Bending Metal With a Powerful Laser

Jan. 27, 2004 -- When it comes to forming tough metal parts that can bear repetitive heavy stress and strain — say, a jumbo jet's landing gear or artificial knee implants for humans — the key is lots of heavy-handed pressure.

Peening, a process of hammering away at a piece of metal to strengthen it, has been used since the early days of the first blacksmiths. But forget about images of a sweaty smithy swinging an old-fashioned ball peen hammer. The metal industry is in the process of implementing a new peening tool for the 21st Century — one that generates a tremendous amount of pressure with literally, the lightest touch.

A new high-powered laser developed by scientists at the Lawrence Livermore National Laboratories in Livermore, Calif. holds promise to improve upon so-called laser peening.

Lloyd Hackel, program manager for laser science and technology at the lab, says the new LaserShot Peening System works much like other laser peening systems.

When high-intensity laser light strikes the metal, the beam creates a miniature shock wave that pushes the atoms of metal closer together. By reducing the microscopic spaces, the metal becomes more resistant to stress-induced cracks and fissures.

High-Pressure Light Beam

But the key to LaserShot system is a powerful new "neodymium-doped laser" first developed by the lab years ago under a DARPA contract that called for a a laser strong enough to illuminate space-based satellites for high-resolution pictures.

"The laser runs 25 times faster than any other laser in the world," says Hackel. "It has a peak power output of a billion watts for 20 nanoseconds. That's the [power] output of a huge electrical power plant for a city neighborhood."

Bringing such tremendous power onto a pinpoint piece of metal for just billionths of a second creates a huge microscopic shockwave — and pressures up to one million pounds per square inch, says Hackel.

And the new laser is fast, producing five high-pressure pulses every second. The best conventional lasers, meanwhile, can produce a pulse only once every four seconds or so, says Hackel.

From Fan Blades to Hip and Knee Joints

Laser peening has been used in critical aircraft components for years. But the new improved laser system from Livermore could be applied to creating high-endurance parts needed in other industries — a venture the scientists have undertaken with Metal Improvement Company in Paramus, N.J.

"One area with a lot of implications: knee or hip implants," says Fritz Harris, a manager at Metal Improvement who has worked with the Livermore scientists over the last few years.

The company is currently working an undisclosed California university to develop improved pediatric knee implants that would use metals crafted from the new laser process.

"If you can make a part that lasts a lifetime, that's a huge advantage," says Harris. You don't have to go in and replace it or repair it."

Harris says the Livermore laser might make that possible because the pounding it performs on metal goes up to five times deeper than conventional peening methods.

"In fatigue failures, a lot of the problems start below the surface — as deep as one millimeter into the part," says Harris. "With the laser, we're putting compressive strength down where stress can form cracks."

Other areas where the new laser-based metal processing system might help: creating stronger barrels to hold toxic waste and lighter, yet stronger transmission gears in cars.

Enough Cents?

"Two or three years ago, this type of process was used in only two or three applications," says Harris. "Now, there are tens or hundreds of applications where this would now be applicable."

But Harris does admit that the Livermore laser process does add about three or four cents to the cost of parts. And while that might seem trivial, Harris says that it is a significant figure to consider — especially since conventional processes are so well-known and "inexpensive."

Still, Harris is optimistic about the new laser system.

"Any process like this starts with high-value parts. But as we get better at it, it comes down," he says. "We'll find new ways to drive it down to other applications."