ME 350 – Lecture 2A

1. ME 350 – Lecture 2A Rapid Prototyping: • Fundamentals of Rapid Prototyping • Rapid Prototyping Technologies • Applications and Benefits of Rapid Prototyping

2. Learning Objectives • What Rapid Prototyping is and why it is “rapid” • What the basic types of rapid prototyping techniques are • Estimate fabrication time • Understand constraint and limitations of RP • Where to find the RP applications

3. The simplified Manufacturing Process Prototypes – to visualize your idea, for functional demonstration, tests, evaluation, etc. Manufacturing

4. Why Rapid Prototyping (RP) ? • Model from clay • Carve from wood • Bend wire meshing • Carve from Styrofoam – perhaps with surface reinforcement • Mill from a block of plastic or aluminum (3- or 4-axes machines)

5. Additive RP • Adds layers of material one at a time to build the solid part from the bottom to the top • Build-up of complex 3D shapes from 2D layers • Also called Layered Manufacturing (LM) or Solid Freeform Fabrication (SFF)

6. Classification of RP Technologies The RP classification is based on the form of the starting material: • Liquid-based: monomers are deposited in layers (SLA & FDM & Objet) • Solid-based: solid sheets that are to create the solid part (LOM) • Powder-based: powders that are (SLS & 3DP)

7. Ford Lab RP Machines We now have 3 high resolution RP machines in the Ford Lab (MEL): • OBJET by Eden: photopolymer ink jet printing followed by UV light soak/harden at each layer (www.objet.com) • SLA by 3D Systems: Liquid photopolymer in a bath cured by UV laser, layer by layer (www.3Dsystems.com) • SLS by EOS: powders that are bondedthermally by a laser, layer by layer (www.EOS.info)

8. Liquid RP: Stereolithography (SLA) Part made out of a photosensitive liquid polymer selectively cured using a directed laser beam • Earliest RP method demonstrated • More installations than any other RP method

9. Rapid Prototyping: SLA

10. + UV light radical Initiator + +heat monomer + +heat Polymer Chemistry of Photoforming Initiation: Line Pattern Illuminated Propagation: Radical diffusion Termination:

11. Laser Scanning Profile Scanning direction, speed U t D Volume solidification rate: Q ≈ D∙t ∙U

12. Roughness on Sidewalls

13. Part Build Time in SLA Time to complete a single layer : where Ti = time to complete layer i; Ai = area of layer i; v = average scanning speed of the laser beam at the surface; D = diameter of the “spot size,” assumed circular; and Td = delay time between layers to reposition the worktable

14. In-class exercise • A cone-shaped part, R= 35 mm, H = 40 mm. Layer thickness t= 0.20 mm, Laser beam: D = 0.22 mm, Scanning velocity U= 500mm/s. H In addition: 10 s/layer to lower the platform that holds the part 2R t . .

15. SLA: • Layers are each 25-50 μm thick • Support “pillars” (~100 μm dia.) needed every 2-3 mm • Recent material improvements: • In the past only brittle fragile yellow photopolymer available • Now lots of material choice, we use either a strong rigid clear photopolymer or a white ductile semi-elastomeric photopolymer • Less shrinkage during UV cure (<1%) than in the past (1-2%) Pros: • Uses less support structures than some other methods • Can produce the highest resolution surface features Cons: • No easy way to remove support scaffolding → must cut • Messy to clean

16. 2μm SLA – resolution pushed to the extreme Spiral Lattice (Zhang, Berkeley) The Nanobull (Kawata, Japan) 200μm Resolution down to 75 nanometers are feasible!

17. Fused Deposition Modeling (FDM) • Droplets or a continuous filament of a molten wax, thermoplastic or slurry are printed from a jet or heated needle extruder head onto a platform surface. • Extrudate is solidified and cold welded to the cooler surface very rapidly. • Need to build a complete support structure everywhere there are overhangs / bridges. • Support material is water soluble (FDM systems generally have at least two extruder heads) • Surface finish is generally not a good as SLA • Layer to layer delay is generally much less than SLA

18. Fused Deposition Modeling Filament extruding D Ink binder U Volume solidification rate: Profs. J.Lewis and A. Alleyne, UIUC

19. FDM machines and structures made Filament of support material Finished shape

20. 10 µm 10 µm Direct Deposition of Microstructures J. Lewis, Nature, 2004

21. FDM: Pros and Cons Pros: • Potential for high resolution • Inexpensive Cons: • Overhanging structures need a lot of support structures • High resolution → small filament → very slow • Difficult to achieve “flat” surface

22. Laminated Object Manufacturing (LOM) Solid physical model made by: • Sheet stock (typically plastic or paper cellulose), is advanced and heat bonded (usually by a heated roller) to previous layer • Laser outlines part, then crosshatches area to be later removed • Sheet stock advanced again, and process repeated. • Excess material removed at completion with putty knife or similar.

23. LOM Example: Landscaping models

24. LOM: Pros and Cons Pros: • Minimal heating and no chemical development • Low shrinkage and low stress • Minimal tooling path around outlines • No supports needed • Cheap and non-toxic materials Cons: • Delicate parts can be damaged when removing tiles (i.e. “crosshatched” regions). • Wasted materials • Rough surface and limited finishing process • Burning fumes

25. Powder-based Approaches Key Properties: • Needs no supports that must be removed! • Uniform bed of powder acts as support. • This powder gets selectively (locally) glued (or fused) together to create the solid portions of the desired part.

26. Selective Laser Sintering (SLS) Moving laser beam sinters heat‑fusible powders in areas corresponding to the CAD geometry model one layer at a time to build the solid part • After each layer is completed, a new layer of loose powders is spread across the surface • Layer by layer, the powders are gradually bonded by the laser beam into a solid mass that forms the 3-D part geometry • In areas not sintered, the powders are loose and can be poured out of completed part

27. Selective Laser Sintering– Powder Based Three dimensional printing: (1) powder layer is deposited, (2) ink-jet printing of areas that will become the part, and (3) piston is lowered for next layer (key: v = motion).

28. SLS: Pros and Cons Pros: • Color ! • Running expenses: moderate,(but overpriced powder) Cons: • Color print head and tubes need some care in maintenance. • Lot’s of dust everywhere • Slow

29. Three Dimensional Printing (3DP) Part is built layer-by-layer using an ink-jet printer to eject adhesive bonding material onto successive layers of powders • Binder is deposited in areas corresponding to the cross sections of part, as determined by slicing the CAD geometric model into layers • The binder holds the powders together to form the solid part, while the unbonded powders remain loose to be removed later • To further strengthen the part, a sintering step can be applied to bond the individual powders

30. 3D Printing: The Z402 3D Printer • Speed: 1-2 vertical inches per hour • Build Volume: 8" x 10" x 8" • Layer thickness: 3 to 10 mils, selectable

31. Problems with Rapid Prototyping • Part accuracy or surface smoothness • Staircase appearance for a sloping part surface due to layering • Shrinkage and distortion of RP parts • Limited variety of materials in RP • Mechanical performance of the fabricated parts is limited by the materials that must be used in the RP process • Removal of support material where applicable

32. RP Applications • Prototypes – to visualize your idea, for wind tunnel testing, or for small batches • Patternfor casting mold • Assembly testing • To make parts with intricate internal geometries • Medical Apps - one-of-a-kind parts