2.5.5 STEP5.SWEEPING USING THE ZEPHYR BLADEAT FIRST GLANCE, THE ZEPH...
4.2.5.5 Step
5.
Sweeping Using the Zephyr Blade
At first glance, the Zephyr blade looks like a "hard squeegee" used to clean a car
window. In fact, it has a long, hollow cavity between two adjacent blades, and this
cavity is under the influence of a slight vacuum pump. This draws SLA liquid into the
bottom of the blade. Thus, as the blade sweeps over the surface, it is "charged" with
liquid and more easily and uniformly deposits the next liquid layer onto the first. At
the same time the sweeping blade distributes the SLA liquid evenly. Note that the
140
Solid Freeform Fabrication (SFF) and Rapid Prototyping
Chap. 4
honeylike SLA fluid is very viscous, and
it
needs the distribution of the vacuumized
Zephyr blade to get an even surface.
As the Zephyr blade traverses the whole vat, it removes excess resin in some
areas, and yet because it is "charged" with resin, it distributes and fills any areas that
lack resin. The sweep takes about 5 seconds (Jacobs, 1992) unless a hollowlike part is
being made where the viscous fluid inside the hollow takes longer to follow the
blade. The sweep gives a uniform thin layer, but given the viscosity of the fluid, there
is a tendency for resin to adhere to the blade, followed by separation and a "bulge"
just downstream from the part's leading edge.