Brake calipers 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.
Brake caliper with temperature detection
The images below are referred to the brake caliper of a sport racing mountain bike where a temperature sensor has been applied. The probe is placed at only one millimeter distance from the brake pistons, which receive the heat from the wear pads. The freeform capability of AM allows the free positioning of the sensor. Here this increases the accuracy of measurements and reduces the environmental disturbances.
Preliminary rough design with sensor positioning inside the caliper body.
Topology optimization and stress/strain structural properties simulation.
Mechanical tooling of surfaces and threadings by using temporary clamps.
The building process
After completing the design, the CAD file is processed by the AM system. The 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 PT100 thermal-resistance from the commerce) is enclosed inside the component. Special hooks have been created on the machine platform to hold the electric cable during the process. At the end of the machine job, the caliper is removed from the platform by wire cutting.
The component, which includes the lightweight optimization typical of AM processes, is highly integrated. Without openings and holes, the sensor is perfectly embedded and protected. The sensor output is stable, reliable and highly accurate thanks to the proximity to the hot parts. In outdoor tests, the sensor is able to detect in real time the breaking oil temperature with no influence from the surrounding air.