---
type: process
name: "Power Beam Welding"
category: "Joining"
subcategory: "Thermal"
materials: ["Metal"]
tolerances: "Beam-to-seam alignment ±0.004 in (±0.1 mm); joint gap ≤ 0.004 in (0.1 mm) for autogenous welds; post-weld distortion roughly an order of magnitude below an equivalent arc weld"
volumes: "100 to 1,000,000+ per year"
lead_time: "Seconds of weld time per joint; 2–8 weeks for precision fixtures and schedule development; EBW adds minutes of chamber pump-down per load"
url: https://manufacturingprocesses.org/processes/joining/power-beam-welding
---

# Power Beam Welding

Power beam welding fuses metal with a laser or electron beam focused to a very small spot, producing deep, narrow welds with little distortion.

- **Category**: [Joining](https://manufacturingprocesses.org/processes/joining.md)
- **Family**: Thermal
- **Materials**: Metal
- **Typical tolerances**: Beam-to-seam alignment ±0.004 in (±0.1 mm); joint gap ≤ 0.004 in (0.1 mm) for autogenous welds; post-weld distortion roughly an order of magnitude below an equivalent arc weld
- **Typical volumes**: 100 to 1,000,000+ per year
- **Lead time**: Seconds of weld time per joint; 2–8 weeks for precision fixtures and schedule development; EBW adds minutes of chamber pump-down per load

## Overview

Power beam welding fuses metal with a laser or electron beam focused to a spot a few thousandths of an inch across. Power density reaches roughly 10⁶ W/cm² — about a hundred times an arc — vaporizing a narrow capillary (a keyhole) through the joint rather than melting a shallow puddle on top of it.

The result is the defining number: depth-to-width ratios of 10:1 for laser and up to 50:1 for electron beam, against roughly 1:1 for arc welding. Because so little metal melts, the heat-affected zone is typically 0.010–0.040 in (0.25–1 mm) wide and distortion is an order of magnitude below an equivalent arc weld — which is why the process is used on finish-machined assemblies.

Two variants: laser beam welding (LBW) with 1–20 kW fiber or disk lasers in air, and electron beam welding (EBW) at 30–200 kV inside a vacuum chamber, capable of single-pass penetration up to about 6 in (150 mm) in steel. Both are autogenous by default, which puts the burden squarely on joint fit-up.

## How it works

1. **Fit-up and fixturing.** Autogenous beam welding adds no metal, so any gap is a missing volume. Butt joints need the faying surfaces closed to under 0.004 in (0.1 mm), or roughly 10% of thickness, whichever is smaller. Parts are machined, not sheared, and held in rigid fixtures.
2. **Beam delivery.** LBW: a 1,064 nm fiber or disk laser routed to a focusing head and focused to a 0.008–0.024 in (0.2–0.6 mm) spot. EBW: electrons accelerated at 30–200 kV in a vacuum near 10⁻⁴ mbar, magnetically focused and steerable at kilohertz rates for beam oscillation.
3. **Keyhole formation.** Above roughly 10⁶ W/cm² the surface vaporizes and recoil pressure opens a vapor capillary that the beam penetrates. Molten metal flows around the keyhole and closes behind it as the beam travels.
4. **Travel.** Laser welds run at 20–400 in/min (0.5–10 m/min). A useful rule for steel is about 1 mm of penetration per kW at 1 m/min, so a 6 kW fiber laser gives roughly 0.25 in (6 mm) at that speed.
5. **Solidification.** Cooling rates are extreme, which refines weld metal but also hardens the HAZ of medium-carbon and low-alloy steels; those may need preheat or post-weld tempering.
6. **EBW chamber cycle.** Pump-down between loads is the throughput limit for electron beam work — minutes per load on production chambers — and the process generates X-rays, so the chamber is also a radiation shield.

### Laser versus electron beam

**Laser beam welding** works in air with an inert shield gas, needs no chamber, and can be delivered on a robot arm or a remote scanner head. It struggles with highly reflective metals at 1 µm wavelength — copper especially — and with aluminum alloys that boil off magnesium and go porous.

**Electron beam welding** has no reflectivity problem, and its vacuum is a perfect shield: it is the standard route for titanium, zirconium, niobium and other reactive and refractory metals, and for thick single-pass welds in steel that would take dozens of arc passes. The costs are the chamber, the pump-down cycle, X-ray shielding, and a part size capped by chamber size.

Both processes also run in conduction mode at lower power density, producing a smooth, wide, shallow weld with a cosmetic surface — used for hermetic seals on thin-wall enclosures.

## Design guidelines

### Fit-up is the whole design problem

An autogenous beam weld cannot bridge a gap. Specify butt joint gaps under 0.004 in (0.1 mm) — machined or laser-cut edges, not sheared. If the assembly cannot hold that, add filler wire (which tolerates roughly 0.010 in / 0.25 mm) or use hybrid laser-arc welding, where the arc fills the gap and the laser provides the penetration.

### Beam-to-seam alignment

The weld is only 0.02–0.06 in (0.5–1.5 mm) wide, so the beam must find the joint to within about ±0.004 in (±0.1 mm). Either hold that with fixturing and part tolerance or add seam tracking. In practice this drives designs toward self-locating joints — a machined step, spigot or shoulder that both centers the parts and presents a consistent seam.

### Joint geometry and root support

Favor square butt joints, with the beam entering perpendicular to the seam. For circumferential welds on shafts and housings, a machined lip that puts the seam on a cylindrical or flat face lets the part rotate under a stationary head. A keyhole weld that only just penetrates has an unstable root and produces spiking and porosity, so either overshoot into a backing or run-out feature, or deliberately design a partial-penetration weld with margin — and keep the unwelded root notch, which is a stress raiser, out of the load path.

### Materials

| Material | Laser | Electron beam | Notes |
| --- | --- | --- | --- |
| Carbon and low-alloy steel | Good | Excellent | Fast cooling hardens the HAZ above about 0.25% C — preheat or temper |
| Austenitic stainless | Excellent | Excellent | The workhorse combination for hermetic housings |
| Titanium and zirconium | Good with full shielding | Excellent | Vacuum is the ideal shield; oxygen pickup embrittles |
| Nickel superalloys | Good | Excellent | Low heat input limits strain-age cracking |
| Aluminum 5xxx / 6xxx | Fair | Good | Magnesium loss causes porosity; filler wire and beam oscillation help |
| Aluminum 2xxx / 7xxx | Poor | Fair | Hot cracking |
| Copper | Poor at 1 µm | Excellent | High reflectivity and conductivity; green or blue lasers change this |
| Refractory metals (Mo, Nb, Ta, W) | Poor | Good | Vacuum welding only |
| Carbon steel to stainless | Yes | Yes | The tiny fused volume limits dilution — an advantage over arc welding |
| Aluminum to steel | No | No | Brittle intermetallics form regardless of beam source |

Melting and boiling points that set the process window are on the [metal melting points chart](/charts/metal-melting-points); gauge conversions are on the [sheet metal gauge chart](/charts/sheet-metal-gauge-chart).

### Inspection

Visual inspection covers undercut, underfill and surface porosity. Radiography detects the porosity, spiking and root voids that keyhole welds are prone to; ultrasonic testing detects lack of penetration, though the narrow weld geometry makes probe positioning critical. Helium leak testing to 10⁻⁹ std cc/s is standard on hermetic enclosures. Because the welds are so small, destructive cross-sections on setup coupons are how penetration depth is actually qualified before a production run.

| Feature | Recommended | Limit | Why |
| --- | --- | --- | --- |
| Butt joint gap, autogenous | 0.001 in (0.025 mm) | 0.004 in (0.1 mm) or 10% of t | No filler is available to bridge a gap |
| Beam-to-seam alignment | ±0.002 in (±0.05 mm) | ±0.004 in (±0.1 mm) | The weld is only 0.02–0.06 in (0.5–1.5 mm) wide |
| Edge preparation | Machined or laser cut | Not sheared | Sheared edges are neither flat nor square |
| Penetration margin | 20% beyond the joint | Full or clearly partial | Marginal penetration gives root spiking and porosity |
| Joint located by geometry | Machined spigot or step | — | Removes the alignment burden from the fixture |

## Variants

- Laser Beam Welding (LBW)
- Electron Beam Welding (EBW)

## Cost drivers

Beam welding is capital-intensive and consumable-light. There is no filler, no flux, and no shielding gas on EBW; cost sits in the machine, the fixture, and — for electron beam — the chamber cycle. That inverts the usual welding economics: the weld itself is fast and cheap, and everything upstream of it is where the money goes.

Fit-up is the dominant hidden cost. Because the joint has to close to within 0.004 in (0.1 mm), parts often need a machining operation they would not otherwise require, and the fixture has to be a precision tool rather than a weld jig. Throughput on EBW is governed by pump-down, so batch size in the chamber matters more than weld time; laser welding avoids that entirely but pays for its flexibility with seam tracking and a Class 1 safety enclosure.

1. **Machine the joint faces in the same setup** that establishes the mating features, so fit-up comes for free rather than as an added operation.
2. **Design a self-locating joint** — spigot, step or shoulder — and you can often delete seam tracking altogether.
3. **Load EBW chambers with a full fixture plate**; pump-down cost is per cycle, not per weld.
4. **Weld last, after finish machining,** and exploit the low distortion — that is the actual value proposition versus arc welding.
5. **Check whether hybrid laser-arc solves the fit-up problem** more cheaply than tightening part tolerance: the arc bridges gaps the laser cannot.

## FAQ

### How deep can a laser or electron beam weld penetrate in one pass?

A useful rule for laser welding steel is about 1 mm of penetration per kW at 1 m/min travel, so a 6 kW fiber laser gives roughly 0.25 in (6 mm) in a single pass. Electron beam welding in vacuum goes far deeper — up to about 6 in (150 mm) in steel in one pass, with depth-to-width ratios reaching 50:1.

### How tight does fit-up need to be for laser welding?

For an autogenous butt weld with no filler, the gap must stay under about 0.004 in (0.1 mm), or roughly 10% of material thickness, whichever is smaller. Adding filler wire raises that to roughly 0.010 in (0.25 mm). Hybrid laser-arc welding tolerates more still, because the arc supplies metal while the laser supplies penetration.

### Laser or electron beam — which should I choose?

Laser if the parts are large or awkward, volume is high, and the material is steel, stainless or nickel alloy — no chamber means no pump-down and easy robot delivery. Electron beam for reactive and refractory metals, for copper, and for thick single-pass welds, since the vacuum is a perfect shield and there is no reflectivity limit.

### Can you laser weld copper?

Not well with a conventional 1 µm fiber laser — copper reflects most of the beam until it melts, and the process is unstable. Green (515 nm) and blue diode lasers absorb far better and have made copper welding practical for battery and busbar work. Electron beam welding has no reflectivity problem at all.

### How are power beam welds inspected?

Radiography for the porosity, root spiking and voids that keyhole welds produce; ultrasonic testing for lack of penetration; visual for undercut and underfill; and helium leak testing down to 10⁻⁹ std cc/s on hermetic enclosures. Destructive cross-sections on setup coupons are how penetration depth is actually qualified before a run.

## Alternative processes

- [Arc Welding](https://manufacturingprocesses.org/processes/joining/arc-welding.md): Arc welding melts and fuses metal with an electric arc between an electrode and the work, shielded from the atmosphere by gas or flux.
- [Soldering and Brazing](https://manufacturingprocesses.org/processes/joining/soldering-and-brazing.md): Soldering and brazing join metals with a molten filler that wets the joint by capillary action while the parent metal stays solid.
- [Adhesive Bonding](https://manufacturingprocesses.org/processes/joining/adhesive-bonding.md): Adhesive bonding joins parts with a cured polymer layer that spreads load over the whole bond area instead of concentrating it at fastener points.
- [Riveting](https://manufacturingprocesses.org/processes/joining/riveting.md): Riveting sets a rivet through aligned holes and upsets its tail so the joint clamps permanently, with no heat and no access to both sides for blind types.

## Related processes

- [Laser Cutting](https://manufacturingprocesses.org/processes/cutting/laser-cutting.md): Laser cutting melts, burns or vaporises a narrow kerf through flat stock with a focused beam, producing profiles from a 2D file with no tooling.
- [Friction Welding](https://manufacturingprocesses.org/processes/joining/friction-welding.md): Friction welding rubs two parts together under load until the interface plasticises and forges together, with no melting and no filler metal.
- [Resistance Welding](https://manufacturingprocesses.org/processes/joining/resistance-welding.md): Resistance welding passes a heavy current through the joint so its own electrical resistance melts a nugget between the sheets.
- [Heat Treatment](https://manufacturingprocesses.org/processes/forming/heat-treatment.md): Heat treatment cycles metal through controlled heating and cooling to change its hardness, strength, ductility or internal stress state.

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*Source: [Manufacturing Processes](https://manufacturingprocesses.org/processes/joining/power-beam-welding)*

*Last updated: August 11, 2026*