Using molybde molybdenum wire num wire or brass wire
1. Process for improving dimensional accuracy
Prior to Wire cutting EDM, the workpiece material has been subjected to overheating and cold working, and there is a certain amount of stress inside the material. Even if the over-annealing process is performed, various stresses will appear during the on-line cutting process, and the workpiece will deformed, thus affecting the final accuracy of wire-cutting parts. In order to improve the dimensional accuracy of the workpiece, in addition to taking the necessary measures to eliminate the internal stress before wire cutting, a reasonable wire cutting process using molybdenum wire or brass wire as electrode should also be adopted.
I) Cutting cavity parts such as dies
(1) Using the first rough machining and last finishing processes. Prior to WEDM, the workpiece materials were roughly processed to remove most of the waste, leaving only a small amount of finishing fish (usually 1 mm – 2mm allowance). Rough machining can be performed by metal cutting methods, but it can also be performed by spark wire cutting after the fire. The purpose is to allow the internal stress to be fully released and produce a certain degree of deformation, and then a secondary wire cutting machine is performed. This not only eliminates deformation due to internal stress release, but also enables higher quality through precision micro fabrication. The low-speed wire-cut WEDM using molybdenum cutting wire can obtain higher machining accuracy after multiple cuttings, and also because it has eliminated the influence of internal stress deformation during the first cutting process. This process method is particularly important for those thicker bonfire parts.
(2) Closed cutting process using a cavity with a threaded hole. The so-called closed-cutting with a perforated wire is to make one threading hole in each cavity first, and the cavities between the cavities and the outer boundary are not cut. Because there will always be a certain residual stress inside the workpiece material, if the cutting cavity is not closed, but cut from the outer boundary or from other adjacent cavity, the workpiece will be deformed badly, which will affect the precision of wire cutting and machining. From this, we can also know that the cavity type of the die should not be decomposed into a mosaic structure and open cut to ensure the precision and service life of the spark wire cutting EDM.
2) Cut core parts such as cut punches
(1) Reasonably select the starting point and cutting direction. When a punch or similar part is subjected to wire electric discharge machining using molybdenum cutting wire or brass wire , it is first necessary to select the starting point of the cutting, that is, from which position of the part to the cutting trajectory. The starting point should be selected at the intersection of the line segment to avoid the occurrence of scratches; the starting point should be close to the center of gravity of the workpiece being machined, so that at the end of machining, the torque generated by the workpiece’s own weight will have less influence. The choice of cutting direction is mainly to avoid the effect of deformation caused by the stress in the workpiece material. For example, when the workpiece shown in Fig. 6-5 is machined, the left side of the workpiece material is clamped and fixed. If the cutting is performed clockwise as shown in Fig. 6-S (a), it will be deformed due to the influence of internal stress, leading to dimensional deviation of the machining. Increase; If you use the counterclockwise cutting shown in Figure 6 – S (b), you can avoid the effect of stress deformation. In this wake-up call, the cutting route shown in Figure 6-S (b), if the starting point is 2, is less effective than starting point 1. Because, at this time, the final cutting is performed from left to right, and the workpiece is attached to the easily deformable scrap.
