CNC electric discharge machine and programming
The CNC electric discharge machine is both a numerical control machine tool and a special machining machine tool. It is different from the traditional machine tool part in that:
1. Numerical control device and servo system,
2. Instead of relying on mechanical energy to cut the workpiece through the tool, it is processed in the form of electrical and thermal energy.
EDM is a more mature process in special processing.
In civilian use, national defense production departments and scientific research have been widely used, their machine tools are relatively stereotyped, and many types, but according to the characteristics of the relative movement of tools and workpieces in the process and use, etc., can be roughly divided into six The largest category, of which the most widely used, the number is more EDM forming machine tools and electric discharge wire cutting machine tools. Here we introduce the WEDM machine.
Wire EDM is based on the EDM process with wire electrodes (molybdenum wire or copper wire) relying on spark discharge to cut the workpiece, it is called EDM wire cutting, sometimes referred to as wire cutting.
The control system is an important part of the WEDM process. The stability, reliability, control accuracy and automation of the control system all directly affect the processing index and the labor intensity of the workers.
First, the types of CNC machining and special processing machine tools
There are two methods for classifying CNC machine tools:
1. According to the control system classification, there are three kinds of control, linear control and continuous control.
2. According to the servo system, there are open-loop, semi-closed-loop and closed-loop control systems.
Traditional cutting methods rely mainly on mechanical energy to remove metallic or non-metallic materials. With the development of industrial production and science and technology, there have been a variety of special processing methods that use other forms of energy for processing, mainly referring to the direct use of electrical energy, chemical energy, acoustic energy, and light energy for processing. Here, the application of energy forms other than mechanical energy is a significant sign of distinguishing special machining from traditional machining.
The new energy form directly acts on the material, resulting in a number of characteristics resulting from the processing. For example, the hardness of the tool for processing does not have to be greater than the hardness of the material being processed, which makes it easier to process high hardness, high strength, and high toughness materials; For example, there is no significant mechanical cutting force between the tool and the workpiece during the machining process, making microfabrication possible. It is these characteristics that have led to a great development of special processing methods, which have been widely used in aerospace, electronics, power, electrical appliances, instruments, machinery and other industries.
The types of special processing are mainly classified according to their energy sources and working principles. The main types are:
Electricity, thermal energy: EDM, electron beam processing, plasma beam processing;
Electrical and mechanical energy: ion beam processing;
Electricity, chemical energy: electrolytic processing, electrolytic polishing;
Electrical, chemical and mechanical energy: electrolytic grinding, electrolytic honing, and anode mechanical grinding;
Light, heat: laser processing;
Chemical energy: chemical processing, chemical polishing;
Sound and mechanical energy: ultrasonic processing;
Mechanical energy: Abrasive blasting, abrasive flow processing, liquid jet machining.
Electron beam and ion beam processing and simultaneous processing with several processing methods.
Second, the principle and prerequisite of WEDM
Wire-cut electric discharge machining is the use of electric corrosion phenomenon caused by the pulse discharge between the tool electrode (molybdenum wire) and the two poles of the workpiece. The main cause of EDM corrosion is that when the two electrodes are close to each other in the insulating liquid, the microscopic surface of both electrodes is uneven, and the electric field distribution is not uniform. The electric field at the nearest bump is the highest, and the dielectric between the electrodes is broken down to form a discharge. Channel, the current rises rapidly. Under the action of the electric field, the negative electrons in the channel run toward the anode at high speed, and the positive ions run toward the cathode to form a spark discharge. The electrons and ions collide with each other under the action of the electric field at high speed, and the anode and cathode surfaces are respectively bombarded by the electron current and the ion current. , to form an instantaneous high-temperature heat source in the electrode gap, the channel center temperature reaches 10000 degrees. As a result, the local metal material melts and gasifies.
Wire-cut WEDM can operate normally and must meet the following conditions:
1. There must be a certain gap between the molybdenum wire and the machined surface of the workpiece. The width of the gap depends on the processing conditions such as working voltage and processing volume.
2. When WEDM machining, it must be carried out in a liquid medium with certain insulating properties, such as kerosene, saponification oil, deionized water, etc. The requirement for high insulation is to facilitate the generation of pulsed spark discharge, liquid medium. It also eliminates the effect of electrolytic corrosion products and cooling electrodes in the gap. Molybdenum wire and the workpiece to maintain a certain gap between the surface, if the gap is too large, the voltage between the poles can not break through the inter-electrode media, you can not produce spark discharge; if the gap is too small, it is easy to form a short circuit connection, can not produce electricity Spark discharge.
3. Pulsed power must be used, that is, the spark discharge must be pulsed and intermittent. In Figure 1, ti is the pulse width, t0 is the pulse interval, and tp is the pulse cycle. During the pulse interval, the gap medium is deionized so that the next pulse can puncture the discharge between the two poles.
Third, the difference between WEDM and molding machine
1. The WEDM tool electrode is a wire electrode that moves along the axis of the wire electrode. The tool electrode of the molding machine is a shaped electrode and has a cross-section or a shape that is suitable for the part to be machined.
2. During wire cutting, the tool and the workpiece have relative servo feed movement in both horizontal directions. The molding machine workpiece and tool have only one relative servo feed motion.
Fourth, the composition of wire EDM
1. Machine body: bed, wire frame, wire taking mechanism, X-Y CNC table 2. Working fluid system
3. High-frequency power supply: Generates high-frequency rectangular pulses. The amplitude and pulse width of the pulse signal can be adjusted according to different working conditions.
4. CNC and servo system
Fifth, the application of wire cutting
1. Widely used in processing various die.
2. Can process micro-shaped holes, narrow slits and complex shaped workpieces. 3. Processing model and forming tool.
4. Processing powder metallurgy mold, insert mold cavity mold, drawing mold, corrugated plate forming mold Process hard materials, cut sheets, and cut precious metal materials.
6. Machining cams, special gears.
7. It is suitable for the processing of small batches and multi-components, reducing the cost of mold making and shortening the production cycle.
Sixth, programming
There are two ways to edit programs in CNC machine tools, one is manual programming and the other is automatic programming. Manual programming uses a variety of mathematical methods, using general calculation tools, to manually process and calculate the data required for programming. In order to simplify the programming work, the use of electronic computers for automatic programming is an inevitable trend. Automatic programming uses dedicated numerical control language and various input means to input necessary shape and size data to the computer. Using special application software, the coordinates of each intersection point can be obtained and the data required for programming the machining program can be obtained.
1. Manual programming
The programming format of the wire cutting machine tool is 3B instruction format: The programming format is shown in Table 1. B in the table is a separator. Its role is to separate X, Y, and J numbers for computer identification. When the program enters the controller, it reads the first B and then it makes the controller ready to accept the value of J. After reading the second B, it prepares to accept the Y-axis coordinate value. After reading the third B, prepare to receive the J value. When processing slashes, X, Y in the program must be the coordinates of the starting point of the end of the slash. When machining an arc, X and Y in the program must be the coordinates of the starting point of the arc relative to its center. The X, Y, and J values ​​are in um units.
(1). Counting direction G and count length J
In order to ensure that the arc or line segment to be machined can be machined to the required length, a general wire-cutting machine tool is achieved by controlling the total length of feed from a starting point to an end table. Therefore, a J-counter is set up in the computer to count, that is, the value of the feed length J of the worktable processing the line segment is placed in the J counter in advance, and the coordinate is determined as the length of the count when processing. For each step of the table, the J counter is decremented by one. In this way, when the J counter is reduced to zero, it means that the arc or straight line has been machined to the end point. When processing slashes, feed must be controlled in a direction with a long feed distance. If the end point of the line is A(Xe, Ye), when |
Xe |>| Ye
|, Take the Gx in the direction of the count, otherwise, take the Gy in the direction of the count. If both coordinates are the same, then both count directions can be used. When the coordinates of the arc end point are close to the Y axis, the counting direction is taken as Gx. When the X axis is close to the X axis, the counting direction is Gy. When the arc is taken, the absolute value of the end point coordinate is the counting direction. As shown in Figure 3.
The count length is the sum of the projected length of the line or arc on the axis of the count direction. For slashes,
When |Xe |>| Ye |, take J=| Xe |, otherwise, take J=| Ye
For an arc, it may span several quadrants. For example, the arc is from A to B, and the direction of the postgraph is Gx, J=Jx1+Jx2+Jx3,
The counting direction is Gy, J=Jy1+Jy2+Jy3.
(2). Processing instructions Z
Z is a machining instruction collective symbol. There are 12 kinds of it, as shown in Fig. 4. There are 8 kinds of arc instructions, SR is a straight circle, NR is a reverse circle, and the number behind the letter indicates the quadrant where the arc starts, such as SR1 indicates that the arc is straight and the starting point is in the first quadrant. For linear machining instructions denoted by L, the number following L indicates the quadrant in which the line segment is located. For a straight line that coincides with the coordinates, the positive X-axis is L1, the positive Y-axis is L2, the negative X-axis L3 is negative, and the Y-axis is L4.
When programming, the students should pay attention to the difference between the line cutting programming coordinate system and the CNC lathe and the numerical control milling machine coordinate system. The line cutting programming coordinate system only has the relative coordinate system. Every machining of a line segment or arc should move the coordinate origin to the straight line. The starting point or arc center.
Programming examples
Machining profile, where point O is the starting point, the cutting path can be from OA-AB-BC-CD-DE-EF-FA-AO, or from OA-AF-FE-ED-DC-CB-BA-AO , OA-AB-BC-CD-DE-EF-FA-AO programming as follows:
Take the straight line OA: B0 B20000 B20000 GY L2
Take the straight line AB: B40000 B0 B40000 GX L1
Take a straight line BC: B30000 B30000 B30000 GX L1
Take the straight line CD: B0 B20000 B20000 GY L2
Take the arc DE:B35000 B0 B70000 GY NR1
Straight EF: B0 B20000 B20000 GY L4
Take the arc FA: B0 B15000 B30000 GX SR2
Take the straight line AO: B0 B20000 B20000 GY L4
Ask students to think about how to program along the OA-AF-FE-ED-DC-CB-BA-AO line.
2. Automatic Programming In order to enter the information and processing routes in a drawing into a computer, a certain automatic programming language (CNC language) is used to express it and constitute a source program. After the source program is input, the necessary processing and calculation work depends on the application software (a compiler for NC language). Our NC programming language processing program is mainly divided into three parts: (1) direct input code processing; (2) drawing into code processing;
(3) Scanning graphics into code processing.
Automatic programming differs according to the input of the programming information and the processing method of the computer to the information, and is divided into an automatic programming method based on an automatic programming language and an automatic programming method based on a computer drawing. In the language-based automatic programming method, when programming, the programmer uses the programming manual and part drawing of the NC language used to express the entire contents of the processing in the form of language, and then inputs these contents to the computer for processing. The NC machining program can be used directly for CNC machine tools. Based on the computer graphics-based automatic programming method, the programmer first automatically programmed the CAD function of the software to construct a geometric figure. After that, the CAM function was used to set the geometric parameters to create an NC machining program.
Nowadays, the more commonly used CAD/CAM software is Mastercam, Pro/e, UG, and so on. The automatic programming software of the WEDM center wire cutting machine uses the domestic CAXA.
1. Workpiece materials and blanks Mold work parts generally use forging blanks, and their wire cutting operations are often performed after quenching and tempering. Due to the effect of hardenability of the material, when the metal is removed in a large area and the cutting process is performed, the relative equilibrium state of the residual stress inside the material is destroyed and deformed, which affects the machining accuracy and even causes sudden cracking of the material during the cutting process. In order to reduce this effect, except for the use of alloy tool steels (such as Cr12, Cr12MoV, CrWMn) with good forging performance, good hardenability, and low heat treatment distortion as the mold materials, the forging and heat treatment processes of the mold blanks should also be applied. Do it correctly.
2, mold blank preparation process Mold blank preparation process refers to the punch or die before the online processing of all processing.
(1) Preparation of the die 1) Blanking Cut the required material with a sawing machine.
2) Forging Improve the internal structure and forge into the desired shape.
3) Annealing Eliminates internal forging stress and improves processing performance.
4) Plane (milling) Plane six sides, and leave grinding margin 0.4-0.6mm.
5) Grind the upper and lower planes and the adjacent two sides, diagonally.
6) Marking Mark out the contour of the cutting edge and the position of the hole (screw hole, pin hole, thread hole, etc.).
7) Processed hole section
When the die is relatively large, in order to reduce the amount of wire cutting, the hole leakage part of the hole must be milled (car), only cutting edge height; for poor hardenability material, part of the hole can be removed, leaving 3 ~ 5mm cutting margin.
8) Hole machining Machining screw holes, pin holes, thread holes, etc.
9) Quenching up to design requirements.
10) Grinding Grind the upper and lower planes and the adjacent sides and square the corners.
11) Demagnetization treatment (2) Preparation process of punch The punch preparation process can be based on the structural characteristics of the punch, referring to the preparation process of the die, and unnecessary steps can be removed. However, the following points should be noted:
1) For ease of machining and clamping, the blanks are generally forged into parallelepipeds. For punches with the same size and shape and smaller cross-sectional dimensions, several punches can be made into one blank.
2) A sufficient cutting margin (usually not less than 5mm) should be allowed between the cutting contour of the punch and the side of the blank. There is also a clamping section on the blank.
3) In some cases, a threading hole is made in the mold blank in order to prevent deformation of the mold blank during cutting. The introduction of cutting starts with the threading hole.
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