Laser welding: a joining process used for fuel injector fabrication

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Laser welding a joining process used for fuel
injector fabrication
Ing. M. Muhshin Aziz Khan
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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
• Nd3YAG 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

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Facts About Laser
Laser Basics

• 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)

Light Amplification by Stimulated Emission of
Radiation

• Properties of Laser
• Coherent (synchronized phase of light)
• Collimated (parallel nature of the beam)
• Monochromatic (single wavelength)
• High intensity (1014W/m2)

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Facts About Laser
Laser Basics
Light Amplification by Stimulated Emission of
Radiation
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Facts About Laser
Laser Quality and Its
Effect
Effects of Beam Quality
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
• Value of M2 tends to increase with
  increasing laser power

• Smaller focus at constant aperture and focal
  length
• Longer working distance at constant aperture
  and spot diameter
• Smaller aperture (slim optics) at constant
  focal diameter and working distance

A higher power density by a smaller spot size
with the same optics, or The same power density
at lower laser power
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Facts About Laser
Primary Adjustable Parameters
and Their Effects
Change in Pulse Duration
Primary Controllable Parameters

• Laser Beam Energy Output Characteristics
• (i) Voltage (ii) Pulse Duration
• Laser Focus Characteristic
• (iii) Laser Beam Diameter

Increased pulse duration results in deeper and
wider melting
Change in Voltage
Change in Voltage and Pulse Duration
Increased voltage results in deeper physical
penetration with less melting due to physical
pressure
Simultanous increase in voltage and pulse
duration results in deeper melting
Change in Beam Diameter
Increased beam diameter results in shallow soft
penetration and wide, but soft melting
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Facts about lasers for welding Laser
Characteristics, Quality and Application

• Typical commercial lasers for welding
• CO2 Laser
• Nd3YAG Lasers
• Lamp-pumped
• LD-pumped
• Disk Laser
• Diode Laser
• Fiber Laser

CO2 Laser M2 values CW
Output power (W) M2
lt500 1.1-1.2
800-1000 1.2-2
1000-2500 1.2-3
5000 2-5
10,000 10
CO2 Laser Characteristics CO2 Laser Characteristics
Wavelength 10.6 µm far-infrared ray
Laser Media CO2N2He mixed gas (gas)
Average Power (CW) 45 kW (maximum) (Normal) 500 W 10 kW
Merits Easier high power (efficiency 10 20)
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Facts about lasers for Welding YAG Laser Laser
Characteristics, Quality and Application
Lamp-pumped YAG Laser Characteristics Lamp-pumped YAG Laser Characteristics
Wavelength 1.06 µm near-infrared ray
Laser Media Nd3 Y3Al5O12 garnet (solid)
Average Power CW 10 kW (cascade type fiber-coupling) (Normal) 50 W4 kW
Merits Fiber-delivery, and easier handling (efficiency 14)
YAG Laser M2 values CW PW
YAG Laser Application Automobile Industries YAG Laser Application Automobile Industries
Lamp-pumped 3 to 4.5 kW class SI fiber delivered (Mori, 2003)
LD-pumped 2.5 to 6 kW
New Development (Bachmann 2004) Rod-type 8 and 10 kW Laboratory Prototype
New Development (Bachmann 2004) Slab-type 6 kW Developed by Precision Laser Machining Consortium, PLM
Output power (W) M2
0-20 1.1-5
20-50 20-50
50-150 50-75
150-500 75-150
500-4000 75-150
LD-pumped YAG Laser Characteristics LD-pumped YAG Laser Characteristics
Wavelength about 1 µm near-infrared ray
Laser Media Nd3 Y3Al5O12 garnet (solid)
Average Power CW 13.5 kW (fiber-coupling max.) PW 6 kW (slab type max.)
Merits Fiber-delivery, high brightness, and high efficiency (1020)
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Facts about lasers for welding Disk Laser Laser
Characteristics, Quality and Application
Disk Laser Characteristics 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(1015)

• 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

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Facts about lasers for welding Fiber Laser Laser
Characteristics, Quality and Application
Fiber Laser Characteristics Fiber Laser Characteristics
Wavelength 1.07 µm near-infrared ray
Laser Media Yb3 SiO2 (solid), etc.
Average Power CW 20 kW (fiber-coupling max.)
Merits Fiber-delivery, high brightness, high efficiency(1025)

• 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

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Facts about lasers for welding Comparison of
different laser systems

• Correlation of Beam Quality to Laser Power
  (Katayama 2001 ONeil 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

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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
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Why do we need laser for welding?

• Traditional 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

• Laser beam welding
• 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

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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.

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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 101)
• High coupling efficiency

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Lasers Beam Welding Laser welding unit
Schematic Diagram
Beam Delivery unit
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Lasers Beam Welding photographic view of laser
welding unit
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Lasers Beam Welding Fuel Injector
Perspective XL2 injector VB-VS Welding
Configuration and Power Profile
Valve Body-Valve Seat Welding Configuration
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LASER BEAM WELDING OF MARTENSITIC STAINLESS
STEELS IN A CONSTRAINED OVERLAP JOINT
CONFIGURATION
A Case Study
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Experimental Procedure and Conditions
Design matrix with actual Independent process variables Design matrix with actual Independent process variables Design matrix with actual Independent process variables Design matrix with actual Independent process variables Design matrix with actual Independent process variables
Std Order Run Order Actual levels Actual levels Actual levels
Std Order Run Order Laser Power, LP (W) Welding Speed, WS (m/min) Fiber Diameter, FD (µm)
1 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
8 8 950 7.50 300
9 6 1100 7.50 300
10 18 800 4.50 400
11 10 950 4.50 400
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
Experimental Design Experimental Design Experimental Design Experimental Design Experimental Design
Process Factors Symbols Levels of Each Factor Levels of Each Factor Levels of Each Factor
Process Factors Symbols 1 2 3
Laser power (W) LP 800 950 1100
Welding speed (m/min) WS 4.5 6.0 7.5
Fiber Diameter (µm) FD 300 - 400
Constant Factors Constant Factors Constant Factors Constant Factors Constant Factors
Base material Outer Shell Inner Shell Outer Shell Inner Shell AISI 416 AISI 440 FSe AISI 416 AISI 440 FSe
Laser source NdYAG Laser NdYAG Laser NdYAG Laser NdYAG Laser
Angle of Incidence (deg) 900 (onto the surface) 900 (onto the surface) 900 (onto the surface) 900 (onto the surface)
Shielding gas Type Flow rate Type Flow rate Argon 29 l/min Argon 29 l/min
Response Factors Response Factors Response Factors Response Factors Response Factors
Weld bead characteristics Weld Zone (WZ) Width (W), Weld Resistance Length (S), and Weld Penetration Depth (P) Weld Zone (WZ) Width (W), Weld Resistance Length (S), and Weld Penetration Depth (P) Weld Zone (WZ) Width (W), Weld Resistance Length (S), and Weld Penetration Depth (P) Weld Zone (WZ) Width (W), Weld Resistance Length (S), and Weld Penetration Depth (P)
Mechanical properties Weld Shearing Force (F) Weld Shearing Force (F) Weld Shearing Force (F) Weld Shearing Force (F)
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Experimental Procedure and Conditions
Mechanical Characterization Weld X-Section
Experimental Measured Responses Experimental Measured Responses Experimental Measured Responses Experimental Measured Responses Experimental Measured Responses
Std Order Response Values Response Values Response Values Response Values
Std Order 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
Characterization of welding cross-section (W
Weld width, P Weld penetration depth, S Weld
resistance length)
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Experimental Procedure and Conditions Mechanical
Characterization Shearing Test
Photographic views of the experimental set-up for
shearing test
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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

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Results and Discussion Effects of Individual
Process Parameters
AA laser power BB welding speed CC fiber
diameter
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Results and Discussion Interaction Effects of
Process Parameters on Weld Width
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Results and Discussion Interaction Effects of
Process Parameters on Penetration Depth
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Results and Discussion Interaction Effects of
Process Parameters on Penetration Depth
Energy density is frequently used as process
parameter in energetic term
LP laser power describing the thermal source,
WS welding speed determining the interaction
time fSpot focal spot diameter defining the
area through which energy flows into the
material
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Results and Discussion Interaction Effects of
Process Parameters on Resistance Length
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Results and Discussion Interaction Effects of
Process Parameters on Resistance Length
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Results and Discussion Interaction Effects of
Process Parameters on Shearing Force
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Results and Discussion Interaction Effects of
Process Parameters on Shearing Force
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Results and Discussion Interaction Effects of
Process Parameters on Shearing Force
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Results and Discussion Effects of Shielding Gas
on Penetration Depth
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Thank You for Patience Hearing