The main content of this article is:

1.       What is the principle of wire cutting?

2.       What is the precision of wire cutting processing?

3.       What materials are suitable for processing?

4.       What material is the cutting line (electrode) made of?

5.       What liquids are commonly used in machining fluids?

6.       What are the advantages and disadvantages of wire cutting?

1.       What is the principle of wire cutting?

Wire cutting is an unconventional machining process based on the principle of electrical discharge machining (EDM), commonly used for cutting hard materials such as hardened tool steel and hard alloys, and can produce metal parts with complex geometric shapes.

The basic working principle of wire cutting can be illustrated with a diagram.

The cutting wire [2] is fed from the wire wheel [1] through the guide wheel [3] and the control unit [4]. To resist wear and tear, the control unit is usually made of diamond. The cutting line is ultimately collected by the collection wheel [5] or cut into small pieces when consumed. By connecting the power supply, the cutting wire acts as the cathode and the workpiece acts as the anode. When the electrode (in this case, the cutting wire) is placed close to the workpiece, spark discharge occurs, causing the material on the workpiece to be removed. The discharge is supported by a dielectric [6], which helps to cool the material, and the process can also be completely immersed in the dielectric. The spark gap [7] causes the machining contour to be slightly larger than the diameter of the wire [8]. The machining contour is usually controlled by the motion of the workpiece in a horizontal plane.

The wire cutting process can be divided into three stages.

Arc formation between electrode and workpiece: In online cutting, a thin and conductive metal wire is used as the electrode. The distance between the electrode and the workpiece is very small, but there is no direct physical contact. By applying high voltage, an arc discharge is formed.

Arc generates high temperature and high pressure areas: The energy generated by arc discharge is very high, causing the metal on the surface of the workpiece to be instantly heated to a high temperature state. This high-temperature and high-pressure area can cause evaporation and corrosion on the metal surface.

Metal corrosion and removal: In high-temperature and high-pressure areas, metals will begin to corrode and dissolve. Corrosive metal particles are washed away by shock waves, thereby achieving the removal of metal workpieces. The arc continuously moves between the electrode and the workpiece, enabling the entire cutting process to form the desired shape on the metal surface.

The  material removal during wire cutting processing occurs due to the  influence of sparks on the surface of the workpiece. These sparks are  not continuous currents, but brief currents that occur millions of times  per second.

2.What is the accuracy of wire cutting processing?

Due  to the fact that wire cutting is a very precise machining method, its  machining accuracy depends on multiple factors, including process  parameters, electrode and workpiece materials, current, pulse interval,  distance between electrode and workpiece, etc.

Finer cutting lines and more precise control systems can achieve higher machining accuracy

Generally speaking, wire cutting can achieve an accuracy range of tens to hundreds of micrometers. The machining accuracy of high-precision wire cutting can reach the level of ± 2.5um, even about ± 1um, and the roughness can also reach 0.15-0.2uRa.

It should be noted that machining accuracy and surface quality are often affected by machining speed. Higher processing speeds may lead to a decrease in processing accuracy and a deterioration in surface quality. Therefore, when selecting processing parameters, it is necessary to balance the relationship between processing speed, processing accuracy, and surface quality.

In theory, the width of the slot is equal to twice the diameter of the wire plus the spark gap, but in practice, it may be slightly larger. Manufacturers may provide precise methods for calculating groove width related to process parameters, which need to be considered when programming online cutting.

Due to the strong heat generated in the wire cutting process of electric discharge, there is always a risk of heat affected zone and recast layer. Therefore, secondary operation is required to remove the recast layer.

03 What materials are suitable for wire cutting processing?

Wire cutting is very practical for processing hard and brittle materials, such as tool steel, hardened tool steel, hard alloy steel, chromium nickel iron alloy and other materials that are difficult to process with traditional processing methods. or process parts with complex contours in the aerospace or medical industries.

In addition, wire cutting machines can also be used to cut any conductive material, including copper, brass, aluminum, Hastelloy, etc.

Can we wire cut graphite?

Yes, wire cutting machines can cut graphite, but graphite is very brittle and requires careful handling, and the cutting speed is very slow; In addition, it is best to perform ordinary machining on graphite through milling and use wire cutting machines to process complex contours. In this way, the process can be made more economical and efficient. After electrical discharge machining, it is necessary to dry the graphite to remove moisture.

Can electric discharge machining be performed on titanium metal?

Yes, wire cutting machines can cut titanium alloys and use galvanized brass cutting wires (electrodes) to achieve better speed and surface finish. In addition, the cutting process may encounter the problem of wire breakage, which can be minimized to the greatest extent by adjusting the current value and the length of the "pulse off time".

04 What is the material of an electrical discharge machining line?

In order to minimize electrode corrosion and maintain a good machining surface finish, electrodes are generally made of brass, galvanized brass, tungsten, molybdenum wire, copper tungsten, carbides, copper graphite, etc. Galvanized brass wire is used for faster cutting and less breakage, while molybdenum wire is used for precise applications and places that do not require brass marks.

The cutting line diameter is 0.25mm, 0.18mm, 0.1mm, 0.015mm, 0.05mm, etc.

The wire in the wire cutting machine is only used once because it weakens after spark discharge. The used wire enters the bottom spool and is then cut into small pieces as waste.

05Dielectric fluid for wire cutting

The continuous flow of liquid in the wire cutting machine will wash away tiny chips, cool the workpiece, and fill the spark gap area with fresh liquid.

Dielectric fluid typically acts as an insulator, preventing current from flowing from the wire (electrode) to the workpiece. However, when the discharge voltage exceeds the dielectric strength, it becomes conductive and allows current to pass through in the form of sparks.

Deionized water is widely used as a dielectric fluid in wire cutting machines for the following reasons:

The dielectric strength of deionized water is lower than that of kerosene (hydrocarbon oil), so compared to kerosene, it allows spark discharge to occur at relatively large spark gaps, which means that the material removal rate is faster.

Moreover, compared to kerosene, deionized water can remove more heat from the spark discharge area, which is very useful when discharging at a high pulse frequency and low current. Due to its high cooling effect, there are fewer issues with the heat affected zone and recast layer when using deionized water.

In addition, compared to kerosene, deionized water has a higher material removal rate and better surface smoothness.

In addition, deionized water does not have harmful vapors or other issues, and is harmless to human skin.

However, deionized water will quickly lose its insulation properties, so you must have a deionized system.

06Advantages, disadvantages, and limitations of wire cutting processing

advantage:

Wire cutting is a precise cutting process that can be used to cut difficult profiles with strict tolerances, and even small-sized workpieces that cannot be cut by traditional processing techniques.

Wire cutting machines can be used to easily cut soft metals such as brass and copper, brittle materials such as graphite, as well as hard materials such as hard alloys and chromium nickel iron alloys.

Wire cutting can cut workpieces with a height of up to 300mm or a weight of up to 1000 kilograms. Can be used to cut sharp corners (with negligible radius) without leaving burrs or tool marks.

The electrode is a simple wire in a wire cutting machine, so the tool cost is relatively low.

Disadvantages and limitations:

Wire EDM can only be used for cutting conductive materials.

The cutting speed or material removal rate of wire electrical discharge cutting is low and uneconomical, so it is often used to process very hard materials or difficult to process profiles.

EDM wire cutting may leave a recast layer on the surface of the workpiece, which requires secondary operations such as polishing to remove it.

Wire breakage is a problem in wire cutting that can result in time and loss of some wires. The wire (electrode) in wire cutting cannot be reused, and it will be scrapped after one use, which increases the cost.

What is the principle of electrical discharge machining? What are the three common forms? What is the processing accuracy?

What are the characteristics and applications of tool steels such as A2, O1, D2, W1, S7, M2, H13, etc?

3. Talk about titanium alloys

What is the difference between copper, brass, and bronze? Why is C17200 beryllium copper so popular?

What is the meaning of roughness Ra? What roughness can be achieved by different processing methods? How to measure roughness?