Application of nano electrolyte in the electrochemical discharge machining process

As a nontraditional machining process, electrochemical discharge machining (ECDM) can apply to hard and brittle materials such as glass and ceramic. Improvement of process efficiency is an important topic that has been addressed in many investigations using various techniques such as magnetic field and ultrasonic vibrations.Nano particles are new and advanced materials that can be dispersed in a fluid to obtain a nano fluid with desirable specifications. This method can be implemented in the ECDM process by the application of the nano electrolyte. Nano electrolyte can present enhanced properties, in particular enhanced electrical and thermal conductivities which lead to more powerful discharges and greater material removal.In order to study the variation of discharge physics, consequent captures from discharges were taken. Besides using current signal diagrams, larger numbers of discharges were found using nano electrolytes. Results of hole depth showed that both Cu and Al₂O₃ nano electrolytes improved the hole depth as 21.1% and 18.7%, respectively. An undesirable effect of nano electrolyte was observed on the entrance overcut, which raised 8.3% and 10.7% using Cu and Al₂O₃ nano electrolytes, respectively, in comparison to the simple electrolyte. This drawback is negligible compared to the significant improvement of hole depth. SEM images of tool wear showed larger molten materials on the tool main edges by the application of nano electrolyte.     

Numerical and experimental study on the effect of vibration of the tool in ultrasonic assisted EDM

In this paper the effect of ultrasonic vibration of the tool in the process of electrical discharge machining is investigated. The ultrasonic vibration of the tool has significant effect on the dynamic behaviour of the vapour bubble generated between the tool and the workpiece due to the electrical discharge. The computational simulation of the bubble behaviour is carried out by employing the boundary integral equation method. Results show that when the electrical discharge occurs in the closest position of the tool to the workpiece, the vapour bubble expands to the largest maximum volume of the bubble and the lifetime of the bubble is the longest. This in turn makes the pressure inside the bubble decrease rapidly to the lowest magnitude and causes melted material at the sparked point vaporize and leave the crater on the surface of the workpiece.     

An experimental study on the effect of magnetic field orientations and electrolyte concentrations on ECDM milling performance of glass

In this work, effects of magnetic field orientation, machining voltage and electrolyte concentration on electrochemical discharge machining (ECDM) performance have been studied. The microchannels have been machined on the glass substrate; microchannel's depth and surface quality have been taken as indexes of machining characteristic. Experimental results show that the Lorenz force of magnetic field affects a direction of bubble's motion, consequently, changes the electrochemical discharge behavior of electrolyte. The presence of magnetic field causes magnetohydrodynamic (MHD) convection which, by its turn, accelerates the repulsion of the bubbles from the cathodic surface. However, it should mention that the direction of bubble movement depends on the magnetic field orientation. If the magnetic field orientation induces upward Lorenz force (downward Lorenz force), the gas bubbles will repel from (will attract to) inter-electrode area. The obtained results demonstrate that when the magnetic field applies, the machined surface will be smoother for the lower concentration values of electrolyte and higher machining voltages. Enhancements of both the machining voltage and electrolyte concentration increase the machining depth. For the same values of applied voltages, application of magnetic field will also increase the machining depth in a certain machining process duration; this will be intensified for the lower values of electrolyte concentration. The results of this study explain how the combination of the magnetic field orientation and the values of machining voltage and electrolyte concentration should be defined in order to increase both the channel depth and surface quality.     

大深径比微小深孔超声电火花加工工艺研究

针对难加工材料的大深径比微小深孔加工这一工艺难题,设计并制造了基于工件振动的超声电火花复合加工装置。该装置包括一个已优化的压电振子和一台普通电火花机床。为提高加工效率,对压电振子进行了优化分析,使压电振子具有合适的纵振模态、固有频率和较大的振幅,压电振子中陶瓷片具有合理地安装位置。选择模具钢作为加工材料进行大深径比微小深孔的加工实验,比较研究了超声电火花复合加工装置和普通电火花机床加工大深径比微小深孔的加工效率。实验表明,超声电火花复合加工装置的加工效率更高。研究了超声激励电压、脉冲电流、脉冲宽度以及脉冲间隙等参数对大深径比微小深孔加工效率的影响,得出各参数较优的设置值。根据实验结果可以看出,超声电火花复合加工装置可以有效地加工出直径为0.5mm、深径比为60的微小深孔,适用于难加工材料的大深径比微小深孔加工。     

Study of the effects of tool longitudinal oscillation on the machining speed of electrochemical discharge drilling of glass

In this study, longitudinal oscillation applied to the cathode electrode during the electrochemical discharge micro drilling of glass and the effects of electrolyte flushing alteration in both discharge and hydrodynamic regimes of the process have been investigated. In this regard, numerous sets of experiments have been conducted using different vibration frequencies and amplitudes. In addition, two geometrically different tools including cylindrical rod and micro drill were used as machining electrode (cathode). In the case of cylindrical rod, two types of longitudinal waveforms including square and sinusoidal ones were applied to the tool. The experiments were resulted in a noticeable improvement in material removal rate (MRR) using square waveform and a slight improvement in the case of sinusoidal waveform. Moreover, the obtained MRR by means of vibrating micro drill has been compared with those achieved by non-vibrating one in several oscillation frequencies and amplitudes. The results showed that the vibration of the micro drill cannot further improve the electrolyte flushing and MRR in comparison with non-vibrating one because of the inherent electrolyte flushing in micro drill through its flutes which is constant in vibrating and non-vibrating cases.     

Theoretical analysis and experimental study on the influence of electric double layer on thin film lubrication

A new mathematical model for thin film lubrication is established by taking into account the effect of an electric double layer. In the present paper, experiments are carried out on a self-made tester. With a composite block and a rotating disk, influence of electric double layer on thin film lubrication is studied. Two different methods are used to reconstruct the field of electric double layer so as to change its effect. One is to change the ionic concentration of lubricants by adding additives, and the other is to apply an external electric field on friction pairs. According theoretical analysis, both the methods will apparently change the electro-viscosity of the lubricant film so as to change the lubrication performances. After theoretical calculation of electro-viscosity is amended according to the experimental results, the equations of electro-viscosity are presented. The results show that the equivalent viscosity of fluid induced by the effect of electric double layer apparently increases with the decrease of thickness of the film while the lubrication film is thin enough. The effect of electro-viscosity is weakened as the thickness of the film increases. Moreover, the effect of electro-viscosity increases with the increase of external electric field at first. When the voltage reaches a certain value, the electro-viscosity begins to decrease. __________ Translated from Tribology, 2005, 25(6) (in Chinese)     

Analytical and experimental study on bonding behavior at the roll gap during complex rolling of sandwich sheets

An extended analytical model for complex rolling of sandwich sheets is proposed. Effects of various rolling conditions such as the flow stress ratio and initial thickness ratio of the raw sheets, total thickness reduction, etc., upon the bonding factors such as the bonding length, mean contact pressure, and the relative sliding distance at the interface as well as the newly generated surface ratio are analyzed. Furthermore, experiments on complex rolling of sandwich sheets are also conducted. The measured rolling force, thickness ratio of the rolled product, bonding length, and the mean contact pressure are close to the theoretical values. Through the comparisons, the validity of this proposed mathematical model is verified and the characteristics of the bonding behavior at the roll gap during complex rolling of sandwich sheets are manifested.