Rapid Prototyping RP

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Rapid Prototyping (RP)

• compiled by Michelle Griffith - Sandia National
  Laboratories
• adapted by John Lamancusa - Penn State

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RP Sequence

• CAD solid model
• .STL file
• Slicing the file
• Final build file
• Fabrication of part
• Post processing

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CAD Solid Model

• Solid model or closed surface model required

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.STL File

• Software generates a tessellated object
  description
• File consists of the X, Y, Z coordinates of the
  three vertices of each surface triangle, with an
  index to describe the orientation of the surface
  normal
• Support generation to hold overhung surfaces
  during build

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solid ascii facet normal 0.000000e000
-1.018113e-001 -9.948037e-001 outer loop
vertex 6.413766e000 9.540946e000
4.174942e-001 vertex 6.663766e000
9.540946e000 4.174942e-001 vertex
6.413766e000 9.467294e000 4.250320e-001
endloop endfacet facet normal 1.587419e-015
-1.018113e-001 -9.948037e-001 outer loop
vertex 6.413766e000 9.467294e000
4.250320e-001 vertex 6.663766e000
9.540946e000 4.174942e-001 vertex
6.663766e000 9.467294e000 4.250320e-001
endloop endfacet . .
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Slicing the File

• Series of closely spaced horizontal planes are
  mathematically passed through the .stl file
• Generate a .sli file a series of closely
  spaced 2D cross-sections of the 3D object
• Typical Z thickness 0.006 (0.150 mm)
• Other Parameters chosen fn(RP technology)

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Final Build File
Part

• Part sliced
• Supports sliced
• RP technology parameters set
• layer thickness, scan speed,...
• Send file to RP machine

Supports
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Fabrication of Part
Models built on stereolithography apparatus.
Part and supports shown attached to platform.
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Post-processing

• Removal of part from platform
• Removal of supports from part
• Cleaning of part (wiping, rinsing, ... )
• Finishing part (curing, sanding, polishing, )

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Rapid Prototyping Technologies

• Several technologies
• Stereolithography (SL) Laminated Object
  Manufacturing (LOM)
• Selective Laser Sintering (SLS)
• Fused Deposition Modeling (FDM)
• Solid Ground Curing (SGC) 3D Printing (3DP)
• Laser Engineered Net Shaping (LENS)

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Stereolithography (SLA)
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Stereolithography (SLA)

• 3D Systems, Valencia, CA
• patent 1986, beginning of RP
• photopolymerization using UV laser
• epoxies, acrylates (brittle)
• excellent accuracy
• relatively slow
• 179,000 (103 in3) to 799,000 (203 in3)

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SLA Video http//www.acucast.com/video.htm
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Laminated Object ManufacturingLOM
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Laminated Object Manufacturing(LOM)

• Helisys, Torrance, CA (out of business in 2000,
  serviced by a successor organization, Cubic
  Technologies)
• patent 1988
• cross-sectional cutouts fused together
• paper, plastic (new)
• accuracy 0.005

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Selective Laser Sintering
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Selective Laser Sintering (SLS)

• DTM, Austin, TX, now 3D systems
• patent 1989, Carl Deckards masters thesis
• fusing polymeric powders with CO2 laser
• accuracy 160 mm
• no supports
• polycarbonate, nylon, wax, glass-filled nylon,
  powder coated metals or ceramics
• can be end-use parts

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SLS Video http//www.acucast.com/multimedia
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Fused Deposition Modeling
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Fused Deposition ModelingFDM

• Stratasys, Eden Prarie, MN
• patent 1992
• robotically guided fiber extrusion
• accuracy 0.005
• casting and machinable waxes, polyolefin, ABS
• water soluble or wax supports

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FDM material
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Solid Ground Curing
http//home.att.net/castleisland/sgc.htm
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Solid Ground Curing (SGC)

• Devleoped by Cubital Ltd. of Israel
• High capital and operational cost
• Large heavy equipment
• Good dimensional accuaracy

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SGC (from Efunda)
http//www.efunda.com/processes/rapid_prototyping/
sgc.cfm
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Instead of using a laser to expose and harden
photopolymer element by element within a layer as
is done in stereolithography, SGC uses a mask to
expose the entire object layer at once with a
burst of intense UV light. The method of
generating the masks is based on
electrophotography (xerography). This is a two
cycle process having a mask generation cycle and
a layer fabrication cycle. It takes about 2
minutes to complete all operations to make a
layer 1. First the object under construction
(A) is given a coating of photopolymer resin as
it passes the resin applicator station (B) on its
way to the exposure cell (C). 2. A mask is
generated by electrostatically transferring toner
in the required object cross sectional image
pattern to a glass plate (D) An electron gun
writes a charge pattern on the plate which is
developed with toner. The glass plate then moves
to the exposure cell where it is positioned above
the object under construction. 3. A shutter is
opened allowing the exposure light to pass
through the mask and quickly cure the
photopolymer layer in the required pattern.
Because the light is so intense the layer is
fully cured and no secondary curing operation is
necessary as is the case with stereolithography.

http//home.att.net/castleisland/sgc.htm
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4. The mask and object under fabrication then
part company. The glass mask is cleaned of toner
and discharged. A new mask is electrophotographica
lly generated on the plate to repeat the cycle.
5. The object moves to the aerodynamic wiper
(E) where any resin that wasn't hardened is
vacuumed off and discarded. 6. It then passes
under a wax applicator (F) where the voids
created by the removal of the unhardened resin
are filled with wax. The wax is hardened by
moving the object to the cooling station (G)
where a cold plate is pressed against it. 7.
The final step involves running the object under
the milling head (H). Both the wax and
photopolymer are milled to a uniform thickness
and the cycle is repeated until the object is
completely formed within a wax matrix.
Secondary operations are required to remove the
wax. It can either be melted away or dissolved
using a dish-washing-like machine. The object is
then sanded or otherwise finished as is done in
stereolithography. The wax matrix makes it
unnecessary to generate extra support structures
for overhangs or undercuts. This, and the large
volume capacity of the system, also makes it easy
to nest many different objects within the build
volume for high throughput.
http//home.att.net/castleisland/sgc.htm
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3D Printing
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Inkjets
http//home.att.net/castleisland/sgc.htm
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3D Printing

• ZCorpSanders Prototype Inc., NH
• ink jet technology
• dual heads deposit part material (thermoplastic)
  and support material (wax)
• build layers as thin as .0005
• very fast and cheap process

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Laser Engineered Net Shaping TM
http//home.att.net/castleisland/sgc.htm
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Laser Engineered Net Shaping TM

• In development (Sandia Labs, Optomec)
• Fully Dense Metal parts with good metallurgical
  properties
• Laser melts metal powder
• Powder delivered coaxially with laser
• Inert gas protects weld pool
• Near net shape with some finish machining

http//home.att.net/castleisland/sgc.htm
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http//www.xpress3d.com/