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How metal is laser marked

How metal is laser marked

Lasers are increasingly used to mark unique identification numbers on parts and products, this allows them to be easily identified in the event of recall. Laser markings are highly durable for medical devices, and can withstand many cycles of sterilization with serial numbers, part numbers, barcode information, and batch bar codes these can be marked on flat or curved products.

Co2 lasers are used in conjunction with a ceramic coating applied to the surface of the metal, as the laser passes over it this creates intense heat that permanently bonds the coating to the surface. The product we use is Cermark produced by Ferro this has been tested by NASA on the exterior of the International space station and has survived nearly four years of low earth orbit. Ferro supplied Cermark as bar code test marks on aluminium and glass which passed NASA’s criteria for its material international space station experiment, they were positioned on the lower section of the ISS’s airlock chamber in the harshest conditions exposed to the maximum amount of ultraviolet radiation and atomic oxidation, created by radiation from the sun and atomic oxygen found in the upper atmosphere that is extremely corrosive. Few products can claim space as a test market, we have marked medical products made from Titanium and Aluminium that have remained in perfect condition after many cycles in an autoclave.

Anodised metals can be laser marked by passing the laser over the surface and engraving away the anodised coating, the ceramic coating is then sprayed onto the surface and another pass of the laser with intense heat is used to bond the coating to the surface producing a permanent black finish.

Types of process

Surface texturing lasers can create patterns and textures onto the surfaces of products or components that increase the physical performance, for example wear rates, grip, load capacity, and optical properties. Laser texturing can create roughness on medical implants which make it easier for bone or new tissue to grow and take a firm hold to a new implant patterns and textures can be produced with very high depth resolution.

Laser ablation is a subtractive machining method that essentially vaporises the material with high precision using the laser beam. Ablation is especially useful for machining delicate and sensitive materials or superconductive materials as this is a non-contact process it does not change the structure or damage its surface.

Laser drilling this is an incredibly effective and accurate method of producing micro-sized holes in a range of materials, acrylics, wood, and ceramics. Many manufactured parts need microscopic features that can only be created by laser light technology. Incredibly small and complex features can be produced with methods such as mask projection, direct write, and trepanning with no material damage from heat effects.

Marking with lasers can be used on many metal materials used in industry, they are commonly used in automotive, medical, electronics and aerospace industries. If you are specifically looking to achieve high quality laser marking results on metal, there are several considerations that must be considered first as there are differing mechanisms of marking that can be achieved by lasers. Fiber lasers use a localised high-energy laser beam which rapidly vaporizes the surface of a metal, leaving an engraved pattern in the material. Fiber laser technology uses a different light wavelength to Co2 lasers and as metals have a high heat resistance a correspondingly high laser energy is required for deep engraving.

Laser annealing Titanium and ferrous metals such as iron and steel, heated from a laser source can cause oxidation of the affected area, which introduces discoloration to the surface where heating  penetrates tens of microns below the surface. This method of laser marking metals is known as laser annealing. Annealed portions of the substrate are typically black, but may also vary between shades of red, yellow, or green, dependent on the temperature of the surface this can be shown on titanium.

Annealing metal is a different process to laser engraving, where the surface of the annealed metal is not modified to remove any surface material, but an oxidized layer is added. Pulsed fiber and Co2 lasers are used for annealing of metals; however, when compared to laser engraving, laser annealing requires a lower power output over a larger application period. Laser annealing is not as commonly used as laser etching or engraving, it can still frequently be seen in medical devices which use stainless steel or titanium materials. Laser annealing is beneficial for smooth laser marked surfaces changing the surface temperature with visible coloured finishes, the annealed surface is more resistant to oxidation and rust than engraved surfaces. This requires time for cooling after the laser annealing is applied and hence is a consideration in mass production settings.

Whether you decide to use laser additive annealing or engraving to perform laser marking on metals is dependent on the application, if you need to perform a large volume of laser marking operations in the shortest amount of time possible, engraving or annealing are appropriate techniques. If working with ferrous metals or titanium and you can compromise on time, or have reason to remove as little material as possible, laser annealing may be appropriate. When deciding to use fiber or Co2 lasers for engraving purposes, the detail to the pattern must be considered and the costs involved in choosing the appropriate laser system. Metal surfaces typically require treatment before and after laser processing by application of a laser marking solution to the metal, this is sprayed onto the surface then the remaining coating is removed from the metal after marking. Fiber lasers, on the other hand, do not necessarily require treatment before or after engraving, and are able to engrave finer details. This is also true for ultrafast pulsed Nd:YAG lasers, which are similarly able to produce finer engraving patterns and minimize undesired heat diffusion into the surrounding area of the metal.

Although there are numerous parameters that need to be taken into account when deciding on a method of metal laser marking, a good understanding of the specific application context and the relevant benefits of each different marking method as outlined above will allow you to decide on the appropriate laser marking device for your needs.

Date: 2 July 2021

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