1st ICAI 2020

International Conference on Automotive Industry 2020

Mladá Boleslav, Czech Republic

To apply this technology to the test specimen geometry (see Figure 2), a two-step heating process was done. During laser heating the metallic joining partner were heated up by a fibre laser with a continuous power of 1.5 kW for 5 s. Based on heat conduction through the aluminium alloy the plastic is molten on the opposite metal side and solidifies quickly. Volumetric heating of the metal can be done by eddy currents generated by a geometry- adapted induction device. Here the heating time and the amount of used energy should be minimized. The process was optimized to 1.5 s at 5.7 kW generator power. Future challenges for industrial applications are as follows: changes in the joint geometry often requires new inductor geometries to keep the coupling distance between inductor and metal below 5 mm. Also, other metallic parts near the connection could be influenced by the eddy currents and heat up involuntarily. 3.1 Pre-treatment of surfaces The surfaces of the aluminium test specimen were treated as follows: • Reference: cleaning inside an ultrasonic bath with isopropanol • Sand blasting with corundum particles (surface quality: Rz = 20 μm) • Laser macro structuring (3 kW fibre laser; spot diameter: 110 μm; speed: 10 m/s; line distance: 220 μm; multi-line processing) The laser structuring realises thin linear grooves with depths of up to 200 μm and widths with an aspect ratio of approximately 2:1. During laser treatment a combination of metal melting and ablating can be observed. Based on the vapour-pressure inside the groove most of the molten material is ejected. A very rough surface is generated. Figure 4 left shows a cross section of a joint with laser pre-treatment. The plastic test specimens for adhesive bonding trials were pre-treated by atmospheric pressure plasma (APP) using a “Plasmatreater AS400” with a rotating unit (company: Plasmatreat GmbH) The energy and processing speed were varied until a significant reduction of the contact angle was observed. The applied measurement-liquid was deionized water. During PLA processing the contact angle has been reduced by 20%. Figure 4 right clearly shows the differences in the wetting behaviour with and without plasma treatment. The optimized parameters were also applied to PET and PP. 3. Results and discussion

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