Gas turbine designers like it hot — very hot. The higher the temperature inside their machines, the more work they can extract from the hot air that flows through them. You might remember this from college. The class was Thermodynamics.
But the party ends at about 1,300 degrees Celsius (2,400 Fahrenheit), when the air starts melting the metal blades spinning inside the turbine. To keep things under control, engineers spray the blades with high-tech thermal barrier coatings and riddle their surface with constellations of tiny cooling holes that bleed in just enough cooler air to keep the temperature down.
Designing and drilling these holes is a very exact science, since too much cooling air makes the turbine less efficient. Workers typically drill first, apply the coatings next and then reopen the holes. This is labor-intensive and time-consuming work.
Engineers at GE Power, however, have a new tool at their disposal. They are using a special laser machine originally developed for the diamond industry that can drill holes so precise they make the blades look like alien technology. The machine, called Laser MicroJet (LMJ), also allows them to reverse the process, coat the blades before drilling and save hours per blade. The savings add up, considering there are hundreds of blades inside the hot section of a gas turbine or jet engine.
GE’s first LMJ specimen is working at GE Power’s new Advanced Manufacturing Works in Greenville, South Carolina, which opened last Friday. The machine shoots a powerful laser beam through a thin jet of water that envelops and focuses the laser like an optic fiber. The water also cools the surface of the blade and flushes out debris.
The Laser MicroJet was originally developed for the diamond industry by the Swiss company Synova. Charlie Hu, an industrial manufacturing engineer at GE Power, spotted it in a trade journal and spent three years perfecting it for use in the turbine industry. The result in Greenville combines Synova’s laser with GE’s hole-drilling software and high-precision-machining technology from Japan’s Makino Milling Machine.
Workers in Greenville now use the LMJ to drill teardroplike holes running at sharp angles that distribute the cooling flow better and reduce the need for outside air. Kurt Goodwin, the GE leader who runs the new plant, says the machine will save as many as seven hours of labor per part when it’s production-ready later this year.
In an interesting twist, Goodwin and his team also use the LMJ to machine a new heat-resistant supermaterial designed to replace metal inside turbines in the first place. The material, called ceramic matrix composites (CMCs), can work at temperatures where most metals grow soft and doesn’t need any cooling holes. But it’s also extremely tough. “The microjet slices through CMCs like a knife through butter,” Goodwin says. “The material is already inside our new jet engines and we are helping GE Aviation come up with new designs. We are helping each other. This is what we call the GE Store.”