Technical Seminar Rapid Pro to Typing Harish
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Transcript of Technical Seminar Rapid Pro to Typing Harish
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RAPID PROTOTYPING
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Abstract
Rapid prototyping is the automatic construction of
physical objects using solid freeform fabrication. The firsttechniques for rapid prototyping became available in the late 1980s
and were used to produce models and prototype parts. Today, theyare used for a much wider range of applications and are even used
to manufacture production quality parts in relatively smallnumbers. Some sculptors use the technology to produce complex
shapes for fine arts exhibitions. Rapid prototyping takes virtual
designs from computer aided design (CAD) or animation modelingsoftware, transforms them into thin, virtual, horizontal cross-sections and then creates each cross-section in physical space, one
after the next until the model is finished. It is a WYSIWYG (WhatYou See Is What You Get) process where the virtual model and thephysical model correspond almost identically. This paper is a
presentation of application of nanotechnology in rapid prototyping.This paper has an emphasis on future applications of
nanotechnology in creation of models in rapid prototyping. Inresponse to these is a proposal to project wide scale applications of
nanotechnology in creative designing process.
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CONTENTS
CONTENTS PAGE NO
1. RAPID PROTOTYPING1
1.1. INTRODUCTION1
1.2. STEREOLITHOGRAPHY...... 21.3. SELECTIVE LASER SINTERING.3
1.4. FUSED DEPOSITION MODELLING...4
1.5. LAMINATED OBJECT MANUFACTURING...51.6. THREE DIMENSIONAL PRINTING.6
2. APPLICATIONS..7
3. FUNCTIONAL PARTS AND TOOLS FROM RAPIDPROTOTYPING.8
3.1. INTRODUCTION..83.2. INDIRECT OR SECONDARY PROCESSES.8
3.3.DIRECT FABRICATION PROCESS..83.4. INVESTMENT CASTINGS.8
3.5. INDIRECT OR SECONDARY PROCESSES THATUTILIZE RP GENERATED PATTERNS...9
3.6. DIRECTED FABRICATION OF INVESTMENTPATTERN9
3.7. SAND CASTING .9
4. MEDICAL APPLICATIONS OF RAPID PROTYPING.10
5. RAPID PROTYPING EQUIPMENTS..11
5.1. SLA-3500.11
5.2. SLA VIPER Si2.. 11
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INTRODUCTION
Rapid prototyping is the most common name given to ahost of related technologies that are used to fabricate physical
objects directly from CAD data source. These methods areunique in that they add and bond materials in layers to form
objects. The general also knows such systems names freeformfabrication (FFF), solid freeform fabrication (SFF) and layeredmanufacturing. Todays additive technologies offer advantages in
many applications compared to classical subtractive fabricationmethods such as milling or turning:
Objective can be formed with any geometric complexity
or intricacy with out the need for elaborate machine set up orfinal assembly; Rapid prototyping systems reduce theconstruction of complex objects to a Manageable,
straightforward, and relatively fast process. This has resulted intheir wide use by engineers as away to reduce time to market inmanufacturing, to better understand and communicate product
designs, and to make rapid tooling to manufacture those products.Surgeons, architects, and individuals from many other disciplines
also routinely use the technology.
Rapid prototyping isnt a solution to every part
fabrication problem.
After all, CNC technology is economical, widelyunderstood and available, offers wide material selection and
excellent accuracy. However, if the requirement involvesproducing a part or object of even moderately complex geometry,and doing so quickly - RP has the advantage. Its very easy to
look at extreme cases and make a determination of whichtechnology route to pursue, CNC or RP. For many other extreme
classes the selection crossover line is hazy, moves all the time,
and depends on a number of variably weighted, case dependantfactors. While the accuracy of prototyping isnt generally as
good as CNC, its adequate today for a wide range of exactingapplications.
At any rate, numerous secondary processes are availableto convert patterns made in a rapid prototyping process to final
materials or tools. The names of specific processes themselvesare also often used as synonyms for entire field. Among these is
stereo lithography (SLA for stereo lithography apparatus).Selective laser sintering (SLS), fused deposition modeling
(FDM), laminated object manufacturing (LOM), inkjets systems
and three dimensional printing (3DP). Each of these
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technologies- and many others has its singular strengths andweakness.
STEREOLITHOGRAPHY
Stereo lithography is the most widely used rapid
prototyping technology. Streolithography builds plastic parts or
objects a layer at a time by tracing a laser beam on the surface ofa vat of liquid photopolymer. This class of materials originally
develops for the printing and packaging industries, quicklysolidifies wherever the laser beam strikes the surface of the
liquid. Once one layer is completely traced, its lowered a smalldistance into the vat and a second layer is traced right on top ofthe first .the self adhesive property of the material causes the
layers to bond to one another and eventually from a complete,three dimensional object after many such layers are formed.
Some objects have overhangs or undercuts, which must
be supported during the fabrication process by support structures.These are either manually or automatically designed or fabricatedright along with the object. Upon completion process, the object
is elevated from the vat and the supports are cut off.
Stereo lithography generally is considered to provide the
greatest accuracy and best surface finish of any rapid prototypingtechnology. Over the years, a wide range of materials with
properties mimicking those of several engineering thermoplasticshas been developed. Limited selectively color changing materialsfor biomedical and other applications are available, and ceramic
materials are currently being developed .the technology is alsonotable for the large object sizes that are possible. On the
negative side, working with liquid materials can be messy andparts often require a post-curing operation in a separate oven-likeapparatus for complete cure and stability. Recently, inject
technology has been extended to operation with photopolymersresulting in systems that have both fast operation and good
accuracy.
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SELECTIVE LASER SINTERING
Thermoplastic powder is spread by a roller the surface ofa build cylinder .the piston in the cylinder moves down one
object layer thickness to accommodate the new layer of powder
.the powder deliver system is similar in function to the build
cylinder. Here, a piston moves upward incrementally to supply a
measured quantity of powder for each layer.
A laser beam is then traced over the surface of this
tightly compacted powder to selectively melt and bond it to form
a layer of the object. The fabrication chamber is maintained at a
temperature just below the melting point of the powder so that
heat form the laser needs only elevate the temperature slightly to
cause sintering. This greatly speeds up the process. The process
is the entire object is fabricated. After the object is fully formed,
the piston is raised to elevate it. Excess powder is simply brushed
away and final manual finishing may be carried out. No supports
are required with this method since overhangs and the solid
powder bed supports undercuts.
SLS offers the key advantage of making functional parts
in essentially final materials. However, the system is
mechanically more complex than stereo lithography and most
other technologies .a variety of thermoplastic materials such as
nylon and polystyrenes are available. Surface finishes and
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accuracy are not quite as good as with stereo lithography, but
material properties can be quite close to those of the intrinsic
materials .the method has also been extended to provide direct
fabrication of metal and ceramic objects and tolls. Since the
objects are sintered they are porous .it may be necessary to
infiltrate the part especially metals, with another material to
improve mechanical characteristics.
FUSED DEPOSITION MODELLING
FDM is the second most widely used prototyping
technology, after stereo lithography. A plastic filament is UN
from coil and supplies material to an extrusion nozzle is heated to
melt the plastic and has a mechanism, which allows the flow of
the melted plastic to be turned on and off. The nozzle is mounted
to a mechanical stage, which can be moved in both horizontal
and vertical directions. As the nozzle is moved over the e table
required geometry, it deposits a thin bead of extruded plastic to
form each layer .the plastic hardness immediately after being
squirted from the nozzle and bonds to the layer bellow .the entire
system is contained within a chamber which is held at a
temperature just below the melting point of the plastic. Several
materials are available for the process including ABS and
investment casting wax. ABS offers good strength, and more
recently polycarbonate and polysuflone materials have beenintroduced which extended the capabilities of the further items of
strength and temperature range. Support structures are fabricated
for overhanging geometries and are later removed by breaking
them away from the object. Water solvable support material,
which can simpled be washed away is also available. The method
is office-friendly and quiet. FDM is fairly for small parts on the
order of a few cubic inches, or those that have tall, thin form-
factors it can very slow for parts with wide cross sections,
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however. The finish of parts produced with the method have been
greatly improved over the years, but arent quiet on a par with
stereo lithography. The closest competitor to the FDM process is
probably three-dimensional printing. However, FDM offers
greater strength and a wider range of materials than at least the
implements of 3DP from crop. Which are most closely
comparable.
LAMINATED OBJECT MANUFACTURING
Profile of object cross sections are paper or other web
material using a laser. The paper is unwound from a feed roll intothe stack and first bonded to the previous layer using a heated
roller, which melts a plastic coating on the bottom side of the
paper. The profiles are then traced by an optics system that is
mounted to an X-Y stage. After cutting of the layer is complete,
excess paper cut away to separate the layer from the web. Waste
paper is wound on take up roll. The method is self-supporting for
overhangs and under cuts. Areas of cross sections which are ton
be removed in the final object are heavily cross hatched with the
laser to facilities removal .it can be time consuming to remove
extra material for some geometries, however.
Variation on this method has been developed by many
companies and researched groups. For e.g. kiras paper
lamination technology (PLT) uses a knife to cut each layer
instead of a laser and applies adhesive to bond layers using the
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xerographic process. There also variations which seek to increase
speed and or material versatility by cutting edges of thick layers
diagonally to avoid stair stepping. In general, the finish, accuracy
and stability of paper objects are not as good as for materials
used with other RP methods. However, material costs are very
low; objectives have the look and feel of wood and can be
worked and finished in the same manner. This has fostered
applications such as patterns for sand castings. While there are
limitations on materials, work has been done with plastics,
composites, ceramics and metals. Some of these materials are
available on a limited commercial basis. The principal
commercial provider of LOM systems, Helisys ceased operation
in 2000. However there are several other companies with either
similar LOM technology or in yearly commercial stages. These
companies are addressing market segments ranging from concept
modeling to very objects for architectural applications.
THREE DIMENSIONAL PRINTING
Three-dimensional printing was developed at MIT. Its
often used as a direct manufacturing process as well as for rapid
prototyping. The process starts by depositing a layer of powder
objects material at the top of a fabrication chamber. To
accomplish this, a measured quantity of powder is first dispensed
from a similar supply chamber by moving a piston upward
incrementally. The roller then distributes and compresses the
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powder at the top of the fabrication chamber. Multi channel
jetting head subsequently deposits a liquid adhesives in a two
dimensional pattern onto the powder which becomes bonded in
the areas where the adhesive is deposited, to form a layer of the
objects.
Once a layer is completed, the fabrication piston moves
down by the thickness of a layer, and the process is repeated until
the entire objects is elevated and the extra powder brushed away
leaving a green objects. No external supports are required
during fabrication since the powder bed supports overhangs
Three-dimensional printing offers the advantages of speedy
fabrication and low materials cost. In fact, its probably the
fastest of all RP methods. Recently color output has also become
available. However there are limitations on resolution surface
finish part fragility and available materials. The closest
competitor to this process is probably fused depositing modeling.
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APPLICATIONS
RAPID PROTYPING IN FINE ARTS,ARCHITECTURE AND JEWELRY AND
INDUSTRIAL DESIGN
FINE ARTS
Today, layered fabrication is being used by an increasing
number of artists to build a wide variety of sculpture objects.
some of these works are realistic and representational while other
are abstract .the abstract objects can be the result of pure
imagination and artistic free will, or may be derived solely from
mathematics or computation. Some of the works created with
rapid prototyping may not have been possible to make any other
way.
JEWELRY DESIGN
Jewelry and the related arts have been particularly affected
.some system manufacturers, such as Meiko in Japan and solids
cape in the US, have concentrated on this application. There are
also service bureaus and university programs which emphasize
the design and manufacture of jewelry using rapid prototyping
system is most often used as a pattern for lost-wax or others types
of castings methods in jewelry manufacture. Direct manufacture
of jewelry is also a long-term possibility, however. While
precious materials are not yet possible for directed output, a few
artists are beginning to explore the use of the existing materials
of processes such as selective lasers sintering and stereo
lithography as final media.
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INDUSTRIAL DESIGN AND ARCHITECTURAL
MODELING
There is some interesting work going on in the industrial
design field, but it will require higher resolution and more
aesthetically pleasing output before rapid prototyping makes
substantial inroads. There is probably more interest in
architectural modeling at present where some complex post
modernist building forms, for example, those of the American
architect. Franck Ghery, are more faithfully and easily
represented than they could be using traditional model
construction methods.
FUNCTIONAL PARTS AND TOOLS FROM RAPID
PROTOTYPING
INTRODUCTIONParts made by rapid prototyping systems may be used
directly in many final applications today. This was not true just a
short a while ago and reflects grate strides in material researchthat have been spurred by instant market forces. Rapid
prototyping generated parts may well offered a direct solution tothe application problem with material requirements ranging fromceramics, to steel or titinaum. However, even the fastest RP
systems are still far too slow and limited in other ways: theysimply cant produce parts in a wide enough range of materials, at
a fast enough rate, to match the enormous spectrum of
requirements of industry. Convention processes such as moldingand casting are still the only means available to do that, but RP is
often or the starting point for making theses manufacturingprocesses faster, cheaper and better. Rapid prototyping is used in
two ways to accomplish this: molds may be directly fabricated byan RP system, or RP-generated parts can be used as patterns forfabricating a mould through so called indirect or secondary
processes.
INDIRECT OR SECONDARY PROCESSESAlthough the properties of RP material improve and
expand continuously a limit less array of applications means that
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there will always be a need to transfer parts formed a materialused in a RP process into yet another material. In addition, its
usually necessary to use very specific materials as the basis ofmost tool fabrication processes. Consequently numerous transfer
technologies have been developed typically a part made by the
RP systems is used as pattern or model in this processes. Whilemore than two dozen of them are in various stages of
development, just a few common and commercial importanttoday.
DIRECT FABRICATION PROCESSESSpecialized rapid proto typing processes have been
developed to meet specific applications and material requirementfor molding and castings. These may be forms of basic RP
processes, such as stereo lithography or selective laser sinteringor may be unique RP methods developed for a specificapplication. As in the case of indirect or secondary processes,
there are a large number of technologies begin explored but onlya few are commercially important today.
INVESTMENT CASTINGSNumerous RP technologies are appropriate for use as
investment castings patterns. These materials displacement-
casting methods are among the first industrial processes everdeveloped and are thousands of years old. The casting produce
can be exquisitely detailed and intricate. Bees wax was the firstmaterial used for patterns to produce stunningly detailed good
jewelry. More environmentally and socially conscious jewelry is
a significant application of rapid proto typing generated castingpatterns even today. There are numerous applications in industry
where parts are produced in a variety of metals with castingweighing up to several hundred pounds.
These processes typically involves thickly coating orinvesting a pattern which is made of a material that melts or
burns out easily with a material such as ceramic, which doesnt.
The pattern may be extended to provide a gate into which metalin a hot, liquid state poured. Passageways are also provided to
allow melted or burned pattern material and air to escape. Theinvested pattern is then fired in furnaces to burn out or melt the
pattern and fuse the ceramics into a strong hallow mold. Moltenmetal is then poured into the ceramic mould. After the metalcools and hardens the mould is broken away to reveal the final
object. Extra gate material is cut off and usually the parks willrequire substantially finish machining and clean up
INDIRECT OR SECONDARY PROCESSES THAT
UTILIZE RP GENERATED PATTERNS
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RP generated patterns can be obtained from fused
deposition modeling (FDM) in wax, selective laser sintering(SLS) in polystyrene or other plastics and inkjet technology in
wax like plastics. These materials may be melted or burned of the
investment very cleanly the patterns from these processes tend tobe small to medium in size and especially for inkjets, offer the
highest resolution and detailStereo lithography is also used to be produced patterns for
investment casting but the photo polymer materials used in thatprocess are more difficult to burn out than the materials used inother mentioned above and also have a tendency to expand and
crack the mould. To get around these problems, 3D systems haveproduced a special build style for this application with the trade
name quick cast. The RP generated patterns is built in hallow thinsections which tend to crumple during burn out rather than
expand and also results in a smaller mass of pattern materialremove the process has been developed over a number of years ina partner ship with large foundry companies and costumers.
A laminated object manufacturing (LOM) has also beenused for investment casting all though a more typical application
is for sand casting. The paper material used in the LOM processis said to some times be difficult to remove completely from the
mould although this is probably a strong function of theparticular geometry being produced
DIRECTED FABRICATION OF INVESTMENT
PATTERNSSoligen is a license of MITS 3D printing process and uses
it to produce investments directly with out patterns at all. Binderis deposited to bond a bed of ceramic powder in layer wise across
section to sequentially build up the investment. Extra powder isbrushed and vacuumed from the green part, which is fired to
consolidate it in a process similar to a convectional burned out.Soligen is vertically integrated to produce the final parts in itsown foundry
SAND CASTINGThe sand casting processes start by tightly compacting
fine, moist foundry sand in a box- like frame around the pattern
which is typically made of wood. The pattern is removed fromthe sand to leave a cavity into which the molten metal is poured.Once the metal cools and hardens its removed from the sand
which is then recycled as with investment casting it may benecessary to remove the extra material and perform finish
machining and cleanup.9
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MEDICAL APPLICATIONS OF RAPID
PROTYPING
Rapid prototyping is impacting medicine in several
important ways. Perhaps the most obvious application is as a
means to design, develop and manufacture medical devices and
instrumentation. This is simply an out growth of recognized
engineering applications of the technology. Any field where its
imperative to decrease product development time to while
simultaneously providing users with functional performance fed
back is an excellent prospect for rapid prototyping it there fore
follows that since human lives depend on the quality and ease of
use of numerous medical products there is a extra incentive to use
rapid prototyping in there development. E.g. of medical
instruments designed using the technology include reactors
scalpels surgical fasteners display system and many other
devices. Rapid prototyping technology is also being used to
fabricate drug dosage forms, which would be difficult if not
impossible to make any other way. Its possible to fabricate pills
with prcised and complex time release characteristics or that
dissolves almost instantly. Medication can be made more
effective and safer in this way, drug companies may be able to
realize stronger revenue streams from older compounds with
expired patience by providing them in novel and beneficialdosage forms.
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RAPID PROTYPING EQUIPMENTS
SLA VIPER Si2
Our latest addition to the lab the viper enables us toachieve small features with its dual laser spot capability: 0.003
inch and 0.01 inch laser spot sizes. The viper also embodies 3Dsystem latest machine design approaches to maximizeproductivity and useful ness installed new in the RPMI in
October 2001.
SLA-3500With its solid state laser, automatic resin dispensing system,
Zephyr recoated, smart sweep, large build envelope, and 0.002-
0.006 layer resolution, the SLA 3500 lets us do more and do itbetter we especially like its large build envelope of 14x14x16
inches for large parts. Installed new in the RPMI in august 1999