can also develop products with free-moving parts
that do not have to be assembled. A 3-D printer
making a set of fully-functioning ball bearings can be
viewed online at http://www .youtube.com/watch? v=u7h09dTVkdw. The definition of 3-D printing is somewhat inex-
act. While some experts in the field would restrict
3-D printing to units with inkjet-based print heads
that create an object on a layer-by-layer basis,
others would apply this term to office or consumer
versions of rapid prototyping machines that are
relatively low-cost and easy to use (Casey , 2009). The word ‘rapid’ relates to the ease of making a copy
of an object due to the simplicity of writing a com-
puter program that controls the object’s shape. The
term ‘prototyping’ refers to this process as being too
slow for use in mass production (in contrast to injec-
tion molding technologies that yield large quantities
at low per-unit costs). Tw o important aspects distinguish 3-D printing
from other rapid prototyping technologies. The first
distinction is cost. While a 3-D printer can cost as
little as $10,000, a rapid prototype machine can cost
as much as $500,000. Desktop 3-D printers now
run from $10,000 to more than $100,000. Current
3-D printer manufacturers include Zcorp (www . zcorp.com ), Objet Geometries (www .objet.com),
Dimension (www .dimensionprinting.com), Design-
craft  (www .designcraft.com ), Stratasys  (www . stratasys.com ), and 3D Systems (www .3dsystems.