Mechanical Knowledge

Is the accuracy and efficiency of the slow wire processing abnormal?

The slow wire machine is a high-precision machining machine, which can achieve 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 slow wire machine tools, thinking that a good machine tool can easily achieve efficient and high-precision machining. In fact, precision machining must establish the concept of precision machining!

slow wire processing

1. Process premise

Slow wire machine tools are equipped with a process parameter library. The process parameters are generally obtained under specific conditions (such as workpiece material, electrode wire, temperature 20±3°C, humidity 40-80%, etc.). 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 Ra0.35μm, you can choose the efficiency-oriented cutting wire (it is recommended to use the same type of wire equipped with the machine tool). When Ra<0.35μm, in order to obtain a good machined surface, choose to focus on the surface Galvanized wire for processing;

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.

slow wire processing

2. The influence of temperature on machining accuracy

In order to perform high-precision and high-quality slow-moving wire cutting processing, 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 three aspects of size, position and shape. As shown in the figure below, the greater the temperature change and the larger the size of the workpiece, the more obvious the effect 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. It is best to complete a larger part in a single start. If it is left overnight, the main cutting effect will not be significant, but it will be difficult to ensure the machining accuracy if it stops during trimming.

The influence of room temperature change on machining accuracy

The thermal characteristics of CNC machine tools have an important impact on machining accuracy, accounting for almost half of the machining accuracy. The machining accuracy of the machine tool 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 tool 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 tools tends to be stable, which shows that even high-precision machine tools can only obtain stable processing accuracy under a stable temperature environment and thermal equilibrium. In the case of high-precision machining and production after starting up, preheating the machine tool is the most basic common sense of precision machining. However, the preparatory part of the "warm-up exercise" of machine tools is ignored or unknown by many factories.

If the machine is left for more than several days, it is recommended to preheat for more than 30 minutes before high-precision machining; if the machine is left for only a few hours, it is recommended to preheat for 5-10 minutes before high-precision machining. The preheating process is to allow the machine tool to participate in the repeated movement of the machining axis. It is best to perform multi-axis linkage, such as moving the XYZ axis from the lower left corner of the coordinate system to the upper right corner, and repeating diagonal lines. When executing, you can write a macro program on the machine tool to make the machine tool repeatedly perform the preheating action.

slow wire processing

3. Factors affecting processing efficiency

There are many factors that affect the efficiency of wire cutting. If there is 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 and the bottom surface is raised, some parts are affected by the pressure plate and the clamping screw position, and the upper nozzle has to be raised, and some are afraid that the operator will not drop the upper nozzle to the lowest point when touching the nozzle . If the lower surface is raised, see whether it is possible to use a fixture with the fixture supporting surface and the work table in the same plane, or to clamp the workpiece directly on the work table.

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) Wire transport system related (related to maintenance)

1) Check whether the cooling water of the conductive block is normal. Especially whether there is cooling water for the lower conductive block, because copper powder will be dropped during the cutting process, after long-term use of the machine tool, the cooling water of the lower conductive block or even the flushing water for the lower nozzle processing may be blocked, and 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 wire guide nozzle and conductive block.

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