Laser marking metal: Annealing

During the annealing process, a color change occurs as a result from the heat that is applied directly to the metal. This means that there is no ablation or material removed from laser processing. Stainless steel, as an example, will change color at around the time that the temperature reaches a range of 200 to 300°C

Various colors will emerge as a result of the different temperatures applied to the material, and typically the most obtainable goal is a “perfect black". Titanium and stainless steel can produce perfect black markings, while other metals cannot achieve this coloration. Additionally, alloys with a composition of iron will allow for annealing to be possible.

To achieve an annealing on metal, it is crucial to only heat the material opposed to vaporizing it. This is accomplished by reducing the energy density of the laser impact on the steel. We recommend defocusing the laser to increase the spot size of the beam, which will allow for the energy density to be reduced as a result of the same energy being applied to a much larger surface.  

The traditional process of annealing is performed with the laser system defocused (to allow for a greater spot size to be used for heating the material), as well as the marking speed set very low, since heating does not happen quickly.

Laser operators can produce deep black (partly even colored) and homogenous markings on stainless steel with this technique, but there are also resulting negative effects due to the larger spot and slow marking speed that is used:

• Small markings can appear fuzzy or unclear
• Increased marking times, compared to more efficient metal marking techniques such as polishing or engraving
• Corrosion can occur from the intense heat applied to the material

With Trotec´s laser marking solutions such as the SpeedMarker Series, laser operators can reduce or avoid these negavite effects altogether during the annealing process.

With Trotec’s SpeedMark laser marking software, users can produce laser markings with annealing in focus, which operates at marking speeds of up to ten times than other methods!

This offers laser operators new capabilities for meeting the requirements for laser marking with annealing using this configuration:

• Little to no corrosion sensitivity (due to the reduced heat that is applied
• Significantly faster marking speeds (depending on the lens and parameters used
• Exceptionally sharp and clear markings possible (marking in focus)

Do you laser mark with annealing or intend to in the future? Then please contact us and one of our top qualified and highly motivated laser experts will gladly help you to find the ideal marking parameter for you specific requirements.

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With a Trotec MOPA laser, you can create annealed colors onto stainless steel. For more information, check out our annealing colors page.