View
220
Download
0
Tags:
Embed Size (px)
Citation preview
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