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part’s right-hand side.
The extra material is due to the overcure
of layers No. 1 and 6. The blue
portion is excess material from layers
No. 2 and 7 curing through layers No.
1 and 6, respectively. That material is
called print-through. Together, overcure
and print-through add the equivalent
of about three layers’ depth—an
unacceptable error.
We deploy Zcomp to raise the bottom
of every feature by the amount
we know will exist due to overcure
and print-through. In effect, we skip
drawing the first two layers and start
with the third (Figure 3). Note the tiny
amount of residual print-through on
the bottom of the main section. We
purposely leave that excess material and
remove it post-process to achieve the
best possible finish and flatness.
In practice, the precise amount of
Zcomp applied is a function of the material,
build style and equipment used.
Because of the size of microscale SL
parts and the tight tolerances involved,
the machines must be rigorously maintained.
This ensures that Zcomp is predictable
from part to part and keeps
process drift in check. µ
About the author: Rob Connelly
is president of FineLine Prototyping,
a Raleigh, N.C., company offering
rapid-prototyping services, including
stereolithography, selective laser sintering
and 3-D printing. Phone: (919) 781-7702.
E-mail: rob@fi nelineprototyping.com.
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