What is the difference between slow wire and medium wire processing

▌ The advantages of slow wire processing technology

With the continuous improvement of the manufacturing precision and surface quality requirements of precision, complex and long-life stamping dies, the fast wire processing technology can no longer meet the manufacturing requirements of precision molds. This situation has promoted the rapid development of slow wire processing technology. It has reached a very high level and is irreplaceable by other processing technologies.

1. Development status of slow-moving wire processing technology

(1) Improve machining accuracy
Multiple cutting technology is the fundamental means to improve the machining accuracy and surface quality of slow-moving wire. Generally, it is formed by one-time cutting, the second-time cutting improves the accuracy, and the third-time cutting improves the surface quality.

Corners collapse due to wire lag when cutting corners. In order to improve the corner cutting accuracy, more dynamic corner processing strategies are adopted. Such as: automatic change of processing speed, automatic adjustment of water pressure, control of processing energy, etc.

The high-precision finishing circuit adopted by the advanced slow wire-feeding machine tool is an effective technology to improve the flatness of the workpiece, so that the machining accuracy of thick parts can be significantly improved; in order to carry out small rounded corners, narrow slits, narrow grooves and fine parts For micro-finishing, the top CNC low-speed wire EDM machine can use 0.02 ~ 0.03 mm electrode wire for cutting.

In order to ensure high-precision processing, the mechanical accuracy of the machine tool, the accuracy of pulse power supply, and the accuracy of servo control (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, which reduces the thermal deformation of the machine tool; the closed-loop digital AC (DC) current servo control system is adopted to ensure excellent dynamic performance and high positioning accuracy, and the machining accuracy can be controlled within a few microns Precision positioning can achieve 0.1μm equivalent control; immersion processing is used to reduce thermal deformation of the workpiece; motor servo, closed-loop electrode wire tension control; voltage modulation tool setting power supply is used to achieve high-precision tool setting, and the tool setting accuracy can reach 0.002 ㎜ , does not damage the workpiece, whether dry or wet.

(2) Surface quality is improving day by day
The advanced slow wire processing machine adopts the non-electrolysis-proof pulse power supply with zero average voltage, 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 generally used, and most of the materials are thrown out of the gas phase, which takes away a lot of heat, and the surface temperature of the workpiece cannot rise, and the phenomenon of cracking is great Reduce; not only high processing efficiency, but also greatly improve the surface quality. The use of electroless power supply for WEDM can control the surface metamorphic layer to be less than 2μm. The wear resistance of the cutting edge of the carbide die is no different from that of grinding, and even better than mechanical grinding. More and more parts are processed "replaced by cutting".

(3) Improve 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-moving wire-feeding machine tools is also constantly improving. ²/min. The processing efficiency of larger thickness workpieces has practical technical improvement. For example, when cutting workpieces with a thickness of 300 mm, the processing efficiency can reach 170 mm²/min. For the processing of workpieces with varying thicknesses, by automatically detecting the thickness of the workpieces and automatically adjusting the processing parameters to prevent wire breakage, the highest processing efficiency in this state is achieved.

In addition, the fast automatic wire threading technology introduced by the advanced slow wire processing machine tool, the automatic wire threading time is less than 15 s, which improves the efficiency of processing operations; Wire switching processing. Thick wire is used for the first cutting, generally with a wire diameter of 0.25 mm, to improve processing efficiency and can be cut without core; then use thin wire for trimming, generally using 0.10 mm thin wire, to cut small rounded corners, and can By improving the accuracy, the overall cutting time can be saved by 30% to 50%.

(4) Development of automation, intelligence and informatization
In the process of processing, in order to reduce human intervention and ensure that the expected process indicators are achieved, the automation, intelligence and informatization of slow-moving wire processing have achieved corresponding development.

The complete process expert system of the slow-moving wire processing machine provides a complete set of parameters according to the processing requirements. Not only includes common electrode wire grades and corresponding workpiece materials, but also provides processing parameters for special materials such as PCD, PCBN, etc., which can be determined according to whether the upper and lower nozzles are in contact with the workpiece, the distance is large, whether it is refined in the cutting wind, or the open surface is refined. Repair, precision, surface roughness and efficiency are the priority processing strategies to generate their respective specifications; the discharge expert system copes with random factors in cutting, such as cutting in, cutting out, section change, center cutting, near-edge cutting, large In the case of high-speed cutting of cross-sections, self-adaptive control strategies and automatic control functions are used in the processing process to obtain continuous, stable and efficient processing.

The automatic no-hole detection function is also very practical. During automatic skip processing, if the pre-hole is forgotten to be punched or the hole position is offset, the machine tool will automatically move to the next pre-hole, which can prevent the machine from shutting down when unmanned processing is performed. When a short circuit occurs after threading the wire, it can automatically search for the position to eliminate the short circuit, which improves the reliability of continuous unmanned operation.

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

2. The technical level of each grade of slow wire-feeding machine tools

The slow-moving wire processing machine tools can be divided into four grades: top, high-grade, mid-grade and entry-level. Typical manufacturers of slow wire-feeding machine tools include Swiss GF Machining Solutions (formerly Agie Charmilles), Japan Makino, Japan Mitsubishi, Japan Sodick, Japan West, Japan Frank and so on.

(1) Top-level slow-moving wire processing machine tools
This kind of slow-moving wire processing machine represents the highest level at present and is mainly manufactured by Switzerland and Japan. The machining accuracy of this type of machine tool can be guaranteed within ±0.002 mm, the maximum machining efficiency can reach 400-500 mm²/min, and the surface roughness can reach Ra0.05 μm. Use Φ0.02 ㎜ electrode wire for micro-finishing, most of the main machines have a thermal balance system, and some machine tools use oil for cutting. This type of machine tool has complete functions and a high degree of automation, and can directly complete the precision machining of molds. The life of the processed molds has reached the level of mechanical grinding.

(2) High-grade slow wire processing machine tools
This type of machine tool is basically produced by Swiss and Japanese companies, with automatic wire threading function, non-resistance anti-electrolysis power supply, overall thermal constant system, can use Φ0.07 mm electrode wire for cutting, the accuracy is about ±0.003 mm, the highest processing The efficiency can reach more than 300㎜²/min, and the surface roughness can reach Ra<0.2μm. It has the function of timely detection of workpiece cross-section changes and real-time optimization of discharge power. This type of machine tool is also widely used for precision stamping die processing.

(3) Mid-range slow wire processing machine tool
This type of machine tool is generally produced by Swiss and Japanese companies in China's manufacturing plants. The technical level of some Taiwanese machines can also reach this level, and its configuration and performance meet the requirements of most domestic precision wire cutting processing. Generally, non-resistance anti-electrolysis power supply is used, and it has the functions of submerged processing and taper cutting. The practical maximum processing efficiency is 150～200 ㎜²/min, the best surface roughness can reach Ra<0.4μm, and the cutting accuracy can reach ±0.005㎜. Generally, electrode wires of Φ0.1㎜ and above are used for cutting. The collision protection system can avoid collision damage caused by programming errors or misoperation, equipped with or optional automatic wire threading mechanism.

(4) Entry-level wire-feeding machine tool
This type of machine tool is generally a Taiwanese 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 one cutting and repairing two can be used, which can stably achieve a surface finish of about Ra0.8μm and a machining accuracy of ±0.008㎜. Most of them can only use electrode wires of 0.15mm and above for cutting, and the processed surface microstructure , There is a certain gap between corners and advanced machine tools.

▌ Advantages of medium wire processing technology

Medium-speed Wire cut Electrical Discharge Machining (MS-WEDM for short) belongs to the category of reciprocating high-speed wire EDM machine tools. Function, commonly known as "middle wire cutting". The so-called middle wire processing does not mean that the wire speed is between high and low speeds, but a composite wire cutting machine, that is, the principle of wire cutting is to use high-speed (8-12m/s) wire during rough machining, and finish machining. Low speed (1-3m/s) wire feeding is adopted, so that the work is relatively stable and the jitter is small, and the error caused by material deformation and molybdenum wire loss is reduced by multiple cutting, so that the processing quality is relatively improved, and the processing quality can be between high speed. Between the wire feeder and the low-speed wire feeder. Therefore, what users call "medium wire cutting" is actually a reciprocating wire EDM wire cutting machine that draws on the processing technology of some low-speed wire cutting machines, and realizes non-stripe cutting and multiple cutting.
In practice, it has been found in practice that the first cutting task in multiple cuttings is high-speed and stable cutting. High peak current and long pulse width can be selected for high-current cutting to obtain higher cutting performance. speed. The task of the second cutting is to refine and ensure the machining dimensional accuracy. The medium standard can be selected, so that the roughness Ra after the second cutting is between 1.4 and 1.7 μm. In order to achieve the purpose of finishing, a low-speed wire-feeding method is usually adopted, the wire-feeding speed is 1-3m/s, and the tracking feed speed is limited to a certain range, so as to eliminate the round-trip cutting stripes and obtain the required machining dimensional accuracy. . The task of the third, fourth or more cuttings (currently the middle wire feed control software can achieve up to seven cuttings) is polishing and polishing, which can be trimmed with the minimum pulse width (currently the minimum frequency can be divided to 1μs). , and the peak current varies with the quality of the machined surface. In fact, the finishing process is a kind of electric spark grinding, and the processing amount is very small, which will not change the size of the workpiece.

For the wire-feeding method, it is sufficient to use low-speed wire-feeding at a limited speed like the second cutting. During the processing of the wire-cutting technology, attention should be paid to the deformation treatment for multiple cuttings, because during the online cutting of the workpiece, with the effect of the original internal stress and the influence of the processing thermal stress generated by the spark discharge, there will be non-directional, The irregular deformation makes the thickness of the subsequent cutting blades uneven, which affects the processing quality and processing accuracy. Therefore, it is necessary to reserve different machining allowances according to different materials, so that the workpiece can fully release the internal stress and completely torsional deformation, and there can be enough allowance for fine cutting in the subsequent multiple cuts, so that the final size of the workpiece can be guaranteed.