Engineers Advance Laser Welding for Bioanalytics

Example of laser welding (Fraunhofer ILT)

A research team at the Fraunhofer Institute for Laser Technology (ILT) in Aachen, Germany has discovered a process to make laser welding more practical and less expensive. The most immediate applications of this advance are in miniaturized bioanalytic, i.e. lab-on-a-chip, technologies.

Laser welding of plastic components has held promise, but also presented many limitations. It works quickly, precisely, generates almost no waste. Laser welding results a weld seam scarcely visible to the naked eye. There are no sparks or particles flying through the air during welding, and the heat generated is confined to a minimal area.

Up to now, however, the upper joining part to be welded had to be transparent to permit the laser to shine through unimpeded while the lower joining part absorbed the radiation. This usually meant soot particles had to be blended into the plastic. These particles absorb the energy of the laser beam and transmit the fusion heat generated to the upper joining part. These requirements made it difficult and costly to weld two transparent pieces of plastic. A work-around, using infrared absorbers, was available, but it’s expensive and leaves a green-yellowish tint on the product.

An ILT team led by Alexander Olowinsky discovered a new process to weld two transparent plastic pieces without infared absorbers. The researchers studied the absorption spectra of a range of transparent polymers to find wavelength ranges within which plastic absorbs laser radiation. Then the scientists tested and perfected the laser systems to match: systems that emit light of the right wavelengths.

To deliver the light energy to the joining level -– the seam along the border between the two transparent plastics –- the ILT engineers came up with a special lens system. The system focuses the beam to direct the highest energy density at the beam waist, where the beam diameter is the smallest.

As a result, the highest temperature is delivered precisely to the joining level. The ILT team also discovered the wavelength that returned the most promising results: 1700 nanometers, which Olowinsky calls “the peak welding-efficiency range.”

The most immediate and promising applications for this discovery are in bioanalytics, particularly labs-on-a-chip that offer automatic, self-contained laboratory analysis of fluids, protein, and DNA.

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