Sensor integration in casting products

Materials, components, and structures with a certain degree of inherent "intelligence" are a central research topic at Fraunhofer IFAM. A typical field of application is the monitoring of mechanically loaded components in operation in all its gradations: from simple load monitoring to damage detection and localization to the prediction of the remaining component lifetime. The basis of such capabilities is a technical nervous system that detects loads and thus provides a basis for their evaluation: sensors.

Challenges for the integration of sensors in casting technology

Today, the integration of electronic components such as sensors in fiber composites is largely state of the art. A far greater challenge is posed by the transfer to casting products. The reason for this is the significantly higher demands that have to be placed on the electronic components concerned and which result from the boundary conditions of casting processes: Depending on the alloy processed, the spectrum of casting temperatures ranges from 420-580°C in the case of zinc alloys to 1500-1700°C for steel castings. When it comes to die casting, post-compression pressures of sometimes well over 1000 bar are added, as well as melt flow velocities of 40 m/s and more. Other casting processes are gentler in this respect, but are characterized by lower cooling rates, synonymous with a correspondingly prolonged high-temperature exposure of the integrated component.

Current interest in these technologies is fed in particular by developments in passenger transport: both in the passenger car sector and in the UAV/air cab sector, clear trends are emerging in the direction of autonomous driving or flying. In both cases, the monitoring of vehicle status and safety must increasingly be taken over by the vehicle itself. For automobiles, a similar situation arises with shared ownership (car sharing). For UAVs/air cabs, there is also a lack of knowledge of critical load cases: Here, sensor technology can additionally help to determine improved bases for structural design.

Solutions for use in die casting and low pressure die casting components

Fraunhofer IFAM, together with partners from the field of microsystems technology, is developing solutions based on thin-film and thick-film technologies specifically for use in die-cast and low-pressure die-cast components under the name CASTTRONICS®. Depending on the application, different strategies are used to ensure the functionality of the respective system after the casting process:

• Use of high-temperature resistant materials ("hardening"),
• distributing the entire system and casting only the most robust components ("distribute"),
• shielding the components from the effects of the casting process ("protect"), and
• and simplifying the sensor with the aim of increasing robustness ("simplify").

With regard to the sensor principles implemented to date, piezoresistive and piezoelectric systems are worthy of mention in addition to simple failure sensors (rip wire principle).