Page 554 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

Chapter 20 Rapid-Prototyping Processes and Operations

20.3.3 Multijet/Polyjet Modeling
The Multijet Modeling (MJM) or Polyjet process is similar to inkjet printing, where
print heads deposit the photopolymer on the build tray. Ultraviolet bulbs, alongside
the jets, immediately cure and harden each layer, thus eliminating the need for any
postmodeling curing that is needed in stereolithography. The result is a smooth sur-
face of thin layers as small as 16 ,um that can be handled immediately after the
process is completed. Two different materials are used: One material is used for the
actual model, while a second, gel-like resin is used for support, such as these shown
in Fig. 20.5. Each material is simultaneously jetted and cured, layer by layer. When
the model is completed, the support material is removed with an aqueous solution.
Build sizes are fairly large, with an envelope of up to 500 >< 400 >< 200 mm. These
processes have capabilities similar to those of stereolithography and use similar
resins (Table 20.2). The main advantages are the capabilities of avoiding part

cleanup and lengthy postprocess curing operations, and the much thinner layers

produced, thus allowing for better resolution.

EXAMPLE 20 2 Coffeemaker Design

Alessi Corporation is well known for its high-end
kitchen products. Although it makes products out of
a wide range of materials, it is best known for its
highly polished stainless~steel designs. An example is Lszgzsi” ig;
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the Cupola coffeemaker, a market favorite that was to
be redesigned from the bottom up while preserving
the general characteristics of the established design.
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Alessi engineers used Multijet modeling to 7 ,;::£l{£%l gif .1S??EZ????§Z2i“ ‘Vi
produce prototypes of components of the coffeemaker,
as shown in Fig. 20.7. The prototypes allowed
engineers to evaluate the ease and security of
mechanical assembly, but a significant effort was
expended on the design of the coffeemaker’s lip in
order to optimize the pouring of coffee. A large
number of lip prototypes were constructed and FIGURE 20.7 Coffeemaker prototypes produced through
evaluated to obtain the most robust and aesthetically Multijet modeling and final product. Source: Courtesy Alessi
pleasing design. The ability to compare physical Corporation and 3D Systems, Inc.
prototypes to the existing product was deemed
essential to evaluating the designs. After a final design translated into cost savings, as well as assuring timely
was selected from the numerous prototypes produced, market launch of the redesigned product.
it was found that a 5-6-week time savings was
achieved in product development. The time savings Source: Courtesy Alessi Corporation and 3D Systems, Inc.

20.3.4 Selective Laser Sintering
Selective laser sintering (SLS) is a process based on the sintering of nonmetallic
or (less commonly) metallic powders selectively into an individual object. The
basic elements in this process are shown in Fig. 20.8. The bottom of the processing