A look at the past, present and future of Rapid Prototyping RP

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A look at the past, present and future of Rapid
Prototyping (RP)

• Richard A. Wysk
• Leonhard Chair in Enginering
• Industrial and Manufacturing Engineering
• The Pennsylvania State University

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Prerequisite manufacturing humorWhich Is It
Jay-Eye-Teaor"JIT"

• Person who oversees the JIT system

JIT HEAD

• Individual who is afraid to implement a JIT
  system

CHICKEN JIT
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• A source who is a little short of equipment to
  implement JIT

MIDJIT

• Those JIT heads involved in developing the big
  picture

STRATEJITS

• Generally the output from stratejits

BULL JIT
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Agenda

• What is RP?
• Limitations of RP
• Economics of RP
• New directions in RP
• Observations and conclusions

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Introduction

• Prototyping is critically important during
  product/process design
• Reduce time to market
• Early detection of errors
• Assist concurrent manufacturing engineering
• Prototypes are used to convey a products
• Form
• Fit
• Function
• Prototype building can be a time-consuming
  process requiring a highly skilled craftsperson
• Time spent testing prototypes is valuable
• Time spent constructing them is not
• Rapid Prototyping (RP) methods have emerged
• (Solid Freeform Fabrication, Additive
  Manufacturing, Layered Manufacturing)

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Stereolithography (SLA)

• Stereolithography is a common rapid manufacturing
  and rapid prototyping technology for producing
  parts with high accuracy and good surface finish.
  A device that performs stereolithography is
  called an SLA or Stereolithography Apparatus.
• Stereolithography is an additive fabrication
  process utilizing a vat of liquid UV-curable
  photopolymer "resin" and a UV laser to build
  parts a layer at a time. On each layer, the laser
  beam traces a part cross-section pattern on the
  surface of the liquid resin.

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Selective Laser Sintering (SLS)

• SLS can produce parts from a relatively wide
  range of commercially available powder materials,
  including polymers (nylon, also glass-filled or
  with other fillers, and polystyrene), metals
  (steel, titanium, alloy mixtures, and composites)
  and green sand. The physical process can be full
  melting, partial melting, or liquid-phase
  sintering. And, depending on the material, up to
  100 density can be achieved with material
  properties comparable to those from conventional
  manufacturing methods. In many cases large
  numbers of parts can be packed within the powder
  bed, allowing very high productivity.

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Fused Deposition Modeling (FDM)

• Fused deposition modeling, which is often
  referred to by its initials FDM, is a type of
  rapid prototyping or rapid manufacturing (RP)
  technology commonly used within engineering
  design. The FDM technology is marketed
  commercially by Stratasys Inc.
• Like most other RP processes (such as 3D Printing
  and stereolithography) FDM works on an "additive"
  principle by laying down material in layers. A
  plastic filament or metal wire is unwound from a
  coil and supplies material to an extrusion nozzle
  which can turn on and off the flow. The nozzle is
  heated to melt the material and can be moved in
  both horizontal and vertical directions by a
  numerically controlled mechanism, directly
  controlled by a Computer Aided Design software
  package. In a similar manner to
  stereolithography, the model is built up from
  layers as the material hardens immediately after
  extrusion from the nozzle.
• Several materials are available with different
  trade-offs between strength and temperature. As
  well as Acrylonitrile butadiene styrene (ABS)
  polymer, the FDM technology can also be used with
  polycarbonates, polycaprolactone, and waxes. A
  "water-soluble" material can be used for making
  temporary supports while manufacturing is in
  progress. Marketed under the name WaterWorks by
  Stratasys this soluble support material is
  actually dissolved in a heated sodium hydroxide
  solution with the assistance of ultrasonic
  agitation.

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Laminated Object Manufacturing (LOM)

• Laminated Object Manufacturing (LOM) is a rapid
  prototyping system developed by Helisys Inc.
  (Cubic Technologies is now the successor
  organization of Helisys) In it, layers of
  adhesive-coated paper, plastic, or metal
  laminates are successively glued together and cut
  to shape with a knife or laser cutter.

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Electron Beam Melting (EBM)

• Electron Beam Melting (EBM) is a type of rapid
  prototyping for metal parts. It is often
  classified as a rapid manufacturing method. The
  technology manufactures parts by melting metal
  powder layer per layer with an electron beam in a
  high vacuum. Unlike some metal sintering
  techniques, the parts are fully solid, void-free,
  and extremely strong. Electron Beam Melting is
  also referred to as Electron Beam Machining.
• High speed electrons .5-.8 times the speed of
  light are bombarded on the surface of the work
  material generating enough heat to melt the
  surface of the part and cause the material to
  locally vaporize. EBM does require a vacuum,
  meaning that the workpiece is limited in size to
  the vacuum used. The surface finish on the part
  is much better than that of other manufacturing
  processes. EBM can be used on metals, non-metals,
  ceramics, and composites.

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Types of RP Systems
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Problem Introduction

• Rapid Prototyping?
• Technology for producing accurate parts directly
  from CAD models in a few hours with little need
  for human intervention.
• Pham, et al, 1997
• Prototype?
• A first full-scale and usually functional form of
  a new type or design of a construction (as an
  airplane)
• Websters, 1998
• Model?
• A representation in relief or 3 dimensions in
  plaster, papier-mache, wood, plastic, or other
  material of a surface or solid
• Websters, 1986

physical models
How can we automatically create toolpath and
fixture plans for CNC?
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CNC Machining

• Computer numerical control, and refers
  specifically to a computer "controller" that
  reads G-code instructions and drives a machine
  tool, a powered mechanical device typically used
  to fabricate components by the selective removal
  of material. CNC does numerically directed
  interpolation of a cutting tool in the work
  envelope of a machine. The operating parameters
  of the CNC can be altered via a software load
  program.

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Economics

• Product cost engineering cost materials cost
  manufacturing cost
• Product cost /part engineering cost / total
  of parts materials cost / part manufacturing
  cost / part

This is the cost for all parts that will be made
and sold.
This is the cost for each part that will be made
and sold.
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Engineering cost

• Product design (Ced)
• Cost of engineering design
• Process design (Cpc)
• Cost of process planning
• How is the part to be made
• Cost of fixtures and tooling
• Production design (Cpd)
• Cost of setting up production

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Material cost

• In most cases this is independent of the number
  of parts

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Engineering cost

• CE Ced / nt Cpc / nt Cpd / nb
• total parts total parts parts
  in a batch

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Manufacturing cost

• One time costs
• Process planning and design
• Fixture engineering and fabrication
• Set up cost (Cset)
• Cost to set up a process
• Processing cost (Cpsc)
• Cost of processing a part
• Production cost (Cpdc)
• Cost of tooling and perishables

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Manufacturing cost

• CM Cone / nt Cset / nb Cpsc
  Cpdc // ntool
• Total parts parts in a batch
  each part tool cost by parts/tool

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So how can engineering costs be reduced for CNC
machining?
Machine cost Fixture cost
Process planning cost
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• CNC-RP Method A part is machined on a 3-Axis
  mill with a rotary indexer and tailstock using
  layer-based toolpaths from numerous orientations
  about an axis of rotation.

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STEPS TO CREATE A PART ( MT. Bike Suspension
Component)
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STEPS TO CREATE A PART ( MT. Bike Suspension
Component)
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Process/fixture planning time Minutes Processing
time 20 hours
Material Steel Layer depth 0.001 (0.025mm)
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Setups/Orientation Planning
VISIBILITY
MACHINABILITY (for a given tool geometry)
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Visibility Machinability Analysis
Inch
Predicted vs. Measured Machinability on sample
part
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CNC RP Methodology

• Creation of complex parts using a series of thin
  layers (slices) of 3-axis toolpaths generated at
  numerous orientations rotated about an axis of
  the part
• Toolpath planning based on layering methods
  used by other RP systems
• Slice represents visible cross-sectional area
  to be machined about (subtractive) rather than
  actual cross section to be deposited (additive)
• Slice thickness is the depth of cut for the 2½-D
  toolpaths
• Tool used is a flat end mill cutter with equal
  flute and shank diameter (or shank diameter lt
  flute diameter)
• Stock material will be cylindrical, therefore
  toolpath z-zero location will be same for all
  orientations

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Methodology (cont.)
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Methodology (cont.)

• Fixturing accomplished through temporary
  feature(s) (cylinders) appended to the solid
  model prior to toolpath planning
• Cylinders attached to solid model along the axis
  of rotation
• Incrementally created during machining operation
  as the model is rotated
• Model remains secured to stock material then
  removed (similar to support structures in current
  RP methods)

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Rapid Prototyping

• Basics
• Solid model (CAD) is converted to STL format
• Facetted representation where surface is
  approximated by triangles
• Intersect the STL model with parallel planes to
  create cross sections
• Create each cross section, adding on top of
  preceding one

CAD (ProE)
STL
slicing operation
2-D cross section
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Rapid Prototyping

• Fixtures are created in-process (Sacrificial
  Supports)
• Secure model to the build platform
• Support overhanging features
• Remove fixture materials in post-process step

FDM Model with/without supports
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Fixture Planning

• Approach uses sacrificial supports to retain
  the prototype within the stock material
• Round stock clamped between opposing chucks
• As prototype is rotated b/w toolpaths sacrificial
  supports are incrementally created
• Supports cut away to remove finished part
• Current approach assumes model surfaces exist
  along axis of rotation
• Only one fixture support cylinder used on each
  end
• No change to visibility calculations

Problems Where do cylinders begin/end? What
diameter?
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RP versus CNC Machining

• RP processes are very flexible and very capable
• However
• RP processes rely on specialized materials
• Limited accuracy in some cases
• CNC Machining is
• Subtractive process
• Accurate
• Capable of using many common manufacturing
  materials
• CNC Machining is NOT
• Automated
• Easily usable except by highly skilled
  technicians
• CNC machining cannot create all parts
• No hollow parts
• No severely undercut features
• The time consuming tasks of process and fixture
  planning are major factors which prohibit CNC
  machining from being used as a Rapid Prototyping
  Process
• Wang et al, 1999

Functional prototypes?
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Wire EDM Rapid Prototyping

• Medical RP, one of the major territories for RP
  application
• Manufacturing of dimensionally accurate physical
  models of the human anatomy derived from medical
  image data using a variety of rapid prototyping
  (RP) technologies
• CNC-RP?
• Typical bio/medical Material
• Titanium
• Stainless steel
• Cobalt alloy
• Advantage of Wire Electric
  Discharge Machining(WEDM)
• Cut any electrical conductive material regardless
  hardness
• Ignorable cutting force
• Capable to produce complex part

Satisfy material requirement
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Motivation(Cond)

• WEDM is different from traditional machining
  process

Point contact
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Motivation(Cond)

• Visibility problems are different
• Can we see it vs. Can we access it using a
  straight line

Can we see it?
Can we access it?
Tool orientation
wire orientation
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Wire EDM RP
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Wire EDM RP

• Investigate the manufacturability
• Part Geometry
• 6-axis Wire EDM
• Rigid machining part
• No internal through features
• Find the B-axis orientation
• Try to minimize number of B-axis orientation

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Wire EDM RP

• Toolpath generation
• Discrete Toolpath for B-axis and other 5-axis
• STEP-NC
• Fixture Design
• Ignorable cutting force Clamp part

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Example- The Jack
Toolpath and Fixture planning time lt 15 minutes!
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Conclusions

• For prototyping, the process is dominated by
  engineering cost
• Product engineering, Process engineering,
  production engineering
• RP has come a long way
• Usable products
• Process and production engineering coasts are
  minimal
• Conventional methods are on their way back
• CNC RP
• Wire EDM RP

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Questions?!?
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