PROCESS INNOVATION FOR SENSORS IN MOBILE APPLICATIONS BASED ON LASER ASSISTED METAL-POLYMER JOINING

The laser joining of metals to polymers is currently an interesting research area thanks to the capability of developing lightweight structures. Considering their miscellaneous applications in the automotive industry, aluminum and polyamide are chosen as the material combination for this study. There are three main challenges regarding laser joining of metals to polymers in general: significant difference between the melting points of the materials, adhesion at the interface, and the mechanical properties of the assembly.
The first challenge is addressed by in-situ heating observation and temperature measurement during the joining process. Therefore, polyamide thermal pyrolysis is effectively avoided by optimizing the laser joining parameters and employing power modulation.
The second one is studied by applying different surface treatments on the materials (laser-based and abrasive-based). The surfaces were tested by several characterization techniques before and after each surface treatment. The modification of the surface structure through an appropriate surface treatment leads to the improvement of wetting and adhesion between the melted polyamide and aluminum surface. Therefore, the alteration of a mixed failure (adhesive/cohesive) to a fully cohesive failure is the major step to enhance the mechanical properties of the assemblies. However, in the absence of bubbles, the structural modification of polyamide during the joining process is responsible for the failure. Energy-dispersive X-ray1 mapping and Time-of-Flight Secondary Ion Mass Spectrometry2 shows the physicochemical bonding between aluminum oxide and the polyamide at the interface.
To further enhance the mechanical properties of the assemblies, the structure of the polyamide near the interface of metal/polymer is addressed. For this purpose, laser treatment of polyamide, post-heat treatment, and joining with different feed rates were implemented. Finally, the shear strength of approximately 45 MPa on average is achieved for the assembly of laser-polished aluminum laser-joined to the polyamide with 2 and 5 mm/s feed rate.