Maybe you are in contact with electric spark processing every day during production, but do you really know the electric spark processing?

First of all, do you know how the electric spark technology came from? In 1943, when the academician of the former Soviet Academy of Sciences Lazarian Coo and his wife’s research switch contact with the phenomenon and cause of spark discharge corrosion, it was found that the instantaneous high temperature of the electric spark could melt, gasification and gasification of the local metal, pioneering and invention. Electric spark processing.

Electric spark processing is a high temperature generated during the micro of the pulse discharge (the instantaneous temperature is as high as 10000 ° C). The processing method of melting materials and eroding materials is eroded.

01

Micro process of pulse discharge

Electric spark processing is the process of continuously discharging erosion. Although the time of one pulse is very short, it is a process of comprehensive effects such as electromagnetics, thermodynamics, and fluid mechanics, which is quite complicated. In summary, the process of pulse electricity can be divided into the following stages:

1) Electricity, breakdown and discharge channels of polar media

When the pulse voltage is applied between the tool electrode and the workpiece, a electric field is formed immediately between the poles. The strength of the electric field is proportional to the voltage, which is inversely proportional to the distance. As the polar voltage increases or the polar distance decreases, the strength of the polar electric field will also increase with. Because the micro -surface of the tool electrode and the workpiece is uneven, and the distance is very small, the strength of the polar electric field is very uneven. The strength of the nearest point or the tip of the tip of the poles is generally maximum. When the strength of the electric field increases to a certain amount, the medium is cut, and the gap resistance of the discharge is rapidly decreased from the insulation state to a quarter of Ohm, and the gap current rises to the maximum value. Because the diameter of the channel is small, the current density in the channel is very high. The gap voltage drops rapidly from the breakdown voltage to the spark maintenance voltage (generally about 20 ~ 30V), and the current rises from 0 to a peak current.

2) Medium heat decomposition, electrode material melting, vaporization thermal expansion

Once the polar medium is ionized and breakdown, after forming a discharge channel, the pulse power supplys the electron at high speed between the passage to the positive electrode, and the positive ion runs towards the negative electrode. Electric energy becomes kinetic energy, and kinetic energy transforms into heat energy through collisions. So the positive and negative surfaces in the channel become instantaneous heat sources, reaching a high temperature. The channel high temperature vaporizes the working liquid medium, and then heats up to break the vaporization. These vaporized working liquids and metal steam instantly increased the volume, and became bubbles in the gap between the discharge, which quickly expanded and had the characteristics of explosion. Observing the electric spark processing process, you can see that bubbles emerge from the gap between the discharge, the working liquid gradually turns black, and hears a slight and crisp explosion sound. Electric spark processing mainly relies on thermal expansion and local micro -explosion, so that the melting and vaporized electrode materials are thrown out.

3) Throw the electrode material

The instantaneous high temperature of the channel and the positive and negative surface discharge points make the work liquid and melt and vaporize the metal material, and the heat expansion produces high instantaneous pressure. The pressure in the center of the channel is the highest, which keeps the vaporized gas expand outward. The melting metal liquid and steam at the high pressure of the pressure is excluded and thrown into the work liquid. Due to the role of surface tension and internal agglomeration, the throwing materials have the smallest surface area, and it is condensed into small ball particles during condensation.

When the melting and vaporized metals are splashing around the surface of the electrode, in addition to most of them throw into the work solution and shrink into small particles, there are a small part of the electrode surface that splashes, plated, and adsorbed on the opposite side. This phenomenon of splashing, plating, and adsorption can be used under certain conditions to reduce or compensate the loss of tool electrodes during processing.

In fact, the erosion and throwing process of metal materials are more complicated. At present, people’s understanding of this complex mechanism is still deepening.

4) EDC of polar media

With the end of the pulse voltage, the pulse current has also rapidly dropped to zero, but there should still be a interval time since then, so that the gap medium is eliminated, that is, the tape particles in the discharge channel are composed of neutral particles, and the medium at the discharge channel is restored to the medium at the discharge channel. The insulation strength and the temperature of the surface of the electrode, so as not to repeat the same discharge in the same place next time, cause the arc discharge, thereby ensuring that the next breakdown and discharge channel is formed at the latest or minimum resistance between the two poles.

It can be seen that in order to ensure that the electric spark processing process is carried out normally, there is generally enough pulse interval between two pulse discharge. In addition, there should be room to leave room for breakdown and discharge points. Otherwise, it will only discharge nearby, which is easy to form an arc.

02

Five different discharge states

The discharge state refers to the basic state of each pulse in the discharge gap during the electric spark processing. It is generally divided into five discharge states, as shown in the figure below.

Pulse parameter and pulse voltage and current waveform

1) Open path (empty pulse)

There is no breakdown in the gap between the discharge, and there is a voltage of greater than 50V on the gap, but there is no current flow in the gap, which is a state of air.

2) Spark discharge (working pulse, or effective pulse)

The insulation performance of the gap is good. After the working liquid medium is penetrated, it can be effectively thrown out and eroded metal. Its waveform characteristics are: small oscobies with high frequency oscillating on the voltage and waveforms.

3) Short circuit (short -distance pulse)

The discharge gap is directly short -circuited. The current is large during the short circuit, but the voltage at both ends of the gap is very small, and it does not erode the processing effect.

4) Arc discharge (stable arc discharge)

Due to poor scandal, the discharge point is concentrated in a certain part without dispersion, local heat accumulation, increased temperature, and vicious cycle. At this time, spark discharge becomes an arc discharge. Because the discharge point is fixed at a certain point or a part. Therefore, it is called a stable arc, which often makes the electrode surface charcoal and burns. The waveform of the arc discharge is characterized by the small jaggedness of the high -frequency oscillation.

5) Transition arc discharge (unstable arc discharge, or unstable spark discharge)

The transition arc discharge is the transition state of normal spark discharge and stable arc discharge, and is a precursor of stable arc discharge. The waveform characteristics are that the breakdown delay is very small or close to zero, and only becomes a spike. The high frequency component on the voltage current meter becomes lower or becomes a sparse sawtooth.

The above -mentioned discharge status is alternately and probably appearing in actual processing (related to processing regulations and feed, use of oil, pollution, etc.), and even in the process of single pulse power release, there may be two types of alternation alternation. The above discharge status.

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