Introduction to the principle of Mopa laser color marking on stainless steel.

In 1999, Ann Marie Carey made a preliminary attempt to laser color marking on niobium bowls, making it possible for laser color marking of metal crafts and jewelry. Since then, the application range of laser color marking technology has been expanding, and it has also become a new technological means to increase the attached value of products.

Nowadays, color stainless steel is widely applied to construction, automobile, arts and crafts and other fields, laser color marking technology provides people with a new and efficient solution. Traditional methods for preparing colored stainless steel such as chemical coloring and electrochemical coloring have the problems of high energy consumption, high pollution, and difficulty in achieving fine coloring. In contrast, laser marking technology takes an advantage due to green, efficient, flexible, and can be permanently retained.

Principle of color rendering of stainless steel

The stainless steel material generates colored oxide on the surface or a colorless and transparent oxide film is formed under the action of the laser heat source, which exhibits various colors due to the interference effect of the light film. This is the basic principle of stainless steel color marking technology. The oxidation product of the metal elements in stainless steel will also show color.

Oxide color

The oxidized product of the metal elements in stainless steel will show the color. The following table shows the colors of several main oxides on the surface of stainless steel after being oxidized by laser.

A colorless and transparent oxide film will be formed on the surface of stainless steel under the action of appropriate laser energy, which will cause light interference.

Oxide film interference

A colorless and transparent oxide film will be formed on the surface of stainless steel under the action of appropriate laser energy, which will cause light interference.

As shown in the diagram above, the reflected light 1'of the light ray 1 and the reflected light 2'of the refraction of the light ray 2 overlap to form an interference beam. White light is a composite light composed of seven colors of red, orange, yellow, green, cyan, blue, and purple. The oxide film presents the light of that color when light interference occurs and the light wave vibration of a certain color is strengthened.

Processing parameters

Power is the most important and intuitive control variable that can affect the laser single pulse output. It is found that the frequency is having a "contest" with the pulse width when stainless steel is being colored, and the frequency parameter has a richer effect on color changes after testing.

The power changes from low to high, and the color displayed on the stainless steel shows very regular changes: yellow, red, blue, green until green slowly becomes darker.

With the changes of frequency power, the color changes show a certain regular phenomena which also applies to the changes of filling spacing. As so far, it is not obvious that the color change in filling,but lot changes are caused by frequency and power.

The advantage of MOPA laser is that its pulse width and frequency are independently adjustable. Adjusting one of them will not affect other laser parameters, which is not available in Q-switch lasers. Therefore, MOPA lasers are more suitable for laser color printing processing.