At present, the electrode wires that can be selected on the market can be divided into the following categories:

I, brass wire

(1) Brass wire is the first generation of professional wire in the field of wire cutting. In 1977, brass wire began to enter the market. This type of wire has led to a breakthrough in cutting speed, when the cutting speed was increased from 12 mm 2 /min to 25 mm 2 /min for a workpiece with a thickness of 50 mm. What makes the speed double? Brass is an alloy of copper and zinc. The most common ratio is 65% copper and 35% zinc. Zinc in brass wire was found to improve rinsing properties due to the lower melting point (420 ° C and copper at 1080 ° C). During the cutting process, the vaporization of zinc due to high temperatures causes the temperature of the wire to decrease and transfer heat to the machined surface of the workpiece. Theoretically, the higher the proportion of zinc, the better, but in the manufacturing process of brass wire, when the proportion of zinc exceeds 40%, the α-phase crystal structure of the electrode wire becomes a two-phase crystal structure of α and β. At this point the material becomes too brittle and is not suitable for drawing it into a filament of small diameter. Kunshan copper wire

2) Brass wire can have different tensile strength to meet different equipment and applications. This is achieved by a series of wire drawing (quenching) and heat treatment (annealing) processes. Ordinary brass wire has a tensile strength of between 490 and 900 N/mm2.

II, the main disadvantages of brass wire:

(1) The processing speed cannot be improved: Since the proportion of zinc in brass is constant, the energy conversion efficiency during discharge cannot be further improved; for example, a steel with a diameter of 30-60 mm is cut by a 0.25 mm brass wire, and the main cut of many domestic users. The speed is around 120mm2/min.

(2) Poor surface quality: copper powder on the surface of the brass wire and copper particles which are discharged due to vaporization of the surface layer of the wire will accumulate on the machined surface of the workpiece to form surface area copper. At the same time, due to the poor rinsing property, a thick metamorphic layer is formed on the surface of the workpiece, which affects the surface hardness and roughness of the workpiece;

(3) The machining accuracy is not high: especially when machining thick workpieces, due to poor rinsing properties, large straightness errors (upper and lower end dimensional errors and drum differences) may occur.

In addition, the poor quality of the copper blank material and the reasons for the drawing equipment and process lead to more copper powder on the surface of the brass wire, and the geometric error of the cross section is too large, etc., which will lead to a decrease in discharge stability, which seriously affects the processing speed and quality. . At the same time, it will also pollute the equipment components and increase the loss of equipment.

(1) Ultra-clean brass wire: The disadvantage of excessive copper on the surface of ordinary brass wire is made by adding a special cleaning process in the subsequent process;

(2) Super-hard brass wire: By adding other trace elements to the brass, the tensile strength of the brass wire is as high as 1200 N/mm2. This wire can improve machining accuracy and speed when machining ultra-thick or super-hard workpieces;

(3) High-speed brass wire: Increase the proportion of zinc in brass to 40% of the limit, which can improve the rinsing property and increase the cutting speed. However, its cutting speed is still slower than that of galvanized wire.

IV, coated electrode wire

Since the low melting point of zinc has a significant effect on improving the discharge performance of the wire, and the proportion of zinc in the brass is limited, it is thought that a layer of zinc is added on the outside of the brass wire, which produces a galvanized electrode. wire. This method, invented by several engineers in Switzerland in 1979, made the development of wire electrode a big step forward and led to the emergence of more new coated wire.

The main advantages of coated wire:

(1) The cutting speed is high and it is not easy to break the wire. Good quality galvanized electrode wire cutting speed can be 30-50% faster than high quality brass wire. At present, many users in Guangdong use 0.25mm galvanized electrode wire, and the cutting speed averages 150-180mm2/min.

(2) The surface quality of the machined workpiece is good, there is no copper accumulation, and the metamorphic layer is improved, so the hardness of the surface of the workpiece is higher and the life of the mold is prolonged.

(3) The machining accuracy is improved, especially the shape error of the sharp corner portion and the straightness error of the thick workpiece are improved compared with the brass wire.

(4) The loss of components such as the guide wire nozzle is reduced. Zinc has a lower hardness than brass, and galvanized wire does not have as much copper powder as brass wire, so it is not easy to block the wire guide and contaminate related parts.

The coating electrode wire production process mainly includes three methods of impregnation, electroplating and diffusion annealing. The core material of the wire is mainly brass, copper and steel. The materials of the coating are zinc, copper, copper-zinc alloy and silver. At present, the more mature such electrode wires on the market are mainly divided into the following types by application:

V, ordinary galvanized electrode wire:

(1) Since the impregnation process is relatively simple, many wire electrode manufacturers use this method to produce galvanized wire. However, the biggest problem is that the uniformity of the coating cannot be controlled after galvanizing. Therefore, the discharge performance of the electrode wire produced by this process is not stable enough, and the speed is only less than 10% higher than that of the brass wire. Some of the poor quality galvanized electrode wires are often not uniform in silver color, and some light yellow and yellow phases can be seen. This is the so-called "bronze" phenomenon. Although these types of wire are cheaper, they are only slightly more expensive than brass wire, but there are not many people.

VI, galvanized electrode wire for high precision machining:

(1) This type of electrode wire is mostly plated, so the thickness of the galvanized layer can be well controlled, the discharge performance is stable, and it is not easy to break the wire, which is suitable for precision machining of four times or more. Cutting speed can generally be about 30% faster than brass wire. See the section of this electrode wire. Common brands include COBRA CUT A, MEGACUT A from Berkenhoff, Germany, STAMMCUT ZC900 and ZC950 from Heinrich Stamm, Germany.

(2) ZENCO series galvanized electrode wire of Korea OPEC company, although it is also used for the impregnation process, its process is different, and it has applied for invention patents in the United States, Japan, Europe and China. The process is characterized by first drawing the brass core material to near the final diameter and then drawing it. The coating consists of multiple layers of copper-zinc alloy. The proportion of zinc is gradient from the inside to the outside. The outer layer of zinc is the most, and the surface is a microporous structure that is beneficial to improve the rinsing performance. This wire has been used by wire cutter manufacturers Sodick and Agie-Charmilles. At the same time, it is also the best-selling galvanized electrode wire in China.

(3) This year, several wire electrode manufacturers in Korea are also trying to produce galvanized electrode wire by electroplating. If it can form a batch into the market, it is believed to bring more benefits to domestic users.

VII, coated wire for high speed machining

(1) The electrode wire is produced by a diffusion annealing process and is a composite electrode wire having a thick coating containing 50% zinc and 50% copper. This coating undergoes a series of heat treatment processes, the color of which changes from bright silver to yellowish brown due to the diffusion of the coating. The core of the wire is of the alpha structure and the coating is of the beta structure, which is finally laminated to the core by cold pressing through a drawing process. The surface of the diffused electrode wire is porous, which helps to improve rinsing properties. The cutting speed of such a wire is currently the fastest. Common brands include COBRA CUT D, BRONCO CUT X, MEGACUT D, SWX, STAMMCUT Xi, etc.

(2) The HUNT-X wire developed by OPEC Korea for Charmilles' wire-cutting machine, although not using diffusion annealing process, has a cutting performance similar to that of this type of wire, and is also a high-speed wire which can be used for speed. Processing with higher requirements.

VIII, coated wire for difficult processing

(1) The steel core wire is a composite wire. It consists of a steel core with an intermediate copper coating and an outer brass coating. The tensile strength of the steel core at room temperature is similar to that of brass wire, but the tensile strength of the brass wire decreases rapidly with increasing temperature, while the tensile strength of steel is higher than that of brass wire. However, due to the poor electrical conductivity of the port, a layer of copper was placed on the outside of the steel core to improve the electrical conductivity. The outer brass layer acts to improve rinsing performance.

(2) For the more difficult wire cutting, although the wire with a thicker diameter (0.30mm) or the galvanized wire can be used to improve the situation, it is best to achieve higher processing requirements. The choice is the steel core wire.

(3) High-thickness machining: Generally speaking, when the workpiece is thick (usually more than 100 mm), the machining speed is significantly reduced, and the straightness error of the machined surface is large. At this time, the steel core wire processing can significantly improve the speed and accuracy.

(4) Processing of poor flushing conditions: for example, high-angle processing, irregular workpiece thickness, processing with a wide range of variations, and processing of stacking multiple workpieces. Poor flushing is likely to cause broken wires, and the processing speed is thus reduced. At the same time, it will also lead to an increase in secondary discharge, affecting the surface quality.

IX, workpiece materials are difficult to process: such as graphite, copper, aluminum alloy and other materials that are difficult to cut.

(1) Common brands include: COMPEED steel core wire from FUJIKURA, Japan.

(2) Electrode wire for ultra-precision machining

(3) The diameter of brass wire or coated wire is generally between 0.30 mm and 0.07 mm. For some fine parts or ultra-precision machining in the electronics, optics and watch industries, the wire diameter is required to be 0.10mm to 0.03mm. In the past, such electrode wires were made of tungsten or molybdenum wire and were very expensive. Nowadays, high tensile strength steel wire (100 carbon piano wire) is commonly used outside with brass plating, commonly known as "piano line". The tensile strength of such a wire is twice that of a general electrode wire and is as high as 2000 N/mm 2 or more. Common brands include the German MICRO CUT and Japan's SPWire.