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quite accuratc for a testing level. This FDM model cost about $650 and took 4 days to
construct, while the metal model cost about $1300 and took a month to design and
fabricate. The conclusion was that FDM technology is a timely and cost effective way of
producing test parts.
In tbis wind tunnel model, the material needs to be strong enough to sustain the air force,
which is on the nose cone and the edges of the wing tails. However, forces on a marine
propeller are around all blades and nose cone and the fluid is much more dcnse. If a
propeller needs to provide a large thrust for a vessel, this polycarbonate plastic material
may not be strong enough. Selective Laser Sintering (SLS) is a better choice to produce a
propellcr where higher strength is required. SLS [34] is a r'apid prototyping technology
that uses a high power laser to fuse small particles of plastic, metal, ceramic or glass
powcrs into a mass to build a desircd 3-dimensional object. The laser selectively fuses
matcrial by scanning cross·sections, which will be used as the solid part of the object. The
scanned parts are melted and become a solid. After each cross-section is scanned, the
platen on which the object is built is moved down by one layer thickness, a new layer of
material is applied on top of the solidified layer and the process is repeated until the
object is completed. As shown in table 2, the SLS technology has a wide range of
available materials. Using SLS technology, objects can be manufactured from high
strength materials, such as uncoated or polymer-coated steel powders, which are
unavailable for other teehnlogies. The layer thickness ofSLS is 0.001-0.004 inch,and
laser diameter is 0.004-0.02 inch [36]. With the small heating diameter, thin process layer
and high strength ofmaterial, propellers can be produced by SLS with a good accuracy,
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