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When using a common rectangular wave pulse power supply, the discharge gap is narrow, processing instability occurs during the processing of 5A large energy, and the short circuit and arc discharge pulses increase. At this time, although the average processing current increases, the WEDM machine tool is effective. The discharge pulse does not increase, so in this case the cutting current continues to increase, the processing speed is basically unchanged, but the probability of broken wire increases. If you want to maintain a stable processing state, continue to increase the current, increase the probability of pulse breakdown, but also improve the cutting efficiency.
For high-speed WEDM, the loss of the electrode wire is also an important indicator. To reduce the loss of the electrode wire, it is first necessary to reduce the bombardment of the ion-pair electrode wire during discharge, and minimize the absorption of the discharge energy of the electrode wire. It is required that the surface of the electrode wire be quickly vaporized so that the surface of the wire electrode can be cooled to release the heat energy back into the discharge channel to form the vaporization pressure, thereby increasing the elimination ability of the etching product, and therefore only the uniform cooling effect between the electrodes can be maintained. The working medium forms an adsorption film on the surface of the electrode wire, so as to slow the bombardment of the positive ion to the electrode wire. At the same time, a large amount of heat is taken away through volatilization of the working medium itself to reduce the loss of the electrode wire and improve its durability.
For the case of cutting that does not guarantee uniform cooling between the poles, the electrode wire passes through the discharge gap and is also the process of etching the product to dry the film attached to the surface of the electrode wire. When the cutting workpiece is thick, the electrode wire is at the outlet of the workpiece. Within a long distance, the protective film will be in a state where there is almost no working medium, and the discharge is performed under extremely poor cooling conditions, and the loss of such electrode wire will naturally increase, and at the same time, the probability of wire breakage will be greatly increased. If the discharge gap is increased, the filament loss will be lower when the same energy is cut, and at the same time, the higher cutting efficiency can be maintained.
The problems with high-speed WEDM are the low cutting efficiency. Secondly, the presence of black-and-white cross-cuts on the cutting surface also affects the macroscopic quality of the machined surface.
The premise of stable machining by WEDM is that it must first ensure that the wire is not broken during the cutting process. The probability of broken wire increases with the increase of discharge energy and cutting thickness, that is, it is closely related to the ion bombardment, cooling state and residence time of the electrode wire in the discharge channel. The cutting efficiency and surface roughness are also related to the inter-electrode cooling and deionization and restoring the insulation state. At present, the use of emulsifiers containing about 5% of mechanical oil as working media is commonly used. After cutting, there are two phenomena:
First, the workpiece is adhered to the substrate, and it usually requires force or even knocking to separate it from the substrate.
Second, the surface of the workpiece is covered with adhesive or even powdered erosion products that require kerosene for scrubbing. This is mainly due to the high temperature above 10000 °C in the discharge channel, which is caused by the decomposition of the emulsion into colloidal or granular materials. These substances stick in the slits and accumulate mainly at the outlets of the slits, seriously affecting the discharge of the electrocorrosion products, and blocking the passage of fresh working fluid medium into the slits. Because the continuous updating of the working medium cannot be maintained between the two stages, the continuous discharge of the normal discharge is directly affected, and discharge is performed even in a gap mixed with a large amount of colloidal substances and an arc discharge is generated, so that the surface of the workpiece and the electrode wire cannot be cooled in time. Insulation is abnormal, causing a series of problems such as a decrease in the normal discharge ratio, a decrease in the cutting speed, a burn of the workpiece surface, a serious commutation fringe, and the like. At the same time, the durability of the electrode wire is lost, and the wire is severely burned.
Because the use of emulsion will cause the erosion product to accumulate at the exit of the incision, discharge in the presence of a large amount of erosion products and insufficient cooling will cause the carbon black material to stick to the surface of the workpiece and may cause surface burn of the workpiece. Black and white cross stripes are produced, so the black and white cross stripes of the cutting surface generally appear at the exit of the yarn, the color gradually becomes deeper from the inside of the workpiece, and due to the effect of gravity, when the upper and lower liquid sprays are basically symmetrical, the electrode wire is When the yarn is lifted upwards, the discharging ability of the erosion product is weaker than when the wire is moved from the top to the bottom, and the stripe at the top of the workpiece is darker and longer than the stripe at the bottom. The worse the washing ability of the emulsion is, the more pronounced the fringes of the cutting surface; therefore, the fundamental reason for the black-and-white cross-streak when the high-speed wire cutting is performed 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 incision by increasing the concentration of the emulsion, adding some detersive substances, and increasing the interval between veins, and weaken the color of the stripes.
Therefore, it is necessary to use a non-oil or less-oily working fluid that does not generate viscous macromolecular compounds as much as possible during the discharge process to ensure the uniform and flow of the working medium in the slits, so as to achieve the purpose of improving the discharge state.
After long-term tests, our company has proved that when the water-soluble wire cutting fluid with good washing property is used, the workpiece after cutting is automatically dropped. There is only one layer of film-like material on the cutting surface, and there is no commutation streaks, which proves that the electrodes show uniform cooling. Under this cooling condition, continuous cutting can be performed with a relatively large discharge energy (average cutting current of 4 to 5 A), and the cutting efficiency exceeds 150 mm2/min. The cutting surface is smoother and flatter than the cutting surface, and less metal droplets remain on the surface. Observed from the typical discharge waveform, when the emulsion with poor washing ability is used, the discharge waveform collected has no breakdown delay due to conductive gel or particulate matter between the electrodes. The short circuit state is exhibited, and the voltage jump during the discharge process is large, indicating that the gap state is unstable during the discharge process. Under the condition of using a water-soluble working fluid, the discharge waveform exhibits the typical characteristic of the gap discharge, which is the discharge breakdown delay phenomenon. The better the washing condition during the gap (if 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 in the interpolar region, thereby reflecting the gap Discharge characteristics.
After the water-soluble working fluid is used, since the uniform cooling can be obtained in the slits, the working medium in the slits penetrates through the electrode wires, so the commutation stripes can be very light or even eliminated.
After the water-soluble working solution 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 WEDM machine poles, and using the higher cutting energy for high efficiency. The need for cutting.
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