
370 Fundamentals of Machining Processes
Dimensional tolerances for ECM are ±0.13 mm for the frontal gap and
±0.25 mm for the side gap. Overcut of 0.05 mm, taper of 1 mm/mm, and a
corner radii of 5 mm are possible and depend on the conguration of the
cathodic tool used.
Surface nish: Surface nish of the machined parts by ECM is usually
0.3–1.9 μm R
a
for the frontal gap area and as rough as 5 μm R
a
or more for
the side gap area. Microscopic surface defects, such as intergranular attack
(IGA), are caused by selective ECM attack on certain constituents of the alloy
at low current. Figure 11.11 shows the effect of gap voltage and feed rate on