Published 2/13/2012

Laser Marking Basics

Learn about the various marking processes that lasers can perform.

Basics

Derek Korn

Editor-in-Chief, Production Machining magazine

I picked up this sample at the Performance Racing Industry show. It shows the various types of marking processes that a Trumpf 6030 laser can perform.

Manufacturing traceability is of paramount importance especially in the aerospace, automotive and medical industries. Lasers are well-suited for marking metal components with critical information, offering the flexibility to perform a number of marking processes. Marking machines such as Trumpf’s TruMark series 3000, 5000 and 6000 can perform annealing, ablation and engraving (both light and deep) on metals in addition to coloring and foaming of plastics. The correct marking method depends on the workpiece material and the quality requirements.

Annealing can be performed on ferrous metals and titanium. Annealed markings are generated using the laser beam to heat the workpiece where the mark is required. This creates oxide layers on the workpiece surface. The marking color depends on the composition of the oxide as well as the temperature to which the workpiece is heated.

The drawing above is an example of annealing.

Ablation and engraving can be performed on virtually all materials, including metals, plastics and ceramics. For both processes, short, powerful laser pulses are used. The power densities are so high that the base material or coating decomposes or melts and evaporates.

Ablation is the partial removal of coating layers from the base material that have a markedly different color. Typical materials for ablation include anodized aluminum, lacquer layers and special laser marking films.

The drawing above is an example of ablation.

For engraving processes, the laser beam removes material from the surface of the workpiece leaving behind a depression. If necessary, colored oxides can be produced to further accentuate the marking. Deep engraving, which creates a more significant depression, is commonly used for molds, dies and stamping tools. The marking depth that can be achieved depends on how the workpiece material absorbs the laser, how much energy the laser has and how long the laser can dwell on the target.

The drawing above is an example of engraving.

To color plastics, the laser beam heats the surface locally, which causes some materials to become darker and others lighter in color depending on the material composition. In blackening, soot particles are generated that show the inscription in dark letters on lighter-colored plastic. To make dark plastics white, foamed marking is used whereby the laser beam melts the workpiece material locally. Small gas bubbles form in the molten material that increase the material’s volume creating foam. The processed area appears much brighter than the surrounding material and, in some cases, the marking is raised above the surface of the workpiece.