Rapid prototyping

• Rapid prototyping technologies are able to produce physical
model in a layer by layer manner directly from their CAD
models without any tools, dies and fixtures and also with little
human intervention.
• RP is capable to fabricate parts quickly with too complex
shape easily as compared to traditional manufacturing
technology.
• RP helps in earlier detection and reduction of design errors.

 Create a CAD model of the design
 Convert the CAD model to STL format (stereo lithography)
 Slice the STL file into thin cross-sectional layers
 Construct the model one layer atop another
 Clean and finish the model

 CAD Model Creation:
• First, the object to be built is modeled using a Computer-Aided
Design (CAD) software package or coordinate measuring machine
or laser scanner.
• Solid modelers, such as Pro/ENGINEER, tend to represent 3-D
objects more accurately than wire-frame modelers such as
AutoCAD, and will therefore yield better results.
• This process is identical for all of the RP build techniques.

 Conversion to STL Format:
• To establish consistency, the STL (stereo lithography, the first RP
technique) format has been adopted as the standard of the rapid
prototyping industry and acts as the interface b/w CAD software and
machines.
• The second step, therefore, is to convert the CAD file into STL
format. This format represents a three-dimensional surface as an
assembly of planar triangular facets.
• STL files use planar elements, they cannot represent curved surfaces
exactly. Increasing the number of triangles improves the
approximation.

 Slice the STL File:
• In the third step, a pre-processing program prepares the STL file to
be built.
• The pre-processing software slices the STL model into a number of
layers from 0.01 mm to 0.7 mm thick, depending on the build
technique.
• The program may also generate an auxiliary structure to support the
model during the build. Supports are useful for delicate features such
as overhangs, internal cavities, and thin-walled sections.

 Layer by Layer Construction:
• The fourth step is the actual construction of the part.
• RP machines build one layer at a time from polymers, paper, or
powdered metal.
• Most machines are fairly autonomous, needing little human
intervention.
 Clean and Finish:
• The final step is post-processing. This involves removing the
prototype from the machine and detaching any supports.
• Some photosensitive materials need to be fully cured before use
• Prototypes may also require minor cleaning and surface treatment.
• Sanding, sealing, and/or painting the model will improve its
appearance and durability.

The Rapid Prototyping Wheel
depicting the 4 major aspects
of RP
• INPUT
• METHOD
• MATERIAL
• APPLICATION

 Input refers to the electronic information required to describe the physical
object with 3D data.
 There are two possible starting points – a computer model or a physical model.
 The computer model created by a CAD system can be either a surface model
or a solid model
 On the other hand, 3D data from the physical model is not at all
straightforward.
 It requires data acquisition through a method known as reverse engineering.
 In reverse engineering, a wide range of equipment digitizer, to capture data
points of the physical model and “reconstruct” it in CAD system.
INPUT

METHOD
 While they are currently more than 20 vendors for RP
systems, the method employed by each vendor can be
generally classified into the following categories:
• photo-curing,
• cutting and gluing/joining,
• melting and solidifying/fusing and joining/binding.
 Photo-curing can be further divided into categories of
• single laser beam,
• double laser beams and
• masked lamp

 MATERIAL
 The initial state of material can come in either
• solid, liquid or powder state.
 In solid state, it can come in various forms such
• a pallets, wire or laminates.
 The current range materials include
• paper, nylon, wax, resins, metals and ceramics.
 APPLICATIONS
 Applications can be grouped into:
• Design
• Engineering, Analysis and Planning
• Tooling and Manufacturing
 A wide range of industries can benefit from RP and these
include, but are not limited to,
• aerospace,
• automotive,
• biomedical, consumer,
• electrical and electronics products.

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

• The price of machinery and materials.
• The surface is usually rougher than machined surfaces.
• Some materials are brittle.
• The strength of RP-parts are weaker in z-direction than in
other.

─────────────────────────────────────────────────────────────────────────────────────
 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.
 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 pallets.
 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.

• Stereo lithography is the most widely used RP-technology.
It can produce highly
• Accurate and detailed polymer parts. SLA was the first
RP-process, introduced in 1988 by 3D Systems Inc.
Principle
SLA uses a low-power, highly focused UV laser to
produce a three dimensional object in a vat of liquid
photosensitive polymer.

Process
• This is based on selective polymerization of a photosensitive resin
using ultraviolet light.
• In this system, an ultraviolet laser beam is focused on the top layer
of photo sensitive resin contained in a vat.

• The beam is positions and moved in horizontal X and Y directions to
polymerize the resin within the boundary a particular cross-section.
• The cured layer of polymer is lowered by a platform attached to it, so that
a fresh layer of liquid resin covers the cured layer.
Working
 A vat containing a mechanism whereby a platform can be lowered and
raised is filled with a photocurable liquid-acrylate polymer.
 The liquid is a mixture of acrylic monomers, oligomers (polymer
intermediates), and a photoinitiator ( a compound that undergoes a
reaction upon absorbing light).
 At its highest position (depth a), a shallow layer of liquid exists above
the platform.
 A laser generating an ultraviolet (UV) beam is focused upon a selected
surface area of the photopolymer and then moved around in the x-y
plane.
 The beam cures that portion of the photopolymer and thereby
produces a solid body.

 The platform is then lowered sufficiently to cover the cured polymer
with another layer of liquid polymer, and the sequence is repeated.
 The process is repeated until level b is reached. Thus far, we have
generated a cylindrical part with a constant wall thickness. Note that
the platform is now lowered by a vertical distance ab.
 At level b, the x-y movements of the beam define a wider geometry,
so we now have a flange-shaped portion that is being produced over
the previously formed part.
 After the proper thickness of the liquid has been cured, the process
is repeated, producing another cylindrical section between levels b
and c.
 Note that the surrounding liquid polymer is still fluid (because it has
not been exposed to the ultraviolet beam) and that the part has been
produced from the bottom up in individual ‘slices’. The unused
portion of the liquid polymer can be used again to make another
part or another prototype.

Abbreviation: SLA
Material type: Liquid(Photopolymer)
Materials: Thermoplastics(Elastomers)
Min layer thickness: 0.02 mm
Surface finish: Smooth
Build speed: Average
Applications: Form/fit testing, Functional
testing, Very detailed parts,
Presentation models, Snap fits..

ADVANTAGES DISADVANTAGES
 Achieving accuracy in
industries
 Capable of high detail and
thin walls
 Good surface finish
 High part complexity
 Requires post-curing.
 Some war page, shrinkage
and curl due to phase change.
 Limited materials (Photo
polymers).
 Support structures always
needed. Removal of support
structures can be difficult.

• (FDM) is a solid-based rapid prototyping method
that extrudes material, layer-by-layer, to build a
model.
• It was developed by Stratasys
Principle
A plastic or wax material is extruded through
a nozzle that traces the part´s cross sectional geometry
layer by layer

Process
• The FDM technique relies on melting and selectively depositing a thin
filament of thermoplastic polymer in a cross-hatching fashion to form
each layer of the part.
• The material is in the form of a wire supplied in sealed spools which is
mounted on the machine and the wire is threaded through the FDM head.

• The head is moved in the horizontal X and Y directions for producing
each layer through zigzag movements.
• The supporting table moves in the vertical direction and is lowered after
the completion of each layer.
Working
• In FDM process, a gantry robot-controlled extruder head moves
in two principal directions over a table, which can be raised and
lowered as needed.
• A thermoplastic filament is extruded through the small orifice of
a heated die.
• The initial layer is placed on a foam foundation by extruding the
filament at a constant rate while the extruder head follows a
predetermined path.

• When the first layer is completed, the table is lowered so that
subsequent layers can be superimposed.
• In some parts, the filament is required to support the slice where no
material exists beneath to support it.
• The solution is to extrude a support material separately from the
modelling material. The use of such support structures allows all of
the layers to be supported by the material directly beneath them.
• The support material is produced with a less dense filament spacing
on a layer, so it is weaker than the model material and can be broken
off easily after the part is completed.
• The layers in an FDM model are determined by the extrusion-die
diameter, which typically ranges from 0.050 to 0.12mm. This
thickness represents the best achievable in the vertical direction.
• In the x-y plane, dimensional accuracy can be as fine as 0.025mm

Abbreviation: FDM
Material type: Solid(Filaments)
Materials: ABS, Polycarbonate, Poly
phenyl sulfonite ;Elastomers
Min layer thickness: 0.15mm
Surface finish: Rough
Build speed: Slow
testing, Small detailed parts,
Presentation models.

 Durable parts can be made
 Minimal wastage
 Easy handling, material
changeover and support
removal.
 No post curing.
 Office environment friendly.
 Low end, economical
machines.
 Easy material changeover and
support removal.
 Variety of materials
 Longer to build
 Low accuracy compared to SLA
 Not good for small features,
details and thin walls.
 Surface finish is rough.
 Support design / integration /
removal is difficult.
 Weak Z-axis.
 Slow on large / dense parts.
 Supports required on some
materials / geometries.

• 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
Principle
The build material is placed on a platform and
a heated roller bonds it to the previous layer and the
sheet is cut to required profile by laser and glued to
previous sheet.

Process
• The main components of the system are a feed mechanism that advances a
sheet over a build platform, a heater roller to apply pressure to bond to the
layer below, and a laser to cut the outline of the part in each sheet layer.

• After each cut is completed, the platform lowers by a depth equal to the
sheet thickness (0.05 –0.5 mm).
• The laser cuts the outline and the process is repeated until the part is
completed.
• After a layer is cut, the extra material remains in place to support the part.
Working
 Lamination implies a laying down of layers that are bonded
adhesively to one another.
 The simples and least expensive versions of LOM involve using
control software and vinyl cutters to produce the prototype.
 Vinyl cutters are simple CNC machines that cut shapes from vinyl or
paper sheets.
 Each sheet then has a number of layers and registration holes, which
allow proper alignment and placement onto a build fixture.

 LOM systems are highly economical and are popular in schools and
universities because of the hands-on demonstration of additive
manufacturing and production of parts by layers.
 LOM systems can be elaborate; the more advanced systems use layers
of paper or plastic with a heat-activated glue on one side to produce
parts.
 The desired shapes are burned into the sheet with a laser, and the parts
are built layer by layer.
 On some systems, the excess material must be removed manually once
the part is completed. Removal is simplified by programming the laser
to burn perforations in crisscrossed patterns.
 The resulting grid lines make the part appear as if it had been
constructed from gridded paper (with squares printed on it, similar to
graph paper).

Abbreviation: LOM
Material type: Solid(Sheets)
Materials: Thermoplasticssuchas PVC;
Paper;
Composites(Ferrousmetals;
Non-ferrousmetals; Ceramics)
Build speed: Fast
Applications: Form/fit testing,
Less detailed parts, Rapid
tooling patterns…

 Wide range of materials
 Fast Build time
 High accuracy
 durability
 High part complexity
 Overheated roller may
damage sheet
 Limited materials (Photo
polymers).
 Support structures always
needed.

• SLS is a process based on the sintering of non
metallic or (less commonly) metallic powders
selectively into an individual object.
• SLS was patented in 1989.
Principle
It uses a moving laser beam to trace and
selectively sinter powdered polymer and/or metal
composite materials.

Process
• In this process a high power laser beam selectively melts and fuses powdered
material spread on a layer.
• The powder is metered in precise amounts and is spread by a counter-rotating
roller on the table.

• A laser beam is used to fuse the powder within the section boundary
through a cross-hatching motion.
• The table is lowered through a distance corresponding to the layer
thickness (usually 0.01 mm) before the roller spreads the next layer of
powder on the previously built layer.
• The unsintered powder serves as the support for overhanging portions, if
any in the subsequent layers.
Working
 First, a thin layer of powder is deposited in the part-build cylinder
 Then, a laser beam guided by a process-control computer using
instructions generated by the 3D CAD program of the desired part is
focused on that layer, tracing and sintering a particular cross-section
into a solid mass.
 The powder in other areas remains loose, yet it supports the sintering
portion.

 Another layer of powder is then deposited; this cycle is repeated again
and again until the entire 3D part has been produced.
 The loose particles are shaken off, and the part is recovered.
 The part does not require further curing-unless it is a ceramic, which
has to be fired to develop strength.
 A variety of materials can be used in this process, including polymers
(such as ABS; PVC, nylon, polyester, polystyrene, and epoxy), wax,
metals, and ceramics with appropriate binders.
 It is most common to use polymers because of the smaller and less
expensive, and less complicated lasers are required for sintering.
 With ceramics and metals, it is common to sinter only a polymer binder
that has been blended with the ceramic or metal powders.
 The resultant part can be carefully sintered is a furnace and infiltrated
with another metal if desired.

Abbreviation: SLS
Material type: Powder(Polymer)
Materials: Thermoplastics: Nylon,
Polyamide and Polystyrene;
Elastomers; Composites
Surface finish: Average
Build speed: Fast
testing, Less detailed parts,
Parts with snap-fits& living
hinges, High heat applications..

 No need of support structures
 No post curing required
 Variety and Flexibility of
materials
 The main advantage is that the
fabricated prototypes are
porous (typically 60% of the
density of moulded parts), thus
impairing their strength and
surface finish.
 Fast build times.
 Rough surface finish.
 Additional powder may get
hardened while solidification
along border line
 Mechanical properties below
those achieved in injection
mouldings process for same
material.
 Many build variables, complex
operation.
 Material changeover difficult
compared to FDM & SLA.

• Three Dimensional Printing (3DP) technology was
developed at the MIT and licensed to several
corporations.
• It was Produced by Z Corporation, USA.
Principle
An ink-jet printing head deposits a liquid
adhesive that binds the starch powder material.

Process
• Spread a layer of powder
• Print the cross section of the part
• Spread another layer of powder
• Parts are printed with no supports to remove

• Post processed by cleaning the excess powder, air blow , gluing and
sanding.
• Paint coated by sprayers or brushers to get finished product
Working
 In 3D printing (3DP) process, a print head deposits an inorganic
binder material onto a layer of polymer, ceramic, or metallic powder.
 A piston supporting the powder bed is lowered incrementally, and
with each step, a layer is deposited and then fused by the binder.
 3DP allows considerable flexibility in the materials and binders used.
 Furthermore, since multiple binders print heads can be incorporated
into a machine, it is possible to produce full-color prototypes by
having different-color binders.
 The effect is a 3D analog to printing photographs using three ink
colors on an ink-jet printer.
 The effect is a 3D analog to printing photographs using three ink
colors on an ink-jet printer.

 A common part produced by 3DP from ceramic powder is a ceramic-
casting shell, in which an aluminium-oxide or aluminium silica powder
is fused with a silica binder.
 The moulds have to be post processed in two steps:
(1) Curing at around 150ºC and
(2) Firing at 1000º to 1500ºC.
 The parts produced through the 3DP process are somewhat porous
and therefore may lack strength.
 3DP of metal powders can also be combined with sintering and metal
filtration to produce fully dense parts, using the sequence.
 The part is produced as before directing the binder onto powders.
However, the build sequence is then followed by sintering to burn off
the binder and partially fuse the metal powders, just as in powder
injection moulding.
 Common metals used in 3DP are stainless steels, aluminium, and
titanium.
 Infiltrating materials typically are copper and bronze, which provide
good heat-transfer capabilities as well as wear resistance

Abbreviation: 3DP
Material type: Powder
Materials: Ferrousmetalssuchas
Stainlesssteel; Non-
ferrousmetalssuchas Bronze;
Elastomers; Composites;
Ceramics
Min layer thickness: 0,05mm
Build speed: VeryFast
Applications: Concept models, Limited
functional testing, Architectural&
landscape models, Consumer
goods& packaging

 High speed
 Versatile - used for
automotive, aerospace,
footwear, packaging , etc
 Simple to operate -
straightforward
 Can recycle
 Enable complex colour
scheme
 No wastage of material
 Limited functional parts
 models are weak
 Limited materials -starch &
plaster-based only.
 poor surface finish
 need post-processing

• The term Rapid Tooling (RT) is typically used to
describe a process which either uses a Rapid
Prototyping (RP) model as a pattern to create a
mould quickly or uses the Rapid Prototyping process
directly to fabricate a tool for a limited volume of
prototypes.

Conventional Tooling vs Rapid Tooling:
 Tooling time is much shorter than for a conventional tool.
Typically, time to first articles is below one-fifth that of
conventional tooling.
 Tooling cost is much less than for a conventional tool.
Cost can be below five percent of conventional tooling
cost.
 Tool life is considerably less than for a conventional tool.
 Tolerances are wider than for a conventional tool.
RT is distinguished from conventional tooling in that,

o Minimize cost
o Increase productivity
o Increase dimensional accuracy
o Decrease tool time
Need for RT
Advantages of RT
o Quantity : large no of parts to be machined
o Design : fabrication of complex parts
o Material : for machining difficult materials
o Speed : to increase the speed of machining

Rapid prototyping

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