Through-mask Electrochemical Machining Research Articles

Enhanced fabrication of conical array via two-stage through mask electrochemical machining process

In response to the issues of low processing precision, poor surface quality, and low array uniformity in the fabrication process of metal array conical structures, this paper proposes a two-stage enhanced process for fabricating metal array conical structures using through-mask electrochemical machining (TMECM). The micro-convex structure with high consistency can be quickly obtained through the first electrochemical machining (ECM), and then the mask is removed and the micro-convex structure is modified twice. The top diameter of the micro-structure is reduced by using the phenomenon of electric field concentration in the ECM process, and the top curvature radius of the micro-structure is further reduced, so as to increase the height diameter ratio of the micro-structure and improve the surface quality. The results show that during the initial ECM, when the machining time is 35 s, the voltage is 20 volts, the flow rate of the acid etching solution is 1 m /s, the duty cycle is 50 %, and the frequency is 200 Hz, the stable machining of the metal array conical structure can be achieved. In the secondary electrochemical surface modification, it was found that under the conditions of working solution containing 2 mol/L nickel-based etching agent, pulse voltage of 20 V and processing time of 35 s, the method effectively improved the surface quality of the workpiece and ensured the stable manufacturing of the micro-conical array structure. The prepared microstructure height was 198 μm and the top diameter was 28 μm.

Numerical simulation and experimental research on through-mask electrochemical machining of micro-dimple arrays using inner-jet cathodes

The surface micro-dimple arrays can effectively improve the friction and lubrication performance of moving parts and are widely used in cutting tools and mechanical transmissions. Through-mask electrochemical machining (TMECM) is a process that uses the anodic dissolution principle to remove materials at low temperatures. It is suitable for efficiently processing large-area micro-dimple arrays on metal surfaces. However, the previous TMECM method still suffers from the problem of low processing adaptability. In this paper, a new method for scanning-cathode TMECM by utilizing the fluid dynamic pressure effect was proposed, and the flow field and electric field models of various inner-jet cathodes were developed as well. Through numerical simulations of the flow field and electric field, the flow velocity, electrolyte pressure, and current density distributions for different inner-jet cathodes were investigated to determine an appropriate cathode. Contrasting experiments were conducted to investigate the variations in electrolyte flow states and machining currents for different inner-jet cathodes. Additionally, the changes in micro-dimple dimensions under different machining parameters were investigated. Moreover, the micro-dimple arrays of 385.7 μm in diameter and 111.8 μm in depth, 288.8 μm in diameter and 40.3 μm in depth, and micro-dimple arrays with an etching factor of 1.69 were fabricated, and the results demonstrated the good processing adaptability of the scanning-cathode TMECM.

Manufacturing of dies and an experimental study on the cold-press surface-texture forming process

Surface texturing can significantly improve the service performance of joint surfaces. However, the fabrication techniques for micro- and nanoscale structures require high-precision equipment and involve complicated processes. An efficient and practicable cold-press forming technique for surface-texture fabrication was proposed. First, the feasible methods for fabricating cold-pressed dies with surface textures were introduced. Three methods for preparing cold-pressing dies having microembossment arrays were explored. The preparation of dies via through-mask electrochemical machining on an alloy steel surface was deemed feasible. Then, the process parameters of cold-press surface-texturing were calculated using the sliding line method. The application of single microembossment to cold pressing of brass verified the validity of the models. Ultimately, cold-pressing experiments were performed using an array microembossment die. A surface texture of 1000 pits was formed in ∼3 s, and the desired quality was achieved. The experimental results showed that cold pressing of surface textures could be accomplished using the manufactured dies at a low cost and high efficiency.

Investigation of through-mask electrochemical machining process using a rib-connected photoresist for microcone array with large height-to-diameter ratio

Metal microcone arrays are widely applied in aerospace, medicine, and chemistry, and usually require precision fabrication with a large height-to-diameter ratio and high array consistency. For this purpose, the present paper describes a method of through-mask electrochemical machining (TMECM) using a rib-connected photoresist. A large mask diameter is found to be beneficial for producing microcones with a large height-to-diameter ratio. However, the larger mask is more easily flushed off, which will destroy the consistency of the array. Therefore, a rib-connected photoresist structure for use during TMECM is developed. The improvement in performance offered by this photoresist is verified by simulations and comparative experiments. Finally, the machining parameters of the TMECM using a rib-connected photoresist are further optimized. When the machining time is 46 s, the flushing speed is 4 m/s, and the HCI concentration is 2 mol/L, the microcone array structure with a large height-to-diameter ratio of 10.28 and the standard deviation of 0.22 is obtained.

Simulation and analysis of through-mask electrochemical machining with moving tools

At present, the development of through-mask micro-electrochemical machining is only limited to static machining, where the size of the tool is usually the same as that of the workpiece. However, in the electrochemical processing, metal with good electrical conductivity is chosen as the tool electrode, and it is usually very expensive. Based on the cost consideration, a moving tool with small size may be preferred. Finite element method is used in this paper to create the electric field model of through-mask micro-electrochemical machining with moving tool. The effects of the parameters, such as applied voltage, mask thickness, on the machining shape are investigated. The results show that the higher the applied voltage, the larger the machining depth and width, and also the better the aspect ratio. When the thickness of the mask is thin, the electric field is unevenly distributed and the lateral corrosion is more serious. There is an island-like phenomenon, which is related to the masking of the mask. When the moving speed is relatively slow, the relative processing time is longer. The current density accumulated on the surface of the workpiece is thus higher and the material removal rate is higher. As the processing time increases, the machining depth becomes deeper, and the forward corrosion rate is slow down.

Ultrasound-Assisted Through-Mask Electrochemical Machining of Hole Arrays in ODS Superalloy.

Micro-hole arrays have found wide applications in aerospace, precision instruments, and biomedicine. Among various methods of their production, including mechanical, laser, and electrical discharge, electrochemical machining (ECM) is considered the most lucrative due to its wide processing range, high surface quality, and excellent productivity. In particular, ultrasound-assisted through-mask ECM exhibits an enhanced machining precision due to ultrasonic cavitation, which promotes the removal of the electrolytic products and bubbles. In this study, the equation of cavitation bubble oscillation was derived and numerically solved to study the influence of six different parameters on the ultrasonic cavitation and electrolysis process, and their optimal values were determined. The feasibility of the proposed ultrasound-assisted through-mask ECM technology with the optimized parameters was experimentally corroborated by the fabrication of a high-quality hole array in an oxide dispersion strengthened (ODS) MA956 superalloy.

Improvement of machining consistency during through-mask electrochemical large-area machining

Electrochemical machining (ECM) is an important machining technique for the aeronautical manufacturing industry. Through-mask ECM is a form of ECM for machining metal parts with a hole array. In order to extend the machining area, a serpentine flow channel with multiple curves was used for through-mask ECM. With the extension of the flow channel, ensuring a machining consistency along the flow channel has been a challenge. The electrolyte conductivity is the main factor affecting the machining consistency. To analyze the change rules of the electrolyte conductivity, variations in the bubble rate and the temperature of the electrolyte in the electrolyte flow were explored under different power sources. Results indicate that pulse-power machining can reduce variations in the bubble rate and the temperature in the serpentine flow channel, and then the electrolyte conductivity can be stabilized within a very small range. Experiments using through-mask ECM were conducted in two types of power sources. Experimental results support the importance of pulse-power machining. A 14 × 28 hole array with a 2.5 mm diameter was fabricated by a pulsed power source. The aperture deviation of the hole array is less than 0.05 mm, and the roundness deviation is less than 15 μm when fabricated with pulse machining.

Through-mask electrochemical machining of hole arrays on molybdenum sheets

Molybdenum is an important modern industrial material. It is widely used in high-energy and high-heat environments due to its high melting point and thermal conductivity, as well as its low thermal expansion coefficient. Hole arrays on molybdenum sheets are commonly used in industry, with applications in ion plating equipment, projection electron microscopes, cryo-electron microscopy, and electron guns. However, fabrication of these arrays on molybdenum sheets is very difficult due to high opening ratio limitations, deformation of thin sheets, and the mechanical properties of the metal. Therefore, high-efficiency, high-precision fabrication of hole arrays on molybdenum sheets has emerged as a focus of research. Through-mask electrochemical machining (TMECM) is an effective method of fabricating hole-type components. This paper describes a method of fabricating hole arrays on a sheet using a TMECM process in a neutral NaNO3 solution. Polarization and current efficiency curves were measured for molybdenum in a NaNO3 solution to identify its electrochemical characteristics in the electrolyte. The results show that molybdenum dissolves well in NaNO3 solutions and exhibits good surface erosion uniformity. Furthermore, it does not produce obvious protuberances, dimples, or stress cracks. The experimental results indicate that hole arrays can be fabricated on molybdenum sheets with relatively high precision via a TMECM process with appropriate processing parameters. The aperture deviation was less than 0.05 mm, and the roundness deviation of the holes was less than 9.8 μm.

Comparison between wire mesh and plate electrodes during wide-pattern machining on invar fine sheet using through-mask electrochemical micromachining

Many research on the fabrication of Organic light emitting diodes (OLED) shadow masks with high resolution have been carried out because of the development of the smart-display industry. It is the parts of display panel which has millions of micro holes on invar (Fe-Ni) fine sheet. Various techniques such as laser machining, chemical etching and Electrochemical micro-machining (EMM) are used to produce micro-hole arrays. In this study, Through-mask electrochemical machining (TMEMM) combine with portion of photolithography process was applied to fabricate micro-hole arrays on invar fine sheet. The sheet was coated with dry film photoresist. Two types of electrode, plate and mesh, was used to compare the influence of electrode type. The sheet was coated with dry film photoresist with micro- sized through holes. The results were compared in regard to uniformity and taper angle. Compared with the plate electrode, the mesh electrode has better uniformity and taper angle which is important criteria of OLED shadow mask. These results could be used to improve TMEMM for invar fine sheet when it is applied to fabricate micro-hole arrays and help to obtain optical uniformity and desired taper angles.

Improvement of electrolyte flow field during through-mask electrochemical machining by changing mask wall angle

Hole arrays are a common mechanical structure in engineering components. Through-mask electrochemical machining has shown good feasibility in the field of machining difficult-to-cut metal parts with a hole array. The electrolyte flow field is an important factor to affect the process of electrochemical machining, therefore, the improvement of electrolyte flow field is always the key point of electrochemical machining. In this paper, a mask with cone-shaped holes is used to improve the electrolyte flow of through-mask electrochemical machining. The effects of mask wall angle on electrolyte flow are researched by using computational fluid dynamics. Four mask wall angles at 90°, 120°, 140° and 160° are analyzed numerically. The simulated results show that a mask with cone-shaped holes is beneficial to electrolyte flow during through-mask electrochemical machining, especially when the mask wall angle is more than 140°. In order to verify the simulated results, four angles of mask wall are applied to machining experiment. The experimental results indicate that the most reasonable mask wall angle is 140°. At this mask wall angle, the average diameter of fabricated holes is 2.764mm, and the deviation of diameter is less than 0.1mm. Meanwhile, the taper angle of fabricated holes is less than 5.8° and the deviation in roundness is 12.04μm.

A Study of Electrochemical Machining of Ti-6Al-4V in NaNO3 solution.

The titanium alloy Ti-6Al-4V is used in many industries including aviation, automobile manufacturing, and medical equipment, because of its low density, extraordinary corrosion resistance and high specific strength. Electrochemical machining (ECM) is a non-traditional machining method that allows applications to all kinds of metallic materials in regardless of their mechanical properties. It is widely applied to the machining of Ti-6Al-4V components, which usually takes place in a multicomponent electrolyte solution. In this study, a 10% NaNO3 solution was used to make multiple holes in Ti-6Al-4V sheets by through-mask electrochemical machining (TMECM). The polarization curve and current efficiency curve of this alloy were measured to understand the electrical properties of Ti-6Al-4V in a 10% NaNO3 solution. The measurements show that in a 10% NaNO3 solution, when the current density was above 6.56 A·cm−2, the current efficiency exceeded 100%. According to polarization curve and current efficiency curve, an orthogonal TMECM experiment was conducted on Ti-6Al-4V. The experimental results suggest that with appropriate process parameters, high-quality holes can be obtained in a 10% NaNO3 solution. Using the optimized process parameters, an array of micro-holes with an aperture of 2.52 mm to 2.57 mm and maximum roundness of 9 μm were produced using TMECM.

Active through-mask electrochemical machining with its interelectrode gap filled with flexible porous material

It has been one of issues that conventional through-mask electrochemical machining is very hard to fabricate surface texture efficiently on the non-planar workpiece. To solve this problem, a modified active through-mask electrochemical machining process (active TM-ECM) with its interelectrode gap filled with flexible porous material was proposed on the basis of development of a special tool cathode. The newly developed tool cathode allows for inlet and distributing of electrolyte as well as discharging of solution. The flow field within the interelectrode was analyzed and optimized numerically, and the effects of key process parameters including mask thickness, flexible porous layer thickness, clamping force and pulsed current parameter on the geometric profiles and their distributing characteristics of the machined microdimple were investigated experimentally. The arrays of microdimples with a fairly good distribution of geometric dimensions were successfully machined on both the stainless steel planar substrate and cylindrical workpiece by using the optimal process conditions. It is showed that the modified active TM-EMM process exhibits favorable machinability and applicability to produce microdimples on the planar and non-planar surfaces.

Through-mask electrochemical machining of a large-area hole array in a serpentine flow channel

Through-mask electrochemical machining has been shown to be very feasible for machining metal parts with hole arrays. However, machining a large-area hole array by through-mask electrochemical machining has been challenging. To machine a large-area hole array, in this paper, a serpentine flow channel is proposed for through-mask electrochemical machining. The principle of the serpentine flow channel is introduced. Computational fluid dynamic simulations show that the flow state in the channel is not uniform. To deal with this problem, circular deflectors are placed in the corners of the channel. By adjusting the circular deflectors, an optimal serpentine flow channel is obtained with a steady flow state. This optimal channel is used in a through-mask electrochemical machining experiment, and a 10 × 20 hole array with 2.564-mm average diameter is fabricated. The maximum deviation of diameters is 0.04 mm, and the roundness is less than 8 μm in this hole array.

Investigation of the hole-formation process during double-sided through-mask electrochemical machining

Through-mask electrochemical machining has been developed to fabricate hole-array in titanium alloys that are difficult to cut using traditional mechanical machining. The taper angle of hole-array is an important criterion to estimate the quality of machined hole-array. Due to the isotropic nature, the machined holes have taper angles by using through-mask electrochemical machining, and it is still a challenge to reduce these taper angles. In this paper, a double-sided through-mask electrochemical machining process is investigated in order to fabricate hole-array with low taper angle. A model of the double-sided through-mask electrochemical machining is established to simulate the hole-formation process. The simulation results indicate that the electric field of the double-sided through-mask electrochemical machining is beneficial to reduce the taper angles of machined holes. In order to verify the simulation results, experimental investigations of hole-formation are implemented. The experimental results indicate that the sidewall of machined hole could be close to the straight at a certain machining time. Finally, a 6×50 hole-array is machined by double-sided through-mask electrochemical machining onto Ti-6Al-4V sheet with thickness 0.5mm. The maximum taper angle of the hole-array is only 2.52°.

Modeling of Electrochemical Machining Through a Monolayer Colloidal Crystal Mask for Metal Surfaces Nanostructuring

Through-mask electrochemical machining is widely used to produce micro- and nanostructured surfaces. Various types of masks are used to localize the areas of anodic dissolution or cathodic deposition. A possibility of producing nanostructured surfaces by using the anodic dissolution of substrate metal through a mask of regularly arranged spherical particles has been experimentally shown in several works. In contrast to the case of metal electrodeposition into spherical mask pores, when the deposit geometry is completely determined by the pore geometry, in the anodic dissolution, the geometry of substrate surface differs essentially from the geometry of mask pores.In this work, the problem of predicting the shape and dimensions of substrate surface as a function of the mask parameters and operation conditions was solved. A method of numerical simulation of electrochemical shaping for the anodic dissolution of substrate metal through a mask of a single-layer colloidal crystal (monodispersed spherical particles) was developed. The Laplace equation and the equation of evolution of workpiece surface, which was prescribed by an explicit function, were used as the mathematical model of the process. The geometry of computational region was determined with regard for the system's symmetry: the region with the regular-hexagonal cross-section was taken as a unit cell. The unit cell was limited above by the outer boundary of diffusion layer and, below, by the workpiece surface. The numerical solution of Laplace equation was performed by a fast multipole boundary element method. The numerical solution of equation of anode surface evolution was performed by the Level Set method. The results of the simulation are presented for various sphere package densities and treatment times.

Modeling of through-mask electrochemical micromachining

A scheme of numerical modeling of through-mask electrochemical machining, which enables one to predict the shape and sizes of workpiece surface, is developed. The effect of mask parameters (a fraction of unprotected area, mask thickness and unprotected region width) on the distribution of an average current density over the workpiece surface is analyzed. The developed mathematic model and the calculated results can be used to design the operations of electrochemical micromachining with partial insulation of workpiece surface.

Distribution Manner of Compaction Circular Cylinders in Through-Active-Mask Electrochemical Machining

Electrochemical machining is widely used in the processing of difficult-to-machine metal materials. And through-mask electrochemical machining is a very important technology in the processing array structure of difficult-to-cut metal materials. Traditional through-mask electrochemical machining always uses a photoresist as the mask. The production process of a mask is complicated, and the mask cannot be reused. In this paper, through-active-mask electrochemical machining to process array structure in difficult-to-machine metal materials was investigated. Compared with traditional electrochemical machining masks, a copper-clad laminate is used to make the mask by mechanical machining in through-active-mask electrochemical machining. Also, the mask does not stick together with the workpiece but covers the workpiece by mechanical compaction, so the mask can be reused. In order to ensure the mask is in close contact with the workpiece, we need to arrange many compaction circular cylinders within the flow channel. The influences on electrolyte flow of compaction circular cylinders were investigated. The distribution of the compaction circular cylinders affects the electrolyte flow state, thereby affecting the processing. By analyzing the electrolyte flow state for the different distributions of compaction circular cylinders, one can find the best distribution of compaction circular cylinders for the required processing.

Reduction of stray corrosion by using iron coating in NaNO3 solution during electrochemical machining

Stray corrosion is a common phenomenon that occurs at the surface adjacent to the machining area during electrochemical machining (ECM). It can cause unwanted metal removal and has a substantial effect on the ECM precision. Standard through-mask ECM prevents stray corrosion with a locally insulated anode, which requires the insulating material to be positioned accurately and applied through a complex process, including resist application, exposure, developing, and stripping. This paper presents a new method for reducing stray current attack by using an iron coating on the surface of the anode workpiece in NaNO3 solution. The application of the iron coating to the whole initial surface of the workpiece does not require precision, and the process is simple and economical. Because the iron coating is passivated at low current densities and can be easily applied or removed, it can be used to reduce the stray current attack. The η-i curves of the nickel-based alloy, Inconel 718, show that its dissolution efficiency is higher at low current densities, indicating poor localization and severe stray corrosion during ECM. A simulation and an experimental study of ECM a convex on iron-coated and uncoated Inconel 718 workpieces were performed. The results showed that the iron coating on the surface of the workpiece significantly improves the machining accuracy. It reduces stray corrosion and the amount of stray removal on the non-machined top surface of the convex workpiece.