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.