Fraunhofer ILT has developed a process for forming hard material components using USP laser technology

Tools made of hard materials are very wear-resistant, but the tools used to produce these tools are prone to wear and tear. Laser tools are the solution. Researchers at the Fraunhofer Institute for Laser Technology (ILT) have developed a process chain that can use ultra short pulse (USP) lasers to shape and polish hard material components without the need to replace clamping devices.

Drills, milling heads, rollers, and even punch inserts made of ceramic hard materials not only bite into the workpiece, but also last significantly longer. Yet the same wear resistance that makes them so durable in production becomes a major challenge during their manufacture. The tools used to shape and finish them find the mixed-carbide hard metals, cermets, and ceramics a tough nut to crack — and wear rates are correspondingly high when mechanical processing methods are used.

Butterfly effect

USP lasers work where mechanical processes flag

This is different with ultrashort laser pulses. Even commercially available USP lasers with a power of 20 to 40 W are capable of efficiently removing the hard materials used in toolmaking. The material vaporizes where their high-energy pulses – lasting just a few picoseconds – hit the surface. Since this happens at frequencies in the megahertz range, laser material ablation reaches surface rates of up to 100 cm2 per minute.

But the potential of USP processing is not limited to forming materials by vaporizing them. Researchers at the ILT have developed a process chain in which the same USP laser not only forms and structures via ablation, but also subsequently polishes the tool surfaces.

“The USP laser is a universal tool we use to conduct various processing steps, sometimes in the same clamping operation,” said Sönke Vogel, team leader for 3D Structural Ablation at the ILT, who has been driving the process forward together with Astrid Saßmannshausen, team leader for Structuring of Transparent Materials.

The key to linking the process steps lies in the parameterization of the laser: While material is ablated with high pulse energy and a low repetition rate, the opposite is true for polishing. The USP laser introduces energy into the surface of the workpiece at a pulse frequency of up to 50 MHz, where this energy accumulates and only melts the top 0.2–2.0 µm.
The material does not vaporize, but forms a molten film that smooths itself out due to surface tension and solidifies as it cools. The surface properties can also be controlled via the process control. “With USP laser polishing, for example, it is possible to smooth out micro-irregularities while retaining macroscopic structures,” said Saßmannshausen.

In addition, the laser process makes it possible to polish complex 3D surfaces with micrometer precision. Specific areas can be selectively treated to adjust surface properties locally or to finish only the necessary zones — saving time in the process.

Mold tool: first USP-structured, then polished with the same laser

Efficient hard material machining

Depending on the process requirements, laser polishing achieves surface rates of ten to 100 cm2 per minute, which is almost on par with the surface rates of the preceding material ablation. “The combination of both processes with a laser in the same clamping operation enables companies to expand their range of services with existing USP lasers or to significantly accelerate the amortization of a new purchase,” said Saßmannshausen.

Above all, however, it is suitable for replacing mechanical processes for machining hard materials, thus putting an end to the sometimes immense tool wear involved in their manufacture. This not only reduces costs, but also specifically improves resource and energy efficiency in practice.

Source: optics.org