Keita Shimada

Fabrication of microstructures on RB-SiC by ultrasonic cavitation assisted micro-electrical discharge machining

Ultrasonic cavitation assisted micro-electrical discharge machining was used to fabricate microstructures on reaction-bonded silicon carbide. To aid the removal of debris from the machining gap and to obtain a good surface finish, carbon nanofibers were added into the dielectric fluid. The suspension of carbon nanofibers in the dielectric fluid and the cavitation bubble effect induced by the vibration of the dielectric fluid proved to be effective in reducing the deposition of tool material on the workpiece surface. The tool material deposition rate was found to be significantly affected by the vibration amplitude and the distance between the oscillator and the workpiece. With a hemispherical electrode and inclined workpiece, high accuracy micro-dimples could be obtained within a short time. A nanometer-level surface finish was successfully obtained on a hard-brittle RB-SiCmoldmaterial.

Effect of Electrorheological Fluid Assistance on Micro Ultrasonic Machining

Ultrasonic machining (USM) is an effective machining method for hard brittle materials. In the USM process, the slurry is supplied to the gap between the ultrasonic vibrating tool and the workpiece. Materials are removed by the accumulation of small brittle fractures made by the impacts of abrasive grains. In a previous study, we proposed electrorheological fluid (ER fluid) assisted-USM, and the effect of ER fluid-assisted USM was confirmed practically by machining precise micro-holes and micro-grooves on hard brittle materials. In the present paper, in order to confirm the effect of ER fluid assistance for micro USM in more detail, the behavior of abrasive grains in the machining area is observed. The effect of dielectrophoretic force acts on the abrasive grains and the effect of using ER fluid assistance are investigated. As a result, the abrasive grains can closely approach the micro tool by the effect of dielectrophoretic force and be fixed around the micro tool by the effect of ER fluid assistance. Under these conditions, the workpiece is removed primarily by the accumulation of small brittle fractures, and the chipping can be reduced.

Analysis of Machinable Structures and Their Wettability of Rotary Ultrasonic Texturing Method

Tailored surface textures at the micro- or nanoscale dimensions are widely used to get required functional performances. Rotary ultrasonic texturing (RUT) technique has been proved to be capable of fabricating periodic micro- and nanostructures. In the present study, diamond tools with geometrically defined cutting edges were designed for fabricating different types of tailored surface textures using the RUT method. Surface generation mechanisms and machinable structures of the RUT process are analyzed and simulated with a 3D-CAD program. Textured surfaces generated by using a triangular pyramid cutting tip are constructed. Different textural patterns from several micrometers to several tens of micrometers with few burrs were successfully fabricated, which proved that tools with a proper two-rake-face design are capable of removing cutting chips efficiently along a sinusoidal cutting locus in the RUT process. Technical applications of the textured surfaces are also discussed. Wetting properties of textured aluminum surfaces were evaluated by combining the test of surface roughness features. The results show that the real surface area of the textured aluminum surfaces almost doubled by comparing with that of a flat surface, and anisotropic wetting properties were obtained due to the obvious directional textural features.

Surface Textures Fabrication on Zirconia Ceramics by 3D Ultrasonic Vibration Assisted Slant Feed Grinding

Zirconia (ZrO2) is a promising material in the field of prosthetic and implant dentistry. Surface grinding has been used for surface roughening of zirconia ceramics to increase the mechanical retention of ceramic/resin cement bonding. In the present study, a three-dimensional (3D) ultrasonic vibration spindle, which can generate three ultrasonic vibration modes referred to as longitudinal vibration, circular vibration and 3D hybrid vibration, was employed to machine zirconia ceramics by slant feed grinding for producing tailored rough surfaces. Different micro/nanosurface textures were generated successfully, proving that the ultrasonic vibration assisted slant feed grinding is a viable method to fabricate tailored rough surfaces composed of micro/nanostructures. The surface texturing procedure was mathematically studied, and the influence of grinding and vibration conditions on the textural features was also analyzed.

Control of the Behavior of Abrasive Grains by the Effect of Electrorheological Fluid Assistance - Study on Electrorheological Fluid-Assisted Micro Ultrasonic Machining -

. Micro ultrasonic machining (micro-USM) is an effective machining method for hard brittle materials. In the micro-USM process, the workpiece materials are machined through the accumulation of small brittle fractures generated by the impacts of abrasive grains. Therefore, it becomes difficult to obtain a smooth machined surface. In the proposed electrorheological fluid-assisted ultrasonic machining (ER fluid-assisted USM), the behavior of abrasive grains is controlled using the effect of dielectrophoretic force acting on the abrasive grains and the ER effect. The behavior of the abrasive grains can be controlled by changing the electric field distribution. In the present paper, the shape and position of the auxiliary electrode are arranged in order to control the abrasive grains to the side surface of the micro rectangular tool. By positioning the auxiliary electrode parallel to the micro rectangular tool, it becomes possible to concentrate abrasive grains to the side surface of the micro rectangular tool. Smoothing of the side surface of the workpiece by using the side surface of the micro rectangular tool is then investigated. As a result, the surface roughness of the side surface of the workpiece can be improved.

Smoothed particle hydrodynamics simulation and experimental study of ultrasonic machining

Hard and brittle materials like glass and ceramics are highly demanded in modern manufacturing industries. However, their superior physical and mechanical properties lead to high cost of machining. Ultrasonic machining has been regarded as one of the most suitable fabrication techniques for these kinds of materials. A smoothed particle hydrodynamics model was proposed to study the material removal mechanism of the ultrasonic machining in this study. Influences of abrasive materials and the particle shapes on the crack formation of work substrates were investigated using this smoothed particle hydrodynamics model. Experiments were also conducted to verify the simulation model. Both of the simulation and experimental results show that using hard and spherical abrasive particles is helpful to improve the material removal efficiency. This work was the first to demonstrate the crack formation mechanisms during ultrasonic machining with different abrasive particles using smoothed particle hydrodynamics, which is significant for improving the machining performance of the ultrasonic machining process.

Micro-/Nano-texturing by Ultrasonic-Assisted Grinding

In this chapter, a novel ultrasonic-assisted micro-/nano-texturing method was proposed and developed. A new 3D ultrasonic vibration spindle was developed for carrying out the proposed processes. The texturing mechanisms were analyzed by mathematically calculating the cutting loci and establishing the surface generation modeling processes. Finally, the tool design principles were proposed and experimentally verified. The experimental results and theoretical analysis proved that the proposed method can rapidly and precisely fabricate tailored surface textures at micrometer and nanometer scales.

Stochastic Simulation of Tape Grinding for Wafer-Like Workpiece

Advanced semiconductor materials including silicon carbide and gallium nitride possess excellent properties like high hardness, and high heat and chemical resistance compared to silicon. Such properties reversely prevent efficient production of wafers, therefore a new wafer finishing method, tape grinding, is developed to improve productivity. This paper proposes a simulation method of tape grinding, which method is developed by modifying the stochastic approach developed for plunge grinding. The distribution of abrasive grains on the grinding tape is represented by number density, and the material existence probability that is represented by Abbott-Firestone curve is modified by considering machining parameters. Tape grinding process were then conducted to confirm the calculation method.

Statistical approach calculating ground surface roughness of ultrasonic-assisted micro-grinding

Micro-grinding is a machining method to create submillimeter structures, and it can be applicable to various kinds of materials with a flexible forming ability. However, the micro tool may be easily bended by the grinding force, which results in relative low form accuracy and worse ground surface roughness. To solve these problems, ultrasonic assistance was applied to micro-grinding. This paper proposes a method to calculate ground surface roughness theoretically using statistical approach, and the ground surface improving mechanism of ultrasonic assistance was clarified. Finally, the theoretical calculation was confirmed experimentally using a developed ultrasonic-assisted micro-grinding device.