Discussion on the research and development of domestic electric wire cutting technology

With the development of science and technology and the continuous expansion of industrial production scale, WEDM is a kind of special processing technology. Because it is not limited by the hardness of processed materials, it is easy to process various complex plane graphics, high material utilization rate and processing precision. High in production, short in production cycle and low in manufacturing cost, it has been widely used in China's machinery manufacturing industry. Especially in the mold processing industry, WEDM technology is widely used in cold die and extrusion die processing, which has changed the processing mode of split mold and curve grinding in the past, shortening the manufacturing cycle, reducing the manufacturing cost and matching the precision. high. In view of the fact that foreign countries mainly focus on the study of one-way slow wire EDM wire cutting, this paper mainly discusses the development and application status of China's WEDM technology. 10. 1 Overview of WEDM wire cutting EDM wire cutting machine belongs to the category of electric machining. It was the phenomenon and reason of the former Soviet Lazarenko couple who studied the switch contacts being damaged by spark discharge corrosion. It was found that the instantaneous high temperature of the electric spark can cause the local metal to melt, oxidize and be corroded, thus creating and inventing the electric spark. processing method. The Soviet Union invented the world's first wire-cutting machine before 1960, and China was the first country to use wire-cutting machines for industrial production.

1.1 Processing principle Step motor wire cutting process principle 0 The principle of WEDM wire cutting is mainly realized by the action of spark discharge. As shown, the electrode wire is connected to the negative pole of the power supply through the power feeding block, the workpiece is connected to the positive pole of the power supply, a pulse voltage is applied between the positive and negative electrodes, and the working fluid having a certain insulating property is continuously injected, and the gap between the two electrodes is small. To a certain extent, because the microscopic surface of the two electrodes is uneven, the distribution of the dots is uneven, and the electric field strength at the nearest bump is the highest. The liquid medium between the machines is broken down to form a discharge channel, and the current rises rapidly. Under the action of the electric field, the electrons in the channel rush to the anode at high speed, the positive ions rush to the cathode, and the spark discharge is formed. The electrons and ions are under the action of the electric field. The fund project: the Sichuan Provincial Department of Education's achievement transformation major cultivation project “Precision control Research on secondary processing line cutting system" (13CZ0007) 1970-), male (Han), Sichuan Deyang, professor, master, research direction: mechanical design and manufacturing.

Zhang Shiyin (1970-), male (Han), Sichuan Meishan, associate professor, master's degree, research direction: mechanical manufacturing, materials engineering, higher education collided with each other during high-speed motion, and the cathode and anode surfaces were respectively subjected to electron and ion currents. Bombardment creates an instantaneous high-temperature heat source (center temperature up to 10 c) in the electrode gap, so that local metal melts and vaporizes. The vaporized working fluid and workpiece material vapor rapidly expands instantaneously and has explosive properties. Under the combined action of thermal expansion, thermal explosion, and working fluid stamping, the melted and vaporized workpiece material is thrown out of the discharge passage, and the secondary spark discharge process is completed. When the next pulse comes, continue the above spark discharge process to cut the workpiece. H. 1.2 Machining characteristics can process high-hardness, high-strength, high-brittle, high-toughness and other conductor materials and semiconductors that are difficult or impossible to process by traditional methods. material.

Due to the small size of the wire, it is possible to machine subtle shaped holes, narrow slits and complex shaped parts. 3) The surface of the workpiece to be machined is less affected by heat and is suitable for processing heat sensitive materials. At the same time, because the pulse energy is concentrated in a small range, the machining accuracy is high. 4) During the processing, the wire is not in direct contact with the workpiece, and there is no macro cutting force, which is beneficial to the processing of low-rigidity workpieces. 5) Due to the narrow slit produced during processing, the actual metal erosion amount is small and the material utilization rate is high. 6) EDM wire cutting directly uses electric energy processing, the electrical parameters are easy to adjust, and the operating system uses a numerical control system to facilitate automatic control of the machining process. 7) Compared with ordinary cutting processing methods, the production efficiency is relatively low; the wire is lossy; the minimum radius of the corner of the workpiece is limited; the processing quality is highly dependent on the operator.

1.3 Processing range and application areas 1) Processing die, such as precision die processing, WEDM is an indispensable key technology. Processing of punches, dies, fixed plates, unloading plates, etc., including large, medium and small dies. 2) Processing inlaid cavity mold, powder metallurgy mold, bending mold, drawing mold and so on. 3) Processing samples, forming tools, etc. 4) Processing micro-holes and slits of fine-shaped holes, narrow slits and complex-shaped parts such as shaped hole spinnerets, jet elements, laser devices, electronic devices, etc. 5) Processing various special materials and special structural parts, such as electronic components, instrumentation, motors, watches and other parts, as well as gears, thin shell devices, etc. 6) Cutting of various conductive materials, especially rare precious metals; cutting of various special structural parts, etc. H. 2 Development status of domestic electric discharge wire cutting machine tools EDM wire cutting machine tools are divided according to wire speed and movement mode For the high-speed reciprocating wire EDM wire cutting machine (hereinafter referred to as the EDM wire cutting machine technology research units and manufacturers are mainly distributed in Zhejiang, Ningbo, Taizhou, Guangzhou, Beijing and other places.

2.1 The development of high-speed wire-cut EDM wire-cutting machine tool The wire-cutting machine tool is a unique electric machining machine tool in China. After 40 years of development, the technology is quite mature and plays an important role in China's machinery manufacturing industry. It is also the main type of machine currently produced in China. Its biggest advantage lies in its simple structure, convenient operation, low cost of use (usually within 100,000 yuan), high processing efficiency and good cost performance.

The wire of the fast wire cutting machine makes high-speed reciprocating motion, the wire speed is 8 ~ 10m / s, the wire can be reused during the processing, the wire diameter range is 0.12 ~ 0.25mm, and the diameter is 0.18mm is the most commonly used The surface roughness of the machined surface can reach Ra: 3. Due to the fast loss of the electrode wire of the fast-cut wire cutting machine and the poor rigidity of the mainframe structure, it is greatly affected by the temperature change of the processing environment, the accuracy is unstable, the open-loop control feed system and the working fluid The conductivity of the machine is affected by factors such as changes in the use time, which limits the machining accuracy of the machine tool. In recent years, domestic manufacturers of fast-moving wire-cutting machine tools will improve the precision of reciprocating wire-cutting machine tools (mainly positioning accuracy and repeat positioning accuracy) and the surface quality of machined parts as the key breakthrough direction for product development. Significant progress has been made in pulse power technology, control technology, processing technology, etc. B-6. 2.1.1 Mainframe manufacturing technology The accuracy of machine tool main machine and wire transport system is an important guarantee for the precision of wire cutting machine tools. At present, the main structure of the machine tool is mostly tuning fork type. This structural advantage is that the manufacturing difficulty is small, the cost is low, and it is easy to assemble and disassemble and repair. Therefore, this structure is currently the mainstream structure of the wire cutting machine tool, especially the fast wire cutting machine tool. The main disadvantages are low rigidity, low natural frequency, and easy resonance during machine operation. In addition, the body of the machine tool is affected by a large amount of heat generated during the electric discharge machining process, which is prone to thermal deformation, which is also an important factor affecting the machining accuracy of the fast wire cutting machine. In order to improve this situation, the structure of the machine tool must be further improved. Therefore, when designing the machine tool structure, it is necessary to use the computer analysis software to carry out the mechanical and thermal stability simulation analysis of the machine tool structure to improve the rationality of the machine tool structure. In addition, the linear guide, double nut ball screw, AC servo motor direct drive has been applied in the machine design, which effectively improves the positioning accuracy and repeat positioning accuracy of the machine.

In the aspect of the wire transport system, the two-way constant tension wire tension mechanism developed by Beijing Electric Processing Research Institute greatly improved the stability of the wire and effectively reduced the vibration of the wire; Suzhou Boma Numerical Control Equipment Co., Ltd. The closed-loop dynamic tension control of the wire-cutting wire-drawing mechanism makes the machine's wire, tight wire and wire become smarter and more stable. The processing precision, surface finish and processing efficiency are greatly improved, and the user's use cost is also reduced.

The mechanism has the following characteristics: 1) the vibration detection speed of the molybdenum wire reaches the micron level through the sensor detection and servo closed loop electrical control with high frequency response; 2) the tension of the molybdenum wire in the processing zone is up and down by the upper and lower symmetrical mechanical tension adjusting device Constant, overcome the problem that the conventional force transmission control device is easy to loosen the wire; 3) By disposing the automatic wire and tight wire device, it overcomes the shortcomings of the manual wire and the tight wire in the middle wire cutting, and conforms to the international electric discharge line. The safe operating standard of the cutting machine; 4) The surface quality of the machined workpiece is significantly improved by the dynamic adjustment of the dynamic micrometer level of the molybdenum wire tension, especially the improvement of the commutating stripe of the workpiece.

2.1.2 Pulse Power Technology Pulse power supply technology is one of the core technologies of EDM machine tools. The performance of pulse power supply directly affects the efficiency of wire cutting and the loss rate of wire. The main gap between domestic and foreign wire cutting technology is in pulse power technology. Domestic wire cutting manufacturers must develop better and more advanced pulse power supply to avoid being squeezed or even swallowed by foreign manufacturers. At present, domestic wire cutting machine manufacturers mainly use digital power pulse power supply and non-resistive pulse power supply.

The digital pulse power supply uses the programmable logic device as the main vibration control chip of the high pulse power supply, and the generated pulse waveform is flexible and variable, realizing the real-time pulse parameter adaptive control of the hardware level. The numerical control system can be used to set the current front rising rate of the pulse power supply, reduce the electrode wire loss, automatic variable gauge quasi-machining, adapt to multiple cutting requirements and improve the stability of large thickness processing, improve processing efficiency, and reduce the probability of wire breakage.

The servo control circuit is based on the servo circuit used in the slow wire EDM machine and combined with the characteristics of the wire-cut wire EDM machine. For the first fine cutting process and the open discharge gap state in which the workpiece is cut into the closed gap state, the cutting process is corrected multiple times on one side. According to the servo tracking characteristics and requirements of two different requirements, the servo tracking is designed by the slow wire servo. Two servo parameters of voltage and tracking sensitivity, so that the pulse power supply is stable under two discharge gap conditions, which improves the efficiency of multiple correction processing and reduces the number of correction cuts. In the last cutting for the purpose of reducing the surface roughness of the workpiece, the last cutting with the slow wire cutting is changed to the constant velocity feeding scheme to achieve the highest surface finish while maintaining the machining accuracy of the workpiece. At present, this technology is testing the application phase. 08. 2.1.3 Control technology The application of artificial intelligence technology to the field of WEDM is a new attempt. At present, domestic research has begun to study this.

It is necessary to pay attention to the experience of foreign development, aiming at the key links of high-speed wire cutting processing, so as to develop intelligently to improve the overall processing performance of high-speed wire EDM wire cutting machine. In addition, another important aspect of artificial intelligence technology, a fuzzy control technology, mainly relies on imitation to achieve control of the machine tool. It has been successfully applied to EDM machines and has a good application prospect in the field of WEDM.

2.1.4 Processing Technology Whether it is a metal cutting machine or a slow wire cutting machine, it is difficult to obtain a good surface effect and high machining accuracy in one processing. All must be processed after roughing, finishing and other processes. The application of multiple cutting processes is an important means to improve the performance of wire cutting machines. In order to improve the processing quality of the fast-cut wire cutting machine, it is necessary to pay attention to the research of multiple cutting processes. In the past, the fast-moving wire cutting machine did not have the function of multiple cutting due to the limitation of function and structure. In recent years, with the improvement of the pulse power technology, the feed strategy and the tension control of the wire wire of the fast wire cutting machine, the application of multiple cutting processes has become possible. At present, some fast-cut wire cutting machine tools have been able to achieve multiple cutting processes, and to some extent improve the machining accuracy and surface quality. This fast-cut wire cutting machine with multiple cutting functions is a medium-cut wire cutting machine 910. Currently, Some manufacturers have established corresponding knowledge bases and expert systems. The operator only needs to input some performance parameters of the processed workpieces, and the system can automatically generate various processing steps, and automatically connect the various processes without manual intervention. The earth reduces the difficulty and strength of the machine operator.

The singularity of the singularity of the singularity of the singularity of the singularity of the singularity of the singularity of the singularity of the slewing machine. s; during the processing, the wire is discarded once, and the tensile strength is not high. The electrode wire material is generally galvanized copper wire or brass wire, the diameter range is 0.03~0.35mm, and the high productivity can be less than 0.3mm. Galvanized brass wire is processed, the surface roughness of the processing is generally Ra: 1.6~0.2pm, and the controllable processing precision is 0.005~0.002mm. The main features are: one-time use of the wire wire, one-time use, uniform tension The vibration is small, so the processing stability, surface roughness and precision index are better than the fast wire machine.

One-way slow wire cutting was the first major machine produced and used abroad. China's research on the slow-cut wire cutting machine started late. However, in recent years, China's scientific research personnel and enterprises have invested a large amount of research and development power with the support of the national special fund. Now, the research and development of a new generation of slow-moving wire-cutting machine tools has been completed. At present, products with independent intellectual property rights are already on the market. Its performance indicators have reached the level of foreign mid-range machines, and it has a certain market share in the mid-end market. There are few domestic manufacturers with independent research and development and production of slow wire cutting machine tools, and they are the backbone enterprises of domestic electric processing machine tool industry, such as Suzhou Sanguang Technology Co., Ltd., Suzhou Electric Machine Tool Research Institute, Beijing Ande Company, Suzhou 41 One City Baoma CNC Equipment Co., Ltd., etc. In addition, there are also some Sino-foreign joint ventures or wholly-owned enterprises of foreign companies in China who are also engaged in technical research and product development in this area, and have technological advantages.

Although in recent years China has made gratifying achievements in the research of one-way slow wire cutting technology, there is a big gap with the level of one-way slow wire cutting technology abroad. In order to meet the requirements of manufacturing and processing technology, the low-speed wire cutting machine developed by foreign countries (Europe, America, Japan, etc.) generally uses a closed-loop control system to ensure good dynamic performance and accurate positioning accuracy, and the machining accuracy can reach micron level. In addition, in the automation and intelligentization of machine tools, foreign manufacturers are far ahead of the micron. We should gradually narrow the gap and seize market share. 0.3 Conclusion The fast wire EDM wire cutting processing technology is a mechatronics and multidisciplinary Comprehensive technology, at present, how to develop fast-cut wire cutting machine tools is a subject that must be seriously studied in the entire electric processing industry. The successful experience of foreign wire-cutting technology should be absorbed, and the basic theory and experimental research of WEDM technology should be emphasized. Organize a professional R&D team to develop a PC-based CNC system with independent intellectual property rights. At the same time, the artificial intelligence technology is combined with the fast-cut wire cutting machine tool, and the computer software technology is used to improve the performance of the machine tool. In addition, the research on the structure of the machine body is strengthened and the application of multiple cutting processes is carried out to improve the overall processing quality of the machine tool and enhance the competitiveness of the fast wire cutting machine in the market. In short, as long as we seize the opportunity, do basic research, develop and innovate, use technology, and multi-disciplinary cooperation, the development prospects of China's reciprocating wire EDM wire cutting processing technology will certainly be better.