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Rapid Prototyping Via Photopolymerizatio n ISE 767 Rapid Prototyping www.finelineprototyping.com

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Page 1: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

Rapid Prototyping ViaPhotopolymerization

ISE 767

Rapid Prototyping

www.finelineprototyping.com

Page 2: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

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.

Page 3: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Part I – Commercially Available Systems

Page 4: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

http://www.youtube.com/watch?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

Page 5: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

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

Page 6: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

SLA Postprocessing

Support removal Cleaning uncured resin with TPM or alcohol Postcuring Sanding

Page 7: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

SLA Tempering

http://home.att.net/~edgrenda/pow/pow21.htm 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: http://home.att.net/~edgrenda/pow/pow21.htm

Page 8: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

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

Source:www.sonysms.com

Page 9: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

3D Systems - ProJet

http://www.youtube.com/watch?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 0.0016" in Z HR model: 0.0015" resolution

in X,Y and 0.0016" in Z Source:www.3dsystems.com

Page 10: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

Objet - Eden

http://www.youtube.com/watch?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!

Source:www.2objet.com

Page 11: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

Envisiontec - Perfactory

http://www.youtube.com/watch?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 layersSource:www.envisiontec.de.com

Page 12: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

V-Flash

3D Systems - $9,900 http://

www.youtube.com/watch?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.

Page 13: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

Part II: The Science Behind Photopolymerization

Page 14: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

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: www.pslc.ws/mactest/images/xlink02.gif

Page 15: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

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

Page 16: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

Photopolymer Chemistry

Monomers, initiators, etc. Radical photo-polymerization Cationic photo-polymerization

Page 17: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

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

Page 18: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

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.

Page 19: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

Representative Material PropertiesStereolithography

Source: www.finelineprototyping.com

Page 20: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

Photocuring

The process of hardening a liquid resin via the selective application of energy (UV, IR, etc).

Penetration Depth (Dp) – the depth at which the energy intensity has been reduced to approximately 1/3 the intensity at the surface.

Scan Velocity (Vs) – the speed (mm/sec) at which the laser beam is scanned over the liquid resin.

Critical Exposure (Ec) – the energy per unit area needed to produce gelation.

Cure depth (Cd) – is a function of penetration depth, critical exposure, energy intensity, exposure area, and exposure time.

Page 21: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

Laser Exposure In Resin

Tells you the laser exposure (mJ/cm2 or equivalent) as a function of depth beneath the surface of the resin (z) and distance from the center of the beam (y). PL = laser power (mW)

W0 = 1/e2 Gaussian half width of the beam (mm)

Vs = velocity of the beam (mm/sec)

Dp = penetration depth (mm) which is depth at which energy is 1/e that of energy at the surface

pDZ

Wy

s

L

VW

PzyE

20

22

0

2),(

Source: Laser-Induced Materials and Processes for RP by Fuh and Wong

Page 22: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

Sample Calculation

What is the laser exposure (mJ/cm2) 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 W0 = 0.125 mm Vs = 200 mm/sec Dp = 0.17 mm

Page 23: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

Solution

2

2

17.0

05.0

125.0

)03.0(2

cm

mJ 15.65

mm

mJ 6515.0

sec/200125.0

402)05.0,03.0(

2

2

mm

mm

mm

mm

mmmm

mWE

Page 24: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

Laser Exposure In Resin

Ec is the critical exposure level needed to initiate curing. If energy density is less than Ec,

then no curing takes place. If you know Ec, 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

Page 25: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

Maximum cure depth

Maximum exposure energy (Emax)

Laser velocity (Vs) to produce a desired cure depth ( )

Cure Depth (Cd)

Page 26: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

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

Page 27: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

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?

Page 28: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

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

Page 29: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

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

Page 30: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

Digital impression is made Software creates steps of tooth

movement 12-48 aligners, each of which is worn

for about 6 weeks each Each SLA machine makes ~100 unique

aligner patterns per build Polycarbonate/Polyurethane sheet

0.030-0.040” 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

Page 31: Rapid Prototyping Via Photopolymerization ISE 767 Rapid Prototyping

http://www.materialise.com/materialise/view/en/2562804-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