of the UV energy was allowed to reflect off the aluminum on the back side. Unfortunately, standard resins do not adhere well to this tape, so it is not a viable option. Rigid 4000 resin does adhere well enough, at least for small models.
Printing on the amber-colored kapton tape produced < 0.1 mm of skirting–practically zero–as the excess energy reflected off the aluminum build plate is absorbed by the red color. Unfortunately, like the green polyester tape, standard resins adhere poorly to this material, making it unsuitable for use. See in the below photo, none of the models from the second column adhered to the tape.
I will next experiment with altering the aluminum build plate by oxidizing/anodizing the surface in an attempt to darken it and minimize its reflectivity.