Through-mask Electrochemical Micromachining Research Articles

Numerical and Experimental Study on Fabrication of Microstructure Array with Topographical Gradient via Through-Mask EMM

To obtain textured surface with low friction and high fluid load support capacity, in this work, based on the basic tenet of fluid film lubrication theory that converging gap is the first necessary condition to generate a hydrodynamic pressure in a confined fluid film, a fabrication method via through-mask electrochemical micromachining (EMM) for microstructure array on metal substrate with topographical gradient in a single micromachining step is investigated. After analyzing the factors that influence the current density distribution on the anode surface in EMM process, three potentially feasible schemes are presented and their fabrication results are predicted through numerical simulation. Combining the simulation results with practical application requirements, the scheme with machining gap gradient is adopted. With the selected fabrication scheme, the experiments are performed and the microstructure array with a feature size of 25μm and a height variance from 12μm to 24μm within 2mm distance has been produced successfully, which is in good agreement with the numerical calculation prediction.

Experimental Study on the Through-Mask Electrochemical Micromachining (EMM) Process

Surface texturing is a widely accepted approach for friction reduction in mechanical components. Through-mask electrochemical micromachining (EMM) is a simple and reliable process for mass manufacturing of microstructure array on metal surface. However, to obtain engineered surface texture with a prescribed shape, size, orientation, and distribution to investigate how forms and shapes of surface texturing affect the tribological properties on interacting surfaces, the machining conditions still need to be optimized. In this work, the electroetching conditions involving the formulation of the electrolyte, voltage, current density, machining gap and agitation method are optimized. With the optimized conditions, the ordered microstructures with a feature size down to 5m and smooth etched surface in large-scale are obtained and the preliminary friction drag reduction effect of the textured surface is demonstrated.

Fabrication of a metal protector for a fiber sensor using through-mask electrochemical micromachining with pulse DC power

The purpose of this study is to fabricate a stainless steel protector for a weak fiber sensor after first stripping the polymer outer-layer off the fiber. In addition to protecting the fiber sensor, the stainless steel protector is required to connect the detection target and the sensor which requires drilling holes in the protector. We accomplished this by electrochemical micromachining the stainless steel protector using pulse DC, using 1 KV/m, 6.62% weight concentration of NaCl electrolyte solution, 500 rpm anode rotating rate, a 5 MHz pulse frequency, a 50% duty factor, and 6 min of machining time with a ring cathode gave the best results, producing an average hole-radius of 231.36 µm.

Significance of Dimple Parameters on the Friction of Sliding Surfaces Investigated by Orthogonal Experiments

Surface texturing has proven to be an effective method to improve tribological performance of sliding surfaces. The pattern of microdimples is the most popular surface texture because it is supposed to obtain additional hydrodynamic pressure easily. In order to evaluate the significance of the dimple parameters, including dimple diameter, depth, and area ratio, to the frictional performance, the dimple patterns with dimple diameter from 50 to 300 μm, dimple depth from 5 to 20 μm, and area ratio from 5 to 20% were manufactured on chromium-coated specimens by through-mask electrochemical micromachining. Experiments were designed using an L 16 (4 5 ) orthogonal array, which contained the above three factors and four levels for each factor. The frictional tests on the above-textured specimens against the specimens of cast iron with oil lubrication were carried out under the contact pressures of 0.2 and 1 MPa and sliding velocities of 0.1 s and 0.5 m/s. The range analysis showed that the optimum dimple pattern was that with dimple diameter of 100–200 μm, dimple depth of 5–10 μm, and area ratio of 5%, which induced the friction reduction up to 77.6% compared to that of untextured surfaces. Both the range analysis and analysis of variance suggested that dimple area ratio is the most important parameter influencing friction coefficient under the test condition of this research.

Finite element simulation and experimental study on the through-mask electrochemical micromachining (EMM) process

In this work, the influence of electrode surface patterning on shape evolution in through-mask electrochemical micromachining (EMM) process is investigated numerically and experimentally. With finite element method, the anodic dissolution process is predicted and the etching behavioral trends under various parameters involving spacing and opening ratio, mask aspect ratio, and the etched feature aspect ratio have been identified and interpreted in which the etched depth non-uniformity is mostly ascribed to the current aggregate effect due to surface patterning on substrate. The validation experiment is conducted and the procedure of island formation and disappearing gradually along with etching progress in the center of the etched region is observed, which is in good agreement with the numerical calculation prediction. With the combination of experiments and numerical simulation, the optimized electroetching conditions and the formulation of the electrolyte in through-mask EMM are achieved, with which the ordered microstructures with a feature size down to 15 μm and smooth etched surface in large scale are obtained.

On the modeling of shape evolution in through-mask electrochemical micromachining of complex patterned substrates

This study is about the optimization of the shape evolution of a printed circuit board (PCB) by means of an auxiliary electrode. Predicting the shape evolution of such complex workpieces calls for a significant reduction of the nodal points in discretization. The authors applied a hierarchic modeling strategy, which breaks the overall problem into three spatial scales: the macroscopic, the mesoscopic and the microscopic scale. Simulations on each scale are performed by considering influences from the other scales in a simplified way. The strategy yields the shape evolution of any chosen trench of the workpiece and allows for the consideration of an auxiliary electrode. The auxiliary electrode was optimized in terms of its geometry and potential. The uniformity of the etch rate was governed by an interplay of different extrema caused by the complex patterning of the workpiece. This interplay was cleared up by investigating the current density of each extremum as a function of the parameters.

Generating micro-dimples array on the hard chrome-coated surface by modified through mask electrochemical micromachining

It has been recently identified that micro-dimples can act as fluid reservoirs and promote the retention of a lubricating film to reduce friction between mechanical components. Various techniques are employed to produce micro-dimples on the surface of friction pair. In this study, a modified through mask electrochemical micromachining (TMEMM), in which the insulation layer was directly attached to the cathode, was developed to produce micro-dimples on the hard chrome-coated surface. By controlling machining parameters, micro-dimples array, with hundreds of micrometers in diameter and several micrometers in depth, were produced. Compared with the traditional TMEMM, the modified method can both reduce cost and improve machining efficiency. Friction experiments show that the friction coefficient of the surface with appropriate micro-dimples array is obviously lower than that with nondimples.

New developments in through-mask electrochemical micromachining of titanium

Aiming at topographical surface micromachining of metallic and in particular Ti surfaces, we have investigated the possibility of using robust SU-8 and more recent electrophoretic photoresist technology in combination with flexible, non-contact maskless UV and electron beam lithography for mask generation in a through-mask electrochemical micromachining process. The shape evolution during diffusion controlled isotropic metal dissolution under circular mask openings of different sizes is in good agreement with numerical simulations, the cavities approaching hemispherical shape before their diameter reaches three times the initial mask opening diameter. Taking advantage of an important size effect in current density in combination with the developed methods, it was for the first time possible to create topographical gradient structures in a single micromachining step, difficult or impossible to achieve with competing techniques. Via through-mask anodization a locally confined nano-topography could be created within Ti surfaces. We further present an original method capable of electrochemical micromachining of highly curved conductive surfaces through electrophoretically deposited photoresist patterned by maskless 3D-UV lithography, going beyond the limitations of existing approaches.

Electrochemical micromachining of titanium surfaces for biomedical applications

Surface microscopic features are critical factors that affect successful application of titanium as a load bearing implant in orthopedic surgery. Electrochemical micromachining (ECM) offers a mean to produce patterns on titanium surfaces. In the present study, a new ECM technique, jet-electrochemical micromachining (Jet-EMM), was employed to produce micro-hole patterns on titanium specimens. Surface holes, which are hundreds of micrometers in diameter and have an aspect ratio of over 1.3, were machined by combining jet flow impingement and electrochemical reaction. Compared with through mask electrochemical micromachining (TMEMM), Jet-EMM exhibits an advantage in producing surface features with a high aspect ratio and in producing the features on curved surfaces. It can be potentially used to modify the surfaces of the titanium implants requiring extensive bone in-growth and better osteointegration.

Comparative study of osteoconduction on micromachined and alkali-treated titanium alloy surfaces in vitro and in vivo

This study sought to evaluate osteoconduction of Ti-6Al-4V surfaces under various conditions, including micro-patterned, alkali-treated, micro-patterned plus alkali-treated, and surfaces without any treatment as the control. The through-mask electrochemical micromachining (EMM) was used to fabricate micro-hole arrays on the titanium alloy surface. In vitro calcium phosphate formation on titanium surfaces was in static and dynamic simulated body fluid (SBF). In vivo comparison was conducted in the medullary cavity of dog femur using the implant cages which could provide the same physiological environment for specimens with different surface conditions. In vitro experiments indicate good conduction of calcium phosphate on the alkali-treated surfaces, and also better calcium phosphate deposition on the micro-hole surface than on the flat surfaces in dynamic SBF. In vivo experiments confirm the beneficial effect of alkaline treatment on osteoconduction. The results of in vivo experiments also indicate a synergistic effect of the alkaline treatment and the topographic pattern on osteoconduction.

Scale-Resolved Electrochemical Surface Structuring of Titanium for Biological Applications

Scale-resolved electrochemical surface structuring of titanium leads to well-defined topographies at the micrometer and nanometer scales, which are of interest for biomedical applications. Electrochemical procedures are described that lead to improved reproducibility and more precise shape control in through-mask electrochemical micromachining of titanium. Nanostructuring of plane or micromachined titanium surfaces is achieved by porous anodization in sulfuric or phosphoric acid electrolytes or by chemical etching. The described methods are used to produce model surfaces for the study of the role of surface topography on the interactions of bone-like cells with implants. © 2003 The Electrochemical Society. All rights reserved.

Recent Advances in the Study of Electrochemical Micromachining

The present paper reviews some fundamental aspects related to the understanding of the high rate anodic dissolution processes and their influence on thin film patterning by electrochemical micromachining. The role of convective mass transport and current distribution on the surface finish and shape evolution is discussed. Several examples of the applications of maskless and through-mask electrochemical micromachining are presented.