This document provides an overview of rapid prototyping (RP). It defines RP as a family of fabrication methods to quickly make engineering prototypes based on CAD models with minimum lead times. The document discusses the evolution of prototyping, the need for RP, different RP categories including material removal and addition processes, the steps to prepare RP control instructions from a CAD model, common RP technologies like stereolithography and fused deposition modeling, applications of RP in design, engineering analysis and tooling, and challenges with part accuracy and limited materials.

1. Dr. Lotfi K. Gaafar 2002
Rapid Prototyping
Group Members
KDDS Dissanayake (IN 11- 2016 M 09)
HS Amarasekara (IN 11 -2015 M04)

2. Dr. Lotfi K. Gaafar 2002
Contents
 Introduction
 Evolution of prototyping
 Need of rapid prototyping
 Rapid prototyping categories
 Rapid prototyping - steps to prepare control
instructions
 Rapid prototyping technologies
 Rapid prototyping application problems with
rapid prototyping

3. Dr. Lotfi K. Gaafar 2002
Introduction
 Prototyping or model making is one of the important
steps to finalize a product design and It helps in
conceptualization of a design
 The traditional method of fabricating a prototype part is
machining, which can require significant lead times
 RP is a family of fabrication methods to make
engineering prototypes in minimum possible lead times
based on CAD models
 RP also known as “ Solid freeform fabrication”,
“Desktop manufacturing” or ”Layer manufacturing
Technology”.

4. Dr. Lotfi K. Gaafar 2002
Evolution of Prototyping
 Manual prototyping
By skilled craftsman has been an age-old practice for
many centuries
 Soft (virtual) prototyping
Second phase of prototyping started around mid-1970s,
a soft prototype modeled by 3D curves and surfaces
could be stressed in virtual environment, simulated and
tested with exact material and other properties.
 Rapid Prototyping (RP)
Third and the latest trend of prototyping, started during
early 1980s with the enormous growth in CAD/CAM

5. Dr. Lotfi K. Gaafar 2002
Why Rapid Prototyping
 Product designers would like to have a physical model
of a new part or product design rather than just a computer
model or line drawing
Creating a prototype is an integral step in design
 A virtual prototype (a computer model of the part design
on a CAD system) may not be sufficient for the designer to
visualize the part adequately
Using RP to make the prototype, the designer can
visually examine and physically feel the part and assess its
merits and shortcomings

6. Dr. Lotfi K. Gaafar 2002
Rapid Prototyping Categories
Available RP technologies can be divided into two
broad categories
 Material removal processes
 Material addition processes

7. Dr. Lotfi K. Gaafar 2002
1. Material removal processes
 This involves machining, milling and drilling, using a
CNC machines
 To use CNC, a part program must be prepared from
the CAD model
 Starting material is often a solid block of wax, which
is very easy to machine
 Removed material can re-solidified for reuse when
the current prototype is no longer needed
 Other starting materials ( wood, plastics, or metals)
can also be used

8. Dr. Lotfi K. Gaafar 2002
2. Material addition processes
 Principal is to adding layers of material one at a time to
build the solid part from bottom to top
 Starting materials
(1) Liquid monomers - cured layer by layer into solid
polymers
(2) Powders - Aggregated and bonded layer by layer
(3) Solid sheets - Laminated to create the solid part.

9. Dr. Lotfi K. Gaafar 2002
Steps to Prepare Control Instructions
 Steps to prepare the control instructions (part program)
in current material addition RP techniques
STEP 1 - Geometric modeling
 This consists of modeling the component on a CAD
system to define its enclosed volume
 Solid modeling is the preferred technique because it
provides a complete and unambiguous mathematical
representation of the geometry
 For rapid prototyping, the important issue is to
distinguish the interior (mass) of the part from its
exterior, and solid modeling provides for this distinction

10. Dr. Lotfi K. Gaafar 2002
STEP 2 - Tessellation of the geometric model
 In this step, the CAD model is converted into a
format that approximates its surfaces by triangles or
polygons, with their vertices arranged to distinguish
the object’s interior from its exterior.
 The common tessellation format used in rapid
prototyping is STL, which has become the de facto
standard input format for nearly all RP systems
 The term tessellation refers to the laying out or
creation of a mosaic, such as one consisting of
small colored tiles affixed to a surface for decoration

11. Dr. Lotfi K. Gaafar 2002
STEP 3 - Slicing of the model into layers
 In this step, the model in STL2 file format is sliced
into closely spaced parallel horizontal layers.
 These layers are subsequently used by the RP
system to construct the physical model.
 By convention, the layers are formed in the x-y plane
orientation, and the layering procedure occurs in the
z-axis direction.
 For each layer, a curing path is generated, called the
STI file, which is the path that will be followed by the
RP system to cure (or otherwise solidify) the layer.

12. Dr. Lotfi K. Gaafar 2002
Conversion of a solid model of an object into layers
(only one layer is shown)

13. Dr. Lotfi K. Gaafar 2002
RAPID PROTOTYPING TECHNOLOGIES
The classification method is based on the form of the
starting material in the RP process
(1) Liquid-based technologies
 Stereolithography (STL)
 Solid Ground Curing (SGC)
 Droplet Deposition Manufacturing (DDM)
(2) Solid-based technologies
 Laminated-object manufacturing
 Fused-deposition modeling
(3) Powder-based technologies
 Selective Laser Sintering (SLS)
 Three-dimensional printing (3D printing)

14. Dr. Lotfi K. Gaafar 2002
Liquid-based
Rapid Prototype
technologies

15. Dr. Lotfi K. Gaafar 2002
1. Stereolithography (STL)
 Stereolithography (STL) is a process for fabricating a
solid plastic part out of a photosensitive liquid polymer
using a directed laser beam to solidify the polymer
 Part fabrication is accomplished as a series of layers, in
which one layer is added onto the previous layer to
gradually build the desired three dimensional geometry
 The Stereolithography apparatus consists of
(1) A platform that can be moved vertically inside a vessel
containing the photosensitive polymer, and
(2) A laser whose beam can be controlled in the x-y
direction

16. Dr. Lotfi K. Gaafar 2002
Stereolithography
At the start of the process, in
which the initial layer is
added to the platform
After several layers have been
added so that the part geometry
gradually takes form

17. Dr. Lotfi K. Gaafar 2002
Solid Ground Curing
 Like STL, Solid ground curing (SGC) works by curing a
photosensitive polymer layer by layer to create a solid
model based on CAD geometric data.
 Instead of using a scanning laser beam to accomplish the
curing of a given layer, the entire layer is exposed to an
ultraviolet light source.
 The hardening process takes 2 to 3 seconds for each
layer.
 The starting data in SGC is similar to that used in
stereolithography: a CAD geometric model of the part
that has been sliced into layers.

18. Dr. Lotfi K. Gaafar 2002
Solid ground curing process for each layer
(1) mask
preparation
(2) applying
liquid photopolymer
Layer
(3) mask positioning
and exposure of
layer,
(4) uncured polymer
removed from
surface,
(5)Wax filling
(6) milling for
flatness and
thickness

19. Dr. Lotfi K. Gaafar 2002
Droplet Deposition Manufacturing (DDM)
 These systems operate by melting the starting
material and shooting small droplets onto a
previously formed layer.
 The liquid droplets cold weld to the surface to form a
new layer.
 The deposition of droplets for each new layer is
controlled by a moving x-y spray nozzle work head
whose path is based on a cross section of a CAD
geometric model that has been sliced into layers
 After each layer has been applied, the platform
supporting the part is lowered a certain distance
corresponding to the layer thickness, in reparation
for the next layer

20. Dr. Lotfi K. Gaafar 2002
Droplet Deposition Manufacturing
(DDM)

21. Dr. Lotfi K. Gaafar 2002
SOLID-BASED
RAPID
PROTOTYPING
SYSTEMS

22. Dr. Lotfi K. Gaafar 2002
Laminated-Object Manufacturing
 Laminated-object manufacturing produces a solid
physical model by stacking layers of sheet stock that are
each cut to an outline corresponding to the cross-
sectional shape of a CAD model that has been sliced into
layers.
 The layers are bonded one on top of the previous one
before cutting.
 After cutting, the excess material in the layer remains in
place to support the part during building.
 Starting material in LOM can be virtually any material in
sheet stock form, such as paper, plastic, cellulose,
metals, or fiber-reinforced materials.

23. Dr. Lotfi K. Gaafar 2002
Laminated-object manufacturing

24. Dr. Lotfi K. Gaafar 2002
Fused-Deposition Modeling
 FDM is an RP process in which a filament of wax or
polymer is extruded onto the existing part surface
from a work head to complete each new layer.
 The work head is controlled in the x-y plane during
each layer and then moves up by a distance equal
to one layer in the z-direction.
 The extrudate is solidified and cold welded to the
cooler part surface in about 0.1 second. The part is
fabricated from the base up, using a layer-by-layer
procedure similar to other RP systems.

25. Dr. Lotfi K. Gaafar 2002
Fused-Deposition Modeling

26. Dr. Lotfi K. Gaafar 2002
POWDER-BASED
RAPID
PROTOTYPING
SYSTEMS

27. Dr. Lotfi K. Gaafar 2002
Selective Laser Sintering (SLS)
 SLS uses a moving laser beam to sinter heat-fusible
powders in areas corresponding to the CAD geometric
model one layer at a time to build solid part
 After each layer is completed, a new layer of loose
powders is spread across the surface using a counter-
rotating roller
 The powders are preheated to just below their melting
point to facilitate bonding and reduce distortion.
 Layer by layer, the powders are gradually bonded into a
solid mass that forms the three-dimensional part
geometry.

28. Dr. Lotfi K. Gaafar 2002
Selective Laser Sintering (SLS)

29. Dr. Lotfi K. Gaafar 2002
Three-Dimensional Printing
 Three-dimensional printing (3DP) builds the part in the
usual layer-by-layer fashion using an ink-jet printer to
eject an adhesive bonding material onto successive
layers of powders.
 The binder is deposited in areas corresponding to the
cross sections of the solid part, as determined by slicing
the CAD geometric model into layers.
 The binder holds the powders together to form the solid
part, while the un bonded powders remain loose to be
removed later.
 When the build process is completed, the part is heat
treated to strengthen the bonding, followed by removal
of the loose powders.

30. Dr. Lotfi K. Gaafar 2002
Three-dimensional printing
1) Powder layer is deposited
2) Ink-jet printing of areas that will become the part
3) Piston is lowered for next layer

31. Dr. Lotfi K. Gaafar 2002
RP Applications
Applications of rapid prototyping can be classified into
three categories
1.Design
2.Engineering analysis and planning
3.Tooling and manufacturing

32. Dr. Lotfi K. Gaafar 2002
RP Applications: Design
Designers are able to confirm their design by building a
real physical model in minimum time using RP
Design benefits :
 Reduced lead times to produce prototype components
 Improved ability to visualize part geometry
 Early detection and reduction of design errors
 Increased capability to compute mass properties

33. Dr. Lotfi K. Gaafar 2002
RP Applications: Engineering Analysis
and Planning
Existence of part allows certain engineering analysis and
planning activities to be accomplished that would be
more difficult without the physical entity
 Comparison of different shapes and styles to
determine aesthetic appeal
 Wind tunnel testing of different streamline shapes
 Stress analysis of a physical model
 Fabrication of pre-production parts for process
planning and tool design

34. Dr. Lotfi K. Gaafar 2002
RP Applications: Tooling & Manufacturing
Small batches of plastic parts that could not be
economically injection molded because of the high mold
cost
Parts with complex internal geometries that could not be
made using conventional technologies without assembly
One-of-a-kind parts such as bone replacements that
must be made to correct size for each user
Used for rapid tool making(RTM) when RP is used to
fabricate production tooling

35. Dr. Lotfi K. Gaafar 2002
Problems with Rapid Prototyping
1.Part accuracy
Staircase appearance for a sloping part surface due to
layering
Shrinkage and distortion of RP parts
2. Limited variety of materials in RP
 Mechanical performance of the fabricated parts is
limited by the materials that must be used in the RP
process

36. Dr. Lotfi K. Gaafar 2002
Rapid Prototyping Products