High Tech Product Design and Rapid Prototyping

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High Tech Product Design andRapid Prototyping

• Prof. Paul Wright, A. Martin Berlin Chair in
  Mechanical Engineering
• Chief Scientist of CITRIS _at_ UC Berkeley
• Co-Director of the Berkeley Wireless
  Research Center
• Co-Director of the Berkeley Manufacturing
  Institute

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A. Business Issues Rapid prototyping plays a
critical role in developing hot products

• Todays high-end CAD systems and high-resolution
  display screens, allow a product to be designed
  and assembled correctly in virtual-space and
  then mass production can begin directly.
• Many sub-systems of the Boeing 777 were analyzed
  virtually 1.
• But experience seems to mediate against this for
  consumer products, for the reasons shown in next
  slidesFor additional reading
• 1. G. Norris and M. Wagner, 2001, The Boeing 777,
  MBI Publishing Company, Osceola WA,

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1. The gut-feeling of a product will it
surprise and delight (Kano)

• Product development today is always done with the
  consumer in mind 2 and in so-called focus
  groups or ideation groups or ethnography
  studies, the invited guinea-pigs prefer to see
  and feel a real product not a computer generated
  image.
• Although these evaluations rely on subjective,
  gut-reactions they are still one of the best ways
  to see if an emerging product generates that
  must have feeling. 2. K.T. Ulrich and S.D.
  Eppinger, 1995, Product Design and Development,
  McGraw Hill, New York, NY.

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2. Classical Ergonomics etc.

• In terms of the feel of the product, there are
  of course important ergonomic aspects to be
  evaluated.
• Including the position and shape of hand grips,
  buttons, screens, dials and ports.

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3. Design interactions between the different
types of designer (electrical, mechanical etc).

• Plan view of component layout from the design of
  Intels Personal Server,
• Perspective view of CAD file of completed device

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4. Electrical interferences

• We have also found that certain evaluations --
  antenna placement in relation to body position
  and electromagnetic interference for example
  cannot be done by simulation.

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5. Broadening the engineering ideas to the rest
of the organization

• Prototypes are also the best way to demo the
  emerging product to the non-engineering parts of
  an organization e.g. promotional image
  development,
• marketing, and
• sales

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6. The overall development cycle is very short.
The creation of a prototype or rather a series
of prototypes is critical.

• Some markets move so fast today that toy-makers
  in particular create two models -- works like
  and look like before they compress everything
  into one footprint and launch into mass
  production during the late-summer months.
• It is no surprise that the annual International
  Consumer Electronics Show (CES) is held in the
  first week of January each calendar year. The
  expectation is that the new gizmos being demoed
  there might take the next 10 months to be fully
  refined, mass produced, shipped and placed in
  stores well before the next holiday season in
  early November.

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7. The electronic components are being updated
and changed on a regular, perhaps monthly, basis.

• The footprints of printed circuit boards are
  changing often. Thus, a quickly regenerated
  physical prototype of the mechanical casing makes
  everyone involved comfortable that the product
  will still go together in the final mass
  production.
• In the figure we showed Intels Personal Server
  a small pager like device for carrying personal
  files to different locations. The casing designs
  that emerged over a period of 3-4 months were all
  tweaked to accommodate modifications in the
  electronic components.

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SLA/FDM/3D-printing

• There are nearly a dozen rapid prototyping
  processes 3 available for producing these first
  looks like components.
• Three of these are especially relevant to
  consumer products stereolithography (SLA), fused
  deposition modeling (FDM) and 3D-printing. We
  begin with a review of SLA launched commercially
  in 1987 by 3D Systems Inc. The key steps are
  described in the next slides
• 3. See as an example http//www.boedeker.com/sl
  a.htm

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1. Tessellation

• The surfaces of a standard CAD file are
  tessellated.
• For visitors to our studio I explain that its
  like throwing a fish-net stocking over the
  surfaces, converting them a sea of 10,000
  triangles.
• In 1987 3D Systems called this file of triangles
  the .STL file -- and like many de facto standards
  this has remained in use since then and
  furthermore adopted by most if not all other
  processes such as FDM.

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2. Slicing

• The file of triangles is sent to the prototyping
  machine and sorted into layers by the z-dimension
  of the triangles.
• Again, to visitors, I explain this is like
  slicing the original CAD model into a stack of
  pancakes.

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3. Curing of a photopolymer with a low power
laser.

• The photocurable liquid, resembling honey in
  appearance, is kept in a vat and the laser begins
  to scan the top surface.
• This cures an initial layer, resembling ice
  forming on a pond,
• The layer is made to sit on a mechanical
  elevator-platform just below the surface.

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4. P.K. Wright, 21st Century Manufacturing, 2001,
Prentice Hall, See Chapter 4 on Rapid
Prototyping, pages 130 to 170. See Chapter 8 on
Plastic Product Manufacturing, pages 330 to 365.
ISBN Number 0-13-095601-5.
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4. More layering

• Once the first layer is cured, the elevator jogs
  down a few tenths of a millimeter
• Liquid flows over it, and then the laser begins
  work on the second layer which, with the correct
  controls, fuses to the first layer.
• The process is repeated many times layers
  accumulate over several hours until the object is
  formed
• The elevator rises and like Excaliburs sword,
  the object appears from the honey! Curing and
  hand finishing are finally needed.

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SLA pros and cons

• SLA retains a preeminent position in the rapid
  prototyping family because it is the most
  accurate (though still less accurate than a
  standard CNC milling machine).
• High resolution lasers SLA can manufacture parts
  with tolerances of /- 0.002 to 0.003 inches 3.
  
• SLA models are used as the master in the
  processes described later.

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So why invent and use FDM and 3D-printing?

• The simple answer is that these are progressively
  cheaper and faster but at the expense of
  accuracy.
• 3D-printing is fast enough to produce two or
  three prototypes in one afternoon for the
  ideation groups mentioned above. Fail often
  fast.Then do it right is the mantra at IDEO the
  leading consumer product design company.
• FDM usually requires an overnight run.

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FDM and 3D printing

• Both FDM and 3D-printing can be run by
  inexperienced students and do not need careful
  calibration or the expensive phototcurable
  liquid.
• Both these other processes use the same file
  format as SLA.
• FDM creates the layers by hot mini toothpaste
  extrusion of plastic --- or like a cake-icing
  tool that extrudes hot plastic in rows (or roads)
  with a super fine point.
• 3D-printing is literally like a Xerox machine
  that squirts epoxy resin layer-by-layer onto a
  ceramic powder that resembles corn-starch.

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Engineering Issues More details on the process

• Now consider issues such as
• STL files
• Slicing etc

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Rapid Prototyping

• Prototype - Centuries old
• usually casting, machining
• Rapid Prototyping - 1987
• usually SLA, SLS, FDM (SFF)

5 step casting
made
500
Master
2 1
SLA
SLA
Time
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Stereo Lithography (SLA)

• Q2 Why is SLA todays industry standard?
• A2 Many subtle issues in process planning since
  1987.
• Good tolerances /- 0.002 to /-0.005

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History
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Details of RP file formats

• We begin with the triangle format

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The .stl file format

• 3D Systems (1987)
• Tesselates the solid model.
• CAD model - Outer shell turned into many
  triangles.
• Soccer ball analogy.

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SLA (bottom surface)
bordering
filling
hatching
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Manufacturing side Laser Movements
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Laser Movements

• Step 1 Trace the boundary
• Step 2 Hatching or weaving

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On the manufacturing side

• CSLICE - sorts the .stl file into layers.
• .stl file
• sort triangles into z-values
• finds the boundary segments

One slice of triangles of one Z-height
Contiguous Boundary
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On the manufacturing side

• Based on the operators knowledge of the laser,
  apply edge compensations for the gaussian laser
  strength.
• We compare with adjacent layers and also make
  edge compensations in the vertical direction -
  smooth boundaries

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SLA - Accuracy
/- 0.003 to /- 0.005
L
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SLA - Accuracy
Stair Stepping
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