Fibre laser hybrid welding of aluminium alloys for the ... 080220.pdf · • TWI is developing...

Copyright © 2008, TWI LtdWorld Centre for Materials Joining Technology

Fibre laser hybrid welding of aluminium alloysfor the rail sector

Chris Allen1, Pak Chong2,Paul Hilton1 and Yoshitomo Watanabe3

1TWI Ltd, 2Formerly TWI, now Subsea7, 3Nippon Sharyo Ltd


Contents• Interest in alternative welding technologies

from the rail sector

• Fibre lasers• Hybrid laser-MIG welding

• Welds in 3mm thick plate• Joint geometry development• Welds in 3mm thick extrusions• Gap tolerance


Interest in alternative welding technologiesfrom the rail sector

• For use in new type of high speed train body manufacture


Interest from the rail sector• Aluminium alloys (extruded sections and

rolled plates) used in high speed train railcar bodies

Image from 'JAPAN RAILFAN MAGAZINE' Vol.45 No.532 Aug., 2005 p86


Interest from the rail sector• MIG welding has been conventionally used in

past

Extrusion design for MIG welded joint


Interest from the rail sector• In modern designs, joint lengths up to 25m• High heat input of MIG can lead to build up of

distortion over weld length• High heat input also leads to loss of strength

and wide HAZ• Area around joint requires thickening, to

maintain strength, adding weight to rail carriage


Interest from the rail sector• Two alternative welding processes are being

considered– Friction stir welding (FSW)– Hybrid laser-MIG (combination of laser and MIG welding)

• Both have a lower heat input than MIG welding⇒ Lower distortion⇒ Lower degree of strength loss in joints

– Higher minimum strength– Narrower HAZ


Extrusion design for FSW joint

Thicker section in joint region

FSW in the rail sector• FSW still requires that

the joint area be thickened, due to factors including– Resistance to tooling

forces during FSW– Wide HAZ

• Weight saving potentially greater with hybrid laser-MIG welded structure

• Welding speeds higher


Hybrid welding at TWI• TWI is developing hybrid fibre laser-MIG welding for Nippon

Sharyo, a Japanese railcar manufacturer

• Weld procedure development on close fitting butt joints– 3mm thickness rolled plates, extruded plates and hollow section

extrusions– A6N01S-T5 (~AA6063, or Al~0.6Mg~0.6Si)– ER5356 (Al~5Mg) MIG consumable used– Weld profile from cross-sections– Weld quality from radiographic inspection

• Optimum joint geometry trials• Gap tolerance of welding conditions developed


Why Fibre lasers?

• Fibre delivered– Flexible welding

• Multi-kW power• Higher efficiency

– (20~25%)• Diode pumped, solid

state design– Reduced servicing

• Smaller footprint– More portable

• Higher beam quality


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Why Fibre lasers?

• Fibre delivered– Flexible welding

• Multi-kW power• Higher efficiency

– (20~25%)• Diode pumped, solid

state design– Reduced servicing

• Smaller footprint– More portable

• Higher beam quality


Why hybrid welding?• So what is hybrid welding?

LaserMIG


Why hybrid welding?• Benefits include

• Greater penetration• Higher welding speed• Improved fit-up tolerance• Improved weld quality and

profile• Filler metal addition

– control of weld microstructure– control of hot cracking

Laser weld

Hybrid weld

Laser weld Hybrid weld


Hybrid welding set up

Laser beam axis

Air-knife

MIG torch axis

MIG torchWelding head

Jig


Hybrid welds in 3mm plate

• Laser / MIG powers typ. 7.0 / 3.0 kW

• Maximum welding speed for full penetration– 5.0 m/min (d = 0.6mm)

• Grade 1 welds– max. pore size typ. 0.5mm


Optimum extrusion geometry trials• First trials on joints

between rolled plates and extruded plates

• Without joint space– Grade 4 welds– 21 pores in diameter

range 1-2mm• With joint space

– Grade 2 welds– 2 pores in diameter

range 1-2mm– ⇒ Joint space essential– But, notch defect in root

Joint spaceExtrusion #1

Extrusion #2 3mm


Asymmetric joint space Symmetric joint space

• Two further types of ‘self jigging’ joint configurations between extrusions tried with joint spaces

Optimum extrusion geometry trials


• Asymmetric joint space leads to Grade 3 quality welds– 5 pores in diameter

range 1-2mm in 300mm test length

• Notch defects still present in root Asymmetric joint

space

Original joint line



• Symmetric joint space leads to Grade 1 or Grade 2 quality welds– 2 pores in diameter

range 1-2mm• Notch defects no longer

present

• Joint is essentially full penetration butt weld Underlying material machined away

(to facilitate radiographic inspection)

Original joint line



Optimum extrusion geometry

Hybrid weld between two close fitting hollow extruded sections


• High quality welds can also be achieved in thicker materials

• Hybrid weld in Al alloy plate up to 12mm thick• Laser power at

workpiece = 7kW• 0.8 m/min (d = 0.6mm)• PF welding position

(vertical up)• Weld profile acceptable

if cap and root machined

Hybrid welds in thicker materials


Gap tolerance: 3mm plates• Continuously tapering gap joint (0-2mm) bridged to

0.7mm gap before under fill exceeded 0.3mm (customer requirement)

Excess 0.5mm at 0mm gap

Excess 0.3mm at 0.4mm gap

Under fill 0.3mm at 0.7mm gap


Gap tolerance: 3mm extrusions• Greater gap tolerance has been developed, through

further modification of extrusion geometry


Gap tolerance: 3mm extrusions

• Weld beads would be machined down after welding• Customer would now accept welds made across a

1.5mm gap

0.7mm gap 1.0mm gap 1.5mm gap


Conclusions• Fibre lasers proven suitable for hybrid welding• Low distortion, high quality hybrid fibre laser-MIG welds can

be made in 3mm 6xxx aluminium alloys at >5m/min• Design of joint geometry essential for

– low porosity• Fully penetrating welds in to a symmetric joint space

– procedures tolerant to joint fit-up, meeting customer requirements on under fill• gap tolerance to 1.5mm possible, if weld cap can be machined

subsequently• gap tolerance to 0.7mm possible, if weld cap not machined

– self-jigging

Fibre laser hybrid welding of aluminium alloys for the ... 080220.pdf · • TWI is developing...

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