1st ICAI 2020

International Conference on Automotive Industry 2020

Mladá Boleslav, Czech Republic

2.2 Surface pre-treatment The pre-treatment of surfaces before adhesive bonding is a sensitive process. Besides wet-chemical pre-treatment or the use of primer solutions, several physical treatment technologies like laser and atmospheric pressure plasma (APP) are state-of-the-art for industrial processes (Amenda et al, 2013). Based on their working principles, a local pre-treatment of the surfaces on complex parts can be realised by laser and APP. Ultrafine cleaning of surfaces with cold atmospheric pressure plasma removes organic, inorganic and microbial surface contaminants and activates the surface by crosslinking the molecules. Sand blasting with corundum particles is often used as a mechanical pre-treatment. Besides cleaning it also results in a beneficial roughening of the surface. During laser pre-treatment, which is preferably done on aluminium surfaces, a well- defined cleaning and ablating of the native oxide layer can be realised. By choosing the right process parameters, also a surface structuring can be achieved in a time-efficient way. 2.3 Adhesive bonding Adhesive bonding can be used for sealing, gap overlapping, structural joining or other functional purposes. For structural bonding a 2-component adhesive, consisting of resin and hardener, is preferable. Typical adhesive thicknesses of 100 – 200 μm are used in combination with proper surface pre-treatment. Surface cleaning and roughening at the metal side and activating the low-energetic plastic surface are recommended (Flock, 2011). After cleaning, the adhesive 3M Scotch-Weld DP490, an epoxy resin based system, was applied. The joining partners were fixed together before curing for 75 h at room temperature. For curing time reduction the test specimen were placed in an oven at up to 80°C. 2.4 Thermal direct joining with laser and induction The thermal direct joining process realises quick joining of metals to thermoplastic without any additional material. After a pre-treatment of the metal surface, e.g. by laser macro structuring, both partners are pressed together. Then an energy source heats up the metal immediately until the molten plastic can fill the cavities at the structured metal. The cooling process starts directly after (Figure 3).

Figure 3: Process steps of the HPCi® technology (HeatPressCool integrative) (left) and joining gun (right)

Source: own elaboration

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