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Title: Micro-Engineering with Lasersby
Chris Chatwin1, Serge Corbel2, Rupert Young1
1Engineering and Information Technology,
University of Sussex, UK
2 CNRS-DCPR, Groupe de Recherche et Applications en
Photophysique et Photochimie UMR 7630, FRANCE
Industrial Technology Programme 3rd Sept 2002 – 10:00 –Whytes Room
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Summary
• A brief review of our Microstereolithography System, which led us to be invited into the BRITE EuRAM project
• A brief review of some of the results from the BRITE- EuRAM project which used optical and laser systems to Manufacture Macro/Micro Ceramic components.
• After de-binding and sintering ceramic parts with relative densities of 95% have been produced.
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Experimental Set-up
UV LASER
(351 or 363nm)
Sh
utt
er
Frame Grab(Ultra-II drive)
IBM PC
(Main control)
Translation
Stage
En
cod
er
Mo
du
le
I/O
In
terf
aci
ng
(AT
-MIO
-16D
E-1
0)
Network (ftp) or GPIB Interfacing
En
cod
er d
rive
rC
ard
(3
7-1
03
9)
SL
M
SunSparc(DUCT CAD/CAM)
Slice Images
m-component
Resin Bath
T132 Shutter
controller
RS-232
Sync.
PolarizerD.O.E
(0.1ms resolution)
I/O Ports(PC-DIO-10)
DDIInterface of data
acquisition
(15)
(7)
(6)
lens
SerialParallel
Microstereolithography System Diagram
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Micro-component Prototyping
SVGA SLM 800x600 pixels
Microstereolithography System
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Micro-components
Micro-motor case (50 micron layers)A micro-gear (50 micron layers) A helix (50 micron layers)
Double helix (50 micron layers) Micro-pyramid (35 micron layers) Micro-pyramids (50 micron layers)
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MicroSLA System
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Fabrication of Dense Ceramic Micro -
Components
2 3
Ceramic
Powder 50%
Al2O3
Dispersant
1.5 % Solvent 50%
MEK/Et
Photopolymerizable
•monomer HDDA
•Initiator : DMPA - 0.5%
Deagglomerated
powder with
adsorbed dispersant
dry/grindMixing
3 Pa.s.
Suspension
Forming by
stereolithography
Green part
Debinding-Sintering
Monomer: hexane-diol-
diacrylate (HDDA)
Photoinitiators:
Irgacure 651 (DMPA) absorbs
300-390 nm – 0.5%
Irgacure 819 absorbs up to
450 nm – 0.5%
50 mJ/cm2 for 100 mm cure
depths, resolution of 50 mm
Dispersant: Phostphate ester 1.5% wrt Al2O3
Solvent: Ethanol or Acetone 50%
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Alumina Powder
Aggregate of Al203 powderAlumina (Al203) Powder: Average
diameter 0.5mm; Refractive index 1.7
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Photoinitiators Cover Emission peaks from:
- Hg Lamp - 365nm, 405nm;
- Argon Ion Laser – 363nm;
- Pulsed YAG Lasers - 355nm.
They are soluble up to 5 wt. % into the monomer,
0.5% seems about optimum
340 360 380 400 420 440 460 480 500
0
1
2
3
4
Ab
sorb
ance
Wavelength l(nm)
Irgacure 819
300 320 340 360 380 4000.0
0.5
1.0
1.5
2.0
2.5
Abso
rban
ce
Irgacure 651
Wavelength l (nm)
DMPA
Absorption spectra of photoinitiators for
0.25 wt.% of dispersant in HDDA
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Cure Depth Versus Dose for three Sources
1 10 100 1000 100000
50
100
150
200
250
300
350
400
Cd
(µm
)
E (mJ/cm2)
Laser
Lamp
Ar+
Laser YAG
Cure depth versus dose (80 wt.% alumina, 1 wt.% DMPA)
Pulsed YAG Laser - 355nm
Hg Lamp - 365nm
Argon Ion Laser – 363nm
Cure depth Cd (µm)
Dp : is the penetration depth,
E : the exposure or energy at the surface,
Ec : is the critical energy or the minimal
exposure dose for the resin to gel.
)ln(c
pdEEDC
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Effect of Photoinitiator on Penetration
0.0 0.5 1.0 1.5 2.00
10
20
30
40
Dp (µm)
% DMPA
Penetration depth versus wt.% photoinitiator ;
irradiation with an argon laser at 363 nm
Optimum about 0.5 wt.%
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Irradiation
Conditions
Laser UV
(364 nm)
Laser Visible
(488 nm)
Composition in wt. %
Alumina 80
Suspension 2:
85
Suspension 1:
80
wt.% Initiator (I 784) 2 3 2.2
Dp (mm) 31 69 105
Influence of the radiation wavelength on the
depth of penetration in alumina suspension
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Debinding/Sintering Process
~ 1~
15
~ 1
~ 1
5
~ 1
5
~ 0.1 °C/min
~ Time (hours)
~ T
em
pera
ture
(°C
)
3 33 36 41
220
400
1200
1350
1550
Debinding
Sintering
Typical thermal treatment for the debinding/sintering process in air
Debinding must be done with
a low heating ramp to avoid
swelling, distortion and
cracking of parts.
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Cracks appear at the Interface between
layers if Debinding is too Rapid
to layers
to layers
Debinding at 5°C/min up to 220°C/10
hours in air
Debinding at 5°C/min up to 600°C/50 min.
in air
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Relative Density and Shrinkage Versus
Temperature
1500 1550 1600
Temperature (°C)
90
95
100
Rela
tive
De
nsity :
D/D
o (
%)
15
20
25
Lin
ear S
hrin
ka
ge (%
)
to layers
to layers
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13 Layer Cylinder with 100 micron layers
Demonstration parts sintered at 1600°C for 5 hours
Before Sintering After Sintering
Some deformation due to faults in
deposition layers and bad recoating
11% Shrinkage 17% Shrinkage
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Monolayer - Typical Lateral Resolution 50 microns
Mask
8mm x 8mm 120 micron thick polymerised layer,
resolution 50 microns; 80 wt% alumina, 0.5 wt%
DMPA wrt HDDA monomer
Cured at 365 nm
with Hg Lamp
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Demonstration Sintered Parts
2 mm
Demonstration part sintered at 1600°C
for 5 hours
Ceramic parts produced with visible source
and CRL XGA mask
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Conclusions
• It is possible to formulate highly loaded suspensions containing
well-dispersed colloidally stable alumina particles.
• The practical limit for the suspension viscosity, which is about
3 Pa.s, is reached for 85 wt.% of alumina with respect to the
photopolymer resin content.
• It has been shown that with an optimised photoinitiator
fraction above 0.5 wt. %, and energy densities less than
50 mJ/cm2 ; 100 µm cured depths can be obtained.
• A good lateral resolution of 50 mm has been demonstrated.
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Conclusions
• The modification of the formulation by changing the amount of
photoinitiator allows the depth of penetration to be increased
by a factor 2 or 3 depending on the alumina loading.
• Satisfactory parts with 100 mm thick layers were built with a
20 seconds exposure and a laser power of 2 W.
• Ceramics with relative densities up to 95% have been
produced.
• Some sample cracking occurred during the final thermal
processes, the control of this process requires further
investigation.
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References1) C Chatwin, M Farsari, S Huang, M Heywood, P Birch, R Young, “UV microstereolithography system that uses spatial light
modulator technology,” Applied optics 37 (32), 7514-7522, 1998
2) M Farsari, S Huang, RCD Young, MI Heywood, PJB Morrell, CR Chatwin, “Holographic characterization of epoxy resins at 351.1
nm,” Optical Engineering 37 (10), 2754-2759, 1998
3) M Farsari, S Huang, RCD Young, MI Heywood, PJB Morrell, CR Chatwin, “Four-wave mixing studies of UV curable resins for
microstereolithography,” Journal of Photochemistry and Photobiology A: Chemistry 115 (1), 81-87, 1998
4) M Farsari, S Huang, P Birch, F Claret-Tournier, R Young, D Budgett, “Microfabrication by use of a spatial light modulator in
the ultraviolet: experimental results,” optics letters 24 (8), 549-550, 1999
5) CR Chatwin, M Farsari, S Huang, MI Heywood, RCD Young, PM Birch, “Characterisation of epoxy resins for
microstereolithographic rapid prototyping,” The International Journal of Advanced Manufacturing Technology 15 (4), 281-286,
1999
6) GD Ward, IA Watson, DES Stewart‐Tull, AC Wardlaw, CR Chatwin, “Inactivation of bacteria and yeasts on agar surfaces with
high power Nd: YAG laser light,” Letters in applied microbiology 23 (3), 136-140, 1996
7) M Farsari, S Huang, RCD Young, MI Heywood, CD Bradfield, CR Chatwin, “Holographic cure monitoring of the DuPont Somos TM
7100 stereolithography resin,” Optics and lasers in engineering 31 (3), 239-246, 1999
8) M Farsari, F Claret-Tournier, S Huang, CR Chatwin, DM Budgett, “A novel high-accuracy microstereolithography method
employing an adaptive electro-optic mask,” Journal of Materials processing technology 107 (1), 167-172, 2000
9) P Birch, R Young, C Chatwin, M Farsari, D Budgett, J Richardson, “Fully complex optical modulation with an analogue
ferroelectric liquid crystal spatial light modulator,” Optics communications 175 (4), 347-352, 2000
10) PM Birch, R Young, D Budgett, C Chatwin, “Two-pixel computer-generated hologram with a zero-twist nematic liquid-crystal
spatial light modulator,” Optics letters 25 (14), 1013-1015, 2000
11) P Birch, R Young, M Farsari, C Chatwin, D Budgett, “A comparison of the iterative Fourier transform method and evolutionary
algorithms for the design of diffractive optical elements,” Optics and Lasers in engineering 33 (6), 439-448, 2000
12) P Birch, R Young, D Budgett, C Chatwin, “Dynamic complex wave-front modulation with an analog spatial light modulator,”
Optics letters 26 (12), 920-922, 2001