Problem description:
Please introduce wire cutting in detail, thank you!
Analysis:
Development history of WEDM machine
In the mid-20th century, the Lazarenko couple in the Soviet Union, while studying the phenomenon and causes of switch contacts being corroded by spark discharge, found that the instantaneous high temperature of spark could melt, oxidize and corrode local metals, thus creating and inventing the EDM method. The WEDM machine tool was also invented by the Soviet Union in 1960. At that time, a projector was used to watch the left and right hands move back and forth in front of the outline for processing. In fact, people think that although the processing speed is slow, it can process fine shapes that are not easy to process by traditional machinery. A representative example is the machining of special-shaped holes of chemical weaving nozzles. At that time, mineral oil (lamp oil) was used as the processing fluid. High insulation, small distance between poles, lower processing speed than existing machinery, and limited practicability.
The model machined by NC in deionized water (close to distilled water) was exhibited by Swiss EDM Machinery Factory for the first time at 1969 Paris Machine Tool Exhibition, in order to improve the machining speed and establish the safety of unmanned operation. However, the manufacture of CNC paper tape is very laborious, and it will be a great burden for users if there is no automatic programming by large computers. Before the appearance of cheap automatic programming tool APT, its popularity was very slow.
The WEDM machine developed by Japanese manufacturers by automatic programming with small computers is cheap, which accelerates its popularization. The machining shape of WEDM is a two-dimensional contour. Simple APT is widely used in automatic programming equipment (APT language is simpler than formal model), and the appearance of simple APT is an important factor in the development of WEDM.
Basic principles of WEDM
In WEDM, copper wire is used as the tool electrode, and a pulse voltage of 60~300V is applied between the copper wire and the workpiece material such as copper, steel or superhard alloy, and a gap of 5~50um is maintained. The gap is filled with insulating media such as kerosene and pure water, which causes spark discharge between the electrode and the workpiece, mutual consumption and corrosion. Numerous pits are etched on the surface of the workpiece, which are monitored by numerical control and executed by servo mechanism.
The physical principle of EDM is as follows:
In order to generate an electric spark between two electrodes, the voltage between the two electrodes must be higher than the gap (electrode-workpiece) breakdown voltage, which depends on:
1) the distance between the electrode and the workpiece;
2) Insulation capacity of dielectric liquid (water resistivity);
Pollution status of gap (corrosive waste).
The discharge first occurs at the point with the strongest electric field, which is a complicated process. Free positive ions and electrons accumulate in the electric field and soon form ionized conductive channels; At this stage, an electric current is formed between the two plates. It leads to numerous collisions between particles, forming plasma, which quickly rises to the high temperature of 8000 to 12000 degrees, instantly melting some substances on the surfaces of the two conductors, and at the same time, bubbles are formed due to the vaporization of the electrode and dielectric liquid, and its pressure rises regularly until it is very high; Then the current is interrupted and the temperature drops suddenly, so that the bubbles explode inward, and the generated power throws the dissolved substances out of the crater, and then the corroded substances re-condense into small balls in the dielectric liquid and are discharged by the dielectric liquid; The asymmetry of corrosion pair between electrode and workpiece mainly depends on the thermal conductivity of electrode, melting point of material, duration and discharge density. What happens on the electrode is called loss, and what happens on the workpiece is called material removal.
job/work safety
In order to ensure the healthy and comfortable working environment of operators and machine tools under the best safety conditions, and to maintain the original machining performance and accuracy of machinery and equipment for a long time and prolong the service life, we must abide by the safety rules of WEDM.
I. Environment:
The selection of environment is directly related to WEDM equipment and its operators, and the quality of environment selection has the following effects: First, it damages the performance and accuracy of equipment and shortens the life of its machine tools; Secondly, it affects the machining accuracy of the workpiece and causes poor quality; Third, it is also harmful to the safety and health of operators. Therefore, please refer to the following items for the selection of environmental sites:
1. Space size meeting the requirements of WEDM;
2. Choose a place that can bear the weight of the machine tool;
3. Choose a place without vibration and shock.
WEDM is a high-precision machining equipment. If there is vibration and impact in the place, it will cause serious damage to the machine, seriously affect its processing accuracy, shorten its service life, and even lead to the scrapping of the machine.
4. Choose a place where there is no dust to avoid flowing beside many channels;
(1) WEDM machine has its own characteristics. There is dust in the air, which will seriously wear the screws of the machine, thus affecting its service life;
(2) The WEDM machine is controlled by a computer, and the disks used by the computer have strict requirements on the dust in the air. When dust enters the disk, the disk will be damaged, and so will the hard disk.
The needs discharger itself emits a lot of heat, so the electric cabinet needs to be ventilated frequently. If there is too much dust in the air, it will attach to various electrical components during ventilation, resulting in poor heat dissipation of electrical components, which will lead to the burning of circuit boards. Therefore, the dust screen of the machine should be cleaned frequently.
5. Choose places with small temperature changes to avoid direct sunlight through windows and top windows, and places close to heat flow.
(1) products processed by high-precision parts need to be processed at a constant temperature, generally at room temperature of 20℃;
(2) Because the WEDM machine itself will generate considerable heat when working, if the temperature changes too much, it will have a serious impact on the service life of the machine.
6. Choose shielding room: Because WEDM is an arc discharge process, strong electromagnetic waves will be generated during the arc discharge process, which will do harm to human health and affect the surrounding environment.
7. Choose a well-ventilated and spacious workshop, so that operators and machine tools can work in the best environment.
Second, the handling:
1. Selection of handling mode: forklift and roller are used for handling WEDM equipment, and crane is used for handling under special circumstances;
2. Locking before handling: Before handling, the lathe bed and shaft must be locked with special random fasteners. In order to prevent the equipment from being damaged during handling, thus affecting the accuracy of the machine and even scrapping the equipment.
Third, the operation safety:
In order not to damage and injure machine tools and personnel, the following matters should be paid attention to when operating wire cutting equipment.
1. Only personnel who have been trained in this machine and equipment can be allowed to use this machine and equipment.
2. In order to avoid overheating of the processing fluid and the electric cabinet, the cooling system must be in a continuous working state;
3. In order to avoid direct contact with live wires, the protective door of the machine must be closed;
4. Two people are not allowed to operate the same machine at the same time. When operating the screen, reduce the brightness of the screen as much as possible, and choose to squint at the screen to reduce the harm of screen radiation to the eyes;
5. The processor should be familiar with the specific functions and usage status of the buttons on the operation panel, use them flexibly in the process of machine operation, and be familiar with the conversion of pictures, especially the functions of several important pictures (such as preparation pictures and observation pictures), so as to avoid all kinds of abnormalities caused by being unfamiliar with the operation panel during processing, and the buttons (especially common keys) are easy to be damaged due to intensive use. Therefore, when operating the panel, a layer of plastic paper should be attached to the surface.
6. Like the operation panel, the processor should be familiar with the specific usage of the remote control. The buttons of the remote control should be protected with a layer of plastic paper. In addition, the remote controller can be operated remotely from the operation panel by conducting with wires, so the protection of the remote controller should also include the protection of wires. Don't pull the wire hard when using, so as to avoid the failure of the remote control. Part of the line array should be circled and placed. Be sure to put it back and hang it up after use.
7. Never put your hands and fingers between the machine head and the workpiece when the machine tool or the machine head is moving, which may cause safety accidents due to incorrect command input or wrong direction keys;
8. Protection of machining platform: When machining workpieces, pay attention to whether the clamping method will hurt the machining platform, blow dry the platform when the machine is in use, and apply antirust oil to protect the machine tool when it is not used for a long time;
9. When the workpiece is erected, pay attention to whether it will meet the upper and lower heads when cutting, and adopt special processing technology for the processing of small holes to avoid being stuck because the waste cannot be taken out, which will affect the accuracy of the machine tool;
10. The clamping of the workpiece is based on the principle of convenience and stability. When the workpiece is erected, the pressing force is based on the principle that the workpiece is not impacted by water, so as not to cause the screw to slip and cannot be taken out;
1 1. In our daily work, we often encounter workpieces that can't be processed by the general formwork method, so we must use special fixtures:
(1) Small workpieces-When the pressure plate cannot stand up, you can consider using a protractor or a wheat stone for processing;
(2) When the workpiece has a large inclination and cannot be tilted, sine table or inclined pad should be used for auxiliary tilting processing;
(3) When processing multiple pieces-consider overlapping processing with protractor or wheat stone.
(4) In the process of using the jig frame, it is necessary to ensure that the jig frame is not damaged (for example, it is not feasible to damage the jig frame in the cutting process for the convenience of formwork erection).
12. Pay special attention to the equipment when processing: whether the voltage of voltmeter is within the specified standard range;
13. Do not directly contact the workpiece and copper wire during machining. Pay attention to the phenomenon that the material head is stuck on the head when blanking. Be careful not to hurt the equipment and fingers when it is difficult to take out the material head;
14. When cleaning the processed products, oxalic acid cleaning solution will be used. When in use, the processed products should be cleaned with a brush, instead of touching oxalic acid directly by hand to clean the work products, so as to reduce the corrosion of oxalic acid. Don't let oxalic acid enter your eyes. If there is, it should be cleaned with clear water immediately.
15. Operators of wire cutting machines should pay attention to washing their hands frequently after processing, especially before eating, so as to avoid harmful intake of processing liquid with more impurities;
16. When carrying out various maintenance and tests in the power cabinet or the electrical part of the machine tool, the main switch must be turned to the off position, and a sign plate should be set (do not turn on the power supply during maintenance);
17. Safety instructions must be observed during maintenance and testing, and the corresponding chapters in the manual must be consulted before any maintenance work;
18. Only when the power supply of the control cabinet is cut off can electronic components be touched;
19. Hold the component only by the handle, and don't touch the gold-plated wire of the printed circuit board;
2 1. Attention should be paid to replacing the wearing parts of the equipment in time to maintain the accuracy.
Four. Safety equipment \ \
A. introduction of mechanical equipment and safety equipment:
1. Buzzer setting (automatic alarm in case of shutdown or abnormality);
2. Screen protection settings (the screen can be automatically turned off to reduce radiation if it is not used for a long time);
3. Setting of emergency braking key (emergency braking can be performed in case of sudden abnormality);
4. Install a cooling fan (mainly responsible for ventilation and cooling of the main chassis);
B, safety equipment operation method:
1. The buzzer can only be used in two states: when the function is selected as "on", the buzzer will automatically give out any abnormal alarm; When the function selection is "Off", the buzzer will not work. The buzzer is mainly used as a reminder to remind the processor to continue processing the machine when the machine is suspended;
2. Use of screensaver: You can set the screensaver of Chaduc model by modifying the parameters. You can choose whether to enable the screen saver, and you can set the activation time. If not, you can turn it off.
3. Use of emergency brake button: When the machine suddenly becomes abnormal and the processor can't come up with a correct solution immediately, press this button to brake the machine; 4. When the main power supply is turned on, the cooling fan will be activated;
Five, emergency escape:
1. Fire: In case of fire, correct fire control measures should be taken and report to the supervisor immediately. When calling the fire alarm telephone number "1 19" (which must be ordered by the senior supervisor), the name and detailed address, substance, fire size, and the name and telephone number of the alarm person should be stated, so as to actively put out the initial fire and prevent the fire from spreading. When surrounded by smoke, cover your nose and mouth with a wet towel, walk low and climb out of the field. When the escape route is sealed by fireworks, you can cover yourself with a wet quilt and bend over to rush through the fire. When the escape passage is blocked, you can escape through the balcony drain pipe or tie a rope to a fixed object and escape from the fire along the rope. If the above measures are not feasible, you should return indoors, close the doors and windows leading to the fire area, water the windows to delay the spread of the fire, and send a distress signal to the windows at the same time. In short, under any circumstances, don't give up the hope of saving your life;
2. When someone is found to get an electric shock, first aid should be done quickly, and the action should be quick. Accurate method is the most critical. Whenever you find a critically ill patient or accident, you can call "120" and ask the emergency center for first aid. First, cut off the power supply quickly. If the power switch is far away, you can open the wire on the electrocuted person with an insulated object, or cut off the power with a tool with an insulated handle. Don't use metal materials or wet objects as rescue tools, and don't touch those who get an electric shock to prevent yourself from getting an electric shock. When the electric shock is cut off, the symptoms should be dealt with quickly according to its specific situation. Those who are not seriously injured and conscious should rest quietly for an hour and then be sent to the hospital for observation; If you are seriously injured and unconscious, but your heartbeat and breathing still exist, you should let him lie on his back comfortably and quietly, and ask a doctor for treatment or send him to the hospital immediately. If the injury is serious, respiratory arrest or cardiac arrest, or both have stopped, artificial respiration and chest compressions should be performed immediately and sent to hospital for treatment.