Tool-integrated temperature measurement for press hardening

Motivation:

If deviations from the designed form hardening process are not reliably proven, faulty components may be joined in the further process chain. This can result in considerable follow-up costs. Sensors integrated in forming tools enable temperature irregularities to be detected and countermeasures to be initiated at an early stage. Furthermore, varying cooling rates in the production cycle, caused by fluctuations in the mold temperature, can be used as an input signal for active control of the holding time. Sensors based on thin-film technology offer the advantage of being in direct contact with the semi-finished product without reducing component quality due to thermal interference. This means that the component can be monitored during the production process and manufactured without errors. Due to the increasing complexity of the forming processes and the production close to the process boundary, these sensors offer a great potential to reduce the produced scrap as well as to reduce the cycle time. This makes it possible to make the production process more economical and contributes to a resource-saving use of raw materials.

Aim:

The aim of this research project (IGF No.: 18338 N) was the development of a tactile thin-film temperature sensor for direct use in forming tools. In order to ensure an economical service life of the sensors, investigations were first carried out to identify a suitable wear protection layer, whereby a layer of Al₂O₃ showed the best results. In parallel, processes for the production of thermoelectric and thermoresistive sensor layers were developed. The sensor concepts were calibrated taking into account different forming tool temperatures. In particular, the thermoresistive sensor showed good agreement in the temperature range up to 400 °C in comparative measurements. A complete presentation of the results can be found in the final report.

Abbildung: Signalverlauf des thermoresistiven Sensors im Vergleich zu konventionellem Messsystemen (Mantelthermoelement, Pyrometer) während des Formhärtens

Funding:

The IGF project 18338 N of FOSTA - Forschungsvereinigung Stahlanwendung e. V., Düsseldorf, was funded by the Federal Ministry of Economics and Energy via the AiF within the framework of the programme to promote joint industrial research (IGF) on the basis of a resolution of the German Bundestag. The project was carried out by the Institute for Microproduction Technology, Gottfried Wilhelm Leibniz Universität Hannover.