LASER MARKING


“Laser marking systems are


increasingly being employed as alternatives to ink-based printing”


be significantly more expensive than CO2


lasers to purchase. Nd:YAG/Nd:YVO4 lasers


Similar to fibre lasers, Nd:YAG/ Nd:YVO4


lasers are compact,


Laser etching regains the upper hand, however, when it comes to creating high-contrast marks. This is because it can be used to create white, black and grey marks, whereas laser engraving can only be used to create black marks.


Laser annealing Laser annealing involves the surface of a metal being slowly heated with a beam. This creates a mark 20-30µm below the surface as the metal begins to oxidise internally. The thickness and thereby colour of the internal oxide layer is determined by the highest temperature reached at the surface of the metal during heating. This temperature is controlled by the intensity of the laser, the speed at which the beam sweeps the surface, and the line spacing between consecutive passes of the beam. Marks created by laser annealing can be made in a variety of colours, are abrasion-proof, and do not affect the corrosion resistance of the part (as is the case with engraving). This makes the process highly suitable for marking materials used in harsh environments, such as ferrous metals and titanium.


Carbon migration Through carbon migration, the base material is heated


with a laser beam, causing it to chemically bond with carbon molecules at or near its surface. This creates a dark, smooth, permanent mark, making it suitable for use on medical devices where any surface roughness might harbour contaminants and/or microbes, and the process is fast compared with annealing. Carbon migration can be used to apply marks to metals, paper, wood, leather and packaging materials. Marks produced using carbon migration will not be easily visible on dark-coloured components, however.


Foaming Foaming is suitable for producing light-coloured marks on dark-coloured plastics, and sometimes stainless steel. Through the process, the surface of a material is heated with a laser so that it melts and creates bubbles that become trapped during cooling. The resulting markings are raised around 20- 40μm high and can be relatively wide. Light then reflects off the raised marks, making them appear bright on dark plastics.


Lasers used for marking While the earliest laser marking systems relied on CO2


lasers,


there are now a variety of technologies available.


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CO2 CO2


lasers laser markers often


take the form of sealed-tube systems with galvo-steered light beams. With their relatively long wavelength of 9-11µm, they are best-suited to marking non-metallic surfaces, such as papers, leather, wood and some plastics. High-power CO2


lasers


can be expensive to maintain, however, and are less energy- efficient than their modern fibre laser counterparts.


Fibre lasers Fibre lasers feature a gain medium of silica glass fibre doped with a rare-earth element, and can produce infrared wavelengths of light of between 780nm and 2,200nm. Fibre lasers are suitable for the production of high-contrast markings through metal annealing, etching and engraving. They have an extremely small focal diameter that increases laser intensity by up to one hundred times compared with CO2


systems,


making them good options for the permanent marking of serial numbers, barcodes and data matrices They are capable of marking a range of materials, but are generally optimised for metal marking. Fibre lasers are smaller, more energy-efficient and require less maintenance than CO2


lasers. They can, however,


Ultraviolet lasers Ultraviolet (UV) lasers have a wavelength of 355nm, far shorter than either fibre or CO2


lasers.


This wavelength is achieved by passing a standard wavelength laser at 1,064nm (infrared) through a nonlinear crystal, reducing it to 532nm (green), this is then passed again through another crystal, which brings the wavelength down even further to the final 355nm (UV). This short wavelength


energy-efficient, and emit around the 1,064nm wavelength. They offer excellent beam quality, depth of focus and high peak powers, and are suited to fine marking (annealing, etching and engraving) heat-sensitive materials in applications where high consistency is required. They can be used to mark metals including steel, iron, aluminium, brass, copper, gold, silver, nickel, titanium and platinum, as well as non-metals such as glass, plastic, paper, plexiglass and ceramic.


g


Parts in the aerospace and automotive industries, such as this tyre, are increasingly being laser- marked with data matrix codes for traceability purposes


THE 2023 GUIDE TO LASER SYSTEMS LASER SYSTEMS EUROPE 47


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