Research Highlights

Macro processing

Modern high-power lasers easily reach several kilowatts of emitted beam power. If this radiation is focused, intensities of more than 1010 W/m2 can be achieved at the focal spot. Together with multi-axis positioning systems, a wide variety of materials can be cut, welded, ablated or drilled or their local materal properties can be changed. Currently, we are operating various solid-state lasers, fiber lasers and CO2 lasers. The positioning system of our 1.5 kW CO2 cutting laser is currently being re-engineered and re-connected to the laser. A robot is connected to our 1.5 kW fiber laser and allows processing of 3D components.

In recent years, we were mainly focused on joining of different materials using laser technology. The combination of different materials to components with tailor-made properties is an interesting possibility for the optimization of components, especially for the aerospace industry and for automotive production. Different materials, for example steel and aluminum, or hard metals, etc., differ from each other in their density, melting point, thermal expansion, etc. In addition, thermal joining can also lead to the formation of brittle intermetallic compounds, which grow more easily at elevated temperatures and can easily lead to failure of the joint if their thickness is too great. If they have enough time for growth, they exceeds the maximum allowed thickness quite easily. Despite the above-mentioned problem areas, we have been able to achieve some success in joining different materials in recent years.

Joining of hard metals and steel

Carbide teeth were welded onto steel saw blades with the help of a diode laser. Well defined pre- and postheating processes with precise heat input resulted in crack- and pore-free welds. The process was patented together with our industrial partner.

gesamtes Bild schwarz/weiß; Hartmetallspitze ist prismenförmig: Querschnitt ist ein Dreieck, Höhe entspricht der dicke des Blatts.

© TU Wien

Detail of laser welded carbide saw blade

Oberes viertel der Bildfläche ist hellgrau mit sehr feinkörniger Struktur, restliche Bildfläche: dunklere, graue Fläche mit helleren, dünnen Horizontalstreifen und große, dunkelgraue, rundliche Strukturen. Prompter Übergang zwischen den Flächen;

© TU Wien

Micrograph of the joint zone between steel and carbide

Joining of aluminum and steel

The excessive growth of brittle intermetallic FexAly phases, together with the very different properties of these two materials, is a major challenge in thermal joining. In cooperation with several industrial partners and some diploma and bachelor theses, we have succeeded in joining steel and aluminum in a reproducible and excellent quality. A diploma thesis, which was developed in the course of these activities, was awarded the Böhler Uddeholm Precision Strip Research Prize.

schwarzer Hintergrund, von links zulaufendes (rechteckiger Querschnitt) Werkstück1, von rechts kommend Werkstück2, Werkstücke liegen übereinander, oberes Werkstück2 hat fasenförmigen Übergang zu Werkstück1 (erster Abschnitt steiler, zweiter flacher), Stirnfläche von Werkstück1 leicht überlappt von kleinem Fortsatz auf Werkstück2;

© TU Wien

Detail of a laser-welded aluminium-steel lap joint

schwarz/weiß Bild: rechteckiger Querschnitt von Werkstück1 wird zangenartig umfasst von Werkstück 2; Übergang von Werkstück1 auf Werkstück2 ist fasenartig mit konstanter Steigung; Werkstücke jeweils in unterschiedlichen Grautönen; restliches Bild schwarz;

© TU Wien

Detail of a laser-welded aluminium-steel butt joint

Simulation of the joining process.

After activation, data may be transmitted to third parties. Data protection declaration., opens in new window

Dissimilar metal joining Steel-Al assisted by laser (cross-sectional transient analysis)

After activation, data may be transmitted to third parties. Data protection declaration., opens in new window

Dissimilar metal joining Steel-Al assisted by laser (formation of intermetallics)

Micro- and Nanomachining

Short and ultra-short laser pulses can be used to process a wide variety of materials with very high precision and almost without thermal changes to the base material. For micromachining, we have laser sources that emit pulses in the ns range as well as lasers that emit pulses in the fs range.

Laser pulses that last only a few femtoseconds are completed long before the atoms in the illuminated workpiece have been brought to oscillation. One of our ultra-short pulse lasers generates pulses that last only about 30 fs. At this extremely short time, the light travels only about 10 µm. In order to be able to properly understand such a short time span, it is helpful to compare it with the propagation of a light beam in space: In one second, the light travels a distance that corresponds to about 3/4 of the distance from the Earth to the Moon (about 384,000 km). In 100 fs, on the other hand, a short light pulse only traverses a distance shorter than half the diameter of a human hair.

Zu sehen ist ein grüner Strahlenverlauf mit allen Bauelementen der Strahlführung sowie anderen Bauelementen der Laseranlage

© Matthias Heisler

Ultra short pulse laser at the research unit Photonic Technologies

Short and ultra-short laser pulses can be used to structure almost all materials in the micro and nano range and thus also change their surface properties. Sample surfaces can thus be made hydrophilic or also hydrophobic.

links: kondensartig verteilte, rundliche Unebenheiten auf Oberflächen_ rechts: von oben nach unten verläuft eine Bildserie, in der ein Tropfen von halbkugelförmig bis eben verteilt auf der Oberfläche verläuft.

© TU Wien

Micro- and nanostructured sample surfaces. Depending on the laser parameters, it is also possible to create hierarchical structures that exhibit both micro- and nanostructures. These structures show hydrophilic behavior after processing, which can be transformed into superhydrophobic behavior by subsequent activation (see the last two columns on the right).

Thin film measurement

This is a method for surface characterization and determines the polarizing properties of the sample. With a mathematical model certain parameters, like film-thickness or refractive-index, can be calculated from the measurement. This method is very fast and is based on polarization-modulation or -switching with a SCPEM. It enables the acquisition of thickness-distributions within ms and is aimed to be used in-line for quality-control.

Zu sehen ist die entsprechende Ausgabedatei der Messung in vier Bildsektionen: Bild 1 zeigt die gesamte Folie, die Dickenunterschiede sind farblich angedeutet. Bild 2+3 zeigen den Dickenverlauf über die Breite der Folie. Bild 4 zeigt eine 3D Nachbildung der Oberfläche

© TU Wien

Inline measurement of thickness-distribution of PEDOT on PET-foil with stroboscopic ellipsometry.

Eine durchsichtige Folie mit roten Streifen wurde aufgespannt zischen mehreren Rollen. Neben der Folie stehen schwarze Bauelemente des Versuchsaufbaus, sowie zwei, verschieden geformte, dicke Glasplatten zwischen einem der Elemente und der Folie.

© TU Wien

Inline 2D-thickness-measurement with stroboscopic ellipsometry.

Auf einer schwarzen Lochplatte sind folgende Elemente fixiert und im Bild textuell Beschriftet: zwei Photodioden, Analysator, Probe, Strahl, Polarisator und SCPEM Modulator.

© TU Wien

Test setup with the individual components