Laser Processes - Introduction 

During the laser engraving process, the target material is essentially vaporized by the laser beam. To achieve this result, the intensity of the laser beam is set to exceed a specific threshold value. This threshold intensity is particularly high with materials that are electrically conductive, such as metals. The result is often a cone-shaped indentation influenced by the laser beam profile and the heat conductivity of the target material. The laser engraving technique is typically the fastest way of processing material.

 

With laser cutting, a plate-type material is separated by a focussed laser beam. Basically, there is a choice between laser beam fusion cutting and laser beam sublimation cutting. With laser beam fusion cutting the material, e.g. acrylic, is melted or vaporised. With sublimation cutting, the material, e.g. wood, is vaporised by missing out the liquid phase.

 

During the ablation process, a covering layer evaporates. Very thin covering layers such as color and/or anodizing layers are especially suited for laser engraving. High contrasts can be achieved with a small amount of laser power since these layers absorb laser radiation extremely well. With varnished plastics, a "day & night" design, e.g. for car dashboards, can be achieved by removing one color layer.

 

A contrasting mark can be created using an annealing effect on metallic target materials. The laser beam heats up the metal, creating structural changes in the surface. The color of the mark is determined by the maximum temperature attained in the metal, the properties of the metal, and the parameters selected on the laser. The annealing technique has a unique characteristic in that it produces a contrasting mark without disrupting the surface finish of the metal.

 

Metal engravings can be made by burning covering layers using ceramic powders (Trotec MetalFix). The covering layer is sprayed on and removed again after the laser engraving process. Using this procedure, metal surfaces can also be engraved with a high contrast CO2 laser. In the case of metals, an oxidation process takes place on the surface. However, there is also a powder available on the market for glass engraving with a Nd:YAG laser.

 

Sometimes the best technique to process a material is foaming. Most commonly used in certain plastics, foaming is easily recognizable because the surface of the affected area is raised. Melting occurs when the laser beam couples with the target material. During the process, gas bubbles form and get trapped as the target material cools, producing an elevated result.

 

This effect is only possible with plastics, and depends highly on the wavelength of the laser radiation used. In most cases, this effect is only possible with an Nd:YAG laser, or a specific type of Nd:YAG laser (double-frequency laser). During this process, the laser radiation penetrates the plastic and is absorbed by the color pigments. As a result, the pigments are chemically modified, resulting in a color change in the material. Since the laser radiation penetrates into the plastic, the surface remains almost undamaged. The color change achieved depends on both the pigment and the basic material used.