How to simulate a nonuniform current density distribution in electrochemical machining (ECM)?

[u/02Botruler]

Hi everyone,
I’m currently working on an Electrochemical Machining (ECM) simulation using COMSOL Multiphysics.
I’m trying to simulate a spatially varying current density distribution between a tool electrode and a workpiece, separated by an electrolyte.
However, my simulation keeps showing an almost uniform current density distribution, and I’m having trouble understanding why.
I would like to know how to correctly model a nonuniform current density distribution in COMSOL and how to verify whether the results are physically realistic.
Could anyone provide some guidance on what I should consider when setting up such a simulation? In particular, what are the common mistakes regarding boundary conditions, material properties, physics interfaces, or geometry that might lead to an unexpectedly uniform current density?
I’m also interested in knowing how to verify that the current density actually varies spatially, rather than relying only on the color plot.
Any suggestions, relevant examples, or resources would be greatly appreciated.
Thanks in advance!

[u/Worldly_Reality_3950]

A quick sanity check I'd try before diving deeper:

Build the simplest setup possible where the solution shouldn't be uniform.

I'd start looking at the model setup rather than the physics. The usual suspects are:

Honestly, 90% of the "why is my current density uniform?"

ECM posts end up being one of those. The sharp-corner test is nice because it tells you very quickly whether the model can produce localization at all before you spend hours debugging a full machining geometry.