Pulse Electrochemical Machining Research Articles

Multi-Objective Optimization of Pulse Electrochemical Machining Process Parameters by CRITIC-TOPSIS

Multi-Objective Optimization of Pulse Electrochemical Machining Process Parameters by CRITIC-TOPSIS

Research on the surface characteristics of 42CrMo alloy steel pulse electrochemical machining

Electrochemical processing, due to its unique material removal mechanism compared to mechanical processing, often results in significantly different micro-morphologies. It is widely used in areas such as aerospace component processing, surface finishing, passivation, micro-structure mold processing, etc. The complexity of alloy steel composition makes uniform etching difficult to achieve, and the post-etch micro-morphology is also complex, making it challenging to describe and analyze. Therefore, it is difficult to analyze the surface morphology of electrochemical etching under different parameters. In this study, a self-developed electrochemical etching device with adjustable DC voltage, pulse width voltage, and pulse width positive and negative voltage output was used. Different parameters of pulse voltage were used to etch the surface of 42CrMo alloy steel. Due to the strong relationship between surface roughness parameters and the chosen measurement scale, as well as the surface morphology and waviness errors introduced by specimen preparation and etching processes, a wavelet filtering method was used to remove the low frequency components in the surface morphology, and only the surface roughness part was retained for fractal parameter calculation and analysis. The research showed that fractal analysis can also be applied to analyze the surface morphology after electrochemical etching. Pulse voltages with characteristic voltages, characteristic pulse frequencies, and duty ratios can achieve better surface quality during positive pulse etching. Positive and negative pulse etching can obtain better surface morphology than positive pulse etching, but the etching amount is lower, making it suitable for precision finishing.

Research on simulation method of multiple time scales dissolution process in tube electrode pulse electrochemical machining

Tube electrode pulsed electrochemical machining (TE-PECM) has received widespread attention as an electrochemical perforation technique that is widely used for machining deep small holes/oblique small holes such as air film holes in blades. However, the TE-PECM process is characterized by complex multi-physics field coupling relationships and multiple time scales for multi-physics interactions, making the simulation of the pulsed electrolytic processing process computationally huge and difficult to perform. To accurately describe the multi-physical field coupling relationship for pulsed electrochemical processing. In this paper, a k-ε gas-liquid two-phase flow model has been introduced to model the interpolar gas-liquid two-phase flow field variation law, and on this basis, a coupled multi-physics field model for pulsed electrochemical machining processing is established to provide an accurate description of the interpolar multi-physics interaction mechanism. A quasi-steady-state iterative simplification algorithm based on heat source averaging is proposed to solve the problem that the time scale span of the dissolution process leads to a huge amount of simulation calculations. The simulation analyzes the dissolution characteristics at the micro time scale and macro time scale and compares them with the full precision method. The results show that the simulation accuracy of the two methods is the same, but the simulation calculation time of the simplified algorithm is reduced by two-thirds. The experimental platform was designed and built to carry out a series of experiments under different processing times, and the results effectively verified the correctness of the simulation method.

Multi-Physical Field Coupling Simulation and Experiments with Pulse Electrochemical Machining of Large Size TiAl Intermetallic Blade

Large size TiAl alloy blade is one of the important parts to reduce the weight of advanced aero-engines. However, the precision manufacturing of such blades is a challenge due to their large size, low ductility at room temperature, and high hardness of the TiAl alloy. Electrochemical machining (ECM) is a very promising method for the precision manufacturing of such blades, considering its unique advantages. In this study, a very comprehensive multi-physical field coupling simulation and pulse ECM experiments on large size TiAl alloy blades are carried out. Geometric and theoretical models involving electric fields, gas-liquid two-phase flow, heat transfer, and anodic dissolution are developed. The variation of bubble, temperature, electrolyte flow rate, and electrical conductivity at the outlet and the different areas on the blade surface with the processing time and distribution along the flow channel in the machining gap are revealed by simulation. It is found that the influence of electrolyte temperature on electrical conductivity is more dominant than that of bubble concentration. Finally, the experiments of pulse ECM on large size TiAl alloy blade are carried out, and the experimental results are analyzed in detail. The high efficiency and high surface quality of large size TiAl alloy blades are realized. The surface roughness and machining accuracy of the blade are about Ra 0.9 μm and 0.18 mm, respectively.

Magnetic field effects on nonlinear dynamic behavior in electro-dissolution and pulse electrochemical machining of Ti-48Al-2Cr-2Nb alloy

Magnetic field effects on nonlinear dynamic behavior in electro-dissolution and pulse electrochemical machining of Ti-48Al-2Cr-2Nb alloy

Implementation of a Picosecond Laser for Micromachining the Cathode of Pulse Electrochemical Machining and a Case Study

Abstract Defined topographic features may be produced on the workpiece surface of difficult-to-machine materials through the pulse electrochemical machining (PECM). Due to the contactless feature of PECM, mechanical influences, and their side effects become ignorable. In this study, a picosecond laser, which induces little thermal impact, was applied to micromachine the cathode of PECM with groove patterns, and replication of the patterns on the anode of PECM was carried out using an industrial PECM installation. The results of the case study show that the picosecond laser achieved high machining precision (<6.5% to the target size) with excellent surface integrity on the cathode of PECM, and the groove patterns were successfully replicated on the anode of PECM, although deviations of certain geometric parameters were detected between the two PECM electrodes. These deviations may result from the rounding and widening effects during the PECM processing.

Significance of waveform design to achieve bipolar electrochemical jet machining of passivating material via regulation of electrode reaction kinetics

Electrochemical machining (ECM) using the bipolar pulse technique shows significant potential for the effective machining of prone-to-passivation materials. However, despite its success in machining specific materials (e.g. tungsten carbide), the underlying mechanism remains unclear. This study presents an in-depth analysis of the interplay between cathodic polarisation (CP) and anodic oxidation in bipolar pulse electrochemical jet machining (bipolar-EJM). An observational study of the structural changes in the anodic oxide film indicated that the oxide broke down by electrochemical reduction and mechanical damage when subjected to CP. The electrochemical kinetics at the electrode interface, particularly the proton transport and discharge reactions, were discussed to elucidate the mechanism. This study first discloses that the bipolar pulse waveform plays a crucial role in overcoming the oxide film and achieving machining in bipolar-EJM. Variations in waveform shape result in distinct interactions of the cathodic pulse with the anodically formed surface oxide. A principal approach of bipolar-EJM was thus developed to effectively remove or eliminate passive oxide films by controlling the bipolar pulse. The material removal mechanism of the developed method is described and the corresponding kinetic model of the electrode reactions is presented. For verification, the bipolar-EJM of the strongly passivating metal niobium (Nb) is first demonstrated in a pH-neutral NaNO3 aqueous solution, demonstrating the effectiveness of the proposed method. The new insights into the bipolar pulse process established here will is believed to provide valuable guidance to advance the bipolar electrochemical process, including ECM and electrochemical polishing.

Research on Electrochemical Machining of Small Deep Holes with Positive and Negative Pulse Power

Background: High-temperature alloys, such as the nickel-based alloy, have become the main materials for core components in the aerospace field because of their high strength and good toughness. Therefore, how to improve the machining accuracy and stability of electrochemical machining (ECM) of small deep holes on nickel-based alloy is an important topic for studies. The instantaneous high-density current during the pulse width of pulse ECM is beneficial to the dissolution of nickel-based alloy. Many experts and scholars have studied pulse ECM of small deep holes. Objective: The purpose of this article is to propose and design a positive and negative pulse (PANP) power supply to study the accuracy and stability of ECM of small deep holes on the nickel-based alloy. Methods: First of all, an H-bridge composed of four MOSFET switches is designed to achieve PANP output in the main circuit of the power supply. Then, this article discusses the influence of the ratio of positive and negative pulses on short circuits, the influence of the ratio of positive and negative pulses on the mass removal rate, and the influence of the electrolyte concentration and pulse width on the mass removal rate. Finally, according to the obtained optimal parameters, the influence of the electrolyte pressure on the average radial overcut of hole depth is analyzed. Results: The experimental results show that the short-circuit frequency is reduced by more than 50% compared with non-negative pulses power supply; the ratio of positive and negative pulses, pulse width, and electrolyte concentration and pressure were optimized by experiments in order to improve the mass removal rate of the workpiece and the average radial overcut of hole depth. Conclusion: The designed PANP power supply can improve the machining accuracy and stability of ECM of small deep holes on the nickel-based alloy.

Investigation of Electrochemical Dissolution Behavior of Near-α TA15 Titanium Alloy in NaCl Solution with Low-Frequency Pulse Current

TA15 material is a typical near-α titanium alloy and widely used for the aircraft key load bearing components. Electrochemical machining (ECM) is a cost-effective method to machine difficult-to-cut TA15. Due to the high chemical reactivity of titanium, titanium alloy is prone to passivation, which increases the difficulty of ECM, especially for some common ECM methods with low-frequency pulse currents. To investigate the change of surface characteristics of titanium alloy in pulse ECM, the dissolution behavior of TA15 in NaCl solution under the low frequency pulse current was analyzed by scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS). The results showed that even after removal of initial air-formed oxide film, TA15 would be passivated to form a new passive film during long pulse-off time. Under short pulse-on time, the passive film formed in pulse-off time could not be effectively removed in one pulse-on time, and the passivation effect would be accumulated, resulting in poor machined surface with humps and pits. When the pulse-on time was long enough to completely remove the newly formed passive film, TA15 was dissolved normally to obtain excellent surface with clear crystal structure.

Study on surface roughness of large size TiAl intermetallic blade in electrochemical machining

Large size TiAl alloy blades as a core component in aero-engines have received a lot of attention due to their light weight and superior performance. However, precision manufacturing of such blades is very difficult using traditional mechanical cutting methods because of the large size, super twisted profile and typical difficult-to-cut materials. Electrochemical machining (ECM) is a preferred method for such blades due to its inherent characteristics. In this work, the surface quality of such blades is studied in detail and some defects on the surface of the blade are overcome. Exploratory experiments of DC ECM and pulse ECM at different pulse frequencies are carried out, and the results show that pulse ECM at low pulse frequency is more likely to obtain blade with high surface quality. A two-step variable parameter ECM strategy is proposed based on low pulse frequency, which completely removed the “patchy” morphology and raised defects on the blade surface, and reduced the surface roughness from about Ra 5.5 μm to about Ra 1.8 μm. A control method of multi-channel pressure difference at the inlet is proposed based on the direction of the flow mark, which effectively eliminated the flow mark defect on the blade surface, further reduced the surface roughness to about Ra 0.9 μm, and obtained the blade with high surface quality.

Research on Multi-Physics Coupling Simulation for the Pulse Electrochemical Machining of Holes with Tube Electrodes.

Electrical parameters of the power supply are significant factors affecting the accuracy and stability of the electrochemical machining (ECM). However, the electric field, flow velocity and temperature in the machining area are difficult to measure directly under the influence of the power supply. Therefore, taking the film cooling hole as an example, the multi-physics coupling simulation analysis of the ECM is performed on the basis of Faraday’s law and fluid heat transfer mathematical model. The machining characteristics of the direct current and pulse ECM are compared through simulation. The results show that the pulse ECM improves the distribution of temperature and current density in the machining area. The period has little effect on the temperature, current density and side removal rate. The side removal rate increases with the increase of the duty ratio and lateral gap. Increasing of the duty ratio and decreasing of the lateral gap will increase the temperature and current density. Increasing the inlet pressure accelerates the frequency of renewal of heat and electrolysis products, which can reduce the single side gap. The experience of the ECM holes verifies the results of the simulation. The accuracy and stability of the ECM of holes are enhanced by optimizing the duty ratio, lateral gap and inlet pressure.

Research on the wettability of localized pulse electrolytic machining mold steel (GCr12)

As one of the most widely used metal materials, steel takes on an important role in deep sea and space exploration fields. However, the annual economic loss caused by steel corrosion is immeasurable. To resolve the problem, the localized pulse electrochemical machining (PECM), an efficient, fast and environment-friendly method, was introduced to fabricate microstructures on the surface of mold steel (GCr12). Results show that a super-hydrophobic surface has been obtained and its corrosion resistance has been significantly enhanced without the need to modify the surface by low surface energy solution. Thanks to the optimal working parameters (7.9 V and 2 ms) identified from the processing, the water contact angle of 161.8° was obtained. After fabrication by PECM, the surface microstructure, chemical element, and wettability were characterized and analyzed by scanning electron microscope (SEM), laser scanning confocal microscope (LSCM), EDS energy spectrometer, and optical contact angle measuring instrument, respectively. According to the experimental results, the surface honeycomb structure (micro/nano binary structure) is proven to be the main factor affecting wettability. Next, durability tests and corrosion resistance tests were carried out and the contact angle decreased by 4.4% and 6.7% respectively compared with the original contact angle, indicating that the surface after PECM has strong durability and good corrosion resistance, which can effectively solve the corrosion problem of steel. Therefore, using localized PECM technology to prepare microstructure on the surface of mold steel has a good application prospect in industry.

Investigation of Pulse Electrochemical Machining of Zr-Based Bulk Metallic Glasses in NaNO3-Ethylene Glycol Electrolyte

Zr-based bulk metallic glasses (BMGs) have unique mechanical and chemical properties, which has attracted much attention from academia and industry. Electrochemical machining (ECM) is a non-contact subtractive method very suitable for these materials without grain boundaries. Nevertheless, past work on ECM of Zr-based BMGs indicated the infeasibility of the traditional non-acid water-based electrolytes. In this research, microsecond pulse ECM of Zr-based BMGs in the NaNO3-ethylene glycol (EG) electrolyte has been explored to overcome the difficulties in conventional salt water-based electrolytes. First, polarization behaviors of four kinds of Zr-based BMGs and related elementals in NaNO3-EG electrolyte were derived to examine the passive and transpassive performance. The dissolution mechanism of Zr-based BMGs according to the dwell time was investigated based on XPS analysis. The effects of the current density and pulse parameters were evaluated according to the surface quality, the groove profile, etc. The results show that pulse parameters have a great influence on stray corrosion, due to the high content of late transition metal components on the surface. Taking micro dimples as an example, the NaNO3-EG electrolyte exhibit ability of reducing the pitting corrosion and offering smooth surfaces with acceptable stray corrosion and high machining localization.

Anodic dissolution characteristics of Inconel 718 in C6H5K3O7 and NaNO3 solutions by pulse electrochemical machining

The mechanism by which electrolytic products are removed during ECM of Inconel 718 in a C6H5K3O7 electrolyte was clarified. Experimental results revealed that Cit3− ions decrease the amounts of flocculent and insoluble products in the machining region considerably. The resulting passivating film presented a looser, more porous structure than that from a NaNO3 solution. This made the Inconel 718 more prone to electrochemical corrosion. The uniformity and microscale nature of the micro-pit structure dispersed on the machined surface improved substantially as the current density increased. This improved the surface quality dramatically. Finally, the anodic dissolution characteristic models were established.

Effect of tool-electrode material in through-hole formation using ECDM process

ABSTRACT An experimental investigation comparing the effect of tool electrode materials on the formation of microholes in glass by the pulse electrochemical discharge machining is presented. Two different materials, i.e., Molybdenum and High carbon steel (HCS), were used in the experiments carried out in 10% wt KOH electrolyte. Other parameters such as machining voltage, pulse frequency, tool feed rates were systematically varied. A lower mean discharge current was noticed when the molybdenum tool having higher electrical conductivity was used. The average reductions in the hole overcut, taper angle, and the heat-affected zone in the microholes were 30%, 55%, and 58%, respectively, when the Molybdenum tool was used compared to the HCS tool. For both tool materials, the hole overcut was measured to be minimum when a tool feed rate of 4 µm s−1 was used. The microhole diameter and heat-affected zone were increasing with the increment in the applied voltage irrespective of the tool electrode material. Due to the higher melting point, molybdenum electrodes had less tool erosion and, therefore, more suitable than the HCS tools for electrochemical discharge machining applications.

Research on the wettability of pulse electrochemical machining GCr12 substrates

Based on mold steel (GCr12), the relationship between pulse electrochemical machining (PECM) parameters and surface for wetting characteristics was explored. The groove structure with the depth of 0.5mm has been machined on the surface of the steel casting GCr12 by impulse electrochemical machine. Under the best processing parameters, the hydrophobic angle can reach 161.8°. The microstructure, elementary composition, and wettability of the sample were characterized and analyzed by scanning electron microscope (SEM), ultra-depth-of-field microscope, EDS energy spectrum, and contact angle measuring instrument. Single factor experiments are used to explore the influence of pulse electrochemical machining voltage and pulse time on the surface wettability of mold steel (GCr12).

Multi-time scale simulation of pulse electrochemical machining process with multi-physical model

To determine the relationship between the pulse current and the physicochemical properties of multi-time scales, a method of multi-time scale simulation is introduced to investigate multi-time scale evolution of temperature and void fraction in PECM process. A multi-time scale iterations method is introduced to reduce computation time of multi-time scale simulation. Simulation results indicate that the method is efficient and pulse current can make the PECM process more stable. Experimental results show that the multi-time scale simulation results can well match the actual machining results, especially in the middle section of the workpiece.

Cathode optimization and multi-physics simulation of pulse electrochemical machining for small inner-walled ring grooves

The small inner-walled ring grooves of the injector nozzles of hard-to-cut metallic materials are difficult to machine in aerospace and aviation field. Nowadays, electrical discharge machining (EDM) technology is often employed to machine this kind of structures. However, a time-consuming process of removing the metamorphic layer is needed after EDM process for some important workpieces. To solve this problem, electrochemical machining (ECM) technology for the inner-walled ring grooves of 1J116 corrosion-resistant material is studied. First, four basic tool cathode structures are designed with equal-clearance method and flow field simulations are performed with k-e turbulence model to optimize their structures to ensure flow field uniformity and machining stability. Simulation results show that the uniformity of flow field distribution and machining stability of structure IV cathode are the best among the four types of cathode structures. Then, electric field characteristics in different machining states between the structure IV cathode and the workpiece are analyzed with multi-physics simulation based on the flow field analysis. Simulation results show that current density can meet the machining requirements of the inner-walled ring grooves of the injector nozzles when voltages vary from 12 to 18 V. Finally, a verification experiment is conducted with the optimized tool cathode and machining parameters. The experimental results show that good machining quality is achieved at voltage of 14 V with structure IV cathode.

Optimal design of cathode based on iterative solution of multi-physical model in pulse electrochemical machining (PECM)

In pulse electrochemical machining (PECM), the control of pulse parameters would result in designing the cathode shape according to a given anode shape more complexly than in direct current electrochemical machining (DC-ECM). To solve the problem, a numerical approach is proposed to achieve optimal design of cathode. A gap model is proposed to describe the influence of pulse parameters on gap size and a multi-physical model is introduced to describe the influence of pulse parameters on the distribution of electrolyte conductivity which can reflect the distribution of gap. An optimization method based on iterative solution of multi-physical model is presented to improve design accuracy of cathode shape. The experiments are conducted to illustrate the method of cathode design in PECM process. The results show that the proposed method can effectively improve processing accuracy.

Quasi-Homogenous Model of Electrochemical Machining of Turbine Engine Parts

Abstract In order to increase the efficiency of jet engines hard to machine nickel-based and titanium-based alloys are in common use for aero engine components such as blades and blade integrated disks (BLISK). Electrochemical Machining (ECM) provides an economical and effective method for machining high strength and heat-resistant materials into complex shapes with high material removal rate without tool wear and without inducing residual stress. This article presents the physical and mathematical models of electrochemical shaping used in the manufacture of turbine engine parts. The modelling is based on the assumption that the multi-phase mixture filling the gap is treated as two-phase quasi-homogenous medium. The model describes the workpiece shape evolution in time, distribution the local gap size, flow parameters such as the static pressure and the velocity, temperature and void fraction as result of gas generation. The major features of the numerical computer program are briefly described with a selected example of machining a typical turbine blade. The results of computer simulation of effects of setting parameters ECM on accuracy-machined profile are discussed. The improvement of accuracy has been reached by using described sequence of ECM and Pulse ECM processes.