The invention is based on a stator having an insulation which is arranged around a coil winding package, wherein a stator packet is arranged on the insulation. The process involves the steps of providing a metallic rod having a cutting portion with a polygonal cross section; torsioning the rod so as to form helical cutting surfaces in the cutting portion of the metallic rod; and chemically milling the cutting portion of the rod so as to taper the cutting portion. The metallic side-plate has a lower edge extending downwards to a position beneath a lower surface of the metallic plate. The first and second reduction gears are supported on a common shaft that is positioned between the input and output shafts. When the surface of the p-type semiconductor is irradiated with electron beams by use of this apparatus, the electrical resistance of the p-type semiconductor can be effectively lowered within a short period of time; i. , a gap bulk density of between 0.