The low speed EDM machine is a high-precision machining machine, which can achieve a machining accuracy of several µm, and the surface roughness Ra can reach <0.2 µm. However, some mold factories do not pay attention to details when using low speed EDM machine, thinking that a good machine tool can easily achieve high-efficiency and high-precision machining. In this article, we will discuss which factors will affect the processing accuracy of low speed EDM machining.
Low speed EDM machine are equipped with a process parameter library, and the process parameters are generally obtained under specific conditions (such as workpiece material, electrode wire, temperature 20±3°C, humidity 40-80%, etc.).
Low speed EDM machine will have their process parameter library without exception. The process parameters are generally obtained under certain specific working conditions, such as specific workpiece materials, electrode wires, working temperature and humidity, etc. . If the actual working environment and working conditions are quite different from the conditions set in the process parameters, and the original process parameters are still used, it may cause large deviations in the processing results. Therefore, in actual processing, the working conditions should be as close as possible to the conditions set in the process parameter library.
If the following conditions change or fail to meet the standards, it may cause deviations in the processing results.
1) Flushing specification: When processing according to standard parameters, after comparing the indicated value of the water pressure gauge with the theoretical value, the difference should be less than 0.5bar.
2) The gap between the workpiece and the nozzle: 0.05~0.10mm.
3) When the surface roughness requires Ra≧0.35µm, you can choose the cutting wire that pays attention to efficiency (it is recommended to use the same type of wire that comes with the machine tool). When Ra<0.35µm, in order to obtain a good processing surface, choose to pay attention to the surface The galvanized wire is processed.
4) During finishing, please ensure that the water µS<10, especially during finishing, please follow the requirements of process parameters. If necessary, replace the resin or purified water.
The electrode wire is generally galvanized wire or brass wire, with a tensile strength of 900 Newtons per square meter. When the roughness of the processed surface is required to be above 0.35 microns, ordinary brass wire can be used, and it is best to use the same type of electrode wire as the brass wire matched with the random bed. When the roughness is required to be below 0.35 microns, galvanized electrode wire should be used as much as possible to obtain a better processing surface. If the workpiece material is Cr12 steel, HRC55 heat treatment must be carried out first.
The Influence Of Temperature On Machining Accuracy
In order to carry out high-precision and high-quality low speed EDM machining, the environment must be stable and must meet the specified requirements, there must be no direct sunlight or airflow, and temperature changes should be monitored. The temperature range of the machine tool to ensure the working accuracy is 20±3º. If the temperature difference is large, it will affect the machining accuracy and surface roughness.
The change of room temperature has a great influence on the machining accuracy, and its influence is reflected in the 3 aspects of size, position and shape. The greater the temperature change and the larger the size of the workpiece, the more obvious the influence of temperature. For example, a workpiece with a length of 200mm will have a size error of 0.01mm when the temperature difference is 5 degrees.
The thermal characteristics of CNC machine have an important impact on machining accuracy, accounting for almost half of the machining accuracy. The machining accuracy of the machine in the state of long-term shutdown and the state of thermal equilibrium is quite different. The reason is that the temperature of the spindle and each motion axis of the CNC machine is relatively maintained at a certain fixed level after running for a period of time, and as the processing time changes, the thermal accuracy of CNC machine tends to be stable, which shows that even high-precision machine can only obtain stable processing accuracy under a stable temperature environment and thermal equilibrium. In the case of high-precision machining and production after the machine is turned on, preheating the machine is the most basic common sense of precision machining. However, the preparatory part of the “warm-up exercise” of the machine tool is ignored or unknown by many factories.
Factors Affecting Machining Efficiency
There are many factors that affect the efficiency of low-speed machining. If there is an inefficiency in processing, you can consider the following two factors.
(1) Limited by the structure of the parts and the clamping, the high-pressure water cannot be effectively flushed
At this time, it depends on whether the cut parts can be improved from the clamping. Some parts are affected by the support fixture, the bottom surface is raised, and some parts are affected by the pressure plate and the clamping screw position, and the upper nozzle has to be raised, and some are that the operator is afraid that the upper nozzle will not fall to the lowest point when the nozzle is touched. If the lower surface is raised, see if it is possible to use a fixture with the fixture support surface on the same plane as the work surface, or to clamp the workpiece directly on the work surface.
Affected by the screw pressure plate and the parts, see whether the jaw clamp can be used for clamping; for the operator who is worried that the upper nozzle is not dropped to the lowest point, a 0.1mm feeler gauge can be prepared as required. For parts that cannot be effectively flushed with high-pressure water due to structural limitations, the cutting energy can only be reduced. At this time, a correct understanding of cutting efficiency is necessary.
(2) Related to the wire transport system (related to maintenance)
1) It is necessary to check whether the cooling water of the conductive block is normal. Especially whether there is cooling water for the lower conductive block, because the copper powder will be dropped during the cutting process, the cooling water of the lower conductive block or even the flushing water for the lower nozzle processing may be blocked after long-term use of the machine tool. It should be cleaned and dredged.
2) The rotation of the lower guide wheel on the lower arm is flexible. Check and clean.
3) Whether the take-up wheel is normal.
4) Check the wire tension and wire speed, and readjust if necessary.
5) Check and clean the guide wire nozzle and conductive block.