Tools made of hard materials and ceramics such as tungsten carbide are particularly wear-resistant. However, the tools used to manufacture them wear out all the faster – unless the tool is light. Researchers at Fraunhofer ILT have now developed a process chain that enables shaping and polishing of hard-material components using an ultra-short-pulse (USP) laser without changing the clamping setup.
Drills, milling cutters, rollers or punching dies made of ceramic hard materials not only have bite but also last significantly longer. As positive as their wear resistance is for service life in production, it is just as problematic in the manufacture of these tools. The tools used for shaping and surface finishing get worn down quickly when working on mixed carbide hard metals, cermets, and ceramics. Accordingly, wear is high when manufacturers rely on mechanical machining methods.
USP Lasers Work Where Mechanical Processes Reach Their Limits
This is different with ultra-short laser pulses. Even commercially available USP lasers with 20 to 40 watts of power can efficiently remove hard materials used in toolmaking. Where their highly energetic pulses of just a few picoseconds hit the surface, the material evaporates. Because this occurs at frequencies in the MHz range, laser ablation achieves area rates of up to 100 cm² per minute.
However, the potential of USP processing goes far beyond shaping ablation. Researchers at the Fraunhofer Institute for Laser Technology ILT in Aachen have developed a process chain in which the same USP laser performs both the shaping material removal and the subsequent polishing of tool surfaces. “The USP laser is a universal tool with which we can implement different processing steps, in some cases in the same setup,” says Sönke Vogel, Team Leader for 3D Structural Ablation at Fraunhofer ILT, who developed the process together with Astrid Saßmannshausen, Team Leader for Structuring of Transparent Materials.
The key to linking the process steps lies in laser parameterization. While material removal takes place at high pulse energy and low repetition rate, polishing uses the opposite setting. The USP laser introduces energy into the workpiece surface at pulse frequencies of up to 50 MHz. The energy accumulates, melting the top 0.2 to 2 micrometers. The material does not evaporate; instead, a molten film forms that smooths itself under surface tension and solidifies as it cools.
Surface properties can also be controlled through process management. “With USP laser polishing, for example, it is possible to smooth micro-irregularities while maintaining macroscopic structures,” explains Saßmannshausen. The laser process also allows complex 3D surfaces to be polished with micrometer precision. Selective polishing of specific areas is likewise possible, enabling localized adjustment of surface properties or polishing only where necessary, which saves time. USP polishing thus complements macro- and micro-laser polishing with an even more precise and locally applicable approach to surface finishing.
Efficient Process for Industrial Hard-Material Machining
Depending on process requirements, laser polishing achieves surface rates between 10 and 100 cm² per minute, nearly matching the rates of the preceding material removal. “Combining both processes with a single laser in the same setup enables companies to expand their offerings with existing USP lasers or significantly accelerate the amortization of a new investment,” says Saßmannshausen.
Above all, the approach is well suited to replacing mechanical machining methods in processing hard materials, putting an end to the sometimes immense tool wear involved in their manufacture. This not only reduces costs but also directly increases resource and energy efficiency. According to Saßmannshausen and Vogel, the potential of this combined process is far from exhausted. With faster polygon scanners, higher laser power, and larger laser spot sizes, area rates could be increased even further. Interested industrial partners are invited to join the Fraunhofer ILT research team in tackling the next optimization steps together.
