On its surface, the work is deceptively simple: Shoot a high-power laser beam onto a piece of metal for a fraction of a second and see what happens. But researchers say the physics of laser welding is surprisingly complex. A better understanding of the interaction between laser and metal could give industry more control over laser welding, a technology that is becoming increasingly popular in manufacturing.

Inside NIST’s laser welding booth, a high-power laser melts a piece of metal to form the letters “NIST.” (Credit: Paul Williams/NIST)

For the past three years, scientists at the National Institute of Standards and Technology (NIST) have been collecting data on the most fundamental aspects of laser welding. The scope of their study is narrow, but the measurements of this complicated process are more accurate and comprehensive than any data ever collected on the subject, the researchers say.

Now, this information is starting to be used by computer modelers to improve simulations of laser welding processes, a necessary step to prepare the work for industry.

Welding is necessary for many industrial processes, from building cars and airplanes to laptops and cellphones. Conventional welding typically uses an arc of electricity to heat and fuse materials. In contrast, a multi-kilowatt laser beam can heat a smaller area of the metals being joined, creating a smaller, smoother seam than a conventional weld, on the order of millimeters rather than centimeters. Laser welding is also faster and more energy efficient than conventional welding, the researchers say.

Even with these and other advantages, laser welding makes up only a small fraction of overall welding efforts in the U.S. that might benefit from this technique. A better understanding of the process could make it easier for industries to consider investing in laser-welding infrastructure, the researchers say.

Better Data, Better Models

If manufacturers want to weld two pieces of an unfamiliar alloy of metal, they might use trial and error to figure out which combination of laser settings will produce the best weld for their application. But most manufacturers would prefer to streamline the research process and move into production as quickly as possible.

That’s where computer models come in. These simulations help manufacturers predict what kinds of welds they can expect with different settings. To make the models, though, researchers need data from past experiments. And at the moment, that research is spread across hundreds of studies, representing decades of work from dozens of laboratories.

In contrast, the NIST team is attempting to build a much firmer foundation for a model. NIST researchers are measuring everything that a simulator would need — the amount of power that is hitting the metal, the amount of energy the metal is absorbing, the amount of material that is evaporating from the metal as it is heated — all in real time.

Where No One Has Gone Before

Many of the techniques the researchers are using to collect the data were either designed or developed at NIST to measure novel aspects of welding. For example, until recently researchers could not gauge laser power during a weld. NIST physicists John Lehman and Paul Williams and their colleagues designed and built a device that can accomplish this using the pressure of the light itself.

They also had to get creative to sense the amount of light absorbed by the heated material, since it changes constantly. “You go from a rough metal to a shiny pool to a deep pocket that is essentially a blackbody,” meaning it absorbs almost all of the light that hits it, Lehman says. The physics, he says, is “super complex.”

To solve this problem, they surrounded the metal sample with a device called an integrating sphere, designed to capture all the light bouncing off the metal. Using this technique, they discovered that the traditional method for making this measurement “severely underestimates” the energy absorbed by the metal during a laser weld. The integrating sphere also allows the data to be measured in real time.

They also found a way to better measure the weld plume, a cloud of vaporized materials that includes tiny amounts of elements that evaporate out of the sample during welding. Detecting the exact amounts of these elements as they leave the weld would give scientists valuable information about the strength of the material that remains. However, traditional techniques fail to accurately sense the concentrations of certain elements, such as carbon and nitrogen, that exist in extremely low concentrations.

This article was written by Jennifer Lauren Lee for NIST. For more information, visit here .


Medical Manufacturing and Machining Magazine

This article first appeared in the October, 2019 issue of Medical Manufacturing and Machining Magazine.

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