The hottest precision CNC low speed wire EDM machi

Precision CNC low-speed wire EDM machining technology

overview

EDM machine tools (EDM) have been quite mature for mold machining. According to statistics, about 80% of WEDM machines are used for mold processing, and about 75% of SEDM machines are also used for mold processing. At present, it is common to have dozens of EDM machine tools in mold enterprises. EDM machine tools have become an indispensable and important equipment in mold manufacturing. With the development of EDM, its role and position in mold industry will continue to rise

China's mold industry is developing rapidly. The mold output value in 2005 is expected to reach 57-60 billion. By the end of the "Eleventh Five Year Plan" in 2010, the mold output value is expected to reach 100 billion. The development of mold industry mainly depends on technological progress. At present, large, precision, complex and long-life molds with high technological content are increasing. The development of these high-tech molds has promoted the technological progress of mold processing equipment. Many high-tech mold processing equipment, such as high-efficiency, precision, CNC low-speed wire EDM machine tool (LSWEDM), precision CNC EDM machine tool (ncsedm), high-speed milling (HSM), have emerged, LSWEDM is unique in stamping die processing. For a long time, LSWEDM has not been used as a means of final processing because the surface quality problems after processing have affected the service life of the mold. In recent years, LSWEDM has solved the problem of machining surface quality, and has made a qualitative leap due to its series of technological progress. Its excellent machining performance, at present, there is no processing technology that can compete with it

the development of precision, high efficiency and long-life stamping dies has promoted the technological progress of LSWEDM

LSWEDM is mainly used for the processing and manufacturing of precision, high efficiency and long-life stamping dies. Marking the advanced level of stamping die is the multi position progressive die, which has a series of characteristics such as complex structure, difficult manufacturing, high precision, long service life, high production efficiency and low energy consumption and consumables. Among these dies, the representative ones are: the electromechanical integrated motor iron core automatic valve sheet cemented carbide multi position progressive die, with an accuracy of 2 μ m. Step accuracy up to 3 μ m. Block precision 1 μ m. Double rotation accuracy 1 ', surface roughness Ra 0.10~0.40 μ m。 It has the functions of automatic stamping, valve plate, twisting groove, grouping, rotation, etc., and the service life of the die is more than 100 million times; Precision, high efficiency and long life multi position progressive die for air conditioner fins, with an accuracy of 2 μ m. There are nearly 1000 working surfaces of concave convex die, and more than 300 blanking gaps of 0.01mm. The same type is interchangeable, and the service life of the die is more than 200million times; It is a highly difficult to form color tube electron gun part. It is a 25 position cemented carbide progressive die at the bottom of G5, with an accuracy of 2 μ m. Punching 0.245mm thick non-magnetic stainless steel, product accuracy ± 5 μ m. Mold life more than 30million times; The price of the high-level integrated circuit frame 32 is still higher than that of the trapezoidal lead screw, and the precision of the station progressive die is up to 2 μ m. The punching speed of the die is 350~500 times/min, and the service life is more than 30million times; The independently innovative connector 50 position progressive die has an accuracy of 2 μ m. Step accuracy 3 μ m. The punching speed is more than 400 times/min, and the die life is 200million times; There are also stamping dies such as 18 position progressive die for digital camera spring sheet, multi position progressive die for automobile parts, and its own heating progressive die when the screw extrudes plastic, 46 position progressive die for connector, 12 position progressive die for micro motor housing, etc., which are the commanding heights of today's level. LSWEDM is an indispensable key equipment for the processing and manufacturing of these dies, especially these precision, high efficiency The machining of cemented carbide holes in key parts of long-life molds is the "place of use" of LSWEDM. At the same time, in order to meet the needs of these high-tech mold processing, it also promotes the continuous progress of LSWEDM technology

new progress of LSWEDM efficient processing technology

first, maximum processing efficiency

the maximum processing efficiency of LSWEDM in foreign countries has remained at 300mm2/min for many years, but there has been a new breakthrough recently, and China has just begun to reach 300mm2/min

the maximum processing efficiency depends on the development of narrow pulse width high peak current pulse power supply. In foreign countries, under the condition of narrow pulse width, the maximum peak current is ≥ 1200A. The maximum processing efficiency can reach 400~500mm2/min when the high peak current is matched with other conditions (various control modes, liquid supply conditions, composite electrode wires, etc.). For example, Agie cut progess machine tool of Swiss Archie company adopts digital IPG intelligent power supply Φ The maximum processing efficiency of 0.33mm electrode wire can reach more than 500mm2/min; Fa-v machine tool of Mitsubishi Electric Corporation of Japan adopts Φ The processing efficiency of 0.36mm electrode wire can also reach 500mm2/min; Lq33w new power supply developed by Sadiq company of Japan is used on aq325l machine tool Φ The processing efficiency of 0.30mm composite electrode wire can reach 400mm2/min, etc. In a word, at present, the maximum processing efficiency abroad is 400~500mm2/min, and new progress has been made

but at present, the most valuable and maximum processing efficiency is the Agie cut progess machine tool of Swiss Archie company. The e-cut power supply developed by the machine tool uses standard electrode wires. When the processing efficiency reaches 350~500 mm2/min, RA can reach 0.8 μ M (see Figure 1), this high-efficiency rough machining can reach RA 0.8 μ M level, for the final realization of precision machining of multiple cutting, it can save about 50% of the processing time, reduce about 40% of the filter consumption, 40% of the resin consumption, 60% of the silk consumption, and has obvious technical and economic benefits

Figure 1 progress machine tool at RA 0.8 μ The maximum machining efficiency at M

Second, the average machining efficiency

the maximum machining efficiency is often difficult to apply in the machining of precision stamping dies, mainly because the maximum machining efficiency requires the use of coarse wires（ Φ 0.33~0.36mm), while coarse wires are difficult to realize precision machining, and fine wires can only be used for precision machining, such as Φ 0.10mm, etc. In order to give full play to the maximum machining efficiency of the machine tool, Swiss Archie Shamir company has developed a double wire cutting machine tool, which can automatically exchange electrode wires, realize the purpose of coarse wires for rough machining and fine wires for fine machining, greatly improve the average machining efficiency, and also realize precision machining

the robofil 2050tw and robofil 6050tw double wire processing machine tools of chamir, Switzerland, solve the contradiction between precision and efficient processing, greatly shorten the total processing time, generally save 30-50% of the processing time, and save expensive filaments and reduce the processing cost

Swiss Archie's double wire cutting system has the same effect, and also: (1) automatically exchange electrode wires with different diameters without replacing the guide; (2) Automatic exchange has no accuracy loss; (3) Automatic threading 3ling material held a press conference in Tokyo on Friday, and the time is generally only 15 seconds; (4) The reliability of threading is 100%

III. machining efficiency of variable cross-section

lswedm will inevitably encounter different machining cross-sections in the actual machining process of molds. With the change of machining section, automatic detection and automatic control of machining energy according to the change of section are effective measures to improve the machining efficiency of variable section

for example, the FA series machine tools of Mitsubishi Corporation of Japan adopt the processing power control system, which is composed of workpiece thickness detector, processing state detector and pulse energy output controller to adapt to the change of processing section, especially suitable for the processing of stepped, hollow, thin and other parts, which can effectively prevent wire breakage and improve processing efficiency

as an example of this intelligent processing technology, it is shown in Figure 2. The maximum energy control expert system can automatically carry out the best processing as long as the diameter and type of electrode wire and workpiece material are input, and the processing energy can be automatically increased or decreased according to the different processing thickness in the processing process, so as to maintain the maximum processing efficiency. The efficiency of this expert system can generally be increased by about 30%

Fig. 2 Comparison of maximum energy control expert system machining

new breakthrough in LSWEDM machining surface quality

the machining surface quality of LSWEDM is the key to the development of LSWEDM, that is, whether LSWEDM can directly enter the field of precision machining. In addition to surface roughness and geometric morphology (dimensional accuracy), the machined surface quality in LSWEDM should also include two aspects: first, the chemical, physical and mechanical properties of LSWEDM machined surface layer, mainly including surface metallographic structure, surface microhardness, residual stress and macro and micro cracks, that is, the so-called surface "metamorphic layer"; Second, because LSWEDM uses water quality working fluid, the electrochemical reaction under the action of pulse power supply forms a surface "softening layer" on the surface of the workpiece, also known as the surface "metamorphic layer". The "metamorphic layer" in these two aspects directly affects the service life and performance (wear resistance, corrosion resistance, fatigue strength) of the die. With the development of LSWEDM, new breakthroughs have been made in the improvement of surface quality. Its technological progress is mainly reflected in the following two aspects

first, a new power supply that optimizes discharge energy

during EDM, metal material erosion is divided into melting and gasification. Wide pulse width (long discharge time) is easy to cause melting EDM, which will deteriorate the machined surface morphology, "metamorphic layer" thickening, internal stress increasing, and easy to produce cracks; When the pulse width is small to a certain value, it is easy to become gasified discharge machining. The deteriorated layer of gasified discharge machining is very small, the internal stress is also reduced, and the generation of surface cracks can be avoided, which improves the surface quality. Therefore, in order to maintain the same machining efficiency, under the principle of the same discharge energy, the method of compressing the discharge time and increasing the peak current I is adopted. This method of optimizing the pulse energy has greatly improved the surface quality. The schematic diagram of optimized discharge energy is shown in Figure 3

Figure 3 Schematic diagram of optimized discharge energy

II. Anti electrolysis (AE) pulse power supply

optimized discharge energy can only improve one aspect of surface quality, such as surface roughness, morphology, internal stress, cracks, etc. However, LSWEDM uses water quality working fluid. Although it uses "deionized" water, there are still a certain number of ions, which produce electrochemical reactions under the action of pulse power supply. When the workpiece is connected to the positive electrode, under the action of the electric field, the hydroxide anion (oh-) will continuously deposit on the workpiece, which will oxidize and corrode iron, aluminum, copper, zinc, titanium, tungsten carbide and other materials, resulting in the so-called "softening layer". When using cemented carbide workpieces, the binder cobalt in cemented carbide becomes ionic and dissolves in water, forming a "softening layer" as well

has been proved to be the most effective method to control the electrochemical reaction on the surface of the workpiece through a series of production practices. AE power supply is a pulse power supply whose alternating pulse makes the average voltage zero (see Figure 4). Because of the alternating pulse, oh- ions are in an oscillating state in the working fluid and do not tend to the workpiece and electrode wire, which can prevent the corrosion and oxidation of the workpiece surface, and the cobalt bond of cemented carbide will not be lost. Combined with the optimized discharge energy, the surface "metamorphic layer" can be controlled at 1 μ M below, so the service life of cemented carbide die processed by LSWEDM can reach the level of mechanical grinding, as shown in Figure 4

Figure 4 AE power waveform and LSWEDM positive polarity machining metamorphic layer distribution

taking IC lead frame die machining as an example, the die life of machining in deionized water with LSWEDM traditional pulse power supply, oil immersion machining with LSWEDM traditional pulse power supply, machining in deionized water with LSWEDM AE power supply and machining with mechanical grinding is tested and compared. The results show that the cemented carbide die machined with AE power supply