Laser Marking Stainless Steel for Medical Passivation

Question recently posed through our website:

We are seeking a laser marking system capable of marking stainless steels with a mark that will remain a darkish black color after passivation (ASTM A962) Citric or Nitric. Some short-pulse machines are successfully accomplishing this, do you have a solution?

Answer:

The short answer to your question is that fiber laser systems are a pretty good solution to dark marks on stainless steel. That type of laser mark is what is referred to as a “stain” mark. The laser marking mechanism is that the laser beam heats the surface of the stainless rather than cutting into it and the resulting heat forms an oxide layer. The more passes from the fiber laser, the thicker the oxide layer and the darker the mark. Fiber lasers have a pulse width of around 100 to 120 ns and that pulse width range allows for laser stain marking at reasonable marking speeds.

Any laser stain mark from any laser can be made to disappear if the passivation is aggressive enough. The trend in the medical device business these days seems to be going toward citric acid passivation rather than nitric acid passivation. Every device manufacturer seems to have developed their own passivation techniques.

1064nm laser light is what the world uses to mark metals. YAG, Vanadate and Fiber lasers all produce this wavelength. YAG lasers have pretty much gone by the wayside for laser marking applications. Vanadates are great for some applications but still have many of the inherent problems associated with YAG lasers. Fiber laser systems dominate the sales of metal laser marking machines these days because of wall plug efficiency, reliability, size and their no maintenance design.