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Observations of the discharge gap were conducted to investigate the discharge plasma motion in reciprocated traveling wire electrical discharge machining (RT-WEDM). It was found that a discharge plasma continuously slides on the surface of a workpiece. An oscillating moving heat source is proposed to better describe the characteristics of discharge plasma motions. Based on an oscillating moving heat source, a novel thermal-fluid coupling model by adopting a level-set method is proposed to investigate the formation of a crater and the effects of machining parameters on craters. Discharge plasma sliding, latent heat, and molten pool forces are comprehensively considered in the proposed model. Simulation and experimental results show that a sliding discharge plasma has a significant effect on a crater. At the end of a discharge, a considerable proportion of molten materials remains in the molten pool. A high sliding speed of discharge plasma can lead to a low aspect ratio in a crater and a thin recast layer. Due to discharge plasma sliding, an increase in pulse duration can significantly increase the length of a crater and decrease the aspect ratio, while an increase in peak current can significantly increase the depth and volume of the crater. Simulation and experimental results also show that morphologies of the simulated crater and experimental craters are consistent, verifying the feasibility and accuracy of the proposed simulation model in explaining the mechanism of crater formation in RT-WEDM. [ABSTRACT FROM AUTHOR]

As a typical non-traditional machining method, reciprocated traveling wire electrical discharge machining (RT-WEDM) has been widely used in mold and die manufacturing industry. However, at present RT-WEDM still suffers from the problem that a large portion of molten material remains in a molten pool after a discharge, due to a relatively long discharge duration. This phenomenon limits the improvement of material removal efficiency and resulting in a thicker recast layer. To facilitate the expelling of the molten material in RT-WEDM, a two-stage discharge current regulation method is proposed in this study, which includes oscillating-current regulation (OCR) during discharge duration and explosive-current regulation (ECR) right before the end of the discharge. A pulse power generator with discharge current regulation modules is developed, and the control principle for generating an oscillating current and an explosive current is elaborated. Regulation parameters are determined based on an analysis of discharge plasma behavior. Both single-pulse discharge experiments and consecutive-pulse machining experiments are carried out to verify the effect of the proposed two-stage regulation method. The results show that the material removal rate (MRR) has been increased by 16.5% and the average thickness of recast layer on the workpiece surface has been reduced by about 15%. [ABSTRACT FROM AUTHOR]

Heat source and pressure source from discharge plasma to electrodes of electrical discharge machining (EDM) are key factors in the analysis of material removal process. To determine the role of distribution of the heat source and pressure source of EDM, this study uses particle-in-cell with Monte Carlo collision (PIC-MCC) simulation to calculate the energy distribution of discharge plasma. The distribution of the energy transfer on the electrode surface as well as heat source and pressure source is further obtained. The results show that the central peak value of the heat source decreases while the diameter increases with the increase of current, which is different from the assumed heat source distribution. A double Gaussian heat source is proposed to quantify the heat source under different conditions. The pressure source is in continuous oscillation so that it cannot be summarized as a stable distribution. Furthermore, the simulation of material removal process with double Gaussian heat source and pressure source of numerical results shows that the ejection of molten metal contributes to the dominant material removal. The width of crater increases with the increase of discharge energy, but the depth keeps constant of dozen microns. Regardless of the discharge energy, more than two-thirds of the molten material in the molten pool cannot leave the electrode surface. The experimental results of morphology of the crater are in agreement with the simulation results, meaning the model provides a more sophisticated energy input for analysis of material removal process in EDM. [ABSTRACT FROM AUTHOR]

Fast electrical discharge milling (fast ED-milling) has become a promising technology in the manufacturing industry for machining complex structures such as diffuser-shaped film cooling holes. However, the mechanism of the efficient removal of materials in this technology is not yet fully understood. To gain a further insight into this matter, an experimental investigation on the morphology of discharge craters including the absolute material removal volume per discharge, material residual volume per discharge, and directionality, is firstly carried out. The obtained results imply that a high-pressure inner flushing can significantly promote the expelling of molten material from a molten pool and is a fundamental reason why fast ED-milling can be of higher machining efficiency than regular ED-milling. To explore the mechanism behind, a novel thermal-fluid coupling model is developed to simulate the evolution process of the molten material under the effect of a flow field. The results of numerical simulation show that during a discharging, the molten material moves along the workpiece surface towards the outlet of a gap channel and solidifies at the side of a crater that is away from the electrode center. Another interesting finding is that an inappropriately high flushing pressure can result in a low machining efficiency because the severe heat convection will consume a large part of the heat generated by a discharge. This well explains the phenomenon that occurred during the experimental investigation. [ABSTRACT FROM AUTHOR]

Spark discharge plasma in electrical discharge machining (EDM) is hard to measure due to its small spatial scale, so particle-in-cell with Monte Carlo collision (PIC-MCC) simulation is a powerful method to analyze the discharge channel of EDM. PIC-MCC simulation suffers from traversing particles, which is high time-consuming, and thus, the discharge duration is limited to nanoseconds. However, the nanosecond simulation results cannot reflect the actual machining of EDM (10–100 μs). For this reason, a parallel PIC-MCC simulation architecture based on GPU for EDM is proposed. This architecture parallels the tasks in PIC, greatly reducing the increase of computing time when the number of particles increases, which makes simulation of duration time in microseconds available. Moreover, the simulation process takes into account the working mechanism of the breakdown/discharge coordination of the EDM circuit, which is more meaningful for actual machining. This paper describes the algorithm architecture and some results of EDM in air at atmospheric pressure with open voltage of 150 V. It is shown that micro-peak geometry limits the plasma size, so it does not expand as the pulse duration time increases. The energy transferred into the anode is much higher than that of the cathode, and the energy absorption coefficient of the cathode is less than 4%. And these results are consistent with the existing related reports. Compared with the large pulse duration measurement (> 100 μs) of discharge, this paper provides a method to calculate heat input which can include transient details and conform to the actual machining pulse duration (≈10 μs). [ABSTRACT FROM AUTHOR]

Deep narrow slot (DNS) structures are commonly used in slots for inserts in tire molds, die-casting molds of heat-dissipating fins, grooves in flexible joints of gyros, and seal slots in turbine blades. Electrical discharge machining (EDM) of DNSs is a time-consuming process, because traditional EDM machines adopt a vertical downward feed direction to remove materials, resulting in debris deposition in the gap by means of gravity. In this paper, systematic experiments are carried out to investigate the effect of different feed directions on the machining efficiency of EDM DNS structures. Thirteen feed directions with an incremental angle of 15° from −90 to 90° have been tested without electrode jumps. Among them, the feed directions of 0° and 15° have the highest machining efficiency, which even exceeds the machining efficiency achieved with electrode jumps. A machining efficiency model with respect to feed direction is built based on experimental results. The gap discharge state is acquired by an FPGA circuit based on discharge state analyzer, associated with machining efficiency curves. For most feed directions, the discharge rate drops significantly after the machining depth around 4 mm, leading to an obvious turning point in the machining efficiency curve. To explore the reasons for machining efficiency changes during the machining of DNS, the movements of bubbles are observed by a high-speed camera for calculating their speeds and sizes. [ABSTRACT FROM AUTHOR]