Modern mold enterprises, almost no lack of EDM, because EDM can effectively process all kinds of special-shaped, all kinds of cavities or high hardness parts, so it has become an indispensable processing means in mold manufacturing and metal processing industry.
According to the feedback information from the enterprise, the accuracy has reached ± 0.002 mm, and the roughness Ra = 0.4 μ M. In order to pursue the machining accuracy, the condition of the WEDM machine tool should be checked at the beginning. The deionization degree of ionic water, the temperature of ionic water, the perpendicularity of wire cutting, the tension force, the cutting wire and the material of the workpiece to be cut should be checked to ensure the good processing speed and accuracy. For WEDM, it is a kind of cutting or cutting material from a whole blank. Therefore, the original stress balance is destroyed in the process of processing, resulting in stress concentration at the corner. When the radius r of the inner corner is less than 0.2, the design department should be advised to improve the die structure. The method of dealing with stress concentration can apply the principle of vector translation. The allowance of 0.8-0.9mm should be reserved before finishing, and the approximate shape of the cavity should be pre processed, and then heat treatment should be carried out to release the machining stress as much as possible before finishing, so as to ensure the thermal stability.
When processing punch, the cutting position and path of cutting wire should be carefully considered. The position of clamping blank should be selected after the first feeding, the workpiece does not form a hanging wall, which always makes the workpiece in good stress state and does not affect the subsequent processing; for the punch with high requirements, the blank can be drilled and threaded, and the processing effect is better than that of cutting in the shape. Now high-precision workpieces, in order to ensure the quality of the parts, four times of cutting is generally used. When there is a part of taper machining in the thickness direction of female die, in order to pursue efficient machining, the straight edge is usually roughened for the first time, tapered for the second time, and then finished for the third time. This process feature is that there is no need to finish the existing taper edge vertically, only the straight edge of the edge section is finished, and the edge of the straight edge is refined after the fourth pass.
Rough and fine electrodes should be made respectively in EDM. The shape of the finishing electrode is required to meet the requirements of the cavity, and the good precision electrode has been processed by CNC machine tool. In terms of electrode material selection, copper electrode is mainly used for general steel parts processing; Cu-W alloy electrode has good comprehensive performance, especially the electrode loss during processing is obviously smaller than that of red copper electrode. Under good chip removal conditions, it is suitable for finishing difficult to machine materials and parts with complex cross-section shape; Ag-W alloy electrode has better performance than Cu-W alloy electrode because of less resources and high price In addition, graphite electrode has been widely used. At present, there are domestic graphite and imported graphite. Imported graphite has the advantages of low loss, high hardness, fast electro etching speed and low surface roughness, and has been applied in many complex parts finishing. When designing the electrode, the clearance and the number of electrodes are calculated. When machining large area or heavy electrode, the workpiece and electrode clamping should be stable and have certain strength to prevent loosening during processing. However, the surface after EDM is more difficult to grind than the surface after conventional machining or heat treatment. Therefore, before the end of EDM, the surface should be trimmed with precision gauge to remove the hardened thin layer formed on the surface.
Surface treatment of mould parts
The content of forming surface treatment includes no porosity on steel surface, uniform hardness, small difference in anisotropy characteristics, low inclusions and stress concentration places such as tool marks and grinding marks left on the surface of parts during processing. Therefore, after the end of processing, it is necessary to strengthen the surface of the parts, through mechanical polishing, fitter grinding, polishing, processing hidden dangers. Blunt the useless edge, acute angle and orifice of the workpiece. Generally, there will be 6-10 μ m metamorphic hardened layer on the surface of EDM, which is gray white in color. This layer is brittle and has residual stress. Before use, the hardened layer should be eliminated completely by polishing the surface and polishing off the hardened layer. In order to obtain high-quality polishing effect, the material, shape, hardness and surface quality of cutting must be fully considered. It is necessary to have high-quality polishing tools, high-quality polishing materials, correct polishing process, rigorous and consistent personnel quality, and good cleaning environment.
Assembly of mould parts
In the process of grinding and electrical machining, the workpiece will be magnetized to a certain extent, with weak magnetic force, which is easy to absorb some small impurities. Therefore, before assembly, the workpiece should be fully demagnetized and the surface should be cleaned with ethyl acetate. During the assembly process: (1) first understand the assembly drawing and complete all kinds of parts; (2) list the assembly sequence of each part; (3) check the dimensional accuracy of each part and make clear the matching requirements; (4) complete the required tools, and then start to assemble the mold; (5) assemble the guide pillar and guide sleeve of the mold base and the assembly of the cavity forming block; (6) assemble the mold (7) open and close the mold, check whether the mold action is reliable.
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