ABSTRACT
A highly specialized adaptation of electrochemical machining (ECM), known as shaped-tube electrolytic machining (STEM) is used for drilling small, deep holes in electrically conductive materials. Being an electrochemical process, STEM is unaffected by either material hardness or toughness. It uses an acid-based electrolyte instead of the salt electrolytes normally incorporated in ECM. As material is removed from the workpiece, the STEM electrode must be fed into the workpiece to maintain a constant electrode-workpiece gap. Carbide or Teflon guide bushings are used to maintain location and straightness with STEM drilling. Multiple electrodes, sometimes of varying shapes and sizes, have been used to produce as many as 100 holes simultaneously. A convenient feature of STEM drilling is that overcut can be changed by manipulating the voltage and the electrolyte pressure. Industrial uses for STEM drilling lie mostly within the aerospace industry and involve drilling deep holes in difficult-to-machine superalloys.
