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Lasergehärtetes Bauteil

Laser hardening

With laser hardening, you benefit from less reworking and the ability to process irregular three-dimensional workpieces, too. Thanks to the low heat input, there is very little distortion, which reduces the need for reworking or eradicates this entirely.

How laser hardening works

Laser hardening is a surface hardening technique. It is used exclusively on ferrous materials that are suitable for hardening. These comprise steels and cast iron that have a carbon content of more than 0.2%.

To harden the workpiece, the laser beam usually heats the surface to just below the melting temperature, which is around 900 to 1400 °C. Once the setpoint temperature is reached, the laser beam starts to move, thereby steadily heating the surface area in the direction of feed. The high temperature causes the carbon atoms in the metal lattice to rearrange (austenitisation). As the laser beam moves on, the surrounding material cools down the hot surface very quickly in a process known as self-quenching. As a result of the rapid cooling, the metal lattice is unable to return to its original form, producing martensite. Martensite is a very hard metal structure. The transformation into martensite increases the hardness of the metal.

Turbocharger shaft is laser-hardened

The laser beam hardens the surface of the workpiece. The hardening depth of the outer layer is normally 0.1 to 1.5 millimetres, although on some materials, it may be 2.5 millimetres or more. Greater hardening depths require a larger volume of surrounding material, to ensure that the heat dissipates quickly and the hardening zone cools down rapidly enough.

Hardening requires relatively low power densities. At the same time, the hardening process involves treating extensive areas of the workpiece surface. That's the reason why the laser beam is designed to cover as large a surface area as possible, which is usually rectangular. Scanner optics are also used in the hardening process. They move a laser beam with a round focal point back and forth very rapidly, creating a line on the workpiece with a power density that is virtually uniform. This method makes it possible to produce hardened tracks up to 60 millimetres wide.

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