CNC wire EDM processing includes fast wire cutting and slow wire cutting, which are widely used in the mold manufacturing industry. What is the current development status of the processing efficiency, cutting precision and surface quality of these two technologies?
▌ Development status of rapid yarn processing technology
As the name suggests, rapid wire processing gets its name from the high-speed unwinding of the wire electrode during the cutting process. The rapid wire processing machine tool is the original electrical processing machine tool in my country. After decades of continuous improvement and development, it has now become an important processing method in the manufacturing industry. It can meet the requirements of mid-to-low-end mold processing and other complex parts manufacturing, and occupies considerable weight in the mid-to-low-end market.
The biggest advantage of high-speed wire processing machine tools is that they have a good performance-price ratio. Due to its practicality and economical nature, it has a large domestic market. Traditional rapid wire processing uses a single cutting process, with a processing efficiency of about 40㎜²/min, a surface roughness of about Ra3.0μm, obvious lines on the surface, and a processing precision of ‘approximately 0.02㎜.
In order to improve the processing quality, rapid wire processing machine tool manufacturers have improved the relevant components of machine tools referring to the multiple cutting process, and the so-called “machine tools of medium wire processing” have appeared. A large number of process technologies such as CNC machine tool precision, pulse feeding, wire moving system and process database have been significantly improved. The processing precision is improved and the surface quality is improved.
The current technical indicators of wire processing machine tools: the efficiency of one cut is 180㎜²/min, the surface roughness after multiple cuts is Ra≤1.0μm, the average efficiency at this time is of 50㎜²/min and the treated product the surface is shiny. There are no obvious cutting scratches, the processing precision is 0.01㎜, and the loss of the electrode wire is ≤01㎜/200,000㎜². These performance indicators seem relatively good, but it should be noted that achieving these indicators requires ensuring all aspects. Once there are deviations, such as changes in the concentration of the working fluid and loss of the electrode wire, it will affect the. stability of processing quality.
Typical manufacturers of wire cutting machine tools in production include Suzhou Sanguang, Suzhou Hanqi, Shanghai Tello, Beijing Ande, Suzhou Baoma, Suzhou New Spark, Shanghai Dajia, etc.
▌ Development status of slow yarn processing technology
With the continuous improvement of manufacturing accuracy and surface quality requirements for precision, complex and long-life stamping molds, rapid wire processing technology can no longer adapt to mold manufacturing requirements precision. This status quo favored the rapid development of slow wire. processing technology and its various process indicators It has reached a very high level and is irreplaceable by other processing technologies.
1. Development status of slow yarn processing technology
(1) Improved processing precision
Multi-cutting technology is the fundamental way to improve the precision and surface quality of slow wire cutting. Generally, it is formed by one cut, two cuts improve the precision, and three or more cuts improve the surface quality.
Due to the hysteresis of the electrode wire when cutting corners, the corners will collapse. In order to improve the corner cutting precision, more dynamic corner processing strategies are adopted. Such as: automatic change of treatment speed, automatic adjustment of water pressure, treatment energy control, etc.
The high-precision finishing circuit adopted by advanced slow wire processing machine tools is an effective technology for improving the straightness of processed parts, which greatly improves the processing precision of thick parts to process small threads, narrow slits, narrow and fine grooves; For microfinishing parts, low tip speed CNC wire EDM machines can use 0.02-0.03mm electrode wire for cutting.
In order to ensure high precision processing, mechanical precision, pulse power precision and servo control precision of the machine tool (including control of mechanical movement, pulse parameters, wire moving system and working fluid system) have reached an extremely high level. A water temperature cooling device is used to make the internal temperature of the machine tool the same as the water temperature, thereby reducing the thermal deformation of the machine tool; A closed-loop digital AC (DC) servo control system is used to ensure excellent dynamics. high performance and positioning accuracy, and the processing accuracy can be controlled within a few microns. In the range, precise positioning can achieve control equivalent to 0.1μm; immersion treatment is used to reduce the thermal deformation of the workpiece servo motor, closed-loop electrode wire; tension control; the voltage modulated tool setting power supply is used to achieve high precision tool setting, and the tool setting accuracy can reach 0.002. ㎜, no damage to the piece, wet or dry.
(2) Surface quality is improving day by day
Advanced slow wire processing machine tools use non-electrolysis pulse power supply with average voltage of zero, and the damage of electrolysis has been reduced to a minimum. In addition, due to the improvement of pulse supply, a high peak value and narrow pulse width (microsecond level) are generally used. Most materials are released in the gas phase, which absorbs a lot of heat. the part cannot rise and the phenomenon of cracking is considerably reduced; not only is the processing efficiency high, but the surface quality is also greatly improved. Using an electrolytic energy source for wire EDM processing can control the surface deterioration layer below 2 μm. The wear resistance of the carbide die cutting edge is no different from that of grinding, and is even better than that of mechanical grinding. More and more parts are processed by “cutting instead of grinding”.
(3) Improvement of treatment efficiency
Due to the development of nanosecond large size peak current pulse power supply technology and detection, control and anti-interference technology, the processing efficiency of machines- Slow wire processing tools are also constantly improving. machine tools can reach 500㎜²/min. The processing efficiency of larger thickness parts presents practical technological improvements. For example, when cutting a 300mm thick workpiece, the processing efficiency can reach 170㎜²/min. For processing parts of varying thicknesses, the maximum processing efficiency in this state can be achieved by automatically detecting the thickness of the part and automatically adjusting the processing parameters to avoid wire breakage.
In addition, the rapid automatic threading technology introduced by advanced slow thread processing machine tools has an automatic threading time of <15s, which improves the efficiency of processing operations; the introduced double wire automatic exchange technology can automatically use 0.20-0.02mm; electrode wire for double wire threading. Use thick wire for the first cut, generally with a wire diameter of 0.25mm, to improve processing efficiency and enable coreless cutting; then use a fine wire for cutting, usually using 0.10mm filament, to cut small round corners, and improved precision can be achieved. save 30-50% of overall cutting time.
(4) Development of automation, intelligence and informatization
During the processing process, in order to reduce human intervention and ensure that the expected process indicators are achieved, the automation, intelligence and computerization of slow yarn processing have achieved corresponding development.
The complete process expert system of the slow wire processing machine tool provides a complete set of parameters according to the processing requirements. It not only includes commonly used electrode wire brands and corresponding workpiece materials, but also provides processing parameters for special materials such as PCD and PCBN. It can be based on whether the upper and lower nozzles are in contact with the workpiece and how far apart they are. are, and whether windbreak finishes or open surface repairs, which should be preferred among precision, surface roughness and efficiency? Strategies are used to generate respective specifications; The discharge expert system handles random factors during cutting and uses adaptive control during the processing process in situations such as cutting, cutting, cross-section changes, center cutting, near edge cutting , high-speed cutting of large sections, etc. Automated strategies and control functions enable stable and efficient processing of continuous yarns.
The automatic hole-free detection function is also very convenient. During automatic skip processing, if the pre-hole is forgotten or the hole position is shifted, the machine tool will automatically move to the next pre-hole, preventing the machine from stopping during unattended operation . Processing when a short circuit occurs after threading, the position of the short circuit can be automatically searched and eliminated, which improves the reliability of continuous operation without a driver.
The CNC system of the machine tool is equipped with a standardized mechanical interface to form an intelligent manufacturing system. Thanks to the manipulator of the 3R system or the EROWA system, the automatic exchange of parts (pallets) can be easily achieved with the expert system. and automatic electrode wire exchange technology, it can automatically complete all treatment processes.
2. The technical level of different grades of slow wire processing machine tools
Slow wire processing machine tools can be divided into four categories: high-end, high-end, mid-range and entry-level. Typical manufacturers that produce slow wire machine tools include Swiss GF Machining Solutions (formerly AgieCharmilles), Japanese Makino, Japanese Mitsubishi, Japanese Sodick, Japanese Western, Japanese Frank, etc.
(1) Best slow wire processing machine tools
This type of slow wire processing machine tool represents the current highest level and is mainly manufactured in Switzerland and Japan. The processing accuracy of this type of machine tool can be guaranteed within ±0.002mm, the maximum processing efficiency can reach 400~500㎜²/min, and the surface roughness can reach Ra0.05μm. It has perfect processing surface quality. with almost no deterioration layer on the surface, and Φ0.02mm electrode wire is used for micro-finishing. Most main machines have a heat balance system, and some machine tools use oil cutting processing. This type of machine tool has complete functions and a high degree of automation. It can directly complete the precision processing of molds. The service life of processed molds has reached the level of mechanical grinding.
(2) High-end slow wire processing machine tools
This type of machine tool is mainly produced by Swiss and Japanese companies. It has an automatic threading function, a resistance-free anti-electrolysis power supply and a global thermal constant system. It can use Φ0.07㎜ electrode wire for cutting. , with an accuracy of about ±0.003㎜, and the highest processing. The efficiency can reach more than 300㎜²/min and the surface roughness can reach Ra<0.2μm. Its function is to detect changes in the cross section of the workpiece. timely and optimizing the discharge power in real time. This type of machine tool is also widely used for processing precision stamping dies.
(3) Mid-range slow wire processing machine tools
This level of machine tools is usually produced by Swiss and Japanese companies in manufacturing plants in China. The technical level of some Taiwanese machines can also reach this level. Their configuration and performance meet the requirements of most domestic precision wire cutting processes. Generally, a resistance-free anti-electrolysis power supply is used, which has the functions of submerged processing and taper cutting. The maximum practical processing efficiency is 150~200㎜²/min, the best surface roughness reaches Ra < 0.4μm, and the cutting precision can reach ±0.005㎜. Generally, electrode wires of Φ0.1㎜ and above are used for cutting. and are equipped with a collision protection system that can prevent damage caused by programming errors or misuse, and are equipped or optionally equipped with an automatic wire threading mechanism.
(4) Entry-level slow wire processing machine tools
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 ordinary household molds and parts. Generally, the process of cutting one and cutting one, cutting one and cutting two is often used, which can stably achieve a surface finish of about Ra0.8μm and a processing accuracy of ±0.008mm. Most of them can only use electrode wires. 0.15mm and above for cutting and microstructure of the processed surface, there is a certain gap between corners and advanced machine tools.
In general, compared with fast wire processing machine tools, slow wire processing machine tools have very obvious advantages in processing efficiency, precision, surface quality, etc. Although machine tools for slow wire processing are more expensive, with the rapid development of the manufacturing industry, they will be more and more used in various processing fields.
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