Laser welding: a joining process
used for fuel injector fabrication
Ing. M. Muhshin Aziz Khan
What shall we discuss in this seminar?
Facts about laser
Laser basics
Laser quality and its effects
Primary adjustable or controllable
parameters and their effects
Facts about lasers for welding
CO2 laser
Nd3+:YAG laser
Lamp-pumped
LD-pumped
Disk laser
Diode laser
Fiber laser
Why do we need lasers for
welding
Laser beam welding
Types
Laser welding unit
Laser beam welding: Fuel Injector
Perspective
Fuel injector section
VS-VB weld configuration and power
profile
Seat to valve body assembly process
steps
Weld quality requirements
A case study: Laser beam
welding of martensitic stainless
steels in constrained overlap
configuration
Experimental procedure and conditions
Results and discussion
Weld bead profile aspect
Parametric effects on weld bead
chararcteristics
Problem associated with
inappropriate parameter selection
Facts About Laser:
Laser Basics
Light Amplification by
Stimulated Emission of
Radiation
Laser Components
Lasing Medium:
Provides appropriate transition and
Determines the wavelength (it must be in a
metastable state)
Pump:
Provides energy necessary for population
inversion
Optical Cavity:
Provides opportunity for amplification and
Produces a directional beam (with defined
length and transparency)
Properties of Laser
Coherent (synchronized phase
of light)
Collimated (parallel nature of
the beam)
Monochromatic (single
wavelength)
High intensity (~1014W/m2)
Facts About Laser:
Laser Basics
Light Amplification by
Stimulated Emission of
Radiation
Facts About Laser:
Laser Quality and Its Effect
Beam Quality
Effects of Beam Quality
 A measure of Lasers’ capability to be
☺ propagated with low divergence and
☺ focused to a small spot by a lens or
mirror
 Beam Quality is measured by M2 or BPP (Beam
Product Parameter, mm.mrad)
 Ratio of divergence of actual beam to a
theoretical diffraction limited beam with
same waist diameter
 M2= 1; Ideal Gaussian Beam, perfectly
diffraction limited
 Smaller focus at constant aperture and focal
 Value of M2 tends to increase with
length
increasing laser power
 Longer working distance at constant aperture
A higher power density by a smaller spot size
and spot diameter
with the same optics, or
 Smaller aperture (‘slim optics’) at constant
The same power density at lower laser power
focal diameter and working distance
Facts About Laser:
Primary Adjustable Parameters and Their Effects
Primary Controllable Parameters
 Laser Beam Energy Output Characteristics
(i) Voltage
(ii) Pulse Duration
 Laser Focus Characteristic
(iii) Laser Beam Diameter
Change in Voltage
Increased voltage results in deeper
physical penetration with less melting
due to physical pressure
Change in Beam Diameter
Change in Pulse Duration
Increased pulse duration results in
deeper and wider melting
Change in Voltage and Pulse
Duration
Simultanous increase in voltage and
pulse duration results in deeper melting
Increased beam diameter results in
shallow soft penetration and wide, but
soft melting
Facts about lasers for welding
Laser Characteristics, Quality and Application

Typical commercial lasers for welding
1. CO2 Laser
2. Nd3+:YAG Lasers
 Lamp-pumped
 LD-pumped
3. Disk Laser
4. Diode Laser
5. Fiber Laser
CO2 Laser: Characteristics
Wavelength
10.6 µm; far-infrared ray
Laser Media CO2–N2–He mixed gas (gas)
Average
45 kW (maximum)
Power (CW) (Normal) 500 W – 10 kW
Merits
Easier high power (efficiency: 10–
20%)
CO2 Laser: M2 values [CW]
Output power (W)
<500
M2
1.1-1.2
800-1000
1.2-2
1000-2500
1.2-3
5000
2-5
10,000
10
Facts about lasers for Welding: YAG Laser
Laser Characteristics, Quality and Application
Lamp-pumped YAG Laser: Characteristics
Wavelength
1.06 µm; near-infrared ray
Laser Media Nd3+: Y3Al5O12 garnet (solid)
YAG Laser:10
M2kW
values
[CWtype
& & fiberAverage
(cascade
PW]
Power [CW] coupling)
2
Output power(Normal) 50MW–4
kW
(W)
Fiber-delivery, and easier
Merits
0-20
1.1-5
handling (efficiency:
1–4%)
20-50
20-50
50-150
50-75
150-500
75-150
500-4000
75-150
YAG Laser Application: Automobile
Industries
Lamppumped
3 to 4.5 kW class; SI fiber
delivered (Mori, 2003)
LD-pumped
2.5 to 6 kW
New
Rod-type: 8 and 10 kW; Laboratory
LD-pumped
YAG Laser: Characteristics
Development
Prototype
(Bachmann
Slab-type:
6 kW;
Developed
by
Wavelength
about
1 µm;
near-infrared
ray
Precision Laser Machining
2004)
3+
Laser Media
Nd PLM
: Y3Al5O12 garnet (solid)
Consortium,
Average
Power
[CW] : 13.5 kW (fiber-coupling
max.)
[PW] : 6 kW (slab type max.)
Merits
Fiber-delivery, high brightness,
and high efficiency (10–20%)
Facts about lasers for welding: Disk Laser
Laser Characteristics, Quality and Application
Disk Laser: Characteristics
Wavelength
1.03 µm; near-infrared ray
Laser Media
Yb3+ : YAG or YVO4 (solid)
Average
Power [CW]
6 kW (cascade type max.)
Merits
Fiber-delivery, high
brightness, high
efficiency(10–15%)
Recent Development (Mann 2004; and
Morris 2004):
 Commercially available disk laser
system: 1 and 4 kW class
 Beam delivery with 150 and 200 µm
diameter fiber
 Even a 1 kW class laser is able to
produce
a deep keyhole-type weld bead
extremely narrow width
in stainless steel and aluminum alloy
Facts about lasers for welding: Fiber Laser
Laser Characteristics, Quality and Application
Fiber Laser: Characteristics
Wavelength 1.07 µm; near-infrared ray
Laser
Media
Yb3+ : SiO2 (solid), etc.
Average
20 kW (fiber-coupling max.)
Power [CW]
Merits
Fiber-delivery, high
brightness, high
efficiency(10–25%)
Recent Development (Thomy et.al. 2004; and
Ueda 2001):
 Fiber lasers of 10kW or more are
commercially available
 Fiber lasers of 100kW and more are
scheduled
 Fiber laser at 6.9kW is able to provide
deeply penetrated weld at high speed
 Fiber laser is able to replace high quality
(slab) CO2 laser for remote or scanning
welding
Facts about lasers for welding
Comparison of different laser systems
Correlation of Beam Quality to Laser Power
(Katayama 2001; O’Neil et. al. 2004; Shiner 2004;
Lossen 2003):
 Overlaid with condition regimes
 Beam quality of a laser worsens with an
increase in power
 LD-pumped YAG, thin disk, CO2 and fiber
lasers can provide high-quality beams
 The development of higher power CO2 or YAG
lasers is fairly static and, hence
Main focus on development:
i.
high-power diode, ii. LD-pumped YAG, iii.
disk and/or
iv. fiber lasers
Facts about lasers for welding
Wavelengths of some important laser sources for materials processing
CO2 Laser
Expanded portion of the electromagnetic spectrum showing the
wavelengths at which several important lasers operate
Why do we need laser for welding?
Traditional welding:
Laser beam welding:
 Natural limitations to speed and
productivity
 Thicker sections need multi-pass
welds
 A large heat input
 Results in large and unpredictable
distortions
 Very difficult to robotize

High energy density input process
 single pass weld penetration up to ¾
inch
 High aspect ratio
 High scanning speeds
 Precisely controllable (close
tolerence: ± 0.002 in.)






Low heat input produces low
distortion
Does not require a vacuum (welds at
atmospheric pressure)
No X-rays generated and no beam
wander in magnetic field.
No filler metal required (autogenous
weld and no flux cleaning)
Relatively easy to automate
Materials need not be conductive
Lasers Beam Welding:
Types of LBW
Conduction Welding
Description
 Heating the workpiece above the melting temperature
without vaporizing
 Heat is transferred into the material by thermal
conduction.
Characteristics
 Low welding depth
 Small aspect ratio (depth to width ratio is around
unity)
 Low coupling efficiency
 Very smooth, highly aesthetic weld bead
Applications
Laser welding of thin work pieces like foils, wires, thin
tubes, enclosures, etc.
Lasers Beam Welding:
Types of LBW
Keyhole Welding
Description
 Heating of the workpiece above the vaporization
temperature and forming of a keyhole
 Laser beam energy is transferred deep into the
material via a cavity filled with metal vapor
 Hole becomes stable due to the pressure from vapor
generated
Characteristics
 High welding depth
 High aspect ratio (depth to width
ratio can be 10:1)
 High coupling efficiency
Lasers Beam Welding:
Laser welding unit
Schematic
Diagram
Beam
Delivery
unit
Beam Delivery Unit
Laser
Processing
Optics
Workpiece Positioning Unit
Lasers Beam Welding:
photographic view of laser welding unit
Specimen
Holder
Shielding Gas
Nozzle
Laser
Head
Specimen
Lasers Beam Welding: Fuel Injector Perspective
XL2 injector: VB-VS Welding Configuration and Power Profile
Segment
Time [ms]
Power [W]
1 2 3 4 5 6 7
0 20 200 20 200 50 0
0 870 870 200 200 0 0
Joint overlap at full
power to ensure
hermetic enclosure
of joint
Post heating to
remove micro cracks
from joint surface
power
Power profile vs angle
Turn
1000
3,5
3
Power [W]
800
2,5
600
2
400
1,5
1
200
0,5
0
0
0
100
200
300
400
500
Angle [°]
Valve Body-Valve Seat
Welding Configuration
600
700
800
900
1000
A Case Study
LASER BEAM WELDING OF MARTENSITIC
STAINLESS STEELS IN A CONSTRAINED
OVERLAP JOINT CONFIGURATION
Experimental Procedure and Conditions
Design matrix with actual Independent process variables
Experimental Design
Process
Factors
Sym
bols
Laser power
(W)
Actual levels
Levels of Each Factor
1
2
3
LP
800
950
1100
Welding speed
(m/min)
WS
4.5
6.0
7.5
Fiber Diameter
(µm)
FD
300
-
400
Constant Factors
Base material
Outer Shell
Inner Shell
AISI 416
AISI 440 FSe
Std
Order
Run
Order
1
Laser
Power,
LP (W)
Welding
Speed, WS
(m/min)
Fiber
Diameter,
FD (µm)
14
800
4.50
300
2
7
950
4.50
300
3
2
1100
4.50
300
4
16
800
6.00
300
5
12
950
6.00
300
6
3
1100
6.00
300
7
4
800
7.50
300
Laser source
Nd:YAG Laser
8
8
950
7.50
300
Angle of
Incidence
(deg)
900 (onto the surface)
9
6
1100
7.50
300
10
18
800
4.50
400
11
10
950
4.50
400
Shielding gas
Type
Flow rate
12
9
1100
4.50
400
13
15
800
6.00
400
14
13
950
6.00
400
15
17
1100
6.00
400
16
11
800
7.50
400
17
5
950
7.50
400
18
1
1100
7.50
400
Argon
29 l/min
Response Factors
Weld bead
characteristics
Mechanical
properties
Weld Zone (WZ) Width (W), Weld
Resistance Length (S), and Weld
Penetration Depth (P)
Weld Shearing Force (F)
Experimental Procedure and Conditions:
Mechanical Characterization: Weld X-Section
Experimental Measured Responses
Response Values
Std
Order
Characterization of welding cross-section (W: Weld width,
P: Weld penetration depth, S: Weld resistance length)
Weld
Width,
W (µm)
Penetration
Depth, P
(µm)
Resistance
Width, S
(µm)
Shearing
Force, F (N)
1
490
960
440
5910
2
490
1290
480
6022
3
580
1610
500
6775
4
530
710
370
6233
5
520
950
470
6129
6
510
1180
450
6355
7
530
560
210
2999
8
590
730
390
5886
9
590
880
510
6861
10
572
790
529
5722
11
612
1043
586
5809
12
638
1307
613
6730
13
622
577
266
4457
14
699
727
481
6154
15
771
920
588
5942
16
600
492
33
1897
17
721
580
273
2602
18
732
749
442
5044
Experimental Procedure and Conditions:
Mechanical Characterization: Shearing Test
Punch
Expeller
Specimen
Holder
Specimen
(b)
Photographic views of the experimental set-up for shearing test
Results and Discussion:
Weld profile Aspect
Curvature of the keyhole profile is
closely related to welding speed.
The higher the welding speed
the larger the curvature of the
keyhole.
 Keyhole is nearly cone-shaped
 Its vertex angle decreases as
the keyhole depth increases
Shape of the keyhole
changes from conical to
cylindrical
Results and Discussion:
Effects of Individual Process Parameters
AA: laser power
BB: welding speed
CC: fiber diameter
Results and Discussion:
Interaction Effects of Process Parameters on Weld Width
Results and Discussion:
Interaction Effects of Process Parameters on Penetration Depth
Results and Discussion:
Interaction Effects of Process Parameters on Penetration Depth
Energy density is frequently used as process
parameter in energetic term:
ED 
LP
WS   spot
LP
: laser power describing the thermal source,
WS : welding speed determining the interaction time
φSpot : focal spot diameter defining the area through which
energy flows into the material
Results and Discussion:
Interaction Effects of Process Parameters on Resistance Length
Results and Discussion:
Interaction Effects of Process Parameters on Resistance Length
Results and Discussion:
Interaction Effects of Process Parameters on Shearing Force
Results and Discussion:
Interaction Effects of Process Parameters on Shearing Force
Results and Discussion:
Interaction Effects of Process Parameters on Shearing Force
Results and Discussion:
Effects of Shielding Gas on Penetration Depth
Thank You for
Patience Hearing