Spindle design of the hottest ultrasonic vibration

2022-08-04
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Spindle design of ultrasonic vibration drilling machine

the use of axial ultrasonic vibration drilling technology to process micro holes (less than 0.5mm) can prolong the service life of the drill bit, improve the accuracy of the hole and the surface quality of the hole wall, and reduce the burr at the drilling outlet, which has an excellent process effect. This paper introduces a design method for the spindle of ultrasonic vibration drilling machine. By using this design scheme, the original spindle of the drilling machine can be replaced by the ultrasonic vibration spindle without changing other structures of the machine tool. The machine tool can be refitted with compact structure and easy to use

1. Keyway 2 Drive shaft 3 Rear matching blocks 4, 6 Piezoelectric ceramics 5 Electrode 7 Front matching block 8 Luffing lever 9 Collector ring 10 Elastic jaw 11 Circular sleeve

structure diagram of main shaft

1 structure design of main shaft

the drill clamp is installed at the lower end of the main shaft of ordinary drilling machine, which should be able to complete the rotary motion and axial feed motion. In addition to the above motions, the main shaft of ultrasonic vibration drilling machine should also have the axial ultrasonic vibration function. The vibrator in the ultrasonic vibration spindle can be a sandwich piezoelectric ceramic transducer (CDE section in the figure), with an electroacoustic conversion efficiency of about 90% and a very compact structure. It is composed of a pair of piezoelectric ceramic sheets, electrodes and front and rear matching blocks. Because the ultrasonic transducer used for micro hole machining has small power and relatively small calorific value, a special cooling system may not be set

the front matching block and the luffing lever can be integrated. The common drill chuck has complex structure and large mass, which is easy to damage the resonance state of the spindle system, resulting in a significant reduction in the amplitude of the drill bit. Therefore, an elastic chuck with simple structure is designed at the end of the luffing rod. The elastic chuck is equipped with four elastic jaws for clamping the drill bit. A collecting ring is installed on the small end of the horn to transmit the current required by the transducer

the rear matching block is integrated with the step drive shaft, and the small end of the drive shaft is provided with a keyway for sliding matching with the drilling machine pulley, so as to drive the spindle system to rotate. A centripetal ball bearing is respectively installed at the small end of the luffing rod and the small end of the transmission shaft to support and install the main shaft. The outer ring of the bearing is transiently matched with the main shaft sleeve of the drilling machine. The sleeve with slots can drive the main shaft for axial feed

2 design principle of transducer and horn

the ultrasonic frequency changing voltage is applied to the two poles of piezoelectric ceramics, and its thickness will change with the change of voltage, so longitudinal ultrasonic vibration is generated, and the longitudinal vibration wave will propagate in the front and rear directions. When the medium of the propagating wave changes, the refraction and reflection of the wave will occur at the interface. The ratio of the reflection amount depends on the density ratio of the two media. The greater the density ratio, the more reflection. Because the density ratio of steel to air is very large, it can be considered that all the waves propagating to both ends of the main shaft are reflected back. The half wave loss of the reflected wave is half a cycle later than the incident wave. It is superimposed with the wave directly sent from the piezoelectric ceramic. The amplitude increases on some sections, decreases on some sections. The rubber isolation bearing can reduce the seismic action, and the amplitude on some sections is constant to zero, forming standing wave conduction. If the system composed of transducer and horn is exactly an integral multiple of 1/2 wavelength of sound wave, the system is in resonance state. The resonance condition can be expressed as l=nl/2

where l is the total length of the system, l is the vibration wavelength (related to material properties), and N is a positive integer

if the structural damping of the medium and the surface acoustic wave radiation are not considered, the amplitude and frequency of the sound wave will not change when it propagates in the elastic medium with constant cross-section. However, the case of the variable cross-section rod in the resonant state is different. When the vibration wave is transmitted from the end with larger cross-section to the end with smaller cross-section, the amplitude will increase. Therefore, the variable cross-section rod has the amplitude variation function in the resonant or near resonant state. For step horn, there is the following relationship between output end amplitude A2 and input end amplitude A1 a2/a1= (d1/d2) 2

where D1 is the input end diameter and D2 is the output end diameter. This indicates that the greater the diameter difference between the two ends of the horn, the greater the amplitude obtained at the output end

in order not to damage the resonance state of the main shaft system, the bearing for fixing the main shaft should be placed at the wave node (i.e. the stagnation point where the amplitude is always equal to zero), and the drill bit should be installed at the wave belly (the point with the maximum amplitude) so that the drill bit can obtain a larger amplitude. 3 Determination of the structure size of the spindle

the transverse size of the spindle is mainly limited by the size of the inner hole of the spindle sleeve of the drilling machine. In order to obtain larger vibration power and amplitude, the inner hole space of the sleeve should be used as much as possible, and the piezoelectric ceramic sheet with larger diameter should be selected. The diameter of the front and rear matching blocks of the transducer can be the same as that of the piezoelectric ceramic sheet. For the convenience of connecting wires, the electrode diameter can be 8 ~ 10mm larger than that of the piezoelectric ceramic sheet. When the spindle system is in the resonant state, the amplitude obtained at the drill bit is the largest. At this time, the total length of the spindle should be an integral multiple of the half wavelength, and the length of each part of the spindle should also be determined according to their respective wavelengths

the transmission shaft (AC section in the figure) and the luffing rod (eg section) are both elastic rods made of the same material. The wavelength can be calculated by the following formula: l=c1/f

where C1 is the longitudinal wave velocity, which is a constant related to the material properties. F is the frequency of ultrasonic frequency change current sent by the ultrasonic generator, which can be selected within the working range of the generator. Generally, f=20khz can be selected. To ensure that the spindle has sufficient axial feed range, the length of the small end (AB section) of the transmission shaft can be taken as 3l/4, and the length of the large end (BC section) can be taken as l/4. The length of the horn shall meet the design principle of 1/2 wavelength horn, and the length of the large end (EF section in the figure) and the small end (FG section) shall be taken as 1/4

there are elastic materials such as steel and non elastic materials such as piezoelectric ceramics in the transducers. The center arranges personnel to determine the length of professional translation of all Chinese in the existing report template for each part of the transducers (CE section in the figure), which can be carried out in three steps. (1) According to the inner hole space of the spindle sleeve and the product catalogue of the piezoelectric ceramic manufacturer, the size of the piezoelectric ceramic sheet (including its thickness l0) is selected; (2) Determine the electrode thickness L3. Generally, aluminum or copper sheets with good conductivity are used as electrodes. In order to meet the needs of connecting wires, the thickness can be 3 ~ 5mm; (3) Determine the length L2 and L1 of the front and rear matching blocks. For the convenience of design, the length of the front and rear matching blocks can take the same value, that is, l1=l2. The length L1 of the rear matching block can be calculated according to the following formula

where: z0=r0c0s0, z1=r1c1s1, z3=r3c3s3, m3=z3/z0, q0=w1l0/c0, q1=w1l1/c1, q3=w1l3/c3, w =ctgq0- (K33) 2/q0

l0 are piezoelectric ceramics sheet thickness; L1 is the length of the post matching block; L2 is the length of the front matching block; L3 is the electrode thickness; C0 is the longitudinal wave velocity of piezoelectric ceramics; C1 is the longitudinal wave velocity of the matching block; C3 is the longitudinal wave velocity of electrode; R0 is the density of piezoelectric ceramics; R1 is the matching block density; R3 is the electrode density; K33 is the electromechanical coupling coefficient of piezoelectric ceramics; W1 is the resonant circular frequency; S0, S1 and S3 are the cross-sectional areas of the piezoelectric ceramic sheet, the back matching block and the electrode respectively; Q0, Q1, Q3, Z0, Z1, Z3, m3 and W are all intermediate parameters. This point can be ignored

when matching the block length L1 after using the above formula, the specific values of each physical parameter must be determined first. The resonant circle frequency W1 is the selected ultrasonic wave, which only controls the product of 1 specific parameter generator operating frequency f and 2; The thickness l0, density R0 and electromechanical coupling coefficient k33 of piezoelectric ceramic sheet can be obtained from the product description of the manufacturer; High quality carbon structural steel or titanium alloy steel can be used for the front and rear matching blocks, horn and transmission shaft. The density R1, longitudinal wave velocity C1, electrode density R3 and longitudinal wave velocity C3 can be found in the relevant material manual

by adopting the above design scheme, the z403 bench drilling machine has been refitted, and satisfactory results have been obtained. The ultrasonic vibration amplitude on the drill bit is more than 2 m

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