The latest development and application of thermal

2022-08-14
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New development and application of EDM forming technology

1 Introduction

it has been more than 60 years since the development of EDM technology. Some people advocate that it should be driven out of the mold processing field, because the efficiency of high-speed milling is 10 times higher than it. However, EDM machine tool manufacturers do not agree. For example, for some narrow slot machining, high-speed milling is still powerless. Similarly, EDM and wire cutting have a development history of only about 40 years, but their technology is much more mature than molding processing, and their output value is almost twice as high. There is no doubt that they have become the leading equipment for mold cavity processing. This is due to the complexity of the EDM mechanism, which has not yet completed its growth period. As the goal of the finishing process in the cavity, there is still a way to go. High speed milling only objectively promotes its development, which should be faster and harder

the internal reason that has plagued the promotion and application of EDM technology for a long time is that due to the increasingly complex processing objects, it is more and more difficult for operators to set processing parameters and maintain the stability and reliability of the processing process. Although the manufacturer also provides some complete sets of parameters, there is still a certain gap from the practical requirements, such as electrode loss, scale force accuracy, surface roughness, safety factor It is more difficult to achieve a balance between processing efficiency and other indicators to achieve the required trade-off sequence. There was a saying among the operators that "one flush" works, that is, no matter how difficult the processing is, as long as the flushing problem is solved, the iron powder, carbon powder and bubbles can be flushed out. But now many cavities are difficult to flush and pump oil, and with the improvement of machining requirements, flushing and pumping oil or side flushing cause uneven flow field and uneven distribution of chips, affecting the flatness of finish machined surface. Moreover, flushing and pumping will also cause the loss of edges and corners, making the machining contour unclear. Therefore, users have raised the question of whether it can be processed without flushing, which will bring problems such as unstable processing and low efficiency to most EDM machines at present. As a finishing method, users of course hope that the cavity can achieve uniform surface roughness and certain dimensional accuracy, but when finishing, the gap is small, it is quite easy to focus on the discharge, which is manifested in the black spots on the processing surface. After wiping off the adhered carbon particles, you can see that this place is relatively rough. If the mold requires a shading effect, such uneven discharge marks will certainly not work. If polishing, It must be sunken here. The uneven machining surface caused by concentrated discharge destroys the dimensional accuracy of the cavity. Now users require micron level cavities, and the flatness error is more than ten microns. What about the dimensional accuracy

in order to overcome the above problems, Swiss Shamir technology company has done a lot of work in the past 10 years, and finally achieved success, which is DS system. Its working principle and characteristics are:

(1) confirm the diversity of EDM process, and develop the corresponding process, that is, application-oriented process, after fully studying and analyzing the characteristics of each type of machining object. At present, EDM is divided into four categories in DS system: general cavity, narrow gap, large area and micro cavity

(2) due to the complexity of EDM process, it can only be done according to experiments before its working mechanism is clear. For specific processing objects, do a lot of process tests. After obtaining appropriate processing parameters and process laws, after long-term processing verification, practical tests of cooperation with users, constantly modify and improve, and finally compile these mature processing know-how into software for easy use. This is the expert system

(3) the DS system contains several expert systems, which perform their respective duties and are linked together, covering the whole processing process. The operator always works from the beginning to the end of the processing with the assistance of the expert system

the first is the program expert system, which specifies the performance configuration and processing parameters required for the whole working process according to the requirements of drawing processing. Specifically: ① automatically generate the machining program from rough machining to finish machining, and the command program that connects the alignment, positioning and several cavity machining process programs. ② The processing input by man-machine dialogue is used to cut off the whole motor source in an emergency state; The requirements are: the trade-off between loss, surface quality, machining accuracy and machining speed, the type of machining cavity, which flushing method to use, which translation method to choose, etc. after that, the system can calculate the electrode shrinkage, the machining depth and manual amount of each gear, and the corresponding service and protection parameters. ③ Through the assembly of standard graphics module, the three-dimensional graphics of electrode are generated on the screen, and the change of discharge area with the increase of machining depth is comprehensively considered; Whether there is a weak dangerous section on the electrode; Actual shrinkage of electrode; Automatically calculate the rough machining power change curve to form the cutting part of the workpiece program

once entering the processing, you will get the help of the pilot expert system. It uses all positive measures to continuously optimize the processing parameters. Under the condition of shallow processing or no gap pollution, it will shorten the tool lifting time as much as possible to increase the discharge time, reduce the detection threshold, and protect the effective discharge pulse

at the same time, there is also the power control expert, which is the protector of processing safety, monitors each pulse and quickly removes harmful pulses. The speed of detecting gap pollution is increased by 10 times, and the dead zone of servo shaft is reduced, so the response time of servo spindle in advance, stop and reverse direction is only 2 μ s. The above measures effectively control the partial concentrated discharge to ensure uniform surface roughness. In addition, during rough machining, the machining area can be detected in real time, the machining standard can be changed in time, and the current density can be controlled, so as to protect the small-size part on the electrode from damage

in the medium and fine machining, due to the narrow gap and the phenomenon of bridging and short circuit, the processing and manufacturing of auto parts has also become much easier. When it is common, the effect of using the spindle to quickly retreat or processing the tool lift is not good, and it wastes time. At this time, there is the cleaning pulse (peak ultra narrow pulse) of the SPAC system to crush the short bridge, so as to greatly reduce the wasted time of retreat. Spac software package has corresponding detection parameters and energy parameters of cleaning pulse for real-time monitoring and processing of different processing conditions

in the case of micro machining, the DS system will automatically activate the micro machining expert system. Based on the accurate control of machining parameters and the strict prior removal of each bad pulse, stable machining is ensured and partial centralized discharge is avoided, so as to have a uniform and good flatness of the finish machined surface (150cm2 is only 5 μ m) The clarity of micro shape (bottom edge radius 0.05 mm) can improve the processing efficiency and reduce the cost of expensive micro cavity electrodes. It can easily realize the exchange of accessories, and the consumption is 30% - 60%

(4) there is no doubt that finishing is a small gap. Because the machining clearance is directly related to the machining accuracy (generally considered as 3:1), if measures are taken to increase the clearance, even if the surface roughness is improved, the clarity and flatness of the cavity will deteriorate. To ensure the stability of the processing of the oil delivery valve under the small gap (at this time, the servo adjustment range: the distance from the first beam discharge of finishing to stable processing is only 10 μ M), what we want is not high acceleration and speed, but very small dead zone and stable low speed (no creeping) of the servo system, as well as gap detection technology. Due to the small gap, various conditions such as no-load, short circuit and gap pollution will exist at the same time in machining (rough machining gap is large, which is rare). Relying on gap voltage feedback alone often cannot reflect the real situation of the gap. Therefore, it is necessary to detect, classify and count the discharge pulses one by one to determine the working condition and remove the bad pulses. However, the threshold of detection is not a fixed value. When the processing depth increases and there is gap pollution, it will be stricter

(5) various interferences are taboo in the medium and fine machining process of EDM molding. The process control must be smoothly adjusted. Whether it is in troubleshooting or shift machining, the transformation of parameters should be carefully divided. For example, the surface roughness should be processed to RA = 0.1 μ m. It should be refined at least 13 times

(6) no washing is required for medium and fine machining, and the tool lift is used for chip removal. When the electrode is lifted, the clean dielectric fluid enters the gap to dilute the polluted dielectric fluid in the gap. After the electrode enters the gap, the dielectric fluid is squeezed out, so that the chip is discharged and the electrode is not discharged and lost in the process of lifting the knife. The ratio of tool lift height to machining clearance is called dilution ratio. For example, gap 10 μ m. Knife lifting height 100 μ m. The chip can be discharged by 9O%. In the DS system, the tool lifting parameters change with the machining depth. The machining is shallow, the tool lifting frequency is low, the machining time is long, and the tool lifting height is low. Only when the machining is deep, in order to overcome the difficulties of lengthening the chip removal path and increasing the resistance, can the tool lifting frequency and height be increased. In the medium and fine machining, there is also the patented three-dimensional translation, end face and lateral tool lifting of Shamir technology company. At this time, the free flushing fluid will not have much impact on the processing stability

(7) the DS system always implements the principle of people-centered. The information of the whole working process should be as clear as possible to the operator, and it is allowed to introduce people at any time to make necessary modifications

ds system has achieved great success in practical application. A narrow groove with a depth of 38.1mm is machined with 45 mm x l.5 mm graphite electrode, and the surface roughness Ra = 1.6 μ M only needs 1h5omin, which is 2.5 times more efficient than in the past; Another example is to process 1-mold 4-cavity CD box, with 1 rough machining and 2 finish machining steel electrodes, with a processing area of 15ocm2, no flushing, and a flatness of 5 μ m。

ds system has become the application software of spark forming machine of Shamir technology company. It is based on the high performance of host and pulse power supply. Without the stability of hardware, the results of process test will not be universal, and the generated software will not be practical. Therefore, the establishment of DS system is a huge system engineering. It can be expected that the development of EDM application software will become a fashion and will become a sign of the new development of EDM technology

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