UKP Glas

Glass welding with ultra short laser pulses

Aim of the development

Glasses and glass ceramics are one of the most important industrial groups of materials with versatile properties and applications. Their properties include optical transparency, high chemical resistance, surface hardness, electrical insulation, and thermal expansion coefficients and refractive indices that can be changed over a wide range. As a result, glasses and glass ceramics are widely used in optics, sensing and measurement, medicine and pharmaceuticals, and electronics and consumer product manufacturing.

Therefore, welded joints on glasses and glass-ceramics have been systematically studied using ultrashort pulse lasers. Although the scientific publications on the subject are numerous, they always deal with laboratory setups, individually manufactured samples and investigations of individual influencing parameters. With a few exceptions, only specimens that have been optically contacted beforehand have been welded. Although this contacting is unproblematic on a laboratory scale, it involves enormous effort for industrial processes. In the project applied for, connections were to be made reproducibly without effort with regard to seam preparation.

In addition, micro-glass welding has so far been performed with microscope objectives, which makes the process slow and allows only small workpiece thicknesses. These limitations were to be overcome.

The goal of the project was to devise a laser process that could be used to join glass without heating or deforming it macroscopically. This process should allow large working distances and workpiece thicknesses, and the effort required for seam preparation should be reduced.

Advantages and solutions

Welding with ultrashort pulse lasers allows energy input and melting of glasses with diameters of a few micrometers. Because a molten pool of this small size can be created within milliseconds, a moving laser beam can be used to weld workpieces several centimeters in size within minutes. Because the molten pool is so small, the workpiece is hardly heated outside the seam. Another advantage is that transparent glass allows internal interfaces to be welded that are geometrically inaccessible. They only have to be visible from the outside.

To achieve these goals, the UKP welding process was transferred from microscope objectives to focusing lenses commonly used in laser material processing. The beam can now be quickly directed over the workpiece with galvo scanners, and the higher focal lengths allow working distances or workpiece thicknesses of several centimeters. This also makes the alignment of the laser to the workpiece much easier.

The experiments were carried out on quartz, Zerodur and BK-7. They also investigated what surface quality is really needed to establish the joint. As it turned out, no nanometer polish or outstanding flatness is necessary for the zero gap. Even glasses with a "poor" polish of SD 80-60 and unevenness of L/2 could be joined.

The welded specimens were subjected to tensile tests and showed a load capacity in the same order of magnitude as the original glass.

Target market

The developed technology can be used to produce glass joints that are free of additive materials, gas-tight and stable over time. This is suitable, for example, for joining optical assemblies, microfluidic chips, sensor encapsulation, microtechnology, glass apparatus engineering, and pharmaceuticals.

Interested parties can view the process at ifw Jena and discuss their own applications with us. Within the framework of bilateral cooperation, the process can be adapted to specific applications. Furthermore, ifw Jena also offers contract manufacturing with this process and continues to research the process within publicly funded projects to solve remaining challenges.