Pulse Electrochemical Micromachining Research Articles

Development of nanosecond spike pulse power supply for electrochemical micromachining

The use of pulse voltage can greatly improve the precision of electrochemical microfabrication, and the narrower the pulse width of the applied pulse voltage signal, the higher the machining precision. However, the commonly used chopper circuit topology of pulse power supplies is limited by the maximum switching frequency of the field-effect transistor. To address this problem, this paper proposes a nanosecond pulse electrochemical micromachining power supply based on a differential circuit. The power supply uses the STM32F103C8T6 microcontroller as the control core to output high-performance rectangular waves through a DDS device. After differential, rectification, filtering, and power amplification processing, stable, frequency, amplitude, and pulse width adjustable spike pulse voltage signals are obtained. By establishing a system mathematical model and optimizing the time constant of the differential circuit, theoretically, the sub-nanosecond pulse width can be obtained. Prototype performance tests show that the power supply has a maximum frequency of 20 MHz, a minimum pulse width of 1.8 ns, and a maximum peak voltage of 10 V. By using this power supply for microhole electrochemical machining experiments, nanometer-level machining precision has been achieved.

Electrochemical micro-machining based on double feedback circuits

Pulsed electrochemical micromachining accuracy predominantly depends on pulse duration. To obtain high accuracy, an expensive power source with ultra-short pulse duration is needed. An electrochemical micromachining method based on double feedback circuits is proposed in this work to achieve this aim. A positive feedback circuit plus a negative feedback circuit is used in the circuit of the pulsed electrochemical micromachining. Thus, the gains of the feedback circuits can control the pulse duration of the machining system. Experiments show that the machining resolution can be improved notably by an increase in the feedback gains. Using the method, one micro double cure beam is produced, and its accuracy gets to nanometer level under the condition of using an ordinary pulse duration power source.

Investigation on Bidirectional Pulse Electrochemical Micromachining of Micro Dimples.

Through-mask electrochemical micromachining (TMEMM) is a promising method to prepare micro dimples on the surface of metallic parts. However, the workpiece is machined one by one in traditional TMEMM. This paper introduced bidirectional pulse to TMEMM to improve the machining efficiency. Two masked workpieces were placed face to face, and connected to the ends of the bidirectional pulse power supply. Along with the change of the pulse direction, the polarities of the two workpieces were interchanged periodically, and micro dimples could be prepared on both workpieces at one time. The simulation and experiment results indicated that with bidirectional pulse mode, micro dimples with same the profile can be prepared on two workpieces at one time, and the dimension of micro dimple was smaller than that with unidirectional pulse mode. In bidirectional pulse current, the pulse frequency and pulse duty cycle played an important role on the preparation of micro dimple. With high pulse frequency and low pulse duty cycle, it is useful to reduce the undercut of micro dimple and improve the machining localization. With the pulse duty cycle of 20% and pulse frequency of 10 kHz, micro dimples with etch factor (EF) of 3 were well prepared on both workpieces surface.

Electrochemical Micromachining Using Real Pulse Signals

The machining resolution of pulse electrochemical micromachining technology can be increased by shorting the pulse duration and changing the voltage signal waveform. With a triangular pulse, the energy per pulse was reduced by about two-thirds, and the machining gap was decreased by about eleven times compared to one with a rectangular pulse. Here, we put forward a real pulse waveform for electrochemical micro-machining. The pulse waveform is obtained by rectangular pulse plus differential circuits. The waveform can greatly reduce energy per pulse and surprisingly improve the precision of micro-electrochemical machining. The basic principle of the micromachining is analyzed. The equations of the machining accuracy and energy per pulse are deduced. Using the equations, the machining accuracy and energy per pulse as a function of the differential times of the differential circuits are calculated and compared with simulated and experimental results. Compared to the rectangular pulse, the energy per pulse for the waveform can be reduced by about six times and the machining gap was decreased can be improved by about 11 times. Using this method, some micro structures are produced and nanometer lever machining accuracy is realized which illustrates the proposed machining method.

Selected Aspects of Electrochemical Micromachining Technology Development.

The paper focuses on the fundamentals of electrochemical machining technology de-elopement with special attention to applications for micromachining. In this method, a material is removed during an anodic electrochemical dissolution. The method has a number of features which make it attractive technology for shaping parts with geometrical features in range of micrometres. The paper is divided into two parts. The first one covers discussion on: general characteristics of electrochemical machining, phenomena in the gap, problems resulting from scaling down the process and electrochemical micromachining processes and variants. The second part consists of synthetic overview of the authors’ research on localization of pulse electrochemical micromachining process and case studies connected with application of this method with use of universal cylindrical electrode-tool for shaping cavities in 1.4301 stainless steel. The latter application was conducted in two following variants: electrochemical contour milling and shaping carried out with sidewall surface of rotating tool. In both cases, the obtained shape is a function of electrode tool trajectory. Selection of adequate machining strategy allows to obtain desired shape and quality.

Improvement in performance criteria of varactor micropattern by pulsed maskless electrochemical micromachining

With the progression of many types of micropattern generation using unconventional micromachining techniques has extensive applications in many advanced fields. In this paper, introducing a defined shape of varactor type micropattern generation on stainless steel samples using pulsed maskless electrochemical micromachining (EMM) is more imperative for the application of radio frequency (RF) and microwave communication systems. In this paper, maskless pulsed EMM system is developed for carrying out the investigation during generation of varactor micropatterns. One single masked tool can produce numerous high quality micropatterned workpieces. Pulse current is used to enhance the regularity of machining. Outcomes of EMM process variables i.e., duty ratio and pulsed frequency on machining criteria i.e., material removal rate (MRR), overcut, depth, surface finish and taper kerf angle are investigated during fabrication of varactor micropattern. From the experimental results, the best parametric combination such as 20 kHz frequency and 30% duty ratio can generate the regular varactor micropattern.

Electrochemical micromachining based on time constant control

Two basic methods to increase machining resolution for pulse electrochemical micromachining are discussed in this paper. The first technique is the widely used method of pulse duration reduction and the second is a seldom used technique of increasing the time constant of the circuit. A novel method to increase the time constant for improved machining resolution is proposed. A positive feedback loop is then added in an equivalent circuit of electrochemical micromachining, and its time constant is controlled by tuning feedback gain. In this way, feedback gain can be an effective control parameter for machining resolution, with experimental results illustrating that resolution is significantly improved with an increase in feedback gain. This technique is used to machine microstructures, and nanometer scale machining resolution is achieved.

Dual-Sensing System for Monitoring Ion Concentration Change in Electrochemical Micro Machining

Currently, no reliable electrolyte concentration monitoring method exists for ultra-short pulsed electrochemical micromachining. A dual-sensing system for electrolyte concentration monitoring is proposed in this work. An inductance element is added into the classical pulsed electrochemical micromachining circuit system. For it, a modified circuit equation is proposed by which the coupled electronic and ion circuit is analyzed, and two modes of the coupled circuit are found. The asynchronous mode is used to monitor the concentration changes of the ions in electromechanical micromachining, and a novel method of electrolyte concentration monitoring is obtained. Combining this method with the short-circuit frequency monitoring method, an electrolyte concentration monitoring method based on the dual-sensing monitoring system is proposed, and corresponding monitoring software is produced. The software is used in actual microstructure processing experiments, obtaining nanometer-scale machining accuracy.

Experimental investigation of machined hole and optimization of machining parameters using electrochemical machining

The electrochemical micromachining in non-conventional machining which suffers from process control in micro level. In addition, the work material i.e. stainless steel provides high strength, high toughness and adherence to tool material, hence machining of such material is arduous. However, the use of stainless steel offers its availability in the field of aerospace fuel injection and orthodontic application, since it possess superior qualities. In this paper, the optimization of micro drilling process is carried out in stainless steel by considering certain metrics like feed rate, voltage and duty ratio. The geometric characteristics to drill the tool depends on response parameters like overcut, removal rate of material and conicity. Such parameter determines both the geometric and machining characteristics of the drill bit. The study is evaluated to observe the effect of response and duty ratio parameters such as material removal rate (MRR), machining time and overcut. Further, the conicity is analyzed using VMS images. Finally, the proposed work establishes duty cycle in pulsed electrochemical micromachining domain of hard materials and tests its performance.

Electrochemical Micromachining with Sinusoidal Signals

In ultra-short pulse electrochemical micro-machining, step voltage signals are used with pulse duration as the only effective control parameter of machining resolution. Decreasing pulse duration increases the machining resolution, but requires an expensive ultra-short pulse power source. A novel electrochemical micromachining technique using sinusoidal signals is proposed in this paper, and a differential equation of the equivalent circuit under sinusoidal signals is developed for the method. From this, the equation of the relationship between machining accuracy and frequency of the sinusoidal signals is provided. Using the equation, machining resolution as a function of the frequency of sinusoidal signals is simulated and compared with the experimental findings. Results show a good correspondence is obtained, and that machining resolution significantly increases with the frequency of the sinusoidal signals. Using the technique, micro structures are fabricated, and good machining resolution is achieved. The proposed technique does not require an expensive ultra-short pulse power source, and as sinusoidal signals are the most readily available electrical signals, this technology will be more convenient in industrial applications.

Improvement in machining accuracy of micro-dimples fabricated in a sandwich-like electrochemical micromachining unit using a porous cathode

Surface texture plays a significant role in improving interfacial performance of mechanical components. Electrochemical micromachining is a feasible method for preparing micro-dimples. Sandwich-like electrochemical micromachining (SLEMM) could be used for generating micro-dimples, in which the cathodic tool keeps in close contact with the mask firmly laminated to the anodic workpiece surface, and the dissolution of the workpiece takes place in the enclosed unit. The shallow micro-dimples could be machined with the electrolytic products accumulating on the workpiece surface in the enclosed unit of SLEMM. A porous metal cathode was employed in SLEMM resulting in an open unit, which could remove electrolytic products and generate deep micro-dimples. However, there is poor machining accuracy of micro-dimples obtained with stationary electrolyte over the porous cathode. Pulse electrochemical micromachining is an effective method for enhancing the machining accuracy of micro-dimples. Therefore, the pulse is applied to improve the machining accuracy of micro-dimples generated in SLEMM with a porous metal cathode. And the different electrolyte flow modes over the porous metal cathode are employed to investigate their influence on machining accuracy of micro-dimples. The experimental results indicate that the pulse current power supply could improve the machining accuracy of micro-dimples, compared with direct current power supply. Furthermore, the machining accuracy of micro-dimples could be improved by lateral flow mode, compared with radial flow mode. With a 40% pulse duty ratio, 4 kHz pulse frequency, 15 V applied voltage, and 6 s effective machining time, the micro-dimples have a good machining accuracy on multiple anodic workpieces.

Investigation of pulse electrochemical sawing machining of micro-inner annular groove on metallic tube

Pulse electrochemical sawing micro-machining (PECSM) is a non-conventional process. Having features of no tool wear, no cutting force, and good surface quality, this process is suitable for machining micro-grooves on the inner wall of hole. The rotating dentate cathode (RDC) is beneficial for the distribution of electrolyte and electrolytic products removal, thus reducing the effects of concentration polarization on the electrochemical reaction. This study focuses on the PECSM of micro-inner annular groove on 304 stainless steel tube using a pH-neutral NaClO3 electrolyte. To study the effects of RDC on the process, the bubble layer structure (BLS) adhered to the surface of RDC was photographed using a high-speed camera. Under the condition of immersion, the symmetric distribution of two kinds of BLS adhered to the RDC surface. The four selected parameters (radius of dentate cathode, rotational speed of RDC, initial gap, feed rate) with different levels were carried out to study the process of PECSM micro-inner annular grooves on 304 stainless steel tube. Experimental results indicate that PECSM has high potential for machining micro-inner annular groove on metallic tube. A micro-inner annular groove that is 340μm in depth and 263μm in width was fabricated on a 304 stainless steel tube.

Electrochemical Micromachining of Bulk Metallic Glasses

Owing to unique structural and functional properties bulk metallic glasses (BMG) are very promising materials. Their outstanding durability aligned with high mechanical strength and/or soft magnetic properties make them suited for micro­-electro­mechanical systems (MEMS), diminutive spring-mass systems, micronsized yokes in positioning systems, magnetic cores or medical gadgets. For shaping the required micro-sized devices thermo-mechanical forming is so far applied, but this is only applicable to selected glassy alloys with appropriate thermal characteristics. An upcoming alternative which allows operating at room temperature is electrochemical micromachining (ECMM). As new technique voltage pulsed electrochemical micromachining with a micro-tool electrode is introduced and a specially designed four-electrode setup for machining glassy plates was developed. The multi-component and reactive nature of metallic glasses demands a strict control of the local electrochemical dissolution process based on the choice of a suitable electrolyte and the identification of the effects of the ideal ultra-short pulse voltage parameters. First studies focused on Zr-based BMGs. Their high susceptibility for pitting corrosion limits the choice of electrolytes to halide-free ones. The standard electrolyte for industrial ECM is a concentrated (250 g/l) sodium nitrate solution. When conducting machining experiments with ultra-short voltage pulses in the transpassive regime, it could be demonstrated that the electrochemical dissolution of the glassy alloy can be focused on the microscale. But machined structures were irregularly shaped and covered with corrosion products and no clear dependence from the machining parameters was given. The underlying reaction mechanism and the role of the amorphous alloy structure and of the alloy constituents are discussed [1,2]. Recent studies were conducted on selected Fe-based glasses. Surface structuring of the soft magnetic glassy alloy Fe65.5Cr4Mo4Ga4P12C5B5.5 (at.-%) using an electrolyte based on a methanolic sulfuric acid solution was successful. The transpassive dissolution process was utilized for a defined, localized material removal. By applying nanosecond pulses between a work piece and a tool electrode, micro-holes of high aspect ratio and depth of up to 100 µm can be machined. But methanolic solutions are highly toxic and flammable and thus, undesirable in industrial mass production. Water-based electrolytes are the better choice, but the BMG is forming a passive layer which is very stable throughout the machining process. The addition of an oxidizing agent (iron sulphate) is successfully introduced to reduce this passivation process. Further, the Fe(III) ion reduction dominates the W-tool cathode reactivity and thus, suppresses disturbing hydrogen evolution. The influence of the applied oxidizing agents is analyzed and robust parameters for a fast and repeatable forming process without corrosion products are evaluated. The impact of the crucial process parameters as voltage, heading velocity or pulse-pause-ratio on the surface structuring is discussed. Optimum hole and line micro-structures were machined on BMG surfaces in 0.1 M sulphuric acid solution with 0.1 M iron sulphate at parameters: pulse on/off voltage = 6.0/0.5 V, pulse period/length = 750/75 ns, machining velocity = 0.1 µm/s (deep hole) and pulse on/off voltage = 6.0/1.0 V, pulse period/length = 2400/300 ns, machining velocity = 0.05 µm/s (line) [3-5]. This work is funded by the German Research Foundation (DFG) under project numbers GE 1106/10 and 1106/11. [1] J. A. Koza, R. Sueptitz, M. Uhlemann, L. Schultz, A. Gebert: Electrochemical micromachining of a Zr-based bulk metallic glass using a micro-tool e lectrode technique, Intermetallics 19 (2011) 437-444 [2] A. Gebert, P.F. Gostin, R. Sueptitz, S. Oswald, S. Abdi, M. Uhlemann, J. Eckert: Polarization studies of Zr-based bulk metallic glasses for electrochemical machining , Journal of the Electrochemical Society 161 (4) (2014) E66-E73 [3] R. Sueptitz, K. Tschulik, C. Becker, M. Stoica, M. Uhlemann, J. Eckert, A. Gebert: Micro-patterning of Fe-based bulk metallic glass surfaces by pulsed electrochemical micro-machining (ECMM), Journal of Materials Research 27 (2012) 3033-3040 [4] R. Sueptitz, P. Dunne, K. Tschulik, M. Uhlemann, J. Eckert, A. Gebert : Electrochemical micromachining of passive electrodes, Electrochimica Acta 109 (2013) 562-569 [5] S. Horn, A. Freidank, M. Uhlemann, M. Stoica, J. Eckert, A. Gebert, Electrochemical micromachining of passive Fe-based bulk metallic glasses in aqueous solutions, Proceedings INSECT 2014, Saarbrücken, Germany (in press)

Pulsed electrochemical micromachining for generating micro-dimple arrays on a cylindrical surface with a flexible mask

Abstract Micro-dimple arrays play an important role in improving the performance and reliability of mechanical systems, and micro-dimples on the surfaces of piston rings and sliding bearings may reduce friction. Although many methods can be employed to create micro-dimples on cylindrical surfaces, it is still a challenge to generate micro-dimple arrays on cylindrical surfaces with high efficiency and low cost. In this paper, a patterned polydimethylsiloxane (PDMS) mask with good flexibility is introduced as a mask in through-mask electrochemical micromachining (TMEMM) for generating micro-dimple arrays on a cylindrical surface, in which thousands of micro-dimples can be fabricated in tens of seconds. In addition, the reusability of the PDMS mask is experimentally verified. To enhance removal of the product, the use of a pulsed current is introduced into TMEMM of micro-dimples. The experimental results show that the pulse duty cycle plays a significant role in enhancing the removal of product and improving the uniformity of the micro-dimple arrays. And the effect was weakened with increasing pulse duty cycle. Compared with duty cycles of 40, 60, and 80%, the highest current efficiency with a duty cycle of 20% is obtained at a frequency of 10 kHz. Finally, micro-dimple arrays with a diameter of approximately 110.6 μm and a depth of 11 μm are successfully generated on the cylindrical surface.

A novel pulse shortcut strategy for simulating nano-second pulse electrochemical micro-machining

Nano-second pulse electrochemical micro-machining is essentially employed in high precision metal processing applications. Simulation wise, such a process involves heavy time-accurate calculations necessary to obtain the confined anodic current density distribution, crucial for the machining copy accuracy. A new alternative simulation method is presented, entitled the Pulse Shortcut Strategy (PSS), that avoids the entire time-accurate procedure and significantly reduces the computational effort and runtime. The PSS relies on calculating a current density Correction Factor (CF) that is based on the local electrolyte resistance, the interface polarization and double layer (DL) properties in combination with the nano-second pulse characteristics. The same confining effect is achieved by simulating a computationally cheap stationary current density distribution and altering it locally through the space-dependent CF. When the system has constant electrolyte resistivity, constant DL capacitance and linear polarization, the CF calculation reacts in full agreement with the time-accurate simulation results for any pulse on-time/off-time combination. The PSS accuracy is compared with full time-accurate simulations and represents a mutual validation method between the two. These results offer promising perspectives for the simulation of nano-second pulse electrochemical micro-machining, making it more attractive from a practical point of view once the general interest in the technology emerges. The approach can be generalized to other pulsating electrochemical systems.

Reducing tool wear in micro electrochemical machining by cryogenic treatment

Pulse electrochemical micromachining (PECMM) is an unconventional manufacturing method suitable for the production of micro sized components on a wide range of electrically conductive materials. Absence of cathode wear during electrolysis is a major advantage of electrochemical machining. However, tools are often chemically corroded by certain electrolytes used in PECMM. In this study, cryogenic treatment was performed to improve the corrosion resistance of tungsten tools to achieve increased tool life in PECMM. Using one-way multivariate analysis of variance method, optimum cryogenic cycle parameters for the PECMM were established. Compared to an untreated tool, a reduction of about 10% to 45% in tool wear rate and 0% to 80% in corrosion rates, and 20% to 200% increase in MRR were observed on electrochemical machining with tools that were cryogenically treated.

Mathematical modeling and verification of pulse electrochemical micromachining of microtools

Pulse electrochemical micromachining (PECMM) is an unconventional manufacturing method suitable for the production of micro-sized components on a wide range of electrically conductive materials. PECMM in this study has been used to manufacture microtools. The non-contact nature of PECMM has necessitated the modeling of the process to estimate the anodic profile (microtool profile). This paper presents a mathematical model for predicting the diameter of the microtools fabricated by PECMM process. Tungsten microtools of diameters less than 100 μm were fabricated using an in-house built microelectrochemical machining system. Experimental results confirm the theoretical prediction of reduction in tool diameter with respect to increasing machining time. Further, from the experimental verification, it was found that the deviations in the tool diameters were within 9 % of the theoretical predictions.

Time-Efficient Simulations of Nano-Pulsed Electrochemical Micro- Machining

Pulsed electrochemical micromachining (PECMM) is a metal shaping process that exploits the double layer's capacitive effect to confine the machining reaction. By applying nano-second pulses this effect is strongly enhanced and confines the faradaic current to electrode regions where the tool-workpiece gap is the smallest. We offer a solution to calculate the final removal shape and to quantify the confinement with respect to the ideal machining profile.The simulations are conducted on axisymmetric geometries which reflect a real case. We use the potential model with time varying boundary conditions. The double layers are modeled by the capacitor equation in parallel with the Butler-Volmer equation. The temperature in the system is calculated based on the internal energy balance equation, having as natural boundary conditions the heat generated by the electrochemical reactions. The cooling is performed through conduction, having jet specific heat transfer coefficients.For obtaining the mesh deformation according to the electrochemical metal removal, the linear elasticity equations are solved, having the Faraday's law as essential boundary conditions.To handle efficiently the large difference between the time scales of the temperature and mesh deformation on one side and the pulses on the other, we developed an average time stepping algorithm. This enables us to shortcut the full calculation, allowing simulations for longer times, independent of the pulsing time.

Theoretical Aspects of Pulsed Electrochemical Micromachining

A first principles model is herein presented aimed at simulating the initial stages of pulsed electrochemical micromachining, ECμM, a technique introduced by Schuster et al. over a decade ago (Schuster et al. Science 2000, 289, 98–101). Our strategy is based on finding solutions to the equations that govern mass transport of all solution phase species coupled to Poisson's equation for the electrostatic potential in solution subject to boundary conditions that relate the potential across the tool|electrolyte and workpiece|electrolyte interfaces to the rates of heterogeneous electron transfer. This complex problem including its moving boundary aspects was solved using COMSOL without assuming a priori a capacitive element. The results obtained for a Pt tool and Cu workpiece employing conditions similar to those specified by Schuster et al. in their original work were found to be in good agreement with those obtained experimentally.

Micropatterning of Fe-based bulk metallic glass surfaces by pulsed electrochemical micromachining

Abstract