Kai Egashira

Microultrasonic Machining by the Application of Workpiece Vibration

Abstract A new method for microultrasonic machining (MUSM) has been developed. In order to obtain high-precision tool rotation, the spindle mechanism employed in micro-EDM machines was introduced. Since the mechanism does not allow the vibration of tools, the workpiece was vibrated during machining. Using this setup, we have succeeded in machining microholes as small as 5pm in diameter in quartz glass and silicon. In this machining range, high tool wear posed a problem. To solve this problem, a sintered diamond (SD) tool was tested and was proven to be effective.

Ultrasonic Vibration Drilling of Microholes in Glass

Abstract Microholes with a diameter of 10 μm were drilled in glass by ultrasonic vibration cutting using a microtool fabricated by wire electrodischarge grinding. The workpiece was vibrated in order to realize high-precision tool rotation. Cutting was performed in the ductile regime at a depth of cut of 0.05 μm, leaving neither fractures nor cracks around the rim of the hole. The application of ultrasonic vibrations resulted in (1) a decrease in the required cutting force, (2) an extension of the tool life, (3) an increase in the permissible penetration and tool length and (4) smoother machined surfaces.

Surface Quality of Textured Surface on Cylindrical Inner Surface Using Whirling Electrical Discharge Texturing

Whirling Electrical Discharge Texturing (WEDT) was developed to create microstructures. It was thought that textured surface with low surface roughness could reduce friction coefficient on the sliding parts. In this research, surface quality was studied to evaluate the quality of WEDT textured surface. Surface quality was evaluated in terms of the surface roughness and surface integrity which were characterized by microstructure, composition and residual stress of the textured surface. The value of Rp and Rv of textured surface after finishing with improved finishing method were obtained as expected for low surface roughness to reduce friction coefficient. In addition, it was clarified that microstructure and composition of textured surface after texturing with WEDT and finishing with lapping-film depend on feed speed. Furthermore, the compressive residual stress was presented on WEDT textured surface and depended on feed speed. It was confirmed that good surface quality of textured surface could be obtained by WEDT.

Fabrication of Micropins Using Micro Turning Tools

The turning of straight micropins with a diameter smaller than 10 µm, which has not been reported so far, was carried out using micro turning tools made of cemented tungsten carbide. Tools of 50 µm diameter were fabricated by electrical discharge machining, which is suitable for fabricating micro cutting tools because it can deal with hard materials and carry out micromachining. A turning machine designed especially for micro turning tools was used in the experiments. A brass workpiece was turned using a tool with a length of cut of 100 µm at a feed speed of 3.0 µm/s, feed per revolution of 0.06 µm and depth of cut of 10–11 µm. As a result, a straight micropin of 7.5 µm diameter and 80 µm length was successfully turned. Furthermore, turning was also performed using a tool with a length of cut of 50 µm at a feed speed of 3.0 µm/s, feed per revolution of 0.06 µm and depth of cut of 8.5–20 µm to fabricate a straight micropin of 3 µm diameter and 30 µm length. This micropin is the pin with the smallest ever diameter fabricated by turning, to the best of our knowledge, indicating the possibility of further minimization of the machinable size in turning. Turning properties were also investigated to determine the maximum depth of cut and feed speed that can be employed without tool breakage.

Micro-structuring on Cylindrical Inner Surface using Whirling Electrical Discharge Texturing

The authors developed Whirling Electrical Discharge Texturing (WEDT) in order to reduce friction coefficient of cylinder-shaped parts. In previous research, the authors verified fundamental characteristics of WEDT by observation of textured surface. It was found that a crater shape and texture-area ratio can be controlled by WEDT. The texture-area ratio depends on feed speed of tool electrode. In this research, crater depth, crater diameter, texture area ratio and total removal volume of craters were investigated to confirm characteristics of WEDT in detail. In addition, tungsten wire was used as a whirling shaft in order to improve stability of whirling phenomenon. Moreover, a textured surface was finished by lapping-film in order to remove protrusions around craters and reduce friction coefficient. As a result, it was verified that the texture-area ratio slightly increased with decreasing feed speed and it was confirmed that crater depth, crater diameter, and total removal volume of craters were also related to feed speed.

Application of USM to micromachining by on-the-machine tool fabrication

Most machining methods have difficulties in machining hard, brittle materials such as glass, ceramics, and silicon. Ultrasonic machining(USM) is a unique method from this point of view, because it easily machines these materials. However, USM has limitation in its application to micromachining because them are problems in fixing microtools to the machine and maintaining high precision. In this paper we propose a technique of micro-USM by applying on-the-machine tool. fabrication by wire electrodischarge grinding (WEDG). As a result, we were able to make microholes as small as 20pm in diameter on a silicon plate. Additional experiments revealed the possibility of wide application.

Drilling of Rod End Faces Using Micro-Cutting Tools

There have been few reports on the drilling of microholes on rod end faces by cutting, which can be employed for fabricating micronozzles or microneedles. Such drilling was therefore attempted in the present study using a micro turn-milling machine with the tool and workpiece axes being parallel. The drilling was performed on the end faces of brass rods with cemented tungsten carbide micro-cutting tools processed by electrical discharge machining (EDM). As a result, a microhole 12 μm in diameter was successfully drilled using a 10-μm-diameter tool at a feed speed of 0.5 μm/s. The feed speed could be increased to 25 μm/s for a tool with a diameter of 20 μm and body length of 50 μm.

Surface Finishing on Arc-Shaped Inner Surface by Ultraviolet Assisted Polishing

Recently, diamonds have been utilized gradually for sliding parts and wear-resistant parts because of their excellent properties. The shape of diamond applied to these parts is not only plane but also arc-shaped inner surface. Therefore, development of diamond polishing technology is required. In this study, ultraviolet assisted polishing was thought to develop to polish polycrystalline diamond (PCD) on arc-shaped inner surface. The authors investigated effect of ultraviolet radiation on polishing efficiency and surface roughness. As a result, the surface roughness Ra of PCD showed less than 15 nanometers. In addition, polishing efficiency was improved about 30 percent due to ultraviolet assisted polishing.

Mirror-Like Surface Finishing of PCD by Fixed Abrasive Polishing

Polycrystalline diamond (PCD) has excellent properties such as high hardness, high chemical inertness, high wear resistance and a low friction coefficient. Thus, it has been expected to be applied to used in various mechanical parts such as sliding parts. However, diamond is difficult to machine owing to its high hardness and chemical inertness. Therefore, a highly efficient and high-quality machining process is required for PCD. In this study, the authors developed fixed abrasive polishing tools for the mirror-like surface finishing of PCD that contain mechanochemical abrasive grains with diamond grains. As a result of fixed abrasive polishing experiments, it was clarified that a mirror-like surface can be obtained by fixed abrasive polishing using a tool containing SiO2 and diamond abrasives. Moreover, it was found that the removal efficiency can be increased under a high-temperature condition.

Development of Deburring Technology with Whirling EDM - Influence of the Motor Rotational Speed Control Conditions and the Electrical Conditions on the Machining Characteristics

The authors developed Whirling Electrical Discharge Machining (Whirling EDM) [1] with the feedback circuit to control gap distance between tool electrode and workpiece. It was found that the probability of discharge was increased by feedback circuit [2]. However, the motor rotational speed control conditions were not optimized and the machining characteristics were not clarified. In this paper, the rotational behavior of tool electrode in Whirling EDM was observed by high-speed camera, and it was considered that the influence of motor rotational speed control conditions on machining characteristics and the relationship between electrical conditions and machining characteristics. As a result, the discharge probability was able to be increased by decreasing range of motor rotational speed in feedback circuit. In addition, the machining characteristics of Whirling EDM which are influenced by electrical conditions were clarified.