Turbine blades with native sensors
The next frontier of structural monitoring
Structural monitoring is a consolidated engineering discipline largely used for remote sensing and control, conditioning, failure prediction and fault analysis. Large numbers of sensors and transducers can be installed inside structures and on their surface to measure physical and environmental parameters.
The additive manufacturing (AM) of structures is available on a large scale with reliable output and controllable quality, though the spread of these processes is still ongoing. Today, many high added value components are built with the AM of metal alloys, including those one normally subjected to structural monitoring.
The research projects we are carrying out in this field started from the same challenging question: how to combine together the potential of additive manufacturing and structural monitoring in metal components?
The native sensors
We use the term 'native sensor' to mean that the sensor is born together with the component. This happens when the component is built with the layer-by-layer additive process, with special reference to the so-called L-PBF (laser powder bed fusion) processes.
After long and tiring trials, an unconventional AM process has been finally defined by modifying the standard process and the corresponding machine.
This new process can provide the embedding of electronic parts and sensors (custom made or commercially available) inside the metal volume of the component. The good news is that the laser heat necessary to melt down the metal powder does not damage the inserted parts. Cables and other external elements can be inserted too.
Turbine blade with temperature detection
The images below are referred to one stator turbine blade made with Hastelloy X. The blade is crossed by two channels with 3 mm diameter for air cooling. The sensor is situated inside the blade and across the air flow. The sensor cable is hosted by a 1.5 mm channel passing through the blade down to the rotor clamping. The freeform capability of AM allows the free positioning of the sensor. Here this increases the accuracy of measurements and reduces the environmental disturbances.
Job design and supporting
The CAD drawing of the blade with a temperature native sensor is optimized by thermo-structural modeling and simulations. The final shape is used to design the building job by deciding part orientation and supports positioning.
The shape and density of supports are crucial parameters to provide the thermal dissipation and structural stability needed during the building process.
The building process
The AM machine is modified to provide the required capabilities of the process. However, as usual, the powder bed is exposed by the laser beam, which melts down the metal alloy and builds the caliper layer by layer. The thermal sensor (a thermocouple type N) is enclosed inside the component. After the building process, the component is annealed and mechanically finished.
The modified AM process can also integrate connectors in the metal (here, the USHK type ceramic connector for high temperature). The electrical interface of the component is crucial for the reliability in applications with hostile environments as turbines.