Innovative research on wire-cut wire cutting system

Development history of WEDM

In the 1960s, a one-way slow-speed wire-cutting EDM wire-cutting machine tool entered China. We are surprised that it relies on a very thin brass wire to process the embossing module of the cold die on the steel workpiece immersed in kerosene, and at the same time is not satisfied with its extremely low processing effect, only a few square millimeters per minute. .

In the early 1970s, Zhang Weiliang invented the high-speed wire-cutting mechanical system, reciprocating infinite loop wire, still using the die cutting method, but the processing efficiency was immediately increased to 10 mm2 / min. Under the instructions of the Shanghai Science and Technology Supervisor, Fudan University designed all the numerical control devices made up of discrete components, forming our unique Fudan-type fast-travel wire EDM machine, commonly known as “fast-cut wire cutting”. Then, in order to apply to plastic molds, we independently invented the taper device and introduced the control of the single-board machine, which has been developed to today's microcomputer CNC control.

During this period, the Western one-way slow wire EDM wire cutting machine tool also developed from the die cutting method to the numerical control mode, commonly known as "slow wire cutting", also has taper cutting, is also a computer CNC control method.

In people's minds, the fast-cut wire cutting machine is a low-end machine with an accuracy of 0.01 to 0.03 mm. The surface roughness is poor and the surface always has black and white stripes. The imported slow wire can reach 2~5 μm through multiple cutting precision, and the surface roughness value can reach 0.2 μm. Habitually, people think that the fast-cut wire cutting can achieve the same precision and surface roughness by slowing down the speed and cutting many times, so the "medium wire" method is produced. The closed-loop controlled medium-wire EDM wire cutting machine improves the precision and reduces the surface roughness value after performing multiple cuttings. However, due to the two-step operation of the reciprocating cycle, the total difference is the last one. Tone.

Summary analysis of the way of walking

Through analysis and collection of different types of EDM machines at home and abroad, the mechanical structure of their research and analysis can be divided into the following four categories: 1 Disposable one-way wire. 2 infinite reciprocating cycle wire. 3 rotary infinite reciprocating cycle wire. 4 one-way infinite loop wire.

(1) Disposable one-way wire is the only main wire-cutting method of foreign EDM wire-cutting machine tools, that is, the “slow wire cutting” in the common name, and its advantages and disadvantages are just as obvious. The wire is slow, and the wire feed slider can be used, so the positioning accuracy is high and the error is almost zero. Under the control of constant tension, the quality of the machined surface roughness is also good. However, because of its slow wire-cutting speed, the cooling capacity in the discharge gap is insufficient, and the loss of the wire is large, and it can only be discarded. Especially in the first cutting, it is more obvious. In order to cut, only the high voltage can be applied to increase the machining current. At this time, the gap is unstable and the precision is very poor. The time utilization of electrical discharge machining is high, but the efficiency is not high, especially the workpiece of large thickness cannot be cut.

(2) The infinite reciprocating cycle is the invention of our own Chinese.

China's fast-track wire EDM wire cutting machine is no exception to this type of wire. Since Zhang Weiliang invented this method of wire-cutting, it has been used ever since. This is true whether it is fast walking or walking. It uses guide wheel positioning, and there are two positioning conditions under the reciprocating cycle. Because it is a reciprocating cycle, the wire will be repeated back and forth, and the wire stress will fluctuate in the forward and reverse directions. The inlet and outlet of the coolant are also exchanged at regular intervals, and the surface of the workpiece must be streaked (can be black and white, or the same color stripe, but must be high and low stripes). When commutating, the wire is suspended, so the time utilization efficiency is low.

However, because of the high wire speed, good cooling effect and high discharge efficiency, it is particularly obvious that it can cut large thickness workpieces up to 1 m. This method of wire-cutting is divided into two types: single-storage wire cylinder and double-storage wire cylinder. Because the effect is similar, the single-storage wire cylinder method occupies an absolute majority.

(3) Rotary reciprocating cycle wire is a wonderful work in the Chinese infinite reciprocating cycle wire-walking method. The inventor is Dr. Yang Xinsheng, who graduated from Shanghai Jiaotong University. This is also a double-carrying wire-carrying method. It is characterized in that the wire-traveling system rotates around the electrode wire at a high speed, and the wire-traveling speed is as low as that of a slow wire-cutting machine. Its appearance has caused great concern and sensation among the technical insiders in the wire cutting industry. At one time, people thought that this might be the direction of Chinese-style wire-cutting, because people naturally think that the wire speed is low and the precision is high. For various reasons (insufficient regional processing capacity and shortage of funds, etc.), this method does not appear to be expected to be brilliant. Therefore, no further evaluation is possible.

(4) One-way infinite loop wire, which is the way the high-end technicians in China's electric discharge wire cutting industry dream of. The experience of decades has taught us that this is the only way for Chinese-style fast-wire EDM wire-cutting machine tools to go to high-end precision. Now we have successfully invented this method of wire-cutting and have applied for invention patents.

The one-way infinite loop wire-cutting method takes into consideration the advantages of the first one-way slow wire and the second reciprocating cycle, and strives to avoid their disadvantages, and thus has very obvious characteristics. It can use the wire electrode in an infinite loop, so that the processing time is highly efficient, and there is no need for a commutation time like a reciprocating cycle. It is a one-way infinite loop, and the wire speed is steplessly adjustable. It can have a wire speed of more than 10 m/min like a quick wire, or it can be as slow as a slow wire to a few millimeters per second. Because of the one-way wire, it can stably implement a single constant tension control, the positioning is very stable, the machining precision is high, and the cooling inlet and outlet are consistent, and the surface roughness value is also low, so that there is no black and white phase difference. stripe.

Innovative concept of one-way infinite loop wire

The one-way infinite loop wire-feeding method and structure is an innovative invention. Its existence has its clear technical characteristics. This technical feature has two points: First, because the end of the infinite loop wire is connected at both ends, it must be able to perform a correct and delicate docking simply and quickly; second, the wire must be able to enter from one end of the cartridge. The cylinder of the storage tube passes through the mechanically reasonable and precise operation, exits from the other end of the storage tube, enters the processing area through the guide wheel, and then returns to the inlet of the storage tube through the guide wheel, thereby completing the cycle of recurrence. An infinite loop of interest.

The first feature is easy to understand. One can weld a wire using a laser beam electron beam ion beam. We have tried to use resistance welding because the wire used for processing is a short-circuit ring and it is difficult to use. The first method: when using laser ion electron beam welding, we burn the ends of the head and the tail into a small melting ball in a protective atmosphere, and then quickly butt and condense together, so that the two ends of the wire are connected by a molten ball. Together, there are good physical properties. At this time, the wire cutting power source is used for the electric spark grinding, and the small balls are ground to make the wire diameters uniform. The second method: We carefully process the two ends of the electrode wire to have a special shape, and then melt a very thin layer at both ends in a protective atmosphere to quickly condense and condense, and the wire diameter is consistent. Although the wire tensile stress is somewhat reduced, we prefer the latter method. Both methods require a sophisticated body (invention patent).

The second feature, understanding, takes a certain amount of energy. The storage tube that people are accustomed to understand is a rigid cylinder like a fast-moving wire. The wire of the fast wire is wound around a plurality of coil wires, and the surfaces of the wire and the wire barrel are in a relatively stationary position during the processing operation. This relatively static state must lead to a reciprocating cycle during the movement, because the electrode wire must have come to the end, and can only be reversed back and forth, thereby reciprocating.

In order to understand our invention, it is conceivable whether there is such a arbitrarily deformable "flexible cylinder" which has two inner and outer faces and is flexiblely connected inside and outside, and the outside can be not only along the storage tube The axis moves in the direction of the axis, and it can also be flexibly turned inside, and the inside can also be turned to the outside. When such a "flexible storage cartridge" is rotated about an axis, "flexible storage cartridge"

When continuously switching inward from the outside, the wire can be moved from one end to the other. When the wire ends are connected, the result of a one-way infinite loop can be achieved (see figure).

Schematic diagram of flexible storage tube

The "flexible cylinder" that exists in this imaginary can be realized by combining several sets of identical mechanical structures and fulfilling the function of such a "flexible cylinder".

The storage tube in the one-way infinite loop wire is divided into two types: the shaft roller and the ring belt. The mechanism of the "flexible storage tube" can be completed by a plurality of different types of mechanisms. The shaft roller type requires a wire-like mechanism like a quick-traveling wire, and the ring-type storage and running wire is completed by itself. These mechanisms can complete the storage and operation of the wire on the "storage cartridge". The wire is stored from one end of the "storage cartridge" to the other end, passes through the guide wheel to the processing zone, and then returns to the "storage cartridge" through the guide wheel. ", and then repeat the one-way infinite loop. Due to space limitations, we will not repeat them here.

The one-way infinite loop wire has its obvious characteristic advantages: 1 Improve the time utilization rate, taking the Shanghai Tielu company's middle wire machine as an example, the time utilization efficiency of the storage tube is increased by 5% when the tube is full or half. 10%. 2 Improve the surface quality, the high and low stripe unevenness caused by the exchange of the fast wire and the middle wire in and out of the cooling water port is reduced from 0.020 to 0.002 mm to the theoretical zero. 3 Improve the processing precision, the one-way operation mechanism can be smooth tension, which is conducive to positioning. The electrode wire torsion tension jump without reciprocating wire drives the secondary deflection of the guide wheel, and the positioning error of the guide wheel is reduced from 0.01 to 0.02 mm to theoretically. Zero. 4 One-way operation mechanism is conducive to smooth discharge voltage, is conducive to feeding, and stabilizes the stress variation of the wire, which is beneficial to improve the efficiency of the line.

The workers engaged in wire EDM in China have long known that the accuracy of the first processing after slow wire processing is less than that of the reciprocating cycle.

Then, with the one-way infinite loop wire-cutting wire-cutting, do you need to cut multiple times under the specified machining accuracy and roughness? The imported slow wire EDM machine requires 3 to 5 cutting precision and surface roughness. We can do it at one time, at most twice. What a wonderful Chinese dream! The Chinese-style fast-travel wire EDM machine tool can be used in the world with high-end precision.

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