Development of thin-film sensors for in-process measurement during injection molding

Resource and energy efficiency in manufacturing is of great significance for future developments. Digitization is becoming an important strategy for meeting these challenges and opening up different paths to sustainability. Injection molding as a high-volume process technology offers great opportunities for this approach due to its wide range of applications, producing polymer parts for use in industrial, automotive and consumer use. Due to process variation and individualizations, manufacturing ramp-ups currently produce significant volumes of scrap due to process variations. For improved process parameter setting and validation of simulation models in-process measurement data is mandatory and expected to be a key enabler for automated real-time quality monitoring in future production. One way to measure temperature and melt flow directly in the cavity with contact to the melt is to use thin-film sensors. They are applied to the surface of the tool with high hardness, high wear resistance, low coefficient of friction and high load capacity, are very small and only a few micrometers thick. This research describes the development of thin-film sensors, starting with the tool concept to integrate a sensor insert, followed by the physical operating principle. The developed thin-film layer system and its fabrication process using vacuum-based deposition techniques such as physical vapor deposition and chemical vapor deposition are explained. Combined with microstructuring techniques such as photolithography, the thin-film sensor structures were fabricated and their thermoresistive behavior is characterized. The applied sensor design with a high spatial resolution to detect both temperature and flow front movement is shown. Finally, the developed sensors were experimentally tested in the laboratory. Results of temperature measurements, sensor performance and flow front movement are presented and future potential for applications are discussed.