Researchers at Germany’s Fraunhofer Institute for Laser Technology have developed a method to laser-weld transparent plastic components together, a task previously thought impossible. What turned the trick? Finding the right wavelength.
In industry, welding plastics with lasers is nothing new. It is quick and precise, generates almost no waste and minimal heat, and produces no sparks or flying particles. Better yet, it works without screws, clamps, or glue. And weld seams are scarcely visible.
But, until now, only the upper joining part could be transparent. In fact, transparency was necessary to let the laser shine through unimpeded. And the lower part usually needed to incorporate soot particles to absorb the laser’s energy so heat could transfer to the upper part.
“The problem was that lots of applications, such as medical devices, needed a combination of two transparent plastics,” says Project Manager Alexander Olowinsky. “The industry already made infrared absorbers, but they are expensive and, although nearly transparent, give devices a green, yellowish tint. Our goal was to get the job done without using absorbers.”
Researchers first studied the absorption spectra of several transparent polymers to find wavelengths at which the plastic absorbs a laser’s power. They then tested and perfected the laser that emits the proper wavelengths. “It’s only been during the past few years that high-brilliance lasers have been developed that emit light in these ranges,” says Olowinsky. The team also developed a lens to focus the beam so it delivers the highest temperature precisely to the joining line.
“So far, we have found that the peak welding efficiency takes place at a wavelength of about 1,700 nm,” says Olowinsky. “But we are continuing to work on the EU Commission-sponsored PolyBright project to find the best combination of absorption ranges and matching light sources. We want to find the most cost-effective laser that can do high-precision welding at the highest possible speed,” he says.
An important application of the new method could be in bioanalytics, where it might help in constructing labs-on-a-chip. They provide automated, self-contained analysis of fluids, proteins, and DNA.