Evosys and DIC develop welding process for PPS
Evosys Laser, a manufacturer of plastic welding systems, and DIC, a Japanese chemical firm, have jointly developed a reliable process for the welding of polyphenylene sulphide, a high-performance engineering thermoplastic.
The two firms combined their experience in materials, laser technology and optics to develop the process, and report that initial customer projects in which real components are being welded are already in the final testing stages.
PPS is often used in high-temperature applications, such as in motor vehicles where sensor technology is positioned close to an engine, or in medicine for assemblies that need to be sterilized.
While laser welding has long been used for joining polymers, the semi-crystalline structure of PPS compounds demonstrates strong absorption during laser processing, resulting in the material often burning. Only a small range of processing parameters can therefore be used to weld the material successfully – also known as a very small process window.
This process window can be significantly enlarged however by using an optimised energy distribution achievable with a set of optics from Evosys called ‘Next Generation Optics’. This energy distribution enables uniform heat management to be achieved when welding the PPS components, which considerably reduces temperature spots and the burning of the material, maximising the output and quality of welded PPS assemblies.
Micrograph: The joining zone shows a good material mixing of the joining partners in the welding area.
The process has so far been tested and proven both with material samples from DIC and with real plastic assemblies in two customer projects. A process monitoring technique is used by Evosys to ensure stable welds were achieved. The resultant assemblies therefore not only have the required tightness, but also the required fatigue strength.
Thumbnail: Material samples have been successfully welded together using a T-joint in a test procedure at DIC. The pull-off forces are determined and compared with other material variants.