Quality improvement of laser-microstructured riblet geometries in forming tools for enhanced efficiency of injection-moulded fan impellers

With the aim of reducing air resistance and thus increasing the efficiency of industrial fans, this study investigates high-rate laser functionalization of complex 3D surfaces to integrate tailored riblets. It focuses on laser micromachining V-grooves into moulding tools to create microstructures on fan impeller surfaces. The riblets with spacings of 100 µm to 300 µm and depths of 50 µm to 150 µm are designed to optimise the air flow. Research shows that nano- and micro structured surfaces, mimicking shark skin, significantly decrease air resistance and energy consumption, especially for 3D streamlined bodies, positively affecting flow separation. By varying the size and shape of the riblets, different effects can be achieved on the textured surface. However, the design and application of riblets on rapidly rotating parts such as fan wheels is still a major challenge today. Ideally, riblet dimensions should change stepless according to the object's geometry, but common adhesive foils including the riblet coating do not meet this requirement. To overcome this challenge, microstructures were fabricated using direct laser writing with ultra-short pulsed laser radiation operating at a wavelength of 1030 nm on the mould. The primary objective of this research was to optimize the surface and shape quality of these microstructures by minimizing roughness, burr, and spatter occurrence. To achieve this, the laser fluence was systematically investigated and the effects of different pulse and line spacings were analysed. Results were quantitatively assessed through measurements of surface roughness, as well as ablated volume per energy and time, which indicate the efficiency and productivity of the laser process. These findings enhance industrial fan production and provide insights into optimizing laser based microstructuring processes for surface functionalization.