An Introduction to Rapid Prototyping

1
An Introduction to Rapid Prototyping

• ME-160
• Fall 2005

2
Rapid Prototyping

• Techniques that construct an object from a
  3-dimensional computer model in a layer-wise
  manner without molds, forms, or machining.
• Selective placement of solid material in a plane.
• Solidifying a liquid
• Fusing solid particles
• Cutting and stacking
• Applications
• Visualization models
• Tooling
• Direct fabrication of objects
• Unique materials, composites, and geometries.

1.1.1
3
Current Uses of Rapid Prototyping
Functional or Ergonomic Models Visual Aids for
Engineering and Toolmaking ... Fit and
Assembly Evaluations Patterns for
Prototype Tooling and Metal Casting. Dir
ect Tooling Inserts... Quoting and
Proposals...
27.3

22.3
18.2
19.7
3.7
5.0
Source 2001 Wohlers Report
4
The Need for Speed in the Product Development
Process
Global Manufacturing Environment

• More competitors more pressure to develop new
  and improved products.
• Shorter model life fewer number of units to
  recover development costs.
• To be profitable, costs must be low. It is much
  more difficult now to pass on costs to the
  consumer.
• New design tools must focus on speeding up the
  product development process and reducing costs
  (read that as getting it right the first time).

5
1980s Design Tools

• Computer-Aided Design (CAD)
• 2-dimensional representation of 3-dimensional
  parts.
• Used more for design documentation than for
  design.
• Finite Element Analysis (FEA)
• No link to CAD, analyst creates model from
  scratch.
• Mostly 2-D linear analysis on PCs, more complex
  problems limited to mainframe computers.
• Used more for design verification than for design
  development.

6
1990s Design Tools

• Solid Modeling
• 3-dimensional representations.
• 2-dimensional drawings created from solid model
  for documentation.
• Links to FEA, tool design, CNC manufacturing, and
  rapid prototyping.
• Finite Element Analysis
• Better hardware, software complex analysis
  possible with PCs.
• Links to solid modeling and 2-D CAD programs
  reduce modeling time.
• Some programs have optimization capabilities.

• Rapid Prototyping
• Physical 3-D models for visualization
• Functional prototypes for some parts
• Tooling patterns for some processes

7
Rapid Prototyping as a Design Tool
Chrysler has reduced time from production
approval to vehicle launch from five years to
two, and credits solid modeling and rapid
prototyping as keys
In the past, the vehicle development process
started with a blank piece of paper on which a
designer sketched a conceptToday, the same
designer uses a pen-like stylus to sketch the
vehicle on the computer. This sketch can be made
quickly into a full-scale 3-D imageIn the past,
time would allow only five designs of an engine
intake manifold. CATIA, however, made possible
1,500 designs in six months less timeWhen
prototype tooling is requiredwe use processes
like stereolithography to create the physical
model directly from the computer data. Instead
of four to five weeks of prototype development, a
rapid prototyping machine develops the model in a
few days. - Chrysler Corporation 1996 Annual
Report
8
Rapid Prototyping as a way to keep your job !

• Cost of engineering changes increase by an order
  of magnitude as the design moves into the next
  stage of development

9
Steps Common to RP Processes

• Construct solid model on CAD system.
• Translate to surface representation .stl file
  (common format read by RP software.)
• Generate 2-D slices with path definitions.
• (RP machine-specific software.)
• Add support structures where needed to support
  the model during fabrication.
• Build object.
• Post processing.

10
STL File Format
(3.00, -1.00, 1.00)
11
Triangle size demonstration
Triangles 38,000 File Size 1.9 MB
12
Triangle size demonstration
Triangles 195,000 File Size 19.5 MB
13
Rapid Prototyping Center Equipment
Laminated Object Modeling
Stereolithography
Fused Deposition Modeling
Selective Laser Sintering
14
MSOE Rapid PrototypingConsortium
15
Advantages of Rapid Prototyping

• No tooling/forms/fixtures
• Complex geometries
• Shapes that cannot be cast
• Internal cooling channels, etc.
• Unattended operation
• Waste-less fabrication
• Rapid days rather than weeks!

16
Disadvantages of Rapid Prototyping

• Reduced accuracy
• RP 50-100 mm (0.002-0.004 in.)
• EDM 1-10 mm (lt0.0004 in.)
• Good-to-fair surface finish
• Inefficient bulk fabrication
• Build envelope size limits
• Limited material choices

17
Stereolithography
18
Stereolithography
19
Stereolithography

• Laser used to selectively cure layer of liquid
  photopolymer.
• Acrylate resin
• Epoxy
• Curing by ultraviolet wavelengths.
• He-Cd or solid state laser.
• Elevator moves downward by one layer thickness,
  allowing liquid photopolymer to form a new layer
  over the part.
• After build is completed, must be postprocessed
• Supports removed.
• Post-cured to develop full strength.

2.0.a
20
SLA Advantages

• Good accuracy and surface finish
• Good speed, especially if multiple parts are made
  in a single build
• Well-characterized and accepted technology
  (oldest RP process)
• Almost no waste

21
SLA Disadvantages

• Resins are skin irritants
• Requires support structures for some part
  geometries
• High material cost (800 per gallon)
• Limited choice of materials

22
Laminated Object Manufacturing
23
Laminated Object Manufacturing
24
Laminated Object Manufacturing

• Uses paper (or other film) sheets coated with
  thermal adhesive to build up parts.
• Each new sheet bonded to part with heat and
  pressure.
• Laser then cuts around the part profile for that
  layer.
• Outside part profile, layer is cross-hatched,
  permitting removal after model is finished.
• Result is part imbedded within a block of
  supporting material.

25
LOM Advantages

• Subtractive method allows large volumes to be
  built rapidly
• Supported building
• Surface quality and accuracy
• Materials
• Dry forming vs. liquids or loose powders
• Only as good as tape casting technology

26
LOM Disadvantages

• Manual cleanup requires skill, time
• Waste
• Majority of the material consumed by LOM does not
  contribute to the part itself
• Safety
• Laser cutting produces smoke and/or fumes -
  venting may be required
• Laminar structure
• Parts are formed from alternating layers of
  material and adhesive.
• Physical properties (strength, modulus)
  inhomogeneous and anisotropic
• Delamination and warping

27
Fused Deposition Modeling
28
Fused Deposition Modeling
29
Fused Deposition Modeling

• Parts built up with thermoplastic polymer
  (usually ABS) or wax.
• Material supplied on flexible filament.
• Material heated to 1o F above solidification
  temperature, extruded onto part where it quickly
  cools.
• No post-processing of model other than removal of
  thin-wall support structures.

30
FDM Advantages

• Safety
• Inert, non-toxic solids.
• No fumes, solvents office environment.
• Reliability
• Low cost
• Ability to create hollow parts (no trapped
  liquid)
• Materials
• ABS is tough, functional material.
• Wax is important as patterns for investment
  castings.
• Possibility for multiple materials.
• Metals and ceramics possible using powder
  processing techniques.

31
FDM Disadvantages

• Poor surface finish due to thick layers
• Supports are required
• Slow build speed (10X slower than other RP
  processes)

32
Selective Laser Sintering
33
Selective Laser Sintering
34
Selective Laser Sintering

• Developed at University of Texas, commercialized
  by DTM corporation.
• Uses powder as bulk material (thermoplastic
  polymer, wax, metal, or ceramic).
• Layer of powder spread over the top of the part,
  leveled.
• Laser used to fuse or sinter layer onto part.
• No support structure is needed, as unfused powder
  supports the part.
• Finished part is embedded within a cake of loose
  powder.

35
SLS Materials

• Polycarbonate
• Polystyrene
• Nylon
• Glass-filled nylon
• Coated metal powder
• Elastomer

36
SLS Advantages

• Wide choice of materials
• Direct functional parts
• Tooling
• Supported build
• Good for complex parts
• Speed

37
SLS Disadvantages

• Surface finish
• Retains granular texture of original particles
• Porosity, strength
• Many materials not fully dense
• Shrinkage, curling
• Process complexity
• Many operational variables laser power, speed,
  supply material temperature
• Concerns about nitrogen leaks, lack of O2
• High cost (400,000)

38
Concept Modelers

• Solidscape
• 3DS Thermojet
• Stratasys Genisys
• Z Corporation Z406

39
Concept Modelers

• Low cost LAN devices, three dimensional
  printers.
• Low noise, office environment.
• Easy to use, no specialized skills.
• Lower resolution, higher speed, low cost per
  part.
• Weak materials, used for visual models only.
• Generally used by designers as a rough draft
  before sending to more expensive rapid
  prototyping equipment.

40
Big Question which is the bestRP system?

• Answer it depends
• 18 different suppliers worldwide,
• all have a niche.
• Two real categories
• Rapid Prototyping equipment
• Concept Modelers
• Selection depends on users needs.