Marking and Laser Engraving on Steel: processes, advantages and sources
Laser marking and engraving can be done on all metals: steel, stainless steel, iron, copper, aluminum, gold, silver, platinum, palladium, among others. The processes that can be carried out range from deep engraving to annealing marking or surface blackening.
Given the many types of lasers and materials that exist, choosing the best laser for a marking or engraving application can be a challenge. Understanding the characteristics of the laser and the properties of the material is essential for making an optimal choice.
Let's see the particularities of laser marking and engraving on steel.
Steel and Laser Processing
Steel is one of the most used metals in modern industry and in particular in the medical sector. It is an alloy of iron, carbon and chromium in an amount of at least 10.5%.This last element forms a layer of oxide and in this way prevents the metal from rusting. This is why stainless steel is also known as corrosion resistant steel.
The presence of chromium increases the hardness and the elasticity limit of the alloy and when its percentage exceeds 12%, it is called stainless steel because it is resistant to chemical agents.
As well as other metals, marking or engraving operations can also be carried out on steel using different types of laser sources:
- CO2,
- Fiber,
- Nd:YAG solid state.
This process produces a permanent, direct mark on the surface of the metal and the laser machine settings can be changed at will to produce a wide variety of stainless steel finishes that include permanent light, halftone or dark marks and a variety of colors. .
This technology is used intensively in industry and especially in sectors such as automotive, medical, aerospace where product traceability is of particular importance. These lighter marking options can be used to improve productivity.
Laser Annealing for Medical Instruments
A very common application of the laser is the annealing of medical components in stainless steel and titanium such as implants and instruments.In this case it is important to have a highly concentrated peak energy with a slightly longer pulse duration to attract the carbon to the surface and obtain a sharp dark mark that resists the requirements of the various tests to which the instrument is subjected such as passivation. and the autoclave cycles.
Whether using a CO2 laser or a fiber laser, the energy of the laser beam causes the oxide to blacken, creating a sharper and darker mark in the case of fiber laser marking because stainless steel absorbs the wavelength of this type of laser.
In addition, depending on the temperature, different colors can be obtained on the surface of the steel through the blackening or annealing process, which allows you to create different designs.
Another way of obtaining permanent black markings on steel is by exploiting ultra-fast USP sources at the picosecond. These vary the surface of the material by creating diffractive traps for the light and thus creating high contrasts in the marking.
The so-called annealing marking process is ideal for marking medical instruments due to the great resistance over time of this operation and the fact that in this way bacterial proliferation on the instruments is avoided.
Laser marking on stainless steel using CO2 laser
Metal marking compounds are specific laser marking products that contain ceramic particles and are thermally activated on a chemical basis.In some cases of laser marking, therefore, these compounds are applied to the surface of the steel and left to dry. When the laser beam heats this compound, the ceramic particles fuse to the surface of the metal, creating a black mark with a very high contrast.
This sign is almost permanent: it cannot be removed without excessive friction and force, which when applied usually damage the underlying steel. This option can be used for general marking on stainless steel including images and bar codes.
Laser Engraving on Stainless Steel using Nd: YAG Laser
Compounds that are sometimes used to blacken a stainless steel surface when marking with a CO2 laser are not needed when using a Nd: YAG laser.It is possible to obtain different effects with a Nd: YAG marking laser on most metals by optimizing: laser power, speed, pulse frequency and focus.
Stainless steel, however, allows for greater variation in the visual effect than most metals. Titanium is the only other metal that comes close to it in this sense.
In general, stainless steel can be marked in black, different shades of gray, gold, white and with a shiny mark where the surface appears smoother than the surrounding area and therefore reflects light in a different way. These surface marks are almost devoid of depth.
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