RAPID PROTOTYPING Concurrent Engineering I

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RAPID PROTOTYPING Concurrent Engineering I

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Title: RAPID PROTOTYPING Concurrent Engineering I

1
RAPID PROTOTYPINGConcurrent Engineering I

Dr. Jack Zhou
Drexel University
Department of Mechanical Engineering and Mechanics

2
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 -gt Real life
Why use Rapid Prototyping
Decreases lead time
Facilitates concurrent engineering
Allows visualization of more ideas

3
Design Process Overview
Concept
Pre-lim Design
Drawings
Iterate
Analysis
Testing
Physical Prototype
Success
4
Prototype Classifications

Conceptual
Make sure all team members of the project are
aware of what is to be designed.
Physical (true prototype)
Form- Design verification, marketing and
communication tool
High dimensional accuracy is NOT required
Non-technical people see how product looks and
feels
Fit- Verify manufacturability, assembly, and fit
Required shape along with good dimensional
tolerances
Material choice is not important
Function- Used to test functionality of real part
Material should be similar to actual part
Function prototype should have same failure modes
and levels as actual part

5
Traditional Prototyping - Steps

Engineering Drawings
Machine or prototype shop to produce part
Part usually machined (Lathe, Mill etc.)
Problems
Material incompatibility
Shop specialization (Cant perform task you need)
Machine deficiencies (You have 3 axis mill, you
need 5 axes)
Part too complex to produce (curved surfaces are
very difficult)
Design limited by prototype tools available
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

6
Numerical Control Machining

Significantly reduces time required for prototype
fabrication-
Steps
Starts with solid model from some CAD package
(I-DEAS or Pro-E for example)
Next create the desired tool paths
Problems/Limitations
Process not totally automatic. Operator must
make of decisions
Appropriate tools
How to fixture the stock
Refixturing during machining

7
NC - Brief history

Early 1800s - 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 1950s - MIT developed a common language to
describe cutting motions with a certain machine.
Code placed on a paper tape the machine could
read
Advantages of NC over traditional machining
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)

8
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

9
NC Machining Rapid Prototyping

NC machining requires a skilled operator to set
up machine and to specify tools, speeds, and raw
materials.
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.

10
Solid Freeform Manufacturing
Many restrict true Rapid Prototyping to the Solid
Freeform Manufacturing (SFM) procedures
(i.e. RPSFM) 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
11
SFM Layer Formation Methods
Solid
Liquid
Liquid Polymerization
Melting Solidification
Powder
Bulk
Shape Melting Fused Deposition
Modeling Ballistic Particle Manufacturing
1 Component Selective Laser Sintering
Gluing Sheets Laminated Object Manufacturing
Light
Heat
Thermal Polymer- ization
Component Binder 3D Printing Gluing
Two frequencies Beam Inter- ference
solid One frequency
Polymerization Foil Polymerization
Solid Base Curing Photosolid. Layer at a Time
Lamps
Lasers
Stereolithography
12
SFM Technology

Stereo-lithography- photopolymer cured by laser
Phostosoldification Layer at a Time-
photopolymer cured by light
Solid Base Curing- photopolymer is cured by UV
light
Fused Deposition Modeling - molten plastic is
extruded solidifies
Ballistic Particle Manufacturing- microparticles
of molten plastic
3D Printing Direct Shell Production Casting-
powder w/ binder
Selective Laser Sintering- fusible powder, fused
by laser
Laminated Object Manufacturing- glued layers of
sheets

13
Stereo Lithography
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
lasers 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.
14
Stereolithograpy 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.
15
SLA Interface

Stereolithograpy was the first commercial Solid
Freeform Manufacturing process, released in 80s
by 3-D Systems
3-D Systems had to develop an interface between
CAD systems and their machine
STL files (.stl) were developed by 3-D systems
to allow CAD systems to interface with their
machine
Virtually all subsequent SFM processes can use
this same format (it is the SFM industry
standard)
Many CAD programs now can export the .stl file
for easy conversion from CAD to part

16
STL Files (.stl)
STL files were based on a program called
Silverscreen CAD In Silverscreen CAD, a boundary
representation style was used, with all
surfaces being approximated by polygons or
groups of polygons .stl files use triangles
or groups of triangles to approximate all
surfaces Obviously, one can never exactly form
curved or rounded surfaces with triangles--
the accuracy of the model depends on the size
of the triangles Triangles are all assigned a
normal vector, which represents the outward
surface normal Parts are defined by representing
all their bounding surfaces as faceted
surfaces, using the triangular patches
17
Example of .stl Representation
Representing a sphere
18
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 in each of the slices are
the cross sections that the modeler will
make 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
19
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.
20
Layer at a Time Solidification
Mask is then placed under an ultraviolet lamp
A glass mask is generated (using an
electrostatically charged toner)
Laser then shines through mask, solidifying
the entire layer in one shot. Result is much
more rapid layer formation, and more thorough
solidification. (Light strikes EVERYWHERE.)
21
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
22
Solid Base Curing Cycle
Generate glass mask
Shine UV Lamp through mask to solidify
photopolymer
Coat with photopolymer
Remove excess polymer, and fill gaps with liquid
wax. Chill to solidify wax.
Mill wax workpiece
23
Fused Deposition Modeling (FDM)
1) A spool of thin plastic filament feeds
material to FDM head 2) Inside FDM, filament is
melted by a resistance heater 3) The semiliquid
thermoplastic is extruded through FDM
head 4) Material is deposited in a thin layer on
formation 5) Material solidifies, forming a
laminate 6) 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).
24
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
25
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.
26
BPM Process
27
3-D Printing Direct Shell Production Casting
(DSPC)
First creates a disposable mold which is used to
cast actual part 1) Thin distribution of powder
is spread over powder bed 2) Inkjet printheads
deposit small droplets of binder 3) Upon contact,
binder droplets join powder to form
solid 4) Piston supporting powder bed lowers so
that the next layer can be spread and
joined 5) Process repeats until completion 6)
The shell that has been created is
fired 7) Shell is filled with molten
metal 8) 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.
28
3-D Printing Process
29
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.
30
SLS Process
31
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).
32
LOM Process
33
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
34
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
35
Expansion of SFM Techniques

Advances in SFM technology have greatly increased
the number of allowable materials and reduced the
cost
However many limitations still exist-- to further
utilize SFM processes they 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

36
Inkjet 3-D Printing

perimeter of the build section printed
area of the build section filled (several times)
support section printed
wait for material to cool
layer surface milled to specific thickness
platform lowered one layer thickness
process repeated

37
Inkjet 3-D Printing
38
Inkjet 3-D Printing
39
Ink-Jet-Principle
Piezo-Transducer
Substrate
Nozzle
Pressure Wave
Build-Material Supply
40
Nozzle Checking Algorithm
One section finished, go to next
Print
Check
Check
OK
OK
Third Failure
Fail
Fail
Second Failure in 1 layer
Purge
Stand by
Mill off Layer
Wipe
41
Technical facts