(3) The surface metamorphic layer is too thick
The surface of the slow-cut wire-cutting mold part produces a metamorphic layer of a certain thickness. The metamorphic layer causes the hardness of the mold to decrease, which is prone to early wear and affect the service life of the mold.
The processing uses pure water as the working fluid, and the conduction of ions in the water causes destructive electrolysis. Therefore, it is necessary to add an ion exchange resin to the water to control the conductivity of the water. The higher the conductivity of the deionized water, the thicker the metamorphic layer of the machined surface. Therefore, the wire cutting process should control the conductivity of the deionized water within a certain range. The finishing should ensure that the conductivity of the deionized water is less than 10 μS. When the allowable range is exceeded, the ion exchange resin should be replaced in time. When processing cemented carbide and PCD tool parts and having strict requirements on the thickness of the surface metamorphic layer, an oily medium with high insulation performance can be used as the working fluid. The oily medium has high insulation performance, and it is difficult to break through the discharge under the same voltage condition, without electrolytic corrosion, and can obtain a superior surface quality than the processing with deionized water, and the processed surface has almost no metamorphic layer.
The anti-electrolytic processing technology of the slow-cut wire cutting machine tool can effectively reduce the damage of electrolysis during processing to a minimum. The processing principle is to apply a reverse polarity voltage during the processing time (pulse gap) where no discharge occurs, and the alternating positive and negative pulse voltages make the average voltage of the gap zero, preventing the occurrence of such harmful phenomena of electrolysis.
The electrode wire is made of galvanized wire, which is not easy to drop copper powder in the processing, the surface of the processing does not accumulate copper, the surface deterioration layer can be improved, and the surface hardness of the workpiece is higher.