Electropolishing is a surface treatment process that is applied to a huge variety of items, ranging from surgical devices (e.g. stents, needles, tubes) to sensors, valves, storage tanks, fasteners, cutting instruments, gears, shafts to even nuclear accelerators. Electropolishing provides an effective and efficient method for removing surface roughness and burrs or involuntary sharp edges that remain from preceding manufacturing steps.

The effectiveness of the process is controlled by the current density distribution and electrolyte refreshment over the substrate – which presents a major challenge. Poorly controlled current density distributions and insufficient electrolyte flow refreshment near the surface to be treated will lead to unacceptable roughness values, or might even cause pitting or burning of the product surface.

Electropolishing challenges

Electropolishing is a process where a metal substrate (often steel, copper, brass, aluminum or titanium, but also a wide range of other metals and alloys) is immersed in an acid containing electrolyte solution and an anodic electrical current is imposed onto it. This invokes a controlled corrosion process, effectively removing surface roughness and other surface irregularities, such as sharp edges caused by scratches, or burrs and hair-line surface cracks from preceding manufacturing steps.

Electropolished surfaces are stress-free and smooth, significantly prolonging the life time of the processed device or part. Often electropolished surfaces have a mirrored appearance. The process also improves adhesion through the removal of oils and oxides, yielding a clean surface for any subsequent production step.

Although some electropolishing processes are based on non-aqueous electrolytes or ionic liquids, the vast majority of industrial electropolishing processes rely on aqueous solution containing phosphoric acid, whether or not in combination with other acids like sulphuric acid or even fluoric acid.

Controlling the current density distribution and electrolyte refreshment (hence effectiveness of the process) over the substrate is a major challenge for electropolishing processes. Low current density areas might lead to unacceptable roughness values, or even pitting of the substrate. High current density areas might lead to an excessive metal removal rate, thereby compromising the dimensional tolerances of the part, or might even lead to burning in more extreme cases.

Elsyca's Solutions

Elsyca has a long track record in Computer Aided Engineering (CAE) projects that encompass the development of complete electropolishing tooling solutions for complex or larger size components, e.g. superconducting radio-frequency (rf) cavities, or the design of novel electropolishing cells with embedded tooling for processing batches of smaller components.

Elsyca's Advanced Engineering Services (AES) for electropolishing processes start with the laboratory characterization and sensitivity analysis of electropolishing baths in combination to a given substrate metal or metal alloy. This laboratory characterization provides essential input data for the computer model simulations in order to provide an accurate prediction of metal removal rate distributions over the surface of the object that is treated. In addition an unparalleled insight into the process is gained, including a definition of the window of operating conditions that ensures attaining the targeted surface quality (roughness, appearance) while avoiding any surface defects like pitting or burning.

Elsyca's AES services also extend to process optimization, which means that Elsyca performs repetitive laboratory tests while changing process parameters like electrolyte acid concentrations, operating temperature, imposed current signal (DC versus pulsed current). This can lead to a broader operating window, or to a higher quality of the electropolished surface (e.g. lower roughness).

An electropolishing feasibility analysis provides a fast performance analysis for an application and process conditions as specified by the customer. This might involve a configuration (cell, rack or jig, part program to be electropolished) that is either intended to be build, or that is already running in a test phase or in production.

A Computer Aided Engineering (CAE) project for an electropolishing process of a specified part program might either involve the optimization of part load and configuration on a rack, combined to the design and optimization of tooling components (integrated configurations of auxiliary cathodes, current robbers and shields), or the design of entirely new electropolishing cells and concepts for high-end applications. The CAE work relies upon computer simulations for obtaining the current density, metal removal rate distribution over the parts. The design of the tooling configuration or novel electropolishing cell is iteratively improved based on the simulations results while accounting for all possible practical restrictions with respect to manufacturability, hardware cost and maintenance issues.

Simulations are based on in-house developed software platforms, in casu PlatingMaster for the current density and layer metal removal rate distribution simulations.

For projects that involve the CAE of an optimised tooling configuration, Elsyca optionally delivers also the CAD of the entire rack skeleton or jig with on-board tooling components, including technical drawings and Bill of Materials.

In case a novel electropolishing cell has been designed, Elsyca also offers the possibility to the customer of building and pre-assembling a prototype cell at Elsyca laboratory facilities. This pre-assembled cell is then shipped to the customer, or further used by Elsyca for carrying out the first wet run tests. In that case Elsyca takes care of construction the entire pilot set-up (electrolyte tank and thermostatic control, pump unit, rotameters, sample part handling, …)

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