laboratory for laser materials synthesis & fabrication department of materials science &...
TRANSCRIPT
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
Ab-initio Computational Approach to Ab-initio Computational Approach to Laser Micro-machining of Laser Micro-machining of
Structural CeramicsStructural Ceramics
Anoop N. Samant, Anoop N. Samant,
Narendra B. DahotreNarendra B. Dahotre
Laboratory for Laser Materials Synthesis & Laboratory for Laser Materials Synthesis & FabricationFabrication
Department of Materials Science & Engineering,Department of Materials Science & Engineering,University of Tennessee,University of Tennessee,
Knoxville, TNKnoxville, TN
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
OUTLINEOUTLINE
Objectives
Structural Ceramics
Methodology
Laser Machining of Structural Ceramics
Physical Phenomena in Machining
Data Analysis
Contribution of current work
Significance of research
Future Work
Conclusions
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
OBJECTIVESOBJECTIVES
Demonstrate feasibility of laser machining of
structural ceramics.
Understand material removal mechanisms (MRM)
Develop an ab-initio computational model based on
MRM.
Use model for advance predictions of laser processing
conditions to attain desired attributes.
Save considerable energy and time.
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
Properties Low thermal and electrical conductivity High hardness Chemical stability High thermal resistance
Applications Machine tools, valves, bearings, rotors Optical and Electronic devices Hazardous Waste Disposal
Examples Silicon Carbide, Alumina, Silicon Nitride, Magnesium Oxide,
Zirconia
STRUCTURAL CERAMICSSTRUCTURAL CERAMICS
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
LASER MACHININGLASER MACHINING
An operation similar to laser drilling subsequently conducted on
neighboring locations.
Advantages :
Non contact processing
Capability of automation
Reduced manufacturing costs
Efficient material utilization
Reduced heat-affected zone (HAZ)
High productivity
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
LASER MACHININGLASER MACHINING
Fig.3 Types of Laser Machining [2]
Fig.2 Laser Machining [1][1]Kalpakjian, Serope and Steven R. Schmid, Manufacturing Engineering
and Technology, Upper Saddle River, New Jersey: Prentice Hall, Inc, 2001.
[2]Samant and Dahotre, Journal of European Ceramic Society, 29(2009) 969.
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
METHODOLOGYMETHODOLOGY Come up with optimum pulse width, pulse energy, and pulse
repetition rate to develop sufficient laser-ceramic interaction.
Vary processing parameters to machine cavities of different
dimensions.
Develop 3D-thermal model to generate temperature profiles.
Incorporate different physical phenomena into the developed
model.
Correlate predicted attributes of machined cavities with
observed features.
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
Symbol Property Value
d Out of focus beam diameter 0.5 mm
λ Laser Wavelength 1,064 nm
δf Focal Length 120 mm
SILICON CARBIDE MACHININGSILICON CARBIDE MACHININGTable 1. Laser Parameters (JK 701 pulsed Nd:YAG laser )
Fig.4 Through holes in 2mm and 3mm SiC plates [1].
25 and 125 pulses machined 2 and 3 mm plates at 6 J, 0.5 ms and 50 Hz.
[1] Samant et. al., International Journal of Advanced Manufacturing Technology, in press.
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
Fourier’s Second Law for maximum surface
temperature:
Radiation losses at the surface :
⎥⎦
⎤⎢⎣
⎡
∂∂
+∂
∂+
∂∂
=∂
∂2
2
2
2
2
2
z
t)T(z,
y
t)T(y,
x
t)T(x,á(T)
t
t)z,y,T(x,
( )404 Tt)0,y,T(x,åóäaIz
t)y,0,T(x,
y
t)y,0,T(x,
x
t)y,0,T(x,k(T) −−=⎟⎟
⎠
⎞⎜⎜⎝
⎛∂
∂+
∂
∂+
∂
∂−
( )0Tt)D,y,T(x, h(T)z
t)H,y,T(x,
y
t)H,y,T(x,
x
t)H,y,T(x,)T(k −=⎟⎟
⎠
⎞⎜⎜⎝
⎛∂
∂+
∂
∂+
∂
∂−
(1)
(2)
(3)
ε - emissivity , k(T) - thermal conductivity, T0- initial temperature, h(T) - heat transfer
coefficient, H – plate thickness, a – absorptivity (1 due to multiple reflections. [1]) [1] Mazumdar et. al., J.Appl.Phys., 51(2), 1980
Convection taking place at the bottom:
TEMPORAL EVOLUTIONTEMPORAL EVOLUTION
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
TEMPORAL EVOLUTIONTEMPORAL EVOLUTION
Temperature during pulse OFF time [1] :
⎥⎥
⎦
⎤
⎢⎢
⎣
⎡
⎥⎥
⎦
⎤
⎢⎢
⎣
⎡
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛−
⎥⎥⎦
⎤
⎢⎢⎣
⎡−−+=
)T(k
t)T()T(herf
)T(k
t)T(hexp)TT(TT
offoffii
'i
αα11
2
2
0
)T(k
/t)T(
d
PaTT on'ii
παπ 218
+= −
(4)
(5)
Ti - Temperature during heating of pulse i, toff - OFF period between
successive pulses, erf - error function, α(T) - thermal diffusivity
T’i-1 - temperature during cooling of the earlier pulse, ton - pulse duration,
P – incident beam power [1] Konstantinos et.al. , Journal of Materials Processing Technology 183 (2007), 96.
Temperature during pulse ON time [1] :
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
TEMPORAL EVOLUTIONTEMPORAL EVOLUTION
Fig.5 Heating curves for a) 2mm and b) 3mm thick SiC plate
Temperature drops during the OFF
time and rises during the ON time of
the laser giving the heating curve a
meandering nature.
Maximum surface temperature
reached while processing 3mm thick
plate is higher than that reached while
processing 2 mm plate.
High temperatures exist for extremely
short time and rapidly drops due to
self quenching.
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
EVAPORATION LOSSESEVAPORATION LOSSES Rate of evaporation :
21
2
/
s
vsd kT
m)T(pj ⎥
⎦
⎤⎢⎣
⎡=
π
mv - mass of vapor molecule, Ts-surface temperature, k - Boltzmann
Constant , p(Ts) - saturation pressure, p0 – ambient pressure
Material loss : ρtimej
z deva
×=
Corresponding drop in temperature :
d
t)T(tgarc
d)T(k
LjT
/vd
eva
απ
4223=Δ
(6)
(7)
(8)
Lv - latent heat of evaporation
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
DISSOCIATION ENERGY LOSSESDISSOCIATION ENERGY LOSSESPossible dissociation species :
Si(l), C(s), C(g), Si(g), Si3(g), Si2(g), SiC2 (g), Si2C(g) and Si(s)
Most likely reaction at 3103 K:
(9)
Volume of hole: 4
2avacyl zdπ
(10)
(assuming cylinder of diameter
zava = available melt depth = ztotal - zeva = melt depth from surface - evaporated depth Energy Loss :
310422 −××Δ.VolumeG
(11)
≈ (Volume/ 22.4 x 10-3) moles)3/d
)s()l( CSiSiC +=
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
RECOIL PRESSURERECOIL PRESSURE
Cause : Evaporation of the melt surface exposed to laser.
Effective melt depth zeff: Portion remaining after expelling a
fraction of the total melt depth.
Recoil pressure pr : Is a function of the material properties,
maximum surface temperature and input energy [1] :
⎟⎠
⎞⎜⎝
⎛+
=2
2
221
691
4 b.
b
L
.
aP
pd
v
rπvvs LmTkb /=2
(12)
[1] Anisimov , Sov. Phys. JETP 27 (1968), 182
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
Surface tension effect : Modifies pressure on melt, thus
affecting depth of machined cavity [1].
Effective beam radius: Beam radius changes with change in
machined depth [2] .
Velocity of expulsion [3]:
SURFACE TENSIONSURFACE TENSION
( ) 21
2
2
41
2/ft
eff d
zdr
⎥⎥⎦
⎤
⎢⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛ ++=
π
δλ
tr
r/p)t(v
eff
effrexp
τρ
−=
1
(13)
(14)
τ - surface tension coefficient of liquid Si , t – time, reff – effective beam
radius, ρ - density [1] Han et.al., Journal of Heat Transfer, 127 (2005),1005.
[2] Salonitis et.al., Journal of Materials Processing Technology 183 (2007), 96
[3] Matsunawa et.al., J. Phys. D: Appl. Phys. 30(1997),798.
(13)
(14)
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
MACHINED CAVITYMACHINED CAVITY DEPTH DEPTHMachined cavity: Depth of
cavity formed due to expulsion of
available melt depth [1] :
∑=t
elledexpt zz0
dt)t(vzt
expelledexp ∫=0
Fig.6 Cavity Evolution
(15)
(16)
zexpelled – Depth expelled at different time instants
zt – Total cavity depth formed at a certain time instant
[1] Semak et. al., J. Phys. D: Appl. Phys. 39 (2006),590.
Predicted pulses: 21 and 103
pulses for machining through a 2
and 3 mm plate.
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
MACHINED CAVITY DEPTHMACHINED CAVITY DEPTH
Fig.7 Stages of Cavity Evolution
Till t2, material expelled
in upward direction.
Around t3, direction of
material expulsion
reversed due to least
resistance to the recoil
pressure by small mass
of supporting material at
the bottom.
At t4, all the rest of
molten material expelled
and a clean through
cavity formed.
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
ALUMINA MACHININGALUMINA MACHINING
Applications: Substrate in hybrid circuits, aerospace industry.
Dissociation at 3250K:
Machining mechanism: Dissociation, melt expulsion by recoil
pressure and evaporation.
Predicted pulses: 3, 7, 16 and 19 pulses for machining 0.26, 0.56, 3.23
and 4.0 mm respectively at 0.5ms, 4J and 20Hz.
232 512 O.AlOAl )s( += (17)
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
ALUMINA MACHININGALUMINA MACHINING
Fig.9 Cavities in alumina [1]
Fig.10 Evolution of cavities [1]
[1] Samant and Dahotre, Int. Journal of Machine Tools and Manufacture, 48 (2008), 1345.
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
MAGNESIUM OXIDE MACHININGMAGNESIUM OXIDE MACHINING
Applications: Refractory and brake linings, thin film semi-conductors.
Dissociation at 3123K:
Machining mechanism: Dissociation followed by evaporation.
Predicted machining times: 0.11, 0.2, 0.25 and 0.8 s for machining
0.25, 0.86, 1.54 and 3mm respectively at 0.5ms, 4 J and 20 Hz.
(19))g()s( OMgMgO +=
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
MAGNESIUM OXIDE MACHININGMAGNESIUM OXIDE MACHINING
Fig.13 Cavities in
MgO [1]
Fig.14 Evolution of cavities with
time [1]
[1] Samant and Dahotre, Optics and Lasers in Engineering, 47(2009),570.
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
PHYSICAL PHENOMENA IN PHYSICAL PHENOMENA IN DIFFERENT CERAMICSDIFFERENT CERAMICS
Melting Dissociation Evaporation
Silicon Carbide (SiC) Alumina (Al2O3) Magnesium Oxide (MgO)
Physical Process
Material
Table 2. Physical Phenomena Governing Machining in Different Ceramics [1]
[1] Samant and Dahotre, Ceramics International, in press.
Melting Dissociation Evaporation
Silicon Carbide (SiC) Alumina (Al2O3) Magnesium Oxide (MgO)
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
Fig.8 Flowchart for computations
FLOW CHARTFLOW CHART
Stepwise procedure to
achieve final machining
parameters starting with
material properties and
process parameters.
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
DATA ANALYSISDATA ANALYSISTable 3. Comparison between experimental and predicted attributes of machined cavities
CeramicDepth of machined
cavity (mm)Pulsesexperimental
(Time, sec)
Pulsespredicted
(Time, sec)
Al2O3
0.26 5 (0.25) 3 (0.15)
0.56 10 (0.5) 7 (0.35)
3.23 20 (1.0) 16 (0.8)
4 30 (1.5) 19 (0.94)
SiC2 25(0.5) 21(0.41)
3 125(2.5) 103(2.05)
MgO
0.25 3 (0.15) 2 (0.11)
0.86 6 (0.3) 4 (0.2)
1.54 9 (0.45) 5 (0.25)
3 20 (1) 16 (0.8)
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
CONTRIBUTION OF CURRENT WORK CONTRIBUTION OF CURRENT WORK
Prior work conclusions: a) Machining comprises of melting
and material removal by expulsion [1].
b) Machining takes place by single step evaporation without
melting [2].
c) Effect of multiple reflections neglected.
Current work conclusions: a) Material removal occurs by a
combination of melt expulsion, dissociation and evaporation.
b) Multiple reflections affect the amount of absorbed energy.
[1] Salonitis et.al, Journal of Materials Processing Technology, 183(2007) 96.
[2] Atanasov et. al, Journal of Applied Physics, 89(2001) DOI: 10.1063/1.1334367
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
SIGNIFICANCE OF RESEARCH SIGNIFICANCE OF RESEARCH
Proposed systematic approach is an advancement of
existing computational approach to ceramic machining.
Advance prediction of number of pulses/ pulse duration/
pulse energy possible.
Developed model can be extended to two and three
dimensional laser machining.
A system with optimum machining rate can be
generated.
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
FUTURE WORKFUTURE WORK
Laser Machining in 2 D (Laser Cutting) and 3D
(engraving complex shapes).
Effect of multiple passes on machined depth by
considering preheating effect.
In-situ temperature measurements and
absorptivity predictions using thermocouples.
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
SUMMARYSUMMARY Structural ceramics were successfully machined.
Theoretical model incorporating several vital effects encountered during machining was developed.
Model predictions compared well with experimental observations for machining.
Model aids to provide an advance estimate of number of pulses required for machining required depth or the depth machined after applying certain number of pulses.
Laser Fluence and machining time could also be predicted.
T M
Laboratory for Laser Materials Synthesis & FabricationDepartment of Materials Science & Engineering
UNIVERSITY OF TENNESSEE, Knoxville, TN
THANK YOUTHANK YOU