Laser welding head

01

Set the spot size from fibre core and focal lengths

TWI explains that welding optics focus a raw beam tens of millimetres across to a spot well under a millimetre, and that keyhole welding of steel needs power densities above 10⁶ W/cm², which it says "are usually achieved with focused spot sizes between 0.2 and 0.6mm diameter". It defines the f-number as focal length divided by raw beam diameter: a smaller f-number gives a smaller spot but a shorter depth of focus, so the choice is a compromise. [1]

Laser Focus World reported a fibre-laser welding set-up with a 125 mm collimator and a 250 mm focusing lens; with a 200 µm core fibre it produced a spot of about 400 µm, sufficient for high-power welding. [2] Hans Laser lists a swing (wobble) welding head rated up to 3 kW with 100 mm collimation and 200, 250 or 300 mm focus, and a coaxial wire-feed head rated up to 8 kW with 100 mm collimation and 300 mm focus for 0.6–1.6 mm wire. [3] [4]

Editorial calculation: the reported optics imaged the 200 µm core at the ratio of focal lengths, 250 / 125 = 2, giving about 400 µm. By the same ratio, a 100 µm fibre with 100 mm collimation and 200 mm focusing gives about 200 µm. At 2 kW on a 0.2 mm spot, power density is 2,000 W / (π × 0.01² cm²) ≈ 6.4 × 10⁶ W/cm², above TWI's keyhole threshold. Fibre size, focal lengths and power are assumed examples; real spots also depend on beam quality.

Give the supplier the laser (wavelength, maximum power, fibre core and connector), joint and material, required spot or seam width, focal length and working distance, wobble or scanning needs, wire feed if any, robot or machine mounting, cooling water, shielding and cross-jet gas, monitoring (cover-glass, seam tracking) and protection class.

02

Protect the optics with cover glass and cross-jet

The same report describes how a fibre laser started above the specimen without a power ramp welded with a loud bang, and how the first tests with a 200 mm focal length easily destroyed a cover glass because of the start explosion and a very large plasma plume beneath the cross-jet; at SLV Rostock a 250 mm focal length gave longer optics life. [2]

Editorial note: ask the supplier for the cover-glass type, how it is changed, whether its contamination is monitored, the cross-jet air flow and pressure, and how the head's focal length and power ramp are chosen to protect the optics in your process.

03

Compare what suppliers offer

Suppliers linked to this page list laser welding heads or their scanning optics; each card links to the page reviewed.

Listings include laser welding heads with laser cutting heads and welding machines, wobble and galvanometer welding heads with F-theta lenses and beam expanders, and galvanometer scan heads with dynamic focusing modules. Ask each for focal lengths, rated power, fibre connector, wobble pattern and protective features.

04

Trace the head components

This is a functional reference built from the sources cited; it is not one maker's specification.

05

Fill the specification fields with values for your process

A laser welding head quotation needs values for your process. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

06

Send the laser, joint and robot data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Laser: [wavelength; power; fibre core; connector]
Joint: [material; thickness; seam type]
Spot: [size; focal length; working distance]
Motion: [wobble or scanner; pattern]
Wire: [diameter; feed]
Protection: [cover glass; cross-jet; monitoring]
Mounting: [robot; payload; cooling]

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