Article outline

Titanium alloys are extensively utilized in aerospace and medical industries due to their exceptional specific strength and corrosion resistance. Electrochemical machining (ECM) is a promising non-contact method for shaping these materials. The process relies on the anodic dissolution of the workpiece within an interelectrode gap. However, ECM of titanium alloys presents a specific challenge: the formation of a natural passive oxide film. While this film protects the material, localized surface defects, such as pits and pitting corrosion, are frequently observed on the side surfaces of the workpiece, outside the direct machining zone. These defects are caused by the stray spread of the electric field beyond the working gap. Local concentrations of electric field strength on the side facets can exceed the passivation threshold of the titanium alloy, triggering non-uniform anodic dissolution. This phenomenon reduces machining accuracy and creates stress concentrators, compromising component fatigue life.

The primary objective of this study is to identify the zones of electric field concentration outside the active interelectrode gap and to quantitatively assess the risk of stray dissolution on the side surfaces of the titanium anode. By mapping the electric field distribution, the research aims to provide a mathematical basis for eliminating hidden surface defects.

To achieve these objectives, a two-dimensional mathematical model of the electrochemical cell cross-section was developed. The theoretical foundation relies on Faraday and Ohm laws, where the electrostatic potential distribution is described by Laplace equation. The calculation of the electric field strength was performed using the Finite Element Method implemented in the ELCUT software suite. The computational domain was discretized using adaptive triangulation, which automatically refines the mesh in areas of expected high gradients, such as corners and the narrow interelectrode gap, minimizing numerical differentiation errors. Boundary conditions included fixed potentials on the working electrodes, electrical insulation on the outer boundaries, and continuity conditions at the metal-electrolyte interfaces.

The numerical simulation revealed distinct patterns of electric field distribution. In the active working gap, the field is highly uniform (approximately 50.0 V/m), ensuring stable material removal. However, on the side surfaces of the anode, the field strength drops to between 0.1 and 10.0 V/m but does not reach zero, indicating a stray electric field. Crucially, the simulation identified severe local peaks of electric field strength in the corner junctions of the workpiece, reaching values up to 9.9 V/m. Analysis demonstrates that for titanium alloys in certain electrolytes, electric fields in the range of 3 to 8 V/m are sufficient to locally rupture the passive oxide film. The modeled peaks significantly exceed this threshold, providing a clear physical explanation for the experimentally observed pitting at angular junctions.

These findings shift the paradigm from empirical trial and error in selecting insulation screens to targeted, mathematically driven tooling design. Engineers can design custom cathode geometries and shielding elements to strictly confine current lines. Furthermore, the quantitative data can be integrated into modern CAM systems for automatic tool-electrode shape correction. The study also highlights the potential of combining electrostatic modeling with pulsed ECM regimes, where inter-pulse pauses allow the passive film to recover on vulnerable side surfaces. Future research will expand this two-dimensional model into a fully coupled three-dimensional multiphase simulation, incorporating the hydrodynamics of the two-phase flow to better understand local passivation layer breakdown under dynamic conditions.