Laser beam power of only 1 kW is sufficient to produce welding seams, for which serveral kilowatts have been used up to now. Schweißprozess

Microinvasive Laser Beam Welding

The new welding method combines a FEHA CO2 Laser with its high beam quality (K > 0,8) and a scanner system which due to the properties of its optical components and to its compact design, enables a thermally stable transmission of beam power up to 2 kW.

Scanner

The method is characterized by following features:

  • Maximum beam focussing results in a tiny penetration hole (microinvasive)
  • Due to the high beam radiation intensity the keyhole is much deeper than wide (significant deep welding effect)
  • Necessary seam width is generated by focus movement (only low beam power has to be handled)
  • The "distributed" plasma remains "non-critical" (low radiation losses, simple safety measures, low thermal load to the welding chamber, welding without shielding gas is possible)
  • Due to the narrow vapor channel the shower of sparks is like a reverse jet out of the keyhole which can easily be bended by cross jet air (no sputter on the welded parts, reduced soiling of the equipment)

For processing of small specimen (250 x 250 mm²) the welding method needs no moving components. Therefore the beam path between the laser and the focussing optics is fixed and is within a solid capsule. This gains the advantage of low adjustment and maintenance efforts.

Microinvasive Laser Beam Welding results in a fine bead surface and nearly parallel bead flanks also in the case of non-through-going widened beads.
 
Beispiel Schweißnaht Beispiel Schliff
 

The quick beam movement enables a more efficient absorption of the beam power resulting in an increased cross section of the weld bead. The following welds have been done on a 1 mm thick mild steel with the same spot diameter and the same energy of 80 J/mm.

 
Schliffbild Schliffbild
linearly moving beam oscillating beam
 

Besides the quick oscillating movement of the focussed beam, the scanner device also enables the weld to be divided into separate weld segments, and the sequence of welding the segments can arbitrarily be chosen.

 
Thermography plots from Microinvasive Laser Beam Welding.
 
Thermografieaufnahme des Blechs Thermografieaufnahme des Blechs Thermografieaufnahme des Blechs
continuous welding 4 segments 8 segments

By a proper choice of the number of segments as well as of the welding sequence the distortion can be reduced by up to 80%.

R&D work on this subject has been financially supported by the Bundesministerium für Bildung und Forschung under contract number 02PD1053.

A collection of lecture slices concerning laser beam welding with FEHA laser can be downloaded (only in German language).