Investigations of the creation of partiallyclosed microchannels on a surface by means of laser radiation for the accelerationof debonding

Investigations of the creation of partially closed microchannels on a surface by means of laser radiation for the acceleration of debonding. Adhesive bonding processes are increasingly important for industrial applications, like light weight construction or when working with sensitive materials. For the purpose of repairing and of recycling adhesively bonded composite workpieces debonding processes are needed. Industrial applications for debonding by using solvents are often note conomical because of the long diffusion time needed for the solvent to penetrate the adhesive. In this work a laser pre-treatment for a bonding area is developed, that is able to reduce the time needed for debonding using solvents. Laser induced micro channel structures are applied to a Ti6Al4V substrate, which can reduce the debonding time from several hours down to a few minutes. The laser process forms a bulge which closes the channels so that tunnels just underneath the substrate surface are formed. The tunnels are accessible from the substrate surface via pores in the covering layer. Experiments are carried out to investigate the influence of the scanning strategy of the laser on the geometry of the channels, tunnels, and pores.For the experiments a 100 W Q-switched infrared laser is used. From the experimental data a phenomenological model is derived, explaining the formation process of these channel structures. Influence on the melt pool dynamics like heating of the substrate via irradiation of multiple laser pulses, the recoil pressure, and plasma shielding are explored. An analytical model is created for the heat accumulation of multiple laser pulses. The temperature model shows the local temperature difference depending on the scanning strategy. Furthermore, an analytical model is developed to successfully predict the size of the channel cross sections and the amount of generated melt. Samples with these channel structures are bonded together by a thermoplastic adhesive. It is demonstrated that a solvent can fow through the fabricated tunnels of the channelstructure. It comes into contact with the adhesive through the pores. Therefor, the bondis quickly weakened, and the parts can be separated. The deboning time is reduced, because the solvent does not need to diffuse through the whole adhesive but gains quick access to the whole bonding area through the tunnels and pores. This work shows that it is possible to accelerate solvent-based debonding processes with laser pre-treatment. Thus, these debonding processes become more economical for industrial repairing and recycling.