07 final rapid prototype report.doc
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CHAPTER - 01
INTRODUCTION
The past decade has witnessed the emergence of new manufacturing technologies that
build parts on a layer-by-layer basis. Using these technologies, manufacturing time for parts
of virtually any complexity is reduced considerably. In other words, it is rapid.
Rapid Prototyping Technologies and Rapid anufacturing offer great potential for
producing models and uni!ue parts for manufacturing industry. Thus, the reliability of
products can be increased" investment of time and money is less ris#y. $ot everything that is
thin#able today is already wor#able or available at a reasonable price, but this technology is
fast evolving and the better the challenges, the better for this developing process.
1.1 Overview of Rapid Proo!pe
The term Rapid prototyping %RP& refers to a class of technologies that canautomatically construct physical models from 'omputer-(ided )esign %'()& data. It is a
free form fabrication techni!ue by which a total ob*ect of prescribed shape, dimension and
finish can be directly generated from the '() based geometrical model stored in a computer,
with little human intervention. Rapid prototyping is an +additive+ process, combining layers
of paper, wax, or plastic to create a solid ob*ect. In contrast, most machining processes
%milling, drilling, grinding, etc.& are +subtractive+ processes that remove material from a solid
bloc#. RPs additive nature allows it to create ob*ects with complicated internal features that
cannot be manufactured by other means.
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In addition to prototypes, RP techni!ues can also be used to ma#e tooling %referred to
as rapid tooling& and even production-!uality parts %rapid manufacturing&. or small
production runs and complicated ob*ects, rapid prototyping is often the best manufacturing
process available. f course, +rapid+ is a relative term. ost prototypes re!uire from three to
seventy-two hours to build, depending on the si/e and complexity of the ob*ect. This may
seem slow, but it is much faster than the wee#s or months re!uired to ma#e a prototype by
traditional means such as machining. These dramatic time savings allow manufacturers to
bring products to mar#et faster and more cheaply.
CHAPTER " 02
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PROCE## O$ RAPID PROTOTYPE
2.1 T%e &a'i( Pro(e''
(lthough several rapid prototyping techni!ues exist, all employ the same basic five-step
process. The steps are0
1. 'reate a '() model of the design
2. 'onvert the '() model to 3T4 format
5. 3lice the 3T4 file into thin cross-sectional layers
6. 'onstruct the model one layer atop another
7. 'lean and finish the model
2.1.1 CAD )ode* Creaio+,
irst, the ob*ect to be built is modeled using a 'omputer-(ided )esign %'()&
software pac#age. 3olid modelers, such as Pro89$:I$99R, tend to represent 5-) ob*ects
more accurately than wire-frame modelers such as (uto'(), and will therefore yield better
results. The designer can use a pre-existing '() file or may wish to create one expressly for
prototyping purposes. This process is identical for all of the RP build techni!ues.
2.1.2 Co+ver'io+ o #T $ora,
The various '() pac#ages use a number of different algorithms to represent solid
ob*ects. To establish consistency, the 3T4 %3tereolithography, the first RP techni!ue& format
has been adopted as the standard of the rapid prototyping industry. The second step, therefore,
is to convert the '() file into 3T4 format. This format represents a three-dimensional
surface as an assembly of planar triangles, +li#e the facets of a cut *ewel.+;
The file contains
the coordinates of the vertices and the direction of the outward normal of each triangle.
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designer must balance accuracy with manageability to produce a useful 3T4 file. 3ince the
3T4 format is universal, this process is identical for all of the RP build techni!ues.
2.1./ #*i(e %e #T $i*e,
In the third step, a pre-processing program prepares the 3T4 file to be built. 3everal
programs are available, and most allow the user to ad*ust the si/e, location and orientation of
the model. mm thic#, depending on the build techni!ue. The
program may also generate an auxiliary structure to support the model during the build.
3upports are useful for delicate features such as overhangs, internal cavities, and thin-walled
sections. 9ach PR machine manufacturer supplies their own proprietary pre-processing
software.
2.1.4 a!er ! a!er Co+'r(io+,
The fourth step is the actual construction of the part. Using one of several techni!ues
%described in the next section& RP machines build one layer at a time from polymers, paper,
or powdered metal. ost machines are fairly autonomous, needing little human intervention.
2.1.5 C*ea+ a+d $i+i'%,
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The final step is post-processing. This involves removing the prototype from the
machine and detaching any supports. 3ome photosensitive materials need to be fully cured
before use. Prototypes may also re!uire minor cleaning and surface treatment. 3anding,
sealing, and8or painting the model will improve its appearance and durability.
CHAPTER " 0/
RAPID PROTOTYPIN TECHNI3UE#
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ost commercially available rapid prototyping machines use one of six techni!ues.
(t present, trade restrictions severely limit the import8export of rapid prototyping machines,
so this guide only covers systems available in the U.3.
/.1 #ereo*i%orap%!
Patented in 1?@;, 3tereolithography started the rapid prototyping revolution. The
techni!ue builds three-dimensional models from li!uid photosensitive polymers that solidify
when exposed to ultraviolet light. (s shown in the figure below, the model is built upon a
platform situated *ust below the surface in a vat of li!uid epoxy or acrylate resin. ( low-
power highly focused UA laser traces out the first layer, solidifying the models cross section
while leaving excess areas li!uid.
$ire /.1, #(%eai( diara of #ereo*i%orap%!.
$ext, an elevator incrementally lowers the platform into the li!uid polymer. (
sweeper re-coats the solidified layer with li!uid, and the laser traces the second layer atop the
first. This process is repeated until the prototype is complete. (fterwards, the solid part is
removed from the vat and rinsed clean of excess li!uid. 3upports are bro#en off and the
model is then placed in an ultraviolet oven for complete curing.
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3tereolithography (pparatus %34(& machines have been made since 1?@@ by 5)
3ystems of Aalencia, '(. To this day, 5) 3ystems is the industry leader, selling more RP
machines than any other company.
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$ire /.2, #(%eai( diara of *ai+aed oe( a+fa(ri+.
Belisys developed several new sheet materials, including plastic, water-repellent
paper, and ceramic and metal powder tapes. The powder tapes produce a +green+ part that
must be sintered for maximum strength. (s of 2==1, Belisys is no longer in business.
/./ #e*e(ive a'er #i+eri+
)eveloped by 'arl )ec#ard for his masters thesis at the University of Texas,
selective laser sintering was patented in 1?@?. The techni!ue, shown in igure 5, uses a laser
beam to selectively fuse powdered materials, such as nylon, elastomer, and metal, into a solid
ob*ect. Parts are built upon a platform which sits *ust below the surface in a bin of the heat-
fusable powder. ( laser traces the pattern of the first layer, sintering it together. The platform
is lowered by the height of the next layer and powder is reapplied. This process continues
until the part is complete. 9xcess powder in each layer helps to support the part during the
build. 343 machines are produced by )T of (ustin, TC.
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$ire /./, #(%eai( diara of 'e*e(ive *a'er 'i+eri+.
/.4 $'ed Depo'iio+ )ode*i+
In this techni!ue, filaments of heated thermoplastic are extruded from a tip that moves
in the x-y plane. 4i#e a ba#er decorating a ca#e, the controlled extrusion head deposits very
thin beads of material onto the build platform to form the first layer. The platform is
maintained at a lower temperature, so that the thermoplastic !uic#ly hardens. (fter the
platform lowers, the extrusion head deposits a second layer upon the first. 3upports are builtalong the way, fastened to the part either with a second, wea#er material or with a perforated
*unction.
3tratasys, of 9den Prairie, $ ma#es a variety of ) machines ranging from fast
concept modelers to slower, high-precision machines. aterials include (
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$ire /.4, #(%eai( diara of f'ed depo'iio+ ode*i+.
/.5 #o*id ro+d Cri+
)eveloped by 'ubital, solid ground curing %3:'& is somewhat similar to
3tereolithography %34(& in that both use ultraviolet light to selectively harden photosensitive
polymers. Unli#e 34(, 3:' cures an entire layer at a time. igure 7 depicts solid ground
curing, which is also #nown as the solider process. irst, photosensitive resin is sprayed on
the build platform. $ext, the machine develops a photomas# %li#e a stencil& of the layer to be
built. This photomas# is printed on a glass plate above the build platform using an
electrostatic process similar to that found in photocopiers. The mas# is then exposed to UA
light, which only passes through the transparent portions of the mas# to selectively harden the
shape of the current layer.
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$ire /. 5, #(%eai( diara of 'o*id ro+d (ri+.
(fter the layer is cured, the machine vacuums up the excess li!uid resin and sprays
wax in its place to support the model during the build. The top surface is milled flat, and then
the process repeats to build the next layer. Dhen the part is complete, it must be de-waxed by
immersing it in a solvent bath. 3:' machines are distributed in the U.3. by 'ubital (merica
Inc. of Troy, I. The machines are !uite big and can produce large models.
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CHAPTER " 04
APPICATION# O$ RAPID PROTOTYPIN
4.1 APPICATION#
Rapid prototyping is widely used in the automotive, aerospace, medical, and consumer
products industries
4.1.1 E+i+eeri+
The aerospace industry imposes stringent !uality demands. Rigorous testing and
certification is necessary before it is possible to use materials and processes for the
manufacture of aerospace components. Eet,
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ear impression is scanned and digiti/ed with an extremely accurate 5-) scanner. 3oftware
specially developed for this converts the digital image into a virtual hearing instrument
shell .Than#s to the accuracy of the process, instrument shells are produced with high
precision and reproducibility. This means the hearing instruments fit better and the need for
rema#es is reduced. In the case of repairs, damage to or loss of the IT9 instrument, an
absolutely identical shell can be manufactured !uic#ly, since the digital data are stored in the
system.
4.1.4 Ar' a+d Ar(%aeo*o!
3elective 4aser 3intering with marble powders can help to restore or duplicate ancient
statues and ornaments, which suffer from environmental influences. The originals are
scanned to derive the 5) data, damages can be corrected within the software and the
duplicates can be created easily. ne application is duplicating a statue. The original statue
was digiti/ed and a smaller model was produced to serve a base
for a bron/e casting process.
4.1.5 Rapid Too*i+
( much-anticipated application of rapid prototyping is rapid tooling, the automaticfabrication of production !uality machine tools. Tooling is one of the slowest and most
expensive steps in the manufacturing process, because of the extremely high !uality re!uired.
Tools often have complex geometries, yet must be dimensionally accurate to within a
hundredth of a millimeter. In addition, tools must be hard, wear-resistant, and have very low
surface roughness %about =.7 micrometers root mean s!uare&. To meet these re!uirements,
molds and dies are traditionally made by '$'-machining, electro-discharge machining, or by
hand. (ll are expensive and time consuming, so manufacturers would li#e to incorporate
rapid prototyping techni!ues to speed the process.
4.2 Rapid Proo!pe v6' Co+ve+io+a* e(%+o*oie'
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RPT does notGand will notGreplace completely conventional technologies such $'
and high-speed milling, or even hand-made parts. Rather, one should regard RPT as one more
option in the tool#it for manufacturing parts. igure 16 depicts a rough comparison between
RPT and milling regarding the costs and time of manufacturing o+e part as a function of part
complexity1=. It is assumed, evidently, that the part can be manufactured by either
technology such that the material and tolerance re!uirements are met.
4./ Adva+ae'
1. 3trength, 9lasticity and Temperature Resistance.2. Typical !uantities
5. 3tandard accuracy
6. Time 3avings
7. 3urface structure
;. 'ost
>. Use any type of model
CHAPTER - 05
CONCU#ION
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inally, the rise of rapid prototyping has spurred progress in traditional subtractive
methods as well. (dvances in computeri/ed path planning, numeric control, and machine
dynamics are increasing the speed and accuracy of machining. odern '$' machining
centers can have spindle speeds of up to 1==,=== RP, with correspondingly fast feed rates.
56 3uch high material removal rates translate into short build times. or certain applications,
particularly metals, machining will continue to be a useful manufacturing process. Rapid
prototyping will not ma#e machining obsolete, but rather complement it.
RE$ERENCE#
1. www.rapidprototyping processes.html
2. www.mcpgroup.com
5. www.me.psu.edu
6. www.alphaform.com
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