Laser marking

With conventional focusing, focus diameters in the range of 10 µm and larger are normally achieved. With this type of focusing, markings with a minimum resolution of 10 µm or more can be produced. This is normally sufficient, but for certain applications, for example in metrology, it can be interesting to be able to create even finer markings. This is made possible by using special optics. The focal diameter can be reduced to a few µm with such optics. This makes markings with a character width of approximately 1 µm and larger possible. The positioning accuracy is also a few µm, so that precisely placed, very small markings can be produced. There are no disadvantages in the length of the focus area. On the contrary, while the focus area or Rayleigh length with conventional focusing is in the order of several 100 µm, the focus area has a length of several millimetres when using the special optics. The adjustment of the focus position relative to the workpiece is thus possible without any problems and even curves or irregularities on the workpiece surface can be compensated for without any problems.

Black marking is a marking process that results in an extremely dark and high-contrast marking. Ultrashort pulse lasers are also used for this process, which induce rough structures in the micro- and nanometre range on the marked surface. For this purpose, the ultrashort pulse laser beam is moved over the workpiece with a scanner system. In the process, self-organised structures form on the surface of the workpiece. If the processing parameters are set correctly, a surface structure is created that absorbs the light through multiple reflections instead of reflecting it, resulting in a stable black colour. The special feature of this type of black colouring is its corrosion resistance and viewing angle stability.
A black marking is a strongly roughened surface structure with a superimposed micro- or nanostructuring. In this way, incident light is captured and not reflected. Whereas with conventional laser markings on a steel surface, oxides are responsible for a large part of the dark colour impression, with black markings this is achieved purely through the surface structure. This results in several advantages:

• Korrosionsbeständigkeit: Solange die Oberflächenstruktur erhalten bleibt, bleibt auch der Farbeindruck erhalten. Oxide wirken sich dabei nicht negativ aus.
• Kein Einfluss der Passivierung: Bei der Passivierung werden Oxide auf der Materialoberfläche aufgelöst. Da beim Schwarzmarkieren die Oberflächenstruktur für den Farbeindruck verantwortlich ist, bleibt dieser auch nach der Passivierung erhalten.
• Kontrastreich: Auf Stahl- und Titanoberflächen wird eine tief schwarze Markierung erzielt, welche sich deutlich von der originalen Oberfläche abhebt.
• Hohe Präzision: Der Ultrakurzpuls-Laser ist aufgrund seiner guten Strahlqualität gut fokussierbar. Die typischerweise verwendeten Fokusdurchmesser liegen im Bereich weniger 10 µm, womit auch kleine Strukturen präzise markiert werden können. Dank moderner Anlagentechnik mit Positionierungskamera kann die Markierung mit einer Genauigkeit <10 µm auf dem Werkstück platziert werden.

While the ultrashort pulse laser has its strengths in the corrosion resistance and viewing angle stability of the markings and the generation of unique structures such as diffraction gratings, materials can be marked much more cost-effectively with nanosecond lasers. In this field, LightPulse LASER PRECISION works together with Frama GmbH from Weil der Stadt. The following marking processes are possible with nanosecond lasers:

• Generation of tempering colors on steel or titanium
  
• Colouring of plastics by means of pigments introduced during the manufacturing process
• Removal of coatings
  
• Deep engraving
• Marking of labels made of PU film