Laser Welding of Sheet Metal: Process Basics and Application Limits

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  Key takeaways
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  How laser welding of sheet metal actually works
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  Joint types that suit thin-gauge laser welding
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  Parameter windows for common sheet alloys
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  When laser welding of sheet metal is the wrong choice
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  Where it pays off in real assemblies
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  Step by step: from drawing to welded assembly
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  Laser welding versus TIG, spot, and riveting

A fiber laser delivers 1,070 nm light through a focusing optic. Spot diameter at the workpiece is typically 0.1–0.6 mm depending on focal length. That small spot is why heat input stays low and why the heat-affected zone on 1 mm stainless is often under 0.3 mm wide.

Two modes matter in production. Conduction mode keeps power density below roughly 1 MW/cm², melts the surface, and forms a shallow bead. Keyhole mode pushes past that threshold, vaporizes a narrow channel, and gives deep penetration at high speed. Most thin-gauge work runs in conduction mode or at the low end of keyhole mode.

The weld forms because both edges melt and the molten pools bridge. That bridging is the whole problem. If the gap is wider than the pool can span, you get incomplete fusion or a hole. On 1 mm 304 stainless, a butt joint with a 0.1 mm gap welds cleanly; at 0.3 mm the bead sags and cracks form as it cools.

Absorption changes with material and surface condition. Cold-rolled steel absorbs well. Aluminum reflects more at room temperature, then absorbs sharply once the keyhole opens. Copper and brass reflect most of the beam, so they need higher power or a green or blue laser source.

Lap joints are the easiest to automate. The parts self-align, the beam melts through the top sheet into the bottom, and you get a strong tack every few millimeters. A 0.8 mm top sheet on a 1.5 mm base is a common enclosure configuration. The main risk is a gap between the sheets from burrs or a poor bend radius.

Butt joints give the cleanest finished surface and the least distortion, but they demand edge quality. Sheared edges with a burr taller than 0.05 mm cause inconsistent penetration. If the part will be visible after finishing, plan a laser-cut or milled edge and hold the gap under 0.1 mm.

Corner and T-joints appear in brackets and chassis. A fillet weld along a bent corner is fast, but the inside radius of the bend changes the effective thickness. On a 2 mm bend, the beam sees roughly 2.8 mm of material at the corner, so drop speed or raise power to match.

For closed profiles you cannot reach, stitch welding from one side is often enough. A 6 mm stitch every 30 mm gives a sealed, stiff joint on a 1.5 mm panel without the heat of a continuous bead.

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  LapMost forgiving. Use for enclosures, brackets, and stacked panels.
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  ButtBest finish. Needs clean edges and gap under 0.1 mm.
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  Corner / TWatch the bend radius; it adds effective thickness.
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  StitchLess heat, less distortion, still stiff enough for most panels.

Numbers below are starting points for a 1,070 nm fiber laser with a 0.2 mm spot. Every machine and optic differs, so treat them as a window to dial in, not a recipe. Weld speed on 1 mm 304 stainless usually sits between 2 and 4 m/min at 1.5–2.5 kW. Too slow and the keyhole collapses into spatter; too fast and you lose penetration.

Aluminum needs more power for the same thickness because of reflectivity. 1 mm 5052 typically runs 2.5–3.5 kW at 3–5 m/min. The surface oxide melts at about 2,050 °C while the metal beneath melts near 660 °C, so a slightly defocused beam helps break the oxide before the pool forms.

Cold-rolled steel and 4130 are the easiest. 1 mm runs 1.5–2 kW at 3–6 m/min. The weld is narrow and hard, so if the assembly will be formed after welding, anneal or expect cracking at the bead.

Shielding gas matters more than most people expect. Argon or a helium-argon mix at 15–25 L/min suppresses oxidation on stainless and titanium. On plain steel, nitrogen can be used and gives a slightly deeper penetration. No gas at all is acceptable only for non-cosmetic internal tacks.

If the gap cannot be closed, a laser will not bridge it. Gaps above 0.2 mm on 1 mm steel need filler wire, a hybrid process, or TIG. Buying a more powerful laser does not fix a fit-up problem; it just makes the spatter bigger.

Reflective and high-conductivity alloys are difficult at 1 μm. Copper, brass, and thick aluminum reflect most of the beam. A 2 mm copper joint that TIG handles in one pass may need a green-wavelength source or a pre-placed filler to weld reliably.

Thick sections move the economics. Above roughly 6 mm in steel, a laser still works but the speed advantage shrinks and the equipment cost per meter rises. For a one-off 10 mm bracket, TIG is usually cheaper than setting up a laser cell.

High-volume cosmetic panels with visible beads are also a poor fit unless you plan a finishing step. Laser beads on stainless are narrow and slightly undercut at the edges. If the customer wants a wide, uniform cap, TIG or a post-weld dressing step is more predictable.

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  Gap over 0.2 mmUse filler wire, hybrid, or TIG.
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  Copper and brassWrong wavelength; expect poor coupling.
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  Over 6 mm steelSpeed advantage shrinks; TIG may win.
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  Visible wide beadPlan a dressing step or choose TIG.

Electronics enclosures are the classic case. A 1 mm aluminum chassis with a lap-welded seam and laser-cut vents comes out flat, seals against dust, and takes a powder coat without filler showing. The low heat keeps the internal mounting bosses within ±0.005 mm of the machined position.

Automotive and EV brackets benefit from stitch welding. A 1.5 mm 5052 battery tray side wall welded in 6 mm stitches every 30 mm holds stiffness and passes vibration testing without the distortion of a continuous bead.

Medical device housings use laser welding because it is clean and repeatable. A 0.8 mm 316L instrument case can be welded, passivated, and inspected without the surface discoloration that TIG leaves. The narrow HAZ keeps the internal bore round.

Robotics and automation frames use laser welding on gussets and corner joints. On a 2 mm 6061 frame, a laser fillet at the corner is faster than TIG and needs less cleanup before anodizing. Where stiffness is critical, we weld the frame first and then CNC the mounting faces so the geometry is true to the datums.