Layer-based laser ablation of three dimensional micro structured freeform surfaces has become of significant importance for technical applications such as biomimetic surfaces in recent years. In order to identify the optimum set of process parameters for a complex laser ablation operation, a design of experiments (DoE) study has been carried out with laser sources covering pulse durations regime of femtosecond (fs), picosecond (ps) and nanosecond (ns). The aim was to identify the optimum parameter set for achieving best surface roughness and, as a second criteria, for machining time to be reduced to a minimum. In a first step, rectangular pockets have been machined and a DoE based parameter variation was performed. In particular, the parameters wavelength (1030 nm, 515 nm, 343 nm), machining speed, laser power, and laser pulse duration (fs, ps, ns) have been modified. Surface roughness and ablated depth were measured and an optimum set of parameters was calculated. The results show that the ultraviolet laser type (343nm) has the best performance to achieve lowest surface roughness and with a laser pulse duration of 3445 fs reaches also the best ablation efficiency in relation to machining time. While machining speed and laser power have an almost linear influence on achievable roughness, laser pulse duration has a quadratic influence in relation to a global minimum on the surface roughness result. For the ablated depth, machining speed and laser power have an almost linear influence while laser pulse duration has a quadratic influence in relation to a global maximum.
Bio-inspired surfaces targeting functional characteristics such as anti-reflectivity, self-cleaning effects or a drag
reduction are of significant interest to industry. In this feasibility study, process chains for the mass production of so-called
shark skin structured surfaces are investigated. Due to their drag reduction properties, such bio-inspired surfaces
are of relevance to a number of applications in which particular aqua- and aerodynamic characteristics are required. The
design of the shark skin structure relies on a bio-mimetic analytical model to generate the 3D surface model necessary to
achieve the targeted surface functionality. The process chains presented combine laser ablation as a method for micro
structuring masters for high throughput replication employing injection molding. In particular, three different process
chains that rely on micro second (μs), nano second (ns) and pico second (ps) laser ablation systems to pattern mold
inserts were investigated. Then, these inserts were integrated into a tool for micro injection molding and replication trials
were carried out. The results show that all three laser sources can be utilized to create this kind of micro cavities. This
research indicates that these micro structures can be replicated successfully, but further work is required to optimize the
replication and laser structuring process.
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