Tohru Ishida

Experimental Investigation on the Joining of Aluminum Alloy Sheets Using Improved Clinching Process

Aluminum alloy sheets have been widely used to build the thin-walled structures by mechanical clinching technology in recent years. However, there is an exterior protrusion located on the lower sheet and a pit on the upper sheet, which may restrict the application of the clinching technology in visible areas. In the present study, an improved clinched joint used to join aluminum alloy sheets was investigated by experimental method. The improved clinching process used for joining aluminum alloy evolves through four phases: (a) localized deformation; (b) drawing; (c) backward extrusion; and (d) mechanical interlock forming. A flat surface can be produced using the improved clinching process. Shearing strength, tensile strength, material flow, main geometrical parameters, and failure mode of the improved clinched joint were investigated. The sheet material was compressed to flow radially and upward using a punch, which generated a mechanical interlock by producing severe localized plastic deformation. The neck thickness and interlock of the improved clinched joint were increased by increasing the forming force, which also contributed to increase the strength of the clinched joint. The improved clinched joint can get high shearing strength and tensile strength. Three main failure modes were observed in the failure process, which were neck fracture mode, button separation mode, and mixed failure mode. The improved clinched joint has better joining quality to join aluminum alloy sheets on the thin-walled structures.

Creation of Cross-Section Changing Hole with a Hemisphere by Means of Electrical Discharge Machining

In general, machined holes have straight axes and their cross-sections are constant circles since holes are machined by drills. In other words, shapes of machined holes do not have so much variety. To solve the problem, the device was developed which can machine a certain shape on an inside wall of a straight hole by means of electrical discharge machining. This results in fabrication of holes whose cross-sections change variously. In the study, the holes are called cross-section changing holes. However, the device had only ability to make two-dimensional shapes. Therefore, the device has been improved so that three-dimensional shapes can be machined inside holes. From the result of the machining experiment, it is found that the improved device can machine a cross-section changing hole with a hemisphere.

Investigation of Grinding Fluid for Prevention of Chip Adhesion in Miniature Drilling of Glass Plate Using Electroplated Diamond Tool

In the hole drilling process, produced chip cannot be released from the inside hole which leads to broken glass plate due to the adhered chip on tool. Chip discharge method was announced by many researchers. However, the method using the tool-only with drilling command is rarely seen. In this laboratory, we have developed a tool in order to discharge chip. The developed tool is capable in preventing chip adhesion and producing high quality and efficient hole drilling process. The developed tool has several hundred times longer tool life than a conventional tool. However, the amount of adhered chips on cutting tool increase as the number of hole drilling process increases. The chip adhesion condition is different according to the kind of grinding fluid. Adhesion of chips on tool can be related to the properties of grinding fluid. Thus, in this study, the types of grinding fluid used during the hole drilling process were investigated to determine the state of chip adhesion. Three types of grinding fluid used are Emulsion, Soluble and Solution and all of them include surfactant which is considered to have an effect on prevention of chip adhesion. The main conclusions obtained in this study are as follows. Chip adhesion state was investigated after drilling process and it was found that instead of grinding fluid properties, surfactant also has significant effect on chip adhesion on tool by absorbing the adhered chip from the tool. The results showed that grinding fluid with long-chain surfactant has small amount of chip adhesion whereas grinding fluid with short-chain surfactant has large amount of chip adhesion. Therefore, it can be concluded that grinding fluid with long-chain surfactant is capable in preventing chip adhesion during hole drilling process.

Ultraprecision Microgrooving of Hard Material by Means of Cutting Point Swivel Machining

Recently, in accordance with the technical development and miniaturization of the information equipments, the demand of optic elements with high precision and miniaturization is increased. The die is used for manufacturing the optic elements. Thus, it is needed to machine the die with high efficiency and high precision. As the material of die, hard material including cemented carbide and ceramics is used. However, when hard material is machined, there is a problem that severe tool wear occurs, and worn tool shape is transferred into the surface so that precision machining cannot be realized. In this study, a method, called cutting point swivel machining, is proposed to suppress tool wear by using the tool with special chamfer and all parts of tool tip. The effect of tool wear suppression is verified by the machining of SiC. Then, the relation between the suppression of tool wear and tool rotation period is verified.

DEVELOPMENT OF CURVED HOLE MACHINING METHOD – SIZE REDUCTION OF HOLE DIAMETER –

ABSTRACT This study deals with a diameter reduction of curved holes that can be machined by the method developed by the authors. In order to improve the productivity of molding, it is necessary to increase the efficiency of the cooling stage in a molding cycle. It depends on the shape and the arrangement of water channels, i.e., pipelines built in molds. However, water channels consist of a series of straight holes due to the fabrication by drilling. Accordingly, it is strongly required to develop a machining method of curved holes since curved water channels are desirable. To meet the requirement, the device has been developed, which can make an electrode move along a curved trajectory with electrical discharge machining. The device can fabricate curved holes. However, the fabricated curved holes have a problem that their diameter is too large to employ them as a water channel. In the study, thus, the size reduction of the curved holes is tried by improving the electrode and its peripheral parts.

MICROCHANNEL ARRAY CREATION BY MEANS OF ULTRAPRECISION MACHINING

ABSTRACT The study deals with ultraprecision machining of microchannel array chips made of several metals to evaluate the compatibility between blood and metallic materials which are buried in human bodies as parts of artificial internal organs, etc. The blood-compatibility of the metallic materials is very important since their influences for human bodies are not completely clear. Therefore, it is essential to estimate their bio- and blood-compatibilities. To evaluate them efficiently, it is planned to employ the blood fluidity measurement by a microchannel array chip with a micro-rheology device. However, the chips are made of silicon and the shape of their microchannels is limited since they are generally fabricated by photolithographic technologies. To solve the problem, it is required to fabricate the chips with various-shaped microchannels made of several metals. In the study, consequently, ultraprecision cutting is applied to the fabrication of the microchannel array. From the experimental results, it is found that ultraprecision cutting has potential of fabricating arbitrary-shaped microchannel array made of various kinds of metals with high accuracy.

Influence of sheet thickness on mechanical clinch–compress joining technology:

A mechanical clinch–compress joining technology was investigated to join sheets with different thicknesses in the present study. A pair of flat dies was used to compress the clinched joint, and a rivet was used to increase the joining strength. Al5052 sheets with different thicknesses were used to conduct the joining experiments. Tensile strength test and shearing strength test were conducted to evaluate the quality of the compressed joint. Failure mode, feasibility of the joining method, neck thickness, tensile strength, shearing strength, and energy absorption were investigated to show the mechanical properties of the compressed joint. The main failure mode of the joints is neck fracture mode, which means that the neck thickness determines the strength in this study. The mechanical clinch–compress joining technology can increase the strength and energy absorption of the joint by increasing the neck thickness. The joint with a thick upper sheet also can get higher strength and energy absorption by producing a thicker neck thickness. The mechanical clinch–compress joining technology can be used in the visible areas where higher strength and lower protrusion are needed.

Experimental research on the compressed joints with different geometrical parameters

In recent years, mechanical clinching has been widely used to join aluminium alloy sheets to build the automotive body. The high protrusion on the joint may limit the use of the mechanical clinching in the visible places. In order to get a lower protrusion, a compressing method was investigated in this work. Clinched joints with different geometrical parameters were used to conduct the experiments. AL5052 was taken as the material of the sheets. The protrusion of the clinched joint was compressed by two flat dies. A rivet placed in the pit of the clinched joint was used to control the metal flow in the compressing process. The top die moved downward to compress the protrusion, and the bottom die was fixed. The study shows that the tension-shearing strength and cross-tensile strength can be increased by the compressing method. The compressing method can increase the tension-shearing strength and cross-tensile strength by increasing the neck thickness. The compressed joint has larger neck thickness and lower protrusion than the clinched joint. Neck fracture mode is the main failure mode of the joints. The energy absorption can also be increased after the compressing process.

5-Axis Control Dexterous Ultraprecision Micromilling of Ruled Surface with Side Cutting Edge

This study deals with 5-axis control tool path generation to create microshapes dexterously and efficiently, while maintaining quality. Concerning 5-axis control machining, the use of ball end mills is generally employed. However, this method needs a lot of time to obtain high quality surface. To solve this problem, a side cutting edge of the ball end mill is positively utilized with its parallel to the ruled surface. Therefore, a new CAM system is developed to detect the surface to be machined with the side cutting edge, and to generate collision-free tool paths between the tool and the work piece. The effectiveness of the developed CAM system is experimentally confirmed by creating a tiny Möbius ring.

Size Reduction and Performance Improvement of Automatic Discharge Gap Controller for Curved Hole Electrical Discharge Machining

The study deals with size reduction and performance improvement of automatic discharge gap controller (ADGC) for a microrobot which can fabricate a long curved hole by electrical discharge machining (EDM). It is strongly required that curved hole machining method is developed so that the pipelines can be made which have arbitrary shape and are located in arbitrary position. However, such pipelines cannot be fabricated since holes are generally formed by drilling. To solve the problem, the authors have proposed the curved hole machining method by means of a microrobot with an EDM function. The microrobot has to have the function of performing stable EDM in the limit space such as the bottom of a long curved hole, in other words, the function of always keeping the equipped electrode in the appropriate position automatically and autonomously so as to maintain stable EDM. To realize the function, ADGC has been devised. Actually, the prototype of ADGC was developed and it had been proved that the prototype had the function. However, the prototype was too large to install on a microrobot and did not achieve the full performance designed. Therefore, in the study, the improvements of ADGC are done so that its size is reduced and its full performance is achieved. From the experimental results, it is found that the improved ADGC, whose size is reduced so that the installation to a microrobot is enabled, realizes the designed full performance.