Papers by Keyword: Micromachining

Abstract: Microstructure fabrication and chemical surface functionalization with low-surface-energy materials are the key steps to achieve hydrophobic surfaces with high water droplet contact angles (CA). In this work we employed wire Electric Discharge Machining (EDM) as a way to induce microstructure topography on stainless steel 304 coupons. The resulting topography was rendered hydrophobic using trichloro-1H,1H,2H,2H-perfluorooctyl silane (PFOTS) via gas phase deposition. The channels created by machining and PFOTS functionalization facilitate water condensation by increasing nucleation sites and enhancing droplet coalescence. The resulting surface is hydrophobic (CA~140^o) in contrast to the bare stainless steel 304, which is hydrophilic (CA~76^o).

Abstract: The work is devoted to the problem of controlled laser micromachining of materials surface layers. The problem of ablation products reverse deposition near the laser processing region is considered. Laser ablation products, in addition to direct interaction with laser radiation, significantly increase lifetime and temperature of laser-induced plasma torch, which leads to decrease in energy entering processing area, as a result of which not removal, but heating of coating material occurs. Ablated particles can be deposited on the processed samples surface, which causes distortions in recorded structure spatial geometry. The possibility of using an electrostatic filtration system is considered as a method for protecting treated surface.

Abstract: This paper demonstrates that 18 μm deep surface understating with a tolerance of 4.5 μm and a roughness Ra=0.4 μm can be produced to the required accuracy by electrochemical die-sinking if configured appropriately.Theoretical analysis shows that the bottom profile error can be presented as a superposition of the errors of surface alignment (non-parallel bottom) and shape (non-flat bottom). In this case, the alignment error accounts for a greater part of the size tolerance (3 μm out of 4.5 μm). This is why the attainment of desired accuracy revolves around the development, analysis, and assessment of ways to reduce this error.

Abstract: Titanium implants with porous surface arranged orderly were fabricated by micromachining through photolithography and chemical etching. The titanium discs were implanted into the canine mandible alveolar bone for 3 and 21 days, for animal experiments. Neogenetic bone was observed onto porous surface after 7 days‘ implantation. This result allows us to expect application of titanium with porous surface as biomaterials.

Abstract: Underwater laser machining process has been employed as an alternative process to ablate materials with minimum thermal damage. Though many studies provide comprehensive investigations to enable the understanding of laser-water-material interactions during the laser ablation process in water, the effect of water temperature on the ablation performance has not been revealed yet. To cope with this challenge, this paper presents the roles of water temperature on cut dimensions in the underwater laser micromachining of titanium alloy (Ti-6Al-4V). The effects of laser power, traverse speed and number of laser passes were also examined in this study, where groove width and depth were measured and analyzed. The experimental results showed that a deep cut can be produced by using slow traverse speed with multiple-pass technique. However, using too high laser power can cause a shallow cut due to the large formation of recast in the laser-ablated area. According to the findings of this study, the laser energy density of about 750 J/mm² can provide the deepest cut among the other conditions examined in this study.

Abstract: The current concept of grinding or abrasive machining involves the formation and removal of segmented strips of material termed chips from the surface of the solid. A novel cutting mechanism is hereby presented in this research study that suggests that the generation of chips from the surface does not occur but only a shearing process that splits material creating added surface features and textures in the silicon surface. This arises from the unique set of factors of abrasive grit size, thrust force, polishing speed, and polishing time that lead to phase transformations in the surface layers of the silicon wafers. Statistical analysis of the factor effects yielded results that show the surface roughness values, Ra and Rz, increasing without any appreciable change in the thickness of the silicon wafers. This can be attributed to the proposed cutting mechanism indicating that only in-plane surface shearing occurred due to the change of the silicon crystal structure from exhibiting brittle behavior to that of ductile mode of deformation. Moreover, experimental quantities of the specific energy for surface machining of silicon was calculated with an overall mean of 50.5 GPa. This is about 33% less than the currently accepted value and can be considered further evidence that polymorphic transitions to a softer material occurred rendering the surface layers more susceptible to longitudinal cutting deformation and fracture. A model based on the inverted spherical cap or spherical bottom geometry for the individual abrasive particle is also proposed, verified by a finite element method analysis simulation, that can mathematically describe this particular micromachining process.

Abstract: Sapphire is an attractive engineering material for the cover glass of smartphones and wristwatches because of its high hardness and resistance to corrosion, wear, and heat. However, the high rate of tool wear and brittle chippings around the holes are serious problems associated with drilling sapphire. To enhance the accuracy and efficiency of the drilling process on sapphire, this paper presents a novel tool-path strategy using helical milling along with various tool path patterns. Experimental results show that the proposed method successfully reduces brittle chippings around the holes.

Abstract: The aim of this paper is to review the recent developments conducted for the achievement of 3C-SiC‑based heterostructures compatible with MEMS applications. Indeed, the research activities engaged since years permitted to demonstrate that the defect density has an impact towards the Young’s modulus of sub-micron 3C‑SiC epilayers. We also gained knowledge about the stress relaxation mechanisms, targeting to master the stress gradient, as stress is a key parameter to consider MEMS applications.Based on these results, we investigated the elaboration of microstructures using 3C‑SiC/Si/3C‑SiC stacks on silicon substrates. Our first noticeable result was the elaboration of a (110)-oriented 3C‑SiC membrane on a 3C‑SiC pseudo-substrate, using the silicon epilayer as a sacrificial one. But the surface of the 3C‑SiC membrane was facetted and rough, which could hamper its use for the development of new MEMS devices. Then, with further improvements, we succeeded to master the growth of a (111)‑oriented 3C‑SiC epilayer. This feature led to a drastic reduction of the roughness in comparison with the (110) orientation. Actually, using the same experimental protocol than previously, we succeeded to complete a (111)‑oriented 3C‑SiC membrane with a RMS roughness limited to 9nm. Such an optimized structure could be the starting point for the achievement of new MEMS devices operating in harsh environment or for medical applications benefiting of the 3C‑SiC biocompatibility

Abstract: A technique for ordered fabrication of periodic freestanding micro/nanostructures on the crystalline germanium (Ge) <100> surfaces with 1064 nm wavelength ultrashort laser pulses under ambient conditions is presented. The laser radiation fluence used for obtaining the structures is close to the melting threshold (0.1 J/cm²) of Ge. The dimensions of structures range from hundreds of nanometres to a few microns. The orientation of the periodic surface structures depends on laser beam polarization direction. Arrays of structures are formed in rows parallel to the sample movement direction for samples machined with s-polarized laser pulses, but formed in the direction perpendicular to the movement for p-polarized pulses. The structures are fabricated under variable temperatures on sample surface owing to the changed interference between incident and reflected laser beams. A micro-Raman analysis of the processed surfaces shows a minor change in the spectral intensity as compared to the unprocessed surface and the material retains its crystallinity after laser irradiation.

Abstract: This research develops a hybrid micromanufacturing technique by combining micromilling and electrochemical micropolishing to fabricate extremely smooth surface finish, high aspect ratio, and complex microchannel patterns. Milling with coated and uncoated ball-end micromills in minimum quantity lubrication is used to remove most materials to define a channel pattern. The milled channels are then electrochemically polished to required finish. A theoretical model accurately predicts surface finish in meso-scale milling, but not in micro-scale milling due to size effect. Electrochemical polishing using an acid-based electrolyte is applied to repeatedly produce stainless steel microchannels with average surface finish of 100 nm when measuring across grain boundaries and 10 nm within a single grain.