Application of Hybrid Laser Arc Welding in Shipbuilding

Hybrid laser arc welding (HLAW) puts a focused laser beam and a consumable arc wire into a single melt pool. The laser drills the keyhole and provides most of the penetration. The arc adds filler metal, widens the root, and stabilizes the keyhole against the small gap changes a shipyard panel actually has. Neither source alone does this job as well. A laser alone needs a fit-up within roughly 0.1 mm; an arc alone cannot reach 10 mm in one pass without a large groove.

The two heat sources are usually arranged along the travel direction. Laser leading is the common setup for shipbuilding because the keyhole stays ahead of the arc and the arc then bridges the gap left behind it. Arc leading is used when the joint has slightly more gap or when the wire needs more time to wet the root. The spacing between the two spots, typically 2–5 mm, is one of the parameters that decides whether the process runs stable or sputters.

The application hybrid laser arc welding is best known for is longitudinal panel stiffener welding, where a laser-arc head on a gantry welds a stiffener to a plate in one pass from one side. Full penetration of 6–12 mm plate is routine. That removes the plate turning, the back gouging, and the second pass that submerged arc welding needs on the same joint.

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  Laser dutyKeyhole formation and deep penetration
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  Arc dutyFiller addition, gap bridging, root shape
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  Travel speed1.5–3 m/min on 8 mm plate
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  Spot spacing2–5 mm between laser and wire axis

Square butt joints with a zero to 0.5 mm gap are the standard case for 6–10 mm plate. The laser penetrates the full section and the arc fills any slight opening. No bevel is needed, which is where the cost saving comes from. On 12 mm and above, a small V or Y preparation helps the arc reach the root, but the included angle can stay far smaller than the 60° a submerged arc groove would need.

T-joints and corner joints are welded from one side with the stiffener standing vertically. The laser fires down the joint line and the arc runs behind it. This is the configuration most shipyards convert first because it removes the need to turn a 12 m panel over. Gap tolerance at the stiffener foot is the tightest variable in the whole setup. If the stiffener is not held down, the gap opens and the keyhole collapses.

Lap joints and fillet welds can be done, but the process loses most of its advantage. There is no deep keyhole to exploit when the load path is through a lap, and the arc has to do more of the work. For those joints a conventional GMAW or FCAW setup is usually the better call.

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  Square butt, 6–10 mmOne pass, no bevel, no backing
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  T-joint at stiffenerSingle-side weld, stiffener clamped down
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  Gap limitRoughly 0.5 mm at 8 mm thickness
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  Lap and filletConventional arc is more economical

Distortion is the reason many yards look at HLAW in the first place. Heat input for a single-pass hybrid weld on 8 mm plate often lands around 0.2–0.4 kJ/mm, against 1.0–2.0 kJ/mm for a submerged arc weld on the same joint. Less heat means a narrower heat-affected zone and less angular pull along the stiffener line.

That does not mean the panel stays flat. The residual stress field still exists, just smaller. Yards usually pair HLAW with clamping fixtures that hold the stiffener in place through the cooling cycle and with a sequence that balances welding on both sides of the panel centerline. On thin plate under 6 mm, the risk shifts from angular distortion to buckling between stiffeners, and a low-heat process helps there as well.

One practical consequence: because the weld is narrow, weld shrinkage is concentrated. If the fit-up sequence lets a gap open while welding, the joint can pull the stiffener out of position rather than distort the plate. Good fixturing matters more with HLAW than with a wide-groove arc process, not less.

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  HLAW heat inputAbout 0.2–0.4 kJ/mm on 8 mm plate
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  SAW heat inputAbout 1.0–2.0 kJ/mm on the same joint
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  Main controlClamping and balanced welding sequence
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  Thin plateWatch buckling, not angular pull

The hard part of HLAW is not the machine. It is the cooling rate. A keyhole weld on 8 mm plate can cool from 1,500 °C to 500 °C in a few seconds, and that is fast enough to form hard, crack-sensitive microstructures in higher-carbon or higher-strength steels. The filler wire does two jobs here: it adds alloying elements to the pool and it slows the cooling slightly by adding mass to the weld.

For standard hull grades such as A, B, D, and E, and for AH36 and DH36, a matching strength GMAW wire works in most qualified procedures. For EH40 and higher-strength grades, or for thick sections, preheating or a slightly higher arc share is usually needed to keep the cooling rate inside a range the procedure allows. The exact numbers come from the yard's welding procedure qualification, not from a table.

Porosity is the other common defect. It comes from the keyhole pulling in air, from damp flux on the plate, or from a gap that is too tight for the vapor to escape. Running the arc slightly behind the laser and keeping the plate dry handles most of it. If porosity appears in a band at regular spacing, look at the wire feed before you touch the laser.

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  Standard gradesA, B, D, E, AH36, DH36
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  Higher strengthPreheat or raise the arc share
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  Common defectPorosity from keyhole or damp plate
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  First checkWire feed stability, not laser power

HLAW is not a general replacement for submerged arc welding. It wins on long, straight, single-pass joints in 6–12 mm plate with tight fit-up. It loses on short, interrupted, or highly curved joints, because the setup and clamping time per meter does not drop with the weld time.

It also loses where the yard cannot hold gap tolerance. A shipyard that fabricates panels on a line with weak stiffener clamping will spend more time fixing porosity and lack of fusion than it saves on passes. The capital cost of the laser head, the optics, and the safety enclosure is high, and the process only pays back at high linear meters per year on a narrow thickness band.

For thick sections above 15 mm, multi-pass arc welding is still the practical answer in most yards. For one-off repairs and small fabrication, GMAW with a bevel is faster to set up. The right question is not whether HLAW is better, but whether the joint at hand is long, straight, thin, and repeatable enough to justify it.

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  Good fitLong straight stiffener lines, 6–12 mm
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  Poor fitShort curved joints, one-off repairs
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  Above 15 mmMulti-pass arc usually wins
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  Payback driverLinear meters per year, not weld speed alone