Abstract
In the customary method of electro-machining of hard metals, it is necessary to initiate some condenced discharges or quenched sparks between the metal to the machined and the tool by incomplete contracts or repeated contacts, where the tool must be kept as the cathode in the circuit of direct current.
In the present method, an ordinary alternating current is used, superposed with some adequate high frequency electric oscillations. The metal and the tool are dipped in water and they are adjusted to keep a certain small separation. Thus, we can initiate favorable quenched discharges in every half cycle, in which the metal is in positive potential.
A merit of the present method is that the developments of any cracks in the machined surface are perfectly prevented even for hard metals, such as tungsten. The time required for drilling a tungsten plate of 3 mm in thickness by a tungsten rod, 1.54 mm in dia., is 4 minutes resulting a hole 1.75 mm in diameter. Screw cutting through a quenched steel plate is proved successful by choosing a brass external thread as a tooling electrode. The mechanism of electro-mechanical machining due to quenched discharges is explained qualitatively; the drilling effect being ascribed to electric attraction working on the melt of the plate, and the consumption of the electrode to a bluster effect of positive ions.
