Process Note

A Brief Discussion on Laser Welding Equipment

This note is for engineers and buyers who weld thin-wall metal parts and want to know where laser welding fits. It covers the main equipment types, what joint fit-up they demand, and when a TIG or e-beam process is the better call.

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Thin-wall metalLow heat inputFiber & YAG sourcesFit-up matters

Scope

What this discussion covers

Laser welding is a heat source, not a finished process. The equipment only works as well as the joint you feed it.

Basics

How a laser weld actually forms

A focused beam raises metal at the joint above melting point in milliseconds. At power densities around 10^6 W/cm² the metal vaporizes, forming a keyhole that traps the beam and lets energy penetrate deeper than the spot size suggests. The keyhole collapses behind the moving beam and the melt solidifies into a narrow weld with a high depth-to-width ratio. Conduction mode, at lower power density, melts the surface without a keyhole and gives a wide, shallow, smooth bead.

That distinction explains most process choices. Keyhole mode welds 1 mm stainless in one pass with little distortion. Conduction mode suits cosmetic seams and thin foils where spatter or undercut would scrap the part. Both run on the same machine; the difference is power density, travel speed, and focus position.

Heat input is the practical number. A fiber laser welding 1 mm 304 at 1.5 kW and 4 m/min puts far less energy into the part than TIG at 60 A, so the heat-affected zone stays narrow and the part holds its flatness. For a 300 mm long seam, that is often the difference between a straight part and one that needs straightening.

1
Keyhole modeDeep penetration, narrow HAZ, needs tight fit-up and shielding gas.
2
Conduction modeShallow, smooth bead; forgiving on gap, good for visible seams.
3
Heat inputLower than arc processes, which limits distortion on thin sections.

Equipment

Equipment types and what each is for

Fiber lasers dominate new installations. A 1–6 kW fiber source delivers a 1,070 nm beam through a flexible armored cable to a compact head, so it can be mounted on a robot, a gantry, or a 5-axis machine. Wall-plug efficiency is high and maintenance is low, since there is no lamp or rod to replace.

Nd:YAG lamp-pumped units still run in older cells. They weld reflective metals and can switch to pulsed output for spot welds, but the optics and flash lamps need regular service. Diode lasers give a wider, more uniform spot, which suits brazing, plastic welding, and conduction-mode seams on thin sheet.

For the joint geometry itself, two hardware choices matter more than source type. A galvanometer scanner moves the beam at high speed to fill a gap or create a wobble pattern, which widens the melt pool without raising average power. A wire feeder adds 0.3–0.8 mm filler to bridge a gap or adjust chemistry. Neither replaces good fit-up, but both buy tolerance.

1
Fiber laserFlexible delivery, low upkeep, the default for 1–6 kW metal welding.
2
Nd:YAGLegacy cells; pulsed mode useful for spot and reflective alloys.
3
Diode laserWide uniform spot; brazing and conduction-mode seams.
4
Scanner + wireBeam wobble and filler wire widen the process window.

Selection

Matching the process to the joint

Use this as a first filter before quoting a weld fixture.

Process	Typical thickness	Gap tolerance	Best fit
Fiber laser, keyhole	0.5–6 mm	Under 10% of thickness	Deep narrow seams, low distortion
Fiber laser, conduction	0.2–2 mm	Up to 0.15 mm	Cosmetic seams, thin sheet
Nd:YAG pulsed	0.1–3 mm	Up to 0.1 mm	Spot welds, reflective alloys
Laser brazing	0.5–3 mm	Up to 0.3 mm	Visible joints, coated steel
TIG	1–12 mm	Up to 0.5 mm	Thick sections, repair work
Electron beam	1–50 mm	Under 5% of thickness	Vacuum parts, deep penetration

Fit-up

Fit-up and gap control decide the result

A fiber laser focused to 0.2 mm will not bridge a 0.3 mm gap in keyhole mode. The beam passes through, the keyhole collapses, and the result is a seam that looks welded but has no penetration. This is the most common failure we see on incoming parts, and it is a fixture problem, not a laser problem.

For butt joints, aim for gap under 10% of material thickness. On 1 mm stainless that means 0.1 mm. Laser-cut edges usually hold this if the cut is clean; sheared edges often do not. If the design cannot hold the gap, switch to conduction mode with a wobble pattern, add filler wire, or change the joint to a lap or flange.

Lap joints are more forgiving. The beam melts through the top sheet into the lower one, so gap only matters where the two sheets meet. A 0.5 mm top sheet on 1 mm lower sheet welds at 1–2 kW and 3 m/min with a 0.1 mm gap. Joint design, not machine settings, is what makes this repeatable.

1
Butt jointGap under 10% of thickness; clean laser-cut edges help.
2
Lap jointMore tolerant; weld through the top sheet into the lower one.
3
Flange or filletUse when the part cannot be held flat for a butt seam.

Materials

Material behavior and the role of filler

Austenitic stainless, 304 and 316L, welds cleanly with argon shielding. 303 contains sulfur for machinability and can crack in the weld; if a part must be 303, use filler wire or expect a hot-crack risk. Aluminum needs higher power because it reflects the beam and conducts heat away fast. 6061 is weldable but loses T6 temper in the HAZ, so do not design a welded 6061 part that must hold full T6 strength without a post-weld aging step.

Titanium and its alloys want a full argon shield, trailing and backing, or the weld picks up oxygen and turns brittle. Inconel welds well but is prone to hot cracking if the joint is restrained. Copper and brass reflect near-infrared light; a blue or green wavelength source helps, but a fiber laser with high peak power and a tight spot still works on thin sections.

Filler wire is not only for filling gaps. 4043 or 5356 on aluminum changes the solidification range and reduces cracking. 308L on 304 keeps the weld chemistry close to the base. ERNiCr-3 on Inconel does the same. The rule is simple: if the base alloy is crack-sensitive or the gap is over 10% of thickness, add filler.

1
304 / 316LClean weld with argon; standard for thin-wall parts.
2
6061-T6Welds, but HAZ loses temper; plan post-weld aging.
3
TitaniumNeeds trailing and backing shield or it embrittles.
4
Copper, brassReflective; high peak power or shorter wavelength helps.

FAQs

Common questions from engineers

Can laser welding replace TIG on a 3 mm stainless part?

Yes, if the joint is a butt or lap with gap under 0.3 mm and the part can be held in a fixture. A 2–3 kW fiber laser will do it in one pass at higher speed and lower heat input than TIG.

No, if the joint is a fillet in a corner with poor access, or if the part needs a wide cap pass for corrosion resistance. TIG is slower but more forgiving and easier to inspect visually.

What shielding gas should we specify?

Argon for stainless, titanium, and most alloys. Helium or a helium-argon mix for aluminum and copper, because the higher ionization energy gives a hotter plasma and better coupling.

Flow rate matters more than mix on thin sheet. Too much flow creates turbulence and porosity; too little lets the weld oxidize. Start around 15–20 L/min through a 10 mm nozzle and adjust from the bead color.

How do we inspect a laser weld without cutting the part?

Visual check for spatter, undercut, and bead uniformity catches most gross errors. For penetration, use a weld seam monitor on the machine or a post-weld ultrasonic or eddy-current check on a sample from the batch.

Destructive testing on a first-article part is still the reference. Cut, mount, polish, and measure penetration and HAZ width. Once the process is locked, in-process monitoring plus a periodic sample is usually enough.

Is laser welding suitable for a 0.3 mm wall tube?

Yes, at low power. A 300–600 W fiber laser in conduction mode, or pulsed Nd:YAG, will weld a 0.3 mm wall without burn-through if the fit-up is tight and the fixture pulls heat away.

The risk is not the laser, it is the gap. A 0.1 mm gap on a 0.3 mm wall is a third of the thickness. If the tube ends are not square, use a lap or sleeve joint instead of a butt.

What post-weld steps are needed after laser welding?

For stainless, a pickling or passivation step removes heat tint and restores corrosion resistance. For aluminum, no tint usually forms under good shielding, but a light brush or blast may be needed before anodizing.

If the part is machined after welding, plan for the HAZ. A 6061-T6 weld loses temper locally, so a post-weld solution treat and age, or a design that keeps the weld outside the load path, avoids a weak spot.

When should we not use laser welding?

When the joint has a gap that cannot be closed, when the part needs a wide cosmetic cap, or when the alloy is highly crack-sensitive without a filler that matches the service environment.

Also when the part is thick. Above roughly 6 mm, keyhole laser welding needs high power and a very tight gap; electron beam or a hybrid laser-arc process is often the better route.