An electrochemical discharge drilling method of small deep holes
Zheng Yang Xu
Received: 5 May 2017 /Accepted: 9 November 2017 /Published online: 5 December 2017
Springer-Verlag London Ltd., part of Springer Nature 2017
This paper presents a hybrid electrochemical discharge drilling method in which a metal tube is used as cathode tool and
workpiece is used as anode. Liquid with weak conductivity flows at high speed between the metal tube and workpiece.
Electrical discharge takes place mainly at the frontal gap, and electrochemical process takes place at both the frontal gap and
side gap. The recast layer generated by electrical discharge at the side gap can be removed electrochemically. The machining
phenomenon at the gap was observed through a designed transparent clamping fixture, voltage and current waveforms during
machining were recorded, and the machining products and removal effect of recast layer were analyzed. The cross section of the
hole and machining surface were analyzed, and the tool wear and machining efficiency were compared with those of other
processes. Finally, the 4-mm-deep hole of 0.5-mm diameter can be produced with low tool wear and almost no recast layer.
Electrical discharge machining
Film cooling hole
Film cooling holes are the important structures of turbine blades
and vanes in aero engine for protecting them against
overheating. Because working under high-temperature and
high-pressure environment, nickel- or cobalt-based superalloys
which are difficult-to-machine metals have been used as com-
ponent materials. The demands on the surface quality of these
holes are very strict. It is essential that the machined surface
should be free of recast layers and micro-cracks. High efficiency
of the hole machining is also important because there are masses
of micro and small film cooling holes on the blade. Thus, it is
difficult to machine them by using traditional processes [1–3].
Electrical discharge high-speed drilling is one of the most
important and effective non-traditional processes used for ma-
chining small holes in difficult-to-cut materials . In electrical
discharge machining (EDM), material is removed by inducing
spark erosion in conductive metals; this erosion frequently oc-
curs between the tool electrode and workpiece [5, 6]. EDM,
which is an electrothermal process, usually causes some unex-
pected surface defects on the workpiece, such as micro-cracks,
recast layers, and heat-affected layers . Tube-electrode wear
also becomes a serious problem while machining small holes.
Electrochemical machining (ECM) is frequently employed to
machine difficult-to-cut metals, regardless of the material hard-
ness and toughness. Because material removal in ECM is based
on electrochemical dissolution reactions, no surface defects or
residual stress is generated and no tool wear occurs .
Therefore, ECM provides good surface quality. However, the
machining efficiency of electrochemical drilling is clearly low-
er than that of electrical discharge high-speed drilling.
The electrochemical discharge machining (ECDM), a com-
bined process of EDM and ECM, has increasingly attracted re-
search interest recently. However, the purposes and the methods
of these researches are different with each other. Kurita and
Hattori  developed an EDM and ECM-lapping complex ma-
chining technology. Shin et al.  studied a finishing process of
micro-hole surfaces machined by micro-EDM and obtained the
finishing surface using ECM in deionized water. Nguyen et al. [2,
11, 12] proposed a unique process, named simultaneous micro-
EDM and micro-ECM (SEDCM). In this process, the EDM and
ECM performed in sequence to improve the surface finish and
machining accuracy. Zhang et al.  researched the influence of
electrolyte flow on the machining quality of hybrid process.
This paper presents a tube-electrode high-speed electrochem-
ical discharge drilling (ECDD) method for machining film
cooling holes with high efficiency, low tool wear, and almost
no recast layer. In this process, electrical discharge drilling and
electrochemical surface finishing occur simultaneously.
Therefore, high-quality micro-holes can be obtained efficiently.
In this study, the machining phenomenon was observed and the
* Zheng Yang Xu
College of Mechanical and Electrical Engineering, Nanjing
University of Aeronautics and Astronautics, 29# Yudao Street,
Nanjing 210016, China
The International Journal of Advanced Manufacturing Technology (2018) 95:3037–3044