WELDSHAPE - Laser welding of hard to weld aluminium alloys

Aim: To develop machine build-up of new coherent beam combining (CBC) technology and experiments of aluminium welding with new beam shaping possibilities.

Challenges: In conventional laser welding processes, high-power fiber-laser sources are commonly used as light sources along with a heavy laser welding head that restricts the process speed, and hence the productivity. An obvious gap between physically possible and technologically realizable welding speeds (in conventional process various factors restrict process speed) led to the development of the remote laser material processing as efficient technology, where a longer focal length than conventional related process is used. This enables a very high possible welding speed and beam shaping possibility (wobbling). However, the wobbling frequency of a scanner (additional oscillating movement while welding) is limited to some kHz due to the mirror's inertia, while only a limited beam shape variability (2-in-1 fiber technology) is offered. In order to use a longer focal length, the laser source must be of high brightness (e.g. single-mode). Due to the longer working distance, small changes of the position of a mirror or an optics manipulator can cause fast and large deflections of the laser beam focus on the workpiece. High-power single-mode laser sources, which can provide small focus spots at a long working distance, are used to reach the threshold intensities to start and keep running the processes. Present single mode systems are limited to ~2 kW and a higher laser power requires a bigger transportation fiber diameter, which results in a bigger beam size and a lower possible intensity distribution of the laser beam. Furthermore, “hard-to-weld” aluminum alloys typically present hot crack susceptibility and pore formation.

Benefits: CIVAN's high-power, Coherent Beam Combined (CBC) laser technology has very unique inherent capabilities such as digital, dynamic controls including, varying beam spot size, shape and beam parameter product, modulating laser power and fast beam steering at MHz speed. To weld “hard-to-weld” aluminum alloys, one can implement wobbling at very high frequency and pre-heating by a superimposed beam shape, which can be both realized with the CBC technology. These superimposed different single mode beams in the far field enable significantly higher laser power and the opportunity of variable superimposed intensity distributions, e.g. multi spot forms.

Activities & Present achievements: The experiment will lead to an innovative remote-welding machine, that operates using Civan's special single-mode fiber laser including the integration of a scanner. BBW will integrate this system into its laser welding machine. The dynamic beam would also enable mid-process control of the laser output, different parameters will be tested: beam steering, shaping and focusing at MHz speed, power modulation at 5KHz speed, fully-digital, real-time control over beam shape and position, remote operation, depth of focus, obliteration of post processing operation.

Current Status: The design of the welding machine is completed. This includes the optical design interface, optical beam delivery, gantry system, cooling system and collimator and scanning unit. Initial trials show the scanner can be used for 2 minutes if there is sufficient cooling air-flow and recovery time between laser-on periods. Next phase of development will see an improved cooling system. The optical beam delivery system has also been tested successfully. The next steps include build-up of the machine and first tests with the new CBC technology at BBW facilities.

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