At present, the rapid development of the mold industry has promoted the progress of mold manufacturing technology. As an important branch of mold manufacturing technology, EDM has been given higher and higher processing requirements. At the same time, under the influence of the new situation in the development of CNC machining technology, EDM technology has been promoted to develop rapidly in a deeper and higher level of numerical control. Although the rapid development of high-speed tooling technology has faced severe challenges in electrical machining, some of the current EDM processes have been replaced by high-speed machining centers, but EDM still has broad prospects. Such as in the mold complex, precision small cavity, narrow slots, grooves, corners, holes, deep cutting and other processing areas are still widely used. At the same time, this technology has been improved and improved, making EDM technology durable in the mold industry. The rapid development of advanced manufacturing technology and the intensified competition in the manufacturing market place higher demands on CNC EDM technology, and at the same time it also provides new development momentum.
1 The basic status of development of CNC EDM technology
1.1 CNC EDM technology is constantly developing towards precision, automation, intelligence and high efficiency. Nowadays, new types of CNC EDM machines have emerged in an endless stream. Machine tools such as Swiss Archie, Swiss Charmilles, Japanese Sodick, Japan Makino and Japan's Mitsubishi have all improved in this area.
Refinement
The precise core of EDM is mainly reflected in the requirements for dimensional accuracy, profiling accuracy, and surface quality. Nowadays, the precision of CNC EDM machining has been improved comprehensively. The dimensional processing requirements can reach ±2-3μm, the bottom corner R can be less than 0.03mm, and the best machining surface roughness can be lower than Ra0.3μm. By adopting a series of advanced processing technologies and process methods, the effect of mirror processing can be achieved and EDM processing of high-precision mold parts such as miniature connectors, IC plastic seals, cell phones, and CD boxes can be successfully completed. From a general point of view, the modern die-molding companies have not yet excavated the precision machining performance of the machine tools in the application of advanced CNC EDM machines. Therefore, it is necessary to comprehensively promote the further development of existing CNC machining technologies and continuously improve the accuracy of mold processing.
Intelligent
The emergence of intelligent control technology has pushed CNC EDM to a new height of development. The new CNC EDM machine adopts intelligent control technology. The expert system is an important embodiment of the intelligentized digital EDM machine tool. Its intelligence is reflected in the precise detection technology and the fuzzy control technology. The expert system adopts the man-machine dialogue method. According to the processing conditions and requirements, after a reasonable input of setting values, a processing program can be automatically created, and a combination of the best processing conditions can be used for processing. On-line automatic monitoring, adjustment of the processing process, to achieve the optimal control of the processing process. When the expert system detects the machining conditions, it can automatically calculate and configure the optimal machining conditions by inputting the parameters such as the machining shape, electrode and workpiece material, machining position, target roughness value, electrode scaling amount, shaking mode, and taper value. The fuzzy control technology is a computer monitor to determine the state of the EDM gap, automatically select the processing conditions that maximize the processing efficiency within the range of maintaining a stable arc, and automatically monitor the process to achieve the most stable process control technology. The application of expert system intelligence technology makes the operation of the machine tool easier and requires less operator skill. The current intelligent technology is constantly upgraded, making the application of intelligent control technology more extensive. With the market's increasing demand for electrical processing, intelligent technology will gain more room for development.
automation
At present, the most advanced CNC EDM machine tool is equipped with an electrode library and a standard electrode holder. As long as the electrode is loaded into the tool magazine before machining, a good machining program is prepared, and the entire EDM process can be automated automatically. Operation, almost no manual operation. The automatic operation of the machine tool reduces the labor intensity of the operator and improves the production efficiency. However, the price of automatic equipment accessories is relatively expensive, and the configuration of CNC electric spark machine tools for most mold companies is not complete. The functions of automatic measurement alignment, automatic positioning, and continuous processing of multiple workpieces of CNC EDM machines have fully demonstrated its automation capabilities. The automatic operation process requires no manual intervention and can improve the machining accuracy and efficiency. The popularity of universal machine tools is one of the trends in the current CNC EDM industry.
Efficient
The requirements of modern machining provide the best machining mode for CNC EDM technology, that is, it is required to greatly improve the rough and finishing efficiency while ensuring the accuracy of machining. For example, mobile phone housings, household electrical appliances, electrical appliances, and electronic instruments require that the discharge time of a large area (for example, 100×100 mm) be significantly shortened, while at the same time reducing the roughness. From the original Ra0.8μm improved to Ra0.25μm, so that no need to hand polishing after discharge. This not only shortens the processing time but also eliminates the hassle of post-processing. At the same time, it improves the quality of the mold, and the use of powder processing equipment can meet the requirements. In addition to reducing the auxiliary time (such as programming time, electrode and workpiece positioning time, etc.), it is necessary to enhance the machine's automatic programming function, configure the electrode and workpiece positioning fixture, device. If graphite material is used in the rough machining of large workpieces, it is also a good way to improve processing efficiency. The best processing model is the capital for companies to expand their market space and increase their market competitiveness. The New Products and new technologies they have developed are also becoming more popular.
other
CNC EDM technology has also achieved considerable development in terms of miniaturization, safety, and environmental protection.
1.2 The rapid development of CNC EDM technology has caused machine tool manufacturers to improve their production technologies. At present, CNC electric spark machine tools have made great achievements in the improvement of servo systems and pulse power supply, and greatly improved the quality and processing efficiency of CNC EDM.
Improvement of Machine Tool Servo System
The precise machine tool servo system is of great significance to EDM. Recently developed linear motor-driven CNC EDM machines have significantly improved processing performance. A linear motor is arranged on the drive shaft to achieve a high-response, smooth drive, which improves the stability of the mechanical system and avoids the action lag. The CNC EDM spindle adopts the high-speed knife raising technology of the linear motor to further improve the discharge performance of the machining chips, thereby improving the processing performance and realizing the free-flow processing. Linear motor-driven machine tools, due to the good tracking ability of high-responsive servos, can minimize machining depth errors to achieve high-precision machining. The application of the linear servo system has obvious technical advantages in deep and narrow micro-cavity processing. The linear motor technology will become the dominant of the 21st century EDM machine servo system.
Improvement of Pulse Power Supply for Machine Tools
Pulse power plays an extremely important role in increasing processing speed, reducing electrode loss, ensuring machining accuracy, and improving surface quality. Various pulse power sources have made great contributions to high-speed, high-grade processing. Ultra-precision machining power is used in EDM precision and micro-machining. This kind of power supply has a very small single pulse energy (nanosecond pulse width), and it solves the slow processing speed, large electrode loss, and low pulse through other measures on the circuit. Wide process contradiction. The intelligent adaptive power supply adopts microcomputer digital control technology, self-selected processing standards, and adaptively adjusts the relevant pulse parameters in the process to achieve the best stable discharge state with high productivity. In addition, new types of pulse power sources include energy-saving pulse power supplies, pulse power supplies of various energy sources, and various dedicated auxiliary power supplies. With the deepening of research and development work, the performance of pulsed power supplies has also made greater progress.
2 CNC EDM operation process
The development of CNC EDM technology makes the processing process faster. The operation process of CNC EDM using ATC (Automatic Electrode Exchange Device) is as follows: After the machine is turned on, it first returns to the mechanical origin; then the workpiece is clamped and the reference ball is fixed at any position within the range of X, Y stroke of the table; The electrode to be processed is loaded into the ATC electrode bank, and the reference electrode is inserted into the spindle chuck; the positioning of the reference electrode center to the workpiece zero is completed by manual control; then the centering of the reference electrode is performed by the reference electrode, and the center of the reference electrode is offset Quantity memory.
Use the automatic programming software to create a program, first input the used electrode number, processing depth, and perform the search processing conditions; then make a program for measuring the offset of the machining electrode center and a combination of processing programs, and save the prepared program; finally call up the program execution. Can start processing. During the processing, the electrode is automatically loaded, the center offset of the machining electrode is automatically measured, the automatic positioning, the oil opening processing, and the monitoring processing are performed. The important operation steps of the whole processing process are in the programming process. The processing ideas must be clear during programming, and the input values ​​must be accurate in order to ensure the correct execution of the automatic machining process. The CNC EDM operation process without the ATC electrode library is the same as the above, except that the steps of changing the electrode and measuring the center offset in the machining must be completed manually. It can be seen that ATC is an important tool for CNC EDM automation, and its application has broken the traditional mode of operation.
3 Application of New Process of CNC EDM
EDM process is a direct means of achieving the purpose of processing. At present, a variety of EDM processes have been developed and certain economic benefits have been achieved in production. The following introduces several new processes and their advantages in CNC EDM.
3.1 Standardized Fixtures for Fast and Accurate Positioning
CNC EDM uses standard clamps that are fast-mounted to ensure extremely high repeatability and reduce processing efficiency. Currently, Switzerland's EROWA and Sweden's 3R devices can achieve fast and precise positioning. The principle of this type of device is that when the electrode is manufactured, the assembly of the collector and the fixture is completed on the same processing equipment equipped with the process positioning reference accessory provided on the CNC electric spark machine tool. The process positioning reference attachments are all concentric and co-located, and each CNC machine tool has its own coordinate origin. Therefore, after the electrode is manufactured, the components of the electrode and the jig are directly taken out and loaded on the reference attachment of the digital EDM machine, and no correction adjustment is required. In the process of processing, if an “emergency†process is inserted, the semi-manufactured product that is being processed can also be unloaded, and the rapid assembly process can be continued after the urgent component is processed. The standardized fixture is a rapid and precise positioning method. Its use greatly reduces the fixture positioning time in the CNC EDM process and effectively improves the competitiveness of the company.
3.2 mixed powder processing method to achieve mirror processing results
The processing method in which the powder additive is mixed in the electric discharge machining liquid to obtain a glossy surface at a high speed is referred to as mixed powder processing. This method is mainly applied to complex mold cavities, especially complex machining of complex surfaces that are not convenient for polishing operations. The surface roughness value of the parts can be reduced, manual polishing process can be omitted, and the use performance of the parts (such as life, wear resistance, corrosion resistance, mold release, etc.) can be improved. The processing principle is mainly that a certain proportion of conductive powder is added into the electric spark working fluid, the discharge gap is increased, the parasitic capacitance and the current density between the electrodes are reduced, and the discharge point is dispersed and the discharge concentration phenomenon is reduced. The main technical requirements for processing mirrors with mixed powder method are: EDM machines have a mirror finishing circuit (with a very small single pulse energy); select suitable powder additives; conduct concentration management of powder additives; use diffusion devices to eliminate concentration errors; No flushing method is used. The development of mixed powder processing technology has made the precision cavity mold mirror processing a reality.
3.3 shaking processing method to achieve high-precision machining
When EDM is used to process complex cavities, the machining difficulty and machining area in different directions are greatly different, which can cause local concentration of machining swarf, triggering unstable machining and uneven discharge gaps. In order to ensure the consistency of high-efficiency lower discharge gaps and maintain high stable processability, electrodes can be continuously shaken during processing. The method of shaking in processing can obtain a more uniform surface roughness on the sides and the bottom surface, and it is easier to control the processing size. The selection of shaking processing is based on the requirements of the shaking pattern of the part to be processed, the shape and accuracy of the shaking amount. If the method of shaking is not used in the processing, it is difficult to achieve stable processing under small gap discharge conditions. It is easy to find the unstable machining phenomenon caused by this reason in the finishing process, and the unstable discharge makes the size not be accurately controlled and the roughness is not uniform. The use of a shaking process can solve these problems and ensure high-precision, high-quality machining.
3.4 Multi-axis linkage processing method to achieve complex processing
In recent years, with the development of mold industry and computer technology, the progress of multi-axis linkage EDM has been promoted. The multi-axis rotary system is coordinated with a variety of linear motions to form a variety of compound motions to meet the processing requirements of different types of workpieces, expanding the processing range of CNC EDM and improving its comparative advantages and technical benefits in precision machining. . CNC EDM machines can use multi-axis linkage to easily realize the processing of complex cavity dies or small parts that are difficult to process with traditional EDM machines, such as three-dimensional spiral surfaces, micro-gears, and micro-racks. At present, CNC electric spark machining of mold companies basically uses axial servo machining of formed electrodes, but it is also possible to use multi-axis linkage methods to improve the processing performance. For example, X, Y, and Z are used in clear corners where processing is feasible. The method of shaft linkage, ie oblique machining, avoids the phenomenon of unstable discharge due to the small area of ​​the processing area. The design of the latent submerged entry of the mould can also be carried out by oblique multi-axis linkage processing by designing the positioning of the electrode inclination.
4 Development Trends of CNC EDM Technology
The future development of CNC EDM technology is very broad. Due to the complexity of the EDM process itself, the mechanism of EDM has not been fully understood so far, and most of the research results are based on a large number of system-based process experiments. Therefore, the EDM mechanism has been studied in-depth. This direct guidance and application of practical processing is the fundamental of the development of CNC EDM technology. On the basis of the current state of the art, continuous development of new processes will be the development direction of CNC EDM technology. For example, CNC EDM milling is an immature technique that deserves to be studied. CNC EDM will develop in a more rational and more advantageous direction in the development of structural design and pulse power supply to improve the processing performance, and at the same time consider reducing the cost of machine tool manufacturing. CNC EDM will advance toward higher level of automation and intelligence in control technology. The network management technology of CNC EDM has been applied to high-end machine tools and will be gradually promoted and applied to obtain better systems. Management effect. In short, CNC EDM technology is continuously developing in the mold industry with the goal of improving the processing quality, increasing the processing efficiency, expanding the processing range, and reducing the processing cost.
Under the new situation of rapid development of mold industry technology, CNC EDM has made breakthrough progress. It is not only widely used in past and present mold manufacturing, but also believes that in the future mold processing it will also be Play an important role.
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