Applications Et Realisations De La Technologie(RAP300 RAP1200) Computer Controlled Polishing Fixed...

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: r.jourdain@cranfield.ac.uk

Content

• Aim and objectives

• Competing technologies

• Fabrication chain for large optics

• RAP technology & RAP process

• RAP figuring results

• Summary

r.jourdain@cranfield.ac.uk 2Journees polissage (Marseille june 2011)

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

r.jourdain@cranfield.ac.uk 3Journees polissage (Marseille june 2011)

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.

r.jourdain@cranfield.ac.uk Journees polissage (Marseille june 2011)

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

RAP machine

Helios 1200 (processing capability)

Helios 1200 (Overview)

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- 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

Journees polissage (Marseille june 2011)

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

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

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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• Thank you for your attention!

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