Thick section laser welding Chris Allen 1
Scope How thick is thick? Possible applications Advantages and challenges of thick section laser welding Traditional thick section laser welding techniques CO 2 laser welding with plasma control Hybrid CO 2 -MIG/MAG welding Newer techniques 1µm laser source welding with plume control Hybrid welding with 1µm laser sources Multi-pass welding Reduced pressure welding Conclusions 2
How Thick is Thick?... t<1mm? 3
How Thick is Thick?... t<1mm? 4
How Thick is Thick?... t<1mm? t<2mm? Courtesy of Fiat 5
How Thick is Thick?... t<1mm? t<2mm? Courtesy of Fiat 6
How Thick is Thick?... t<1mm? t>100mm? t<2mm? Courtesy of Fiat 7
How Thick is Thick?... t<1mm? t<2mm? t>100mm? Courtesy of Fiat 8
Applications www.jcb.co.uk Off-road vehicles Shipbuilding Airframe Railcars Containment vessels Pipelines 9
Advantages and Challenges Advantages Deep penetration Low heat input Low distortion Often single pass Often single-sided Narrow welds Non-contact Vacuum not essential Automated Robotic fibre-delivered lasers Challenges High power systems Investment Running costs Beam safety Process caveats, including Part preparation, positioning and fit-up Weld pool control Plasma or plume control 10
Traditional High Power Laser Welding CO 2 laser sources High powers possible Plasma build-up between keyhole and beam Can attenuate power arriving at workpiece Needs replacement with a gas which is hard to ionise: He Single-sided welding to 12mm Double-sided to 25mm 11
Traditional High Power Laser Welding CO 2 laser sources High powers possible Plasma build-up between keyhole and beam Can attenuate power arriving at workpiece Needs replacement with a gas which is hard to ionise: He Single-sided welding to 12mm Double-sided to 25mm Keyhole Weld pool Parent Weld 12
Traditional High Power Laser Welding CO 2 laser sources High powers possible Plasma build-up between keyhole and beam Can attenuate power arriving at workpiece Needs replacement with a gas which is hard to ionise: He Single-sided welding to 12mm Double-sided to 25mm Keyhole Weld pool Parent Weld 13
Traditional High Power Laser Welding CO 2 laser sources High powers possible Plasma build-up between keyhole and beam Can attenuate power arriving at workpiece Needs replacement with a gas which is hard to ionise: He Single-sided welding to 12mm Double-sided to 25mm Keyhole Weld pool Parent Weld 14
Traditional High Power Laser Welding CO 2 laser sources High powers possible Plasma build-up between keyhole and beam Can attenuate power arriving at workpiece Needs replacement with a gas which is hard to ionise: He Single-sided welding to 12mm Double-sided to 25mm Keyhole Weld pool Parent Weld 15
Hybrid Laser-Arc Welding Advantages over laser welding Filler metal addition Improved fit-up tolerance Improved weld quality and profile Control of weld microstructure Control of hot cracking Advantages over arc welding Higher speed Deeper penetration Higher productivity Lower distortion Lower rework Lower per part manufacturing costs 16
Hybrid Welding for Shipbuilding Hybrid CO 2 -MIG/MAG welding used in ship panel fabrication Image courtesy FORCE Institute 17
Hybrid Welding for Shipbuilding Hybrid CO 2 -MIG/MAG welding used in ship panel fabrication 4mm butt weld 4mm sub-arc weld to same scale Image courtesy FORCE Institute 18
Hybrid Welding for Shipbuilding Hybrid CO 2 -MIG/MAG welding used in ship panel fabrication 4mm butt weld 4mm sub-arc weld to same scale 6 to 8mm T weld Image courtesy FORCE Institute 19
Hybrid Welding for Shipbuilding Hybrid CO 2 -MIG/MAG welding used in ship panel fabrication 1000.0 Local stress range, MPa 4mm butt weld 100.0 8mm plate with 0.5mm gap 8mm BAE butt welds Class D mean curve Class D design curve Class E mean curve 6 to 8mm T weld 4mm sub-arc weld to same scale Class E design curve 10.0 Image courtesy FORCE 1.00E+04 Institute 1.00E+05 1.00E+06 1.00E+07 Number of cycles, N 20
Thick Section Welding with 1µm Sources A range of engineering alloys can be welded to high quality Optimisation of parameters (power, focused spot size, welding speed etc) essential PPAW weld, 5mm IN718 Materials exhibit a maximum thickness beyond which a given welding approach will no longer produce acceptable quality welds 21
Thick Section Welding with 1µm Sources A range of engineering alloys can be welded to high quality Optimisation of parameters (power, focused spot size, welding speed etc) essential PPAW weld, 5mm IN718 Laser weld Materials exhibit a maximum thickness beyond which a given welding approach will no longer produce acceptable quality welds 22
Thick Section Welding with 1µm Sources A range of engineering alloys can be welded to high quality Optimisation of parameters (power, focused spot size, welding speed etc) essential PPAW weld, 5mm IN718 9 Laser weld Cum. por. in 76mm 8 7 6 5 4 3 2 1 B A 0 10W3 10W4 10W5 10W7 10W8 10W9 10W10 Materials exhibit a maximum thickness beyond which a given welding approach will no longer produce acceptable quality welds 23
Thick Section Welding with 1µm Sources A range of engineering alloys can be welded to high quality Optimisation of parameters (power, focused spot size, welding speed etc) essential PPAW weld, 5mm IN718 Laser weld Cum. por. in 76mm 9 Weld, 21ºC 8 7 6 5 4 3 2 1 0 Parent, 750ºC Weld, 750ºC Parent, 550ºC Parent, 21ºC B A 10W3 10W4 10W5 10W7 10W8 10W9 10W10 Materials exhibit a maximum thickness beyond which a given welding approach will no longer produce acceptable quality welds 24
Thick Section Welding with 1µm Sources A range of engineering alloys can be welded to high quality Optimisation of parameters (power, focused spot size, welding speed etc) essential PPAW weld, 5mm IN718 Laser weld Cum. por. in 76mm 9 Weld, 21ºC 8 7 6 5 4 3 2 1 0 Parent, 750ºC Weld, 750ºC Parent, 550ºC Parent, 21ºC B A 10W3 10W4 10W5 10W7 10W8 10W9 10W10 Materials exhibit a maximum thickness beyond which a given welding approach will no longer produce acceptable quality welds 25
Thick Section Welding with 1µm Sources A range of engineering alloys can be welded to high quality Optimisation of parameters (power, focused spot size, welding speed etc) essential PPAW weld, 5mm IN718 Laser weld Cum. por. in 76mm 9 Weld, 21ºC 8 7 6 5 4 3 2 1 0 Weld, 21ºC Parent, 21ºC Weld, 750ºC Parent, 550ºC Parent, Parent, 750ºC 550ºC B A 10W3 10W4 10W5 10W7 10W8 10W9 10W10 Weld, 550ºC Materials exhibit a maximum thickness beyond which a given welding approach will no longer produce acceptable quality welds 26
Thick Section Welding with 1µm Sources A range of engineering alloys can be welded to high quality Optimisation of parameters (power, focused spot size, welding speed etc) essential PPAW weld, 5mm IN718 Laser weld Cum. por. in 76mm 9 Weld, 21ºC 8 7 6 5 4 3 2 1 0 Weld, 21ºC Parent, 21ºC Weld, 750ºC Parent, 550ºC Parent, Parent, 750ºC 550ºC B A 10W3 10W4 10W5 10W7 10W8 10W9 10W10 Weld, 550ºC Materials exhibit a maximum thickness beyond which a given welding approach will no longer produce acceptable quality welds 27
Thick Section Welding with 1µm Sources Plume dispersion (e.g. using a high mass flow gas jet) can then be required for process/keyhole stability and weld quality 28
Thick Section Welding with 1µm Sources Plume dispersion (e.g. using a high mass flow gas jet) can then be required for process/keyhole stability and weld quality 29
Thick Section Welding with 1µm Sources Plume dispersion (e.g. using a high mass flow gas jet) can then be required for process/keyhole stability and weld quality 30
Thick Section Welding with 1µm Sources Plume dispersion (e.g. using a high mass flow gas jet) can then be required for process/keyhole stability and weld quality nt in Pores in 76mm weld length 80 60 40 20 0 0l/min 10l/min 15l/min 18l/min 20l/min jw3 jw21 jw22 jw24 jw25 jw26 jw27 jw28 jw14 jw16 jw17 jw20 jw15 31
Thick Section Welding with 1µm Sources Thick section stake welds made through dissimilar steels, using plume dispersion 3mm 6mm 4mm 3mm 32
Hybrid Welding with 1µm Sources Hybrid welding also possible using high power fibre-delivered fibre and disc laser beams High speed, low distortion hybrid fibre laser-mig butt welds in Al box sections 33
Hybrid Welding with 1µm Sources Hybrid welding also possible using high power fibre-delivered fibre and disc laser beams High speed, low distortion hybrid fibre Vertical-up laser-mig butt welds hybrid welding in Al box sections of thick Al alloy plate 34
Hybrid Welding with 1µm Sources Hybrid welding also possible using high power fibre-delivered fibre and disc laser beams Butt weld, thick section TWB Butt weld, 8mm S355 steel Butt weld, 6mm 304L High speed, low distortion hybrid fibre Vertical-up laser-mig butt welds hybrid welding in Al box sections of thick Al alloy plate Root weld in steel pipe 35
Multi-pass welding Suitable for materials typ. >25mm in thickness TWI has completed butt joints in materials up to 60mm in thickness Joint completion strategy can comprise Double sided root weld Using keyhole welding Subsequent fill and cap sequence Using conduction-limited beam melting of a wire feed, in to a narrow groove preparation 36
Multi-pass welding Suitable for materials typ. >25mm in thickness TWI has completed butt joints in materials up to 60mm in thickness Joint completion strategy can comprise Double sided root weld Using keyhole welding Subsequent fill and cap sequence Using conduction-limited beam melting of a wire feed, in to a narrow groove preparation 37
Multi-pass welding Suitable for materials typ. >25mm in thickness TWI has completed butt joints in materials up to 60mm in thickness Joint completion strategy can comprise Double sided root weld Using keyhole welding Subsequent fill and cap sequence Using conduction-limited beam melting of a wire feed, in to a narrow groove preparation 38
Multi-pass root welding Single or double-sided root welding possible, depending on access Overall root face thickness needed depends on parameters used e.g. laser power 8mm single-sided root 13mm single-sided root 39
Multi-pass root welding Single or double-sided root welding possible, depending on access Overall root face thickness needed depends on parameters used e.g. laser power 8mm single-sided root 13mm single-sided weld 13mm single-sided 20mm root doublesided weld 40
Multi-pass fill welding Conduction-limited melting of wire in to groove using defocused beam Power, speed and wire feed rate optimised for high quality fills Two examples using 5kW laser shown Method can complete joints in 60mm thickness material Transfer of method to other materials possible 41
Multi-pass fill welding Conduction-limited melting of wire in to groove using defocused beam Power, speed and wire feed rate optimised for high quality fills Two examples using 5kW laser shown Method can complete joints in 60mm thickness material Transfer of method to other materials possible 42
Multi-pass weld qualities and properties Following process development Quality Welds free of cracks, pores and lack of fusion Positive cap and root profiles Properties Welds strength over-matched (in steels) Rp(0.2%) ~400MPa, UTS ~560MPa, ε ~23% (for S355 steel) Without preheat Root welds can be unacceptably hard (dep. on codes), 400HV10 Parts of welded joint can be unacceptably brittle, CVN 22J at -20 C 43
Multi-pass weld economics Based on coupon trials, when compared with arc welding Joint completion comparable with or faster Uses less gas shielding and filler wire Five-fold running cost savings estimated possible Energy usage not excessive Laser wall-plug efficiency improving Beam on times short, given joint completion rate Joint completion still faster with EB But EB requires a vacuum! 140 120 100 80 60 40 20 0 Fill welding time, min, for 1m long butt in 40mm plate 44
Reduced pressure welding Atmospheric pressure welding 10µm source = plasma 1µm source = plume Both can attenuate beam If attenuation varies during welding, process can be unstable Welding in vacuum Boiling point significantly supressed Plasma: temperature and density reduces Plume: beam attenuation also measurably reduces Katayama S, Mizutani M and Kawahito Y: Trans JWRI, 40, 2011, No. 1. 45
Reduced pressure welding These changes can also occur at reduced pressure TWI has been applying its sliding seal technology developed for reduced pressure EBW to LBW Penetration depth, mm 25 20 15 10 5 0 0 0.2 0.4 0.6 0.8 1 1.2 Welding speed, m/min He, 50mbar, 10mm hole He, 50mbar, 5mm hole He, 35mbar, 5mm hole Ar, 50mbar, 10mm hole Ar, 35mbar, 10mm hole Shielded, 1bar With plume control, 1bar 46
Reduced pressure welding Reduced pressure welding recently demonstrated using a small-sized, robot-manoeuvrable, sliding seal chamber Laser beam focusing optics Cover slide holder and drawer First port for inert gas for cover slide protection Mounting for robot Port for connection of dial gauge (not shown) Coaxial gas-filled tube Observation window Second port (manifold) for inert gas for cover slide protection Seal Port for connection of vacuum pump (not shown) Atmospheric pressure Brush Reduced pressure 47
Conclusions Thick section laser welding relevant to land, sea and air transport applications, and vessels and pipelines Advantages include single pass deep penetration welds, introducing little distortion Traditionally done by high power CO 2 lasers, often requiring plasma control Process hybridised with arc welding, e.g. for fit-up tolerance High power disc and fibre lasers now have the same or better capabilities, albeit plume control can still be needed New processes also being developed, including multi-pass and reduced pressure welding 48
Contact Chris Allen Principal Project Leader Laser and Sheet Processes TWI Ltd Tel: +44 (0)1223 899 000 E-mail: chris.allen@twi.co.uk Web: www.twi-global.com 49