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Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

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Presentation on theme: "Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping"— Presentation transcript:

1 Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

2 Introduction  Numerous commercially available RP systems are based upon the principle of photo- polymerization.  The aims of this module are:  To provide you with an overview of which systems are available, and what their operating principle is.  To introduce the theory behind light-resin interactions as a means of explaining some of the dozens of process parameters you can control when using one of these systems.

3 ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Part I – Commercially Available Systems

4  h?v=NRc8yP-YM1A h?v=NRc8yP-YM1A  SLA Viper  355 nm solid state Nd:YVO4 laser up to 100mW  Dual resolution  0.25mm or 0.075mm beam diameter 3D Systems Stereolithography

5 CAD-To-SLA Process  CAD models are saved as STL files  Models are brought into the Lightyear software  Translated, rotated, scaled, copied as needed  Nest as many parts on the platform as possible  STL files are verified to ensure that the surfaces are water tight  Supports are generated beneath downward-facing surfaces  The build is sliced  The slice images to be drawn by the laser are stored in a new slice file format read by the SLA machine

6 SLA Postprocessing  Support removal  Cleaning uncured resin with TPM or alcohol  Postcuring  Sanding

7 SLA Tempering   SLA parts are typically more brittle than thermoplastic resins  A patented tempering process (see photos and article above) calls for fabricating parts with small channels.  A composite material is injected into the channels that dramatically increases impact resistance and flexibility. Tempered SLA parts Untempered SLA parts Source:

8 Sony – Solid Creation System  Identical in concept to 3D Systems stereolithography process  Systems available with  Two lasers for faster builds  1,000 mW lasers (our SLA has a 40 mW laser!)  Adjustable laser spot size and layer thickness during the build

9 3D Systems - ProJet  ch?v=5hhnXFmdUHQ ch?v=5hhnXFmdUHQ  Multi-jet inkjet printing of UV curable photo-polymer.  UV flood lamp curing after printing of each layer  Two resolutions available  SR model: 0.003" resolution in X,Y and " in Z  HR model: " resolution in X,Y and " in Z

10 Objet - Eden  ch?v=r_2-4SFlsHk ch?v=r_2-4SFlsHk  Array of 8 inkjet print heads scan back and forth jetting a photopolymer onto the platform  UV lamp cures the photopolymer (no laser)  Support material is removed with warm water  Suitable for printing parts with extremely fine details  600 μm thick walls, 16 μm layer thickness  New multi-material deposition capabilities!

11 Envisiontec - Perfactory  v=LZIy4LU-Qz0 v=LZIy4LU-Qz0  Uses Texas Instruments DLP chip (same as that used in some projection TV's) to project a visible light image onto a visible light curing photo-polymer.  Two resolutions available:  Standard res: 148 μm in X, 93 μm in Y, and 50 to 150 thick layers  High resolution: 60 μm in X, 32 μm in Y, and 25 to 50 thick layers

12 V-Flash  3D Systems - $9,900  ch?v=0Rs7RQpO8p0 ch?v=0Rs7RQpO8p0  Resin is printed onto plastic film.  A platform lowers down onto the film, thus transferring resin from the top of the film to the bottom of the plate.  UV light cures the resin, and the process is repeated.  The parts come out completely dry with no postprocessing needed.

13 Part II: The Science Behind Photopolymerization

14 Photopolymers  Highly crosslinked or networked polymers that effectively form a giant macromolecule  Strong covalent bonds  Cannot be melted once they've been cured  Crosslinking significantly raises the glass transition temperature  They are generally very resistant to solvents  They can generally withstand higher temperatures than TP’s Source:

15 Curing of Cross Linked Polymers  Light-curing  Photocuring resins that are liquid until exposed to light of a specific wavelength  Examples: 3D Systems stereolithography, 3D Systems Invision, Envisiontec Perfactory, Objet Eden  Heat activated  Thermoset in powder form is molded to a particular shape, and heat initiates molecular cross linking  No RP systems use this approach that I'm aware of  Catalyst and mix-based systems  When two components are mixed together, the resulting chemical reaction leads to the desired cross linking  Ex: polyurethane casting into rubber molds

16 Photopolymer Chemistry  Monomers, initiators, etc.  Radical photo-polymerization  Cationic photo-polymerization

17 Radical Polymerization  Used to photo-polymerize acrylate resins  Photons are absorbed by the photoinitiator thus producing free radicals  Only happens when laser power exceeds the threshold curing exposure  Photoinitiators are sensitive to a specific range of wavelengths (mostly in the UV range)  Free radicals react with monomer

18 Cationic Polymerization  Used for photo-polymerization of epoxy and vinylether resins  Higher strength and lower shrinkage  Oxygen will not inhibit reaction  Water (humidity) will inhibit reaction  Do not react as quickly, so a more powerful laser is needed to cure at the same rate as with acrylate resins.

19 Representative Material Properties Stereolithography Source:

20 Photocuring  The process of hardening a liquid resin via the selective application of energy (UV, IR, etc).  Penetration Depth (D p ) – the depth at which the energy intensity has been reduced to approximately 1/3 the intensity at the surface.  Scan Velocity (V s ) – the speed (mm/sec) at which the laser beam is scanned over the liquid resin.  Critical Exposure (E c ) – the energy per unit area needed to produce gelation.  Cure depth (C d ) – is a function of penetration depth, critical exposure, energy intensity, exposure area, and exposure time.

21 Laser Exposure In Resin  Tells you the laser exposure (mJ/cm 2 or equivalent) as a function of depth beneath the surface of the resin (z) and distance from the center of the beam (y).  P L = laser power (mW)  W 0 = 1/e 2 Gaussian half width of the beam (mm)  V s = velocity of the beam (mm/sec)  D p = penetration depth (mm) which is depth at which energy is 1/e that of energy at the surface Source: Laser-Induced Materials and Processes for RP by Fuh and Wong

22 Sample Calculation  What is the laser exposure (mJ/cm 2 ) at a depth of 0.05 mm and a distance of 0.03 mm from the center of the beam?  Given:  Z = 0.05 mm and y = 0.03 mm  Laser power (PL) = 40 mW  W 0 = mm  Vs = 200 mm/sec  Dp = 0.17 mm

23 Solution

24 Laser Exposure In Resin  E c is the critical exposure level needed to initiate curing.  If energy density is less than E c, then no curing takes place.  If you know E c, then you can determine the maximum value of y where curing takes place (i.e. you can figure out the width of the cured line at the surface  Scan pitch is the step over distance between adjacent laser tracks when filling in an area.  Many different fill strategies exist.  In general, you don't want track lines from one layer exactly on top of track lines with previous layers as shown in the illustration.  They are staggered to promote more complete curing  They are often shifted 90 degrees in orientation between subsequent layers to balance shrinkage stresses that lead to curling. Source: Laser-Induced Materials and Processes for RP by Fuh and Wong

25  Maximum cure depth  Maximum exposure energy (E max )  Laser velocity (V s ) to produce a desired cure depth ( ) Cure Depth (C d )

26 Curling and Distortion  Curling of large flat horizontal surfaces is a significant problem.  Each layer shrinks during solidification.  When one layer shrinks on top of a previously solidified (pre- shrunk) layer, then there is stress between the two layers.  The result is curling  Preventing/minimizing curling  Re-orient the part if possible  Use lots of supports that anchor the downward facing surface in place. Source: Rapid Prototyping and Manufacturing by P. Jacobs

27 Beam Shape  A round laser beam that is projected straight down onto a perpendicular surface will produce a round spot.  When the beam is swept at an angle to other (non-perpendicular) spots on the vat of resin, the spot will have the shape of an oval.  Newer SLA machines (very expensive) have active optics that can reshape the spot on the fly in order to maintain a round spot anywhere on the surface of the resin.  Do print-based systems have this problem?

28 Electroplating of SLA Components  A handful of companies in the U.S. are able to electroplate SLA parts  Parts shown in the photos are nickel-plated SLA parts assembled into a functioning handheld air compressor (courtesy of Fineline Prototyping) Source: Fineline Prototyping

29 Plating of Plastics  Step 1: Make the surface electrically conducting  Brush on silver paint (typically shows poor adhesion)  Chromic acid will etch ABS plastic  Activate surface in palladium or tin chloride to deposit conducting metal into etched surface  Step 2: Very thin electroless nickel plating  Step 3: Electroplating with copper  Step 4 (Optional): Electroless nickel (or other metal) plating

30  Digital impression is made  Software creates steps of tooth movement  aligners, each of which is worn for about 6 weeks each  Each SLA machine makes ~100 unique aligner patterns per build  Polycarbonate/Polyurethane sheet ” thick is thermoformed over the SLA pattern ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Case Study: Invisalign Braces

31  Rapid+Shell+Modelling+%28RSM%29.html Rapid+Shell+Modelling+%28RSM%29.html  Download brochure ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Case Study: Hearing Aids

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