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Rapid Prototyping
Department of Mechanical Engineering, The Ohio State University
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DTM Sinterstation 2500plus, http://www.dtm-corp.com/products/sinterstation.html
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Rapid Prototyping
• What is Rapid Prototyping?
 A CAD technique to allow “Automatic” creation of a
physical model or prototype from a 3-D model.
 Create a 3-D ‘Photocopy’ of a part.
» Computer  Real life
• Why use Rapid Prototyping?
• Decreases lead time
• Facilitates concurrent engineering
• Allows visualization of more ideas
Department of Mechanical Engineering, The Ohio State University
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Design Process Overview
Concept
Pre-lim Design
Iterate
Drawings
Analysis
Testing
Physical
Prototype
Manufacturing
Department of Mechanical Engineering, The Ohio State University
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Prototype Classifications
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Conceptual
 Team members are aware of what is to be designed.
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Physical (true prototype)
1. Form- Design verification, marketing and communication tool
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High dimensional accuracy is NOT required
Non-technical people see how product looks and feels
2. Fit- Verify manufacturability, assembly, and fit
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Required shape along with good dimensional tolerances
Material choice is not important
3. Function- Used to test functionality of real part
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Material should be similar to actual part
Function prototype should have same failure modes and levels
as actual part
Department of Mechanical Engineering, The Ohio State University
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Traditional Prototyping - Steps
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Engineering Drawings
Machine or prototype shop to produce part
 Part usually machined (Lathe, Mill etc.)
 Problems:
• Material incompatibility
• Shop specialization (Can’t perform task you need)
• Design limited by prototype tools available
• Part too complex to produce (curved surfaces are very difficult)
• Machine deficiencies (You have 3 axis mill, you need 5 axes)
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Costs of traditional prototyping
 Skilled Craftsman ($60-70/Hour shop time)
 Time to receive model from shop
 Time to get model into the public domain
Department of Mechanical Engineering, The Ohio State University
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Numerical Control Machining
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Process:
 Starts with solid model from some CAD package
» (Solid Edge, Solid Works, I-DEAS or Pro-E for example)
 Next create the desired tool paths
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Advantages of NC over traditional machining
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Significantly reduces time required for prototype fabrication
Identical parts created from one source code
Faster feed rates then a human could handle
Store the code conveniently (floppy or in NC machine itself)
Problems/Limitations:
 Process not totally automatic. Operator must make many decisions:
» Appropriate tools
» How to fixture the stock
» Re-fixturing during machining
Department of Mechanical Engineering, The Ohio State University
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NC - Brief History

Early 1800’s - first programmable machine
created
 Weaving machine controlled by holes punched in metal cards.
 Machine can now read a code and follow a specified path

Late 1950’s - MIT developed a common
language to describe cutting motions with a
certain machine.
 Code placed on a paper tape the machine could read
Department of Mechanical Engineering, The Ohio State University
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NC - in Present Day

Machining Centers
 In prototyping many tools required by the user to create the parts.
 Machining centers hold & manage a large number (up to 120) of tools
» Eliminates tool-change time by machine operator
 Much more complex parts with less operator interaction
 Ex: T500 (Cincinnati Milacron)

NC software
 Early program languages for NC required the path to be explicitly
defined (Exact path known - no modification allowed -program
began with the user entering the tool paths, NOT the workpiece
shapes as is desired)
 Programs now perform calculations for the user
 Very complicated geometries easily handled by computer
Department of Mechanical Engineering, The Ohio State University
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NC Machining & Rapid Prototyping
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NC machining requires a skilled operator to set up machine
and to specify tools, speeds, and raw materials.
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For this reason, many do not consider NC machining to be a
true Rapid Prototyping (RP) technique. True RP should
create a part from some model without any assistance.

NC Machining does have some benefits over “true” RP
• NC Machining allows a wide range of materials for prototypes (true
RP techniques often prohibit material for function prototype)
• NC Machining allows better accuracy than most “true” rapid
prototyping techniques (may be needed for fit prototypes)
• True RP techniques can produce a prototype of a part that is
impossible to manufacture. NC machining often reveals
manufacturing limits in a given design.
Department of Mechanical Engineering, The Ohio State University
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Solid Freeform Manufacturing
Many restrict true Rapid Prototyping to the Solid Freeform
Manufacturing (SFM) procedures (i.e. RP=SFM)
All the SFM procedures are based on some layering operation
The CAD/CAM program takes the shape and models it as a series
of thin layers stacked upon one another
The SFM process then forms the part a layer at a time, starting
at the bottom and working toward the top
This can cause trouble with large overhangs-- one must somehow
support the overhang in order to form the next layer
Support must be used
to form next layer
Overhang
Department of Mechanical Engineering, The Ohio State University
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SFM Layer Formation Methods
Solid
Liquid
Powder
Bulk
1 Component
Gluing Sheets
Selective Laser
Sintering
Laminated
Object
Manufacturing
Component
& Binder
3D Printing &
Gluing
Polymerization
Foil
Polymerization
Liquid
Polymerization
Melting &
Solidification
Shape Melting
Light
Two
frequencies
Beam Interference
solid
One
frequency
Heat
Thermal
Polymerization
Fused Deposition
Modeling
Ballistic Particle
Manufacturing
Solid Base Curing
Lamps Photosolid. Layer at a Time
Lasers Stereolithography
Department of Mechanical Engineering, The Ohio State University
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SFM Technology
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Stereo-lithography- photopolymer cured by laser

Photosolidification Layer at a Time- photopolymer cured by
light

Solid Base Curing- photopolymer is cured by UV light
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Fused Deposition Modeling - molten plastic is extruded &
solidifies
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Ballistic Particle Manufacturing- microparticles of molten plastic
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3D Printing Direct Shell Production Casting- powder w/ binder
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Selective Laser Sintering- fusible powder, fused by laser
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Laminated Object Manufacturing- glued layers of sheets
Department of Mechanical Engineering, The Ohio State University
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Stereolithography
Stereo Lithography (SLA) was the first commercially available
Solid Freeform Manufacturing system. It is still the industry
leader, setting many industry trends.
1) Laser traces current cross section onto surface of photocurable
liquid acrylate resin
2) Polymer solidifies when struck by the laser’s intense UV light
3) Elevator lowers hardened cross section below liquid surface
4) Laser prints the next cross section directly on top of previous
5) After entire 3-d part is formed it is post-cured (UV light)
Note: care must be taken to support any overhangs
The SLA modeler uses a photopolymer, which has very low
viscosity until exposed to UV light. Unfortunately this
photopolymer is toxic. Warpage occurs.
Department of Mechanical Engineering, The Ohio State University
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Stereolithography
3D Systems SLA 3500
Department of Mechanical Engineering, The Ohio State University
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Ref: http://www.3dsystems.com/index_nav.asp?nav=products&content=products/index.asp
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Stereolithography Overview
Laser is focused/shaped through
optics. A computer controlled
mirror directs laser to appropriate
spot on photopolymer surface.
Polymer solidifies wherever laser
hits it.
When cross section
is complete, elevator
indexes to prepare
for next layer.
Department of Mechanical Engineering, The Ohio State University
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SLA Interface

Stereolithograpy was first commercial Solid Freeform
Manufacturing process, released in 80’s by 3-D Systems
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3-D Systems developed interface between CAD systems and
their machine
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STL files (*.stl) allow CAD systems to interface with 3-D
system machines
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Virtually all subsequent SFM processes can use this same
format (SFM industry standard)
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Many CAD programs now can export the *.stl file for easy
conversion from CAD to part
Department of Mechanical Engineering, The Ohio State University
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STL Files (*.stl)
• STL files were based on a program called Silverscreen CAD
• Silverscreen CAD represent boundary with all surfaces being
approximated by polygons or groups of polygons
• *.stl files use triangles or groups of triangles to approximate
surfaces
• Accuracy depends on the triangle sizes
• Triangles assigned normal vectors for outward surface normal
• Parts are defined by representing all their bounding surfaces as
faceted surfaces, using the triangular patches
Department of Mechanical Engineering, The Ohio State University
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Example of *.stl Representation
Representing
a sphere
Department of Mechanical Engineering, The Ohio State University
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Processing of *.stl Files
•After the CAD system has generated *.stl file, it can be passed
to the SLA machine (or any SFM machine)
•Machine then processes the *.stl file, slicing it into many thin
layers stacked on one another. The resulting files are called
slice files.
•The shapes of the slices represent cross sections
•In SLA (and in many SFM processes) thick solid sections of
material are often removed and replaced with cross hatching
•Thus SLA (& many SFM) parts are usually hollow, with cross
hatching on the inside to add strength/stability
Department of Mechanical Engineering, The Ohio State University
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Photosolidification Layer at a Time
1) Cross section shape is “printed” onto a glass mask
2) Glass mask is positioned above photopolymer tank
3) Another rigid glass plate constrains liquid photopolymer from
above
4) UV lamp shines through mask onto photopolymer- light only
can pass through clear part, polymer solidifies there, polymer
in masked areas remains liquid
5) Due to contact with glass plate, the cross linking capabilities
of the photopolymer are preserved- bonds better w/ next layer
6) New coat of photopolymer is applied
7) New mask is generated and positioned, and process repeats
8) 12-15 minute postcure is required
Much less warpage than SLA, but still uses photopolymers
which are toxic.
Department of Mechanical Engineering, The Ohio State University
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Layer at a Time Solidification
Mask is then placed under an
ultraviolet lamp
A glass mask is generated
Laser then shines through mask, solidifying the
entire layer in one “shot.” More rapid layer
formation, and thorough solidification.
Department of Mechanical Engineering, The Ohio State University
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Solid Base Curing
1) Cross section shape is “printed” onto a glass mask
2) Glass mask is positioned above photopolymer tank
3) UV lamp shines through mask onto photopolymer- light only
can pass through clear part, polymer solidifies there, polymer
in masked areas remains liquid
4) All excess polymer is removed- part is again hit with UV light
5) Melted wax is spread over workpiece, filling all spaces
6) Workpiece is precisely milled flat
7) Glass is erased and re-masked, workpiece is placed slightly
below surface in photopolymer, process repeats
8) After fabricating part, wax is melted and removed.
Accurate, no support or post cure needed, but expensive & toxic
Department of Mechanical Engineering, The Ohio State University
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Solid Base Curing Cycle
Shine UV Lamp
Generate glass mask
through mask to
solidify photopolymer
Remove excess polymer,
and fill gaps with liquid wax.
Chill to solidify wax.
Coat with
photopolymer
Mill wax &
workpiece
Department of Mechanical Engineering, The Ohio State University
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GATEWAY
Fused Deposition Modeling (FDM)
1)
2)
3)
4)
5)
6)
A spool of thin plastic filament feeds material to FDM head
Inside FDM, filament is melted by a resistance heater
The semiliquid thermoplastic is extruded through FDM head
Material is deposited in a thin layer on formation
Material solidifies, forming a laminate
Next layer is formed on previous- lamina fuse together
FDM modelers typically use nylon or some wax. The material is
non toxic and can be used anywhere, including offices.
Machines can be equipped with second head to extrude a
support structure (BASS breakaway support system).
Department of Mechanical Engineering, The Ohio State University
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FDM Layer Formation
FDM generated
cross section
Notice that the FDM filament cannot
cross itself, as this would cause a high
spot in the given layer
Department of Mechanical Engineering, The Ohio State University
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Fused Deposition Machine
Stratasys FDM 2000
http://www.stratasys.com/
Department of Mechanical Engineering, The Ohio State University
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Ballistic Particle Manufacturing (BPM)
Employs a technology called Digital Microsynthesis
1) Molten plastic is fed to a piezoelectric jetting mechanism,
similar to those on inkjet printers.
2) A multi-axis controlled NC system shoots tiny droplets of
material onto the target, using the jetting mechanism.
3) Small droplets freeze upon contact with the surface, forming
the surface particle by particle.
Process allows use of virtually any thermoplastic (no health
hazard) & offers the possibility of using material other than
plastic.
Department of Mechanical Engineering, The Ohio State University
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BPM Process
Department of Mechanical Engineering, The Ohio State University
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3-D Printing Direct Shell
Production Casting (DSPC)
First creates a disposable mold which is used to cast actual part
1)
2)
3)
4)
5)
6)
7)
8)
Thin distribution of powder is spread over powder bed
Inkjet printheads deposit small droplets of binder
Upon contact, binder droplets join powder to form solid
Piston supporting powder bed lowers so that the next layer
can be spread and joined
Process repeats until completion
The shell that has been created is fired
Shell is filled with molten metal
Metal solidifies & shell is broken away from part
Process allows use of metal for parts. Uses alumina powder
& silica binder for shell. 3-D printing can have other uses.
Department of Mechanical Engineering, The Ohio State University
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3-D Printing Process
Department of Mechanical Engineering, The Ohio State University
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Selective Laser Sintering (SLS)
1) A cartridge feeding system deposits a thin layer of heat fusible
powder into a workspace container
2) The layer of powder is heated to just below its melting point
3) Carbon-dioxide laser traces the cross section. Particles hit by
laser are heated to sintering point and bond into a solid mass.
4) A new layer of material is deposited on top of previous layer
5) Process repeats
SLS modelers use nylon/polycarbonate powders, which are health
hazards (dangerous to breathe). SLS does not require external
support of overhangs, as loose powder provides support for
new layers. Improvements in SLS technology have expanded
allowed materials to ABS, PVC, and metals encapsulated
in plastic. Some powdered metals have been directly sintered.
Department of Mechanical Engineering, The Ohio State University
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SLS Process
Department of Mechanical Engineering, The Ohio State University
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Laminated Object Manufacturing (LOM)
1) Sheet of material is laminated onto existing stack-up
2) Laser perforates the outline of cross section into top sheet
(cross section is NOT completely cut out- full sheet remains)
3) Edges of top sheet are trimmed to match rest of stack-up
4) Next layer is bonded and process repeats
5) When finished- have solid block with perforations separating
the actual workpiece from “extra” material. Extra material
must be removed & part is sanded.
LOM modelers use paper w/ polyester adhesive. They pose no
health hazards and can be set up in offices. Further they
are comparatively inexpensive, and require no supports for
any overhangs. Unfortunately, LOM modelers also require
more post-processing work (removing part from block).
Department of Mechanical Engineering, The Ohio State University
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LOM Process
Department of Mechanical Engineering, The Ohio State University
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LOM Example
Department of Mechanical Engineering, The Ohio State University
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Shape Deposition Manufacturing (SDM)
Newer technique developed at Stanford & Carnegie Mellon
Is it a pure SFM process?
1) Deposition- material is
added by plasma or
laser based welding
techniques
2) Filler material is deposited
around part
2) Material is shaped using
conventional CNC
3) Solid is stress relieved
4) Components can be
embedded
5) Filler is removed to leave only finished part
Department of Mechanical Engineering, The Ohio State University
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Sample Part Made from SDM
Material: Stainless Steel (308)
Support Material: Copper
Deposition Method: Microcasting
Support Removal: Etching
Size: 75 x 50 x 42 mm
Average Tensile Strength: 670 MPa
Number of Layers: 29
Layer Thickness: 1.0 - 1.7 mm
Department of Mechanical Engineering, The Ohio State University
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Expansion of SFM Techniques
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Advances in SFM technology have greatly increased the number of
allowable materials and reduced the cost
However many limitations still exist-- can be combined with traditional
processes
3-d Printing Direct Shell Production Casting
SFM process creates a mold- casting is traditional process
Similarly one can generate a part from SFM process and then use
investment casting
Molds can also be made from SFM part by encasing in RTV RTV
mold can make urethane or epoxy parts
Can also create SFM mold and then coat with metal (process called
metal spraying) to get functional mold
Department of Mechanical Engineering, The Ohio State University
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Summary
Many different processes for Rapid Prototype
• Machining
• Stereo-lithography
• Phostosolidification Layer at a Time
• Solid Base Curing
• Fused Deposition Modeling
• Ballistic Particle Manufacturing
• 3D Printing Direct Shell Production Casting
• Selective Laser Sintering
• Laminated Object Manufacturing
Department of Mechanical Engineering, The Ohio State University
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Credits

This module is intended as a supplement to design classes in
mechanical engineering. It was developed at The Ohio State
University under the NSF sponsored Gateway Coalition (grant EEC9109794). Contributing members include:

Gary Kinzel …………………………………….. Project supervisor
Chris Hubert and Alan Bonifas ..……………... Primary authors
Phuong Pham and Matt Detrick ……….…….. Module revisions
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Department of Mechanical Engineering, The Ohio State University
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Disclaimer
This information is provided “as is” for general educational purposes; it can
change over time and should be interpreted with regards to this particular
circumstance. While much effort is made to provide complete information,
Ohio State University and Gateway do not guarantee the accuracy and
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described and/or contain herein and assumes no responsibility for anyone’s use
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Department of Mechanical Engineering, The Ohio State University
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