What is the differences between the fast wire and the slow wire processing?

CNC EDM wire cutting processing includes fast wire processing and slow wire processing, which are widely used in the mold manufacturing industry. What are the current developments in processing efficiency, cutting accuracy and surface quality of these two technologies?
As the name suggests, the fast wire processing is named for the high-speed wire running operation during the cutting process. The fast wire processing machine tool is China’s original electric processing machine tool. After decades of continuous improvement and development, it has become an important processing method in the manufacturing industry. It can meet the requirements of medium and low-grade mold processing and other complex parts manufacturing, and has a considerable weight in the middle and low-end market.
The biggest advantage of the fast wire processing machine is its good performance and price ratio. Because of its practicability and economy, it has a large market in China. The traditional fast wire processing adopts a one-time cutting process, the processing efficiency is about 40 mm 2 /min, the surface roughness is about 3.0 μm, the surface has obvious lines, and the processing precision is about 0.02 mm.
In order to improve the processing quality, the manufacturer of the fast wire processing machine tool has improved the relevant parts of the machine tool by referring to the multiple cutting process, and the so-called “medium wire machine tool” has appeared. A large number of process technologies such as numerical control precision, pulse power supply, wire routing system and process database of machine tools have been greatly improved. Improve machining accuracy and improve surface quality.
At present, the technical index of the wire-cutting machine tool: the efficiency of one-time cutting is 180mm2/min, and the surface roughness after multiple cutting is Ra≤1.0μm. The average efficiency at this time is 50mm2/min, and the surface gloss is processed. No obvious cutting stripe, processing accuracy 0.01mm, electrode wire loss ≤0. 01 mm /200,000 mm2. These performance indicators seem to have been relatively good, but it should be noted that obtaining these indicators requires ensuring good links. Once there are discrepancies, such as the concentration of the working fluid and the loss of the wire, the stability of the processing quality will be affected.
Precision, complex, long-life stamping die manufacturing precision and surface quality requirements continue to improve, fast wire processing technology cannot adapt to the precision mold manufacturing requirements, this situation has promoted the rapid development of slow wire processing technology, its various aspects of the process indicators It has reached a fairly high level and is irreplaceable by other processing technologies.

1. Development status of slow wire processing technology

(1) Improved processing accuracy

Multiple cutting technology is the fundamental means to improve the accuracy and surface quality of slow wire processing. Generally, the cutting is performed by one cutting, the secondary cutting is used to improve the precision, and the cutting is performed three times or more to improve the surface quality.
Due to the hysteresis of the wire when cutting the corner, the corner collapses. In order to improve the corner cutting accuracy, more dynamic corner processing strategies have been adopted. Such as: automatically change the processing speed, automatically adjust the water pressure, control the processing energy.
The high-precision finishing circuit adopted by the advanced slow wire processing machine is an effective technique to improve the straightness of the workpiece, which makes the precision of thick parts processing significantly improved; for small rounded corners, narrow slits, narrow grooves and fine parts Micro-finishing, the top CNC low-speed wire-cut EDM machine can be cut with 0.02 ~ 0.03 mm wire.
In order to ensure high-precision machining, the machine’s mechanical precision, pulse power supply accuracy, servo control accuracy (including control of mechanical motion, pulse parameters, wire routing system and working fluid system) have reached a very high level. The water temperature cooling device is used to make the internal temperature of the machine tool the same as the water temperature, which reduces the thermal deformation of the machine tool. The closed-loop digital AC (straight) flow servo control system ensures excellent dynamic performance and high positioning accuracy. The machining accuracy can be controlled in several micrometers. Within the precision positioning, 0.1μm equivalent control can be realized; immersion processing can be used to reduce the thermal deformation of the workpiece; motor servo and closed-loop wire tension control; and high-precision tool setting can be realized by voltage modulation tool supply, the tool setting accuracy can reach 0.002 mm Does not damage the workpiece, whether it is wet or dry.

(2) Surface quality is improving day by day

The advanced slow wire processing machine uses a non-electrolytic pulse power supply with an average voltage of zero, and the destruction of the electrolysis has been minimized. In addition, due to the improvement of pulse power supply, high peaks and narrow pulse widths (microseconds) are generally used. Most of the materials are gas phase throwing, which takes away a lot of heat, and the surface temperature of the workpiece does not go up. The phenomenon of cracking is greatly Reduced; not only the processing efficiency is high, but also the surface quality is greatly improved. The electroless spark cutting process using an electroless power source can control the surface metamorphic layer to be less than 2 μm. The wear resistance and grinding of the cut carbide die are no different, even better than mechanical grinding. More and more parts are processed by cutting.

(3) Improvement of processing efficiency

Due to the development of nanosecond large peak current pulse power supply technology and detection, control and anti-jamming technology, the processing efficiency of slow wire processing machine tools is also constantly improving. The current processing speed of the advanced wire moving machine tool can reach 500mm. 2/min. The machining efficiency of workpieces with larger thicknesses has practical technical improvements. For example, when cutting a workpiece with a thickness of 300 mm, the machining efficiency can reach 170 mm 2 /min. For the processing of workpieces with varying thickness, the machining parameters are automatically adjusted by automatically detecting the thickness of the workpiece to prevent yarn breakage and achieve the highest machining efficiency in this state.
In addition, the advanced automatic wire-drawing technology introduced by the advanced slow wire processing machine, the automatic threading time <15 s improves the efficiency of the processing operation; the introduced double-wire automatic exchange technology can automatically double the wire with 0.20-0.02 mm Wire switching processing. The first cut is made with thick wire, the general wire diameter is 0.25 mm, to improve the processing efficiency, and the core can be cut; then the filament is used for dressing, generally 0.10 mm filament is used to cut the small round corner, and Improve accuracy and save 30% to 50% of the total cutting time.

(4) Development of automation, intelligence and information

In the process of processing, in order to reduce human intervention and ensure the expected process indicators, the automation, intelligence and informationization of slow wire processing have achieved corresponding development.
The complete process expert system of the slow wire processing machine tool gives a set of parameters according to the processing requirements. It not only includes common electrode wire numbers and corresponding workpiece materials, but also provides processing parameters for special materials such as PCD, PCBN, etc., depending on whether the upper and lower nozzles are in contact with the workpiece, and how large the distance is, whether it is refined in the cut wind or open surface Repair, accuracy, surface roughness and efficiency which prioritizes the processing strategy to generate the respective criteria; the discharge expert system deals with random factors in the cut, in the cut, cut, section change, center cut, near edge cut, large In the case of high-speed section cutting, etc., adaptive control strategy and automatic control function are used in the process to obtain stable and efficient processing.
The automatic non-porous detection function is also very practical. When the automatic hole skipping process is performed, if the pre-hole is forgotten to be played or the hole is offset, the machine will automatically move to the next pre-hole, which will prevent the machine from being stopped during unmanned operation. When a short circuit occurs after wearing the wire, the position of eliminating the short circuit can be automatically searched, and the reliability of continuous unmanned operation is improved.
The CNC system of the machine tool is equipped with a standardized mechanical interface to form an intelligent manufacturing system. The robot (3T) or EROWA system robot can easily realize the automatic exchange of workpieces (tray), with expert system and automatic wire exchange technology. Automate all machining processes.

2. The technical level of each grade slow wire processing machine

(1) Top-level slow wire processing machine

This slow wire processing machine represents the highest level currently, mainly manufactured in Switzerland and Japan. The machining accuracy of this type of machine can be guaranteed within ±0.002 mm, the maximum processing efficiency can reach 400-500mm2/min, the surface roughness can reach Ra0.05μm, the surface quality is perfect, and the surface has almost no metamorphic layer. Micro-finishing is performed using a wire of Φ0.02 mm. Most of the main engines have a heat balance system, and some machines use cutting in oil. This type of machine tool has complete functions and high degree of automation. It can directly complete the precision machining of the mold, and the life of the processed mold has reached the level of mechanical grinding.

(2) High-grade slow wire processing machine

This type of machine is basically produced by Swiss and Japanese companies. It has automatic threading function, non-resistive anti-electrolysis power supply, and overall thermal constant system. It can be cut with Φ0.07 mm electrode wire with an accuracy of ±0.003 mm. The efficiency can reach more than 300mm2/min, and the surface roughness can reach Ra<0.2μm. It has the function of detecting the cross-section change of the workpiece and optimizing the discharge power in real time. These machines are also widely used in precision stamping.

(3) Mid-range slow wire processing machine

This machine is generally produced by Swiss and Japanese companies in China. The technical level of some Taiwanese machines can also reach this level. Its configuration and performance meet the requirements of most domestic precision wire cutting processing. Generally, it adopts non-resistive anti-electrolysis power supply, with water-immersed processing and taper cutting function. The practical maximum processing efficiency is 150-200 mm2/min, the best surface roughness is Ra<0.4μm, the cutting precision can reach ±0.005mm, and the electrode wire with Φ0.1mm and above is generally used for cutting. The collision protection system avoids damage caused by programming errors or mishandling, and is equipped with an optional automatic threading mechanism.

(4) Entry-level slow wire processing machine

This machine tool is generally a Taiwan machine tool or a domestically developed machine tool. Its configuration and performance meet the processing requirements of common domestic molds and parts. Generally, the process of cutting and repairing one by one, cutting and repairing two can achieve stable surface roughness of about 0.8μm, processing precision is ±0.008mm, most of them can only be cut with 0.15mm and above electrode wire, and the surface microstructure is processed. There is a certain gap between the corner and the advanced machine tool.
In general, the slow wire processing machine has obvious advantages in processing efficiency, precision, surface quality, etc. compared with the fast wire processing machine. Although the price of the slow wire processing machine is more expensive, with the rapid development of the manufacturing industry, it will be more and more applied to various processing fields.

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