Through Mask Electrochemical Machining

Abstract

A pulse and pulse reverse through mask electrochemical machining (ECM) process is being developed for fabrication of gas flow field channels on metal bipolar plates used in PEM fuel cells. The process involves patterning a photoresist mask on the surface of the bipolar plate to protect specific areas during the ECM process. A pulsed electric field is applied between the bipolar plate and a suitable counter electrode to remove the metal not protected by the photoresist mask. The application of pulsed electric fields, as opposed to constant direct current (DC) electric fields provides an improved level of control through optimization of the pulse parameters. The influence of the through mask pulse and pulse reverse ECM processing parameters, such as electrolyte composition, flow rates, pulsed voltage, pulsed on-times and off-times on material removal rates, surface finish, accuracy and dimensional control for the channel fabrication are examined.

Review—Through-Mask Electrochemical Micromachining

“…In an attempt to achieve specific dimensional tolerances, these variations need to be minimized. Otherwise, the functionality 6,58,108,109 and yield 110 of the desired part may be compromised. Key factors in governing the uniformity of machined parts are the dissolution rate, cell geometry and mask design.…”

“…5,58,59,80,91,112,113,127,128,146 Non-noble metals encompass hafnium, 91 molybdenum 5 and zirconium. 91 In addition, iron-nickel, 33,147 nickel 91 and titanium alloys, 62,145,[148][149][150] as well as a range of austenitic and martensitic stainless steels 5,6,43,44,58,59,108,[112][113][114]129,137,[142][143][144][151][152][153][154][155] are machinable. The frequent application of saline electrolytes is based on their non-toxicity, low cost, and long-term stability.…”

“…Example structures thus machined include spiral-shaped and straight microchannels, 35,122 interconnected chambers, 50,135 multilevel cavity and channel networks 105,107 (Figure 11a), and parts of a microvalve 119 and a micromixer. 162 Studies closer to the application stage 6,108 showcase the formation of serpentine gas-flow-field channels in stainless-steel bipolar plates, which have already been tested in proton-exchange-membrane fuel cells. 109 As is discussed in the following section, TMEMM has the potential to play an important role in the microfabrication of microfluidic components.…”

“…Immersion etching while stirring is usually slower (2-20 μm min −1 ) 91 than etching in a flow cell (10-100 μm min −1 ). 5,33,108,111 In general, TMEMM proceeds much faster than PCM. 15,19 In fact, where direct comparisons are made under similar hydrodynamic conditions, the etch rate is at least one order of magnitude larger.…”

A Twice Electrochemical-Etching Method to Fabricate Superhydrophobic-Superhydrophilic Patterns for Biomimetic Fog Harvest

“…Electrochemical-etching, a very commonly used non-traditional machining technology has been employed to process diverse metal materials 58 – 61 and when combined with masking technology, it can also fabricate structures with various patterns 62 . In this work, a twice electrochemical-etching method was proposed for the first time to fabricate superhydrophobic-superhydrophilic patterned surface on Al substrates.…”