Numerous teeth on the mandrel surfa

Numerous teeth on the mandrel surface are made by EDM technique. EDM provides the means to machine materials with
high strength/hardness (i.e. tool steel) with very high degrees of precision even at very small characteristic scales (i.e.
mandrel’ teeth).
When EDMing, main parameters (most notably the pulse current and the pulse-on duration) should be adjusted properly
in order to obtain satisfactory results. Tai et al. [15] and Lee et al. [16] reported that surface crack formation is directly related
to the EDM parameters (i.e. surface cracking can be suppressed by increasing the pulse current and reducing the pulse-on
duration)