AD&P; > June 2013 > ACCELERATE
by Scott Anderson
ACCELERATE
ACCELERATE
> Contributing Editor
Development Aid Made
3D printing companies pride themselves on creating oneof objects or working parts when wider-scale production
is too expensive or time consuming. But the stakes
usually aren't as high as, say, in Ethiopia, where a small
hospital was without electricity thanks to a defective
turbine wheel.
The clinic, in Walga, Ethiopia, did not have the funds to
replace the commonly used, yet very intricate Francis
wheel. The clinic worked with German 3D printing frm
voxeljet technology GmbH (voxeljet.de), which created
a mold for a replacement wheel via its 3D printing
technology.
voxeljet produced a 250-mm mold for the wheel in about
fve hours. voxeljet says accuracy reached 0.2mm on
the X- and Y-axes. That's one of the smaller molds for
voxeljet, whose large-format printers have churned out
objects sized 4 x 2 x 1 meters.
u Inserting
the 3D-printed
core into the
conventional
sand mold
q The rough
wheel cast in
steel.
52
The molds were forged based on CAD designs and created
in layers made of 300-mm thick quartz sand that were
glued together with a binder via the system's print head.
Once the printing was done, and the mold cleaned of
excess sand, it was ready for casting.
"In this case, we decided on a combination of a 3D-printed
sand core for the complicated turbine geometry and a
conventionally produced exterior mold," said voxeljet CEO
Ingo Ederer. "This means that we use the advantage of 3D
printing where it pays of the most—for the production
of the complicated interior. Instead of many individual
core segments which are strung together, the mono sand
core impresses with higher component accuracy, smaller
tolerances and fewer cleaning requirements, and does away
with the need for many core separation devices." Also
contributing to the project was German steel foundry
Wolfensberger AG, which cast the wheel; and solar and
heat technology frm H. Lenz AG from Switzerland.