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FREEFORM SURFACE FABRICATION
Presented by:
David Mohring
APOMA Workshop 2016 Tucson, Arizona
OptiPro Systems, LLC
Ontario, NY 14519
Outline
• Freeform Surface Definition
• Toolpath generation
• Grinding
• Sub Aperture Polishing
• Surface Metrology and Analysis
• Corrective Toolpath
• Acylinder Manufacture
Freeform Applications
• AKA: Conformal Surfaces
• Aerospace
• Reflective Mirrors
• X-Ray grazing incidence
• Solar Energy
• Electronics
Input Surface Definition
• Mathematical Equation
– Basis functions
– Zernike polynomial
• Wireframe model
• Solid model
• Cloud of points
• Off-Axis Asphere
• Acylinder
Input Surface Definition
• Updated to improve the usability for the operator to set the perpendicular spacings more easily
• Added visual aid to show across and along directions
• Increase flexibility of shape definition orientation
New Solid Spacing Definition
• Deterministic Grinding (DMG)
• UltraForm Finishing (UFF)
• UltraSmooth Finishing (USF)
Manufacturing Tools
• OptiSonic 3X: 3-axis ultrasonic machining
• OptiSonic 5X: 5-axis ultrasonic machining
PROSurf
• OptiPro’s CAM package tailored specifically for manufacturing freeform optics
• Supports OptiPro’s grinding, UltraForm, and UltraSmooth Finishing technologies
• Can generate corrective metrology based tool paths for both grinding and dwell-based polishing
• Contains a built-in tool path animator as a visual aid for tool path verification and collision detection
Shape Inputs/Definitions
Solid Model (.igs files) Point Cloud
Mathematical Equations Built-in Common Shapes
Toolpath Generation
• Looking into alternative methods for point distribution on solid models
• Allow mapping of an even grid to surface
• First step in handling multiple surfaces in PROSurf
Solid Model Toolpath Generation
Advanced Point Spacing
Even Arc Spacing
• Based on solutions for removing surface signatures from actual parts
• Even arc spacing, even curve spacing, cusp height minimization
Tangent Extension
Example of an asphere that behaves badly outside of the designed aperture
Change definition outside of aperture to make it easier to manufacture.
The “Tangent Extension” allows you to control the shape of the asphere outside of its final diameter out to the processing diameter for
manufacturing. It can be controlled with a linear extension or of a user defined convex or concave radius.
Grinding Operation
• Bonded or plated diamond tools
• Spherical or toric
• Tool path is a raster motion (up to 5-axis)
• Metrology can make the process deterministic
Rough -> Fine Grind
• Surface Texture
• Mid Spatial Errors
(4-60 cycles /aperture)
• Radial In Feed – C-axis driven grinding tool path
• Used point cloud as input format for shape
• Looking at allowing different types of tools for processing
Radial In Feed Changes
Polishing
• UltraWheel specifications
• Clearances
• Abrasives
• Toolpath orientation
• Irregularity
• Roughness
• Mid-Spatials
UltraForm Finishing (UFF) • 5-axis/6-axis CNC controller with simple to use GUI
• Wheel size range 8 to 100 mm in diameter
• Wheel nominal hardness range from 30 to 80 Shore A
• Bound/fixed abrasives or commercial polyurethane belts with slurry
• Capable of finishing a wide range of materials from optical glass to hard ceramics and metals to sub-micron form tolerances.
Deterministic sub-aperture CNC polishing 10 to 300 mm optics: Flats, spheres, aspheres and freeforms
Measure Removal Function
• Integrated STIL pen
• Onboard metrology
Input Initial Figure Error
• Zygo Interferometer Input
• Profilometer Input
Optimize Polishing Tool Path
• Reduce figure error
• Fine control of polishing path
UltraForm Finishing (UFF) Process
• Prepare part for UFF correction
– Lower stock removal will leave less signature
• Smooth MSF post UFF
USF
• Tool design allows for high compression in vertical direction and possesses great torsion stiffness
• Tooling's compliant layer can be configured with different stiffness materials.
• Ideal tool design for USF high-pressure, high-speed polishing setup
PROSurf USF Toolpath
UltraSmooth Finishing (USF)
• Abrasives
• Toolpath orientation
• Irregularity
• Roughness
• Mid-Spatials
Freeform Metrology
• Non-contact • Not slope limited • Can measure spheres,
aspheres, and freeform optical components as well as optical thickness for meniscus shapes
• Scanning Stylus • Equipped with optional
Y/theta stages • Y-axis can take multiple
scans across an acylinder
UltraSurf
OptiTrace
UltraSurf
• Non-Contact • High-Resolution • 5 Motion Axes (X, Y, Z, B, C) • Measure rough or polished
surfaces • Several Non-contact probes • Low Coherence Interferometry • Chromatic Confocal • Define shapes by equation,
CAD, cloud of points • Adjust resolution to measure
form or local surface texture
25
Non-Contact Probes
White Light &
Spectrometer Fiber Optic
First Surface Reflects Light
Chromatic Confocal Sensing (CCS)
Am
plit
ud
e
Wavelength
Probe
1-10 μm Lateral and 10 nm Vertical resolution
5-Axis Freeform Example
Freeform Linear: X,Z Rotary: B
Linear: Y Rotary: C
UltraSurf Measurements
• Surface measurement
• Fixture measurement
• In process and final data
• Sensor flexibility
Depth of Field 20 µm 300 µm
Working Distance 0.6 mm 4.5 mm
Z Axis Resolution 1 nm 10 nm
Accuracy 10 nm 0.1 µm
Spot Diameter 1 µm 4 µm
Lateral Resolution 0.5 µm 2 µm
Numerical Aperture 0.69 0.5
Max Angular Slope (+/-)**
44º 30º
• Better location of the part would keep the probe in the +/- 2 degree angle limitation – The CCS probe has a +/- 25 degree
angle limitation, but measures closer to the part
• The 3D printed fixture could be improved by – Increase rigidity or structural accuracy – Use a large flat base instead of 4 small
legs, this would give more area to secure the surface
– Improve the sphericity of the locating surfaces, or change their shapes. Conical?
Freeform Measurement Lessons
Measurement Analysis
6-Axis UFF @ MSFC
• X,Y,Z linear axis • A,B,C Rotary Axis • Tool Rotation motion control • Work Piece motion control • Freeform capabilities • Tool normal -> Surface • Full CNC Control • Optical Fabrication software • Bound and loose abrasives • Deterministic / corrective
Acylinder ProSurf
• Schott F2 Glass • Dimensions 16x16x200 mm
Tool Diamond Size
(micron) Concentration Bond
Depth of cut/Pass
(mm)
Feed rate
(mm/min)
Rough 65 75 Bronze 1.0
Fine 15 75 Bronze 0.05
Coolant : UltraCool 5000, 5% concentration
Acylinder Grind
Cut PV (microns) RMS (microns)
Initial 44.3 10.7
Corrected Grind 6.98 0.886
Data measured on a OptiTrace 5000, 1mm stylus, λc = 0.080mm filter
Acylinder Polish
Roughness: 2nm rms
PV (microns) RMS (microns)
Final Figure 0.442 0.068
• Improved the controls for mapping the error to the surface of the part
• This greatly reduces the difficulty in making sure the rotation of symmetric parts are correct
Improved Error Mapping
Acylinder Over Clear Aperture
• There are many challenges to manufacturing acylinder and freeform optical components, but Don’t Panic!
• OptiPro continues to develop technologies in Grinding, UFF, UltraSurf, and ProSurf to deterministically fabricate precise complex optical surfaces.
Thank You
The Hitchhiker's guide to the galaxy
37
Center for Freeform Optics (CeFO)
http://centerfreeformoptics.org
OptiPro Systems www.optipro.com
OptiPro Systems 585-265-0160
Advanced Process Development
Partners in Precision