1. introduction
As an important branch of advanced manufacturing technology, special processing technology, especially EDM technology, has been an indispensable part of advanced manufacturing technology since its inception in the 1940s. Especially after entering the 1990s, with the development of high-tech such as information technology, network technology, aviation and aerospace technology, materials science and technology, EDM technology is also developing towards a deeper level and a higher level. Although some traditional processing technologies have been developed in some difficult-to-machine materials processing areas (especially in the field of mold processing) through their continuous updating and integration with other related technologies, the application of these technologies is not possible. It completely replaces the position of EDM technology in the processing of difficult materials, complex profiles and molds. On the contrary, EDM technology is developing in the direction of miniaturization, high efficiency, precision, automation and intelligence by learning from the development experience of other processing technologies.
2. Development status of EDM technology
At present, in the field of basic theory research of EDM, due to the complexity, randomness and lack of innovation of the research process, no breakthrough has been made so far. However, in the field of processing technology and control theory research, since the research results can be directly applied to production practice, it has become an active field in the research of EDM technology, and its research focus is mainly on high-efficiency processing technology and high-precision processing technology. (such as mirror processing technology), low-loss processing technology, micro-machining technology, non-conductive material processing technology, EDM surface treatment technology, intelligent control technology (such as artificial neural network technology, fuzzy control technology, expert system, etc.) and operational safety, Environmental protection and other aspects. In terms of process equipment development, the current new EDM machine tools have been comprehensively improved in terms of machining functions, machining accuracy, automation, reliability, etc. Many machine tools already have functions such as online detection, intelligent control, and modularization. It is a special machine tool in the traditional sense, and more like a CNC machine tool or even a machining center in machining.
3. Development trend of EDM technology
The rapid development of advanced manufacturing technology and the intensification of competition in the manufacturing market have put forward higher requirements for EDM processing technology, and also provided new impetus for the research of EDM processing technology and process development and equipment renewal. In the future, the processing object of EDM should be mainly oriented to the processing of difficult-to-machine materials and complex profiles that are difficult to achieve by traditional cutting. Fine processing, precision machining, narrow groove machining, and deep cavity machining will become the development priorities. At the same time, it should also pay attention to the composite application with other special processing technologies or traditional cutting processing technology, give full play to the advantages of various processing methods in the processing of difficult-to-machine materials, and achieve joint value-added effects. Compared with cutting technology, EDM technology is still a relatively young technology. Therefore, in the future development, we should learn from the experience and achievements in the development of cutting technology, and process it according to EDM. Technical characteristics, select appropriate processing theory, control principles and process methods, and continue to improve and innovate on the basis of existing achievements. The trend of EDM machine tool development towards CNC is irreversible, but it should be noted that it is not possible to blindly pursue “big and completeâ€. It should be market-oriented and establish an open CNC system. In general, the future development trend of EDM technology should be high efficiency, high precision, low loss, miniaturization, automation, safety and environmental protection.
3.l Development trend of EDM technology
In recent years, the basic theoretical research on EDM has not yet made substantial progress. Although some scholars have put forward some new ideas on the discharge traces of materials and the principle of material erosion, they have not made significant progress in the research of EDM mechanism. breakthrough. The more active research areas focus on process technology theory and control theory.
In the research of processing technology theory, the research hotspots are mainly how to improve the surface quality and processing speed of EDM, reduce the loss, expand the scope of EDM, and explore the processing methods of complex and fine structures. By applying the research results to production practice, the processing performance of EDM is improved. In the field of control theory research, intelligent control has always been the focus of research. Most of the new EDM machines produced at home and abroad use intelligent control technology. The application of this technology makes the machine operation easier and requires less operators. At the same time, the intelligent control system has self-learning ability, which can automatically monitor and adjust the processing process online to achieve optimal control of the machining process.
Although the theoretical research of EDM has a certain development and improvement in basic theory, processing technology theory, control theory, etc., but the processing technology theory and control theory should be further developed in an all-round way, it must be studied in the whole discharge process mechanism. A breakthrough has been made. Therefore, the development trend of EDM technology research will be to further explore the processing technology theory and control theory, improve the processing performance and processing range of EDM, and obtain better control effect, while focusing on the mechanism of discharge process.
In addition to the complexity and randomness of the discharge process itself, the main reasons for the breakthrough in the research on the mechanism of EDM are the lack of innovation in research methods and methods. Therefore, it is necessary to learn from the successful experience of other research fields, introduce advanced research methods and experimental techniques, overcome the limitations of traditional research methods, deeply analyze and reveal the inherent nature of the entire discharge process, and establish an objectively reflecting the law of the discharge process. Theoretical models to guide the research of EDM process theory and control theory, and computer simulation technology may be an effective tool to achieve this process.
3.2 Improvement of the structure of EDM equipment
Drawing on the development experience of modern cutting machine tools, the development of EDM equipment in the direction of numerical control is an irreversible trend. On the one hand, we should pursue the goal with high precision, high speed and automation, and occupy the market with technological advantages. On the other hand, we should fully consider the performance-price ratio of equipment, and make structural improvement and modular design through reasonable positioning of machine tools. The open CNC system improves the rationality of the machine design, and provides users with various EDM machines that can meet different processing needs at the lowest price and sufficient function.
Affected by the development of modern cutting technology, a part of the processing field that was previously suitable for EDM has gradually replaced the cutting method. However, the development of modern technology puts higher demands on the manufacturing precision of parts, and the application of various high-performance materials is increasingly widespread. At the same time, some parts tend to be complicated, miniaturized and thinned, which makes the cutting technology The application of some processing fields is limited, and these are precisely the technical advantages of EDM, and also the realistic basis for its survival space and development potential.
In order to comprehensively promote the technological advancement of EDM equipment, while adopting advanced control systems, the design of machine tool structure needs to be further improved. Its main development direction is as follows:
(1) Application of linear servo system
The electric spark forming processing equipment adopts the linear motor servo system to obtain a significant improvement in the processing performance. The specific performance is as follows: 1 can realize the direct linear motion of the shaft, eliminating the screw-nut drive link, thereby ensuring the high-speed movement of the shaft; The integrated structure of the motor and the slide plate can eliminate the mechanical response hysteresis caused by the intermediate link between the slide plate and the motor, improve the sensitivity of the system, shorten the dynamic response time, and ensure the stability of the machining process; 3 the movement of the linear motor servo system The method determines that the position detection link must adopt the linear position feedback component to realize the direct position detection without intermediate links, thus forming a full closed loop system to ensure high precision and precision retention of the machining process. At present, the application of linear servo system has obvious technical advantages in deep and narrow, micro-cavity processing and multi-cavity processing of molded parts. However, these technical advantages must be realized. In addition to the characteristics of the discharge process in EDM, and solving the technical problems of the linear servo system itself, it is also necessary to solve a series of related technologies related to the linear servo system, such as the power of the linear motion system. Balance, structural improvement of the workbench, etc.
(2) Improvement of machine tool movement mode
Breaking through the limitations of the existing EDM machine tool movement mode is another important way to bring into play its technological advantages and promote its industrial development. Drawing on the development experience of modern cutting technology, it can introduce circular motion on the basis of the main machining and forming motion of the machine tool, especially the multi-axis rotary system and various linear motions can be combined into a variety of composite motion modes to adapt to different kinds of workpieces. The processing requirements expand the processing range of EDM processing and improve its comparative advantages and technical benefits in precision machining. At present, many EDM machines at home and abroad have made some improvements in the movement mode. For example, the AGIF MONDO STAR20 (50) machine produced by Swiss Archie has the EQUIMODE function, which can realize the hemispherical translation in any direction of the space. The dynamic function has high practical value in actual processing. However, the current movement mode of the EDM machine tool is still relatively simple, and the application range is limited. EDM processing has to make major breakthroughs in machining precision, machining efficiency, processing range, etc. An important development direction is the innovation and diversification of machine tool forming motion. Recently, Dr. Yu Jiyuan and Professor Zeng Zengjiu from the University of Tokyo in Japan have proposed the concept of loss of electrodes, that is, through reasonable planning of the processing path, the electrode loss can be in an equal loss state, making the compensation of electrode loss extremely simple. . The proposal of this concept provides the necessary theoretical basis for the improvement of the movement mode of EDM. Of course, the resulting changes in machine tool structure and related technical theories need to be further deepened and perfected, and it is even possible to develop a new processing theory.
Affected by the development of modern cutting technology, a part of the processing field that was previously suitable for EDM has gradually replaced the cutting method. However, the development of modern technology puts higher demands on the manufacturing precision of parts, and the application of various high-performance materials is increasingly widespread. At the same time, some parts tend to be complicated, miniaturized and thinned, which makes the cutting technology The application of some processing fields is limited, and these are precisely the technical advantages of EDM, and also the realistic basis for its survival space and development potential.
In order to comprehensively promote the technological advancement of EDM equipment, while adopting advanced control systems, the design of machine tool structure needs to be further improved. Its main development direction is as follows:
(1) Application of linear servo system
The electric spark forming processing equipment adopts the linear motor servo system to obtain a significant improvement in the processing performance. The specific performance is as follows: 1 can realize the direct linear motion of the shaft, eliminating the screw-nut drive link, thereby ensuring the high-speed movement of the shaft; The integrated structure of the motor and the slide plate can eliminate the mechanical response hysteresis caused by the intermediate link between the slide plate and the motor, improve the sensitivity of the system, shorten the dynamic response time, and ensure the stability of the machining process; 3 the movement of the linear motor servo system The method determines that the position detection link must adopt the linear position feedback component to realize the direct position detection without intermediate links, thus forming a full closed loop system to ensure high precision and precision retention of the machining process. At present, the application of linear servo system has obvious technical advantages in deep and narrow, micro-cavity processing and multi-cavity processing of molded parts. However, these technical advantages must be realized. In addition to the characteristics of the discharge process in EDM, and solving the technical problems of the linear servo system itself, it is also necessary to solve a series of related technologies related to the linear servo system, such as the power of the linear motion system. Balance, structural improvement of the workbench, etc.
(2) Improvement of machine tool movement mode
Breaking through the limitations of the existing EDM machine tool movement mode is another important way to bring into play its technological advantages and promote its industrial development. Drawing on the development experience of modern cutting technology, it can introduce circular motion on the basis of the main machining and forming motion of the machine tool, especially the multi-axis rotary system and various linear motions can be combined into a variety of composite motion modes to adapt to different kinds of workpieces. The processing requirements expand the processing range of EDM processing and improve its comparative advantages and technical benefits in precision machining. At present, many EDM machines at home and abroad have made some improvements in the movement mode. For example, the AGIF MONDO STAR20 (50) machine produced by Swiss Archie has the EQUIMODE function, which can realize the hemispherical translation in any direction of the space. The dynamic function has high practical value in actual processing. However, the current movement mode of the EDM machine tool is still relatively simple, and the application range is limited. EDM processing has to make major breakthroughs in machining precision, machining efficiency, processing range, etc. An important development direction is the innovation and diversification of machine tool forming motion. Recently, Dr. Yu Jiyuan and Professor Zeng Zengjiu from the University of Tokyo in Japan have proposed the concept of loss of electrodes, that is, through reasonable planning of the processing path, the electrode loss can be in an equal loss state, making the compensation of electrode loss extremely simple. . The proposal of this concept provides the necessary theoretical basis for the improvement of the movement mode of EDM. Of course, the resulting changes in machine tool structure and related technical theories need to be further deepened and perfected, and it is even possible to develop a new processing theory.
(4) Expansion of application range
At present, EDM can process not only various conductive metal materials and complex cavities, but also processing semiconductor materials and non-conductive materials, and achieve better processing results. At the same time, the types of electrode materials are also increasing. The main development trends in this respect are: further study of the electrical discharge mechanism of semiconductor materials and non-conductive materials, to promote the processing efficiency, processing accuracy, stability of the processing process, and expand the range of machinable materials; in addition to processing complex cavities, Further realize the processing of three-dimensional cavity and complex surface; develop a new electrode material with superior performance.
3.4 Development trend of CNC system for EDM
The numerical control system is the core part of the numerical control machine tool. The improvement of its performance not only can directly improve the machining efficiency, machining accuracy and machining stability, but also an important way to expand the processing range and realize complex precision machining. The application of advanced numerical control system can bring significant economic benefits and broad development prospects for EDM, and has become an important indicator to measure the technical level of EDM. The development trend of EDM in numerical control system is mainly reflected in the following aspects:
(1) Establish an open CNC system based on PC
The open CNC system is the mainstream of the current CNC system, and the characteristics of the PC itself determine that it is a standard open structure system. The rapid development of PC technology and the continuous improvement of performance and price ratio provide a superior software and hardware platform, a more friendly human-machine interface and online real-time control functions for the CNC system. Compared with the previous CNC system, the PC-based CNC system has the following advantages: 1 system has higher integration and reliability; 2 rich resources, suitable for product development; 3 powerful control, various forms, can achieve more Machine control, multi-target control; 4 systems with higher flexibility. At present, the PC-based CNC system applied to CNC machine tools is mostly a dedicated structure. Although it has the advantages of simple structure, mature technology and low development cost, with the further development of technology, its software and hardware are closed. The shortcomings are becoming more and more obvious. For example, the numerical control system of this structure is difficult to apply the latest achievements of computer technology in time; it is difficult for different systems to be compatible with each other; users are not easy to add or improve special functions suitable for their own actual use; PC resource utilization is low, it is difficult to fully play PC Advantages of the machine; imperfect control system functions. In view of the above defects, the establishment of a PC-based EDM CNC system should focus on the following aspects:
1 modular system
The modular system structure should be established according to the uniform rules of the open CNC system. Through the systematic research on the EDM, select the necessary functions, expand the optional functions, and eliminate unnecessary functions. At the same time, each module should have a standardized application interface. Different modules can run on different system platforms, and each should have the ability to coordinate work.
2 Scalability Users can implement the “dedicated system†of the user by adding or removing specific function modules according to their own processing requirements.
3 Interchangeability Modules with similar functions and reliability levels can be interchanged.
Making full use of PC resources to develop high-performance CNC systems will be an important development trend in EDM.
(2) Intelligentization of process control
Improving the automation of the EDM process is an inevitable trend in the development of this process technology. Since EDM is a complex object based on complex tasks in complex environments, traditional control systems can no longer meet the requirements of automated machining. Therefore, it is necessary to establish a multi-input and multi-output control system. Intelligent control will solve this kind of problem. An effective way to solve complex problems. The intelligent control system has self-learning and self-adaptive functions, and can independently adjust the control structure, parameters and methods of the system to make decision planning and generalized problem solving. It is like an experienced operator. It can simulate the thinking mode of the skilled operator by qualitative characterization of the machining information, adjust the machining parameters according to the current machining state, and thus improve the machining efficiency, machining accuracy and process stability. And simplify the operation process and broaden the scope of processing. The intelligent control of the processing mainly includes three aspects: 1 artificial neural network technology; 2 fuzzy control; 3 expert system.
Although the intelligent control system has been widely used in EDM, there are still many imperfections. The main problems need to be solved: 1. Determine the reasonable gap between the tool electrode and the workpiece surface and the reasonable processing according to different processing requirements. Parameters; 2 development of pulse power supply that can be adaptively changed according to the change of gap state during processing; 3 reasonable selection of working fluid and its influence on the processing process; 4 reduce the impact of various disturbances on the processing process. In response to the above problems, the EDM intelligent control system should focus on the following technologies:
1 application of expert system
Due to the complexity of EDM, operators need to be proficient in CNC programming technology, processing specification selection, electrode loss compensation and other related technologies. The lack of any one of these links will cause defects or failures in the machining process. This problem can be better solved by using an expert system. The establishment of the expert system and the improvement of its functions need to be based on the characteristics of EDM, combined with years of experimental research results and practical experience, continuously enrich and improve the expert system knowledge base, refine the reasoning process, and establish a good human-machine interface. Therefore, according to different processing requirements, the processing parameters are optimized and the online real-time adjustment in the processing process is achieved, thereby achieving the purpose of reducing the operation difficulty, achieving high efficiency, high precision and stable processing.
2 Application of Artificial Neural Network Technology Although the expert system can make the computer control system have the ability to solve problems with human experts, it has difficulties in acquiring knowledge and has poor self-learning ability. Artificial neural network is a highly nonlinear system established by abstracting, simplifying and simulating human brain function by using computer. It has the ability of self-organization, self-learning, fault tolerance and parallel processing of information, especially suitable for dealing with complex problems. It is a powerful complement to the expert system. At present, artificial neural network technology has many different structural models. In the future, various structural models should be reasonably combined, and the advantages of artificial neural network technology should be fully utilized. The expert system and fuzzy control technology can complement each other and improve the discharge state. The prediction accuracy of processing efficiency, discharge position, etc., improves the on-line real-time control effect, and promotes the EDM process control to a higher level.
3 application of fuzzy control technology
Fuzzy control technology is an advanced computer control technology developed on the basis of fuzzy set theory, fuzzy linguistic variables and fuzzy logic inference technology. By inputting a small number of parameters, the fuzzy control system can automatically select the optimal parameters and automatically monitor the processing process to achieve Automation, optimal control. In addition, the adaptive and learning ability is introduced into the fuzzy control system, which can automatically adjust and improve the fuzzy control rules, membership functions and fuzzy quantization in the control. Since the mechanism of EDM is not fully understood, there are still many imperfections in the application of fuzzy control technology in EDM. It needs further research, such as the calculation of fuzzy set membership function and fuzzy control parameters. The optimization method of adjustment, the modeling of machining state by fuzzy method, the design of fuzzy prediction, and the improvement of operation speed. It is necessary to further improve the combination of fuzzy control and adaptive control, artificial neural network and expert system, and give full play to the advantages of various control methods to solve the above problems and achieve high efficiency, high precision, low loss and stable process control.
In order to keep up with the development of advanced manufacturing technology, the most advanced artificial intelligence technology should be introduced into the EDM process control, and the intelligent and modular EDM machine tools should be developed by utilizing the characteristics and advantages of various control technologies. Control components and actuators to promote comprehensive technological advancement in the electrical processing industry.
3.5 Operational safety and environmental protection
With the advancement of science and technology and the development of human civilization, people are increasingly demanding improvements in working conditions and environmental protection. Due to its own characteristics, EDM processing inevitably produces unsafe factors and pollution of working fluid splash, smoke, noise, electromagnetic radiation, harmful gases, etc., and the harm to the operator's personal safety and environment cannot be ignored. Therefore, in order to ensure the sustainable development of the electric processing industry, the most efficient use of resources and the minimum generation and emission of waste must be realized according to the principle of “green manufacturingâ€. Specifically, the following measures should be taken: 1 closed machine working area. This is beneficial to improve the pollution of working fluids, smoke, electromagnetic radiation, etc. to the human body, machine tools and working environment, and is conducive to the prevention of electric shock during operation and the centralized treatment and discharge of harmful gases; 2 the use of alternative technologies. For example, in order to reduce the environmental pollution caused by the use of working fluid, under the premise of ensuring processing efficiency, processing accuracy, processing cost and stability of the processing process, the working fluid with less pollution should be selected as much as possible, and at the same time, research and development should be vigorously used. Forming processing technology of working fluid; 3 post-treatment of waste. Waste liquid and waste gas generated during processing must be treated before discharge. It is necessary to point out that the reasonable treatment of the pollutants generated during the processing process is not only conducive to improving the safety of work, reducing environmental pollution, but also improving the working environment of the operator and making the operator feel happy when working. The social image and market competitiveness of the processing industry are also very beneficial.
4. Conclusion
EDM technology plays an important role in the manufacturing industry and is an effective means to realize the precision machining of difficult materials and complex parts. Researchers should learn from the successful experience of other processing technology development, develop strengths and circumvent weaknesses, make full use of the relevant achievements of modern science and technology development, and guide the research on EDM technology and control theory based on the research mechanism of EDM. Structure and design method, establish an open CNC system based on PC, realize the organic combination of intelligent control technology and EDM technology, and attach great importance to operation safety and environmental protection, and promote the development of EDM technology faster.
As an important branch of advanced manufacturing technology, special processing technology, especially EDM technology, has been an indispensable part of advanced manufacturing technology since its inception in the 1940s. Especially after entering the 1990s, with the development of high-tech such as information technology, network technology, aviation and aerospace technology, materials science and technology, EDM technology is also developing towards a deeper level and a higher level. Although some traditional processing technologies have been developed in some difficult-to-machine materials processing areas (especially in the field of mold processing) through their continuous updating and integration with other related technologies, the application of these technologies is not possible. It completely replaces the position of EDM technology in the processing of difficult materials, complex profiles and molds. On the contrary, EDM technology is developing in the direction of miniaturization, high efficiency, precision, automation and intelligence by learning from the development experience of other processing technologies.
2. Development status of EDM technology
At present, in the field of basic theory research of EDM, due to the complexity, randomness and lack of innovation of the research process, no breakthrough has been made so far. However, in the field of processing technology and control theory research, since the research results can be directly applied to production practice, it has become an active field in the research of EDM technology, and its research focus is mainly on high-efficiency processing technology and high-precision processing technology. (such as mirror processing technology), low-loss processing technology, micro-machining technology, non-conductive material processing technology, EDM surface treatment technology, intelligent control technology (such as artificial neural network technology, fuzzy control technology, expert system, etc.) and operational safety, Environmental protection and other aspects. In terms of process equipment development, the current new EDM machine tools have been comprehensively improved in terms of machining functions, machining accuracy, automation, reliability, etc. Many machine tools already have functions such as online detection, intelligent control, and modularization. It is a special machine tool in the traditional sense, and more like a CNC machine tool or even a machining center in machining.
3. Development trend of EDM technology
The rapid development of advanced manufacturing technology and the intensification of competition in the manufacturing market have put forward higher requirements for EDM processing technology, and also provided new impetus for the research of EDM processing technology and process development and equipment renewal. In the future, the processing object of EDM should be mainly oriented to the processing of difficult-to-machine materials and complex profiles that are difficult to achieve by traditional cutting. Fine processing, precision machining, narrow groove machining, and deep cavity machining will become the development priorities. At the same time, it should also pay attention to the composite application with other special processing technologies or traditional cutting processing technology, give full play to the advantages of various processing methods in the processing of difficult-to-machine materials, and achieve joint value-added effects. Compared with cutting technology, EDM technology is still a relatively young technology. Therefore, in the future development, we should learn from the experience and achievements in the development of cutting technology, and process it according to EDM. Technical characteristics, select appropriate processing theory, control principles and process methods, and continue to improve and innovate on the basis of existing achievements. The trend of EDM machine tool development towards CNC is irreversible, but it should be noted that it is not possible to blindly pursue “big and completeâ€. It should be market-oriented and establish an open CNC system. In general, the future development trend of EDM technology should be high efficiency, high precision, low loss, miniaturization, automation, safety and environmental protection.
3.l Development trend of EDM technology
In recent years, the basic theoretical research on EDM has not yet made substantial progress. Although some scholars have put forward some new ideas on the discharge traces of materials and the principle of material erosion, they have not made significant progress in the research of EDM mechanism. breakthrough. The more active research areas focus on process technology theory and control theory.
In the research of processing technology theory, the research hotspots are mainly how to improve the surface quality and processing speed of EDM, reduce the loss, expand the scope of EDM, and explore the processing methods of complex and fine structures. By applying the research results to production practice, the processing performance of EDM is improved. In the field of control theory research, intelligent control has always been the focus of research. Most of the new EDM machines produced at home and abroad use intelligent control technology. The application of this technology makes the machine operation easier and requires less operators. At the same time, the intelligent control system has self-learning ability, which can automatically monitor and adjust the processing process online to achieve optimal control of the machining process.
Although the theoretical research of EDM has a certain development and improvement in basic theory, processing technology theory, control theory, etc., but the processing technology theory and control theory should be further developed in an all-round way, it must be studied in the whole discharge process mechanism. A breakthrough has been made. Therefore, the development trend of EDM technology research will be to further explore the processing technology theory and control theory, improve the processing performance and processing range of EDM, and obtain better control effect, while focusing on the mechanism of discharge process.
In addition to the complexity and randomness of the discharge process itself, the main reasons for the breakthrough in the research on the mechanism of EDM are the lack of innovation in research methods and methods. Therefore, it is necessary to learn from the successful experience of other research fields, introduce advanced research methods and experimental techniques, overcome the limitations of traditional research methods, deeply analyze and reveal the inherent nature of the entire discharge process, and establish an objectively reflecting the law of the discharge process. Theoretical models to guide the research of EDM process theory and control theory, and computer simulation technology may be an effective tool to achieve this process.
3.2 Improvement of the structure of EDM equipment
Drawing on the development experience of modern cutting machine tools, the development of EDM equipment in the direction of numerical control is an irreversible trend. On the one hand, we should pursue the goal with high precision, high speed and automation, and occupy the market with technological advantages. On the other hand, we should fully consider the performance-price ratio of equipment, and make structural improvement and modular design through reasonable positioning of machine tools. The open CNC system improves the rationality of the machine design, and provides users with various EDM machines that can meet different processing needs at the lowest price and sufficient function.
Affected by the development of modern cutting technology, a part of the processing field that was previously suitable for EDM has gradually replaced the cutting method. However, the development of modern technology puts higher demands on the manufacturing precision of parts, and the application of various high-performance materials is increasingly widespread. At the same time, some parts tend to be complicated, miniaturized and thinned, which makes the cutting technology The application of some processing fields is limited, and these are precisely the technical advantages of EDM, and also the realistic basis for its survival space and development potential.
In order to comprehensively promote the technological advancement of EDM equipment, while adopting advanced control systems, the design of machine tool structure needs to be further improved. Its main development direction is as follows:
(1) Application of linear servo system
The electric spark forming processing equipment adopts the linear motor servo system to obtain a significant improvement in the processing performance. The specific performance is as follows: 1 can realize the direct linear motion of the shaft, eliminating the screw-nut drive link, thereby ensuring the high-speed movement of the shaft; The integrated structure of the motor and the slide plate can eliminate the mechanical response hysteresis caused by the intermediate link between the slide plate and the motor, improve the sensitivity of the system, shorten the dynamic response time, and ensure the stability of the machining process; 3 the movement of the linear motor servo system The method determines that the position detection link must adopt the linear position feedback component to realize the direct position detection without intermediate links, thus forming a full closed loop system to ensure high precision and precision retention of the machining process. At present, the application of linear servo system has obvious technical advantages in deep and narrow, micro-cavity processing and multi-cavity processing of molded parts. However, these technical advantages must be realized. In addition to the characteristics of the discharge process in EDM, and solving the technical problems of the linear servo system itself, it is also necessary to solve a series of related technologies related to the linear servo system, such as the power of the linear motion system. Balance, structural improvement of the workbench, etc.
(2) Improvement of machine tool movement mode
Breaking through the limitations of the existing EDM machine tool movement mode is another important way to bring into play its technological advantages and promote its industrial development. Drawing on the development experience of modern cutting technology, it can introduce circular motion on the basis of the main machining and forming motion of the machine tool, especially the multi-axis rotary system and various linear motions can be combined into a variety of composite motion modes to adapt to different kinds of workpieces. The processing requirements expand the processing range of EDM processing and improve its comparative advantages and technical benefits in precision machining. At present, many EDM machines at home and abroad have made some improvements in the movement mode. For example, the AGIF MONDO STAR20 (50) machine produced by Swiss Archie has the EQUIMODE function, which can realize the hemispherical translation in any direction of the space. The dynamic function has high practical value in actual processing. However, the current movement mode of the EDM machine tool is still relatively simple, and the application range is limited. EDM processing has to make major breakthroughs in machining precision, machining efficiency, processing range, etc. An important development direction is the innovation and diversification of machine tool forming motion. Recently, Dr. Yu Jiyuan and Professor Zeng Zengjiu from the University of Tokyo in Japan have proposed the concept of loss of electrodes, that is, through reasonable planning of the processing path, the electrode loss can be in an equal loss state, making the compensation of electrode loss extremely simple. . The proposal of this concept provides the necessary theoretical basis for the improvement of the movement mode of EDM. Of course, the resulting changes in machine tool structure and related technical theories need to be further deepened and perfected, and it is even possible to develop a new processing theory.
Affected by the development of modern cutting technology, a part of the processing field that was previously suitable for EDM has gradually replaced the cutting method. However, the development of modern technology puts higher demands on the manufacturing precision of parts, and the application of various high-performance materials is increasingly widespread. At the same time, some parts tend to be complicated, miniaturized and thinned, which makes the cutting technology The application of some processing fields is limited, and these are precisely the technical advantages of EDM, and also the realistic basis for its survival space and development potential.
In order to comprehensively promote the technological advancement of EDM equipment, while adopting advanced control systems, the design of machine tool structure needs to be further improved. Its main development direction is as follows:
(1) Application of linear servo system
The electric spark forming processing equipment adopts the linear motor servo system to obtain a significant improvement in the processing performance. The specific performance is as follows: 1 can realize the direct linear motion of the shaft, eliminating the screw-nut drive link, thereby ensuring the high-speed movement of the shaft; The integrated structure of the motor and the slide plate can eliminate the mechanical response hysteresis caused by the intermediate link between the slide plate and the motor, improve the sensitivity of the system, shorten the dynamic response time, and ensure the stability of the machining process; 3 the movement of the linear motor servo system The method determines that the position detection link must adopt the linear position feedback component to realize the direct position detection without intermediate links, thus forming a full closed loop system to ensure high precision and precision retention of the machining process. At present, the application of linear servo system has obvious technical advantages in deep and narrow, micro-cavity processing and multi-cavity processing of molded parts. However, these technical advantages must be realized. In addition to the characteristics of the discharge process in EDM, and solving the technical problems of the linear servo system itself, it is also necessary to solve a series of related technologies related to the linear servo system, such as the power of the linear motion system. Balance, structural improvement of the workbench, etc.
(2) Improvement of machine tool movement mode
Breaking through the limitations of the existing EDM machine tool movement mode is another important way to bring into play its technological advantages and promote its industrial development. Drawing on the development experience of modern cutting technology, it can introduce circular motion on the basis of the main machining and forming motion of the machine tool, especially the multi-axis rotary system and various linear motions can be combined into a variety of composite motion modes to adapt to different kinds of workpieces. The processing requirements expand the processing range of EDM processing and improve its comparative advantages and technical benefits in precision machining. At present, many EDM machines at home and abroad have made some improvements in the movement mode. For example, the AGIF MONDO STAR20 (50) machine produced by Swiss Archie has the EQUIMODE function, which can realize the hemispherical translation in any direction of the space. The dynamic function has high practical value in actual processing. However, the current movement mode of the EDM machine tool is still relatively simple, and the application range is limited. EDM processing has to make major breakthroughs in machining precision, machining efficiency, processing range, etc. An important development direction is the innovation and diversification of machine tool forming motion. Recently, Dr. Yu Jiyuan and Professor Zeng Zengjiu from the University of Tokyo in Japan have proposed the concept of loss of electrodes, that is, through reasonable planning of the processing path, the electrode loss can be in an equal loss state, making the compensation of electrode loss extremely simple. . The proposal of this concept provides the necessary theoretical basis for the improvement of the movement mode of EDM. Of course, the resulting changes in machine tool structure and related technical theories need to be further deepened and perfected, and it is even possible to develop a new processing theory.
(4) Expansion of application range
At present, EDM can process not only various conductive metal materials and complex cavities, but also processing semiconductor materials and non-conductive materials, and achieve better processing results. At the same time, the types of electrode materials are also increasing. The main development trends in this respect are: further study of the electrical discharge mechanism of semiconductor materials and non-conductive materials, to promote the processing efficiency, processing accuracy, stability of the processing process, and expand the range of machinable materials; in addition to processing complex cavities, Further realize the processing of three-dimensional cavity and complex surface; develop a new electrode material with superior performance.
3.4 Development trend of CNC system for EDM
The numerical control system is the core part of the numerical control machine tool. The improvement of its performance not only can directly improve the machining efficiency, machining accuracy and machining stability, but also an important way to expand the processing range and realize complex precision machining. The application of advanced numerical control system can bring significant economic benefits and broad development prospects for EDM, and has become an important indicator to measure the technical level of EDM. The development trend of EDM in numerical control system is mainly reflected in the following aspects:
(1) Establish an open CNC system based on PC
The open CNC system is the mainstream of the current CNC system, and the characteristics of the PC itself determine that it is a standard open structure system. The rapid development of PC technology and the continuous improvement of performance and price ratio provide a superior software and hardware platform, a more friendly human-machine interface and online real-time control functions for the CNC system. Compared with the previous CNC system, the PC-based CNC system has the following advantages: 1 system has higher integration and reliability; 2 rich resources, suitable for product development; 3 powerful control, various forms, can achieve more Machine control, multi-target control; 4 systems with higher flexibility. At present, the PC-based CNC system applied to CNC machine tools is mostly a dedicated structure. Although it has the advantages of simple structure, mature technology and low development cost, with the further development of technology, its software and hardware are closed. The shortcomings are becoming more and more obvious. For example, the numerical control system of this structure is difficult to apply the latest achievements of computer technology in time; it is difficult for different systems to be compatible with each other; users are not easy to add or improve special functions suitable for their own actual use; PC resource utilization is low, it is difficult to fully play PC Advantages of the machine; imperfect control system functions. In view of the above defects, the establishment of a PC-based EDM CNC system should focus on the following aspects:
1 modular system
The modular system structure should be established according to the uniform rules of the open CNC system. Through the systematic research on the EDM, select the necessary functions, expand the optional functions, and eliminate unnecessary functions. At the same time, each module should have a standardized application interface. Different modules can run on different system platforms, and each should have the ability to coordinate work.
2 Scalability Users can implement the “dedicated system†of the user by adding or removing specific function modules according to their own processing requirements.
3 Interchangeability Modules with similar functions and reliability levels can be interchanged.
Making full use of PC resources to develop high-performance CNC systems will be an important development trend in EDM.
(2) Intelligentization of process control
Improving the automation of the EDM process is an inevitable trend in the development of this process technology. Since EDM is a complex object based on complex tasks in complex environments, traditional control systems can no longer meet the requirements of automated machining. Therefore, it is necessary to establish a multi-input and multi-output control system. Intelligent control will solve this kind of problem. An effective way to solve complex problems. The intelligent control system has self-learning and self-adaptive functions, and can independently adjust the control structure, parameters and methods of the system to make decision planning and generalized problem solving. It is like an experienced operator. It can simulate the thinking mode of the skilled operator by qualitative characterization of the machining information, adjust the machining parameters according to the current machining state, and thus improve the machining efficiency, machining accuracy and process stability. And simplify the operation process and broaden the scope of processing. The intelligent control of the processing mainly includes three aspects: 1 artificial neural network technology; 2 fuzzy control; 3 expert system.
Although the intelligent control system has been widely used in EDM, there are still many imperfections. The main problems need to be solved: 1. Determine the reasonable gap between the tool electrode and the workpiece surface and the reasonable processing according to different processing requirements. Parameters; 2 development of pulse power supply that can be adaptively changed according to the change of gap state during processing; 3 reasonable selection of working fluid and its influence on the processing process; 4 reduce the impact of various disturbances on the processing process. In response to the above problems, the EDM intelligent control system should focus on the following technologies:
1 application of expert system
Due to the complexity of EDM, operators need to be proficient in CNC programming technology, processing specification selection, electrode loss compensation and other related technologies. The lack of any one of these links will cause defects or failures in the machining process. This problem can be better solved by using an expert system. The establishment of the expert system and the improvement of its functions need to be based on the characteristics of EDM, combined with years of experimental research results and practical experience, continuously enrich and improve the expert system knowledge base, refine the reasoning process, and establish a good human-machine interface. Therefore, according to different processing requirements, the processing parameters are optimized and the online real-time adjustment in the processing process is achieved, thereby achieving the purpose of reducing the operation difficulty, achieving high efficiency, high precision and stable processing.
2 Application of Artificial Neural Network Technology Although the expert system can make the computer control system have the ability to solve problems with human experts, it has difficulties in acquiring knowledge and has poor self-learning ability. Artificial neural network is a highly nonlinear system established by abstracting, simplifying and simulating human brain function by using computer. It has the ability of self-organization, self-learning, fault tolerance and parallel processing of information, especially suitable for dealing with complex problems. It is a powerful complement to the expert system. At present, artificial neural network technology has many different structural models. In the future, various structural models should be reasonably combined, and the advantages of artificial neural network technology should be fully utilized. The expert system and fuzzy control technology can complement each other and improve the discharge state. The prediction accuracy of processing efficiency, discharge position, etc., improves the on-line real-time control effect, and promotes the EDM process control to a higher level.
3 application of fuzzy control technology
Fuzzy control technology is an advanced computer control technology developed on the basis of fuzzy set theory, fuzzy linguistic variables and fuzzy logic inference technology. By inputting a small number of parameters, the fuzzy control system can automatically select the optimal parameters and automatically monitor the processing process to achieve Automation, optimal control. In addition, the adaptive and learning ability is introduced into the fuzzy control system, which can automatically adjust and improve the fuzzy control rules, membership functions and fuzzy quantization in the control. Since the mechanism of EDM is not fully understood, there are still many imperfections in the application of fuzzy control technology in EDM. It needs further research, such as the calculation of fuzzy set membership function and fuzzy control parameters. The optimization method of adjustment, the modeling of machining state by fuzzy method, the design of fuzzy prediction, and the improvement of operation speed. It is necessary to further improve the combination of fuzzy control and adaptive control, artificial neural network and expert system, and give full play to the advantages of various control methods to solve the above problems and achieve high efficiency, high precision, low loss and stable process control.
In order to keep up with the development of advanced manufacturing technology, the most advanced artificial intelligence technology should be introduced into the EDM process control, and the intelligent and modular EDM machine tools should be developed by utilizing the characteristics and advantages of various control technologies. Control components and actuators to promote comprehensive technological advancement in the electrical processing industry.
3.5 Operational safety and environmental protection
With the advancement of science and technology and the development of human civilization, people are increasingly demanding improvements in working conditions and environmental protection. Due to its own characteristics, EDM processing inevitably produces unsafe factors and pollution of working fluid splash, smoke, noise, electromagnetic radiation, harmful gases, etc., and the harm to the operator's personal safety and environment cannot be ignored. Therefore, in order to ensure the sustainable development of the electric processing industry, the most efficient use of resources and the minimum generation and emission of waste must be realized according to the principle of “green manufacturingâ€. Specifically, the following measures should be taken: 1 closed machine working area. This is beneficial to improve the pollution of working fluids, smoke, electromagnetic radiation, etc. to the human body, machine tools and working environment, and is conducive to the prevention of electric shock during operation and the centralized treatment and discharge of harmful gases; 2 the use of alternative technologies. For example, in order to reduce the environmental pollution caused by the use of working fluid, under the premise of ensuring processing efficiency, processing accuracy, processing cost and stability of the processing process, the working fluid with less pollution should be selected as much as possible, and at the same time, research and development should be vigorously used. Forming processing technology of working fluid; 3 post-treatment of waste. Waste liquid and waste gas generated during processing must be treated before discharge. It is necessary to point out that the reasonable treatment of the pollutants generated during the processing process is not only conducive to improving the safety of work, reducing environmental pollution, but also improving the working environment of the operator and making the operator feel happy when working. The social image and market competitiveness of the processing industry are also very beneficial.
4. Conclusion
EDM technology plays an important role in the manufacturing industry and is an effective means to realize the precision machining of difficult materials and complex parts. Researchers should learn from the successful experience of other processing technology development, develop strengths and circumvent weaknesses, make full use of the relevant achievements of modern science and technology development, and guide the research on EDM technology and control theory based on the research mechanism of EDM. Structure and design method, establish an open CNC system based on PC, realize the organic combination of intelligent control technology and EDM technology, and attach great importance to operation safety and environmental protection, and promote the development of EDM technology faster.
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