Elementary Study on the Creation of Cross Section's Changing Holes by Means of Electrical Discharge Machining

Abstract

This study deals with the development of a new method to machine holes whose cross sections variously change along their axes. Machined holes have straight axes and constant circular cross sections, since holes are generally machined by drills. In other words, the shapes of machined holes do not have much variety. This study, however, develops a new, elementary device which can machine a certain shape on the inside wall of a straight hole by means of electrical discharge machining. This results in the creation of holes with variously changing cross sections. The aforementioned device consists of an electrode for electrical discharge machining and some mechanical parts, and is installed on a die-sinking electrical discharge machine (EDM). The device and EDM operate as a reciprocating block slider crank mechanism, so a translational movement of the main axis of the EDM can be converted into a rotational movement of the electrode. As a result, shapes which are identical to the envelope of the locus of the electrode movement can be machined. This leads to the creation of a semicircular space on the inside wall of a straight hole by starting the machining after setting the electrode in the hole. Experimental results show that, by changing the shape of the electrode, the device can produce variously shaped, semicircular spaces inside a straight hole. This proves that the new method of machining has the ability to create holes which have complicatedly changing cross sections.