Electrical machining remains an important area of industrial activity and research in the UK. Historically, British universities have made notable contributions which have helped to shape the state-of-the-art. There is also a healthy network of machine makers and machine users in the UK which support the stalwart aerospace industry. This paper briefly introduces the UK electrical machining microcosm and then focuses on the electrical discharge and electrochemical machining contributions made at the University of Nottingham since 2010. The paper introduces the people and their ideas alongside the collaborations that have made this work possible.

It is well known that electrochemical machining (ECM) of Cr-containing materials such as stainless steel produces hexavalent chromium, which is often taken up as a problem of electrochemical machining. In this study, using the relationship among the standard electrode potential, we investigated whether the formation of hexavalent chromium itself could be suppressed during ECM and developed the method of using divalent iron ions in the electrolyte. If the electrolyte contains many easily oxidized ions, it can be considered that the oxidation of trivalent chromium is prevented by the oxidation of these ions. To supply divalent iron ions to the electrolyte, an iron-ion supply device composed of iron chips was fabricated. It was clarified that the electrolyte must be kept non-alkaline to contain a large amount of iron ions and that with a sufficient amount of divalent iron ions, the formation of hexavalent chromium can be suppressed.

To achieve high-speed machining of sintered carbide, a new process of milling using an electrochemical reaction is proposed. In this report, the principle of this method and its effectiveness were confirmed. First, the phenomena on the sintered carbide surface occurring in the electrochemical reaction were investigated. The reactions that could occur on the sintered carbide surface are the elution of Co, the oxidation of Co, and the oxidation of WC. It was found that the elution of Co occurs first, followed by the oxidation of WC. Then, the cutting resistance and the machining phenomena were evaluated and compared in the cases with and without the electrochemical reaction. It was shown that the cutting resistance becomes significantly lower when the electrochemical reaction occurs. The analysis results showed that the reason for the reduction in cutting resistance was the elution of Co and that most of the electric charge was used for the elution of Co, not the oxidation of Co and WC, when machining was carried out under certain conditions.

Electrochemical milling using a delta-type parallel mechanism is proposed to achieve high-speed translation of the tool electrode, which is known to improve the surface finish. Experimental results of machining a groove show that the surface roughness decreases with increasing translation speed of the tool electrode. Moreover, it is found that the high-speed translation of the tool electrode is effective at preventing electrical discharge damage of both the tool electrode and the workpiece. Large areas can be machined at high translation speeds with improved surface finish, and the machined profile accurately matches the desired profile. The experimental results indicate that there is an optimum pick feed that ensures both a better surface flatness and finish.

The assisting electrode method has enabled the EDM of insulating materials. However, there is a need to change the machining conditions, otherwise the stability of EDM drops. To solve this problem, it is important to clarify the mechanism of EDM for insulating materials. We built a measurement system that enables the synchronized observation of machining phenomena and the discharge waveform. The observation clarified the two facts. The main role of a long pulse discharge is to form a conductive layer on the workpiece surface. Machining of the insulating material progresses with the concentration of normal discharge in the same area after a long pulse discharge. But, when the amount of pyrolytic carbon is large, the machining accuracy will deteriorate due to concentration of the discharge generated. Thus, the discharge conditions were changed according to the amount of pyrolytic carbon generated, resulting in the improvement of the machined shape accuracy

A thin wire electrode of copper–zirconium (Cu–Zr) with high conductivity was proposed to obtain high cutting speed in fine wire electrical discharge machining (EDM). The wire EDM characteristics by using the bare Cu–Zr wire and zinc– or brass–coated ones were experimentally investigated. The results showed that the cutting speed using the bare Cu–Zr wire was lower than that using the conventional–coated wires. However, the cutting speed could be significantly improved by coating a thin layer of brass or zinc around the Cu–Zr wire, and exceeded that using conventional wires. This is because, the pulse frequency and peak discharge current increase with the brass or zinc coating．

Small hole electrical discharge machining (EDM) typically uses brass or copper pipe electrodes of diameter 0.2–3 mm for machining. However, it has been empirically proven that in high aspect ratio machining, machining speed decreases because of deterioration in the discharge state, which is attributed to insufficient removal of machining debris. This study investigates the usage of straight grooves electrodes in small hole EDM to improve removal of debris and thereby enhance discharge performance during deep hole machining using a commercial small hole EDM machine. Machining experiments were conducted to compare the performance of EDM with normal pipe electrodes and straight grooves electrodes. The electrode was tested for diameters 1 and 3 mm. As a result, the machining of 125 mm height stainless steel using the normal pipe electrode was slower than the case of straight grooves electrode.

Pure titanium (Ti) and its alloys have been widely applied for metal implants in human body, while they have a disadvantage of lacking for bioactivity. Therefore, adding a new surface function to Ti is required to overcome the disadvantage. One method for adding new function is formation of periodic surface structures on the pure Ti as a biomaterial, which can control cell spreading. Previous study revealed that osteoblasts (MG-63) spread along grooves of nanostructures produced with ultrashort pulsed laser on Ti surface. In this study, surface profile variation of nanostructures with laser conditions was experimentally investigated. Influence of the surface profile on cell orientation of osteoblasts was also discussed. Results show that aspect ratio of nanostructures increases with the pulse duration under constant laser fluence and shot number. Furthermore, the nanostructures with a high aspect ratio is more effective for enhancement of cell orientation than those with a small one.

Sintered polycrystalline diamond (PCD) is widely employed for cutting tools because of its great hardness and high wear resistance. However, it is extremely difficult to shape PCD tools by conventional machining methods. We describe the truing of a PCD tool by electrical discharge machining (EDM). Although EDMing of PCD is possible under the PCD positive polarity, the removal rate is relatively low. In this paper, we discuss the possibility to apply the bi-polar pulse for the EDMing of PCD. It is confirmed that the removal rate of PCD using the bi-polar pulse is higher than using normal pulse(electrode positive or negative polarity). Moreover, the electrode wear ratio is also improved.