The low speed wire cut EDM machine is mainly used for processing high precision parts. There are many varieties of low speed wire EDM machine tools and the operations of various machine tools are similar in many ways. Some basic operation contents and requirements are similar to those of high speed wire cut electrical discharge machine tools. However, the surface roughness, roundness error, linear error and dimensional error of the workpiece processed by the low speed wire cut EDM machine are much better than that of the high speed wire cutting machine, and its operation requirements pay more attention to the processing accuracy and surface quality.

Technical process preparation

• Technical performance analysis of workpiece materials

Different workpiece materials have different performance indicators such as melting point, vaporization point, and thermal conductivity. Even if processed in the same way, the quality of the workpiece obtained is different. Therefore, the workpiece material must be selected according to the actual surface quality required. For example, to achieve high precision, you must choose cemented carbide materials, rather than stainless steel or unquenched high-carbon steel, otherwise it will be difficult to achieve the required requirements. This is because the internal residual stress of cemented carbide materials has less influence on processing, and the processing accuracy and surface quality are better.

• Selection of working fluid

Spark discharge must be carried out in a liquid medium with certain insulating properties. The insulating performance of the working fluid can compress the discharge channel after breakdown, thereby limiting the spark discharge in a smaller channel radius. Instantaneous and local high temperature melts and vaporizes the metal, and after the discharge is completed, the discharge gap is quickly restored to an insulating state. If the insulation performance is too low, electrolysis will occur and no breakdown spark discharge will be formed. If the insulation performance is too high, the discharge gap will be small, chip removal will be difficult, and the cutting speed will be reduced.

Tap water has the advantages of good fluidity, non-flammable, and fast cooling rate. However, when tap water is used directly as the working fluid, due to the conductivity of ions in the water, the resistivity is low, about 5kΩ•cm, which not only affects the deionization of the discharge gap and prolongs the insulation recovery time, but also produces electrolysis. Therefore, deionized water is generally used as the working fluid for wire EDM. Generally, the resistivity should be 10～100kΩ•cm, and the specific value depends on the workpiece material, thickness and machining accuracy. For example, when processing steel with brass wire, the resistivity of the working fluid should be low to increase the cutting speed, but the opposite is true when processing hard alloy.

Before processing, you must observe the display of the resistivity meter. Especially when the machine tool is just started, it is often found that the resistivity is not within this range. Don't rush to process at this time. Let the machine run for a period of time before reaching the required resistivity before starting formal processing. In order to ensure the processing accuracy, it is necessary to increase the electrical resistivity of the processing fluid. When the electrical resistivity of water is no longer increased, the ion exchange resin should be replaced.

Furthermore, the conditions related to the coolant must be checked. In the low speed wire cut electrical discharge machine processing, the working fluid sent to the processing area usually adopts the pouring liquid supply method, or the workpiece full immersion liquid supply method. So check the fluid volume of the working fluid and the filter pressure gauge. When the machining fluid flows in the reverse direction from the dirty tank to the cleaning tank, the filter needs to be replaced to ensure that the insulating performance, washing performance, and cooling performance of the machining fluid meet the requirements.

Kerosene with higher insulation performance can also be used as the working fluid when special finishing processing is carried out with the low speed wire cut EDM machine.

• Selection and correction of electrode wires

Copper wire, brass wire, brass plus aluminum, brass plus zinc, brass zinc plating and whatnot are mostly used for the low speed wire cut electrical discharge machine processing. For precision WEDM, the tension of the electrode wire should be increased as much as possible under the premise of continuous wire. Molybdenum wire or tungsten wire can also be used.

At present, the wire diameter specifications of Chinese domestic electrode wires are 0.10mm, 0.15mm, 0.20mm, 0.25mm, 0.30mm, 0.33mm, 0.35mm, etc. The wire diameter error is generally within 2gm. The wire diameters of foreign produced electrode wires can be as small as 0.03mm, or even 0.01～0.003mm, and are used to complete the precision and fine wire EDM machining of clear corners and narrow slits. The surface of the wire electrode exposed to the air for a long time is easily oxidized in contact with the air, and cannot be used to process high-precision parts. Therefore, care should be taken not to damage the packaging film of the electrode wire when storing it. Before processing, the quality of the electrode wire must be checked. When one of the following situations occurs, the verticality correction of the electrode wire must be performed again. Generally, the wire cutting machine must consider replacing the guide wheel or its bearing after processing for 50-100 hours; changing the cutting position of the conductive block or replacing the conductive block. When dirty, it needs to be cleaned with detergent. It must be noted that when changing the position of the conductive block or replacing the conductive block, the verticality of the wire electrode must be re-calibrated to ensure the accuracy and surface quality of the processed workpiece.

• The processing of threaded holes

In actual production and processing, in order to prevent the residual stress deformation inside the workpiece blank and the thermal stress deformation caused by electrical discharge, whether it is processing a concave mold-type closed workpiece or a punch-type workpiece, it should be first Process the wire cut EDM machine with a certain diameter of the wire hole in the appropriate position for closed cutting, avoiding open cutting. If the workpiece has been rough cut on the high speed wire EDM machine, and then further processed on the low speed wire cut EDM machine, the wire hole is not punched.

• Clamping and alignment of workpieces

For workpieces that are to be processed by low speed wire cut EDM machine tools, an accurate reference surface should be processed in the previous process to facilitate clamping and Rectify. Make full use of machine tool accessories to clamp the workpiece. For the clamping of some complex structures and easily deformable workpieces, special fixtures can be designed and manufactured when necessary.

After the workpiece is clamped on the machine tool, you can use the machine's contact perception, automatic centering of the circle and other functions or use the dial indicator to find the exact position of the workpiece, so as to set the origin of the coordinate system and determine the starting point of programming. When aligning, you should pay attention to the operation several times, strive to be accurate in the position, and control the error to the minimum.

When the workpiece is about to be cut, the strength of its connection with the parent material is bound to decrease. At this time, attention should be paid to fixing the workpiece to prevent the workpiece from skewing due to the impact of the working fluid, thereby changing the cutting gap, which will affect the surface quality of the workpiece or make the artifact scrapped.