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  • Product Name: Research on Constant Tension Mechanism of New Composite Wire Cutting Machine
  • Added time: 2018-07-18

(1 Xiangtan University, Xiangtan 411100 2 Hunan Electric Power Survey and Design Institute, Changsha 410007) Realization method of composite rotating wire method with fast rotation. By analyzing the shortcomings of the tension control mechanism of high-speed wire-cut EDM machine, the tension control mechanism of two new type of composite wire-cut EDM machine tools is proposed, which uses inertial force and electromagnetic force to control the tension of the wire. Device. The structure and working principle of the two tension devices are described. The device can overcome the shortcomings of manually operating the tensioning wheel or the heavy hammer tension mechanism, and realize the automatic adjustment of the tension.
 
 
 
JournalElectronicPublisl wire life is reduced, the processing cost is reduced. At the same time, the electric wire EDM machine is also divided into high-speed wire EDM machine and low-speed wire EDM wire cutting machine. machine tool. In the high-speed wire-cut EDM machine, the electrode wire is used for high-speed reciprocating linear motion. Generally, the wire speed is 7m/s~11m/s. The wire is mostly molybdenum wire, which can be reused and the processing cost is low. High-speed wire-cut EDM wire cutting machine usually adopts manual operation of tensioning wheel or heavy hammer mechanism to achieve constant tension control. The tension device is simple and the adjustment is inconvenient. The wire of the low-speed wire-cut EDM machine is used for low-speed one-way linear motion. The wire speed is generally lower than 0.25m/s. The wire is mostly made of copper wire, which is a disposable consumable and has high processing cost. The tension control device of the low-speed wire-cut EDM wire cutting machine is mostly powder brake, electromagnetic, and double-machine speed difference loading.
 
 
 
A new type of composite wire-cut type EDM machine, the wire is used for reciprocating low-speed linear wire in its own direction, and also rotates around its own axis at a high speed. The wire speed is generally 0025m/s~0200m/s. The speed of 600r/min~3000r/min uses molybdenum wire as the wire electrode, and the wire can be used repeatedly. The test proves that the wire-cutting machine combines the advantages of the two types of wire-cutting methods and reduces the loss of the wire. It extends the function and effect of the EDM machining 15|, which improves the machining accuracy of the product.
 
 
 
Because the composite wire EDM machine is a new type of machine tool, composite wire is a novel wire-cutting method. This paper introduces the implementation method and basic principle of this method, and proposes inertial force and electromagnetic force tension adjustment device. The structure and working principle of the two tension devices are described. The two tension devices are also unique and worthy of further research and improvement.
 
 
 
1Composite wire-drawing principle The key to composite wire-feeding is that the machine tool can realize the high-speed rotation of the wire around its own axis while realizing the traditional linear reciprocating wire, thereby increasing the movement rigidity of the wire and reducing the processing vibration. The combined machining effect of spark cutting and electric spark grinding | 51. The basic structure of the machine tool is as shown in the figure. The composite wire-drawing process can be divided into four parts: rotating, winding, wire and layering.
 
 
 
1.1 Rotating and Wound Wire In order to realize the composite wire drawing of the electrode wire, we designed a double wire barrel structure, and the upper and lower two identically configured wire barrels are relatively installed. The principle structure of the wire barrel is as shown. When the motor is started, the upper wire barrel and the lower wire barrel are driven to rotate synchronously, and the wire electrode is straight-lined up or down at the same time as the wire barrel rotates.
 
 
 
Under the condition that the whole drum is rotated at a high speed, the wire and the wire of the wire should be realized at the same time, and the speed difference between the internal gear 1 and the internal gear 5 is required from the structural point, which can be different by the pinion 2 and the pinion 4 The number of teeth is transmitted to achieve. The storage tube 14 passes through the internal gear 5 to 1.2. The wire and the layering actually require the electrode wire to be uniformly and evenly arranged on the storage tube (referred to as the wire), and can be multi-layered (referred to as layering). . The middle guide wire 13 is fixed on the two-way screw sleeve 12, and the two-way screw sleeve 12 moves regularly with the rotation of the two-way screw 8, and the pinion 6 on the two-way screw 8 passes through the storage tube 14. Only one toothed gear 7 rotates and moves. As the gear 7 moves one turn with the storage drum, the single tooth on the gear 7 drives the pinion 6 to a position of one tooth. Thus, the number of teeth of the pinion gear 6 determines how many turns of the thread on the two-way screw 8 can be arranged, and the design is very convenient. The two-way screw has a characteristic: when it is directional rotation, the two-way screw sleeve 12 on it will move back and forth regularly on the two-way screw. This walking guides the wire to be evenly wound around the storage drum.
 
 
 
The high-speed wire cutting machine has a fast wire-traveling speed. The storage drum can only be wound with more than 300 meters in a single layer. The commutation time is short (about 20s), and there are obvious commutation stripes in the processing. The wire barrel structure of the composite wire-traveling mechanism realizes the winding of more than 1000 meters of wire on a small storage tube due to the slow wire-cutting speed, and the commutation time can be as long as 2h~10h to eliminate the commutating stripe.
 
 
 
2 high-speed wire tensioning device drives the combination of the over-loading clutch 90 to produce the broken wire s. Therefore, the fixed device is placed, and the bookmark4 wire-feeding system is very important for the wire-cutting machine. Different wire rods with different diameters, hardnesses and materials are used. The wire-drawing system uses different tension and wire-traveling speeds, and with different discharge parameters, it becomes a wire cutting tool. During the online cutting process, the wire is thinned due to heat extension and discharge loss, which causes the wire to relax and the tension to decrease. In addition, the pulse discharge has an explosive impact on the wire, causing the wire to vibrate and the wire to pass. Loose, will result in unstable processing, high surface roughness, affecting processing quality and friction, and the effect of 011 will be greatly improved.
 
 
 
High-speed wire tensioning devices typically use a manually operated tensioning wheel or a heavy hammer tensioning mechanism for tension control. The heavy hammer tensioning mechanism can maintain the constant tension of the wire, and the manual operation of the tensioning wheel is omitted, and the principle is as shown. The tension device uses the gravity of the weight to generate a pulling force on the wire to keep the tension of the wire in the processing zone stable. Although the tension device has a simple structure, there are some drawbacks: First, the wire running path is twisted and twisted, and the linear velocity of about 10 m/s increases the fatigue stress of the wire, which increases the longitudinal vibration of the wire and affects the service life; The initial tension of the weight wire on the electrode wire is large, causing the tension of the wire in the processing area to fluctuate; the third is due to the limitation of the wire frame structure, the wire tension can not be adjusted by itself, and the wire adjustment should be stopped. 16. 3 composite wire tension device composite walking The tension adjusting device of the wire mechanism adopts a double-storage tube structure, which has a completely uniform structure by the upper and lower two wire cylinders, and is relatively installed. The wire electrode rotates up and down linearly while rotating with the wire barrel, and the other end is closed at the other end. Release the wire. The wire receiving end of the composite wire feeding mechanism is in an active state, and the wire end must have a tension tension, otherwise the wire is in a state of free relaxation and cannot work normally. At present, the device for generating tension of the composite wire-feeding mechanism has mainly developed two kinds of devices: an inertial force tension adjusting device and an electromagnetic force tension adjusting device.
 
 
 
3.1 Inertia force tension adjusting device Inertial force Tension device The structural principle is the structure of the inertial force tensioning device. The composite wire and the wire are rotated together at high speed, as shown. On the storage drum and the main shaft, the support and the wire are rotating. The angular velocity of the storage drum*2 is the angular velocity of the support on the main shaft. When there is a difference between the angular velocities, the wire can be loaded on the storage drum. When the speed difference between the storage tube and the spindle holder is formed, the moment of inertia of the inner wall of the bracket on the spindle due to the centrifugal force F generates a friction force P, which is the cause of the tension.
 
 
 
The centrifugal force principle can be used to know the radius of the centrifugal force drum, *U is the friction coefficient, and *k is the other resistance interference such as wind resistance. The tension thus shows that the magnitude of the tension is related to these factors: proportional to the mass m of the inertia mass; proportional to the square of the angular velocity around the drum, that is, proportional to the square of the rotational speed; The Capricorn coefficient is related.
 
 
 
It is proportional to the number n of inertial blocks; it is related to other factors k.
 
 
 
The characteristics of the composite wire inertia moment tensioning device In the work of the composite wire cutting machine, the 1000m long electrode wire will cause the wire to stretch continuously due to repeated winding, tension and processing loss; At the same time, the radii of the discharge drum are not equal, that is, the angular velocities of the upper and lower winding drums are not equal. The inertia moment device solves this problem subtly: when the wire is relatively elongated, its tension will decrease instantaneously. The storage tube "2 is lower than the bracket on the spindle, and the speed of the wire is slowed down, so that the centrifugal force P is lowered. The resistance torque Tf generated by the inertia block is also reduced, so that the rotation speed 4 of the storage drum rises, so that the difference between T and Tf is kept constant, which ensures that the tension is constant, and vice versa when the wire is relatively When shortening, the tension will increase instantaneously, and the storage tube "2 is also raised relative to the support on the main shaft, the speed of the discharge is increased, the centrifugal force P is increased, and the resistance torque Tf generated by the inertia block is increased. The rotational speed A is lowered, so that the difference between T and Tf is kept substantially constant, and the tension is also ensured to be constant. Therefore, regardless of the state of the wire during the specific wire feeding process, the inertial force device can always automatically adjust the rotation speed % of the storage drum to ensure that the tension is held by the principle of the tension generated by the inertial force device, and the device can automatically adjust The tension of the wire.
 
 
 
The angular velocity of the storage drum "2 is an important variable factor determining the tension. The number of moments of inertia is not easy to change when installed. * The tension wire T of the rising wire is increased. Such a feature meets the requirements of wire-cutting processing characteristics: because the composite wire-cutting machine processes the discharge force of the wire (including electromagnetic force, discharge channel force and passing surrounding bubbles) under large process parameters and high-efficiency processing conditions. The greater the force, etc.), the more constant the wire must be applied to the wire, so that the wire must be applied with greater tension to ensure that the wire does not lag and bend, maintaining linear rotation. This moment of inertia device has such a characteristic that the higher the rotational speed n of the wire, the greater the tension T generated, thus ensuring accurate and efficient wire cutting processing under large process parameters and high efficiency machining conditions.
 
 
 
32 Electromagnetic force tension adjusting device (1) Electromagnetic force tension device structure principle The rotor wire is embedded in the wire barrel of the composite wire, and a stator winding is placed outside the wire barrel, as shown.
 
 
 
The rotor coil on the storage wire is proportional to the square of the current I of the stator winding; and the rotation speed n of the discharge drum is proportional to the rotational speed n of the armature being dragged; =2:n, so the braking electromagnetic torque M and The angular velocity is proportional to.
 
 
 
(2) The characteristics of the composite wire-wound electromagnetic tension device are the same as those of the inertia moment device, and the tension device of the electromagnetic force can also ensure the tension is constant. When the wire is relatively elongated, the rotation speed of the discharge drum "2 is lower than the drop of the take-up drum, the speed of the discharge is slowed down, the brake electromagnetic torque Mf is also reduced, and the rotation speed of the storage drum "2 will rise, Therefore, the difference between M and Mf is kept constant, which ensures that the tension is constant. When the wire is relatively shortened, the wire is lifted relative to the upper bracket of the spindle, and the speed of the wire is fast, and the tension can be kept constant. The magnitude of the electromagnetic force tension and the following state of the art map 0U7S is a block diagram of the MCU work flow. When used as a take-up reel, the stator windings are not energized, and the storage drum is rotated at an angular velocity under the action of a mechanical power source. When the wire is used, the stator winding is connected with a direct current I, and the storage drum is at an angular speed. When rotating, the discharge device corresponds to a DC motor in a power generation state, and the rotor winding is subjected to electromagnetic resistance applied from the stator winding coil. The electromagnetic resistance is the cause of the wire tension T, and the generated electromagnetic torque is the braking torque. When the DC motor is used as a generator, the brake electromagnetic torque generated by the motor is 171 knots; * is the magnetic flux, and *n is the rotational speed at which the motor is dragged. It can be known from the above that once the motor structure is determined, Ce, CM, Kf, and Ro are constant, and the armature is driven to rotate at a constant speed n, whereby the electromagnetic tension can quickly and quickly adjust the tension of the wire. Since the wire diameter of the wire barrel device and the number of gear teeth are determined, the wire speed of the wire electrode is proportional to the rotation speed of the wire barrel, so that the tension between the wire speed and the current I of the armature winding can be adjusted in real time. Adjustment, so the detection and control system realized by the high frequency counter and the single chip microcomputer is developed, and the principle is as shown.
 
 
 
The speed sensor check machine has a simple workflow and a fast execution speed, and the working cycle of the entire control device is lower than the discharge pulse period of the wire cutting process. The system not only can control the tension freely, but also allows the storage tube to achieve constant tension at any speed, and can display the tension through the tension display in real time.
 
 
 
33 Two tension adjusting devices compare the inertial force tension device with simple structure and ingenious design, which can effectively apply tension for composite wire processing. However, the device is still not perfect, and mainly has the following defects: the trapping end of the inertial force tension device generates energy that hinders the action, causes bad vibration of the wire, and affects the cutting speed.
 
 
 
During the wire cutting process, the inertia block momentarily rubs against the inner wall of the spindle bracket. The mass of the inertia block for long-term rotation will gradually decrease and the inner wall of the spindle bracket will wear continuously, and the friction coefficient between them will gradually change. These factors can cause tension changes that affect long-term stable wire cutting.
 
 
 
At the lower speed rotation or stop, the winding end of the wire end is separated from the spindle support. That is, the inertia block and the spindle bracket are not combined or tightly coupled, so that it is difficult to produce a good stable tension, and the processing cannot be performed normally.
 
 
 
Compared with the inertial force tension device, the electromagnetic force tension device has the following advantages: when the electromagnetic force tension device applies a controllable electromagnetic tension at the discharge end, the stator coil of the wire receiving end is not energized, and the wire take-up drum is normally operated by the gear transmission without additional The power loss, the discharge tube and the stator coil interact by electromagnetic force, no mechanical loss.
 
 
 
The inertial force tension device during the wire cutting process is subjected to the centrifugal force by the inertia block, and the friction is generated by the frictional force on the inner wall of the bracket on the main shaft to realize the tension control. The electromagnetic force tension device realizes tension control through the interaction of electromagnetic force, without mechanical direct contact, without mutual wear, so the tension change will not be caused after long time work, and the stability of the processing will not be affected.
 
 
 
The electromagnetic force tension device has a longer service life, higher processing precision, more convenient control, more direct observation, and a more complete automatic control system.
 
 
 
4 Conclusion The composite wire-cutting machine realizes the high-speed rotation of the wire around the axis while performing the reciprocating low-speed straight wire. The composite machining of WEDM and EDM is realized. The multi-layer winding is eliminated. Reversing stripes. The test shows that the inertial force tension adjusting device and the electromagnetic force tension adjusting device can realize the automatic adjustment of the tension. The inertial force tension device has better effect on the automatic adjustment of the wire tension in a certain processing period; the electromagnetic force tension device is the electrode wire. The tension adjustment effect is good, but the structure is complicated and the manufacturing process is high. Since the composite wire-cutting machine is a new type of machine tool, its components need to be further researched and improved.

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