Laser marking metals: The annealing process

When annealing metals, no material is removed unlike when laser engraving. However the process produces a colour change in the material as it is heated using laser marking equipment. As an example, a colour change will occur in stainless steel when it reaches temperatures between 200 and 300°C.

With an industrial laser, many finishes can be achieved on materials. While a "perfect black" mark is usually the desired result,  it is possible to achieve different colours with different temperatures. A perfect black marking is possible only on stainless steel and Titanium, though it is possible to anneal any alloy which contains iron.

To anneal metal it is important that you only heat them material rather than vaporising 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 work out of focus which increases the laser spot size, as the same energy on a much bigger surface will reduce the energy density. A slow laser marking speed should be used as heating the metal will take time.

When using the conventional method of annealing, work with the industrial laser out of focus and with a very low laser marking speed.

This process allows you to create deep black (even partially coloured) and homogenous markings on stainless steel, however there are also some negative effects caused by the low speed and working out of focus:

• Small markings will appear fuzzy
• Long marking times compared to other metal marking methods, such as laser engraving or polishing
• The intense heating of the material can cause the marking to corrode (corrosion sensitivity)

Using Trotec´s SpeedMarker industrial laser marking machines, you can avoid the negative effects of the annealing process.

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

This configuration opens new possibilities for meeting the requirements of laser marking with the annealing process:

• Less or even no corrosion sensitivity (thanks to the heating reduced heating)
• Faster laser marking times (depending on parameters and lens used)
• Extremely sharp markings are possible when laser marking in focus

Are you currently laser marking or intend to in the future? Contact us! Our experts will help you find the ideal laser marking parameters for your requirements and how a laser marking machine could benefit your business.

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