Because of the high melting point and brittleness of cemented carbide, it is necessary to have sufficient pulse current density to be processed, but rougher processing standards cannot be used. Electrode materials such as copper, graphite, etc. will have large losses when the existing pulse power source is used for medium and precise machining with a smaller pulse width.
According to the existing qualitative theory of low-loss processing, the ratio of peak current to pulse width should be made ≤A (A is a constant, such as copper processing steel, A≤0.1A/μs), but the electric pulse with this parameter is used to process hard High-quality alloys are often of practical significance due to their low productivity.
Cemented carbide machining strategy
From the principle of EDM, any conductive material can be processed, and it is also possible to achieve low-loss processing, and cemented carbide is no exception. However, at present, according to the qualitative theory of low loss, when ≤0.01 A/μs is selected, it has the phenomenon of carbon adsorption, and the effect of low loss processing can be obtained. In order to improve the processing productivity, the no-load voltage amplitude can be increased to expand the spark gap value under a given processing surface roughness condition, improve the chip removal conditions, and reduce the pulse stop time accordingly.
The pulse parameters listed in the above table can be used to obtain better and low-loss process indicators
Techniques to reduce surface cracks
The thermal conductivity of cemented carbide is relatively small. For example, the thermal conductivity of tungsten drill type cemented carbide is 58.62~87.92W/(m•K), and the thermal conductivity of tungsten-cobalt-titanium alloy is generally 16.75~62.8W/(m• K). In order to avoid cracks, it is impossible to choose a processing rule with a large pulse width. For example, a transistor pulse power supply was used to process cemented carbide, and a pulse width of 800μs and a peak current of 1.5A were selected. As a result, serious network cracks were generated on the processed surface.
Therefore, in rough machining, relatively small pulse width (for example, less than 100μs) and higher peak current are used, so that the heat-affected layer of the so-called EDM is thinner. Even if there is a crack, its depth is relatively shallow. Then during finishing, the same small pulse width and higher peak current can be selected to almost completely remove the shallow cracks produced by rough machining. Such selection rules can not only avoid cracks, but also have better surface roughness.
Cracks have a great influence on the service life of cold forging dies, so the cold forging dies after finishing EDM must be polished to remove all the heat-affected layers produced by EDM, otherwise the die may crack during use.
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