Multi beam fiber laser welding

Multifiberlaserstrålesvejsning

The PhD project "Multi beam fiber laser welding" is a study of multi laser beam welding with high impact single mode (SM) fiber laser with the purpose of developing optimal welding configurations in industry. To achieve an improved welding quality work has been done on increasing the stability of the melt during laser welding by applying several laser spots to achieve minimum one of the following advantages:

• An increase in the width of the melt pool by applying multiple spots on a line perpendicular to the welding direction. This allows for controlling of the welding widths and depths independent of each other.
• Extension of the melt pool by placing one or several secondary keyholes behind the primary keyhole(s).
• A more stable process in which phenomena like humping beads are avoided, and the process window is extended.

The project is a cooperation between IPU and The Faculty of Engineering and Science at Aalborg University. The PhD candidate is Klaus Schütt Hansen, who has been employed at IPU Technology Development since 2008. Klaus primarily counsels in laser processes and welding technology.

The project supervisors are Senior Engineer Flemming Ove Olsen from IPU and Professor Ole Madsen from Aalborg University. The project is backed by the companies Danfoss and Grundfos, who can see several possible applications of this new technology in their production.

The defense shall take place at Aalborg University in Aalborg on 9 September 2015. The exact time and place will be available on this page sometime after the summer holiday. You are welcome to write to Klaus, who will then send you additional information and invite you to the presentation on 9 September.

THE SUMMARY OF THE DISSERTATION IS REPRINTED BELOW:
This dissertation presents work and results achieved in the field of multi beam fiber laser welding. The project has had a practical approach, in which simulations and modelling have been kept at a minimum. Different methods to produce spot patterns with high power single mode fiber lasers have been examined and evaluated. It is found that both diamond turned DOE’s in zinc sulphide and multilevel etched DOE’s (Diffractive Optical Elements) in fused silica have a good performance. Welding with multiple beams in a butt joint configuration has been tested. Results are presented, showing it has been possible to control the welding width in incremental steps by adding more beams in a row. The laser power was used to independently control the keyhole and consequently the depth of fusion.

An example of inline repair of a laser weld in butt joint configuration was examined. Zinc powder was placed in the weld causing expulsion of the melt pool. Trailing beams were applied to melt additional material and ensure a melt pool. The method showed good results for increasing tolerances to impurities and reduction of scrapped parts from blowouts during laser welding.

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