Advanced Design of Hierarchical Topographies in Metallic Surfaces by Combining Micro‐Coining and Laser Interference Patterning

Abstract

A new process idea to create hierarchical surface structures is based on the combination of micro‐coining and laser interference patterning. Micro‐coining already proved to be a high precision cold bulk metal forging process which allows for the production of small surface structures in the range of 20–200 µm while fulfilling high requirements related to the geometrical accuracy of those structures. In addition to that, laser interference patterning utilizes interfering laser beams from a pulsed solid state Nd: YAG laser to generate precisely defined surface topographies with a long‐range order on the micron‐scale. For the first time, initial results of a process combination consisting of micro‐coining and laser interference metallurgy to induce hierarchical surface structures will be presented. The results highlight the advantages of the sequence micro‐coining prior to laser interference patterning due to smaller defects in contrast to the inverted process cycle. Additionally, process limitations such as shadowing which may result from steep flank angles of the coined structures and surface roughness effects are discussed by the use of finite element simulations within this research work.

Multi-Scale Surface Texturing in Tribology—Current Knowledge and Future Perspectives

“…Generally speaking, almost every two texturing techniques can be combined to create multi-scale surface textures. Thereby, upon combining different texturing techniques, three factors have to be considered in particular: (i) the complexity of the individual processes and, hence, the overall effort for the texturing approach, (ii) the sequence of the texturing steps [54], and (iii) the respective size limitations of each method. Regarding tribologically effective surface textures, suitable texturing techniques are those which generate surface textures on significantly different scales.…”

“…In contrast, the shot blasted textures are with a surface roughness (Rq) of 450 nm much smaller, even though their exact dimensions are not given. Gachot et al and later Grützmacher et al combined micro-coining with laser surface texturing, specifically direct laser interference patterning (DLIP), to create multi-scale surfaces [48,49,54,70,72]. DLIP is a technique, which uses overlapping laser beams to modulate the laser intensity spatially by interference.…”

“…By applying this technique, multiple texture features can be created on the surface in a single laser shot [62]. Micro-coining is a fast process, which allows for the generation of high-quality textures in the range of 20-200 µm at low cost, while DLIP is a fast and versatile technique especially suited to create smaller textures with feature sizes between 200 nm and 30 µm [54]. It is shown that the process sequence is important for this combination.…”

Effects of Multi‐Scale Patterning on the Run‐In Behavior of Steel–Alumina Pairings under Lubricated Conditions

“…In order to coin high strength materials, like stainless steel (AISI 304), the workpiece needs to be heated up to reduce the flow stress, thus decreasing the load on the die. [22,23,27] Without this preheating, the tool stresses would become too high during the coining process, which could lead to tool damages. In Szurdak et al, the influence of the coining temperature on the maximum tool stress was studied by FEM simulations.…”

“…Thereby, the samples are first coined and subsequently superimposed by a cross-like laser pattern in order to prevent damaging of the laser pattern by the coining process. [27] …”