Question

vat: dimensional accuracy
use the information below to answer the question.
in vat polymerization, the dimensional accuracy of the prints is largely dependent on the choice of material as well as the amount of form warpage.
material warpage
large flat prints are susceptible to warping. however, there are several ways to decrease that possibility. one way to prevent material warpage is to have a good structure to the base which helps to eliminate some of the stresses built up between layers. in some cases, adjustments can be made to the design that will decrease the possibility of material warpage. one method is to reduce the amount of large flat surfaces used in a form. another strategy is to angle the print in a position where the largest and flattest portion of the build is orientated
onparallel\ to the print bed.
top - down printers
warpage often occurs during the top - down printing process when the light source shines and hardens the resin. with each layer that is built, the material will shrink slightly. if there is not enough force holding the printed form to the print bed, the material has a tendency to warp and curl.
bottom - up printers
for the bottom - up printing process, if your printed form is not well anchored to the build plate, it may begin to peel up slightly each time the lift arm moves up and down to bring in more resin. if the part begins to swell, you may see a \compound effect\ where the warpage found on one layer carries through each layer of the build.
material selection
another aspect to keep in mind is your choice of material. some resins are very flexible when cured, which makes them less suitable for high - accuracy applications.
when does warpage often occur during the bottom - up process for vat polymerization?
when a form does not have enough detail to distinguish parts
when a form is not well anchored to the build plate
when a form has too many support structures
when a form is not hollow enough to allow for shrinkage and expansion

Explanation:

The text under "Bottom - Up Printers" states that for the bottom - up printing process, if the printed form is not well anchored to the build plate, it may begin to peel up slightly each time the lift arm moves up and down. This is a direct cause of warpage in the bottom - up process.

Answer:

when a form is not well anchored to the build plate