RU2697314C1 - Method of electrical erosion machining of parts - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to electric erosion processing of materials and can be used for high-precision processing of parts from metals and alloys with complex surfaces. Method includes electric spark machining of part in dielectric liquid with heating of electrode-tool surface to melting temperature by pulses of nanosecond duration current, equal to time of streamer interelectrode gap, which is summed with heating time of surface of electrode-tool to melting point t_c.p= S/V_str+ t_mp, where t_c.p - duration of current pulse, S - interelectrode gap, V_str is streamer development speed, t_mp - heating time of surface of electrode-tool to melting point.

EFFECT: invention is aimed at radical elimination of electrode-tool wear due to nanosecond contact of conducting channel formed by streamer with electrode-tool surface.

1 cl, 2 dwg

Description

The invention relates to electroerosive methods of processing materials and can be used for high-precision machining of parts with complex surfaces from engineering materials (metals and alloys) in general engineering, instrumentation, machine tool industry and other engineering industries with a radical elimination of electrode-tool wear.

Known methods of electrical discharge machining of metals and alloys (Library of an electrical technologist. Issue 2. Electric discharge processing of materials. Levinson EM, Lev BC, Gudkin VG, Livshits AL, Yutkin LA L., Engineering. 1971 256 pages. Table 26. Ill. 135. Bible 60 titles.). This book describes methods, technological schemes, physical fundamentals, modes and technological equipment of electric discharge machining. Data are given on the dependence of the wear of the electrode electrodes on the duration of voltage pulses.

Electroerosive processing is carried out by controlled removal of molten or vaporized metal or alloy from the workpiece by creating a plasma channel between the two electrodes when an external voltage is applied, separated by a dielectric fluid. One of the electrodes is a tool, and the second is a workpiece.

The disadvantage of the described method is the long formation of the plasma channel, which leads to a significant heating of both electrodes. From the literature it is known that in a plasma channel the temperature can reach 15-40 tons. Kelvin. Such a substantial heating of the billet electrode ensures the formation of erosion holes and the necessary shaping. At the same time, the thermal process on the surface of the electrode-tool leads to its wear, which is a significant drawback of the method.

The plasma channel formed in the working fluid can occur by two mechanisms:

1. The thermal mechanism of breakdown of the interelectrode gap;

2. The electrical breakdown mechanism of the interelectrode gap.

The thermal breakdown mechanism takes place at a small electric field in the interelectrode gap (up to 36 kV / cm). Such a breakdown mechanism is best studied and occurs mainly when using relaxation pulse generators and their sufficiently long durations (up to hundreds of microseconds).

The electrical breakdown mechanism occurs at high electric field strengths in the interelectrode gap (more than 36 kV per cm2) and consists in the formation of an electrical streamer. It is known that the streamer develops at a speed of 1-2 km / s. In most cases, the streamer develops from one of the electrodes. With an interelectrode gap of 5–40 μm, it is bridged by an electrically conductive plasma channel (streamer) in 3–7 ns. Such a short time of formation of a plasma breakdown channel was not previously considered, since the widely used relaxation type current pulse generators did not allow electric breakdown of the interelectrode gap due to the insufficient power of such generators with nanosecond current pulse duration.

In turn, transistor current pulse generators did not allow receiving such short pulses until recently due to the lack of an appropriate electronic base.

A known method of electrical discharge machining in which the radical elimination of wear of the electrode-tool is achieved by applying a current pulse with preliminary and power steps, which helps to create conditions for the formation of a protective film on the electrode-tool, not allowing to reach the melting temperature of its material (A.S. No. 515614 В23Р 1 / 02 Published on 05/30/76 Bulletin No. 20, 06/28/76.).

The disadvantage of this method is the presence of wear of the electrode tool.

The objective of the proposed processing method is to radically eliminate the wear of the electrode tool due to nanosecond contact of the conductive channel formed by the streamer with the surface of the electrode tool.

The method of electric discharge machining, which is performed in a dielectric liquid with heating the surface of the electrode-tool to a melting temperature by pulses of nanosecond current pulses, equal to the time of interconnection of the electrode gap by the streamer, summed with the time of heating the surface of the electrode-tool to the melting temperature t _imp.t = S / V _str. + t _square where t _imp.t. is the duration of the current pulse, S is the interelectrode gap, V _p is the speed of development of the streamer, t _PL is the time of heating the surface of the electrode-tool to the melting temperature.

The method is as follows: current pulses of nanosecond duration ensure the creation of a plasma channel only for a period of time before the streamer touches the opposite electrode-tool, summed with the time of heating the surface of the electrode-tool to the melting temperature t _imp.t. = S / V _p. + t _square (Fig. 1, Fig. 2).

In FIG. Figure 1 shows the process of forming a conducting plasma channel by a moving streamer in an interelectrode gap filled with a dielectric fluid, until the opposite electrode is touched.

In FIG. Figure 2 shows the processing process after bridging the interelectrode gap by the streamer until the electrode-tool material is heated to its melting temperature.

Based on the fact that the interelectrode gap during electroerosive processing in most cases can be from 5-40 microns, the time required to reach the streamer head opposite to the electrode-component of the tool electrode will be t = S / V _ctp. where S is the interelectrode gap, microns; V _p is the streamer development rate, km / s.

After the streamer head reaches the surface of the electrode-tool, it is possible to continue the processing process for a time t _pl. to the melting temperature of the material of the electrode tool. A preliminary calculation showed that this time can be several nanoseconds (2–9 ns).

Thus, the duration of the current pulse is t _imp.t. = S / V _pp . + T _pl.

The proposed method of electrical discharge machining was tested using the following processing parameters: S = 5 μm, t _imp.t. = 9 ns, U = 150 V. As a result of processing, it was found that erosion holes with an average diameter of about 2.5 μm are formed on the workpiece electrode. The electrode tool had practically no significant wear.

Claims (6)

A method of electroerosive machining of a part, comprising treating the part in a dielectric liquid with current pulses with heating the surface of the electrode-tool to a melting temperature, characterized in that the processing is carried out by current pulses of nanosecond duration equal to the time the inter-electrode gap is interrupted by the tape drive, summed with the time of heating the surface of the electrode-tool to melting point: t _imp.t = S / V _p + t _pl , where t _imp.t - current pulse duration, S is the interelectrode gap, V _p is the speed of development of the streamer, t _PL - the time of heating the surface of the electrode-tool to the melting temperature.

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