RP-prest by fanzhongqing

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									 RAPID PROTOTYPING
   Concurrent Engineering I

             Dr. Jack Zhou
           Drexel University
Department of Mechanical Engineering and
               Mechanics
           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 -> Real life
• Why use Rapid Prototyping
  – Decreases lead time
  – Facilitates concurrent engineering
  – Allows visualization of more ideas
Design Process Overview
              Concept


          Pre-lim Design         Drawings


Iterate                     Analysis
            Testing
                            Physical
                            Prototype


                  Success
           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
Traditional Prototyping - Steps
• Engineering Drawings
• Machine or prototype shop to produce part
   – Part usually machined (Lathe, Mill etc.)
   – Problems:
      • Material incompatibility
      • Shop specialization (Can’t 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
      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
               NC - Brief history
• Early 1800’s - 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 1950’s - 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)
             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
         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.
   Solid Freeform Manufacturing
Many restrict true Rapid Prototyping to the Solid Freeform
   Manufacturing (SFM) procedures (i.e. RP=SFM)
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
     SFM Layer Formation Methods
                Solid                                       Liquid

   Powder               Bulk              Liquid                      Melting &
                                       Polymerization                Solidification
1 Component       Gluing Sheets                                     Shape Melting
Selective Laser   Laminated          Light           Heat
  Sintering        Object                                           Fused Deposition
                                                    Thermal          Modeling
                   Manufacturing
Component                           Two              Polymer-
& Binder          Polymerization     frequencies      ization       Ballistic Particle
3D Printing &     Foil              Beam Inter-                      Manufacturing
 Gluing            Polymerization     ference
                                      solid
                                                            Solid Base Curing
                                                   Lamps Photosolid. Layer at a Time
                                    One
                                     frequency
                                                   Lasers   Stereolithography
                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
               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 laser’s 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.
           Stereolithograpy Overview
Mirror
                Optics       Laser
                                           Elevator




Laser is focused/shaped through       When cross section
 optics. A computer controlled        is complete, elevator
mirror directs laser to appropriate   indexes to prepare
spot on photopolymer surface.         for next layer.
Polymer solidifies wherever laser
hits it.
               SLA Interface
• Stereolithograpy was the first commercial Solid
  Freeform Manufacturing process, released in 80’s
  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
                 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
Example of *.stl Representation
           Representing
             a sphere
         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
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.
        Layer at a Time Solidification
                              Mask is then placed under an
                              ultraviolet lamp
                                                              UV Lamp

                                             Clear                                  Glass
                                             Plate                                  Mask



                                        Photo-
                                        polymer



A glass mask is generated                    Laser then shines through mask, solidifying the
(using an electrostatically                  entire layer in one “shot.” Result is much more
charged toner)                               rapid layer formation, and more thorough
                                             solidification. (Light strikes EVERYWHERE.)
              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
               Solid Base Curing Cycle
                   UV Lamp                                 Generate glass mask
 Photo-                          Glass Shine UV Lamp
 polymer                         Mask through mask to
                                       solidify photopolymer

Wax


                                                      Coat with
Remove excess polymer,                                   photopolymer
and fill gaps with liquid wax.
Chill to solidify wax.                                Milling
                      Chiller
                                          Work-       Cutter

 Liquid                                   piece
 Wax
                                           Wax
  Solid
  Wax                               Mill wax &
                                    workpiece
       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).
FDM Layer Formation
                            FDM generated
                            cross section
 Filament

Heated
FDM Head

Molten
Filament


            Supply

                     Notice that the FDM filament cannot
                     cross itself, as this would cause a high
                     spot in the given layer
  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.
                 BPM Process

       Ejector Head
  Has multi-axis control
to "aim" droplet stream

    Droplets
    of Molten
    Material



                    Build
                Platform
        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.
              3-D Printing Process
                                      Print-
                                      head
                                               Powder
                                                Bed
Powder                      Binder
 Bed              Print-
                  head
     "Fast"
      Axis


                                     Piston

              "Slow" Axis
  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.
                           SLS Process
         Mirror                                     Leveling
                    Optics   Laser
                                     Powder         Roller
Powder
                                      Bed
 Bed




                  Piston
                                         Powder Feeding
                                           System
 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).
                       LOM Process
          Mirror                                              Cut "edge"
                          Laser                               of layer


          Optics              Lamination
                              Material                      Perforate
 Heated
 Roller                                                     Workpiece
                                                            Boundary


Take-up
                                           Supply
 Reel
                                           Reel       Cross Hatch
                   Platform
                                                    "Excess Material"
    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
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
  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
        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
Inkjet 3-D Printing
Inkjet 3-D Printing
                   Ink-Jet-Principle
Piezo-Transducer                           Substrate
                            Nozzle


       Pressure
        Wave




                   Build-Material Supply
          Nozzle Checking Algorithm
            One section finished, go to next

                OK                                    OK
     Check              Print             Check
Third         Fail                     Fail
Failure                                        Second
                                               Failure
                        Purge                  in 1 layer
   Stand
    by
                                         Mill off
                        Wipe             Layer
                Technical facts
• Build material
   – thermoplastic, melting point 90 - 113 deg. C
• Support material
   – natural and synthetic waxes, melting point 54 - 76 deg. C
   – soluble in BIOACT at 50 - 70 deg. C
• Building layer thickness
   – 0.0005in (0.013mm) up to 0.005in (0.13mm)
• Accuracy
   – 0.005in over 9in (229mm) in z-axis
• Free standing wall thickness
   – 0.004in (0.1mm)
Pump Housing (with support material)
Pump Housing (Final Part)
            Golf Club

Support


Prototype


 Part
     Making an STL File in I-DEAS
•   Build solid model
•   From the FILE Menu select EXPORT
•   A form appears for the format to export …
•   Select RAPID PROTOTYPE FILE….a form
    appears
•   Select the file for RP machine (sla250.dat)
•   Specify position
•   Specify Absolute Facet Deviation
•   Show facets
•   Examine facets and adjust Absolute Facet Deviation
•   Save STL file (ASCII or BINARY)
Solid Model in I-DEAS
Solid Model in I-DEAS
Facets Generated in I-DEAS
Facets Generated in I-DEAS
              Slicing a Part
•   Import STL file to ModelWin
•   Position the part properly
•   Specify layer thickness
•   Create BIN file
•   View BIN file in BinView
•   Examine and adjust vectors
•   Change name and export BIN file
         Preparing the RP Machine
• Adjust temperature control
    – Build Jet and Line     115 deg. Celsius
    – Support Jet and Line   105 deg. Celsius
•   Command: C:\MDL_MKR\mm file.bin
•   Put Styrofoam on the platform and mill smooth
•   Purge and test jets
•   Start building process
    Post Processing of RP Part
• Remove plate with part from machine
• Heat plate and take off Styrofoam with part
• Put part in heated BIOACT solution until
  foam and support material desolves
• Wash part with soap
• Done

								
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