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Pay attention to these three points! "Prevention" of abnormal accuracy and efficiency of slow wire processing!

Source: Browse:22 The release date:2021.01.11 [ Large medium small ]

Slow moving machine tool is a kind of high precision machine tool, which can achieve several μ m machining accuracy, and the surface roughness Ra can reach < 0.2 μ M. But some mould factories don't pay attention to the details when they use the slow moving machine tool. They think that a good machine tool can achieve high-efficiency and high-precision machining casually. In fact, precision machining must establish the concept of precision machining!

 

Process premise

Slow moving machine tools are equipped with process parameters library, and the process parameters are generally obtained under specific conditions (such as workpiece material, electrode wire, temperature 20 ± 3 , humidity 40-80%). If the following conditions change or fail to meet the standard, the machining result may be deviated.

 

1) Flushing specification: when processing according to the standard parameters, the difference between the indicated value of the water pressure gauge and the theoretical value should be less than 0.5bar;

 

2) Clearance between workpiece and nozzle: 0.05 ~ 0.10 mm;

 

3) When the surface roughness requires RA 0.35 μ m, the efficiency oriented cutting wire can be selected (it is recommended to use the same type of wire as the machine tool). When RA < 0.35 μ m, in order to obtain a good processing surface, the surface oriented galvanized wire is selected for processing;

 

4) When finishing, please ensure that the water is less than 10, especially when finishing, please follow the process parameters. If necessary, change the resin or purified water.

Influence of temperature on machining accuracy

In order to carry out high-precision and high-quality WEDM, the environment must be stable and meet the requirements. There must be no direct sunlight or air flow, and the temperature change should be monitored. The temperature range to ensure the working accuracy of the machine tool is 20 ± 3?. if the temperature difference is large, the machining accuracy and surface roughness will be affected.

The change of room temperature has a great influence on the machining accuracy, which is reflected in the size, position and shape. As shown in the figure below, the larger the temperature change and the larger the size of the workpiece, the more obvious the influence of temperature. For example, a 200 mm long workpiece with a temperature difference of 5 degrees will produce a dimension error of 0.01 mm. It's better to finish a larger part in one start-up. If it's put in one night, the main cutting has little effect, but if it's stopped in the trimming process, it's difficult to guarantee the machining accuracy.

 

The thermal characteristics of CNC machine tools have an important impact on the machining accuracy, accounting for almost half of the machining accuracy

There is a big difference between the machining accuracy of the machine tool in the state of long-time stop running and the state of heat balance. The reason is that the temperature of the spindle and each moving axis of the CNC machine tool is relatively maintained at a fixed level after running for a period of time, and with the change of processing time, the thermal accuracy of the CNC machine tool tends to be stable, which indicates that even the high-precision machine tool has only one Stable machining accuracy can be obtained only under stable temperature environment and heat balance state.

In the case of high precision machining production after starting up, preheating the machine tool is the most basic common sense of precision machining. However, the "warm-up movement" of machine tools is ignored or unknown by many factories.

If the machine tool is put on hold for more than a few days, it is recommended to preheat it for more than 30 minutes before high precision machining; if the machine tool is put on hold for only a few hours, it is recommended to preheat it for 5-10 minutes before high precision machining. The process of preheating is to let the machine tool participate in the repeated movement of the machining axis. It is better to carry out multi axis linkage, for example, let the XYZ axis move from the lower left corner of the coordinate system to the upper right corner, and walk diagonally repeatedly. When executing, a macro program can be written on the machine tool to make the machine tool repeatedly perform the preheating action.

 

Factors affecting processing efficiency

There are many factors that affect the efficiency of WEDM. If there is inefficiency in processing, the following two factors can be considered.

 

(1) Due to the limitation of parts structure and clamping, high pressure water cannot be effectively flushed

At this time, it depends on whether the cutting parts can be improved from the clamping. Some parts are affected by the supporting fixture, the bottom is raised, some parts are affected by the position of the pressing plate and the clamping screw, so they have to raise the upper nozzle, and some operators are afraid of touching the nozzle and do not lower the upper nozzle to the lowest position. If the low surface is raised, it depends on whether the fixture with the fixture support surface and the worktable in the same plane can be used, or the workpiece can be directly clamped on the worktable.

Depending on the influence of screw pressing plate and parts, whether it can be clamped by jaw clamp; for the upper nozzle not falling to the lowest position due to the operator's worry, a 0.1 mm feeler gauge can be prepared according to the requirements. For the parts that can not effectively flush with high-pressure water due to the limitation of structure, the cutting energy can only be reduced. At this time, we must have a correct understanding of the cutting efficiency.

 

(2) Related to wire handling system (related to maintenance)

1) It is necessary to check whether the cooling water of the conductive block is normal. In particular, if there is cooling water for the lower conductive block, because copper particles will fall out during the cutting process, the cooling water for the lower conductive block may be blocked after long-term use of the machine tool, and even the flushing water for the lower nozzle processing should be cleaned and dredged;

2) The lower guide wheel on the lower arm rotates flexibly. Check and clean;

3) Whether the take-up wheel is normal;

4) Check the tension and speed of the yarn, and readjust if necessary;

5) Check and clean the guide wire nozzle and conductive block.