Micro-machined Surface Research Articles

Investigation of micro-electro-discharge machining process parameters during machining of M2 hardened die-steel

Micro-electro-discharge machining (micro-EDM) is a well-known micromachining method to create microstructures on hard-to-cut materials. To further exploit the capability of micro-EDM, the present research work investigates the effect of various important micro-EDM process parameters on the material removal rate (MRR), tool wear rate (TWR), and overcut (OC) during micro-cavity machining of M2-hardened die-steel. A Taguchi experimental design was used to study the effects of three process parameters namely pulse-on-time (Ton), peak current (Ip), and gap voltage (Vg). The experimental results showed that the most influencing process parameter in the present experimental investigation is peak current, Ip followed by pulse-on-time, Ton and gap voltage, Vg. Furthermore, a recent and effective method i.e. Measurement of Alternatives and Ranking according to COmpromise Solution (MARCOS) has been successfully employed to determine optimal process parametric combination for micro-EDM process to achieve maximum MRR and minimum TWR and OC during machining of micro-cavity on M2-hardened die-steel. From the present research investigation, the optimal micro-EDM process parametric combinations obtained for higher MRR, lower TWR and OC are found as 1 A of peak current, 30 μs pulse-on time and gap voltage of 60 V. Furthermore, through various scanning electron microscope micrographs of micro-cavities and micro-machined surfaces, analysis has been done to find out the micro-cavity with best geometrical accuracy and surface feature to validate the best and most ideal combinations of micro-EDM input parameters for micromachining operations. The results of this study show that micro-EDM is a promising process for machining M2-hardened die-steel. The optimization of process parameters using the MARCOS methodology can further improve the machining efficiency and accuracy of micro-EDM.

The Effect of Cutting Parameters on Surface Quality and Corrosion Resistance of Micro-machined Surfaces of 7075 Aluminum Alloy

The Effect of Cutting Parameters on Surface Quality and Corrosion Resistance of Micro-machined Surfaces of 7075 Aluminum Alloy

Random, aligned and grassy: Bioactivity and biofilm analysis of Zirconia nanostructures as dental implant modification

Zirconium (Zr)-based implants are rapidly gaining popularity due to their excellent physical, mechanical and biological properties. While Zr-based dental implants have shown promising outcomes, their performance may be suboptimal, especially in compromised conditions. To address this, conventional Zr implants have been modified via physical, chemical and biological means to augment cellular functions to achieve enhanced osseointegration, soft-tissue integration and local therapy. In this study, we fabricated controlled ZrO2 nanostructures (ZONs), including aligned nanopores, random nanopores and nanograss, on clinically relevant micro-machined and rough Zr surfaces via optimized electrochemical anodization. In-depth surface topographical and chemical characterization was performed to confirm the formation of ZONs. Further, the bioactivity performance of ZONs was investigated in vitro using primary human osteoblasts, and the effect on salivary polymicrobial biofilms was explored. The findings revealed that nano-engineered Zirconia augments the activity of osteoblasts without increasing biofilm formation. Anodized nano-engineered Zirconia implants are proposed as potential next-generation dental implants, featuring enhanced healing properties without promoting biofilm formation.

Effect of heat treatment process on the micro machinability of 7075 aluminum alloy

This work aims to investigate the effect of heat treatment process on the micro machinability of 7075 aluminum alloy,7075 aluminum alloy was treated with T6, T73 and RRA.T6 single-stage aging process is 120 °C × 24 h; T73 two-stage aging process is 140 °C × 8 h + 180 × 12 h; retrogression and reaging (RRA) process is 120 °C × 16 h + 190 °C × 10min + 160 °C × 30 h. Finite element simulation and single-factor testing are used to examine how different heat treatment processes and different cutting parameters affect the cutting force, surface roughness, surface quality, and residual stress of 7075 aluminum alloy during micro machining.Under all three heat treatment processes, the cutting force of 7075 aluminum alloy increases with increasing cutting speed and cutting depth, but it is less affected by feed rate. Under the same cutting parameters, the cutting force of 7075 aluminum alloy under the three heat treatment processes is T73 > T6 > RRA. Under all three heat treatment processes, the surface roughness of 7075 aluminum alloy is negatively correlated with cutting speed and cutting depth, but positively correlated with feed rate. In the meantime, the micro-machined surface quality of 7075-RRA aluminum alloy is worse than that of 7075-T73 and 7075-T6 aluminum alloy. As cutting speed and cutting depth increase, the residual stress of 7075 aluminum alloy displays a typical “ladle” profile under all three heat treatment processes. When cutting speed changes, the machined surface residual tensile stress of 7075 aluminum alloy changes in much the same way under all three heat treatment processes. When cutting depth changes, the residual tensile stress of 7075 aluminum alloy under the three heat treatment processes is T73 > RRA > T6.

Femtosecond Laser Machining of Flexible Printed Circuit Boards

As the demand grows for high-density electronic components and highly integrated printed circuit boards, femtosecond laser micromachining provides unique opportunities for creating fine conductive tracks and patterns on flexible printed circuit boards (FPCBs) without the use of a mask. Here, the effects of femtosecond laser power and pulse frequency on micromachining depth, surface roughness and copper content of the machined zone were investigated, and optimum laser parameters, i.e., laser power 280 mW and pulse repetition frequency 39.5 kHz, were achieved with the help of a 3D optical profilometer and energy dispersive spectroscopy (EDS). On this basis, a single conductive track with varying widths and two parallel conductive tracks with different widths/spacings were micromachined on FPCBs without noticeable substrate damage. The results indicate that a single conductive line with a feature width as small as 25 µm can be achieved, and two parallel copper tracks can be created with no evidence of the presence of copper residues between the tracks when the pre-defined spacing is no less than 45 µm . In order to achieve high micromachining accuracy, look-up tables that correlate measured widths/spacing of conductive tracks with the pre-defined ones were built.besides, machining conductive tracks with 135 degree corner is possible and by selecting optimized processing parameters. Finally, a driving circuit for a display panel was micromachined on FPCBs using femtosecond laser, and an average micromachining accuracy of 0.67 μm was achieved. This work will be quite useful for creating high density and precision patterns on FPCBs using femtosecond laser.

STATE OF THE ART OF SURFACE TEXTURING FOR BIOTRIBOLOGY APPLICATIONS

Surface texturing can be defined as a technique that consists of creating micro cavities in the surface of a material. There are different texturing techniques such as chemical etching, electromechanical micromachining, diamond embossing, electric discharge, pellet-pressing and laser surface, the last being the most common. For years, these surface texturing techniques have been used in tribological applications because microcavities can store oils or fluids and constantly lubricate the surfaces that are subjected to wear; they can also be used to trap wear particles (debris) that would otherwise act as abrasive particles (three body abrasive wear). This literature review seeks to analyse and compare the advantages that the use of surface texturing techniques can offer in reducing the wear of prosthetic components and therefore lengthening their useful life, to provide a better quality of life to patients. The results of this review showed a growing interest in the scientific community in the use of surface texturing for biotribogical applications, using to a greater extent the Laser Surface Texturing (LST) technique and the surface pattern composed by dimples.

Fabrication and characteristics of VO x microbolometer integrated into gold black absorbing layer

Using vanadium oxide (VO x ) thin film as active layer, microbolometer with gold black absorber was fabricated due to the high mid-infrared (8-14μm) absorption property of gold black. This paper describes the design and fabrication of microbolometer with micromachining surface technology. The characteristics of the device are investigated. The detector performance exhibits maximum detectivity of 1.96 × 108cmHz1/2/W at 17 Hz with 8.8μA.

Ultrafast laser micromachining the ultra-low expansion glass-ceramic: Optimization of processing parameters and physical mechanism

To fulfill the precise requirements of laser gyroscope for inertial navigation, using the mean surface roughness, taper angle and circularity degree as indicators, we optimize the processing parameters about ultrafast laser micromachining a commercial ultra-low expansion glass-ceramic (ULGC). Furthermore, through careful characterizations, we identify the sequential appearance of photo-darkening, crystalizing, melting, foaming and vaporizing regions during the interactions of ultrafast laser with ULGC. Especially, the foaming region is identified to effectively mediate the thermal stress at the interfaces between different regions. Originated from the Gaussian distribution of energy, poor processing quality by a Gaussian beam is mainly ascribed to the formation of various regions. By using a Bessel beam, higher surface quality could be obtained due to the possibility of the occurrence of only a foaming region in irradiated regions. This discovery gives us an important clue to optimize processing parameters to obtain high-quality ultrafast laser micromachining surface.

Materials Selection Approaches and Fabrication Methods in RF MEMS Switches

A state of the art review on Radio Frequency Micro-Electromechanical Systems (RF MEMS) capacitive switches is reported by considering two key aspects: (1) materials selection approaches for improving performance, and (2) fabrication methods used in capacitive MEMS switches. The beam and dielectric materials used in capacitive MEMS switches and the performance achieved through them are reviewed and reported by a rigorous literature survey. Further, materials selection approaches for the beam membrane and the dielectric layer are discussed using Ashby’s methodology, and other associated methods based on it, which uses material indices to evaluate the performance of a switch. Performance indicators for the beam materials selection are the pull-in voltage, RF loss, thermal residual stress, contact resistance, thermal conductivity, and maximum displacement, whereas the hold-down voltage, dielectric charging, leakage current, heat dissipation, capacitance ratio, and stability are performance indicators in dielectric materials selection. MEMS switch fabrication can be achieved through bulk micromachining processes and surface micromachining processes, but the surface micromachining process has been preferred over the last few decades. The fabricated MEMS switch components can be integrated using a monolithic complementary metal oxide semiconductor–micro-electromechanical systems (CMOS-MEMS) process for the realization of applications in sensors, resonators, amplifiers, phase shifters, and MEMS satellite vehicles for space applications. CMOS-MEMS monolithic fabrication is discussed further with the help of fabrication process involved and the process technology. The TSMC-CMOS 0.35 $$\upmu \hbox {m}$$ technology is one of the leading technologies in CMOS-MEMS fabrication and is mainly used.

Single image detecting enhancement through scattering media based on transmission matrix with a deep learning network

Random scattering media that scatters incident light waves for optical diffraction-limit break imaging has important application prospects and significance in biomedical imaging, lithography micromachining and nanomaterial surface shape analysis. However, the transmission matrix, which represents the relationship between incident and output pixels in monochromatic image detecting through scattering media, suffers from severe noise and limited resolution in the reconstructed image owing to its imaging characteristics. In this study, we propose a deep convolution neural network to achieve single image enhancement effects, including denoising and super-resolution on images that are reconstructed by a monochromatic transmission matrix. We demonstrate significantly higher quantitative scores in peak signal-to-noise, SSIM and correlation coefficient compared to conventional methods. We further show that our method is effective for the transmission matrix-based reconstruction operator for both phase conjugation and pseudo-inversion.

Combining microcavity size selection with Raman microscopy for the characterization of Nanoplastics in complex matrices

Nanoplastic particulates (pNP) are widely considered as being potentially harmful to the environment and living organisms while also being technically difficult to detect and identify in the presence of biological matrices. In this study, we describe a method for the extraction and subsequent Raman analysis of pNP present in the tissues of salt-water mussels. The process combines a step of enzymatic digestion/filtering to eliminate the biological matrix with a detection/identification procedure, which uses a micro-machined surface, composed of arrays of cavities with well-defined sub-micron depths and diameters. This sensor surface, exploits capillary forces in a drying droplet of analyte solution to drive the self-assembly of suspended nanoparticles into the cavities leaving the individual particles isolated from each other over the surface. The resulting array, when analysed using confocal Raman microscopy, permits the size selective analysis of the individual sub-micron pNP trapped in the cavities structure.

Roughness characterization and formation mechanism of abrasive air jet micromachining surface studied by power spectral density

Roughness of abrasive air jet micromachining surface has a significant influence on electro-osmotic flow characteristics, optical properties and adhesion properties. The characterization of surface roughness based on power spectral density approach is studied. The formation mechanisms of surface topography are analyzed. The influence of process parameters on the roughness of abrasive air jet micromachining surface is discussed. The results show that surface profiles with close values of usual roughness parameters can be distinguished by power spectral density curves. The power spectral density curves can be classified into four categories based on the marked knee points on spatial frequency of 0.01 μm−1 and 0.1 μm−1 approximately. Power spectral density curve can be divided into three regions, namely, low frequency region, intermediate frequency region and high frequency region. The roughness of low frequency region and the roughness of intermediate frequency region play dominant roles in the surface roughness, while the contribution of the roughness of high frequency region is negligible. The low frequency region is associated with the overlap of craters. The intermediate frequency region is associated with the indentation removal mechanism and edge cutting mechanism. The high frequency region is associated with micro-dents removal. The roughness of low frequency region increases with an increase in air pressure, while it decreases with an increase in standoff distance. The roughness of low frequency region decreases firstly and then it increases with an increase in nozzle traverse speed. The roughness of intermediate frequency region increases firstly and then it decreases with an increase in air pressure, standoff distance and nozzle traverse speed. The Rq increases with an increase in air pressure, while it decreases with an increase in standoff distance. The Rq decreases firstly and then it increases with an increase in nozzle traverse speed.

Rheological study of the developed medium and its correlation with surface roughness during abrasive flow finishing of micro-slots

Abrasive flow finishing (AFF) is an advanced finishing process employed for finishing macro- to micro-features of workpieces. Finishing improves the functioning of the components by reducing their surface roughness. AFF process uses a polymer-based flexible medium containing abrasive particles as a finishing tool. Medium used during the AFF process plays a vital role in deciding the final surface roughness on the workpiece surface. It is the medium properties in combination with AFF input parameters that decide the end surface roughness. Micro-features on the components are mostly machined with the help of processes involving thermal energy (electrical discharge micro-machining, laser beam micro-machining). This leads to the formation of hard recast layer on the micro-machined workpiece surface. Component size and hardness of the recast layer possesses a great challenge to the finishing processes. In the current article, an economic viscoelastic medium is developed for the finishing of micro-features and its detailed rheological study is carried out. Later, experimental study of the AFF process during the finishing of micro-slots (440 ± 10 µm width) in surgical steel is performed. Developed medium successfully finishes the micro-slots with an initial surface roughness of 3.54 µm to a final surface roughness of 0.21 µm (94.07% reduction in surface roughness).

Investigation of the Effect of End Mill-Geometry on Roughness and Surface Strain-Hardening of Aluminum Alloy AA6082.

Micro-milling is a promising technology for micro-manufacturing of high-tech components. A deep understanding of the micro-milling process is necessary since a simple downscaling from conventional milling is impossible. In this study, the effect of the mill geometry and feed per tooth on roughness and indentation hardness of micro-machined AA6082 surfaces is analyzed. A solid carbide (SC) single-tooth end-mill (cutting edge radius 670 nm) is compared to a monocrystalline diamond (MD) end-mill (cutting edge radius 17 nm). Feed per tooth was varied by 3 μm, 8 μm and 14 μm. The machined surface roughness was analyzed microscopically, while surface strain-hardening was determined using an indentation procedure with multiple partial unload cycles. No significant feed per tooth influence on surface roughness or mechanical properties was observed within the chosen range. Tools’ cutting edge roughness is demonstrated to be the main factor influencing the surface roughness. The SC-tool machined surfaces had an average Rq = 119 nm, while the MD-tool machined surfaces reached Rq = 26 nm. Surface strain-hardening is influenced mainly by the cutting edge radius (size-effect). For surfaces produced with the SC-tool, depth of the strain-hardened zone is higher than 200 nm and the hardness increases up to 160% compared to bulk. MD-tool produced a thinner strain-hardened zone of max. 60 nm while the hardness increased up to 125% at the surface. These findings are especially important for the high-precision manufacturing of measurement technology modules for the terahertz range.

Laser beam machining of zirconia ceramic: An investigation of micro-machining geometry and surface roughness

Micro-machining of dental ceramics namely as zirconium oxide is carried out through laser beam machining. Micro-channels of different sizes are fabricated under different laser parameters. The laser process performance is evaluated by considering the geometrical and quality responses associated with micro-channels. Laser intensity, pulse frequency, scanning speed and layer thickness per laser scan are opted as the influential controlling parameters. Geometrical characteristics of micro-channels include upper width (WU), lower width (WL), depth (D), taper angle of micro-channel’s sidewalls at right side (θR), and taper angle at left side (θR ). Quality of the machined micro-channels is evaluated by means of surface roughness (Ra of the bottom surface. Effects of each of the laser parameters on each of the geometrical and quality responses are studied in order to get the influential trends of laser parameters. SEM analysis is further performed to assess the micro-details of machining results. The results reveals that the shape and size of micro-channel are very sensitive to the variation in laser parameters. Two types of micro-channels shapes are obtained having V-shaped and U-shaped cross-sections. Furthermore, it is quite challenging to achieve the micro-channels with reasonable amount of lower width (WL).

Scraping force characteristics of frost formed on vertical cooling surfaces having different structures and wettability

Frost formation and deposition on cooling surface inevitably cause serious damage as well as economic losses. To establish effective technologies for removing frost mechanically, the scraping force required to remove frost on vertical cooling surfaces was studied experimentally. The four types of copper surfaces investigated were a flat surface, micro-machined surface, laser fabricated surface, and hydrophobic surface. The results revealed that the scraping force increased with frost formation. With a distance less than 0.2 mm, the scraping force seems to increase exponentially. The surface structure and wettability considerably affect the freezing process and the growth of the initial frost crystals. The growth of frost could be delayed by 30% by micro-machining the cooling surface, which made the frost layer looser and easier to scrape off. The scraping force of the laser fabricated surface was approximately four times that of the hydrophobic surface at a height of 0.01 mm.

Complex Micro Machining of an Injection Mold Surface for a Conductive Polymeric Composite Product

Hydrogen and fuel cell technologies were identified amongst new renewable energy technologies which contribute strongly to mitigating climate change. Important research activities were directed to the injection molded bipolar plates made by conductive polymeric composites. The mold surface quality can help obtaining better conductivity. In this paper are presented the experiments regarding complex micro-machining of the surfaces of an injection mold for a conductive polymeric composite product by micro-milling and for finishing and cleaning by laser beam micro-machining. The laser ablation consists in removing material from a solid surface by irradiating it with a laser beam, in successive layers in order to achieve complex geometries with accuracy of about micrometres. Injection moulding experiments evidenced the very good replication of the micro-machined surface pattern.

Floor surface roughness model considering tool vibration in the process of micro-milling

The high quality of the micro-machined surface is the basic for promoting micro-milling technology, so the understanding of surface forming mechanism and the relationship between micro-milling parameters and the surface roughness are important. In this paper, we establish a comprehensive floor surface model which predicts the surface roughness of the grooves under different cutting parameters and tool geometrical parameters in micro-milling. This model is based on the movement and vibration of micro-end mill and the forming of workpiece surface governed by elastic recovery and tool geometry. The kinematics of micro-milling operations directly affects the topography and is calculated by the trochoidal trajectory formula. The relative vibration of the tool to the workpiece, which affects the ultimate movement trajectory, is measured through experiments. Besides, the elastic recovery and the minimum cutting thickness included in the surface generation procedure are calculated based on the microscopic mechanics of strain gradient theory. Finally, experiments of slot micro-milling under different cutting parameters validate the accuracy of the surface prediction model.

In-Plane Optical Beam Collimation Using a Three-Dimensional Curved MEMS Mirror

The collimation of free-space light propagating in-plane with respect to the substrate is an important performance factor in optical microelectromechanical systems (MEMS). This is usually carried out by integrating micro lenses into the system, which increases the cost of fabrication/assembly in addition to limiting the wavelength working range of the system imposed by the dispersion characteristic of the lenses. In this work we demonstrate optical fiber light collimation using a silicon micromachined three-dimensional curved mirror. Sensitivity to micromachining and fiber alignment tolerance is shown to be low enough by restricting the ratio between the mirror focal length and the optical beam Rayleigh range below 5. The three-dimensional curvature of the mirror is designed to be astigmatic and controlled by a process combining deep, reactive ion etching and isotropic etching of silicon. The effect of the micromachining surface roughness on the collimated beam profile is investigated using a Fourier optics approach for different values of root-mean-squared (RMS) roughness and correlation length. The isotropic etching step of the structure is characterized and optimized for the optical-grade surface requirement. The experimental optical results show a beam-waist ratio of about 4.25 and a corresponding 12-dB improvement in diffraction loss, in good agreement with theory. This type of micromirror can be monolithically integrated into lensless microoptoelectromechanical systems (MOEMS), improving their performance in many different applications.

Scaffold design for artificial tissue with bone marrow stem cells

ObjectiveThe aim of this study was to test polymeric materials (collagen, fibrin, polyimide film, and polylactic acid) for single- and multi-layer scaffold formation. Materials and methodsIn our study, we used rabbit bone marrow stem cells (rBMSCs) and human mesenchymal stem cells (hMSCs) with materials of a different origin for the formation of an artificial scaffold, such as a collagen scaffold, fibrin scaffold produced from clotted rabbit plasma, electrospun poly(lactic acid) (PLA) mats, polyimide film (PI), and the combination of the latter two. Cell imaging was performed 3–14 days after cell cultivation in the scaffolds. Time-lapse imaging was used to determine hMSC mobility on the PI film. ResultsCell incorporation in collagen and clotted fibrin scaffolds was evaluated after 2-week cultivation in vitro. Histological analysis showed that cells penetrated only external layers of the collagen scaffold, while the fibrin clot was populated with rBMSCs through the entire scaffold thickness. As well, cell behavior on the laser micro-structured PI film was analyzed. The mobility of hMSCs on the smooth PI film and the micro-machined surface was 20±2μm/h and 18±4μm/h, respectively. After 3-day cultivation, hMSCs were capable of spreading through the whole 100±10μm-thick layer of the electrospun PLA scaffold and demonstrated that the multilayer scaffold composed of PI and PLA materials ensured a suitable environment for cell growth. ConclusionsThe obtained results suggest that electrospinning technology and femtosecond laser micro-structuring could be employed for the development of multi-layer scaffolds. Different biopolymers, such as PLA, fibrin, and collagen, could be used as appropriate environments for cell inhabitation and as an inner layer of the multi-layer scaffold. PI could be suitable as a barrier blocking cell migration from the scaffold. However, additional studies are needed to determine optimal parameters of inner and outer scaffold layers.