Laser welding of thermoplastic elastomers

Thermoplastic elastomers (TPE) are a group of plastics that exhibit rubber-elastic properties. Unlike the conventional, chemically wide-meshed crosslinked elastomers, their polymer chains are embedded in a thermoplastic matrix. The physical crosslinking points dissolve reversibly under the influence of heat without the macromolecules decomposing. As a result, the processing methods of ordinary thermoplastics – such as injection molding or extrusion – can be used with their advantages.
These include shorter cycle times compared to elastomers, a high degree of design freedom, and the possibility of multicomponent injection molding, e.g. as a hard-soft combination with a thermoplastic. In addition, TPE usually have a lower density and thus a lower weight than elastomers and can be recycled due to their meltability.
This group of plastics has a wide range of applications and is at home in practically all industries, whether in the automotive, consumer or medical technology sectors. Automotive applications include sealing and damping elements, air ducting parts or soft-touch and design components. Medical technology benefits from the high-quality, smooth and dirt-repellent surfaces, compatibility with a wide range of substances and media, sterilizability and high transparency or colorability. Typical applications include hoses, diaphragms and valves, packaging and a wide variety of seals.
The above-mentioned material properties also make thermoplastic elastomers suitable for welding. However, the high elasticity and damping properties of the material make many processes more difficult, especially if the thermal energy is to be applied by external or internal friction (as in the ultrasonic or friction welding processes). Due to its process principle, laser welding often proves to be advantageous or even the only option for material-to-material joining. Not only can similar materials be combined, but – depending on physical and chemical compatibility – also different materials. Hard-soft combinations are widespread here as well, especially with polyolefins (e.g. PP or PE) and numerous other engineering thermoplastics, such as PC, ABS or PBT.
The specific characteristics of TPE require various special features in process control and clamping technology when joining by laser. Also, not all process variants can always be considered, but the elastic material favors the often critical gap bridgeability. Overall, laser welding is therefore an attractive and efficient joining process for this group of plastics as well.

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