Slow wire machine is a high -precision machining machine. Advanced slow wire processing has reached amazing accuracy level. Size and accuracy can be controlled within 1 μm. Precision positioning can achieve control of nano -level equivalent. Surface roughness indicator can reach less than RA0.05 μm.
However, some factories do not have concept of precision processing when using a slow wire machine. It is thought that good machines can achieve high precision processing. In fact, precision processing must pay attention to a series of processing details.

Slow-to-wire machines have process parameter libraries. Process parameters are generally found under specific conditions (such as workpiece materials, electrode wire, temperature 20 ± 1 ℃, humidity 40-80%, etc.). If following conditions change or cannot meet standards, processing results may cause deviation.
1) Water flush specification: When processing according to standard parameters, after comparing value of water pressure meter, difference should be less than 0.5bar;
2) Gap between workpieces and nozzles: 0.05 ~ 0.10mm;
3) When surface roughness requires RA ≧ 0.35µm, you can choose cutting wires that focus on efficiency (recommended to use same type with same type as machine). When RA <0.35µm, in order to obtain a good processing surface, use galvanized wires focusing on the surface for processing;
4) When processing, please ensure that water µS <10, especially during refined processing, please according to process parameters. If necessary, replace resin or pure water.

In order to carry out high -precision and high -quality slow wire thread cutting and processing, environmental stability must meet requirements of prescribed requirements. There must be no direct or airflow of sunlight. Temperature changes should be monitored. Temperature range of machine to ensure accuracy of working accuracy is 20 ± 3º. If temperature difference is large, it will affect processing accuracy and surface roughness.

 

Changes in room temperature have a great impact on processing accuracy of processing. Effect is reflected in size, location, and shape. As shown in figure below, the greater temperature change and the larger size of workpiece, the more obvious it is affected by temperature. For example, when workpiece of 200mm is 200mm, size error of 0.01mm is generated when temperature difference is 5 degrees. A larger part is best completed in a boot at one time. If it is put on a night, it is only main impact of main cutting, but it is difficult to ensure processing accuracy if it is stopped.
Effect of room temperature changes on processing accuracy
Thermal characteristics of CNC machines have an important impact on accuracy of processing, and they account for almost half of processing accuracy. Processing accuracy of processing of machines in state of stop running and under heat balance is large. Reason is that main axis of CNC machines and axes of each movement are running for a period of time, its temperature is relatively relatively fixed. And with changes in processing time, thermal accuracy of CNC machines tends to be stable, which shows that even high -precision machines can obtain stable processing accuracy only under a stable temperature environment and thermal balance. After turning on, high precision processing production must be invested. Preheating machine is the most basic common sense of precision processing. However, preparation session of "warm -up movement" of machine has been ignored or unknown by many factories.
If machine is put on hold for more than a few days, it is recommended to preheat 30 minutes before high precision processing; if state is only hours, it is recommended to preheat 5-10 minutes before high precision processing. Preheating process is to allow machine to participate in repeated movement of processing shaft. It is best to perform multi-axis linkage, such as moving the XYZ axis from lower left corner to upper right corner of coordinate system, and repeatedly moving diagonally. When performing execution, you can write a macro -proclaimed order on machine to allow machine to repeatedly perform preheating actions.

Accuracy of slow wire processing is directly related to maintenance of machine, especially maintenance of wire transport system. Pay attention to following aspects:
1) Check whether cooling water of electric block is normal. Especially if there is cooling water for the lower conductive block, because copper powder will fall off during cutting process, and after long-term use of machine tool, cooling water of lower conductive block and even flushing water for lower nozzle processing may be blocked, so it should be cleaned and dredged;
2) Whether lower guide wheel on lower arm rotates flexibly. Inspect and clean;
3) Whether wire collection wheel is normal;
4) Check tension and silk speed of silk, re -adjust if necessary;
5) Check guides and conductive blocks.

You can take certain measures to control deformation of slow wire processing to prevent deformation from affecting processing accuracy.

If a large area of cutting is needed, relatively balanced state of internal residual stress inside material will be damaged, and material will produce great deformation. We can first eliminate most of stress of material, to carry out rough processing (rough processing), remove most of balance first, or cut path of release stress.
For slow wire processing of large concave molds, you can do two main cuts. First, increase offset of main cutting of main cut of 0.1-0.2mm for the first main cut, let stress release, and then use standard to be defined. Displacement is used for second main cut, as shown in figure below.

 

Rough processing of release stress reduces deformation
For long narrow shape, first cut stress path in the interior of this hole, then process shape of pores, as shown in figure below,

 

Release stress cutting

When cutting punch, if punch hole is not processed and punch is cut directly from outside of material, as shown in figure (a) below, deformation will occur due to unbalanced stress in material, resulting in open or closed deformation. Wire holes can be processed on material and closed contour processing can be performed. As shown in figure (b) below, deformation caused by slow wire processing can be significantly reduced.

 

(a) Large deformation (b) Small deformation
Processing of wire holes to reduce deformation

Under normal circumstances, it is best to arrange starting point of processing close to clamping end, arrange cutting section that separates workpiece from its clamping part at the end of processing path, and set pause point close to clamping end of blank. In some processes, unreasonable processing path arrangements are also cause of wire cutting deformation. As shown in figure below, the more reasonable processing path is: A → B → C → D ... → A. If you follow clockwise direction: A → L → K → J ... → A, since workpiece is cut off from clamping part at the beginning of cutting, when processing reaches the end of program, cutting accuracy of punch is directly affected by unreliable clamping factors.

 

Arrangement of processing paths

When mold plate is being processed by slow wire cutting, due to effect of original internal stress and influence of thermal stress generated by wire cutting, non-directional and irregular deformation will occur, making subsequent cutting thickness uneven, affecting processing quality and processing accuracy.
In response to this situation, mold plates that require relatively high precision are cut and processed multiple times. In the first cutting, waste material of all molded holes is cut off. After taking out waste material, automatic shifting function of machine tool is used to complete trimming and cutting of molded holes in sequence: Mainly cut cavity a, take scrap → Mainly cut cavity b, take scrap → Mainly cut cavity c, take scrap →…… → Mainly cut cavity n, take scrap → Trim cavity a → Trim cavity b →…… → Trim cavity n, and processing is completed.
This cutting method allows enough time for each hole to release internal stress after each hole is processed, minimizes mutual influence and trace deformation of each hole due to different processing sequences, and better ensures dimensional accuracy of mold plate.
However, this method requires more wire threading times and a larger workload, so it is more suitable for slow wire cutting machine tools with automatic wire threading mechanisms. After cutting is measured after cutting, shape size meets high -precision requirements.

 

For processing of large and complex-shaped workpieces, two or more temporary allowances should be set and multiple starting cutting points should be set, as shown in figure below. During programming, process it in an open shape. Before programming, first decompose graphic into multiple paragraphs, connect them separately. When processing, process contour, and finally leave temporary part of processing.

 

Set multiple sections of temporary retention