Laser marking metal: Annealing

During the annealing process no material is taken away, which means there is no ablation. But a colour change occurs through heating up the metal. Stainless steel, for example, changes colour when it reaches temperatures between 200 and 300°C.

Different colours can be achieved with different temperatures, though, the goal is usually a "perfect black". Perfect black markings are possible on stainless steel and Titanium, but not on other metals. Annealing is also possible on any alloys which contain iron.

To anneal metal, it is important to only heat it instead of vaporizing it. This can be achieved by reducing the energy density of the laser impact on the steel. The best way to do so is to go out of focus to increase the laser spot size, as the same energy on a much bigger surface will reduce the energy density. Heating up metal takes time, therefore, slow marking speeds should be used.

Using the conventional method of annealing, the laser is used out of focus (to get a large laser spot for heating the material) and the marking speed is set very low becauseheating takes some time.

With this process, the user can create deep black (partly even colored) and homogenous markings on stainless steel. But due to the large spot and the slow marking speed, there are also some negative effects:

• Fuzziness at small markings
• Long marking times compared to alternative metal marking methods, such as engraving or polishing
• Corrosion sensitivity, because the intense heating of the material can cause the marking to corrode

With the laser marking solutions of Trotec's SpeedMarker Series, the user can avoid these negavite effects while using annealing process for marking.

With the use of the latest fiber laser generation and the new SpeedMark 3.6 laser marking software, the user can create laser markings with annealing in focus, which leads to up to ten times faster marking speeds!

With this configuration, the user has new possibilities for meeting the requirements for laser marking with annealing:

• Less or no corrosion sensitivity (as the heating is much lower)
• Much faster marking times (depending on parameter and lenses)
• Extremely sharp markings possible (marking in focus)

Do you laser mark with annealing or intend to in the future? Then please contact us! Our experts are here for you and help you to find the ideal marking parameter for you specific requirements.

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