pre baked graphite electrodes
Requirements for discharge conditions of pre baked graphite electrodes
1. Requirements for gap voltage (SV): The characteristics of gap voltage: the larger the value, the better the processing stability, and the faster the discharge processing speed. The size of the discharge gap has little effect on the loss and surface roughness of pre baked graphite electrodes: Different spark machines have different levels of the gap voltage set. They are generally divided into: 40～60V, 90～120V, 150～190V, 200～250V. High current processing with pre baked graphite electrodes. To use a larger gap voltage, up to 200 ~ 250V. In the finishing process, a smaller gap voltage (40 ~ 60V) is used. When the gap voltage is not used, the processing current is also different.
2. Requirements for processing polarity: In EDM, the polarity of the pulse power supply determines the direction of the current, and different polarities of pre baked graphite electrodes directly affect the electrical processing effect. In positive polarity processing, pre baked graphite electrodes are used as The positive electrode, as the current flows, the temperature rises, and the released hot electrons increase. Therefore, more parts of the workpiece are eroded, and the processing speed is fast. When processing mold steel, pre baked graphite electrodes are used for negative polarity processing. Compared with positive polarity processing: pre-baked graphite electrodes have high loss, slow processing speed and good surface quality. When the pulse width is longer, such as the pulse width of 200us, the loss of the pre baked graphite electrodes processed with positive polarity is almost zero, and sometimes reverse loss occurs, but the surface roughness value increases. When the pre baked graphite electrodes are rough processed, With a longer pulse width, if you focus on the loss of pre-baked graphite electrodes, you should use positive polarity processing (that is, the pre-baked graphite electrodes are set as the positive electrode and the workpiece is set as the negative electrode). The pre-baked graphite electrodes have low loss; if the processing speed of the workpiece is first considered , Also adopts positive polarity processing (that is, the workpiece is set as the negative electrode, and the pre-baked graphite electrodes are set as the positive electrode), and the processing speed is fast. In the fine processing or micro-finishing of red copper pre-baked graphite electrodes, the shorter pulse width should be processed with negative polarity, which is conducive to obtaining better surface quality, but the loss of pre-baked graphite electrodes is larger: different workpiece materials, pre The polarity of baked graphite electrodes is also different. General tool steel, stainless steel, copper alloy, aluminum alloy, and tungsten steel are processed with positive polarity, while titanium alloys are mostly processed with negative polarity.
3. Adjustment of processing speed: During electrical discharge machining, tools and workpieces are simultaneously subjected to different degrees of electrical corrosion. The amount of electrical corrosion removal of the workpiece per unit time is called processing speed, which is productivity. In the process of electrical discharge machining, the processing speed is affected There are many factors, mainly including processing polarity, electrical parameters, workpiece materials and working fluids. Increasing the processing speed is often given priority in rough machining, usually the greater the discharge energy, the faster the processing speed, so:
①. Relying on a larger current to ensure high-speed processing of pre-baked graphite electrodes;
②. Enough spark position must be ensured to use larger machining current;
③. Increasing the pulse width can also increase the processing speed, but in the pre-baked graphite electrodes electric discharge machining, the excessive pulse width will make the processing unstable and affect the processing speed, and the phenomenon of carbon deposits is prone to occur;
④. The processing speed can be increased with a shorter discharge stop, but the processing stability should be paid attention to;
⑤. Using a larger inter-electrode voltage or high-voltage current is beneficial to increase the processing speed;
⑥. Different pre-baked graphite electrodes, different workpiece materials and different spark machines should choose different discharge parameters.