The wire electric discharge machining mold has been widely used in mold manufacturing. However, the wire cutting process will also have some negative effects on the mold surface. Under the instantaneous high temperature of the wire cutting and the rapid cooling of the working fluid, the surface of the mold will be deformed after the wire is cut, which will reduce the surface hardness and produce microscopic. Cracks and other defects, seriously affecting the manufacturing quality and service life of the mold, should be given enough attention. First, the formation of metamorphic layers Wire EDM is a processing method that utilizes the thermal effect of instantaneous discharge energy to melt and evaporate workpiece materials to meet dimensional requirements. Since the wire-cut working fluid mostly uses a dielectric liquid, it is accompanied by a certain electrolysis during the processing. The thermal effect and electrolysis during cutting usually produce a modified layer of a certain thickness on the machined surface, such as a decrease in the hardness of the surface layer, microcracking, etc., which causes the wire-cutting mold to be prone to early wear, directly affecting the retention of the die blanking gap and The die edge is prone to chipping and shortens the life of the mold. For carbon steel, the molten layer on the surface of the workpiece (the metamorphic layer consists of the molten solidified layer and the heat-affected layer) appears white on the metallographic photograph and becomes a white layer. It is completely different from the base metal and is a dendritic quenched cast structure. The combination with the inner layer is not very strong. It consists mainly of martensite, a large amount of finely retained austenite and some carbides. Second, the influencing factors of the metamorphic layer 1. Metallographic structure and elemental composition of workpiece materials Due to the discharge of the electric spark, the metallographic structure of the surface layer of the workpiece material changes significantly, forming discontinuity. A deteriorated layer of uneven thickness. It is related to the workpiece material, wire material, pulse power and working fluid. After metallographic analysis, large austenite remains in the metamorphic layer. When using molybdenum wire electrode and carbon-containing working solution, the content of molybdenum and carbon in the metamorphic layer is greatly increased by spectral analysis and electron probe detection; and the working solution using copper wire electrode and deionized water is used. At the time, it was found that the content of copper in the metamorphic layer increased without carburization. 2, the thickness of the metamorphic layer Generally, the thickness of the metamorphic layer becomes thicker as the pulse energy increases. Due to the randomness of the spark discharge process, the thickness of the metamorphic layer is often uneven under the same processing conditions. The data of the thickness of the metamorphic layer measured from the relevant test piece indicates that the wire cutting electrical standard is opposite to the thickness of the metamorphic layer. There is a clear impact. For example, the wire is brass wire, the low-speed wire (0.6m/s) processing voltage is 60V, the current is 5.5A, the maximum thickness of the metamorphic layer is 20.0μm, and the average is increased to 13.8μm. 3, the microhardness is significantly reduced, and microcracks appear Due to the change in the metallographic structure and element content of the metamorphic layer, the microhardness of the surface of the workpiece is significantly reduced. For example, after wire EDM in deionized water, the surface hardness value of the workpiece is reduced from 970 HV before wire cutting to 670 HV after wire cutting, and a wire-cut softening layer is usually formed at a depth of a few ten micrometers from the surface. At the same time, the surface metamorphic layer generally has tensile stress and microcracks may occur. Especially when cutting cemented carbide, under the condition of conventional electrical standard parameters, cracks are more likely to occur and voids exist. It is extremely harmful. Third, the formation mechanism and preventive measures of microcracks Wire cutting is processed by the discharge heat effect. The surface of the mold material is melted due to the high temperature generated by the discharge, and then the metamorphic layer is formed by quenching. The micro-cracks often appear on the metamorphic layer. Most of the micro-cracks are due to the molten state of the metal. Suddenly, it freezes and solidifies, and the material shrinks to cause tensile thermal stress. Different workpiece materials have different third properties to cracks, and hard and brittle materials are prone to cracks. The pre-heat treatment state of the workpiece also has a great influence on the crack generation. The processing quenching material is prone to cracking after the quenching or quenching material, because the quenching material is hard and brittle, and the original stress is also large. In order to prevent microcracks on the surface of the mold, it is necessary to pay full attention to and pay attention to the hot processing (casting, forging) and heat treatment of the steel until all the parts of the mold are made, and take corresponding measures. (1) The heat treatment before the online cutting process should not be overheated, carburized, decarburized, etc .; (2) The electric gauge should be optimized when cutting the wire : 1 Using high peak and narrow pulse electrical parameters, the workpiece material is thrown out in the gas phase, and the heat of vaporization is much higher than the heat of fusion to take away most of the heat to avoid overheating of the surface of the workpiece; 2 Effectively perform pulse-by-pulse detection, control the length of the concentrated discharge pulse train, and also solve the local overheating problem and eliminate the generation of microcracks; The effect of 3 pulse energy on microcracks is extremely obvious. The larger the energy, the wider and deeper the microcracks; the pulse energy is very small, for example, the finishing electrical standard, the surface roughness value is less than Ra1.25μm, generally not easy to appear Microcrack (3) Electrolytic products (such as liquid slag, etc.) in the working fluid often cause concentrated discharge and form microcracks. In addition, in the online cutting processing center, in order to prevent cracks and deformation, the processing conditions should also be carefully selected, especially for large, thick-walled, complex-shaped, uneven thickness mold parts, it is advisable to use multiple cutting methods, which is reduced and A very effective way to remove surface defects. It is also important to set the starting point for the line cut to be flat, easy to finish, or to have little effect on the performance of the workpiece. For some molds with high requirements, various effective measures can be taken. After the online cutting process, the surface metamorphic layer is thrown away and polished to improve the surface quality of the parts. Fourth, the conclusion Optimize the process plan of wire cutting, select reasonable process parameters to prevent overheating of the mold surface, reduce and avoid the formation of metamorphic layer, eliminate surface microcracks, improve the quality of mold manufacturing and extend the service life of the mold. Effective. Cold Basin Faucets,Single Cold Basin Taps,Wash Basin Mixer Cold,Cold Wash Basin Taps JIAHAOJIA SANITARY WARE INDUSTRY CO., LTD. , https://www.gagalfaucet.com