applications et realisations de la technologie(rap300 rap1200) computer controlled polishing fixed...
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Applications Et Realisations De La TechnologiePlasma “Reactive Atom Plasma” (RAP) Pour La
Fabrication De Grands OptiquesR. Jourdain, M. Castelli, P. Morantz, P. ShoreCranfield University, Precision Engineering Centre,
email: [email protected]
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Content
• Aim and objectives
• Competing technologies
• Fabrication chain for large optics
• RAP technology & RAP process
• RAP figuring results
• Summary
[email protected] 2Journees polissage (Marseille june 2011)
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Some Facts and Figures
• Specialist postgraduate institution
• 3,500 students & 4,500 qualified professionals
• Strong links between teaching, research and innovation
• The UK’s only wholly STEM focused Postgraduate University
• 75% of all aerospace engineering postgraduates in the UK graduate at Cranfield
• 10% of the UK’s engineering and sciences PhDs are awarded by Cranfield
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Aims and Applications
Figuring process Form accuracy
<10 nm RMS
Texture
< 1 nm RMS
European Extremely Large Telescope
HiPER (England)
Laser Mega Joule (France)
National Ignition Facility (USA)
metre scaledoptical component
Extreme Ultra Violet Lithography
8 Hours processing time
Laser fusion program
Earth orbiters
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Precision Optical Processes
Material Removal Rate [mm3/min]
Ro
ugh
nes
s [n
m]
RM
S
Ion Bean figuring
Magneto Rheological Finishing
Reactive Atom Plasma (RAP300 RAP1200)
Computer Controlled Polishing
Fixed Abrasive Grinding
“Ductile” Mode Grinding
0.1
1
10
100
1000
0.1 1 10 100 10000.01
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Possible processing route
Form accuracy
<10 nm RMS
Surface roughness
< 1 nm RMS
metre scaleoptical component
BoX / Ultra precision grinding
1 mm form accuracy 1 μm form accuracy
Stage 2
Polishing process
Stage 1
Grinding process
Stage 3
RAPprocess
Helios1200 / Figuring machine
Polishing machine
300nm form accuracy
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RAP process
0
0.5
1
1.5
2
2.5
0 1000 2000 3000 4000 5000 6000
MR
R [
mm
3/m
in ]
Travelling speed [ mm/min ]
Reactive Atom Plasma
ULE
fused silica
7
Reactive Atom Plasma is a dry chemical etching process developed to figure silicon based optical surfaces at atmospheric pressure.
Materials such as Si, ULE, Borosilicate, fused silica, SiC can be processed.
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RAP process
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RAP plume Footprint
RAP Torch (RAP1200)
-Dwell time 10x1sec- FWHM 11mm- Outer diameter 25mm
- Reduced heat transfer- Low contamination- Easily tuneable- Power can be increase- Reliable and deterministic-De-Laval nozzle
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RAP machine
Helios 1200 (processing capability)
Helios 1200 (Overview)
- 3 axis - CNC FANUC controller. - Dedicated software.- Dwell time based tool path algorithm.- Double skin sealed unit.- Scrubber
- Optical component facing down- No clamping mechanism. - Can load more than one components- Loading time is about few minutes
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Tool Path Algorithm
XXZZ
YY
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The surface is raster-scanned following a reversed staggered meander-type tool-path algorithm. Processing conditions and first tool motion loop are illustrated in the left schematic
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RAP Processing time
Roughness after polishing: Sa = 1.8nm
Roughness after RAP processing(0.5um removal)
100mm diameter surface
Measurement time [min.] 30
Computational time [ min.] 20
Torch startup-time [ min.] 3
Sample loading time [ min.] 5
Figuring time [ min.] 6
Processing time
Processed areaAssessed area
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Targeted surface figure Processed surface profile
Results RMS: 31nmProcessing time 2x 6min
Convergence ratio of about 78 percent
Residual surface error
RAP Surface figuring results
Interferogram
Surface profile deformation before processing
RMS: 31nm
RMS: 139nm RMS: 31nm
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RAP Surface figuring repeatability
RESIDUAL FIGURE ERROR MAPS
FINAL SPHERICAL HOLLOWS
31 nmrms
31 nmrms
16 nmrms
16 nmrms
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RAP Surface figuring on 6 inches
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128 RMS down to 18nm RMS
79 RMS down to 16nm RMS
6inch flat
6inch sphere
16nmrms
158nmPV
79nmrms
374nmPV
500nmPV
128nmrms
146nmPV
18nmrms
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Processing time for metre class segmented mirrors and NIF wedge focus lenses
Scenario: Material removal of a 0.5um thick layer. Processing time prediction based on experimental results involving turbo torch on fused silica material.
0
2
4
6
8
10
00.511.522.533.5
Pro
cess
ing
tim
e
(ho
urs
)
Feed Speed (m/min)
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• Achievements– Development of a new fast figuring process
– Figure correction: better than Lambda/40 over 6”
– Development and optimisation of tool path algorithm
– Understanding of processing parameters
– Metre scale operational figuring machine
• Further work– Scaling up figuring capability
• Up to 8” for free form surfaces few micron deep (August)
• Up to 16” for three metre ROC (November)
Summary
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