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Transcript of Frictional Investigation of Magnetorheological Finishing ... · ClP = modified Preston’s...
Frictional Investigation of Magnetorheological Finishing (MRF) for Optical Glasses and Hard Ceramics
C. Miao,S. N. Shafrir, H. J. Romanofsky, J. Mici, J. C. Lambropoulos, and S. D. JacobsUniversity of RochesterLaboratory for Laser Energetics
Optical Fabrication andTesting Topical Meeting
Rochester, NY19–23 October 2008
Elapsed time (s)
Systemat rest
Part depressedinto ribbon (10 s)
Systemat rest
Normal force
Drag force
In-situfrictional force sensors
In-situfrictional force sensors
A frictional investigation of MRF for optical glasses and hard ceramics is carried out
G8620
• Adual-loadcellisusedforsimultaneous,in-situ measurement of frictional forces on optical glasses and hard ceramics
• Dragforcedecreaseslinearlywithincreasingmaterialhardness, whilenormalforcesaturatesathighhardness
• Coefficientoffrictioniscloselycorrelatedwithmechanicalpropertiesof materials and the particles in the MR fluid
Summary
We demonstrate that both drag and normal forces play an important role in material removal in MRF for both glasses and ceramics
The drag and normal forces are measured in MRF
G8621
• Employadual-loadcellforrealtime,simultaneousmeasurement of both drag force and normal force on materials during MRF
• Determinehowdragforce(FD) and normal force (FN) respond to material mechanical properties
• Studytherelationshipbetweencoefficientoffriction(COF) and material removal rate
Objectives
MaterialremovalinMRFisknowntobebased on drag force and shear stress
G8622
Preston’s equation (1929)
Shorey’s modification (2000)
ClP = modified Preston’s coefficientn = friction coefficient = FD/FNFD = drag forceAS = spot areax = shear stress = FD/AS
MRR = material removal rateCP = Preston’s coefficientP = normal pressureV = relative velocityFN = normal forceAC = nominal contact area
C PV CAF
V CAF
V CAF
V C VMRR P PC
NP
S
NP
S
DP
nx= = = = =l l l
Materials of interest include optical glasses and hard ceramics
G8623
Materials in each group are listed by the order of increasing Vickers hardness
Materials Mat. ID Grain Size (nm)
Young’s Modulus E
(GPa)
Vickers Hardness Hv (GPa)
Fracture Toughness
Kc (MPa•m1/2)
Source
Optical glasses (100-gload,literaturevalues)Phosphate LHG8 – 62 3.7 0.5 HoyaBorosilicate N-BK7 – 81 6.0 0.8 SchottFused silica FS – 69 7.5 0.8 Corning
Hard ceramics (500-gload,Shafrir2007)Magnesium aluminum oxide
Spinel 100–200 273 14 2.2 TA&T
Aluminum oxynitride ALON 150–250 334 15 2.7 Surmet
Polycrystallinealumina PCA ~0.3 400 22 3.3 CeraNova
Silicon carbide CVC SiC 5–20 460 29 4.5 Trex
MRF spots are taken on a research platform: aspot-takingmachine(STM)
G8624
• Partmountedonanonrotating z-axisslide
• MRFspotcreatedbyloweringnonrotating part into the rotating MR fluid ribbon
• Volumetricremovalrate(VRR) calculated from spot volume and spot time
• STMmachineparametersheldconstantforthiswork
• Allpartspre-polishedflats
Interferometric map of polishing spot on part surface
Flowdirection
STM
Nozzle
Z axis
Z axis
Part
Ribbon
The drag force (FD) and normal force (FN) are measured in situ on the STM using piezoelectric sensors
G8625
• Sensors† measure dynamic, normal and shear forces
• Sensorsrespondtochangesin – substrate type – substrate surface condition – STM machine settings – MR fluid composition
• Allspotstakenonmachine z axis
†Single-axisslimlineshear(K9143B21) and compressive (K9133B21) load-cellmeasuringsystem(KistlerInstrumentCorp.,Amherst,NY).
FN
Z axis
Fluiddirection
FD
Drag forcesensor
Ribbon Wheelrotating clockwise
Part
Normal forcesensor
Drag forcesensor
Normal forcesensor
The sensor output signals are stable throughout the measurement
G8626
• LabViewinterfacerecordsthedragandnormalforcessimultaneously• Datacollectingrate:10datapointspersecond• Forceisaveragedoverthewholespottingtime
15
Forc
e in
New
ton
s
Elapsed time (s)
15 s
FS
Spinel
FN: ~11 NFN: ~9 N
FD: ~3.5 NFD: ~4 N
10
5
0 2 s
Both drag force (FD) and normal force (FN) strongly correlate to material hardness
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Drag force (FD)
• Decreaseslinearlywithincreasinghardness(STM parameters fixed)
Dual-load-cellresults
• PriorworkdoneontheSTMunderdifferentmachineconditions• SignificantexpansionofpriorworkontheSTM
00
1
2
3
F D (
N)
4
5
6
5 10 15
Hv (GPa)
20 25 30
LHG8 FS
FSSapphire
Spinel
ALON
PCASiC
BK7
LHG8
][DeGroote2007
Shorey2001 ][
BK7
y = –0.09x + 4.9R2 = 0.79
• Pressureshowsthesametrendfrom0.15to0.3MPa
Normal force (FN)• Increaseslinearlywithincreasinghardness• Saturatesat~11 N for hard ceramics
Both drag force (FD) and normal force (FN) strongly correlate to material hardness
G8637
Dual-load-cellresults
LHG8
FS
Spinel ALON(Line to guide eye)
PCA SiC
BK7
0
5
F N (
N) 10
15
0 5 10 15
Hv (GPa)
Pre
ssu
re(M
Pa)
20 25 3530
0.30
0.15
The coefficient of friction (FD/FN)shows aninversecorrelationwithmaterialhardness
G8628
InteractionbetweenMRfluidparticlesandthepartismechanicallydominant
LHG8
FS
Spinel ALON
Co
effic
ien
t o
f fr
icti
on
(C
OF
), n
PCA SiC
BK7
1.0
0.8
0.6
0.4
0.2
0.00 10
Hv (GPa)
20 30
Thematerialremovalrateshowsastrongdependence on the process coefficient of friction (FD/FN)
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Both drag and normal forces play an important role in material removal in MRF for glasses and ceramics
LHG8
FS
Spinel
ALON
Coefficient of friction (COF), n
Volu
met
ric
rem
oval
rat
e (m
m3 /
min
)
PCA
SiCBK7
0.8
0.6
0.4
0.2
0.00.0 0.2 0.4 0.6 0.8 1.0
y = 0.9x – 0.1R2 = 0.70
Acknowledgments
• AlexMaltsevandMikeKaplun(LLE) for polishing parts
• ScottRussell(UR)forLabViewsoftwareinterface
• SpineldiskswereprovidedbyTA&T
• CVCSiCmaterialwasprovidedbyTrex
• PolycrystallinealuminadiskswereprovidedbyCeraNovaCorporation.Development of this material by CeraNova is funded by NAVAIR through the U.S. Government SBIR program; SBIR data rights apply
• Continuousfinancialsupport
– Laboratory for Laser Energetics
– HortonFellowship
– U.S. Army Armament, Research, Development, and Engineering Center
– U.S. Department of Energy Office of Inertial Confinement Fusion
A frictional investigation of MRF for optical glasses and hard ceramics is carried out
G8620
• Adual-loadcellisusedforsimultaneous,in-situ measurement of frictional forces on optical glasses and hard ceramics
• Dragforcedecreaseslinearlywithincreasingmaterialhardness, whilenormalforcesaturatesathighhardness
• Coefficientoffrictioniscloselycorrelatedwithmechanicalpropertiesof materials and the particles in the MR fluid
Summary/Conclusions
We demonstrate that both drag and normal forces play an important role in material removal in MRF for both glasses and ceramics