Charles L. Brown Department of Electrical and Computer Engineering
Mool C. GuptaLangley Distinguished Professor & NSF I/UCRC Center Director
Department of Electrical & Computer Engineering
University of Virginia
Workshop, November 10, 2010
Laser Based Manufacturing
Charles L. Brown Department of Electrical and Computer Engineering
Outline
I. Introduction & Laser matter Interaction Process
II. High Power Lasers
III.Optical, Thermal and Electrical Properties of
Materials
IV. Beam Delivery and Scanning systems
V. Examples of Laser Applications
VI. Laser Process Monitoring
VII. Laser Market and Future Prospects
Outline
Charles L. Brown Department of Electrical and Computer Engineering
Section I. Introduction & laser
matter interaction process
Charles L. Brown Department of Electrical and Computer Engineering
National Science Foundation Center
For Laser Based Manufacturing
Develop Science, Engineeringand Technology Base for
Laser and Plasma Processing of Materials, Devices and
Systems for Advanced Manufacturing
Center Mission
Charles L. Brown Department of Electrical and Computer Engineering
Partnership
Projects
Industry
Fed. LabsUniv.
State NSF
MembershipMembership
Member
ship
CIT
Overhead &
Facility
Funds& National
Recognition
University of Virginia (Lead)
University of Michigan-Ann Arbor
University of Illinois
Southern Methodist University
NSF Industry University Cooperative
Research Center for Laser Based
Manufacturing
Charles L. Brown Department of Electrical and Computer Engineering
•AREVA Inc. NAVAIR
•GE Global Research A Army Research Lab.
NASA-Langley
•General Motors R&D Trinity Industries
Trumpf Lasers
•Lockheed Martin Lee Lasers
•Halliburton Lesker Corp
•Focus Hope Huettinger
•Cymer Corp. Dexter
• FIT Star Fire
•IMRA Begnaud
Industrial Advisory Board Members
Charles L. Brown Department of Electrical and Computer Engineering
•$30k membership allows
•Technical project for 1 year
•Access to center facility
•Access to center technology
•Interaction with all center board members
•Benefit from other NSF supported projects
NOTE: Board Members have access to
center research of over $1M with an
investment of $30k in membership. NSF
report shows $7 return for every dollar
invested.
NSF I/UCRC Center
Charles L. Brown Department of Electrical and Computer Engineering
Laser Welding: - Laser welding of light materials
-Rapid manuf. by e-beam welding
-Gas tungsten arc welding
-Galvanized steel welding
Laser Micromachining: -Laser texturing of Mo for solar
-Laser micromachining for fluidics
- Laser drilling of Ni superalloys
Laser Cladding: -Laser sintering of inconel 690
- Laser Cladding for erosion
Laser Diagnostics- -Laser corrosion detection-Navair
-Composition diagnostics during DMD
Plasma Processing: -Transparent coatings, pulsed plasma
Summary of Center Projects
Charles L. Brown Department of Electrical and Computer Engineering
• Laser and Optics Lab– Two fiber lasers (IPG), 50 ns pulse width
– High power CW diode laser (250W)
– Fs laser
– Two Nd-YAG laser (10 ns pulse width)
– Optical measurement equipment
– Computer controlled stages and galvo systems
• Clean Room Facility for Microfabrication– Optical Lithography, e-Beam Lithography,
sputtering, e-beam deposition, ion etching
• Characterization Facility- SEM, TEM, AFM, X-ray, …..
• Sensor and Photovoltaic Device Fabrication and Characterization Labs
Research Infrastructure
Charles L. Brown Department of Electrical and Computer Engineering
Diode pump Solid state laser
Diode laser
IPG fiber laser
YAG laserYAG laser
Research Infrastructure
Charles L. Brown Department of Electrical and Computer Engineering
Automotive
• Panel hole cutting
• Surface modification
• Sheet metal welding
Aerospace
• Laser cutting & welding
• Laser brazing
General manufact.
• Micromachining
• Microfabrication
Others
• Laser crystallization
• Pulsed laser deposition ∙∙∙∙∙∙
Medical
• Eye surgery
• Tissue removal
• Biostimulation
Military
• Laser weapons
• Army laser goggles
• Laser designator
Brazing
Cladding
Soldering
Seam welding
Spot welding
Diode pumping
Surface melting
Epoxy curing
Laser sintering
Laser welding
Paint stripping
Laser forming
Medical applications
Laser illumination
Composite forming
Free form fabrication
Laser Applications
Charles L. Brown Department of Electrical and Computer Engineering
LaserMaterial
Beam Delivery & scanning
Power source
& electronicsX-Y-Z computer
controlled stage
Process
monitor &
safetyEnvironment
Fundamentals of Laser Matter
Interactions
Charles L. Brown Department of Electrical and Computer Engineering
•Laser material interactions
•Laser systems
•Optics and beam delivery systems
•Materials and metallurgical aspects
•Process sensing and control
•Application specific process
Various Aspects of Laser Based Manufacturing
Charles L. Brown Department of Electrical and Computer Engineering
•Light Absorption
•Temperature Rise
•Melting
•Vaporization
•Cooling and
solidification
Material
Laser
beam
Ablated particles
•Laser parameters
•Optical properties of materials
•Thermal properties of
materials
•Electrical properties
Plasma
Plume
Light
emission
Laser Matter Interactions
Charles L. Brown Department of Electrical and Computer Engineering
http://ej.iop.org/links/q35/KI7QquaireEtwti,zstKpA/oa3451.pdf
Interaction
time
Charles L. Brown Department of Electrical and Computer Engineering
Laser rod
100 %
Reflecting
mirror
Partially
reflecting
mirror
Coherent
radiation
Pump source
High Power Lasers
Charles L. Brown Department of Electrical and Computer Engineering
Charles L. Brown Department of Electrical and Computer Engineering
Beam profile: GaussianSpectral Information
Pulse widthPolarization
-15 -10 -5 0 5 10 15
Re
lative
in
ten
sity
Time (ns)
Temporal Profile of a ns laser pulse
Pulse width at
FWHM
-6 -4 -2 0 2 4 6
Beam
width
Re
lative
in
ten
sity
Distance
I = Io exp[-r2/a]
Spatial distribution of intensity of a laser beam
Outp
ut p
ow
er
Wavelength (nm)
T.E
T.M
Laser Parameters
Charles L. Brown Department of Electrical and Computer Engineering
Laser Beam Profile
Charles L. Brown Department of Electrical and Computer Engineering
http://www.etechnologie.fh-stralsund.de/Daten/Fundamentals%20of%20laser%20drilling.pdf
Laser pulse characteristics
Charles L. Brown Department of Electrical and Computer Engineering
pp
apeak
ft
PP
Tf p
1
ppeakp tPPdtE
p
ppeak
At
E
A
PI
A
tP
A
EW
ppeakp
Peak Power
Intensity
Pulse energy
Fluence
Repetition ratetp=pulse width
Pa =Average power
A=area
Ppeak = Peak power
Ep = peak energy
Charles L. Brown Department of Electrical and Computer Engineering
I. Continuous (CW)- Important parameter is
the power in Watts Between 100W and 20kW
for materials processing
II. Pulsed - Important parameters are Joules
per Pulse and number of Pulses per Second
–Energy per pulse: 1mJ -1kJ
–Pulse length: 1ms -1ns-100 fs
–Pulse repetition rate: 0.1/s to 1 MHz
Lasers
Charles L. Brown Department of Electrical and Computer Engineeringhttp://www.electro-optics.org//files/laser%20workshop/martukanitz.pdf#search
Laser
Types
Charles L. Brown Department of Electrical and Computer Engineering
Important commercial lasers
Excimer 193-248nm Pulsed 10’s of Watts
Nd-YAG 1064 nm CW or Pulsed kW
CO2 10600 nm CW or Pulsed kW
Cu-Vapor 534 nm Pulsed 10’s of Watts
Ti-Sapphire 700-1000 nm CW or Pulsed 10’s of Watts
Other gas Solid State & Semiconductor Lasers
Important Commercial Lasers
Charles L. Brown Department of Electrical and Computer Engineering
Power density of welding and others
http://www.uni-ulm.de/ilm/AdvancedMaterials/Presentation/Admasulaserconductionwelding.pdf
Laser Power Density Regimes
Charles L. Brown Department of Electrical and Computer Engineering
http://t1.gstatic.com/images?q=tbn:ANd9GcRDgYhJ4I0kfhbHS83UQcsA0nWgSd0aQsdYPeuJRU2rS1jSsY0&t=1&usg=
__eqVU_YCOd-vi4yZ7qTvs_5iwyRs=
Fiber Laser Nd:YAG laser
Lasers
Charles L. Brown Department of Electrical and Computer Engineering
Section III. Optical, thermal and electrical
properties of materials
Charles L. Brown Department of Electrical and Computer Engineering
•Reflectivity
•Thermal Conductivity
•Specific Heat
•Latent Heat
The lower these parameters the more
efficient the process since less energy is
required to melt and vaporize the material.
Important Physical Parameters
Charles L. Brown Department of Electrical and Computer Engineering
Beer Lambert’s Law
I = I0 exp (-4παd/λ)
Where: α = extinction coefficient; λ =
Wavelength; I = Intensity at depth d; I0 =
Intensity at the surface
Beer Lambert’s Law
Charles L. Brown Department of Electrical and Computer Engineering
http://www.intel.com
Absorption coefficeint for various semiconductors
Charles L. Brown Department of Electrical and Computer Engineering
Table: Complex refractive index and reflection coefficient
for some materials to 1.06 micron radiation
Source: W. M. Steen
Optical Properties
Charles L. Brown Department of Electrical and Computer Engineering
Figure: Reflectivity of steel to polarised 1.06 micron radiation,
Source: W. M. Steen
Reflectivity variation with angle
Charles L. Brown Department of Electrical and Computer Engineering
Figure. Reflectivity of some common metals for normal incidence as
a function of wavelength. (After F. A. Jenkins and E. White, Fundamentals of Optics,
4th ed., McGraw-Hill, 1976)
Reflectivity vs. Wavelength
Charles L. Brown Department of Electrical and Computer Engineeringhttp://free.pages.at/bastieh/download/source/vortrag/lama.pdf
Absorption vs Wavelength
Charles L. Brown Department of Electrical and Computer Engineering
http://www.ensc.sfu.ca/people/faculty/chapman/e894/e894l15g.pdf
Schematic variation of absorption with temperature for a typical metal
surface for both the YAG and CO2 laser wavelength
•Absorption and
reflectivity are very
temperature
dependent
•Often undergo
significant changes
when material melts
•eg Silicon, steel
becomes highly
reflective on melting
Temperature
effect on
absorption
Charles L. Brown Department of Electrical and Computer EngineeringLaser Material Processing by W. Steen
Thermal properties of metals and
semiconductors
Charles L. Brown Department of Electrical and Computer Engineering
Temperature Distribution
tqerIAz
TK
t
TPc z
p
.
2
2
P= mass density, = specific heat, k= thermal
conductivity
; I(r) = radial distribution of laser beam
Represents attenuation of beam in z-direction a = optical
Absorption coefficient. A is absorptivity (between 0 and 1)
For flat beam
pcpPc
KD
ze
constIrI 0
Dt
zicrfc
K
DtAIztT
2
2, 0
http://www.etechnologie.fh-stralsund.de/Daten/Fundamentals%20of%20laser%20drilling.pdf
Charles L. Brown Department of Electrical and Computer Engineering
http://www.etechnologie.fh-stralsund.de/Daten/Fundamentals%20of%20laser%20drilling.pdf
Temperature vs time
Charles L. Brown Department of Electrical and Computer Engineering
Figure: Temperature vs. depth by copper
http://www.etechnologie.fh-stralsund.de/Daten/Fundamentals%20of%20laser%20drilling.pdf
Temperature vs Depth
Charles L. Brown Department of Electrical and Computer Engineering
Section IV. Beam delivery and scanning
systems
Charles L. Brown Department of Electrical and Computer Engineering
http://www.electro-optics.org//files/laser%20workshop/martukanitz.pdf#search
Hard Optic Delivery
(CO2, Nd:YAG, and Excimer Lasers)
Fiber Optics Delivery
(Primarily Nd:YAG Lasers)
•Mirrors must be properly aligned and
clean
•Can be used with practically any
wavelength
•Hard optical systems are fairly
reliable
•Versatile delivery to work station
•No practical fiber materials for
use with CO2 lasers (10.6 micron
radiation)
•Require high fiber bend radius
(approx 0.2m) to prevent leakage
•Destroys coherency of beam,
resulting in larger focal spot
Focus HeadFibersLaser
Optics
Moving
Workplaces
Moving
Optics
Beam delivery systems for laser processing
Charles L. Brown Department of Electrical and Computer Engineeringhttp://www.aerotech.com/pressbox/uk/release.cfm/ID/254.html
http://www.laserod
.com/mirrors.shtm
Laser Scanning Systems
Charles L. Brown Department of Electrical and Computer Engineeringhttp://www.uslasercorp.com/catalog/fobd.html
Fiber optic beam delivery system
Charles L. Brown Department of Electrical and Computer Engineering
Section V. Applications
Charles L. Brown Department of Electrical and Computer Engineering
• Surface Processing
– Alloying
– Surface Hardning
– Cladding
– Annealing & Doping
– Crystallization
– Texturing
• Patterning
– Direct writing
• Bulk Processing
– Cutting
– Drilling Holes
– Marking
– Welding
• Etching & Coating
– Pulsed Laser
Depostion
– Laser CVD
Applications
Charles L. Brown Department of Electrical and Computer Engineering
Laser micromachining
Charles L. Brown Department of Electrical and Computer Engineering
Laser Micro-machiningEDM
● Sharp notch tip
● Smaller heat effected zone
Laser micro notch fabrication
Charles L. Brown Department of Electrical and Computer Engineering
AFM Image of
Double Grating in
Si<100>
Diffraction Pattern
from Double
Grating
Micro/nano fabrication
Charles L. Brown Department of Electrical and Computer Engineering
Charles L. Brown Department of Electrical and Computer Engineering
Laser marking for CD disks
Charles L. Brown Department of Electrical and Computer Engineering
Schematic of laser cleaning process
Charles L. Brown Department of Electrical and Computer Engineering
Wavelength: 800 nm
Pulse Repetition Rate: 1 KHz
Pulse Energy: 1 mJ
Laser texture-experimental setup
Charles L. Brown Department of Electrical and Computer Engineering
Laser surface texture
Charles L. Brown Department of Electrical and Computer Engineering
Laser surface texture of thin films
Charles L. Brown Department of Electrical and Computer Engineering
Surface Reflectivity Control
Charles L. Brown Department of Electrical and Computer Engineering
Laser Generated Nanopores
Charles L. Brown Department of Electrical and Computer Engineering
Superhydrophobic Surfaces
Charles L. Brown Department of Electrical and Computer Engineering
Cell growth on laser textured surface
Charles L. Brown Department of Electrical and Computer Engineering
Laser Marking
Charles L. Brown Department of Electrical and Computer Engineering
Lasers for Photovoltaics
Charles L. Brown Department of Electrical and Computer Engineering
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.51E16
1E17
1E18
1E19
1E20
1E21
Rsheet
= 9 ohms / sq
P C
on
cen
tra
tio
n (
ato
ms/
cm3)
Depth (m)
V=6 ; 10X Scan; P=28 W
V=6 ; 1X Scan; P=39 W
Rsheet
= 45ohms/sq
Laser Doping
Charles L. Brown Department of Electrical and Computer Engineering
200 400 600 800 1000 1200
0
20
40
60
80
100Q
ua
ntu
m E
ffic
ien
cy
(%
)
Wavelength (nm)
300 nm junction with passivation
300 nm junction without passivation
Laser Textured Surfaces for Photodetector
Charles L. Brown Department of Electrical and Computer Engineering
Laser imaging of weld pool surface
Charles L. Brown Department of Electrical and Computer Engineering
http://www.cohr.com/Downloads/Paper5713Afinal.pdf#search=
Displays
Charles L. Brown Department of Electrical and Computer Engineering
1 μm
Laser texturing
Laser notch
formation
Laser sintering
Laser surface cleaning
Laser
microma
chining
Examples of Laser Processing
Charles L. Brown Department of Electrical and Computer Engineering
Inconel 690 laser cladding on Inconel 600 for nuclear applications
Laser Aided Manufacturing for Nuclear Energy
SEM cross-section
• Improve corrosion resistance of coolant
pipes by laser cladding
lower cost / higher processing speed
good adhesion & high density
minimal residual stress in base material
good chemical/mechanical/thermal
stability
avoid premature failure & enhance life
reduce repair costs
maintain generator safety, efficiency,
and up-time
transfer technology of laser metal
cladding
Charles L. Brown Department of Electrical and Computer Engineering
x
y
Nd:YAG LaserMirror
Lens
Argon gas environment
Nd:YAG Laser
High power CW laser
Stage
Advantages:
-Non-contact process, eliminating
contamination from walls
-Achieving extremely high temperature
(>4000°C), and the control of rapid
heating and cooling rates
-Sintering to high density, with minimal
post processing requirements
Objectives:
-Provide basic understanding of laser
sintering mechanism for ultra high
temperature ceramics (UHTCs)
-Fabrication of cladding layer and 3-D
structures using UHTCs for Air Force
applications.
Laser processing of ultra high temperature ceramics
Charles L. Brown Department of Electrical and Computer Engineering
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0.009
0.01
15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120
2 Theta (degree)
Inte
ns
ity (
a.u
.)
-
Laser sintering of nanoparticles
Charles L. Brown Department of Electrical and Computer Engineering
Laser generated nanofibers and rods
Charles L. Brown Department of Electrical and Computer Engineering
LASER-DRIVEN COMPRESSIVE WAVE
GENERATION
Turbine Blade & Vessel in Power Plants
Medical applications
Laser shot peening
Charles L. Brown Department of Electrical and Computer Engineering
Section VII. Process monitoring
Charles L. Brown Department of Electrical and Computer Engineering
• Welding
• Cutting
• Sintering
• Surface cleaning
• Micromachining
• Texturing
• Peening
Types of Laser Processes
Charles L. Brown Department of Electrical and Computer Engineering
Types of Physical Phenomenon for
Sensing
Optical
• Emission
• Absorption
• Reflection
• Fluorescence
• Direct imaging
Plasma related
• Sheath voltage, thickness etc
• Density
• Temperature
Acoustic
• Acoustic emission from melt pools
• Structural modification
• Defect generation
Charles L. Brown Department of Electrical and Computer Engineering
Example : Laser Welding
• Optical signals
• Acoustic signals
• Plasma signals
Process signal during laser
welding
Shao et al., Journal of Physics: Conference Series 15 (2005) 101–10
Charles L. Brown Department of Electrical and Computer Engineering
• Imaging in harsh environments
• Better spectral and spatial resolution
• Compact, reliable, low cost
• High speed
• Fiber optic based systems
Future prospects for laser process monitoring
Charles L. Brown Department of Electrical and Computer Engineering
Section VII. Laser market and future prospects
Charles L. Brown Department of Electrical and Computer Engineering
5%3%
11%
12%
13%
24%
32%
Marking
Cutting
Engraving
Microprocessing
Welding
Drilling
Other
• Worldwide, by Units Sold
Source: Industrial Laser Solutions
2005 Laser Applications
Charles L. Brown Department of Electrical and Computer Engineering
http://www.optoiq.com/index/photonics-technologies-applications/lfw-display/lfw-article-display/283868/articles/laser-focus-world/volume-43/issue-2/features/laser-marketplace-2007-diode-laser-market-takes-a-breather.html
Commercial Laser Market
Charles L. Brown Department of Electrical and Computer Engineering
•Lasers provide a competitive edge in
manufacturing
•Significant growth is expected in Laser Based
Manufacturing
•Progress in high power diode, fiber and disk
lasers will generate lower cost, compact , better
efficiency and hands free operation laser
systems.
•Desktop manufacturing may be possible
•Our Center has long experience in laser based
process development and sensor monitoring with
excellent infrastructure and resources for
education and training
Future Prospects
Charles L. Brown Department of Electrical and Computer Engineering
THANK YOU