Wire Electrical Discharge Machining is called Wire EDM.The accumulation of free positive ions and electrons in the field quickly forms an ionized conducting channel. At this stage, an electric current is formed between the two plates. It causes numerous collisions between the particles, forming a plasma zone, which quickly rises to a high temperature of 8,000 to 12,000 degrees, melting some materials instantaneously on the surfaces of the two conductors, and forming a bubble due to the vaporization of the electrodes and the dielectric solution, and its pressure rises regularly until very high. Then the current interrupts, the temperature suddenly drops, causing bubbles to explode inward, generating momentum to throw the melted material out of the crater, and then the corroded material condenses back into a small sphere in the dielectric solution and is expelled by the dielectric fluid. Then, through the monitoring and control of NC control, the servo mechanism is executed to make the discharge uniform.
According to wire traveling speed, WEDM machine can be divided into high speed reciprocating wire traveling WEDM machine (Reciprocating type High Speed Wire cut Electrical Discharge Machining commonly known as “fast wire traveling”), low speed one-way wire traveling WEDM machine (low Speed one-way Wire cut Electrical Discharge Machining commonly known as “slow wire traveling”). There are three types of wire traveling machine, Vertical Wire Electrical Discharge Machining Machine Tool with Rotation Wire. It can also be divided into single column cross worktable type and double column type (commonly known as Longmen type) according to the working table.
Reciprocating wire EDM machine tool
The wire speed of the reciprocating wire WEDM is 6~12 mm/s, which is a unique product of our country. Since September 1970, the “Digital Programmed Automatic Wire Cutting Machine Tool” has been developed by the State-owned General Factory of Fan Machinery under the Ministry of the Third Machinery Industry, which is the first of its kind in China. In 1972, the Ministry of the Third Machinery Industry carried out technical appraisal on the CKX NC WEDM machine tool manufactured by the factory, and considered that it had reached the advanced level in China at that time. In 1973, according to the decision of the Ministry of the Third Machinery Industry, NC WEDM machine number CKX-1 began to put into mass production. In September 1981, a coordinate CNC machine DK3220 with taper cutting function was successfully developed. The most important feature of the machine is that it has 1.5 taper cutting function. Major technical improvements in line cutting machine have been completed. With the gradual improvement of large taper cutting technology, variable taper, upper and lower profile cutting processing has also made great progress. With the breakthrough of large thickness cutting technology, the accuracy of cross section and vertical section has been greatly improved, and the machining thickness can exceed 1000mm. The reciprocating wire cutting machine has more advantages. At the same time, it meets the needs of customers both at home and abroad. The number of such machine tools is increasing rapidly from 2-3,000 to tens of thousands a year. At present, there are more than 200,000 reciprocating wire-cut machine tools in China, which are used in all kinds of medium and low-grade mold manufacturing and special parts processing, and become one of the most widely used CNC machine tools in China. However, because the reciprocating wire-cutting machine can not control the constant tension of the electrode wire, the electrode wire trembles greatly and is easy to break in the process of machining. Because of the reciprocating use of electric grade wire, it will cause electrode wire loss, machining accuracy and surface quality reduction.
Low speed unidirectional wire cutting electric discharge machine
The electrode wire of low-speed wire-cutting machine takes copper wire as tool electrode, and generally moves unidirectionally at a speed below 0.2mm/s. A pulse voltage of 60-300V is applied between copper wire and copper, steel or superhard alloy and other processed materials, and the gap is kept between 5-50um. The gap is filled with insulating medium such as detached water (close to distilled water), which makes electricity. Spark discharges occur between the poles and the processed objects, and they are consumed and corroded each other. Numerous pits are etched on the surface of the workpiece. Through the monitoring and control of NC control, the servo mechanism executes the discharge so that the discharge phenomenon is uniform and consistent, so that the processed objects can be processed and become the required size and shape precision. Products. At present, the accuracy is up to 0.001mm, and the surface quality is also close to the grinding level. The electrode wire is no longer used after discharge, and the resistance-free anti-electrolysis power supply is adopted, generally with automatic wire piercing and constant tension device. Smooth, uniform, small jitter, high machining accuracy, good surface quality, but not suitable for processing large thickness workpiece. Because of the high precision, high technology content and high price of machine tools, the cost of using machine tools is also high.
The single way wire electrical discharge machine (WEDM) has only the unique type of foreign companies in the early stage. The low speed WEDM in Taiwan started late, but it has developed rapidly over the past few years. One of its key initiatives is to be co-financed by a number of household electrical machine tool manufacturing enterprises, with the support of relevant departments to a certain extent, the Taiwan Institute of Industrial Technology has invested a lot of manpower and material resources in the development of key technologies. After more than 10 years of research, we have made breakthroughs in key technologies such as control system and power supply. The low-speed wire-EDM WEDM machines manufactured by Taiwan’s enterprises should be in the range of medium-sized machines at present. In the past three years, the annual growth rate has reached 20%-30%. It is estimated that in the next five years, the annual output of Taiwan’s low-speed wire-EDM WEDM machines will reach 2000 sets, accounting for more than 25% of the world market. Low-speed wire EDM WEDM has high technology content, good market prospects, and can obtain higher returns. It is the “necessary place” and “strategic highland” of various manufacturers in the electrical processing industry. It can also be said that whoever masters the low-speed wire-EDM WEDM technology, who will be the next step in the development of enterprises opportunities. In order to seize the Chinese market, Japanese, Swiss and Taiwanese electric machine tool manufacturers have set up factories in mainland China to produce such machines. With the support of the special fund of the Ministry of Science and Technology, the scientific and technological workers of our country have invested a great deal of research and development power, and have completed the research and development of a new generation of low-speed wire-EDM machine, which has made a great breakthrough. At present, they have owned the products with independent intellectual property rights and occupied a certain market share, and their performance indicators can be reached. Gear level. At present, some domestic enterprises hope to develop low-speed wire-EDM technology through cooperation with Taiwan-related enterprises.
Vertical self rotating WEDM machine
Vertical self rotating WEDM (horizontal self rotating WEDM). The characteristics of vertical rotary WEDM are different from those of traditional high-speed WEDM and low-speed WEDM. Firstly, the motion of electrode wire is one more rotating motion of electrode wire than that of traditional WEDM; secondly, the wire traveling speed of electrode wire is between high-speed wire traveling and low-speed wire traveling. The speed is between 1 and 2mm/s. Because of the increase of rotating motion of the electrode wire in the machining process, the biggest difference between the vertical rotary WEDM and other types of WEDM is the wire traveling system. The wire traveling system of vertical rotary WEDM is composed of two sets of two ends with identical structure, the traveling end and the placing end. The high speed rotating motion of electrode wire and the compound movement of low speed traveling wire are realized. The area between the two sets of spindle heads is an effective processing area. Apart from the wire removal system, other components of the machine tool are the same as those of high-speed WEDM.
Compared with the one-way low-speed WEDM machine tool, the reciprocating high-speed WEDM machine tool still has a big gap in the average productivity, cutting accuracy and surface roughness and other key technical indicators. To address these gaps, at the beginning of this century, a number of high-speed reciprocating WEDM manufacturers in China have realized multiple cutting on high-speed WEDM machines (commonly known as Medium Speed Wire Cut Electrical Discharge Machining). The so-called “middle-speed wire” does not mean that the wire traveling speed is between high speed and low speed, but the composite wire-cutting machine. Its principle of wire traveling is to use 8-12mm/s high-speed wire traveling in rough machining and 1-3mm/s low-speed wire traveling in finish machining, so that the work is relatively stable and the jitter is small, and material deformation and molybdenum wire can be reduced by multiple cutting. The error caused by the loss makes the machining quality relatively improved, and the machining quality can be between the high speed wire feeder and the low speed wire feeder. Therefore, it can be said that what the user calls “middle wire” is actually a reciprocating wire EDM machine learning from some of the low-speed wire machine processing technology, and realize stripeless cutting and multiple cutting. After several years of development, almost all domestic manufacturers of high-speed wire-EDM machine tools are in the production and sales of wire, but ultimately shows that not all reciprocating wire-EDM machine can carry out multiple cutting, or that not all reciprocating wire-EDM machine uses multiple cutting technology. After that, good technological results can be obtained. Multiple cutting is a comprehensive technology, which involves the numerical control accuracy of machine tools, pulse power supply, process database, wire feeding system, working fluid and a large number of process problems. It is not simply possible to add a set of wire feeding variable frequency speed control system to the high-speed wire feeding machine, only those with high manufacturing accuracy, and in various ways. The reciprocating wire EDM WEDM machine with multiple cutting conditions is capable of multiple cutting and stripeless cutting, and has achieved remarkable technological results. Therefore, our production enterprises must pay full attention to this problem, we must do according to the system engineering, really make good use of this technology, to do a good job of this product. For example, some enterprises have adopted DC or AC servo motor as driving unit to drive ball screw directly in X and Y coordinate workbench to further improve the accuracy of machine tool. At the same time, full closed-loop control with pitch compensation function is adopted, and the positioning accuracy error of machine tool can be compensated and corrected by NC system. On the premise of guaranteeing the accuracy, it can reduce the reduction of machining accuracy caused by long-term use and prolong the service life of machine tools. The special (mostly diamond) wire holder is used in the wire conveying system to keep the electrode wire relatively stable and reduce the tension change of the electrode wire during the processing. In the cooling system, the conventional extensive cooling mode is changed, and the key parameters such as dielectric constant are controlled by multi-stage filtration to ensure the smooth finishing process. The control software provides an open database of machining parameters, which can be selected according to the material’s texture, thickness, roughness and other conditions. We believe that through our efforts, multiple cutting technology will be more perfect, reciprocating wire WEDM technology will also be better application and development.
Although the machining quality of reciprocating WEDM has been improved obviously by using multiple cutting technology, it still belongs to the category of high-speed WEDM. The cutting accuracy and smoothness are still far from those of low-speed WEDM, and the accuracy and smoothness need to be further improved. Medium-speed wire-feeding machine has the characteristics of simple structure, low cost and less consumption, so it also has room for survival. At present, the implementation of the standards is still the high-speed wire-feeding machine related standards, so the production enterprises should pay attention to the publicity of users, must be realistic.
Classification of WEDM
Distinguish between fast moving WEDM, medium thread cutting and slow wire cutting. 1: The wire traveling speed of WEDM is 6-12 mm/s, and the electrode wire travels back and forth at high speed. The cutting accuracy is poor. 2: WEDM is a new technology developed in recent years, which realizes the function of frequency conversion and multiple cutting on the basis of WEDM. 3: The wire traveling speed of WEDM with slow wire is 0.2mm/s, and the electrode wire moves in one direction at low speed. The cutting precision is very high.