In the industry of laser processing, there are four basic methods of marking as following:
1. Engraving or Deep Marking
For a marking device, by illuminating a laser beam onto an X-ray film which is a light-photosensitive heat-developing photosensitive material, an inner portion of a surface layer is melted, a cavity is formed, and a dot, which projects a surface out in a convex shape, is formed. At this time, an illumination time of the laser beam is controlled in order to control melting of the surface layer. In the marking device, when conveying of an X-ray film is stopped, oscillation of a laser oscillating tube is continued until a predetermined period of time elapses. When stoppage is for a short time, control is carried out such that marking can be started quickly. Deep marking is a method used to flexibly create a durable, direct product marking that is forgery-proof and resistant to wear and corrosion.
2. Annealing
Laser Annealing is a surface heat-tempering mark. As a burr-free process, annealing offers significant advantages when marking already finished surfaces. Laser annealing creates an indelible mark induced by heat and oxygen without noticeable material ablation. Process speed is lower compared to laser engraving because annealing relies solely on thermal effects. Laser annealing is used with all metals which show a color change when exposed to heat and oxygen, especially stainless steel.
3. Color Change
The heat effect of the laser beam causes an oxidation process underneath the material surface, resulting in a color change on the metal surface. This dark, permanent mark is ideal for medical device applications where material removal is prohibited to ensure part integrity and performance.
Laser marking of polymers relies on carbonization or foaming processes caused by laser beam absorption. Carbonization produces dark marks. Foaming creates gas-bubbles within the material, scatters the light and produces light marks.
4. Surface Removal
Originally developed for day and night marking, this laser marking method removes opaque lacquer coats from transparent parts. The same process is used for laser marking anodized aluminum and labels made of special multiple layer foils. After marking, the labels are cut out without damaging the carrier foil, also called the kiss-cutting. In order to remove a dielectric coating from a conducting material, a high energy radiation source, such as a laser source, is focused in a region having a predefined relationship with the coating of the conducting material. The focused radiation results in a plasma or ionized region being formed. The coating in the vicinity of the plasma region is removed.
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