In industrial laser marking four marking methods are commonly used:
Today most applications use vectorized marking data.
1. Engraving / Deep Marking
Deep marking and engraving are technologies based on the same procedural principle, laser-induced ablation through melting displacement and/or evaporation. 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 creates an indelible mark induced by heat and oxygen without noticeable material ablation. Laser annealing is used with all metals which show a color change when exposed to heat and oxygen, especially stainless steel.
As a burr-free process, annealing offers significant advantages when marking already finished surfaces. Process speed is lower compared to laser engraving because annealing relies solely on thermal effects.
3. Color Change
Laser marking of polymers relies on carbonization or foaming processes caused by laser beam absorption. Carbonization (a thermochemical process) produces dark marks. Foaming, a partial degradation creating gas-bubbles within the material, scatters the light and produces light marks. Additives can help improving absorption properties. Applicable laser sources are Nd: YAG-, Nd: Vanadate- or fiber lasers. Furthermore, harmonic wavelengths of 532 nm (green) and 355 nm (UV) can be used for bleaching and photo reduction processes. UV-induced photo reduction is often called „cold marking“, as there is no noticeable heating of the material.
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 (kiss-cutting).
Vector-based Laser Marking Software
Vector-based laser marking, which holds the largest market share today, relies on galvanometer scanner heads. The laser beam is reflected from two scan mirrors and can be positioned anywhere within the marking field, following any desired path. Running on a standard PC, the laser marking software controls the scan mirrors and switches the beam on and off as required.
Already with standard laser marking software the options for alphanumeric and graphical marking contents are manifold. Graphics designed with other applications (e.g. CAD software) or scanned and vectorized free-hand drawings may serve as marking patterns as well.
