Electrochemical Grinding Wheel Dressing and Conditioning



Background Synopsis

Electrochemical Grinding (ECG) is a metal removal process, made possible by passing a direct current from the work piece, to a conductive grinding wheel in the presence of a conductive solution called an electrolyte.  The metal at the interface of the grinding wheel, electrolyte and work piece is oxidized and removed by the abrasive particles in the wheel and flow of the electrolyte.

The electrochemical grinding wheel is a matrix of abrasive particles and copper powder held by a resin bond.  The copper makes the grinding wheel conductive while the abrasives serve to remove the metal oxides from the work piece.  The small cavities between the abrasive grains serve as a galvanic cell to facilitate the electrolytic process.

Dressing

The electrochemical grinding wheel requires truing upon initial mounting and occasional dressing to maintain the geometric integrity.  Truing and dressing in ECG are essentially the same process, i.e: the use of a diamond tool (single point, cluster, static form or rotating diamond roll) to cut the periphery of the wheel.  Truing is the initial process to make the wheel concentric to the axis of rotation and periodic dressing is used to preserve the desired form and control size.

The process of diamond dressing an electrochemical wheel results in the restoration of the geometry but also smears the soft copper over the newly exposed abrasive particles.  The smeared copper, if not removed, will cause a short circuit between the wheel and the work piece.  The excess copper on the wheel surface will be dissipated quickly during the cut but the high current arc created initially can overload the power supply and possibly damage the work piece.  The process of removing the smeared copper resultant from the dress cycle is called ‘Wheel Conditioning’.

Wheel Conditioning

Electrochemical grinding wheel conditioning is routinely accomplished manually using a tin-coated copper braided strap.  The strap is applied to the rotating ECG wheel with the DC power supply and electrolyte flow on.  The process involves rubbing the braided strap against the dressed area of the grinding wheel until the sparking diminishes and the grinding wheel exhibits a darkened color.

The same process can be accomplished in a CNC machine by programming the wheel to contact a tin-coated copper braided strap.