The goal of the FAST project was to assess how recent galvoscanning system improvements could be used to improve the speed and/or quality of high-definition laser surface texturing processes. A fast gating mode and a faster / small aperture scan head were tested for an application where mould inserts needed to have a micropillar texture. SKF, end-user of this project, uses the mould inserts for the production of seals. The texture is used to change the properties and appearance of the seal. Achieving faster laser micro-milling processes means having to use a higher average laser power, which in turn generally requires one to use high scan speeds to avoid heat accumulation, which can have a negative effect on the surface quality or cause excessive melt, causing the definition of the texture to suffer. Surface texturing on a double-curved surface means the processing of the target surface needs to be split into small tiles, which can result in a low duty cycle when the scanner is spending a significant amount of time is on jumps and run-ins. A small aperture scan head with smaller / lighter scan mirrors can be used to reduce the time needed for run-ins / re-positioning. A high definition texture will often have many small features that. A fast process for making such textures requires a complex gating pattern where the laser needs to be rapidly and accurately toggled on and off, especially for high scan speeds. Ideally, the scan system control hardware should support laser output modulation at full speed that the laser hardware can handle (> 2 MHz).
Fast pixel mode for SCANLAB RTC5
A faster pixel output mode for the SCANLAB RTC5 control board was integrated and tested using scan speed of up to 6 m/s. This fast pixel mode allows scanning of straight lines while modulating / gating the laser at the full rate that the laser hardware is capable of (> 2 MHz). A hatch pattern stroke with many small line segments can be scanned in a single pass at high speeds without loss of texture definition.
Small aperture scan head with digital encoders The intelliSCANse® 10 is SCANLAB's smallest aperture scan head which features the digital encoder technology required for highly accurate laser micromachining. Compared to the intelliSCANde® 14 mm the tracking error / time lag is almost twice as small (0.11 ms vs 0.21 ms). Both scanners were tested, and the results confirm that for the same high accuracy the time spent on re-positioning (jumps) and accelerating (run-ins) can be halved when using the smaller aperture.
Mould inserts
Mould inserts for a bearing seal mould were textured using the improved scan system. The process used a relatively high scan speed (2 m/s) to avoid heat accumulation. Thanks to the fast and accurate gating the texture’s small features still have a high definition. The fast dynamics of the small 10 mm aperture scan head enable a relatively high duty cycle when processing small tiles (70–90 %).
Demonstrators
The developed technology was used to machine different pillar patterns in rings on balls made of stainless steel and cemented carbide, to be used for dissemination of the results. The picture shows a measurement of the texture on a steel demonstrator ball.
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