China Education Equipment Purchasing Network News: When using ordinary rectangular wave pulse power supply, the discharge gap is narrow, the processing instability occurs during 5A high energy processing, and the pulses of short circuit and arc discharge increase. At this time, although the average processing current increases, the electric However, the effective discharge pulse of the wire spark cutting machine tool has not increased, so in this case, the cutting current continues to increase, the processing speed is basically unchanged, but the probability of wire breakage will increase. If you want to maintain a stable processing state, continue to increase the current, increase the probability of pulse breakdown, and also improve the cutting efficiency.
For high-speed wire EDM, the loss of the electrode wire is also an important indicator. To reduce the loss of the electrode wire, it is necessary to first reduce the bombardment effect of the ion on the electrode wire during the discharge process, and minimize the absorption of the discharge energy by the electrode wire. It is necessary to quickly vaporize the surface of the electrode wire, so that the surface of the electrode wire is cooled and releases the heat energy back into the discharge channel, forming a vaporization pressure, thereby improving the ability to exclude erosion products, so only to maintain uniform cooling between the electrodes The working medium forms an adsorption film on the surface of the electrode wire to slow down the positive ion bombardment of the electrode wire, and at the same time, a large amount of heat is taken away by the evaporation of the working medium to reduce the loss of the electrode wire and improve its durability.
For cutting conditions that cannot guarantee uniform cooling between the electrodes, the electrode wire passes through the discharge gap and is also the process of drying the film attached to the surface layer of the electrode wire by the erosion product. When the cutting workpiece is thick, the electrode wire is at the outlet of the workpiece It will be in a state of substantially no working medium protection film for a long distance, and the discharge will be carried out under extremely harsh cooling conditions. The loss of such electrode wire will naturally increase, and the probability of wire breakage will also increase greatly. If the discharge gap is increased, the wire loss will be lower when cutting at the same energy, and at the same time it can maintain the reason for higher cutting efficiency.
The problems with high-speed EDM wire cutting technology are firstly the low cutting efficiency, and secondly the existence of black and white cross stripes on the cutting surface also an important issue that affects the macroscopic quality of the processed surface.
The premise of stable machining of wire EDM is to ensure that the wire is not broken frequently during the cutting process. The probability of wire breakage increases with the increase of discharge energy and cutting thickness, which is closely related to the ion bombardment, cooling state and residence time of the electrode wire in the discharge channel. Cutting efficiency and surface roughness are also related to inter-pole cooling and deionization and restoration of insulation. At present, an emulsion containing about 5% of mechanical oil is generally used as the working medium, and two phenomena appear after cutting:
First, the workpiece is adhered to the substrate, and generally requires force or even knocking to detach it from the substrate;
Second, the surface of the workpiece is covered with sticky or even powdered erosion products, and kerosene is needed to clean it. This is mainly due to the high temperature above 10000 ° C in the discharge channel, which is caused by the decomposition of the emulsion to form colloidal or granular materials. These substances adhere to the slit and accumulate mainly at the outlet of the slit, which seriously affects the discharge of electrical corrosion products and blocks the fresh working fluid medium from entering the slit. Because the working medium cannot be continuously updated between the two stages, which directly affects the continuation of normal discharge, even discharge in the gap mixed with a large amount of colloidal material and arc discharge, so that the surface of the workpiece and the electrode wire cannot be cooled in time. The insulation state is abnormal, which results in a decrease in the ratio of normal discharge, a reduction in cutting speed, a burn on the surface of the workpiece, and serious commutation stripes. At the same time, the durability of the electrode wire is lost, and the wire is burned in severe cases.
Since the use of emulsion will cause the erosion products to accumulate at the exit of the slit, the discharge generated under the condition of a large amount of erosion products and insufficient cooling will cause the carbon black material to stick back to the surface of the workpiece and may cause burns on the surface of the workpiece. Black and white cross stripes are generated, so the black and white cross stripes on the cutting surface generally appear at the exit of the wire. The color gradually darkens from the inside of the workpiece, and due to the effect of gravity, when the upper and lower sprays are basically symmetrical, the electrode wire bottoms When the wire is transported upward, the discharge capacity of the erosion product is weaker than when the electrode wire is transported from top to bottom, and the stripes on the upper part of the workpiece will be darker and longer than the stripes on the lower part. The worse the washing ability of the emulsion, the more obvious the streaks on the cutting surface; therefore, the root cause of the black and white cross streaks during high-speed wire cutting is still the problem of the washing performance of the working medium. At present, people can only improve the cooling and washing state in the cutting seam by increasing the concentration of the emulsion, adding some washing substances and increasing the space between the veins, and weakening the color of the stripes.
Therefore, it is necessary to select non-oil or oil-less working fluid that does not generate viscous polymer compounds as much as possible during the discharge process to ensure the uniformity and flow of the working medium in the slit, so as to achieve the purpose of improving the discharge state.
Our company has proved through long-term tests that when the water-soluble linear cutting fluid with good washing properties is selected, the workpiece will automatically fall after cutting. There is only a thin film-like substance on the cutting surface, and there is no reversing streak, which proves that it is uniformly cooled between the poles. Under this cooling condition, a large discharge energy (average cutting current of 4 to 5A) can be used for continuous and stable cutting, and the cutting efficiency exceeds 150mm2 / min. The cutting surface is smoother and smoother, and there are fewer metal droplets remaining on the surface. Observed from the typical discharge waveforms, when using emulsions with poor washing ability, due to the fact that the electrodes are filled with conductive colloids or particulate matter, the collected discharge waveforms have basically no breakdown delay, and a large proportion of pulses are at the beginning It shows a short circuit state, and the voltage jump is large during the discharge process, indicating that the gap state is unstable during the discharge process. Under the condition of using water-soluble working fluid, the discharge waveform shows the typical characteristics of gap discharge-discharge breakdown delay phenomenon. And the better the washing conditions during the gap (such as when the cutting thickness is smaller), the higher the ratio of the discharge breakdown delay, and the smaller the fluctuation of the discharge voltage, indicating that there is a more uniform working medium between the poles, thus reflecting the gap Characteristics of discharge.
After the water-soluble working fluid is used, since the slit can be uniformly cooled, the working medium in the slit flows through the electrode wire, so the commutation stripes can be very light or even eliminated.
After the water-soluble working fluid is used to improve the washing state between the poles, the discharge gap can also be increased by the improvement of the pulse power supply, thereby further improving the washing state between the poles of the EDM machine tool, which is suitable for higher efficiency with higher cutting energy The need for cutting.
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