A team at the UPV/EHU-University of the Basque Country have validated the use of moving optics for laser hardening, finding that the process can be adapted to the shape of the metal part, for increased flexibility.
Hardening is a surface heat treatment which is applied to steel parts, with the aim of increasing their hardness. This process is crucial for steel parts that require high wear resistance, such as sheet steel stamping dies.
In hardening, the steel piece of heated to about 800 to 1000°C, followed out by rapid cooling, leading to a change in the structure of the steel.
Since 2000, parts of the industry have used laser hardening. As laser is a highly localised heat source, it enables only the surface to be hardened, while the core of the parts are left in their original state. This results in the parts have a balance of hardness and flexibility, reducing the brittleness, and the parts also do not become distorted from the heat, reducing the need for them to be finished using other methods.
However there is a limitation to laser hardening: the laser sweeps a constant bandwidth so the hardened zone thus ends up with a constant thickness.
Hoping to make the technology more flexible, the UPV/EHU team decided to look into whether it is possible to incorporate moving, scanning optics into the laser hardening process. The optics, a galvanometric scanner, moves a very small laser at great speed, sweeping the surface of the part line by line. The hardening width can be adapted simply by changing the program parameters, allowing high precision and flexibility.
In their experiments, the team found that the technique could be used to carry out the hardening, and that the result of the treatment changed according to the speed of the laser movement, the power used, and other variables.
They found that when the laser moves very fast, the results are similar to those of conventional laser hardening.
The team then ran a project in collaboration with companies in the Basque Country and Italy to see if the process was viable. The results were positive: not only was the process viable, it could be transferred to industry.
According to Aitzol Lamikiz, Professor of the UPV/EHU’s department of Mechanical Engineering and member of the High Performance Manufacturing group that carried out the research, there are still improvements needed before the technology can be rolled out for industrial production.
"It is very important to get the material treated to the necessary temperature so that the treatment takes place, but it must not be exceeded otherwise we would melt the material. In our process, as the laser is constantly moving, control is more complex,” explained Lamikiz.
"To use the process on an industrial scale, it would be important to try it out with more powerful lasers, different types of lasers, on other materials, etc.,” he said.