Laser welding: a joining process used for fuel injector fabrication

Ing. M. Muhshin Aziz Khan

What shall we discuss in this seminar?What shall we discuss in this seminar?

Facts about laserFacts about laserLaser basicsLaser basics

Laser quality and its effectsLaser quality and its effects

Primary adjustable or controllable Primary adjustable or controllable parameters and their effectsparameters and their effects

Facts about lasers for weldingFacts about lasers for welding

COCO22 laser laser

NdNd3+3+:YAG laser:YAG laser

Lamp-pumpedLamp-pumped

LD-pumpedLD-pumped

Disk laserDisk laser

Diode laserDiode laser

Fiber laserFiber laser

Why do we need lasers for Why do we need lasers for weldingwelding

Laser beam weldingLaser beam weldingTypesTypes

Laser welding unitLaser welding unit

Laser beam welding: Laser beam welding: Fuel Injector Fuel Injector PerspectivePerspectiveFuel injector sectionFuel injector section

VS-VB weld configuration and power VS-VB weld configuration and power profileprofile

Seat to valve body assembly process Seat to valve body assembly process stepssteps

Weld quality requirementsWeld quality requirements

A case study:A case study: Laser beam Laser beam welding of martensitic stainless welding of martensitic stainless steels in constrained overlap steels in constrained overlap configurationconfiguration

Experimental procedure and conditionsExperimental procedure and conditions

Results and discussionResults and discussion

Weld bead profile aspectWeld bead profile aspect

Parametric effects on weld bead Parametric effects on weld bead chararcteristicschararcteristics

Problem associated with Problem associated with inappropriate parameter selectioninappropriate parameter selection

Facts About Laser:Facts About Laser: Laser BasicsLaser Basics

Laser ComponentsLaser Components

Lasing Medium:Lasing Medium: Provides appropriate transition and Determines the wavelength (it must be in a metastable state)

Pump:Pump: Provides energy necessary for population inversion

Optical Cavity:Optical Cavity: Provides opportunity for amplification and Produces a directional beam (with defined length and transparency)

Properties of LaserProperties of LaserCoherentCoherent (synchronized phase of light)

Collimated Collimated (parallel nature of the beam)

MonochromaticMonochromatic (single wavelength)

High intensityHigh intensity (~1014W/m2)

LLight ight AAmplification by mplification by SStimulated timulated EEmission of mission of RRadiationadiation

Facts About Laser:Facts About Laser: Laser BasicsLaser Basics

LLight ight AAmplification by mplification by SStimulated timulated EEmission of mission of RRadiationadiation

Facts About Laser:Facts About Laser: Laser Quality and Its EffectLaser Quality and Its Effect

A measuremeasure of Lasers’ capabilitycapability to be☺ propagatedpropagated with low divergencedivergence and ☺ focusedfocused to a small spot by a lenslens or mirrormirror

BeamBeam Quality is measured by MM22 or BPPBPP (BBeam PProduct PParameter, mm.mradmm.mrad)

Ratio of divergencedivergence of actualactual beam to a theoretical diffractiontheoretical diffraction limited beam

with samesame waistwaist diameter MM22= 1= 1;; Ideal Gaussian BeamGaussian Beam, perfectly

diffraction limited ValueValue of M2 tends to increaseincrease with increasingincreasing laser powerpower

Effects of Beam QualityEffects of Beam QualityBeam QualityBeam Quality

SmallerSmaller focus at constantconstant aperture and focal length LongerLonger working distance at constantconstant aperture

and spot diameter SmallerSmaller aperture (‘slim optics’) at constantconstant

focal diameter and working distance

A higher power densityhigher power density by a smallersmaller spot size with the same opticssame optics, or

The same same power density at lowerlower laserlaser power

Facts About Laser:Facts About Laser: Primary Adjustable Parameters and Their EffectsPrimary Adjustable Parameters and Their Effects

Laser Beam Energy Output CharacteristicsLaser Beam Energy Output Characteristics(i) Voltage (ii) Pulse Duration

Laser Focus CharacteristicLaser Focus Characteristic(iii) Laser Beam Diameter

Primary Controllable ParametersPrimary Controllable Parameters

Change in VoltageChange in Voltage

IncreasedIncreased voltage results in deeperdeeper physical penetrationpenetration with lessless melting due to physicalphysical pressure

Change in Pulse DurationChange in Pulse Duration

IncreasedIncreased pulse duration results in deeperdeeper and widerwider melting

Change in Voltage and Pulse Change in Voltage and Pulse DurationDuration

Simultanous increase Simultanous increase in voltage and pulse duration results in deeperdeeper melting

Change in Beam DiameterChange in Beam Diameter

IncreasedIncreased beam diameter results in shallow softshallow soft penetration and widewide, but softsoft melting

Facts about lasers for weldingFacts about lasers for weldingLaser Characteristics, Quality and ApplicationLaser Characteristics, Quality and Application

Typical commercial lasers for welding Typical commercial lasers for welding

1. COCO22 Laser2. NdNd3+3+:YAG:YAG Lasers

Lamp-Lamp-pumped LD-LD-pumped

3.3. Disk Disk Laser4.4. DiodeDiode Laser5.5. FiberFiber Laser

CO2 Laser: Characteristics

Wavelength 10.6 µm; far-infrared ray

Laser Media CO2–N2–He mixed gas (gas)

AveragePower (CW)

45 kW (maximum)(Normal) 500 W – 10 kW

Merits Easier high power (efficiency: 10–20%)

Output power (W)

M2

<500 1.1-1.2

800-1000 1.2-2

1000-2500 1.2-3

5000 2-5

10,000 10

COCO22 Laser: Laser: MM22 values values [[CW] CW]

Lamp-pumped YAG Laser: Characteristics

Wavelength 1.06 µm; near-infrared ray

Laser Media Nd3+: Y3Al5O12 garnet (solid)

AveragePower [CW]

10 kW (cascade type & fiber-coupling)

(Normal) 50 W–4 kW

Merits Fiber-delivery, and easier handling (efficiency: 1–4%)

LD-pumped YAG Laser: Characteristics

Wavelength about 1 µm; near-infrared ray

Laser Media Nd3+ : Y3Al5O12 garnet (solid)

AveragePower

[CW] : 13.5 kW (fiber-coupling max.)

[PW] : 6 kW (slab type max.)

Merits Fiber-delivery, high brightness, and high efficiency (10–20%)

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

YAG Laser: YAG Laser: MM22 values [CW & values [CW & PW] PW] YAG Laser Application: Automobile Automobile

IndustriesIndustries

Lamp-pumped

3 to 4.5 kW class; SI fiber delivered (Mori, 2003)(Mori, 2003)

LD-pumped 2.5 to 6 kWNew Development

(Bachmann (Bachmann 2004)2004)

Rod-type:Rod-type: 8 and 10 kW; Laboratory Prototype

Slab-type:Slab-type: 6 kW; Developed by Precision Laser Machining Consortium, PLM

Facts about lasers for Welding: Facts about lasers for Welding: YAG LaserYAG LaserLaser Characteristics, Quality and ApplicationLaser Characteristics, Quality and Application

Disk Laser: Characteristics

Wavelength 1.03 µm; near-infrared ray

Laser Media Yb3+ : YAG or YVO4 (solid)

AveragePower [CW]

6 kW (cascade type max.)

Merits Fiber-delivery, high brightness, high efficiency(10–15%)

Recent DevelopmentRecent Development (Mann 2004; and Morris 2004): CommerciallyCommercially available diskdisk laser system: 11 and 44 kW class Beam deliverydelivery with 150150 and 200 µm

diameter fiberfiber Even a 1 kW1 kW class laser is ableable to produce

a deepdeep keyhole-typekeyhole-type weld bead extremelyextremely narrow width in stainlessstainless steel and aluminumaluminum alloy

Facts about lasers for welding: Facts about lasers for welding: Disk LaserDisk LaserLaser Characteristics, Quality and ApplicationLaser Characteristics, Quality and Application

Fiber Laser: Characteristics

Wavelength 1.07 µm; near-infrared ray

Laser Media

Yb3+ : SiO2 (solid), etc.

AveragePower [CW]

20 kW (fiber-coupling max.)

Merits Fiber-delivery, high brightness, high efficiency(10–25%)

Recent DevelopmentRecent Development (Thomy et.al. 2004; and Ueda 2001): FiberFiber lasers of 10kW10kW or moremore are commerciallycommercially available Fiber lasers of 100kW100kW and moremore are scheduledscheduled FiberFiber laser at 6.9kW6.9kW is able to provide deeply penetrateddeeply penetrated weld at high high speed FiberFiber laser is able to replacereplace high quality (slab) COCO22 laser laser for remoteremote or scanningscanning welding

Facts about lasers for welding: Facts about lasers for welding: Fiber LaserFiber LaserLaser Characteristics, Quality and ApplicationLaser Characteristics, Quality and Application

Correlation of Correlation of Beam Quality Quality to Laser Power Power (Katayama 2001; O’Neil et. al. 2004; Shiner 2004; Lossen 2003): OverlaidOverlaid with conditioncondition regimes Beam qualityquality of a laser worsensworsens with an increaseincrease in powerpower LD-pumpedLD-pumped YAG, thin diskdisk, COCO22 and fiberfiber lasers can provide high-qualityhigh-quality beams The development of higherhigher power COCO22 or YAG lasers is fairlyfairly static and, hence Main focus focus on development:development:

i. high-powerhigh-power diode, ii. LD-pumped LD-pumped YAG, iii. diskdisk and/or iv. fiberfiber lasers

Facts about lasers for weldingFacts about lasers for weldingComparison of different laser systemsComparison of different laser systems

Expanded portion of the electromagnetic spectrum showing the wavelengths at which several important lasers operate

CO2 Laser

Facts about lasers for weldingFacts about lasers for weldingWavelengths of some important laser sources for materials processingWavelengths of some important laser sources for materials processing

Laser beam welding: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

Why do we need laser for welding?Why do we need laser for welding?

Traditional 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

Lasers Beam WeldingLasers Beam Welding::Types of LBWTypes of LBW

Conduction WeldingConduction Welding

DescriptionDescription Heating the workpiece above the melting temperature without vaporizing Heat is transferred into the material by thermal conduction.

CharacteristicsCharacteristics Low welding depth Small aspect ratio (depth to width ratio is around unity) Low coupling efficiency Very smooth, highly aesthetic weld bead

ApplicationsApplicationsLaser welding of thin work pieces like foils, wires, thin tubes, enclosures, etc.

Lasers Beam WeldingLasers Beam Welding::Types of LBWTypes of LBW

Keyhole WeldingKeyhole Welding

DescriptionDescription 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

CharacteristicsCharacteristics High welding depth High aspect ratio (depth to width

ratio can be 10:1) High coupling efficiency

LaserLaser

Beam Delivery UnitBeam Delivery Unit

Workpiece Positioning UnitWorkpiece Positioning Unit

Processing Processing OpticsOptics

Schematic Schematic DiagramDiagram

Beam Beam Delivery Delivery unitunit

Lasers Beam WeldingLasers Beam Welding::Laser welding unitLaser welding unit

Lasers Beam WeldingLasers Beam Welding::photographic view of laser welding unit photographic view of laser welding unit

Specimen

Laser Head

Shielding Gas Nozzle

Specimen Holder

Lasers Beam Welding:Lasers Beam Welding: Fuel Injector PerspectiveFuel Injector PerspectiveXL2 injector: VB-VS Welding Configuration and Power Profile XL2 injector: VB-VS Welding Configuration and Power Profile

Power profile vs angle

0

200

400

600

800

1000

0 100 200 300 400 500 600 700 800 900 1000

Angle [°]

Po

wer

[W

]

0

0,5

1

1,5

2

2,5

3

3,5

power

Turn

Post heating to remove micro cracks from joint surface

Joint overlap at full power to ensure hermetic enclosure of joint

Segment 1 2 3 4 5 6 7Time [ms] 0 20 200 20 200 50 0Power [W] 0 870 870 200 200 0 0

Valve Body-Valve Seat Valve Body-Valve Seat Welding ConfigurationWelding Configuration

LASER BEAM WELDING OF MARTENSITIC LASER BEAM WELDING OF MARTENSITIC STAINLESS STEELS IN A CONSTRAINED STAINLESS STEELS IN A CONSTRAINED

OVERLAP JOINT CONFIGURATIONOVERLAP JOINT CONFIGURATION

A A Case StudyCase Study

Experimental Procedure and ConditionsExperimental Procedure and Conditions

Experimental DesignExperimental Design

Process Factors

Symbols

Levels of Each Factor

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

Base material Outer Shell Inner Shell

AISI 416AISI 440 FSe

Laser source Nd:YAG Laser

Angle of Incidence (deg)

900 (onto the surface)

Shielding gas Type Flow rate

Argon29 l/min

Response Factors

Weld bead characteristics

Weld Zone (WZ) Width (W), Weld Resistance Length (S), and Weld Penetration Depth (P)

Mechanical properties

Weld Shearing Force (F)

Design matrix with actual Independent process variablesDesign matrix with actual Independent process variables

Std Order

Run Order

Actual levels

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 Measured ResponsesExperimental Measured Responses

Std Order

Response Values

Weld Width, W (µm)

Penetration Depth, P

(µm)

ResistanceWidth, 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:Experimental Procedure and Conditions: Mechanical Characterization: Weld X-SectionMechanical Characterization: Weld X-Section

Characterization of welding cross-section (W: Weld width, Characterization of welding cross-section (W: Weld width, P: Weld penetration depth, S: Weld resistance length)P: Weld penetration depth, S: Weld resistance length)

Photographic views of the experimental set-up for shearing testPhotographic views of the experimental set-up for shearing test

Experimental Procedure and Conditions:Experimental Procedure and Conditions:Mechanical Characterization: Shearing TestMechanical Characterization: Shearing Test

(b)

Specimen

Specimen Holder

Expeller

Punch

Results and Discussion:Results and Discussion:Weld profile AspectWeld profile Aspect

Curvature of the keyhole profile is Curvature of the keyhole profile is closely related to welding speed. closely related to welding speed.

The higher the welding speed The higher the welding speed the larger the curvature of the the larger the curvature of the keyhole.keyhole.

Keyhole is nearly cone-shaped Keyhole is nearly cone-shaped Its vertex angle decreases as Its vertex angle decreases as the keyhole depth increases the keyhole depth increases

Shape of the keyhole Shape of the keyhole changes from conical to changes from conical to cylindricalcylindrical

Results and Discussion:Results and Discussion:Effects of Individual Process ParametersEffects of Individual Process Parameters

AA: laser power BB: welding speed CC: fiber diameter

Results and Discussion:Results and Discussion:Interaction Effects of Process Parameters on Weld WidthInteraction Effects of Process Parameters on Weld Width

Results and Discussion:Results and Discussion:Interaction Effects of Process Parameters on Penetration DepthInteraction Effects of Process Parameters on Penetration Depth

Energy density is frequently used as process Energy density is frequently used as process parameter in energetic term:parameter in energetic term:

spot

WSLP

ED

LP : laser power describing the thermal source, WS : welding speed determining the interaction timeφSpot : focal spot diameter defining the area through which

energy flows into the material

Results and Discussion:Results and Discussion:Interaction Effects of Process Parameters on Penetration DepthInteraction Effects of Process Parameters on Penetration Depth

Results and Discussion:Results and Discussion:Interaction Effects of Process Parameters on Resistance Interaction Effects of Process Parameters on Resistance LengthLength

Results and Discussion:Results and Discussion:Interaction Effects of Process Parameters on Resistance Interaction Effects of Process Parameters on Resistance LengthLength

Results and Discussion:Results and Discussion:Interaction Effects of Process Parameters on Shearing ForceInteraction Effects of Process Parameters on Shearing Force

Results and Discussion:Results and Discussion:Interaction Effects of Process Parameters on Shearing ForceInteraction Effects of Process Parameters on Shearing Force

Results and Discussion:Results and Discussion:Interaction Effects of Process Parameters on Shearing ForceInteraction Effects of Process Parameters on Shearing Force

Results and Discussion:Results and Discussion:Effects of Shielding Gas on Penetration DepthEffects of Shielding Gas on Penetration Depth

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