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

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Non-Contact Probes

White Light &

Spectrometer Fiber Optic

First Surface Reflects Light

Chromatic Confocal Sensing (CCS)

Am

plit

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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

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Center for Freeform Optics (CeFO)

http://centerfreeformoptics.org

OptiPro Systems www.optipro.com

OptiPro Systems 585-265-0160

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