Technologies for Laser Marking
Annealing marking is when an oxide layer is created on ferrous metals (iron, steel, high-grade steel) and titanium through localized heating.
Generally, the oxide layer is black, but it can also have other annealing colors (such as yellow, red and green). The color depends on the temperature of the heated layers.
The material surface remains even during annealing because nothing is removed from it; the color change is achieved through localized material heating only.
The heat usually penetrates 20 to 30 µm deep in the metal surface. This makes the marking non-abrasive and ensures that it can be removed by re-heating (min 700°C for ferrous metals).
Plastics absorb laser light. The color pigments (from additives, colors etc.) and carbon in plastics are destroyed and vaporize as a result of localized heating. A color change becomes visible and the frothing of the material can be felt.
The carbon in the plastic oxidizes to form CO2, which comes out of the plastic and forms a layer of froth.
The discoloration is either lighter or darker depending on the composition. Dark plastics discolor to white at the places to be marked, while light plastics discolor to gray or black (see carbonization).
Discoloration and frothing appear exclusively in case of plastics.
Marking by removing color and material is used especially in coated materials and anodized aluminum as well as in fittings, packaging materials and labels. The existing color, coating and surface layers are partially removed and the base material becomes visible.
The layers to be removed absorb the laser light, the material heats up and vaporizes at relevant places. Since the surface layer and protruding base material have different colors or the base material is often also back-lit, the marking becomes clear and visible.
Since the final markings are very rich in contrast, this laser marking procedure is mainly used in the automobile industry for the day/night design, in the marking of the most varied control elements and keyboards as well as in the packaging industry.
In case of carbonization using laser, the laser marked material always gets a darker color.
Plastic bonds are broken and the carbon from these bonds is released. The discoloration thus produced ranges between gray to blue-gray and black.
Carbonization is used for light plastics and organic materials (paper, packaging materials, wood, and leather), in which the color changes from light to dark.
In case of engraving using laser marking, material is taken out or removed from the surface of the component to be processed. This marking effect can be created in almost all materials.
Especially metals, plastics and ceramics are engraved using laser markers. The laser beam penetrates into the surface and removes it, so that there is a visible depression of up to 50 µm in that area.
Since the material gets simultaneously heated and reacts with the ambient air, there is often a discoloration at the engraving areas, which stand out more distinctly due to the laser marking.