Laser surface structuring for metal-polymer hybrid connections using fast modulated cw-laser radiation
- 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 part is structured by laser radiation 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 high aspect ratios 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 ofLaser 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 part is structured by laser radiation 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 high aspect ratios 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]. Modern high-power and comparatively inexpensive cw-fiber lasers feature fast optical modulation capability with modulation frequencies in the range of up to 100 kHz [4], enabling increased temporal control of the laser-material interaction by using pulses in the μs range and temporal pulse shaping. As shown in Fig. 1, surface structuring using fast modulated laser radiation was found to lead to increased melt expulsion and therefore higher removal rates compared to remote ablation cutting with continuous wave laser radiation at the same average and peak power levels. Therefore, shorter processing times and in some cases a single irradiation can be sufficient to achieve the desired structuring depth. In addition, the lower overall heat input reduces distortion in thin-walled specimens.
References
[1] A. Klotzbach; M. Langer; R. Pautzsch; J. Standfuß; E. Beyer; Thermal direct joining of metal to fiber reinforcedthermoplastic components. J. Laser Appl. 2017, 29, 22421.
[2] K. van der Straeten; C. Engelmann; A. Olowinsky; A. Gillner; Comparison of laser-based joining approaches forplastic-metal-hybrids - Strength vs. process speed. In Proceedings of the 3rd Hybrid Conference, Bremen,Germany, 2018, pp. 203–309.
[3] C. Engelmann, D. Meier, A. Olowinsky; M. Kielwasser, Metal meets Composite - Hybrid Joining for AutomotiveApplications, Lasers in Manufacturing Conference 2015, 2015.
[4] D. A. V. Kliner et al.; Next-generation industrial fiber lasers enabled by high-performance components, Proc.SPIE 10513, Components and Packaging for Laser Systems IV, 2018, 105130S.…

