Sunday, June 01, 2014

Air Travel Could Be Made Safer With Tiny Monitoring Devices Inside Jet Engines: GE Puts Sensors in Hard-to-Reach Places With 3-D Inking

The Wall Street Journal
By Deborah Gage
June 1, 2014 4:48 p.m. ET

Making jet engines communicate their vital signs while they're in flight has the potential to make air travel safer. It could signal when a stressed engine part needs replacing, or give clues to how engines could be better designed.

But first, those parts have to be made smarter.

A team of manufacturing engineers, materials scientists and testing experts at a General Electric Co. lab in upstate New York is trying to make that happen. They're using a robotically driven stylus—like a needle, no thicker than a sheet of paper—to create tiny sensors on parts that make up jet engines and other complex structures. The sensors can measure the stress on parts that are inside harsh environments—places that are too hot or have too many gasses for more conventional sensors—and transmit that data to GE.
New Materials

Such sensors require new materials—ceramics that can withstand high temperatures, or new combinations of materials that are compatible with GE turbine blades.

New manufacturing techniques are required, too. Traditionally, a sensor would be machined and stuck onto a part. But those techniques don't work so well when a part is cylindrical, or needs a sensor that can go around corners.

So, the team at GE developed a process using 3-D inking, something similar to 3-D printing but on a much smaller scale. Also referred to sometimes in the industry as direct-write, 3-D inking is used in nanotechnology to deposit materials on very small objects.

What the GE team does is combine sensing materials, which are in the form of a powder, with various polymers or solvents to make a gummy, somewhat runny substance—a slurry that has the consistency of toothpaste.

Then they direct the stylus to draw the slurry onto a surface, in thin layers, until the sensor is built up. It's like "elaborate cake decorating," says Christine Furstoss, GE's global technology director for manufacturing and materials technologies.
Thermal Bonding

When the stylus is finished and the sensor is complete, heat can be applied until the extra materials in the slurry evaporate and the particles of ceramic or metal that constitute the sensor bond and join to the part.

The process enables GE to put sensors in places that are hard to reach, and to place different types of sensors—one for temperature, say, and one for pressure—next to each other when space is tight. It's also useful for improving parts in other ways—adding a ridge, for instance, to a part that needs more aerodynamic performance.

GE is considering 3-D inking applications for turbomachinery, which includes jet engines and gas turbines, and is testing prototypes of the sensors with customers. Though they're starting with new products, current products could be retrofitted with the new sensors as they come in for repair.

Both wired and wireless sensors are being developed. But wireless frequencies don't like harsh environments, "so we may need to develop new types of transmitters," Ms. Furstoss says.