Methods Used for the Electrode Dressing
A choose of electrode machining method is mainly affected by the electrode
material and its dimension. Large enough electrodes, made from well machinable
material, as graphite, can be simply turned or milled. Small electrodes for micro
EDM are usually made of tungsten and the only way to form it into the desired
shape and dimension is the use of EDM machining.
The most common method of rotational microelectrodes production is its EDM
dressing by a precisely grinded AgW sacrificial block [1, 2]. The rotating electrode
is pushed towards the sacrificial block by appropriate path and velocity till it erodes
itself to desired dimension, as it is shown in the Fig. 1, left. This simple technique
has few practical disadvantages. The first, it is a compromise between machining
time and precision. The precise diameter can be reached under fine machining
condition, but this condition extends the machining time. The second disadvantage
is a local wear of the AgW sacrificial block. This local wear, see Fig. 1 in the
middle, affects the precision of the electrode final diameter. If a new electrode will
be dressed at the same place as previous, the electrode reaches other diameter. This
is a limiting factor affecting the sacrificial block lifetime.
The worn area of the sacrificial block can be minimized by electrode dressing by
its sinking into the sacrificial block [3, 4], as it is shown in the Fig. 1, right. In this
case the sacrificial block can be made of easily EDM worn and cheap material,
compared to AgW sacrificial block.
Another electrode dressing methods eliminate local sacrificial block wear by
using moving elements like a wire or disc [1, 2]. Disadvantage of use wire electrode
dressing can be a low stiffness of dressing wire, given by its tension. This drawback
can be overcome by using a wire guide [5]. Based on this review we decided to
design a disc grinder for micro electrodes dressing, where the wear is applied along
large area of the disc and the impact of the wear on the disc dimensions could be
minimized.
