How to ensure high-speed and stable machining on a medium-speed wire EDM machine? Through continuous practice and experience, we've found that peak current can be selected, and a longer pulse width allows for cutting with a larger current to achieve higher speeds. To ensure workpiece machining accuracy, low-speed wire cutting is typically used, tracking the speed within a certain range to eliminate cutting striations and improve accuracy. For users, medium-speed wire EDM is the final process, so accuracy is crucial. Therefore, selecting the appropriate medium-speed wire EDM machine with suitable precision and structural design is very important.
The experience in ensuring the machining quality of wire EDM machines can be summarized in the following three points:
I. For medium-speed wire EDM, a good machine tool structure and mechanical components are crucial. First, it's essential to improve the precision of the mechanical transmission. The displacement accuracy of the worktable and the movement accuracy of the molybdenum wire both affect machining accuracy. The worktable is driven by gear pairs, lead screws, and nuts. The movement of the molybdenum wire is greatly affected by the rotational accuracy of the guide rollers, uneven wear of the guide rollers, and the looseness or excessive tightness of the molybdenum wire. If the precision of the medium-speed wire EDM transmission mechanism is low, it will significantly impact machining quality.
Second, choosing the right cutting material is very important. Generally, mold materials are processed after the blank is hardened. If the material is carbon steel, it is difficult to harden through and the hardened layer is shallow. After processing, the hardness may be reduced. However, in order to have a good processing quality and precision, alloys and cemented carbides with good hardenability should be selected for processing. These materials do not have a significant reduction in hardness from the surface to the center.
3. Deformation during wire EDM: Due to the influence of the internal stress generated by the initial spark discharge, thermal stress will be generated. Reducing residual stress is very important when using wire EDM. During cutting, a large piece of metal is cut off, which will disrupt the internal stress balance of the material and redistribute the stress. The residual stress in the material is greater than that affected by mechanical and other factors, which can cause deformation to reach the level of the naked eye, and even the material may crack and be damaged during the cutting process.
To reduce material deformation caused by residual stress, the workpiece contour should be 8-100mm away from the edge of the blank; aging treatment can be performed before wire EDM; pre-processing should be performed before quenching to remove most of the excess material; when performing wire EDM, a two-stage cutting method should be used, with the first stage being a rough cut for the hole, and the second stage being a fine cut for the hole when the stress reaches a new equilibrium; the correct cutting sequence should also be selected.
In summary, several factors affect the quality of medium-speed wire EDM machining. Additionally, human factors such as programming and selection of process parameters can also cause abnormalities in machining accuracy. Of course, judging the quality of a medium-speed wire EDM machine cannot be based solely on cutting accuracy; positioning accuracy is also crucial. Since these machines often exceed their lifespan in practical use, maintaining accuracy is paramount. The nature of the machine's structural castings can also lead to poor accuracy. Therefore, the rigidity of the medium-speed wire EDM machine determines its accuracy retention performance. A medium-speed wire EDM machine with high rigidity, minimal deformation, and stable, reliable operation during machining is highly reliable.
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