Fundamental study on internal space forming by EDM

Yuta Inaba, Shuoxun Li, Atsushi Yamaguchi, Akira Okada

Research output: Contribution to journalConference articlepeer-review

2 Citations (Scopus)


Machining of internal space shapes inside metal through a small-diameter entrance hole is difficult by current mechanical machining methods. For such shapes, it is necessary to insert a slender cutting tool with bending or curving function from the small hole, and to remove material by the bended or curved tool in a direction different from the tool inserting direction. Since large machining force acts on the tool in mechanical machining methods, it is difficult to maintain the deformed tool attitude, and excessively large machining force may cause the tool failure. On the other hand, electrical discharge machining (EDM) has high flexibility in the electrode shape, since it is non-contact machining method and the machining force is extremely small. Therefore, it is highly expected that internal space machining would be possible by EDM if an optimum electrode structure can be designed and prepared. This study proposes a new internal space machining method by EDM using a revolution ball electrode. This electrode consists of a vertical rotation rod fixed on z-axis of machine head, a tilting rod connecting to the lower end of the rotation rod with a flexible hinge joint, and a copper tungsten ball electrode fixed to the lower end of the tilting rod. After the electrode in straight attitude is inserted into a small-diameter entrance hole, the material removal for internal space is performed, rotating the electrode. A centrifugal force acts on the ball by the electrode rotation, and the tilting angle of tilting rod may be controlled with the rotation speed, since the magnitude of centrifugal force is varied with the rotation speed. In order to confirm the controllability of tilting angle, the variation of tilting angle with the rotation speed was measured by a high-speed camera observation. It was found that the angle was well controlled by the rotation speed, which indicates that the ball can be positioned at any positions with the z coordinate of electrode and the rotating speed, if the tilting rod length is changeable during the process. Next, the EDM characteristics including surface roughness and electrode wear were experimentally investigated using the revolution ball electrode. Furthermore, machining of some axially-symmetric spacial shapes, such as cylindrical shape and spherical one were tried into a zinc alloy workpiece. The machining results show that this method has high possibility to form internal space shapes inside metal.

Original languageEnglish
Pages (from-to)215-219
Number of pages5
JournalProcedia CIRP
Publication statusPublished - 2020
Event20th CIRP Conference on Electro Physical and Chemical Machining, ISEM 2020 - Zurich, Online, Switzerland
Duration: Jan 19 2021Jan 21 2021


  • EDM
  • Internal space shapes
  • Revolution ball electrode

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Industrial and Manufacturing Engineering


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