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Wire Cutting
2019-09-27

Wire cut Electrical Discharge Machining (WEDM) is a category of electrical processing. It was discovered by the former Soviet Union Lazarenko that the switch contacts were damaged by spark discharge corrosion and found that the instantaneous high temperature of the spark The local metal can be melted, oxidized and etched away, thereby inventing and inventing the EDM method. The wire cutter was also invented in the former Soviet Union in 1960, and China was the first country to use for industrial production. The basic physical principle is that free cations and electrons accumulate in the field and quickly form an ionized conductive channel. At this stage, a current is formed between the two plates. Leading to numerous collisions between particles, forming a plasma zone, and quickly rising to a high temperature of 8000 to 12000 degrees, melting some materials instantaneously on the surface of the two conductors, and at the same time, forming a bubble due to vaporization of the electrodes and the dielectric fluid, And its pressure rules rise until it is very high. Then the current is interrupted and the temperature suddenly drops, causing the bubble to blast inward. The generated power throws the dissolved material out of the crater, and then the corroded material recondenses into a small sphere in the dielectric liquid and is drained by the dielectric liquid. Then, through the NC-controlled monitoring and control, the servo mechanism performs the uniformity of the discharge phenomenon, so that the processed product is processed to become a product of a desired size and shape accuracy. The wire electric discharge machine can be divided into high-speed reciprocating wire EDM (Reciprocating type High Speed Wire Cut Electrical Discharge Machining commonly known as "fast walking wire"), low-speed one-way wire EDM wire cutting machine (Low) Speed one-way walk Wire Cut Electrical Discharge Machining is commonly known as "slow wire" and Vertical Wire Electrical Discharge Machining machine tool With Rotation Wire. It can also be divided into a single column cross table type and a double column type (commonly known as the gantry type) according to the work table form.

YISHANG -Wire Cutting

Working principle

Its working principle is shown in the figure below. The wire 1 wound around the wire barrel 4 is moved at a constant speed in the direction of rotation of the wire barrel, and the workpiece 3 mounted on the machine table is formed by the table in a predetermined control trajectory with respect to the wire. One pole of the pulse power supply is connected to the workpiece, and the other pole is connected to the electrode wire. A certain discharge gap is always maintained between the workpiece and the wire, and the working fluid is sprayed. The spark discharge between the electrodes erodes a certain gap, and the continuous pulse discharge cuts out the workpiece of the desired shape and size.


Efficacy

The wire of the low-speed wire cutting machine uses copper wire as the tool electrode, generally moves at a speed of less than 0.2 m/s, and applies 60~ between the copper wire and the workpiece material such as copper, steel or super-hard alloy. The pulse voltage of 300V is maintained at a gap of 5~50um. The gap is filled with insulating medium such as deionized water (close to distilled water), causing spark discharge between the electrode and the workpiece, and they are consumed and corroded by each other and charged on the surface of the workpiece. Numerous small pits are eroded, and the servo control is executed by the NC control and control, so that the discharge phenomenon is uniform, so that the processed object is processed to become a product of the required size and shape accuracy. The current precision is up to 0.001mm and the surface quality is close to the grinding level. The electrode wire is no longer used after discharge, and the non-resistive anti-electrolysis power supply is generally provided with an automatic threading and constant tension device. The work is stable, uniform, with small jitter, high machining precision and good surface quality, but it is not suitable for processing large thickness workpieces. Due to the precise structure of the machine tool, high technical content and high machine price, the cost of use is also high. The one-way wire EDM wire cutting machine was only an organic species of foreign companies in the early days. Although Taiwan's low-speed wire-cut EDM wire cutting machine started late, it has developed rapidly in recent years. One of the key measures is to jointly fund a number of home appliance processing machine tool manufacturers. With the limited support of relevant departments, the Taiwan Industrial Technology Research Institute has invested a large amount of manpower and material resources to develop key technologies. After more than 10 years of research, it has made breakthroughs in key technologies such as control systems and power supplies. The low-speed wire-cut EDM wire-cutting machine manufactured by various enterprises in Taiwan should be in the range of mid-range machines. It has reached a growth rate of 20% to 30% every year in the past three years. It is estimated that in the next five years, Taiwan’s low-speed wire-cut EDM wire cutting machine The annual output can reach 2,000 units, which can account for more than 25% of the world market. The low-speed wire-cut EDM wire cutting machine has high technical content and good market prospects, and can obtain high returns. It is the “ground place” and “strategic highland” for various manufacturers in the electric processing industry. It can also be said that whoever masters the technology of the low-speed wire-cut EDM wire-cutting machine will have the opportunity to develop and grow in the next step. In order to seize the Chinese market, electric processing machine tool manufacturers in Japan, Switzerland and Taiwan set up factories in mainland China to produce such machine tools. With the support of the special fund of the Ministry of Science and Technology, China's science and technology workers have invested a large amount of research and development, and have completed the research and development of a new generation of low-speed wire-cut EDM wire-cutting machines, and have made major breakthroughs. At present, they have owned intellectual property rights. The product, and occupied a certain market share, its performance indicators can reach the mid-range machine level. At present, some domestic companies hope to develop low-speed wire EDM wire cutting processing technology through cooperation with related companies in Taiwan.

Vertical self-rotating electric discharge wire cutting machine (horizontal self-rotating electric discharge wire cutting machine). The characteristics of the vertical rotary electric discharge wire cutting machine are different from the traditional high-speed wire cutting and low-speed wire-cut wire EDM. First, the wire movement mode is one more electrode than the traditional two-wire wire cutting process. The rotary motion of the wire; secondly, the wire speed of the wire is directly between the high speed wire and the low speed wire, and the speed is 1 to 2 m/s. Due to the increased rotational movement of the wire during processing, the biggest difference between a vertical rotary wire EDM machine and other types of wire cutters is the wire-traveling system. The wire-traveling system of the vertical rotary electric discharge wire cutting machine has two sets of the same structure at the wire end and the discharge end as the wire structure, realizing the high-speed rotary motion of the wire and the composite movement of the low-speed wire. The area between the two sets of spindle heads is the effective machining area. Except for the wire cutting system, the other components of the machine are the same as the high-speed wire cutting machine.

Compared with the one-way low-speed wire-cut EDM machine, the reciprocating high-speed wire EDM machine has a large gap in the key technical indicators such as average productivity, cutting accuracy and surface roughness. In response to these gaps, at the beginning of this century, several high-speed reciprocating wire EDM machines in China achieved multiple cutting operations on high-speed wire-cutting machines (this type of machine tool is commonly known as “medium wire” Medium Speed Wire cut Electrical Discharge Machining). The so-called "medium wire" does not mean that the wire speed is between high speed and low speed, but a composite wire cutting machine. The wire routing principle is to use 8-12m/s high speed wire for roughing and fine machining. 1-3m/s low-speed wire, so the work is relatively stable, 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 the high-speed wire-cutting machine. Between the low speed wire machine. Therefore, it can be said that the user said "medium wire", in fact, the reciprocating wire EDM wire cutting machine borrowed from the processing technology of some low-speed wire-cutting machines, and realized the stripless cutting and multiple cutting. After several years of development, almost all domestic manufacturers of high-speed wire EDM wire cutting machines are in the process of production and sales, but in the end it is not all the reciprocating wire EDM machines can cut many times. In other words, not all reciprocating wire EDM machines can achieve good process results after multiple cutting techniques. Multiple cutting is a comprehensive technology, which involves the numerical control precision of the machine tool, pulse power supply, process database, wire routing system, working fluid and a large number of process problems. It is not simply a set of high speed wire machine. The wire frequency control system can be realized, only those reciprocating wire EDM machines with high manufacturing precision and multiple cutting conditions in various aspects can carry out multiple cutting and stripeless cutting, and obtain remarkable Process effect. Therefore, our production enterprises must fully pay attention to this problem, we must do it according to system engineering, and really use this technology well and do this product well. For example, some enterprises have adopted the DC or AC servo motor as the drive unit to directly drive the ball screw, and the X and Y coordinate worktables use the full-closed control with the pitch compensation function. The system compensates and corrects the positioning accuracy error of the machine tool. Under the premise of ensuring accuracy, reduce the machining accuracy caused by long-term use and prolong the service life of the machine. The wire system uses a special (mostly diamond) wire retainer to keep the wire filament relatively stable and reduce the tension change of the wire during processing. In the cooling system, the commonly used extensive cooling method is changed, multi-stage filtration is adopted, and key parameters such as dielectric constant are controlled to ensure smooth finishing. The control software provides an open database of processing parameters, which can be selected according to the material's texture, thickness, roughness and other conditions. It is believed that after our efforts, the cutting technology will be more perfect, and the reciprocating wire EDM technology will also be better applied and developed.

After the reciprocating wire EDM wire cutting machine adopts multiple cutting technology, although the processing quality is obviously improved, it still belongs to the category of high-speed wire EDM wire cutting machine. The cutting precision and smoothness are still relatively large with the low speed wire cutting machine. The gap, and the retention of precision and finish, also needs to be further improved. The “medium wire feeder” has the characteristics of simple structure, low cost and low consumption. Therefore, it also has room for survival. The current implementation standard is still the relevant standard of high-speed wire-cutting machine. Therefore, the production enterprise should Be careful, be sure to seek truth from facts.

YISHANG -Wire Cutting-1

Operating procedure

(1) Turn on the machine's main power supply, controller switch, 24V step drive power switch and high pulse power switch.

(2) Calculate the coordinate point preparation procedure according to the paper size and the actual situation of the workpiece, pay attention to the clamping method of the workpiece and the diameter of the molybdenum wire, and select a reasonable cutting position.

(3) Turn on the high frequency switch on the wire motor, pump motor and control panel.

(4) Put the coarse adjustment switch in the automatic position, unplug the feed switch, and enter the machining stage. During the machining, the fine adjustment switch and software fine adjustment are further adjusted to adjust to the most stable state.

(5) After the processing is finished, the high-frequency pulse switch of the machine tool should be turned off first, and the water pump switch should be turned off. When the brake is turned off, press the red button of the main power switch.


Material deformation prevention in wire cutting

Because the material itself has stress, the cutting must break the original stress balance and reach a new balance, but the stress is large and small, and the deformation will be different. This is like a bamboo piece splitting in the middle, two halves. All bends, the majority bends less, and the small half bends much. The wire cutting process is the same, but the deformation is small to the final accuracy range, and the machining is completed.

Stress is an elastic force inherent in a material that increases with strength and hardness and temporarily balances. Therefore, the harder the harder the better the material is. Such materials require repeated forging prior to quenching and uniform organization. And a large amount of machining allowance and large pieces of waste are removed before quenching, that is, the part of the stress that has temporarily maintained balance during quenching is basically removed. What is cut off after quenching is the small part of the stress balance. This will result in much less distortion due to wire cutting. When there is no treatment before quenching and no allowance is removed, what is the result of a piece of solid material with strong and complete stress? Then we have to cut ourselves to eliminate stress and remove the margin. That is rough cut, remember to keep a good amount, set the chuck, and remove most of the margin first. Get a new shape that is very close to the final workpiece, and has no large deformation ability. If it is accompanied by high and low temperature aging treatment, the material deformation can be completely solved.

The above is mainly the deformation of the material, because the parts of the special elongated shape will also be deformed, such as the punch of the clock second hand die, the die of the spring clamp die and the punch, which will cut a small narrow on the large block. The strips make the removed workpieces completely unrecognizable, let alone a few μ at most only a tolerance of more than a dozen μ. Such parts that are easily deformed due to the shape are only pretreated by the bad material, and processed into a semi-finished product with a small margin before quenching. The workpiece is fully deformed during the quenching process, and the cutting route and the clip are selected during the cutting. The position of the head is sure to get qualified parts.

There is also a prominent phenomenon in the deformation of the material, that is, the cutting inlet cannot be closed, which is mostly because the position of the pressing plate is not correct, and the inlet and outlet are not crushed. During the cutting process, the inlet has been displaced with the deformation, although The coordinates returned to their original position, but the entrance had already ran, causing the entrance to be staggered. It took a long time to get a waste. This is based on the full understanding of the material deformation, the corresponding measures taken in the early stage, the cutting also takes the corresponding method, the so-called cutting experience is also here.


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