The Use of Hard Alloys and Machining Them by the Electrochemical Method

Recently, components made of hard alloys have been widely used in manufacturing rockets, engines and in the defense industry.
The hard alloy components are sintered in molds at high temperatures and under high pressures using titanium carbide, tungsten carbide and other micropowders.
The shape and surface relief of such components is determined by the sintering mold.
Because of a high hardness of the material (the hardness is about Rockwell A 90 or even higher), no subsequent machining is practiced, except grinding.
Rather inefficient electric discharge machining is used in rare cases only.
At the same time, there is a need for machining such components after sintering because in many cases a mold does not allow obtaining the required finished surface.
If such technology existed, the design of hard alloy components could be perfected, and thereby the general parameters of products could be improved.

We have developed an electrochemical machining technology for hard alloy components.
The technology allows machining shaped surfaces, shaped holes, slots, grooves, apertures, pockets and undercuts.
The machining accuracy is up to the 7th quality, and the machined surface roughness height is 1 to 5 microns.
The rate of electrode immersion into hard alloy (i.e., the rate of hard alloy dissolution) is 0.1 to 1 mm/min which value is two orders of magnitude higher than that for electric discharge machining.
Electrolyte in an electrochemical machine consists of the aqueous solution of NaOH and some additional components.
The representative machining parameters used in one of successful tests were as follows: electrolyte pressure: 0.12 MPa; interelectrode gap: 0.060 mm; cathode vibration amplitude: 0.3 mm; cathode vibration frequency: 50 cycles per second; operating current pulses: positive, rectangular, 50 Hz; pulse voltage: 15 V; relative pulse duration: 3; current density: 15 A per square cm of the surface under machining.
Thus, it is the first industrial technology that allows machining hard alloy components to a high precision and at a high production rate.


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