U-1.pptx

UNIT -1 INTRODUCTION – LIQUID BASED RAPID
PROTOTYPING SYSTEMS Syllabus: INTRODUCTION:
Prototyping fundamentals, historical development,
fundamentals of rapid prototyping, advantages and
limitations of rapid prototyping, commonly used terms,
classification of RP process. LIQUID-BASED RAPID
PROTOTYPING SYSTEMS: Stereo lithography
Apparatus (SLA): models and specifications, process,
working principle, photopolymers, photo polymerization,
layering technology, laser and laser scanning,
applications, advantages and disadvantages, case
studies. Solid Ground Curing (SGC): models and
specifications, process, working principle, applications,
advantages and disadvantages, case studies.

Introduction to Additive Manufacturing: Additive
manufacturing (AM) is a recent trend in production
processes owing to its many benefits. It can be defined
as the process of producing parts through the deposition
of material in a layer-by-layer fashion using 3D CAD
modeling. In subtractive technology, layers of materials
are removed to produce a desired geometry. But
Additive technology is based on the addition of material
layers to create a desired work piece shape. AM can be
described as a technique of blending materials by either
fusion, binding, or solidifying materials such as liquid
resin and powders. The terminologies such as 3D
printing (3DP), Rapid Prototyping (RP), Direct Digital
Manufacturing (DDM), Rapid Manufacturing (RM), and
Solid Freeform Fabrication (SFF) can be used to
describe AM processes.

PROTOTYPING FUNDAMENTALS: DEFINITION OF
PROTOTYPE:
• A prototype is an important and vital part of the product
development process.
• A prototype is the first or original example of something
that has been or will be developed. It is a model or
preliminary version.
e.g.: A prototype supersonic aircraft; A Flying Car

TYPES OF PROTOTYPES:
1. Based on the Implementation of the prototype
a) Complete or Entire product
b) Sub-assemblies and components
2. Based on the form of the prototype
a) Virtual prototype
b) Physical prototype.
3. Based on the degree of the approximation of the prototype
a) Rough representation of the product
b) Exact replication of the product

1. a) Complete Prototype: The complete prototype, as its name suggests,
models most the characteristics of the product. It is usually implemented
full-scale as well as being fully functional. One example of such prototype
is one that is given to a group of carefully selected people with special
interest, often called a focus group, to examine and identify outstanding
problems before the product is committed to its final design.
Ex: A Self driving Car

1 .b) Sub-assemblies or Component type : There are prototypes that are
needed to study or investigate special problems associated with one
component, sub-assemblies or simply a particular concept of the product
that requires close attention. An example of such a prototype is a test
platform that is used to find the comfortable rest angles of an office chair
that will reduce the risk of spinal injuries after prolonged sitting on such a
chair. Most of the time, sub-assemblies and components are tested in
conjunction with some kind of test rigs or experimental platform.

Rough prototypes and Exact Prototypes:
Rough Prototype: A foam model, used primarily to study the general form
and enveloping dimensions of the product in its initial stage of
development. Some rough prototypes may not even look like the final
product, but are used to test and study certain problems of the product
development.
Exact Prototypes: The prototype that can be an exact full scale and exact
replication of the product that models every aspects of the product.
Exact” prototypes are especially important towards the end-stage of the
product development process.

ROLES OF THE PROTOTYPES:
1. Experimentation and learning: To the product development team,
prototypes can be used to help the thinking, planning, experimenting and
learning processes whilst designing the product.
2. Testing and proofing: Prototypes can also be used for testing and proofing
of ideas and concepts relating to the development of the product.
3. Communication and interaction: The prototype also serves the purpose of
communicating information and demonstrating ideas, not just within the
product development team, but also to management and client.
4. Synthesis and integration: A prototype can also be used to synthesize the
entire product concept by bringing the various components and sub-
assemblies together to ensure that they will work together.
5. Scheduling and markers: Prototyping also serves to help in the scheduling
of the product development process and is usually used as markers for the
end or start of the various phases of the development effort.

RAPID PROTOTYPING
Rapid Prototyping: Rapid prototyping is basically an additive
manufacturing process used to quickly fabricate a model of a part using 3-
D CAM data. It can also be defined as layer by layer fabrication of 3D
physical models directly from CAD.

THREE PHASES OF DEVELOPMENT LEADING TO RAPID PROTOTYPING:
1. First Phase: Manual Prototyping: (Mid-1960s)
• Began several centuries ago.
• Not very sophisticated.
• Fabrication of prototypes takes on average about four weeks.
• The techniques are craft-based and usually extremely labor intensive.
2. Second Phase: Soft or Virtual Prototyping (the early 1980s)
Application of CAD/CAE/CAM become more.
For example, analysis of stress and strain can be accurately predicted
on the product because of the ability to specify exact material attributes
and properties.

THREE PHASES OF DEVELOPMENT LEADING TO RAPID PROTOTYPING:
3. Third Phase: Rapid Prototyping (Since 1988)
• Rapid Prototyping of physical parts or freeform fabrication or desktop
manufacturing or layer manufacturing.
• The invention of this series of rapid prototyping methodologies is
described as a “watershed event because of the tremendous time
savings, especially for complicated models.
• Since 1988, more than twenty different rapid prototyping techniques
have emerged.

THE BASIC APPROACH OF RAPID PROTOTYPING
1. A component is modeled on a Computer-Aided Design/ Computer-
Aided Manufacturing (CAD/CAM) system.
2. The solid or surface model is converted into a “STL” (Stereo
Lithography) file format which originates from 3D Systems.
3. The STL file format approximates the surfaces of the model by
polygons.
4. A computer program analyzes the STL file of the model to and “slices”
the model into cross sections.
5. The cross sections are systematically recreated through the
solidification of either liquids or powders.

THE BASIC APPROACH OF RAPID PROTOTYPING
6. First layer of model is created.
7. Model is then lowered by thickness of next layer.
8. Process is repeated until completion of model
9. The model & any supports are removed.
10. Surface of the model is then finished and cleaned.

RP WHEEL:
Fundamentally, the development of RP can be seen in four primary areas.
The Rapid Prototyping Wheel in the below Figure represents these four
key aspects of Rapid Prototyping. They are: Input, Method, Material and
Applications

ADVANTAGES OF RP:
1. Almost any shape or geometric feature can be produced
2. Reduction in time and cost (could range 50 –90%)
3. Errors and flaws can be detected at an early stage.
4. RP/RM can be used in different industries and fields of life (medicine,
art and architecture, marketing etc.)
5. Discussions with the customer can start at an early stage.

ADVANTAGES OF RP:
1. Almost any shape or geometric feature can be produced
2. Reduction in time and cost (could range 50 –90%)
3. Errors and flaws can be detected at an early stage.
4. RP/RM can be used in different industries and fields of life (medicine,
art and architecture, marketing etc.)
5. Discussions with the customer can start at an early stage.
6. Assemblies can be made directly in one go.
7. Material waste is reduced.
8. No tooling is necessary.
9. The designers and the machinery can be in separate places.

DISADVANTAGES OF RP:
1. The price of machinery and materials
2. The surface is usually rougher than machined surfaces.
3. Some materials are brittle
4. The strength of RP-parts are weaker in z-direction than in other
5. Quality control is still a major pitfall of rapid prototyping

RP PROCESS CHAIN:
RP techniques adopt the same basic approach. All RP systems generally
have a similar sort of process chain. Such a generalized process chain is
explained below. There are a total of five steps in the chain and these are
3D modeling, data conversion and transmission, checking and preparing,
building and post processing.
1. 3D MODELING: Advanced 3D CAD modeling is a general prerequisite in
RP processes and, usually is the most time-consuming part of the entire
process chain. It is most important that such 3D geometric models can be
shared by the entire design team for many different purposes, such as
interference studies, stress analyses, FEM analysis, detail design and
drafting, planning for manufacturing, including NC programming, etc.
Many CAD/CAM systems now have a 3D geometrical modeler facility with
these special purpose modules.

RP PROCESS CHAIN:
2. DATA CONVERSION AND TRANSMISSION: The solid or surface model
to be built is next converted into a format dubbed the STL file format. This
conversion step is probably the simplest and shortest of the entire
process chain. However, for a highly complex model coupled with an
extremely low performance workstation or PC, the conversion can take
several hours. The transmission step is also fairly straightforward. The
purpose of this step is to transfer the STL files which reside in the
workstation to the RP system’s computer.
3. CHECKING AND PREPARING: At present, the CAD model errors are
corrected by human operators assisted by specialized software such as
MAGICS. This process of manual repair is very tedious and time
consuming. Preparing building parameters for positioning and stepwise
manufacturing in the light of many available possibilities can be difficult if
not accompanied by proper documentation

RP PROCESS CHAIN:
4. BUILDING: For most RP systems, this step is fully automated. Thus, it is usual
for operators to leave the machine on to build a part overnight. The building
process may take up to several hours to build depending on the size and
number of parts required. The number of identical parts that can be built is
subject to the overall build size constrained by the build volume of the RP
system.
5. POSTPROCESSING: The final task in the process chain is the post processing
task. The cleaning task refers to the removal of excess parts which may have
remained on the part. Thus, for SLA parts, this refers to excess resin residing in
entrapped portion such as a blind hole of a part, as well as the removal of
supports. Finishing refers to secondary processes such as sanding and painting
used primarily to improve the surface finish or aesthetic appearance of the
part. It also includes additional machining processes such as drilling, tapping
and milling to add necessary features to the parts.

STEREO LITHOGRAPHY APPARATUS (SLA)
Details: Stereo lithography process creates three-dimensional plastic
objects directly from CAD data. SLA is the most widely used RP-
technology. SLA can produce highly accurate and detailed polymer parts.
It was the first RP-process, introduced in 1988 by 3D Systems Inc. SLA
uses a low-power, highly focused UV laser to produce a three dimensional
object in a vat of liquid photosensitive polymer.

SLA – PROCESS:
1. The vat is filled with the photo-curable liquid resin.
2. The elevator table is set just below the surface of the liquid resin.
3. The operator loads a three-dimensional CAD solid model file into the
system.
4. The translator converts the CAD data into a STL file.
5. The control unit slices the model and support into a series of cross
sections from 0.025 to 0.5 mm thick.
6. The computer-controlled optical scanning system then directs and
focuses the laser beam.

SLA – PROCESS:
7. The laser beam solidifies a two dimensional cross-section
corresponding to the slice on the surface of the photo-curable liquid
resin.
8. The elevator table then drops enough to cover the solid polymer with
another layer of the liquid resin.
9. A leveling wiper vacuum moves across the surfaces to recoat the next
layer of resin on the surface.
10. The laser then draws the next layer.
11. This process continues building the part from bottom up, until the
system completes the part.
12. The part is then raised out of the vat and cleaned of excess polymer

SLA – WORKING PRINCIPLE:
The SLA process is based fundamentally on the following principles:
• Parts are built from a photo-curable liquid resin that cures when
exposed to a laser beam which scans across the surface of the resin.
• The building is done layer by layer, each layer being scanned by the
optical scanning system and controlled by an elevation mechanism which
lowers at the completion of each layer.

SLA MODELS AND SPECIFICATIONS:
• 3D Systems produces a wide range of machines
• Models available: SLA 250/30A, SLA 250/50, SLA-250/50HR, SLA 3500,
SLA 5000, SLA 7000 and Viper si2
• The SLA 250/30A is an economical and versatile SLA starter system that
uses a Helium Cadmium (He–Cd) laser.
• The SLA 250/50 is a supercharged system with a higher powered laser,
interchangeable vats and Zephyr recoater system
• SLA 250/50HR adds a special feature of a small spot laser for high-
resolution application.
• All SLA 250 type systems have a maximum build envelope of 250 × 250 ×
250 mm and use a He–Cd laser.

SLA MODELS AND SPECIFICATIONS:
• For bigger build envelopes, the SLA 3500, SLA 5000 and SLA 7000 are
available. These three machines use a different laser from the SLA 250
(solid-state Nd:YVO4 ).
• The SLA 7000 is the top of the series. It can build parts up to four times
faster than the SLA 5000.
• The Viper si2 system builds parts with a smooth surface finish, excellent
optical clarity, high accuracy, and thin, straight vertical walls.

PHOTOPOLYMERS:
Liquid photopolymers can be solidified by exposure to electro magnetic
radiation, including gamma rays, X-rays, UV and visible range, or electron-
beam (EB). The vast majority of photopolymers used in the commercial
RP systems SLA machines are curable in the UV range. UV-curable
photopolymers are resins. The process through which photopolymers are
cured is referred to as the Photopolymerization process.
PHOTOPOLYMERISATION:
Polymerization is the process of linking small molecules (known as
monomers) into chain-like larger molecules (known as polymers).When
the chain-like polymers are linked further to one another, a cross-linked
polymer is said to be formed. Photopolymerizationis polymerization
initiated by a photochemical process.

LAYERING TECHNOLOGY: Almost all RP systems use layering technology in
the creation of prototype parts. The basic principle is the availability of
computer software to slice a CAD model into layers. Reproduce it in an
“output” device like a laser scanning system. The layer thickness is
controlled by a precision elevation mechanism.
LASER AND LASER SCANNING: The important component of the building
process is the laser and its optical scanning system. To rapidly direct
focused radiation of appropriate power and wavelength onto the surface
of the liquid photopolymer resin. In the SLA, a laser beam with a specified
power and wavelength is sent through a beam expanding telescope. The
optical scanning system includes the optical aperture of a pair of cross
axis, galvanometer driven, beam scanning mirrors. The solidification of
the liquid resin depends on the energy per unit area deposited during the
motion of the focused spot on the surface of the photopolymer.

Applications of SLA include:
1. Models for conceptualization, packaging and presentation.
2. Prototypes for design, analysis, verification and functional testing.
3. Parts for prototype tooling and low volume production tooling.
4. Patterns for investment casting, sand casting and molding.
5. Tools for fixture and tooling design, and production tooling.

ADVANTAGES OF SLA:
1. Round the clock operation: The SLA can be used continuously and
unattended round the clock.
2. Good user support: The computerized process serves as a good user
support.
3. Build volumes: The different SLA machines have build volumes ranging
from small to large to suit the needs of different users.
4. Good accuracy: The SLA has good accuracy and can thus be used for
many application areas.
5. Surface finish: The SLA can obtain one of the best surface finishes
amongst RP technologies.
6. Wide range of materials: There is a wide range of materials, from
general purpose materials to specialty materials for specific
applications.

DISADVANTAGES of SLA:
1. Requires support structures: Structures that have overhangs and
undercuts must have supports that are designed and fabricated
together with the main structure.
2. Requires post-processing: Post-processing includes removal of
supports and other unwanted materials, which is tedious, time
consuming and can damage the model.
3. Requires post-curing: Post-curing may be needed to cure the object
completely and ensure the integrity of the structure.

CASE STUDY-1 for SLA:
Ex: 1: Ford Uses Stereo lithography to Cast Prototype Tooling: With a
single project triumph, Ford has begun a new era of “rapid
manufacturing” — applying QuickCast technology to the development of
prototype and production tooling. This innovation demonstrates the
potential to save manufacturing industries millions in tooling costs.
Ingenuity was Ford’s most critical ingredient. Traditional methods would
have provided the tool in three months. Ford used QuickCast in its first
application of rapid tooling by investment casting Stereolithography mold
halves to create the hard tool. The turnaround time for the second set of
tooling was only four weeks, and the cost for “QuickCast Tooling” was
only $5000 per tool set, compared to the $33 000 quoted for machining a
single tool. Ford was able to start durability and water flow testing 18
months ahead of schedule, with costs reduced by 45% and time savings
of more than 40% achieved. (Fig.1)

CASE STUDY- 2 for SLA:
Ex: 2. Black & Decker Saves a Year by Using Stereo lithography:
Designers at Black & Decker had only 100 days to transform an idea for an
improved shearer/shrub trimmer power tool into an attractive
functioning prototype that could be introduced at an important trade
show. The new power tool, which would expand the company’s Versa Pak
outdoor power tool product line, had to undergo design, proofing,
building, assembly and testing of at least 30 copies of the product in that
time frame. Failing to deliver functioning prototypes would put Black &
Decker back one year in introducing the product to the market place. The
new concept would offer a more ergonomically designed shearer/shrub
trimmer. This model would also be more streamlined in appearance.

CASE STUDY- 2 for SLA:
The new design was also to incorporate, in the single body of the
trimmer, an easy-access battery pop-out. Black & Decker turned to Mass
Engineered Design Inc., of Toronto, Ontario, where engineers used
stereolithography (SL). SL dealt quickly with the complexity of the design
features and was the only option that Mass had, to design and build 30
prototypes of the product in the 100- day time frame. A SLA 500 built a
master of product components from the approved CAD file.
The initial 30 prototypes were painted, labeled with logos and assembled
together with mechanical components. The now-functioning prototypes
were tested, packaged and shipped before the 100-day deadline and in
time for the trade show. The attractive and functioning prototype
products were a success at the trade show, garnering a number of sales
orders. Black & Decker could move the now successful product into full
production. (Fig. 2)

CUBITAL’S SOLID GROUND
CURING (SGC):
The Solid Ground Curing (SGC)
System is produced by Cubital
Ltd., Israel. Solid Ground Curing,
also known as the Solider
Process. The SGC process uses
photosensitive resin hardened in
layers as with the SLA process.
Many parts can be created at
once because of the large work
space. The multi-part capability
also allows quite large single
parts (e.g. 500 × 500 × 350 m) to
be fabricated. Wax replaces
liquid resin in non-part areas
with each layer so that model
support is ensured.

SOLID GROUND CURING (SGC) PROCESS:
Step1: First, a CAD model of the part is created and it is sliced into layers
using Cubital's Data Front End (DFE®) software. At the beginning of a layer
creation step, the flat work surface is sprayed with photosensitive resin,
as shown below:

Step 2: For each layer, a PHOTOMASK is produced using Cubital's
ionographic printing technique, as illustrated below:

Step 3: The Photomask is positioned over the work surface and a
powerful UV lamp hardens the exposed photosensitive resin.

Step 4: After the layer is cured, all uncured resin is vacuumed for
recycling, leaving the hardened areas intact. The cured layer is passed
beneath a strong linear UV lamp to fully cure it and to solidify any
remnant particles, as illustrated below:

Step 5: In the fifth step, wax replaces the cavities left by vacuuming the
liquid resin. The wax is hardened by cooling to provide continuous, solid
support for the model as it is fabricated. Extra supports are not needed.

Step 6: In the final step before the next layer, the wax/resin surface is
milled flat to an accurate, reliable finish for the next layer.
Once all layers are completed, the wax is removed, and any finishing
operations such as sanding, etc. can be performed. No post-cure is
necessary.

MODELS AND SPECIFICATIONS OF SGC

ADVANTAGES OF SGC SYSTEM:
1. Self-supporting: The primary advantage of the solid ground curing
system is that it does not require a support structure.
2. Accuracy: Highly accurate products can be obtained.
3. Low Cost: It is a time and cost saving process.
4. Minimum shrinkage effect: Full curing of every layer minimizes
shrinkage effect.
5. Good strength: The products are much less brittle.
6. Safe: No hazardous odors are generated.

DISADVANTAGES OF SGC:
1. Requires large physical space.
2. Wax gets stuck in corners and gaps.
3. The Solider system generates a high level of noise as compared to
other systems.
4. This process produces too much waste.
5. Its operating costs are comparatively high due to system complexity.
6. Poor market acceptance.

APPLICATIONS OF SGC:
1. General applications: Conceptual design presentation, design
proofing, engineering testing, integration and fitting, functional
analysis, exhibitions and pre-production sales.
2. Tooling and casting applications: Investment casting, sand casting.
3. Mold and tooling: Silicon rubber tooling, epoxy tooling, spray metal
tooling.
4. Medical imaging: Diagnostic, surgical, operation and reconstruction
planning and custom prosthesis design.

CASE STUDY: 1 – SGC: Cubital Prototyping Machine Builds Toy Jeep in 24
Hours:
Toledo Model and Die Inc. (TMD) of Toledo, Ohio, has used Cubital’s
Solider 5600 rapid prototyping system to produce three design iterations
of a toy jeep in three days. The plastic push toy is about 30 cm long, 23
cm, wide and 23 cm high. Using the Cubital Solider 5600, TMD was able
to produce each design iteration in 13 hours of machine time. By using
the Cubital front-end software, the parts were “nested” within a working
volume only 10 cm deep, within the Solider’s working area 50 cm × 35
cm. Initial file checking and post production wax removal accounted for
the rest of the 24 hours.

CASE STUDY: 2 – SGC : New Cubital-based Solicast Process Offers
Inexpensive Metal Prototypes in Two Weeks: Schneider Prototyping
GmbH created a metal prototype for investment cast directly from CAD
files in two weeks with SoliCast. Starting with a CAD file, Schneider can
deliver a metal prototype in two weeks, whereas similar processes with
other rapid prototyping methods take four to six weeks and conventional
methods based on CNC prototyping can take 10 to 16 weeks. In general,
Schneider’s prototypes can be as much as 50% cheaper than those
produced by other rapid prototyping methods.

CASE STUDY: 3 – SGC : Cubital Saves the Day - In Fact, About Six Weeks
— For Pump Developers:
Engineers and technicians in the production engineering department of
Sintef, a research and development firm in Trondheim, Norway, made an
accurate, full scale plastic model of the impeller, which measures about
220 mm in diameter and 50 mm high, using their Solider 5600. This
model was used to create an investment casting pattern that was used to
cast a prototype impeller in metal. From the time the engineers in Sintef
got the CAD files till they had the investment casting pattern was three
weeks — about a third the time it would have taken using CNC tools.

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