Hideki Takezawa

Accretion of titanium carbide by electrical discharge machining with powder suspended in working fluid

Abstract A surface modification method by electrical discharge machining (EDM) with a green compact electrode has been studied to make thick TiC or WC layer. Titanium alloy powder or tungsten powder is supplied from the green compact electrode and adheres on a workpiece by the heat caused by discharge. To avoid the production process of the green compact electrode, a surface modification method by EDM with powder suspended in working fluid is proposed in this paper. After considering flow of working fluid in EDM process, the use of a thin electrode and a rotating disk electrode are expected to keep powder concentration high in the gap between a workpiece and an electrode and to accrete powder material on the workpiece. The accretion machining is tried under various electrical conditions. Titanium powder is suspended in working oil like kerosene. TiC layer grows a thickness of 150 μm with a hardness of 1600 Hv on carbon steel with an electrode of 1 mm in diameter. When a disk placed near a plate rotates in viscous fluid, the disk drags the fluid into the gap between the disk and the plate. Therefore, the powder concentration in the gap between a workpiece and a rotational disk electrode can be kept high. A wider area of the accretion can be obtained by using the rotational electrode with a gear shape.

A New Process of Additive and Removal Machining by EDM with a Thin Electrode

Abstract Removal machining or additive machining can be performed in electrical discharge machining (EDM), under proper machining conditions. In this paper, rapid accretion of a thin electrode material and rapid manufacturing of a thin electrode are proposed. The material of a thin electrode can be accreted onto a work piece in an instant through an explosion process. A needle of 35μm in diameter and 300μm length can be made under a single discharge pulse instantaneously from a tungsten wire of 125μm in diameter. Micro drilling and rapid implantation of electrode material onto a work piece can be performed. The machining mechanisms are discussed taking into consideration the thermal properties of the thin electrode and the machining conditions.

On-the-Machine Measurement in EDM Process by a Calibration System with Polyhedra

Summary In order to realize electrical discharge machining (EDM) with high precision, it is necessary to take into account of the change of the shape of electrode and workpiece with machining time. This paper deals with on-the-machine measurement of an electrode and a workpiece in electrical discharge machining (EDM). A newly developed calibration system with polyhedra is installed on the machine. The probe can be detached from the machine in machining stage and it is attached to the machine in measuring stage at any attitude according to the portion being measured. The position of the edge of a measuring probe is determined with the equations of planes on the polyhedron. This paper describes the principle of calibration method and the change of complex shape of an electrode and a workpiece measured in the process of machining.

Multiple degrees-of-freedom arm with passive joints for on-the-machine measurement system by calibrating with geometric solids

To fabricate three-dimensional profiles with high accuracy, on-the-machine measurement is useful. Methods for the on-the-machine measurement by calibration with geometric solids used for references have been developed. In this paper, an arm with passive joints for on-the-machine measurement is proposed. As a prototype, the arm has 4 degrees of freedom (DOF) including two passive joints. The probing system has 7 DOF, including the DOF of the machine tool, in total. Angles of the passive joints are changed by driving the numerically controlled (NC) table and the main spindle of the machine tool, where the arm is mounted. To calculate the optimal posture of the arm for the shape to be measured, a numerical method of the inverse kinematics is also proposed. The arm has enough positioning accuracy to calibrate its posture. Shapes can be automatically measured with the accuracy of micrometer order by the on-the-machine measurement method as well as a commercial three-dimensional (3-D) coordinate measuring machine and a profilometer.

Accretion Machining by EDM with Thin Electrode (1st Report)

Accretion machining by electrical discharge machining (EDM) with a high wear rate of green compact or semisintered electrodes has recently been carried out. Also, it has been observed that the wear rate of thin electrodes for various materials is very high with a high discharge current. In this study, a thin tungsten electrode is used for material accretion or surface modification of a small area. For this purpose, continuous discharge and single discharge machining experiments were performed by EDM with a thin electrode. Then the voltage and current waveforms and the cross section of the accreted surface were observed. In accretion machining, these waveforms revealed a continuous short-circuit phenomenon and a wire explosion phenomenon subsequent to the continuous short-circuited state. These observations indicated that the accreted layer was very hard (1000HV) and that the accretion area was very small (150μm in diameter). This clearly indicates that microaccretion machining can be performed using this technique.