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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
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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
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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
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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)
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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ExperimentalTheory
푴푹푹풕풐풕풂풍 = 푴푹푹풇풍풐풘(large amplitude vibrations)푴푹푹풕풐풕풂풍 = 푴푹푹풄풎 +푴푹푹풇풍풐풘
(small amplitude vibrations)
Experimental Vs. Theory
Keanini
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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