Combination of short and ultrashort pulse laser processing for productive large scale structuring of 3D plastic mould steel

Surface functionality is an increasing and crucial factor for the success and acceptance of a product. Through structured surfaces, products can gain additional functions: for example, friction reduction in combustion engines and bearings or optimizing lighting efficiency in light-emitting diodes. Furthermore, not only technical properties but also optical and haptic functions can be generated by surface structuring. Especially in the area of consumer products, these functions determine essentially the product quality. The most common way to create surface functionality in mass production is replication processes via structured mold tools. Currently used manufacturing processes for tool structuring like photochemical etching are limited in precision (manual preparation and execution) and in flexibility (limited design). This is the reason why laser ablation with (ultra-) short laser radiation is becoming an increasingly important technology that is able to generate structure sizes in the range of several hundred nanometers to several hundred micrometers. In this paper, the possibility of combining nanosecond (ns) pulsed laser radiation with picosecond (ps) pulsed laser radiation for microstructuring is investigated. This approach promises an increase of the productivity of the manufacturing process, similar to the strategy of roughing and finishing in milling processes. Within a first laser process, the workpiece is pretreated by short nanosecond laser pulses and a large amount of the volume is removed. A second, following laser process using picosecond pulses is utilized to ablate the remaining volume and to finish the surface by fabricating precise microstructures. This combination brings the advantages of both processes together: (comparable) short processing time (short pulses = roughing) while achieving high precision (ultrashort pulses = finishing). Main research activities presented are different approaches for combination strategies, discussions about achievable and from industrial site acceptable processing times, and accessible surface qualities for the combined process.