Hybrid System Builds Sensors into Metal

Ohio-based manufacturing technology company Fabrisonic has developed a hybrid production process that promises to help equipment makers build sensors directly into 3D-printed metal parts. In one of the first applications of the technique, which combines ultrasonic additive manufacturing (UAM) with a computer numerical control (CNC) framework, the company built an embedded fiber-optic strain sensor. Watch the video below for more info.

Creating the sensor represents a step in the instrumentation of the “things” populating the internet of things (IoT). Embedded sensors promise to provide the means to effectively capture in-situ data from industrial equipment, opening the door for advanced setup, maintenance and diagnostics. This, in turn, clears the way for a smart infrastructure of real-time contextual data.

One factor that makes Fabrisonic’s hybrid manufacturing technique stand out from other technologies on the market is that it overcomes a key hurdle that has limited sensor deployment. Whether the application involves monitoring the structural integrity of an airframe or appraising the operational health of a manufacturing system, engineers have conventionally attached sensors to the external surface of the component or system. Unfortunately, harsh operating conditions—such as high temperatures, moisture, electromagnetic interference and vibration—can compromise data collection, limiting the amount of usable data.

Embedding sensors mitigates these effects and provides a robust system for in-situ data collection.

How the Hybrid Process Works

The manufacturing process distinguishes itself largely via the solid-state nature (the materials do not melt) of its ultrasonic welding technology. The UAM process builds solid metal objects using a rotating sonotrode, driven by piezoelectric transducers, to apply ultrasonic vibrations (>20 kHz) to metal foils. This creates a scrubbing action between the foil and the material to which it is bonding, often a metallic baseplate, part or other foils. The scrubbing action displaces surface oxides and contaminants that interfere with the bonding process. With this physical impediment eliminated, the system bonds successive layers of metal foils together to build a solid 3D component.

CNC milling helps create the desired shape, with the required tolerances and surface finish. The subtractive process can deliver higher accuracy of complex internal shapes.

Examining how the fiber-optic strain sensor is manufactured offers a clear view of how the UAM and CNC technologies work together. First, CNC machining cuts a channel into which the sensor is placed. The metal flow in the UAM process then creates a strong mechanical joint between the metal baseplate and the sensor material. This structure enables excellent strain transfer for stress and temperature measurements.

The UAM process delivers many advantages over some other technologies on the market. Most of these stem from the fact that Fabrisonic’s technology does not require a directed energy heat source (e.g., laser and e-beam).

By staying below transformation temperatures of most metals, the UAM process avoids altering the inherent mechanical properties of the feedstock, avoiding significant changes in material properties, such as grain size, precipitation reactions and state. And because of the low process temperature, the system can embed complex electronic components—such as microprocessors, sensors and telemetry—without risking damage to delicate circuitry caused by overheating.

UAM also provides flexibility. Low-temperature operation allows it to safely function in a shop environment without special shielding. Plus, it can use commercially available foil feedstock.

A Work in Progress

Fiber-optic strain sensors embedded in metal components are still in the fundamental stages of development. However, mechanical testing and analysis of the strength of the bond between the sensor and the metal structure of the component show promise.

Collaborative efforts of Fabrisonic, EWI and the NASA Langley Research Center indicate that the strength of the bond is stronger than the yield stress of the metal and that the bond shows no sign of fatigue loading.

As part of these ongoing research efforts, Fabrisonic and EWI are exploring other metal matrix alloys and applications of the manufacturing technology.

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Fabrisonic

EWI