Slow silk processing: dance on the tip of a needle

1、 What is jogging?

Slow wire is a CNC machine tool that uses continuously moving fine metal wire (called electrode wire, generally copper wire) as electrode to conduct pulse spark discharge on the workpiece, produce a high temperature of more than 6000 degrees, etch the metal and cut the workpiece. The principle of slow wire processing is that there is a gap between the on-line electrode and the workpiece, and the metal is removed by continuous discharge.

2、 Development status of slow wire processing technology:

With the continuous improvement of manufacturing accuracy and surface quality requirements of precision, complex and long-life stamping dies, fast wire walking processing technology can not meet the manufacturing requirements of precision dies. This situation promotes the rapid development of slow wire walking processing technology, and its process indicators have reached a relatively high level, which can not be replaced by other processing technologies.

(1) Improve machining accuracy

Multiple cutting technology is the fundamental means to improve the machining accuracy and surface quality of slow wire walking. Generally, it is formed by one-time cutting, the accuracy is improved by two-time cutting, and the surface quality is improved by more than three times cutting.

Due to the lag of electrode wire when cutting corners, the corners will collapse. In order to improve the accuracy of corner cutting, more dynamic corner processing strategies are adopted. Such as: automatically changing the processing speed, automatically adjusting the water pressure, controlling the processing energy, etc.

The high-precision finish machining circuit adopted by the advanced slow wire machining machine tool is an effective technology to improve the flatness of the machined workpiece, which significantly improves the machining accuracy of thick parts; In order to carry out micro finishing of small round corners, narrow slots, narrow grooves and micro parts, the top CNC low-speed WEDM machine tool can use 0.02 ~ 0.03 mm electrode wire for cutting.

In order to ensure high-precision machining, the mechanical accuracy, pulse power accuracy and servo control accuracy of the machine tool (including the control of mechanical motion, pulse parameters, wire feeding system and working fluid system) have reached a very high level. The water temperature cooling device is adopted to make the internal temperature of the machine tool the same as the water temperature and reduce the thermal deformation of the machine tool; The closed-loop digital AC (DC) servo control system is adopted to ensure excellent dynamic performance and high positioning accuracy. The machining accuracy can be controlled within several microns, and the precision positioning can be realized by 0.1 μ Control of m equivalent; Immersion machining is adopted to reduce the thermal deformation of the workpiece; Motor servo, closed-loop electrode wire tension control; The voltage modulation tool setting power supply is adopted to realize high-precision tool setting, and the tool setting accuracy can reach 0.002 mm, without damaging the workpiece, whether dry or wet.

 (2) The surface quality is improving day by day

The advanced slow wire processing machine tool adopts the non anti electrolysis pulse power supply with an average voltage of zero, and the damage of electrolysis has been reduced to a minimum. In addition, due to the improvement of pulse power supply, high peak value and narrow pulse width (microsecond level) are widely used. Most of the materials are thrown out in gas phase, which takes away a lot of heat, the surface temperature of the workpiece can not go up, and the phenomenon of cracking is greatly reduced; It not only has high processing efficiency, but also greatly improves the surface quality. Using non electrolytic power supply for WEDM can control the surface deterioration layer to 2 μ Below M. The wear resistance of the cutting edge of cemented carbide die is no different from that of grinding, and even better than mechanical grinding. More and more parts are processed “cutting instead of grinding”.

 (3) Improvement of processing efficiency

Due to the development of nanosecond high peak current pulse power supply technology and detection, control and anti-interference technology, the processing efficiency of slow wire processing machine tools is also improving. At present, the maximum processing efficiency of advanced slow wire processing machine tools can reach 500 mm ²/ min。 The processing efficiency of workpieces with larger thickness has practical significance. For example, when cutting workpieces with a thickness of 300 mm, the processing efficiency can reach 170 mm ²/ min。 For the processing of workpiece with thickness change, the processing parameters are automatically adjusted by automatically detecting the thickness of the workpiece, so as to prevent wire breakage and achieve the highest processing efficiency in this state.

In addition, the fast automatic threading technology introduced by the advanced slow threading machine tool, the automatic threading time is less than 15 s, which improves the efficiency of processing operation; The double wire automatic exchange technology introduced can automatically switch between two wires by using electrode wires of 0.20 ~ 0.02 mm. Thick wire is used for the first cutting, and the wire diameter is generally 0.25mm to improve the processing efficiency, and coreless cutting can be carried out; Then the fine wire is used for trimming. Generally, the fine wire of 0.10mm is used to cut small rounded corners, which can improve the accuracy and save 30% ~ 50% of the cutting time.

 (4) Development of automation, intelligence and informatization

In the process of processing, in order to reduce human intervention and ensure the expected process indicators, the automation, intelligence and informatization of slow wire processing have made corresponding development.

The complete process expert system of the slow wire processing machine gives a complete set of parameters according to the processing requirements. It not only includes the commonly used electrode wire brand and corresponding workpiece materials, but also provides the processing parameters of special materials such as PCD and PCBN, which can generate their own standards according to whether the upper and lower nozzles are in contact with the workpiece, the distance, whether they are refined in the cutting air or open surface, and which processing strategy gives priority to precision, surface roughness and efficiency; The discharge expert system deals with the random factors in cutting. Under the conditions of cutting in, cutting out, section change, center cutting, near edge cutting and large section high-speed cutting, the adaptive control strategy and automatic control function are used in the machining process to obtain continuous wire stable and high-efficiency machining.

The automatic non hole detection function is also very practical. During automatic skip processing, if the pre hole is forgotten or the hole position is offset, the machine tool will automatically move to the next pre hole, which can prevent shutdown during unattended processing. In case of short circuit after threading, it can automatically search the position to eliminate the short circuit, and improve the reliability of continuous unmanned operation.

The CNC system of the machine tool is equipped with standardized mechanical interface to form an intelligent manufacturing system. The automatic exchange of workpieces (pallets) can be easily realized through the manipulator of 3R system or EROWA system. With expert system and electrode wire automatic exchange technology, the whole processing process can be completed automatically.

3、 Technical level of various grades of slow wire processing machine tools

The slow wire processing machine tool can be divided into four grades: top-grade, high-grade, middle-grade and entry-level. Typical manufacturers of slow moving machine tools include GF processing scheme in Switzerland (formerly archishamir), Makino in Japan, Mitsubishi in Japan, Sadik in Japan, western Japan, Frank in Japan, etc.

 (1) Top slow wire processing machine

This kind of slow wire processing machine tool represents the highest level at present and is mainly made in Switzerland and Japan. The machining accuracy of this kind of machine tool can be guaranteed within ± 0.002 mm, and the maximum machining efficiency can reach 400 ~ 500 mm ²/ Min, the surface roughness can reach Ra0 05 μ m. It has perfect processing surface quality and almost no metamorphic layer on the surface, which can be used Φ The electrode wire of 0.02mm is used for micro finishing. Most of the main machines have a heat balance system, and some machine tools are cut in oil. This kind of machine tool has complete functions and high degree of automation. It can directly complete the precision machining of the mold, and the service life of the processed mold has reached the level of mechanical grinding.

 (2) High grade slow wire processing machine

This kind of machine tool is basically produced by Swiss and Japanese companies. It has the function of automatic threading, no resistance anti electrolytic power supply, and the overall thermal constant system. It can be used Φ The electrode wire of 0.07mm is cut, the accuracy is about ± 0.003 mm, and the maximum processing efficiency can reach 300 mm ²/ Min above, the surface roughness can reach RA < 0.2 μ m. It has the function of timely detecting the change of workpiece section and optimizing discharge power in real time. This kind of machine tool is also widely used in precision stamping die processing.

 (3) Medium grade slow wire processing machine tool

The performance of machine tools manufactured in Japan and most of its precision machining lines in China can meet the requirements of this grade. Generally, non resistance anti electrolysis power supply is adopted, which has the functions of immersion machining and taper cutting. The practical maximum processing efficiency is 150 ~ 200 mm ²/ Min, the best surface roughness is ra < 0.4 μ m. The cutting accuracy can reach ± 0.005 mm, which is generally used Φ The electrode wire of 0.1mm and above shall be cut, and the anti-collision protection system shall be equipped to avoid collision damage caused by programming error or misoperation. Automatic threading mechanism shall be equipped or optional.

 (4) Entry level slow wire processing machine tool

This machine tool is generally a Taiwan machine tool or a machine tool independently developed and produced in China. Its configuration and performance meet the processing requirements of domestic ordinary molds and parts. Generally, the process of cutting one and repairing one and cutting one and repairing two is used, which can stably achieve the surface finish of Ra0 eight μ M, and the machining accuracy is ± 0.008mm. Most of them can only use electrode wires of 0.15mm or more for cutting. There is a certain gap between the processed surface microstructure and corners and advanced machine tools.

In general, compared with fast wire walking machine tools, slow wire walking machine tools have obvious advantages in processing efficiency, accuracy and surface quality. Although the price of slow wire processing machine tool is expensive, with the rapid development of manufacturing industry, it will be more and more used in various processing fields.