 precise.”
Improved Lasers Shape New Designs
In the early 1990s, working with Prima Power Laserdyne customers, designers began to develop new engine component designs to take advantage of lasers, VanderWert said. “Having seen what lasers could do, they came up with a whole new design of the engine involving smaller, shallow [hole] angles that can be as shallow as 10º from the surface,” he noted. “A hole is typically 0.5 mm in diameter. Implementing the design, which they call effusion cooling, improves the energy efficiency of, and reduces the emissions from, turbine engines.”
With effusion cooling, the number of holes in aircraft turbine engine designs has expanded, noted Mark Barry, Prima Power Laserdyne vice president. An early design from Allison in Indianapolis of a turbine engine combustor had 2000 holes, Barry recalled. “We thought, ‘2000 holes, that’s going to take forever,’” he said. “A portion of the JSF engine has 2.5 million holes in it. That’s the difference in the designs of 20–25 years ago and those of today.”
Current designs involve very complex hole shapes and hole patterns that can change throughout the part, Barry noted. “Years ago, we might drill at one particular angle to the surface; today, it’s multiple angles, different hole sizes and different patterns,” he said. “It’s become very complex and you can understand that the designers have this incredible urge to run their engines hotter and hotter, because the hotter the engine runs, the more fuel-efficient it is. And that’s what it’s all about—reducing emissions, increasing fuel efficiency and prolonging the life of the engine components.”
With effusion cooling, thousands of holes are drilled in the combustors used in the hot sections of turbine engines, Barry noted. The designs enable cooling the hot section of the engine that frequently runs into temperatures above the metal’s melting point, he adds. “The temperatures that the engines run today are above the melt point of the materials. So if it wasn’t for the effusion cooling laying a boundary of air between the flame, so-to-speak—the combustion—and the material, the components would melt,” Barry said. “And occasionally, when we go into MRO [maintenance repair and overhaul] facilities, you can see signs of combustors that have actually burnt through. No one gets on an airplane today that doesn’t have laser-drilled holes.”
A key trend in turbine design is using many different complex hole shapes, using a combination of cylindrical and shaped holes, that are more frequently laser-drilled, often with either high-power pulsed Nd:YAG lasers or increasingly with fiber lasers. Processing is typically either through percussion drilling, which pierces a hole in the material, or through trepanning, a method of moving either the laser, the workpiece, or a combination of these, to produce the holes. In either process, high-power density is accomplished by using a high-power laser with a focused spot size of 0.002–0.030" (0.05–0.75 mm). “To support the designer's goal for greater engine efficiency, Laserdyne had to develop new capabilities,” said Barry. “There are various shaped holes—fan tail and race track—that are designer buzzwords, and hole shapes and angle can vary across the surface.”
Use of fiber lasers for producing turbine components is increasing, Barry noted. Prima Power Laserdyne began an extensive R&D project in 2011, aiming to quantify the capability of fiber lasers with 12, 15, and 20-kW peak power, for drilling as a possible alternative or complement for Nd:YAG lasers, the predominant lasers used. In a paper presented in 2012, the company described its early experiments in fiber laser drilling. “Based on the experiments and experiences in the field, we’ve gone on to work with fiber laser makers. Not only is the fiber laser producing good holes at a good rate and meeting quality and throughput requirements, but it is doing so at a lower cost,” he said. The laser used in the early experiments was about $750,000. “We’ve driven the price point down,” Barry said. “We recognized the problem of lase