Laser hardening

Homogeneous heat treatment, suitability for all component geometries, and high efficiency are the characteristics of laser hardening with high-power diode lasers.

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Hardening of steel is one of the oldest industrial methods; its roots reach back into antiquity. Also, today’s laser hardening still has the same classical goals: via targeted hardening of defined surface areas, a component is protected from wear and corrosion.

Metal hardening process & method

The goal of all metal hardening processes is to ensure a structural transformation of steel and cast iron materials with greater strength. First, the original ferritic-perlitic material structure is austenitized by heating, and then transformed into hard martensite by quenching. Here, hardening with high-power diode lasers has the decisive advantage of making an exclusive locally heat input at stressed areas possible. By this, at complex components, a partial hardening can be realized, while in other zones the ductility of the initial structure can be maintained. With induction hardening, such a local treatment is not possible in many cases and thus has disadvantages compared to laser hardening. As the workpiece is only heated near the surface with a low hardening depth at laser brazing and the heat is discharged very efficiently over the neighboring material, in most cases there is no need for an additional quenching media, which keeps costs low. As the warpage is compared to other hardening techniques in quite a minimal way, additional methods to correct the material deformations can mostly be omitted.

Hardening material surfaces with diode lasers

The processes of surface hardening with laser are generally usable for all materials at which classical hardening methods can be used due to the adequate carbon content. At laser hardening, only the especially stressed areas of the components are locally hardened, e.g. at steels and cast iron in tool manufacturing. The thermal treatment of wear or cyclical stressed component areas – e.g. in job order production – can be realized quite effectively and flexibly in combination with a Laserline OTZ Zoom optic.

Hardening of components

Diode lasers are especially suitable for surface hardening of steelwork components. The laser beam heats up areas close to the surface of a workpiece at between 900°C and 1500°C, causing a heat-induced austenitization of the originally ferritic-perlitic steel structure. When the beam moves on, the material on the processed part cools down quickly (self-quenching) and hard martensite is created. For many reasons, this process can clearly be realized more efficiently with laser than with induction coils or gas flames. First, the material physically heats up more quickly than with other methods. Second, hardening relevant zones can be treated more selectively, meaning that by local heat input only certain parts of the workpiece can be heated. And third, the heat input can be dosed in an exact manner by special beam shaping optics with integrated pyrometers or thermal cameras, last but not least with particular focus on local different heat conductions at the same component. Due to these characteristics, the diode laser is extremely well-suited for treating geometric complex structures that require in some zones a hardening; in others, however, they have to keep their ductility. Furthermore, these process advantages allow for cost savings. That is, because of the low deformation and self-quenching of the material, usually no (or only little) actions are required for distortion compensation and cooling. Finally, this is reflected positively in terms of required time and material.

Where are diode lasers used for hardening?

Particularly predestined for this treatment are wear or cyclically stressed components such as camshafts. In every gasoline and diesel engine, steel rubs against steel. Thus, the contact zones must be hardened, otherwise the longevity of the parts would be hard to imagine. At these complex structures, the inductive method does not help much; the construction of modern camshafts (with different shaped cams and shifting gates for the cylinder deactivation or change in the engine control) requires a precise surface hardening, which is only possible with diode lasers. Even in manufacturing of large sheet metal tools, diode lasers have established themselves for a long time now. The oldest hardening plants have here already been in use since 10 to 15 years. As the prices of laser beam sources have continued to decrease for years now, additional to these typical fields of use are new applications that are permanently being explored.

Process advantages of the diode laser

Hardening with diode lasers makes it possible to achieve the respective material-specific maximum hardness at machine components, tools, component parts, and commodities. The temperature regulation during the metal hardening process ensures that the respective optimal process results for each material and application are reached. However, heat treatment can also be used to locally reduce the firmness of high-strength materials to make sure better deformability in those local areas.

Compared to other processes, a diode laser offers many advantages:

  • Ideal adjustment of the focus to the hardness contour
  • Local heat treatment of defined partial areas
  • Integration of the heating process in existing production lines
  • Hardening of complex geometries is made possible

Application examples

Surface hardening

Hardening with laser is related to surface hardening processes, and usually even though only locally, the especially stressed areas of components made of steel or cast iron are hardened, e.g. in tool manufacturing for car bodies.

The beam structure is only heated and changed in the near-surface areas of a workpiece, e.g. in a surface layer. With quenched and tempered steels, this area of hardening depth can be up to 1.5 mm thick. As the diode laser beam can be directed selectively and flexibly onto the workpiece from just about any directions and the temperature can be controlled precisely on the workpiece, the surface hardening of geometrically, highly complex components becomes possible. From gearwheels, sprocket wheels, cam and worm shafts to gripping and cutting tools in rope drums, almost every surface geometry can be successfully hardened with Laserline’s diode lasers.

Hardening of camshafts

Camshafts are used in combustion engines. The complex geometry of today’s camshafts, needed for switching control times or the partially cylinder deactivation and their extremely material stressing usage scenario, requires an accurate and selective hardening at which the beam structure of the component edge layer is hardened exclusively locally. In the subjacent material, the ductile structure ought to remain so that the permanently stressed shaft can withstand both highly static and dynamic loads.

Job order hardening

Production companies rely on job order hardening, as buying their own hardening equipment is not worth it from different reasons. These companies operate in different areas, such that hardening agents ought to be able to handle various requirement demands. Laserline's diode lasers are an excellent tool. Due to the possibility of flexible beam guidance and precise temperature, they can treat almost every workpiece successfully. When it comes to buying, they are the cheapest among all available beam sources due to their comparatively low costs. Furthermore, they have an outstanding level of efficiency during operation because of their high-energy efficiency, long lifetime, and low maintenance costs.

MATEX PM, a company from Pilsen in the Czech Republic, offers job-shop solutions for different metal applications with diode laser. Together with Laserline, MATEX PM has, for example, come up with a way that allows laser hardening to protect a rope drum made of cast iron with a diameter of two meters and a weight of 2.5 tons from too much wear when in use.