Laser marking units use pulsed nanosecond lasers generating a variety of wavelengths, from infrared to green and ultraviolet. The units best suited for marking metals are diode-pumped, solid-state lasers with yttrium aluminum garnet or vanadate as the active laser medium. Fiber lasers are also perfectly appropriate.
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Further examples of the laser marking process
Traceability, individualisation and design: Laser marking has established a permanent place in industry as a reliable tool for marking applications.
For all the usefulness of coatings, they can be an impediment when welding. Which is where the cleaning power of short-pulse lasers comes in.
Marking ever more information onto an ever smaller space on a microchip is something only lasers can do. Plus, they can be integrated into the quality control process.
Different kinds of lasers offer a variety of advantages in differing applications and when marking any of a number of metals. Not only does the type of laser make a difference; the pulse duration, peak pulse power, beam quality and mean power will have an influence on the marking results.
Broad range of marking lasers
That is why TRUMPF offers a broad range of marking lasers exhibiting various power classes, pulse lengths and wavelengths. Higher mean power will usually achieve higher velocities.
However, not only power is important, but the beam’s quality, too. High quality makes it possible to focus the laser beam on a very small spot. In this way, great power densities can be achieved on the surface of the workpiece.
Laser marking on metal
Metals are very amenable to using the laser as a marking tool. When marking steel, infrared light at a wavelength of 1064 nm is normally used for processing. Metals with higher reflectivity – such as aluminum, copper and gold – will absorb only a fraction of the laser power, however.
Here the lasers built by TRUMPF – with excellent beam quality and high peak pulse power – offer advantages. Over and above that, selecting a short wavelength (green) can also bring about good marking results, since these metals will absorb a shorter wavelength more readily.
Small area subjected to thermal effects
Precision is even better in this situation, since shorter wavelengths can be focused even better. The marking on the workpiece itself is in the form of a series of dots, either adjacent or overlapping, which the pulsed laser beam leaves on the material. Pulsing makes for a more carefully defined introduction of energy and thus heat into the material.
Only a very small area is subjected to thermal and mechanical effects. In principle, there are three processes widely used in industry to mark metals. These are engraving, ablation and annealing.
Engraving with the laser: black and whiteWhen engraving, the laser beam strikes the surface of the metal, fusing and vaporizing the material. This leaves recesses in the surface of the component. One usually distinguishes between “black” and “white” engraving. The former is associated with higher power levels and lower advancing speeds.
Black engraving leaves a depression with a dark, oxidized surface and a build-up of the flux at the edge. White engraving only roughens the surface slightly and thus alters the visual impression. Light falling on the object is diffused when reflected and appears to be brighter than the untreated metal surface on the component.
To take one example, a QR-code can be applied with a combination of black and white engraving. This brings about greater contrast and thus improves legibility. Engraving is preferable where components are susceptible to corrosion and whenever coating is to follow marking. The deeper the engraving, the longer the laser will take, since it will have to make several passes to achieve the desired depth.
Ablating with the laser – in preparation for welding processes, too
A further technique used for laser marking is the ablation of a layer on the workpiece. Repeated passes will result in differing ablation depths. Once the layer has been removed, the substrate becomes visible. This is the situation for anodized aluminum, painted metals, or where there is a film covering.
Marking lasers can, however, also be used to prepare for other steps in the production process. Laser welding and bonding are just two examples. If, for instance, a component with an oily, dirty or oxidized surface is to be joined, then the laser beam can be used to remove the contaminant. In this way, a uniform and defined surface can be prepared so that the subsequent welding procedure can be carried out correctly.
Applications such as these are being requested ever more frequently. This is because not only good joins are achieved, but cleaning agents can be eliminated. That is easy on both the environment and the pocketbook.
Annealing with the laserOne property of metals is that they will discolor when heated and subsequently cooled. Laser annealing makes use of this phenomenon. The laser can be used to induce heat in a closely defined area on the surface of a workpiece.
An oxide layer is formed and it determines what color will be seen. Differences in annealing hues arise from differing temperatures on the surface of the workpiece. This process leaves the surface of the part intact – perfect for labeling surgical instruments or implants.
Stringent requirements in medical technology
The surface remains smooth and clean and complies with the stringent requirements prevailing in medical technology as regards biocompatibility and corrosion resistance. Here the annealing procedure exploits its advantages to the full. Metals like titanium and stainless steel are highly suitable for marking by annealing.
An essential prerequisite for success is closely defined energy introduction. This is guaranteed by the precise power regulation incorporated into TRUMPF marking lasers. It is even possible during annealing marking to achieve certain nuances in the change of color. In addition to its uses in the fields of medical technology, annealing is increasingly being used to create design elements on metallic surfaces and thus to enhance and individualize products.
Decisive for a competitive edge: holistic support for applications
In addition to its advanced technology and innovations, TRUMPF sets itself apart from the market due to its extensive user support. Both before and after the purchasing decision is made, this laser manufacturer offers extensive support for the application.
To satisfy this promise, applications laboratories have been set up in Germany, Switzerland, and the USA. If, for example, the potential user has settled on certain specifications in advance – the size of the marking area, quality, marking depth, duration of the marking procedure in the manufacturing process, or the material being worked – then he can forward the data and the material to the applications laboratory and have TRUMPF conduct laboratory testing.
Experienced applications engineers seek out the perfect laser and the matching optical system. They determine the parameters needed to achieve the desired results.
Software assistance to set parametersTRUMPF also provides assistance in regard to setting parameters using software tools. This helps the user achieve additional utility thanks to optimum adjustment of the system. The so-called navigator software uses menu prompts to determine what is to be done – annealing, engraving or ablation.
Working on the basis of the responses, the navigator makes a preliminary selection, manipulating a number of parameters including peak pulse power, pulse repetition rate and advancing speed. Among them might be the right set of parameters to achieve the desired results. Then a matrix is applied to a part with the laser. The squares in the matrix are worked using the various parameter sets.
If the correct effect – quality or color, for instance – is found, then it can easily be selected from the matrix and the parameters can be used for processing. If the selection of the parameters is to be refined even further, then the software tool offers an option for delving deeper into a particular parameter area. This user-friendly tool makes it simple to arrive at very good marking results even though the materials may change from time to time.
Telepresence permits troubleshooting and diagnoses
Telepresence is another important offer that TRUMPF extends to its users. Telepresence makes it possible to access laser systems for remote maintenance. This permits troubleshooting and diagnoses. Some technical problems can even be rectified directly, without having a service technician call.
This gives customers a high degree of laser availability and thus an economic lead. Not only does TRUMPF offer the advantages of telepresence; it also maintains a world-spanning service network, should it ever be necessary to dispatch a technician to the customer’s site.