Functionality, various beam sources and design
Laser marking is currently the best method to mark thermoplastics. It is:
- Indelible or can be removed only be leaving conspicuous traces
In general, pulsed lasers (QS mode) with an output of 10 watts and a wavelength between 980-1074 nm – that is, lasers operating in the infrared range, also known as IR lasers – are usually used today for marking plastics.
The term laser is an acronym of Light Amplification by Stimulated Emission of Radiation.
At the center: a crystal or gas
To generate a laser beam one needs a source beam – also called an active medium. If it is a crystal, one speaks of a solid-state laser, which may have various shapes. If it is a gas, it is called a gas laser.
In order to stimulate the active medium to emit light in a specific wavelength, it is charged with energy from lamps or diodes. The active medium is contained in a resonator, which repeatedly reflects the emitted light back and forth between mirrors. Each time the light passes through the active medium its energy level increases: Finally, it leaves the resonator through a semitransparent mirror.
The photons that comprise the light are identical with respect to their frequency, phase, polarization and propagation direction. What wavelength the laser light has depends on which active medium is being used.
Marking with lasers
The vector laser allows the reproduction of the finest structures even at high processing speeds since it controls the beam, like a hand controls a pen. On one hand this guarantees high dynamics, on the other an exact positioning of the laser beam on the workpiece made of plastics or powder-coated metal.
A special option of marking with the vector laser is “marking on the fly”. Here, the laser beam and the workpiece are being moved simultaneously to mark the product without distortion. The speed of the transport unit is measured continuously with a decoder signal to obtain a consistent mark, even during the acceleration and deceleration phases.
Depending on the desired application, different radiation sources and designs are recommended.
An overview of the lasers that are used in the practice of laser marking:
|Laser beam source||Description||Wavelength|
|YAG doped with Nd:||Yttrium aluminium garnet (solid-state laser) Nd:YAG||1064 nm|
|YVO4 doped with Nd:||Yttrium vanadat (solid-state laser) Nd: YVO4||1063 nm|
|CO2||CO2-Laser (gas laser)||10.6 µm|
|H2, Ar2, F2, Xe2, KrF, XeF, XeCI||Excimer laser (gas laser)||UV range 150–355 nm (depending on molecule)|
|Fiber doped with Yb:||Fiber laser (solid-state laser)||1062 nm|
|Diode laser||940, 980 nm|
Different laser designs and their advantages
Depending on individual need, differently designed solid-state lasers can be used for marking plastic. According to the shape of their crystal, they are called:
- Rod laser
The classic shape of the laser crystal is rod-shaped – therefore the name of this design is rod laser. This type is the most widespread.
- Fiber laser
If the doped core of a glass fiber forms the active medium, one speaks of a fiber laser. Its advantages include an outstanding beam quality, compact, maintenance-free, and robust design as well as its longer service life.
- Disk laser
When the active medium has the form of a disk, it is called a disk laser. It generates the laser beam through multiple passes of the pump radiation through its laser disk (typically between 80 µm and 200 µm). The advantage of the disk laser is the superior cooling of its crystal, which adheres with the mirrored side to a heat sink. Because it is exposed to less tension and mechanical stresses, the disk laser can be better focused in comparison to other solid-state lasers
You will find more information on the use of lasers in plastic marking and marking of powder coated surfaces, under Processes and Laser Settings
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