A Process Optimization Strategy for Texturing 3D Surfaces Using Direct Laser Interference Patterning

Abstract

Due to its flexibility and adaptability, laser materials processing is used in various fields of applications, such as cutting, welding or surface modifications, breaking in several cases the limits of conventional processing methods. [1][2][3][4] Ultrashort pulsed laser modification enables the creation of microstructures for individual functionalities on almost every material. [5,6] For example, direct laser writing (DLW) or direct laser interference patterning (DLIP) are laser micromachining techniques that are capable to create surface structures with high resolutions down to μm-range. [7][8][9] Such microstructures enable the realization of unique surface properties such as hydrophobic or antibacterial characteristics as well as optimized tribological properties. [10][11][12] A particular challenge in laser surface functionalization is the adaptability to 3D freeform components, which has become a significant importance for technical applications in recent years. [13] Typical approaches that are being implemented in industry or research laboratories for treated 3D parts are for instance, Computerized Numerical Control (CNC) systems as well as robot systems, which are in some cases limited in accuracy (in particular the robot systems). [14,15] Further progress requires the adaption of texturing results to real parts with 3D shaped geometries.In this frame, the presented work herein examines the utilization of the DLIP technology in combination with a new hexapod positioning system and its influence on the uniformity of the produced microstructures. The main advantage of the new hexapod system is the high motion accuracy and repeatability as well as its simplicity to be combined with existing DLIP optical heads.The structures were fabricated using the DLIP technology. The used setup is illustrated in Figure 1a. To produce the line-like pattern geometry, two Gaussian laser beams were overlapped on the substrate at a certain angle (Θ). At the region where the beams overlap, a periodic intensity profile is produced which can be directly transferred to the materials surface by selective melting or ablation at the interference maxima positions. [16] The used system utilizes a solid-state Nd:YVO 4 laser (Edgewave PX200) emitting 1064 nm wavelength with 10 ps pulse duration and maximum output power of 100 W. The laser fluence was set to 1.21 J cm À2 and the spot diameter of the interference area was about 100 μm (irradiated spot on the sample). Further relevant processing parameters are the distance between the DLIP pixels which can be described by the overlap and the hatch distance (HD). For instance, Aguilar-Morales et al. mentioned that the HD has been identified as the most critical parameter for the homogeneity. [17] Additional information about the experimental setup has already been published in previous work. [18] The positioning of the samples were performed using a hexapod (Aerotech HEX500-350 HL) (see Figure 1a). The main advantages of this system are the flexible sample positioning with six degrees of fre...

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