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8/2/2019 Edited Paper

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Recent trends in Rapid Prototyping technology

Shashi Kiran.M

Department of Mechanical Engineering, S.J.C. Institute of Technology, [email protected]

Abstract---Global competition, customer-drivenproduct customization, accelerated product

obsolescence and continued demands for cost savings

are forcing companies to look for new technologies to

improve their business processes and speed up the

product development cycle. The competition in the

world market for manufactured products has

intensified tremendously in recent years. It has become

important, if not vital, for new products to reach the

market as early as possible, before the competitors.

The term "rapid prototyping" is a relatively new

expression for the generation of three-

dimensional models manufactured without the

need for machining or tooling.

Keywords--- StereoLithography, FDM, LOM, SLS.

I. IntroductionProduction of models by machining has a number of

limitations:-

1. Material removed during forming is difficult to

reclaim.2. Machining, in the form of drilling, turning,

milling, spark erosion etc., is limited by the

shapes it can produce.

3. In the event of design change conventional

tooling such as patterns, core boxes, dies, jigs

etc., become expensive to alter and, in many

cases, may require complete re-manufacture.

Rapid prototyping differs by:-

Adding material layer by layer until the

desired shape is achieved, immediately reducing

or avoiding the loss of material. Cutting out the

conventional draftsperson, patternmaker and in

some situations even the moulder. The system

goes a long way towards reducing time taken andcost and improving accuracy.

The principle advantages of using this technology are:

-

1. Speed at which the solid model is generated.

2. The complexity of the model does not form any

limitations to its production.

3. The early use of these models was to assist the

designer in determining fit and form. It also

provided the sales team with a 3 dimensional

object to show to a prospective customer, this

being far better than the traditional orthographic

drawing which many people find difficult to

interpret.

4. Concept modeling

5. Aesthetic

6. To make an impossible object.


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II. PrototypingIn many situations, especially those involving cutting-edge

technology, new designs have unanticipated problems that

are difficult to predict by modeling or simulations. When

the performance of a new device is uncertain, an early

development of a prototype can be useful for testing keyfeatures of the design, exploring design alternatives,

testing theories, and conforming performance prior to

starting production. Prototyping is typically an iterative

process, in which a series of products will be designed,

constructed, and tested to progressively refine the final

design. It is thus essential to minimize the latency of each

prototyping cycle so that projects adhere to the original

design schedules. A typical prototyping flow of a high-

performance embedded signal processor begins with a

design phase in which the desired system capability is

analyzed to determine hardware and softwarerequirements. Next, in the implementation phase, the

signal processing software and appropriate computational

hardware are developed accordingly.

Figure 1. Types of prototypes described along the

three aspects of implementation, form and

approximation


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III. HistoryTable 2: Parallels between geometric

modeling and prototyping


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Consumer product manufacturers find value in

having tangible models of their proposed products to

show to customers.

IBM used SLA to produce operating displayunits of its ThinkPad tablet computer for the

annual COMDEX show.

Key Tronics, who manufacture computerkeyboards, create physical parts for customerapproval.

Logitech, the worlds largest manufacturerof pointing devices, was asked, by a "blue

chip computer company" to quote on a

unique two-button mouse; in less than two

weeks from the initial request Logitechs

team returned with a functional SLA

prototype. The customers reaction was one

of disbelief '. Part quality was so superior

that the computer giant awarded the contracton the spot. It is thought that this single

order paid for the SLA system.

Coca-Cola used RP to design the nostalgic(coke bottle) curves into a contemporary 20

ounce plastic Coke bottle.

In rapid prototyping the term 'rapid is used

relatively. The reality is that the generation of the

desired model with available methods andprocedures can talk many hours or even stretch to a

number of days in tandem with the method adopted

as well as the size and the complexity of the desired

model. The term rapid is thus used in a relative

sense considering that the additive technologies can

in some instance be produced desired models in

hours but again it will depend on the type of a

machine being used, the size of model in focus as

well as the number of models to be generated

simultaneously in cases of multiple model

production. Convectional injection molding is

known to be more cost effective especially in

manufacturing polymer products in large volumes.

On the other end additive technology is also known

to be speedy and cost effective in the cases where

there is a production of relatively small quantities of

parts. The remarkable merit of rapid prototyping is

that it has enabled designers as well theme or

concept modeling teams to generate components or

parts as well concepts representations by use of

convenient and portable desktop size printers.Printing and design technologies abound in the

market yet rapid prototyping cashes in on the merits

of cost effectiveness and speedy print output and


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premium quality, which give designers and concept

developers the real sense, and representation of their

design models.

Common to all the different techniques of RP is the basic

approach they adopt, which can be described as follows:

A model or component is modeled on aComputer-Aided Design/Computer-Aided

Manufacturing (CAD/CAM) system. The model

which represents the physical part to be built must

be represented as closed surfaces which

unambiguously define an enclosed volume. This

means that the data must specify the inside,

outside and boundary of the model. This

requirement will become redundant if the

modeling technique used is solid modeling. This

is by virtue of the technique used, as a valid solid

model will automatically be an enclosed volume.

This requirement ensures that all horizontal cross

sections that are essential to RP are closed curves

to create the solid object.

The solid or surface model to be built is nextconverted into a format dubbed the STL

(STereoLithography) file format which originatesfrom 3D Systems. The STL file format

approximates the surfaces of the model by

polygons. Highly curved surfaces must employ

many polygons, which mean that STL files for

curved parts can be very large. However, there are

some rapid prototyping systems which also accept

IGES (Initial Graphics Exchange Specifications)

data, provided it is of the correct flavor.

A computer program analyzes a STL file thatdefines the model to be fabricated and slices the

model into cross sections. The cross sections are

systematically recreated through the solidification

of either liquids or powders and then combined to

form a 3D model.

Another possibility is that the cross sections are already

thin, solid laminations and these thin laminations are glued

together with adhesives to form a 3D model. Other similar

methods may also be employed to build the model.

IV. BASIC PRINCIPLE OF RAPIDPROTOTYPING PROCESSES

RP process belong to the generative (or additive)

production processes unlike subtractive or forming

processes such as lathing, milling, grinding or coining

etc. In which form is shaped by material removal or

plastic deformation. In all commercial RP processes, the

part is fabricated by deposition of layers contoured in a (x-

y) plane two dimensionally. The third dimension (z)

results from single layers being stacked up on top of each

other, but not as a continuous z-coordinate. Therefore,

the prototypes are very exact on the x-y plane but have

stair-stepping effect in z-direction. If model is deposited

with very fine layers, i.e., smaller z-stepping, model

looks like original. RP can be classified into two

fundamental process steps namely generation of

mathematical layer information and generation of

physical layer model. Typical process chain of various RP

systems is shown in figure 2.


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Figure 2: RP process chain showing fundamental

process steps

It can be seen from figure 2 that process starts with 3D

modeling of the product and then STL file is exported by

tessellating the geometric 3D model. In tessellation

various surfaces of a CAD model are piecewise

approximated by a series of triangles (figure 3) and co-

ordinate of vertices of triangles and their surface normals

are listed. The number and size of triangles are decided by

facet deviation or chordal error as shown in figure 3.

Figure 3: Tessellation of a typical surface of CAD

model

These STL files are checked for defects like flip triangles,

missing facets, overlapping facets, dangling edges or faces

etc. and are repaired if found faulty. Defect free STL files

are used as an input to various slicing softwares. At this

stage choice of part deposition orientation is the most

important factor as part building time, surface quality,amount of support structures, cost etc. are influenced.

Once part deposition orientation is decided and slice

thickness is selected, tessellated model is sliced and the

generated data in standard data formats like SLC (stereo

lithography contour) or CLI (common layer interface) is

stored.

This information is used to move to step 2, i.e., generation

of physical model. The software that operates RP systems

generates laser-scanning paths (in processes like Stereo

lithography, Selective Laser Sintering etc.) or materialdeposition paths (in processes like Fused Deposition

Modeling). This step is different for different processes

and depends on the basic deposition principle used in RP


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machine. Information computed here is used to deposit the

part layer-by-layer on RP system platform. The

generalized data flow in RP is given in figure 4.

Figure 4: Generalized illustration of data flow in RP

The final step in the process chain is the post-processing

task. At this stage, generally some manual operations are

necessary therefore skilled operator is required. In

cleaning, excess elements adhered with the part or supportstructures are removed. Sometimes the surface of the

model is finished by sanding, polishing or painting for

better surface finish or aesthetic appearance. Prototype is

then tested or verified and suggested engineering changes

are once again incorporated during the solid modeling

stage.

V. CLASSIFICATION OF RAPIDPROTOTYPING SYSTEMS

While there are many ways in which one can classify the

numerous RP systems in the market, one of the better

ways is to classify RP systems broadly by the initial form

of its material, i.e. the material that the prototype or part is

built with. In this manner, all RP systems can be easily

categorized into

liquid-based solid-based Powder-based

Liquid-Based

Liquid-based RP systems have the initial form of its

material in liquid state. Through a process commonly

known as curing, the liquid is converted into the solid

state. The following RP systems fall into this category:

1. 3D Systems Stereo lithography Apparatus (SLA)2. Cubitals Solid Ground Curing (SGC)3. Sonys Solid Creation System (SCS)4. CMETs Solid Object Ultraviolet-Laser Printer

(SOUP)

5. Autostrades E-Darts6. Teijin Seikis Soliform System7. Meikos Rapid Prototyping System for the

Jewelry Industry

8. Denkens SLP9. Mitsuis COLAMM10.Fockele & Schwarzes LMS11.Light Sculpting


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12.Aaroflex13.Rapid Freeze14.Two Laser Beams15.Microfabrication

As is illustrated in the RP Wheel, three methods are

possible under the Photo-curing method. The single

laser beam method is most widely used and includes all

the above RP systems with the exception of (2), (11), and

(13) and (14). Cubital (2) and Light Sculpting (11) use the

masked lamp method, while the two laser beam method is

still not commercialized. Rapid Freeze (13) involves the

freezing of water droplets and deposit in a manner much

like FDM to create the prototype.

Solid-Based

Except for powder, solid-based RP systems are meant to

encompass all forms of material in the solid state. In this

context, the solid form can include the shape in the form

of a wire, a roll, laminates and pellets.

The following RP systems fall into this definition:

1. Cubic Technologies Laminated ObjectManufacturing (LOM)

2. Stratasys Fused Deposition Modeling (FDM)3. Kira Corporations Paper Lamination Technology(PLT)4. 3D Systems Multi-Jet Modeling System (MJM)5. Solidscapes ModelMaker and PatternMaster6. Beijing Yinhuas Slicing Solid Manufacturing

(SSM), Melted

7. Extrusion Modeling (MEM) and Multi-FunctionalRPM Systems (M-RPM)

8. CAM-LEMs CL 1009. Ennex Corporations Offset Fabbers

Referring to the RP Wheel, two methods are possible forsolid-based RP systems. RP systems (1), (3), (4) and (9)

belong to the Cutting and Glueing/Joining method, while

the Melting and Solidifying/Fusing method used RP

systems (2), (5), (6), (7) and (8).

Powder-Based

In a strict sense, powder is by-and-large in the solid state.However, it is intentionally created as a category outside

the solid-based RP systems to mean powder in grain-like

form. The following RP systems fall into this definition:

1. 3D Systems Selective Laser Sintering (SLS)2. EOSs EOSINT Systems3. Z Corporations Three-Dimensional Printing

(3DP)

4. Optomecs Laser Engineered Net Shaping (LENS)5. Soligens Direct Shell Production Casting (DSPC)6. Fraunhofers Multiphase Jet Solidification (MJS)7. Acrams Electron Beam Melting (EBM)8. Aeromet Corporations Lasform Technology9. Precision Optical Manufacturings Direct Metal

Deposition (DMDTM)

10.Generis RP Systems (GS)11.Therics Inc.s Theriform Technology12.Extrude Hones Prometal13.TM 3D Printing Process

All the above RP systems employ the Joining/Binding

method. The method of joining/binding differs for theabove systems in that some employ a laser while others

use a binder/glue to achieve the joining effect.


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VI. Some processes:Although there are different RP systems, for thispaper only three of them have been selected which are

widely used nowadays and are having numerous

advantages over others.

1) Fused Deposition Modeling (FDM)Materials used include:-

ABS Medical ABS Investment casting wax Elastomers similar to low and high density

Polyethylene

Polypropylene.In Fused Deposition Modeling (FDM) process a

movable (x-y movement) nozzle on to a substrate

deposits thread of molten polymeric material. The

build material is heated slightly above

(approximately 0.5 C) its melting temperature so

that it solidifies within a very short time

(approximately 0.1 s) after extrusion and cold-welds

to the previous layer as shown in figure 5. Various

important factors need to be considered and are

steady nozzle and material extrusion rates, addition

of support structures for overhanging features and

speed of the nozzle head, which affects the slicethickness. More recent FDM systems include twonozzles, one for part material and other for support

material. The support material is relatively of poor

quality and can be broken easily once the complete

part is deposited and is removed from substrate. In

more recent FDM technology, water-soluble supportstructure material is used. Support structure can be

deposited with lesser density as compared to part

density by providing air gaps between two

consecutive roads.

Figure 5: Fused Deposition Modeling Process

A thermo-polymer is

extruded from a travelling head having a single, fine

nozzle. The head travels in the X axis while the table

or platform travels in the Y axis and descends at

predetermined increments in the Z axis. On leaving

the nozzle the thermo- polymer adheres and hardens

to the previous layer.

2)3)


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2) Laminated Object Manufacturing(LOM)

LOM was developed by Michael Feygin of Helysis.

As the name implies the process laminates thin

sheets of film (paper or plastic), the laser has only to

cut/scan the periphery of each layer and not the

whole surface as in SLA.The build material (paper with a thermo-

setting resin glue on its under side) is stretched froma supply roller across an anvil or platform to a take-

up roller on the other side. A heated roller passes over

the paper bonding it to the platform or previous layer.A laser, focused to penetrate through one thickness of

paper cuts the profile of that layer. The excess paper

around and inside the model is etched into small

squares to facilitate its removal. Meanwhile, this

surplus material provides support for the developing

model during the build process. The process of gluing

and cutting continuous layer by layer until the modelis complete.

Typical system of Laminated Object

Manufacturing (LOM) has been shown in figure 6. It

can be seen from the figure that the slices are cut in

required contour from roll of material by using a 25-50 watt CO2 laser beam. A new slice is bonded to

previously deposited slice by using a hot roller, which

activates a heat sensitive adhesive. Apart from the

slice unwanted material is also hatched in rectangles

to facilitate its later removal but remains in place

during the build to act as supports. Once one slice is

completed platform can be lowered and roll ofmaterial can be advanced by winding this excess onto

a second roller until a fresh area of the sheet lies over

the part. After completion of the part they are sealed

with a urethane lacquer, silicone fluid or epoxy resin

to prevent later distortion of the paper prototype

through water absorption.

Figure 6: Laminated Object manufacturing

Process


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In this process, materials that are relatively cheaper

like paper, plastic roll etc. can be used. Parts of fiber-

reinforced glass ceramics can be produced. Large

models can be produced and the building speed is 5-

10 times as compared to other RP processes. The

limitation of the process included fabrication of

hollow models with undercuts and reentrant features.Large amount of scrap is formed. There remains

danger of fire hazards and drops of the molten

materials formed during the cutting also need to be

removed (Pham and Demov, 2001).To reduce the

build time, double or even triple layers are cut at

one time which increases the size of the steps on

curved surfaces and the post processing necessary to

smooth those surfaces.

Applications of LOM objects:

LOM objects are durable, multilayeredstructures which can be machined, Sanded,

polished, coated and painted.

Used as precise patterns for secondarytooling processes such as rubber moulding,

sand casting and direct investment casting.

Used for limited testing. Used as visual models.

NASA have used the LOM to produce 12 Hot gas

manifold for the shuttle main engine

3) Selective Laser Sintering(SLS)In Selective Laser Sintering (SLS) process, fine

polymeric powder like polystyrene, polycarbonate or

polyamide etc. (20 to 100 micrometer diameter) is spread

on the substrate using a roller. Before starting CO2 laser

scanning for sintering of a slice the temperature of the

entire bed is raised just below its melting point by infrared

heating in order to minimize thermal distortion (curling)and facilitate fusion to the previous layer. The laser is

modulated in such a way that only those grains, which are

in direct contact with the beam, are affected. Once laser

scanning cures a slice, bed is lowered and powder feed

chamber is raised so that a covering of powder can be

spread evenly over the build area by counter rotating

roller. In this process support structures are not required as

the unsintered powder remains at the places of support

structure. It is cleaned away and can be recycled once the

model is complete. The schematic diagram of a typicalSLS apparatus is given in figure 7.

Figure 7: Selective Laser Sintering System


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VII. ADVANTAGES OF RAPIDPROTOTYPING

Todays automated; toolless, patternless RP systems can

directly produce functional parts in small production

quantities. Parts produced in this way usually have an

accuracy and surface finish inferior to those made bymachining. However, some advanced systems are able to

produce near tooling quality parts that are close to or are

the final shape. The parts produced, with appropriate post

processing, will have material qualities and properties

close to the final product. More fundamentally, the time to

produce any partonce the design data are available

will be fast, and can be in a matter of hours.

VIII. APPLICATIONS:Rapid prototyping is widely used in the automotive,

aerospace, medical, and consumer products industries.

Although the possible applications are virtually limitless,

nearly all fall into one of the following categories:

Prototyping.Rapid tooling.Rapid manufacturing.

SL model with the resection template; Silicon implant

molded from a tool

Figure 9: Applications of RP processes

Figure 8: Project time and product complexity

in 25 years time frame.


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IX. CONCLUSIONTodays market is customer oriented market.

R & D is the heart of any progressing,

developing industry because R&D is the

flowing new blood in industry, so that noobsolesce stage will be covered in the life of

industry.

R & D Engg. Is developing new shapes, sizes,

design, type of various component for the

establishment of a machine or a product but

the major hurdle is to produce the part

according to the decided design immediately

for getting immediate solution to the problem.

Now the time has come where, in design egg.

One can just imagine a new design, reproduce

it on paper and within a few minutes the

product will be ready through this technology

(prototyping). A few parameters input in to

the system carrying the right interface can

immediately produce products in minutes.

This paper gives the description of various

stages of data preparation and model building.

An attempt has been made to include someimportant factors to be considered before

starting part deposition, for proper utilization

of potentials of RP processes.

X. REFERENCESa) Rapid prototyping principle and

applications.

b) Rapid Prototyping technologies,applications and part deposition planning-

Pulak. M. Pandey.

c) Rapid prototyping technology HuyNguyen and Michael vai.

d) Gebhardt, A., (2003) Rapid Prototyping,Hanser Gardner Publications, Inc.,

Cincinnati.

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