Keywords:
introduction
At present, the rapid development of the mold industry has promoted the advancement of mold manufacturing technology. As an important branch of mold manufacturing technology, EDM is being given higher and higher processing requirements. At the same time, under the influence of the new situation of CNC machining technology development, the EDM technology is rapidly developing towards a deeper and higher level of numerical control. Although the rapid development of high-speed mold processing technology has made electrical processing face severe challenges, some processes of EDM have been replaced by high-speed machining centers, but EDM still has broad prospects. For example, in the complex, precise small cavity, narrow slit, groove, corner, pop hole, deep cutting and other processing fields of the mold are still widely used. At the same time, this technology has been improved and upgraded, making EDM technology lasting in the mold industry. The rapid development of advanced manufacturing technology and the intensification of competition in the manufacturing market have put forward higher requirements for CNC EDM technology, and also provided new development momentum.
1 Basic status of the development of CNC EDM technology
1.1 CNC EDM technology is constantly developing in the direction of precision, automation, intelligence and efficiency. Nowadays, new types of CNC EDM machines are emerging one after another. For example, Swiss Archie, Swiss Charmilles, Japan Sodick, Japanese Makino, and Japanese Mitsubishi have all improved their technology in this area.
Precision
The precision core of EDM is mainly reflected in the requirements of dimensional accuracy, profiling accuracy and surface quality. Nowadays, the precision of CNC EDM machining has been improved. The size processing requirements can reach ±2-3μm , and the bottom corner R value can be less than
Intelligent
The emergence of intelligent control technology has pushed CNC EDM to a new level of development. The new CNC EDM machine uses intelligent control technology. The expert system is an important embodiment of the intelligentization of CNC EDM machine tools. Its intelligence is reflected in both accurate detection technology and fuzzy control technology. The expert system adopts the man-machine dialogue mode. According to the processing conditions and requirements, the machining program can be automatically created after the set value is input reasonably, and the best processing condition combination is selected for processing. Online automatic monitoring and adjustment of the processing process to achieve optimal control of the machining process. When the machining system detects the machining conditions, the input machining shape, electrode and workpiece material, machining position, target roughness value, electrode scaling amount, shaking mode, taper value and other indicators can be automatically calculated and configured. The fuzzy control technology is to monitor the state of the EDM machining gap by computer monitoring, automatically select the processing conditions that maximize the machining efficiency within the range of maintaining stable arc; automatically monitor the machining process to achieve the most stable control technology of the machining process. The application of expert system intelligence technology makes machine tool operation easier and requires less skill level for operators. At present, the intelligent technology is continuously upgraded, making the application range of intelligent control technology more extensive. As the market demands for electrical processing, intelligent technology will gain a broader space for development.
automation
At present, the most advanced CNC EDM machine is equipped with an electrode library and a standard electrode fixture. As long as the electrode is loaded into the tool magazine before processing and the machining program is programmed, the entire EDM process can be automated. It runs almost without 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 device accessories is relatively expensive, and the configuration of CNC EDM machines for most mold companies is not complete. The functions of automatic measurement and alignment, automatic positioning, and continuous machining of multiple workpieces of CNC EDM machine have already exerted its automation performance. The automatic operation process does not require manual intervention, which can improve the processing accuracy and efficiency. The degree of automation of machine tools is one of the development trends of the current CNC EDM machine industry.
Efficient
The requirements of modern machining provide the best machining mode for CNC EDM technology, which requires a substantial increase in roughing and finishing efficiency under the premise of ensuring machining accuracy. For example, mobile phone casings, home appliances, electrical appliances, electronic instruments, etc., all require large areas (for example, 100×
other
CNC EDM technology has also made great progress in miniaturization, safety and environmental protection.
1.2 The development of CNC EDM technology is changing with each passing day, so that machine tool manufacturers have improved their production technology. At present, CNC EDM machine has achieved significant results in the improvement of servo system and pulse power supply, greatly improving the quality and processing efficiency of CNC EDM.
Improvement of machine tool servo system
Precision machine tool servo systems are of great significance for EDM. The linear motor-driven CNC EDM equipment developed recently has significantly improved the processing performance. The linear motor is arranged on the drive shaft to achieve high response and smooth drive, which improves the stability of the mechanical system and avoids the action lag. The spindle of the CNC EDM machine adopts the high-speed lifting technology of the linear motor, which further improves the discharge performance of the machining chips, thereby improving the processing performance and realizing the no-flush processing. The linear motor-driven machine tool can control the machining depth to a minimum and achieve high-precision machining due to the good tracking performance of the highly responsive servo. The application of linear servo system has obvious technical advantages in the processing of deep and narrow micro-cavity. Linear motor technology will become the leading force in the 21st century EDM machine servo system.
Improvement of machine tool pulse power supply
Pulsed power supplies play an extremely important role in increasing machining speed, reducing electrode losses, ensuring machining accuracy and improving surface quality. Various pulse power supplies have made great contributions to the processing of high speed and high grade. The ultra-precision power supply is used in EDM precision and micro-machining. This type of power supply has a small single pulse energy (nanosecond pulse width), and the processing speed is slow, the electrode loss is large and the low pulse is solved by other measures on the circuit. Wide process contradiction. The intelligent adaptive power supply adopts the microcomputer digital control technology, selects the processing standard, and adaptively adjusts the relevant pulse parameters in the processing to achieve the optimal stable discharge state with high productivity. In addition, the new pulse power supply also has an energy-saving pulse power supply, an equal energy pulse power supply, 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 process
The development of CNC EDM technology makes the operation of the process faster. The operation process of the numerical control electric spark machine using ATC (automatic electrode exchange device) is as follows: after the machine is turned on, it returns to the machine origin; then the workpiece is clamped, and the reference ball is fixed at any position within the X and Y strokes of the table ; The electrode to be processed is loaded into the ATC electrode library, and the reference electrode is inserted into the spindle chuck; the positioning of the workpiece zero point by the center of the reference electrode is completed by manual control; then the centering of the reference electrode to the reference ball is completed, and the center of the reference electrode is shifted. Volume memory. Use the automatic programming software to create the program, first input the used electrode number, processing depth, and perform the search processing conditions; then make a combination of the program and the machining program for measuring the offset of the machining electrode center, and save the created program; Processing can begin. The electrode is automatically loaded during the machining process, and the center offset of the machining electrode is automatically measured, the automatic positioning, the oil processing, and the monitoring processing. The important operation steps of the whole process are in the programming process. The programming ideas must be clear when programming, and the input values ​​must be accurate to ensure the correct execution of the automatic machining process. The numerical control 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 process need to be completed manually. It can be seen that ATC is an important tool for CNC EDM automation, and its application breaks the cumbersome operation mode of traditional machining.
3 application of new technology of numerical control EDM
The EDM process is a direct means of achieving processing goals. At present, a variety of EDM processes have been developed and achieved certain economic benefits in production. The following describes several new processes and their advantages in CNC EDM.
3.1 Standardized fixtures for fast and precise positioning
CNC EDM is a standardized fixture that uses fast clamping to ensure extremely high repeatability and without reducing machining efficiency. There are currently EROWA in Switzerland and 3R devices in Sweden for fast and precise positioning. The principle of this type of device is that the electrode is manufactured at the same time, and the assembly of the collector and the clamp is completed on the same processing equipment as the process positioning reference attachment equipped with the numerical control electric discharge machine. The process positioning reference accessories are unified concentric and co-located, and each CNC machine tool has a coordinate origin. Therefore, after the electrode is manufactured, the components of the electrode and the clamp are directly removed and loaded into the reference accessory of the numerical control electric spark machine, and no correction adjustment is needed. To insert a processing "urgent" process, can also be processed semi-finished products are unloaded, processed and then finished continue to be urgent fast setup process. The standardized fixture is a fast and precise positioning process. Its use greatly reduces the clamping positioning time in the CNC EDM process and effectively enhances the competitiveness of the enterprise.
3.2 Mixing powder processing method to achieve mirror surface processing effect
A processing method in which a powder additive is mixed in an electric discharge machining liquid to obtain a glossy surface at a high speed is called a mixed powder processing. This method is mainly applied to complex mold cavities, especially precision machining of complex surfaces that are not convenient for polishing operations. It can reduce the surface roughness value of the parts, eliminate the manual polishing process, and improve the performance of the parts (such as life, wear resistance, corrosion resistance, mold release, etc.). The processing principle is mainly to add a certain proportion of conductive powder into the electric spark working fluid, the discharge gap is increased, the parasitic capacitance and current density between the electrodes are reduced; the discharge point dispersion and the discharge concentration phenomenon are reduced. The main technical requirements for the processing of mirrors by the mixing method are: EDM machines with mirror finishing circuits (with very small single pulse energy); selection of suitable powder additives; concentration management of powder additives; use of diffusion devices to eliminate concentration errors; No flushing treatment. The development of the mixed powder processing technology has made the mirror processing of precision cavity molds a reality.
3.3 shaking processing method to achieve high precision machining
When EDM machining complex cavity, the processing difficulty and processing area in different directions are very different, which will cause local concentration of machining chips, triggering unstable processing and uneven discharge gap. In order to ensure the uniformity of the discharge gap at high efficiency and maintain high stable processability, the method of continuously shaking the electrode can be used in the process. The method of shaking in the processing can obtain a more uniform surface roughness of the side and the bottom surface, and it is easier to control the processing size. The selection of the shaking processing is determined according to the shaking pattern of the processed portion, the shape of the shaking amount, and the accuracy. If the method of shaking is not used in the process, it is difficult to achieve stable processing under small gap discharge conditions. Unstable processing phenomena due to this cause are easily found in finishing, and the unstable discharge makes the size not accurately controlled and the roughness is uneven. The use of the shaking processing method can solve these problems well and ensure high-precision, high-quality machining.
3.4 Multi-axis linkage machining method to achieve complex machining
In recent years, with the development of the mold industry and computer technology, the advancement of multi-axis linkage EDM technology has been promoted. The multi-axis rotary system is combined with a variety of linear motions to form a variety of composite motion modes to meet the processing requirements of different types of workpieces. The processing range of CNC EDM is expanded, and its comparative advantages and technical benefits in precision machining are improved. . CNC EDM machine tools can easily realize the processing of complex cavity molds or tiny parts that are difficult to process in traditional EDM machines, such as three-dimensional spiral surface, fine gears, and fine racks. Currently used CNC EDM mold enterprise substantially axially servo processing molding using an electrode, it may be clever use of multi-axis machining methods to improve properties, such as clearance angle at the processing site by X feasible, Y, Z three The method of shaft linkage, that is, oblique processing, avoids the phenomenon that the discharge is unstable due to the small area of ​​the processing portion. The processing of the mold latent rubber mouth can also be performed by oblique multi-axis linkage processing by designing the positioning of the electrode inclination.
4 development trend of CNC EDM technology
The future development of CNC EDM technology is very broad. Due to the complexity of the EDM process, the mechanism of EDM has not been fully understood so far. Most of the research results are based on the process experiments of a large number of systems. Therefore, the mechanism of EDM is deeply studied. This direct guidance and application to practical processing is fundamental to the development of CNC EDM technology. On the basis of the state of the art, the continuous development of new processes will be the development direction of CNC EDM technology. For example, CNC EDM milling is a new technology that is still immature and worthy of further research. In the development of structural design and pulse power supply, CNC EDM machine will develop in a more reasonable and more advantageous direction, improve processing performance, and consider reducing the cost of machine tool manufacturing. CNC EDM technology will develop at a higher level in automation and intelligence. 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 constantly developing in the mold industry with the goal of improving processing quality, improving processing efficiency, expanding processing range, and reducing processing costs.
5 Conclusion
Under the new situation of rapid development of mold industry technology, CNC EDM technology has made breakthrough progress. It is widely used not only in past and present mold manufacturing, but also in future mold processing. Play an important role.
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