EP2389273B1

EP2389273B1 - Ultrasonic treatment device

Info

Publication number: EP2389273B1
Application number: EP09838694.9A
Authority: EP
Inventors: Esa Rouvinen
Original assignee: Elpro Oy
Current assignee: Elpro Oy
Priority date: 2009-01-26
Filing date: 2009-01-26
Publication date: 2013-07-17
Anticipated expiration: 2029-01-26
Also published as: EP2389273A4; EP2389273A1; WO2010084234A1

Description

The present invention relates to an improved treatment device operated by ultrasound for smoothing the surface of a workpiece, the device being intended especially for smoothing the surfaces of metal pieces or pieces made of hard plastic. The device according to the invention may also be used for other machining, for example drilling or engraving.
Known prior art is represented, for example, by the Applicant's earlier international patent publication W02007/060284 . From this publication is known a treatment device comprising a machining unit with a tool placed against the surface of a workpiece, the tool being arranged to direct a hammering impact effect of essentially ultrasonic frequency on the surface of the workpiece, and means for supplying machining fluid to the area being machined.
US 5 741 173 A discloses a method and an apparatus for machining semiconductor material with a grinding tool. In the method a liquid cleaning agent is exposed to sound waves having a specific frequency and a specific intensity. US 5 968 841 A discloses a chemical-mechanical polishing pad provided with vibration means for vibrating a slurry used in the polishing process in order to prevent settlement of particles from the slurry on the pad. US 2007/077871 A1 discloses a chemical-mechanical polishing pad. In the polishing process a pad conditioning liquid is supplied onto the polishing pad the liquid being exposed to megasonic vibration.
Ultrasonic treatment by peening, that is, ultrasonic peening, causes plastic deformation to take place on the surface of the piece being treated, due to which compressive stress is formed on the surface. At the same time, a thin nanocrystalline layer is formed on the surface which closes the surface tighter and protects against corrosion, while improving the durability and increasing the hardness of the surface in connection with most materials.
Ultrasound can also be used for drilling or, for example, for embossing or welding. The invention is also applicable to other ultrasonic machining than smoothing surfaces.
The aim of the present invention is to provide a more efficient ultrasonic treatment device than the previously known. To achieve this aim, at least two vibration-generating transducers are connected to the ultrasonic treatment device for producing energy of ultrasonic frequency in such a way that the first transformer and the second transformer function at different frequencies or in different vibrational modes. In this way, the speed of the impacts effected by the tool on the piece or the force generated by them can be increased or the directional distribution of the impacts be changed. Moreover, the sensitivity of the tool to the force pressing the tool against the workpiece can be altered by changing the path of the tool without unreasonably increasing the amplitude and the power used for machining.
The invention is described in greater detail in the following, with reference to the accompanying drawings.

Figure 1: shows a diagrammatic view in principle of the components of a known treatment device.
Figure 2: shows the vibrators and the booster of the device according to the invention.

Figure 1 shows diagrammatically a treatment device for which the sonotrode according to the invention is used. The treatment device of Figure 1 comprises a generator 6 which generates, from the three-phase alternating current supplied to it by a supply cable 10, an ultrasonic frequency electric current, which is conducted through cabling 11 to the machining unit 2. The machining unit operates as a transformer transforming the ultrasonic frequency electric current into mechanical movement, which is conducted to the tool 3 arranged in the transformer 2. The tool 3 directs the hammering impact effect on the surface of the workpiece under treatment, through the effect of which the surface of the workpiece becomes smoother and harder. In the transformer 2 are also arranged machining fluid nozzles 4 by means of which the machining fluid jet 5 delivered from the machining fluid supply line 9 through a filter 8 to the transformer is directed at the object being machined. The purpose of the machining fluid supplied to the transformer is to cool the transformer 2 and also to function as a lubricant in the treatment process. The alternating current may also be a one-phase current. In the treatment device is preferably also arranged a remote control 7 for controlling the treatment device. In the transformer 2 is preferably arranged a spring mechanism (not shown), by means of which the machining force exerted by the tool 3 on the workpiece can be regulated. The position of the tool 3 is preferably adjustable and it may be realised in different forms, for example, there may be specific special tools for the treatment of the inner surfaces of holes and/or for the treatment of different materials. The tool is preferably made of hard bit material, such as hard metal, ceramic cutting material and diamonds. Figure 1 does not show the parts comprised by the transformer 2 in detail and the transformer of Figure 2 usually comprises a booster in addition to a piezoelectric or magnetostrictive transformer, the booster acting as a resonator and an impedance matching means. By means of the booster, the ultrasonic power can be supplied more efficiently to the tool. The booster acts as an acoustic transformer matching the impedance of vibration and as a resonator. The booster usually increases the amplitude and speed of vibration.
Figure 2 shows one embodiment of the transformer of the treatment device according to the invention. The device of Figure 2 comprises a first ultrasonic transducer, for example a piezovibrator 21, and a second transducer, for example a piezovibrator 22. The vibration energy generated by the first and second piezovibrators is conveyed via a booster 23 to the possible sonotrode part and the tool 3. The booster 23 is an impedance transformer and a mechanical vibration circuit, which transforms the vibration impedance level of the vibration energy of the first and second vibrators 21, 22 and the amplitude of vibration to suit the intended use. According to another preferred embodiment of the invention, an additional vibrator is integrated to the booster which may further be used in an existing device, such as that shown in Figure 1. The first and second vibrator may be of different types, for example, one may be piezo and the other magnetostrictive.
In the treatment device according to Figure 1, the amplitude is usually increased by means of a booster in order to increase the speed of the impact treating the surface. Another vibrator supplies the booster with, for example, preferably an odd harmonic wave of higher frequency, such as a 3- or 5-fold ultrasonic frequency. An odd harmonic wave is advantageous if the vibrational mode is the same for both vibrations and only one booster adapted to both frequencies is used simultaneously at two frequencies, as shown in Figure 2. In this case, the nodal point of the vibrations of the vibrator 22 producing the higher frequency is at the same point as the lower frequency. Thus the common nodal point of both vibrations acts as a low-loss suspension point 23a of the booster and the booster resonates simultaneously at the frequency of both vibrators. If the second vibrator 22 produces a 3-fold frequency and the vibration maximum of both vibrators 21 and 22 meets the tool-side end of the booster, and the only node of the standing wave produced by the first vibrator 21 is at the attachment point 23a of the booster, one additional node is produced at the vibrator's 22 frequency and an antinode between the booster's tool-side end and suspension point 23a. The advantage of the second vibrator according to the present invention, which uses an odd harmonic wave frequency, is that the second vibrator 22 can be added to the apparatus even afterwards with relatively small alterations. By means of the sum of odd harmonic waves, an almost triangular wave can be produced in the tool, whereupon the speed of the tool is almost constant for a large part of the vibration cycle. Thus, the speed of the impact of the tool is not so highly dependent on the moment of impact and the dependency of the impact on the force pressing the tool against the object being machined decreases.
The second vibrator may also be fitted elsewhere than in connection with the booster, as shown in Figure 2. The second vibrator may be fitted, for example, in connection with the fixing means of the booster tuned to the first frequency or in connection with a resonator arranged at a different point in the booster and tuned to the frequency of the second vibrator. The second vibrator fitted to the fixing means may thus be connected by means of a second booster, that is, a tuned vibrator, to the fixing point at the zero position of the first frequency. Low-loss suspension is thus obtained at the frequency of the first vibrator, and energy produced by the first vibrator is not connected to the second vibrator, because the fixing point is at the nodal point of the standing wave produced by the first vibrator. Through the first zero position of vibration can, therefore, also be connected second vibration to the booster, which produces a non-odd harmonic wave, by using a second vibrator tuned to a second vibration frequency. In this case, it is preferable to use, for example, the even harmonic frequency of the first vibrator as the frequency of the second vibrator and the resonator connected to it, whereupon the zero position of the frequency of the first vibrator and the antinode of the frequency of the second vibrator meet at the fixing point. In this case it is possible to dimension the booster in such a way that both frequencies form resonating standing waves in the booster.
Should one of the vibrators operate in a different vibration mode, for example, the second vibrator producing transverse vibration or rotary vibration and the first vibrator producing longitudinal tool-impacting vibration, the propagation speed of the vibrations in the booster and the sonotrode is usually different for different vibration modes. In such a case, the resonance frequencies are generally not each others' multiples and vibrations producing standing waves of equal length are of different frequencies. Different vibration modes include, for example, longitudinal waves, transverse vibration and a circulating waveform. When several vibration modes are used for machining, the distribution and direction of the impacts produced by the tool become variable. Thus, impacts deviating from the perpendicular are directed on the surface or piece. Due to them, the properties of the nanocrystalline layer formed on the surface during ultrasonic hammering can be adjusted and improved, for example, by changing the amplitude of the vibrators producing a sweeping and perpendicular impact component.
Also in material-removing machining, for example, in machining embossing in graphite or in drilling, a combination of two vibration directions may preferably be used.
According to the first preferred embodiment, the sonotrode and the booster are thus dimensioned in such a way that the standing wave maximum, or antinode, of both frequencies is at the cutter head and the zero or nodal points of the standing waves are at the fixing point of the booster, whereupon the dissipation power leaking to the fastening is minimised and the structure is simple. For example, the zero point of a threefold frequency matches the zero point of the booster's main frequency which normally acts as the booster's suspension point. The zero points of also other higher odd harmonic frequencies are at the same point as the main frequency, when the maximum is at the end of the vibrator. 1-, 3- and 5-fold frequencies operating in the same mode thus produce common zero points with a 1-fold frequency and higher frequencies in addition produce other zero points. Thus, for example, 20 kHz, 60 kHz and 100 kHz longitudinal waves may be in resonance in the same booster at the same time and they have at least one common nodal point. Should only 60 kHz and 100 kHz vibrators be used, the impact frequency may still be 20 kHz, because the sum waveform envelope has a 20 kHz component. In this case, both vibrators are connected to the booster's primary side, at the antinode point of the standing wave of its respective frequency. In this case, too, the vibration of the first vibrator passes through the second vibrator, but it is possible to decrease the connection between the vibrators by selecting the frequencies in such a way that the antinode points are not on top of each other.
According to a second preferred embodiment, the booster, that is, the first resonator, is connected at the nodal point of the first vibration in series with the second vibration resonator. The second vibration may, however, also be connected elsewhere to a suitable point, in which case the connection changes the operation of the booster and the resonance frequency. The second resonator may preferably operate at a lower frequency than the first resonator, in which case the first resonator acts as a part of the second resonator. In a booster operating at the frequency of the first resonator, there is no standing wave at the frequency of the second resonator, but the second resonator is only tuned when the first resonator is a part of a resonance circuit operating at the frequency of the second vibrator.
If the second resonator operates at a higher frequency than the first resonator, it is preferable to use an even harmonic frequency, in which case there is an antinode at the suspension point at the frequency of the second resonator and a zero point at the frequency of the first resonator.
By connecting the boosters in series at their zero points in the manner described above, the mutual coupling of the vibrators becomes smaller than in the first embodiment. The structure is, however, usually more complex than in the example of Figure 2 and the retrofitting of a second vibrator is not as easy to carry out.
Different connecting systems may be combined and also used simultaneously for more than two vibrators. If two different vibration modes are used simultaneously, the propagation speeds of the vibrations of the different modes generally differ from one another and the frequencies of the waves in resonance are not divisible by one another in the resonator. In such a case, the frequencies are dimensioned so that a standing wave is formed for each vibration mode desired.
In addition to suspension by means of a second resonator, it is also possible to use other types of flexible and low-loss suspension, which do not dampen the vibration of either resonator, even if they were connected elsewhere than to the node of the standing wave. Solutions based, for example, on springs, gas pressure or magnetic suspension may be used. A mass vibrating with flexible suspension always slightly changes the resonance frequency of the vibrator, and magnetic suspension also causes electromagnetic radiation. Magnetic suspension must be constructed in such a way that losses are small at the operating frequency. In practice, the eddy currents and hysteresis losses must be made small at the operating frequency. The ultrasonic frequency is reasonable for many magnetic materials, and suspension may also be used in electrical resonance, and magnetic suspension may also be used for supplying mechanical power to the resonator. By means of liquid or gas flow can be produced low-loss bearings, which allow for low-friction coplanar impacting or rotary movement in two coplanar directions. In this case, a force pressing the tool may be generated, for example, magnetically or pneumatically. The advantage of this suspension method is that resonators may be connected more freely at the suitable points in the booster or resonator without regard to the locations of the nodal points. A piezoelectric vibrator requires a power supply, whereupon the electric conductors may bring about vibration losses in connection with suspension. A magnetostrictive vibrator is usually biased by mechanical stress and/or by a permanent magnetic field. The suspension of the tool must be carried out in such a way that external factors will not impair the operation of the vibrator.
The vibrators may be, for example, piezoelectric or magnetostrictive. The most common vibrator used in the field is a piezoelectric element, the efficiency and durability of which are good.
In addition to smoothing surfaces, the device and method according to the invention may be used, for example, for ultrasonic drilling or ultrasonic machining, for example for embossing a machined surface. Also in these applications it may be advantageous to combine two different vibration modes.
The peening tool according to the invention is preferably provided with fixing means allowing lathe attachment and it may be equipped with, for example, taper shank means, by means of which it may also be fixed, for example, to a milling machine or a machining centre or other similar machining device instead of to a lathe.

Claims

A treatment device for treating a workpiece by means of a vibrating movement, the device comprising a first vibrator (21) and a means (23) connected to it which transfers the vibration or changes the vibration impedance for directing the vibration to the tool (3) treating the workpiece, characterised in that the device comprises at least one other vibrator (22) which produces to the said means (23) an odd harmonic wave of higher frequency than the first vibrator (21).
A treatment device as claimed in claim 1, which comprises a booster or sonotrode means (22, 23) including a second vibrator (22).
A treatment device as claimed in claim 1 or 2, characterised in that the impact frequency of the tool (3) of the treatment device on the piece being machined is lower or equal to the operating frequency of the first and second vibrator (21, 22).
A treatment device as claimed in claim 3, characterised in that the vibration produced by the first (21) and second vibrator (22) is essentially perpendicular to the piece being treated.
A treatment device as claimed in claim 4, characterised in that the operating frequency of at least one vibrator is the odd multiple of the impact frequency of the tool .
A treatment device as claimed in any of the claims 1 to 3, wherein the vibration modes of the first and at least one other vibrator differ from one another.
A treatment device as claimed in any of the claims 1 to 6, characterised in that the treatment device is an ultrapeening device (1) for treating surfaces.
A treatment device as claimed in any of the claims 1 to 6, characterised in that the treatment device is an embossing device or a drill.
An ultrasonic treatment device as claimed in claim 1, characterised in that the device comprises two interconnected resonators acting as boosters and the vibrators supplying them.
A booster or sonotrode vibrating at ultrasonic frequency to be used in an ultrasonic treatment device comprising an ultrasonic vibrator, characterised in that the booster or the sonotrode comprises a second ultrasonic vibrator producing an odd harmonic wave of higher frequency than the first vibrator.
A method for treating a piece by using ultrasound, characterised in that in the method are used two vibrators (21, 23) of different frequencies connected to a means (23) which transfers the vibration or changes the vibration impedance for directing the vibration to a tool (3) treating the piece, the second vibrator (22) producing an odd harmonic wave of higher frequency than the first vibrator (21).