5/1/2013

1

Center For

Precision Metrology

Surface Finishing Processes

Brigid Mullany

Associate ProfessorDepartment of Mechanical Engineering

Center for Precision MetrologyUNC Charlotte

North Carolina, USA

Center For

Precision Metrology

Finishing Processes- High value added

Lith

ogra

phy

Imag

ing

Met

rolo

gy

Tele

scop

es

http://images.businessweek.com/ss/08/07/0717_idea_winners/23.htmhttp://www.asml.com/asml/show.do?ctx=6720&rid=36951

http://www.zygo.com/?/met/interferometers/&gclid=CM7VvYDRl6gCFSRe7AodDVp1EA

http://www.eso.org/sci/facilities/eelt/telescope/dome/http://www.worldoforthopedics.com/tag/partial-knee-replacement/

www.hiwtc.com/photo/products/37/03/76/37637.jpg

Optics Medical Energy/Aerospace

o Challenging geometrieso Difficult to machine materialso Tight form and finish specifications

Abrasive finishing

Image sources

5/1/2013

2

Center For

Precision Metrology

Loose Abrasive Processes

Lapping

Polishing

Magnetic Assisted Finishing

Abrasive Flow Machining (AFM)

Drag Finishing

Elastic Emission Machining (EEM)

Vortex Machining (under development at UNCC)

Typical surface finishes, Rq10-7 m 10-8 m 10-9 m 10-10 m

Tumbling

Centrifugal

Turbo Abrasive Machining (TAM)

Common process perceptionso Operator skill dependento Trial and error approacho Expensive

o Process instrumentationo Surface metrologyo Fluid dynamicso Contact mechanics

Collaborators: Mainuddin, Keanini, Williams

Center For

Precision Metrology

Traditional Optics Polishing Process

Applications:o Laser and Lithography opticso Larger one off opticso High throughput of higher quality optics

WorkpieceSlurrydispenser

Polishing tool(Ø 30 cm)

5/1/2013

3

Center For

Precision Metrology

Polishing Tool Material - Optical PitchPolishing Pitch: o Tree or petroleum based resins o Synthetic versions availableo Shore D: 70 – 80o Highly viscoelastic

Day 239 Day 261 Day 267Day 1

History in Polishing: o First use accredited to Newton in 1700so Synthetic versions available since 2000so Dynamic properties evaluated in 2010*

* B. Mullany, S. Turner, Applied Optics, Vol. 49, No. 3, pp. 442,449, 2010

Center For

Precision Metrology

Tool fabricationo Heat pitch (T < 100 °C)o Pour onto substrateo Cut grooveso Condition: embed abrasives in surfaceo Life span: months →years

Tool: Ø 300 mm

Synthetic pitch : Acculap™ soft

Embedded Ceria particles

Workpiece

Pitch tool

do≈ 3Rq

Pitch tool construction

1 µmThe abrasives embedded in the tool are responisble for material removal 1 mm

SEM of Tool surface

5/1/2013

4

Center For

Precision Metrology

Pitch Polishing and VibrationsMachine 1 Machine 2

1 10 100 1000 10k0

0.005

0.01

0.015

0.02

Frequency, Hz

g,m

/s2

New MachineOld MachineAccelerometer Noise

Machine 1Machine 2

Machine 1: 6nmMachine 2: 0.6nm

Machine 1: 2 ÅMachine 2: 0.2 Å

Spindle: 20 rpmOverarm: 5rpmLoad: 10N

Mainuddin

Center For

Precision Metrology

Do vibrations affect process metrics?Fused silica samples (Ø 25.4 mm) were polished on both machinesPolishing conditions: Platen speed: 20rpm, Load: 20 kPa, Slurry: 1 mm (250nm) Ceria + H2O

SWLI2.5 x

SWLI50 x

AFM10mmx10mm

Material removal rates Surface FinishesNoisier

Mainuddin

5/1/2013

5

Center For

Precision Metrology

Isolate Frequency and Amplitude

Shaker table

Load cellPitch Sample

WeightWorkpiece

Input vibration

Stage

Linear bearing

Signal amplifier

Signal generator

(10Hz – 20kHz)

Testing conditionsFrequency: VariedAmplitude: VariedLoad: 2kgSlurry: ‘1 mm’ Ceria + H2OWorkpiece: Fused silicaTranslation speed: 7mm/s

Shaker table

Tool

W/piece

Shaker table

Pitch Polishers

Ultrasonic Processes

Mainuddin, Browy

Center For

Precision Metrology

Energy versus material removal rates

1.5 kHz, 500nm

3 kHz, 500nm

5.5 kHz, 500nm

500 Hz, 500nm

8 kHz, 500nm

(Nm/s)Vibration Input (Nm/s)

8 kHz, 500nm, 1kg

8 kHz, 100nm & 500 Hz, 1.6 mm

500 Hz, 100nm

푾풊풏̇ = 퐦퐠퐀퐟M = massG = gravityA = vibration amplitudeF = freqency

Results:o Comparable power, comparable MRRo Holds for changes in A, f and m!

Except where noted, all tests were conducted with a 2kg load

Mainuddin

Power input, W

5/1/2013

6

Center For

Precision Metrology

Workpiece

Embedded Ceria particlesPitch tool

do≈ 3Rq Embedded Ceria particlesPitch tool

do≈ 3Rq

Further testing at 500Hz

500 Hz, 5 mm

500 Hz, 10 mm

500 Hz, 15 mm 500 Hz,

25 mm 500 Hz, 30 mm

500 Hz, 1600nm

500 Hz, 500nm

500 Hz, 100nm

Vibration Input (Nm/s)

Workpiece

Mainuddin

Phas

e di

ff.=

0

Phas

e di

ff.≠´

0

Power input, W

Center For

Precision Metrology

Theoretical modeling

Embedded Ceria particles

Workpiece

Pitch tool

z

r

do≈ 3Rq

Z(t)

R

Hertzian contact zones & enhanced chemical interaction between abrasives and workpiece

o MRRcm is insensitive to vibration

푴푹푹풄풎

푴푹푹풕풐풕풂풍 = 푴푹푹풄풎 + 푴푹푹풇풍풐풘

AA

A = amplitudeω = freq.do = gap (~200nm)

Keanini

5/1/2013

7

Center For

Precision Metrology

Theoretical modeling

Embedded Ceria particles

Workpiece

Pitch tool

z

r

do≈ 3Rq

Z(t)

R

o ws ~ us ~ 퐴푑 ω

o 휏~ 휇 ω

o 훻푃~휇 ω푴푹푹풇풍풐풘 ∝ 푨

풅풐흎

푴푹푹풇풍풐풘 = 푴푹푹푰 + 푴푹푹푷 + 푴푹푹푺

푴푹푹풕풐풕풂풍 = 푴푹푹풄풎 + 푴푹푹풇풍풐풘

AA

A = amplitudeω = freq.do = gap (~200nm)

Keanini

Based on:o General equation of fluid motiono Continuity equationo Order of magnitude analysis approach

Considers:o Viscosity of water-abrasives mixtureo Topography of the tool surfaceAFM Scan (20 mm ˣ 5 mm) of Tool

Sq: 66 nmSkewness: -0.67

휏~ 훻푃 ≫ 푖푛푒푟푡푖푎푙푓표푟푐푒푠

Vertical motion of system induces lateral, us , and vertical, ws, velocity gradients within fluid

Center For

Precision Metrology

푴푹푹풕풐풕풂풍 = 푴푹푹풄풎 + 푴푹푹풇풍풐풘

Constant (2.1 mg/hr)

ExperimentalTheory

푀푅푅 ∝ 휔

o Based on Pitch Tool AFM measurementso Fixed do, value supported by phase measurements

Test conditions

Theoretical modeling

Keanini

Small ̀ A`values

Vibration Input (Nm/s)Power input, W

5/1/2013

8

Center For

Precision Metrology

Theoretical modeling

Embedded Ceria particles

Workpiece

Pitch tool

z

r

Z(t)

R

푀푅푅 ∝ 휔

푴푹푹풇풍풐풘

AA

A = amplitudeω = freq.do = gap >6Rq

Workpiece completelyseparated from tool by slurrylayer (supported by processmeasurements)

푴푹푹풄풎= 0

Test conditions

Varies with A:Based on phase differences measured between workpiece and tool

Keanini

Large `A`values

푴푹푹풕풐풕풂풍 = 푴푹푹풄풎 + 푴푹푹풇풍풐풘

Center For

Precision Metrology

ExperimentalTheory

푴푹푹풕풐풕풂풍 = 푴푹푹풇풍풐풘(large amplitude vibrations)푴푹푹풕풐풕풂풍 = 푴푹푹풄풎 +푴푹푹풇풍풐풘

(small amplitude vibrations)

Experimental Vs. Theory

Keanini

5/1/2013

9

Center For

Precision Metrology

SummarySystem vibrations investigatedo Process variations explainable by vibration signatureso While not shown here – MRRs can be varied by passive damping

or addition of vibrations

Within certain limits the MRR is proportional to input power

Analytical model presented: MRR = MRRcm + MRRflowo Good fit between experimental and theory for wide range of

conditions

Financial Support:o NSF/CMMI/MCME 0747637. Any opinions, findings and conclusions or recommendations

expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation).

Selected papers:o B. Mullany, M. Mainuddin, Annals of the CIRP, 61/1/2012, 555-558, 2012.o B. Mullany, S. Turner, Applied Optics, Vol. 49, No. 3, pp. 442,449, 2010o Mullany, Mainuddin, Williams, Keanini, planned submission to JAP, April 2013

Center For

Precision Metrology

Workpiece

Slurrydispenser

Polishing tool(Ø 30 cm)

1 µm1 mm

SEM of Tool surface

Power input, W

ExperimentalTheory

Questions