2.6 STEREOLITHOGRAPHY DETAILS

4.2.6

Stereolithography

Details:

Laser-Based

Manufacturing

and Prototyping

During stereolithography, selective laser sintering, or any laser-based process, many

details of the

"laser energy delivered"

to the resin (or powder for SLS) control solid-

ification and the accuracy that can be achieved. First consider penetration depth.

Note that the bottom of each SLA layer has to adhere to the previous layer, and so

the topic of main interest is the "energy at depth z" of the laser. Lasers give much

more energy (i.e., are able to cause more "polymerization by irradlence") than reg-

ular arc lamps. But as they travel down through the resin or powder they do never-

theless decay exponentially by the Beer-Lambert exponential Jaw of absorption:

H(x,y.d

=

H(x.y.OJ

ex

p(-

~)

(4.1)

A critical exposure

H(c)

is needed to "gel" the resin.

Dp

is a resin constant defined

by the depth of a particular resin that results in a reduction of irtadiance level to

lie

(=

112.718)of the H, level on the surface (Figure 4.6).That is, at a depth ot r

=

D

p

the