Machining Characteristics of Electrochemical Polishing Using Ultrasonic Vibration for Nanoscale High Surface Quality.

This study demonstrates a method to improve the surface quality by adding artificial vibration to the electrolyte in electrochemical polishing (ECP, electropolishing). ECP is a typical non-contact surface polishing process that has been used to improve surface quality without leaving any of the mechanical scratch marks that can arise when applying mechanical processes. ECP can polish work material via electrochemical dissolution between the surfaces of an anode and a cathode, and irregular defects are generated on the surface by impurities and bubbles generated during machining. This study confirms that our novel ECP method yields improved results over conventional ECP based on experiments using vibration electrochemical polishing (VECP) with ultrasonic vibrations. VECP minimizes nanoscale surface defects, improves surface roughness, makes it possible to quickly remove materials at nanoscale by increasing the material removal rate (MRR). Under high current density, where the electrochemical relatively reaction is active, value of the current is increased when ultrasonic vibration is added. The localized roughness of the work material was measured by atomic force microscopy (AFM) according to various electrical conditions. In addition, we also compared the overall surface quality and productivity to those obtained by conventional ECP.

Fabrication of Superhydrophobic Surface with Curved Grooves Using High Power Diode Laser.

Most studies on hydrophobic surfaces processed by lasers rely on the use of pico- or femtosecond lasers. However, in industrial application, the fabrication methods using pico- or femtosecond lasers have the disadvantages of high cost and low efficiency In this study, we tried to fabricate hydrophobic surfaces using a high-power general-purpose diode laser. We have fabricated various micro/nano hierarchical structures for aluminum (Al5052) surface using laser groove processing technology. The surface of laser ablated micro structure is decorated with nano roughness, resulting in micro/nano hierarchical structure. Specimen with curved grooves are fabricated, and the correlation of wettability characteristics with spaces, widths, and curvature radii of grooves are presented. It was found that the higher contact angle was formed with a decrease of the curvature radius. We have also fabricated specimens with various micro-wavy surface pattern. The water droplets on the micro-wavy pattern kept the spherical shape with a high contact angle of 165 degrees or more.

A Study on Focused Ion Beam (FIB) Milling Machining and Fabrication Technology of Nano-Scale Diamond Tool for Machining Fine-Patterns in a Free-Form Surfaces.

Recently, the technology of the industry has been increasing for diffractive optical elements, holograms, optical components, and next-generation display components. The advanced high value-added industry is designing fine patterns on ultra-precision optical components and applying them to various industries. In the case of the ultra-fine pattern, a contact-type machining technique is required because it requires a precise pattern in nano-scale units. In this paper, the fabrication technology of ultra-precision diamond which is essential in the ultra-precision processing technology was suggested. The material used in the experiment was a single-crystal diamond tool (SCD), and the equipment for machining the SCD used a focused ion beam (FEI COMPANY, system Nova 600) equipment. The back fire method was applied without metal coating in order to carry out the process study and the focused beam of 30 keV Ga+ ions were carried out processing for various fabrication of diamond cutting tools. As a result of applying the backfire method through the process experiment, the cutting edge width of the ultra-precision diamond tool was verified 275 nm.

Cold Tribo-Nanolithography on Metallic Thin-Film Surfaces.

This paper demonstrates a modified tribo-nanolithgraphy (TNL), micro- to nanometer scale mechanical machining processes, on metallic thin film surfaces which have poor machinability in micro scale under several mN normal loads. TNL is one of the promising atomic force microscopy (AFM)-based lithography processes which is more effective fabrication technology, as compared to conventional photolithography due to its relatively simple processes, high resolution, short processing time, and low cost. We propose ultra-precision machining at sub-0 °C temperatures using a lab-made micro polycrystalline diamond (PCD) tool on a retrofitted piezo stage with a Peltier device. The workpiece, located on the stage, is cooled artificially, and a normal load of several mN is applied by a micro PCD tool for micro scale machining processes. The machining results indicated considerably different machinability when the work was performed at sub-0 °C, as opposed to the ambient surface temperature, due to the changed mechanical characteristics of surface by the forced cooling of the workpiece. Although the normal load, machining speed, and machining area remained constant, the width and depth of machined grooves are significantly increased at sub-0 °C temperature conditions. In addition, we analyzed the TNL characteristics when machining with the PCD tool in four different machining directions. The mechanical surface properties, surface topography, scanning electron microscope (SEM) images, chip formation and other physical properties are investigated for more discussions.

Anisotropic Wetting Characteristics of Biomimetic Rice Leaf Surface with Asymmetric Asperities.

Rice leaf surface has known as having functional performances such as self cleaning and antifouling as well as directional flowing due to a unique micro structure with groove. In this study, we investigated the effects of asymmetrical cone protrusions on the surface of droplet flow through the contact angle and contact angle hysteresis of the droplet. First, static and dynamic contact angles of droplet on the rice leaf are measured. We found that the rice leaf surface has a directional flow characteristic through the difference of the contact angle hysteresis with flow directions. We also fabricated the rice leaf-like surfaces with asymmetric asperities along microgrooves using rapid prototyping technique and evaluated anisotropic wettability properties for the produced biomimetic surfaces. The experimental results show that the direction of the micro asperity tip relative to the droplet flow and its inclined angle has a very important influence on the anisotropic flow. This research can help to clarify the anisotropic wettability by the surface structure.

A Study on Proposal of E-Beam Drilling Machining Criterion by Using on Vaporized Amplification Sheets in a High-Power Density Electron Beam.

As the consumer market in the mold, automation and aerospace industries grows, the demand for laser machining using on electron beam drilling. To enhance the machinability and productivity of the e-beam (electron beam), we want to develop a vaporized amplification sheet. The e-beam was used to mainly utilize for polishing, finishing, welding, a lithography process etc. However, the electron beam drilling machine does not develop in the country because it is difficult to make high power density and vaporized amplification sheets. The vaporized amplification sheets with fine particles are one of the essential factors and decided the quality of machined micro holes according to the macromolecule. So, this paper considers the preparation process of vaporized amplification sheets and the analysis of macromolecule for improving the electron beam processability and machinability efficiency. Also, we analyzed process conditions for the optimization of the electron beam machining process.

Study on Platinum Coating Depth in Focused Ion Beam Diamond Cutting Tool Milling and Methods for Removing Platinum Layer.

In recent years, nanomachining has attracted increasing attention in advanced manufacturing science and technologies as a value-added processes to control material structures, components, devices, and nanoscale systems. To make sub-micro patterns on these products, micro/nanoscale single-crystal diamond cutting tools are essential. Popular non-contact methods for the macro/micro processing of diamond composites are pulsed laser ablation (PLA) and electric discharge machining (EDM). However, for manufacturing nanoscale diamond tools, these machining methods are not appropriate. Despite diamond's extreme physical properties, diamond can be micro/nano machined relatively easily using a focused ion beam (FIB) technique. In the FIB milling process, the surface properties of the diamond cutting tool is affected by the amorphous damage layer caused by the FIB gallium ion collision and implantation and these influence the diamond cutting tool edge sharpness and increase the processing procedures. To protect the diamond substrate, a protection layer-platinum (Pt) coating is essential in diamond FIB milling. In this study, the depth of Pt coating layer which could decrease process-induced damage during FIB fabrication is investigated, along with methods for removing the Pt coating layer on diamond tools. The optimum Pt coating depth has been confirmed, which is very important for maintaining cutting tool edge sharpness and decreasing processing procedures. The ultra-precision grinding method and etching with aqua regia method have been investigated for removing the Pt coating layer. Experimental results show that when the diamond cutting tool width is bigger than 500 nm, ultra-precision grinding method is appropriate for removing Pt coating layer on diamond tool. However, the ultra-precision grinding method is not recommended for removing the Pt coating layer when the cutting tool width is smaller than 500 nm, because the possibility that the diamond cutting tool is damaged by the grinding process will be increased. Despite the etching method requiring more procedures to remove the Pt coating layer after FIB milling, it is a feasible method for diamond tools with under 500 nm width.