How can colours be laser marked onto stainless steel?
Annealing is a process that does not remove material during processing. The creation of colours when laser marking stainless steel is caused by heat application. Whilst the possibility of creating colours with a laser machine had been around for a long time, the capability to accurately mark colours and to reproduce them is new with MOPA source. In addition to the power, speed and frequency of the laser source, pulse durations can also be adjusted. This means that the parameters can be tweaked precisley to the respective stainless steel so that annealing colours can be produced in consistent quality. A large focal length (and therefore a larger spot diameter) as well as very small filling line distances ensure that the annealing colours can all be generated directly in the focus. Note that because of small filing distances, colour marking by tempering takes a relatively long time.
Annealing colors are superficial colorations of stainless steels that result from the application of heat. The possibility to generate these colors with a laser has been around for a long time and has been scientifically investigated more than once, too. What is new, however, is the possibility of marking the desired colors so accurately and – above all – reproducibly. This is made possible by the MOPA lasers, in which – in addition to power, speed, and frequency – the pulse durations can be variably selected. The laser parameters can thus be tuned so precisely to the respective stainless steel that the desired annealing colors can be produced in consistent quality. A large focal length (and therefore a larger spot diameter) as well as very small filling line distances ensure that the annealing colors can all be generated directly in the focus. Thanks to the small filling line distances, the marking of colors by tempering takes a relatively long time.