Laser direct joining of metals and plastics is a promising process for producing hybrid material joints without the need for adhesives, fasteners or additional materials [1,2]. In this process, a metallic component is structured by means of laser radiation in order to increase the surface roughness and to create undercuts. A thermoplastic or thermoplastic composite material is then brought into contact with the metal component and melted in the contact zone. The melt flows into the structures and, after cooling, a stable joint is formed.

The properties of such joints strongly depend on the properties of these structures. So far, two main approaches have been used for the structuring process: By repeated irradiation with continuous laser radiation, linear grooves or grid structures can be introduced at high removal rates [3]. More complex structures with a high aspect ratio can be generated with short and ultra-short pulsed laser radiation [2]. Such structures can lead to higher bond strengths, but due to the limited average power and high cost per watt of those laser systems, the process is usually much slower than with cw beam sources [2].

Some modern, high-power and comparatively inexpensive cw-fiber lasers feature a fast optical modulation capability with modulation frequencies in the range of 100 kHz [4]. These open up new possibilities for temporal control of the laser-material interaction by using pulses in the µs range and temporal pulse shaping at high average powers.

In this work, we investigate the achievable ablation rates, the properties of the generated structures and the resulting bond strengths using a fast modulated cw-fiber laser, comparing the continuous and short pulsed operation with the use of temporal pulse shaping. Furthermore, a machine concept is presented that uses this beam source for both the structuring process and the thermal joining process, providing a particularly compact and highly integrated processing station for the production of metal-polymer composites.

References

[1] A. Klotzbach; M. Langer; R. Pautzsch; J. Standfuß; E. Beyer; Thermal direct joining of metal to fiber reinforced thermoplastic components. J. Laser Appl. 2017, 29, 22421.

[2] K. van der Straeten; C. Engelmann; A. Olowinsky; A. Gillner; Comparison of laser-based joining approaches for plastic-metal-hybrids - Strength vs. process speed. In Proceedings of the 3rd Hybrid Conference, Bremen, Germany, 18–19 April 2018, 2018, pp. 203–309.

[3] C. Engelmann, D. Meier, A. Olowinsky; M. Kielwasser, Metal meets Composite - Hybrid Joining for Automotive Applications, Lasers in Manufacturing Conference 2015, 2015.

[4] D. A. V. Kliner; B. Victor; C. Rivera; G. Fanning; D. Balsley et al.; Next-generation industrial fiber lasers enabled by high-performance components, Proc. SPIE 10513, Components and Packaging for Laser Systems IV, 2018, 105130S.