07 FINAL RAPID PROTOTYPE REPORT.doc

8/19/2019 07 FINAL RAPID PROTOTYPE REPORT.doc

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RAPID PROTOTYPE 2014-15

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.

Department of Mechanical Engineering, AIT, Tumkur Page 1


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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.

Department of Mechanical Engineering, AIT, Tumkur Page !


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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.

Department of Mechanical Engineering, AIT, Tumkur Page 1#


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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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07 FINAL RAPID PROTOTYPE REPORT.doc

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