Adrian Hugh Alexander Lutey

Friction Stir Extrusion (FSE), Direct Extrusion (DE) and Indirect Extrusion (IE) are all valid processes for the production of round profiles. However, differences and similarities between them have yet to be analyzed by the scientific community, since with the same geometry, each technology instills specific properties to the extruded product. In this context, the present work proposes an in-depth analysis via QForm UK Finite Element Method (FEM) software of the effect that each process has on a AA6061 extruded wire. Various combinations of rotational speed (200, 400, 600 rpm), feed rate (1, 2, 3, 4 mm/s) and pre-heating temperature (450, 500°C) were analyzed to assess differences and similarities between FSE, DE and IE. The feedstock material for FSE was chosen to be powder, while a solid billet was used for conventional extrusion.

A data-driven optimization algorithm is described for maskless grayscale laser lithography (MGLL), providing effective correction for topography errors deriving from the non-linear response of the photoresist to exposure dose, proximity effects and sharp dose transitions near edges and vertices. The algorithm employs an artificial neural network (ANN) to represent the physical process, with the MGLL virtual photomask and its radial averages as input variables and the predicted surface topography as the output. Virtual photomask optimization is achieved by predicting the surface topography obtained with a given virtual photomask and implementing corrections based on the predicted error. An elaborate training model with a range of different surface features is employed to acquire a comprehensive dataset comprising approximately one million rows of data for training the ANN. Hyperparameter optimization with an independent test set sees greatest accuracy and ability to generalize achieved with a simple ANN comprising a Sigmoid activation function and a single hidden layer with 15 neurons. Optimized virtual photomasks are calculated for the training model and an ultrathin free-form micro-optical element (FFMO), with the average Euclidean distance between the experimental and target surfaces reduced from 3.6 μm with an experimental contrast curve to 1.0–1.2 μm with the optimization algorithm in a single build. The developed approach provides an effective, versatile and adaptable pathway towards first time right MGLL.

A hybrid approach based on laser texturing and surface coating for the combined modification of surface topography and chemistry has been proposed to provide a versatile approach for the development of functional surfaces. The experimental procedure comprised nanosecond pulsed laser texturing of AISI 304 stainless steel substrates followed by the deposition of thin (a) in the range 0.2–6.4 µm. Coatings were then deposited on laser-textured substrates to quantify the deposition effectiveness and the influence of the coating type and parameters on the resulting surface topography and chemistry. Sol–gel deposition was found to be more effective with a polymeric interlayer, improving adhesion between the coating and the textured surface; however, this also led to an increase in Sa of approximately 0.5 µm. Conversely, PE-CVD was effective in modifying the surface chemistry while inducing no measurable differences in surface morphology, effectively decoupling the texturing and coating processes. Analysis of the surface chemistry showed a higher concentration of silicon for PE-CVD than sol–gel deposition and therefore a more pronounced effect on the surface chemical composition.