Criteria design of optimalization ultrasonic concentrators.

Pechacek, Ffrantisek ; Charbulova, Marcela ; Javorova, Angela 等

1. INTRODUCTION

Technology of ultrasonic machining requires use of ultrasonic tool resonator, which is the part of ultrasonic resonant system.

Term of ultrasonic system in machining includes whole set of components and parts, which are needed for realization, whereby those parts are energetic and mechanically connected. Ultrasonic system in machining performs transfer of incoming electric energy to outgoing mechanical energy of the tool, or to oscillating movement of the tool.

Ultrasonic resonant system consists of:

* ultrasonic transducer,

* ultrasonic concentrator,

* waveguide.

2. ULTRASONIC RESONANT SYSTEM PARTS CHARACTERISTICS

2.1 Ultrasonic transducer

Transducer is transforms electric energy of the generator to mechanical ultrasonic energy. Transducer generates harmonic deviation in longitudinal direction, as surface source of forced mechanical oscillation for ultrasonic resonant system.

In engineering praxis are used mostly piezoceramic transducers, which have lesser dimensions, larger use variability and higher efficiency and power stability, than magnetostrictive transducers. On the fig. 1 are schemes of piezoelectric ultrasonic transducers (a--symmetric arrangment of transducer's piezoceramics, b--asymmetric arrangment). They are characterized by lower material cost, undemanding technology of manufacturing and simplicity of design for various frequencies in used wave-length.

Nowadays all of the important manufacturers offer ultrasonic transducer on the basis of piezoceramic materials, where the transformation of the electric energy to mechanical energy depends on piezoelectric properties of the materials.

For power applications is necessary, that transducers transforms the energy under high deformations. By this reason must the piezoceramics have high toughness, quality and good piezoelectric properties. In term of process efficiency is necessary, that transducers are characterized by low electric losses under high electric intensities (Mankova, 2000).

[FIGURE 1 OMITTED]

2.2 Ultrasonic concentrator

The most important property within ultrasonic resonant system, has the concentrator, whose task is concentration of mechanical oscillation energy on outgoing front, what makes the harmonic deviation stronger.

Among basic shapes of resonators belong circular resonators with following shapes: conic, exponential, catenoid, gradual. Besides those basic types we recognize combined resonators, which are combination of basic shapes. (e.g. conic--cylindrical, exponential--cylindrical, cylindrical--exponential--cylindrical etc.)

Important properties of resonators in ultrasonic resonant system are: amplitude of voltage course, amplitude of mechanical deviation course, amplitude of voltage peak, node plane placement etc.

For achievement of required results in ultrasonic machining, must be the resonator, transducer and other parts of system in frequency tune (Dillinger et al., 1997).

2.3 Waveguide

Waveguide is special example of ultrasonic concentrator with zero amplification of amplitude of mechanical deviation, with constant profile of the intersection. On the fig.2 is scheme of the ultrasonic waveguide. Major task of the waveguide is lengthening of ultrasonic resonant system. From several interesting and used properties in engineering praxis is for example clear definition of node plane and amplitude of voltage peak, which is used for safe and clear gripping of the whole resonant system in technological application (Mankova, 2000).

[FIGURE 2 OMITTED]

3. OPTIMIZATION CRITERIA DESIGN

Optimization of ultrasonic tool resonators presents primarily achievement of required amplification of deviation amplitude, and not exceed allowed endurance strength, which depends on the material of the resonator. Important element of the optimization is choice of the material with good mechanical a physical properties, which depends on application. In choosing of the material is required to make provision for energy loss factor, endurance strength, abrasion resistance, machinability, availability and price.

To resonator optimization is required to know relations and patterns of calculation of particular types of resonators, but is also necessary to make provision for knowledge and results from the praxis (Tolnay, et al., 2000)..

According to that, practical criteria design is:

* Calculation of required values of particular parameters by means of known patterns for ultrasonic resonators calculation and substitution of the specific values.

* Comparison of calculated values and knowledge from praxis, to designation of advantages and disadvantages.

* Choosing the resonator for required application of ultrasonic machining.

Materials, which are used in ultrasonic tool resonators must have good mechanical properties, characterized by energy loss factor and longitudinal speed of wave propagation (Wilk &Tota, 2007).

Input parameters for resonator calculation without technological load:

* Amplitude of input harmonic deviation of the resonant system--[u.sub.x].

* Modulus of elasticity of concentrator material--E.

* Resonant frequency of the concentrator--f.

* Density of material of the concentrator--[rho].

* Dimensions of input and output diameter of the concentrator--[D.sub.1] and [D.sub.2].

* Function parameters of the geometric representation of the concentrator--S.

Besides of that, to calculation of the concentrator with technological load:

* Values and course of the technological load.

Output parameters of the concentrator without technological load:

* Placement of node plane on the concentrator.

* Placement of maximum amplitude of voltage on the concentrator.

* Value of the maximum amplitude of voltage on the concentrator.

* Acoustic amplification on the concentrator.

* Resonance length of the concentrator--l.

* Course of deviation amplitude on the whole length of the concentrator.

* Course of voltage amplitude on the whole length of the concentrator.

Besides of that outputs we use for concentrators with technological load:

* Formulation of single vibration work.

* Formulation of delivered technological input of the technological application process.

For achievement of equable distribution of mechanical tension along the axis and for larger amplification are used combined resonators. Those are combined of several parts of constant and variant intersection, whereby the basic shapes are used in combination.

Special solutions of the ultrasonic resonant system are combinations of the three basic parts, transducer, concentrator and waveguide integrated to one unit. By this design, the length of the ultrasonic resonator is reduced and there is a possibility to reduce spatial demandingness (Melo et al., 1997).

4. CONCLUSION

From calculated values, crafted graphic relations for particular shapes, data form literature and information form praxis is possible to evaluate the shapes of resonators for ultrasonic machining. In choosing of optimal concentrator shape is necessary to consider all advantages and disadvantages and choose the most favorable resonator for particular ultrasonic application. Way of designing and optimization of the ultrasonic resonators by means of mathematical patterns and graphic relations is suitable only for basic shapes of resonators. This way is not accurate for designing of combined resonators and is very work-intensive as well. More suitable is to use a software, which is designed for this task.

This paper was created thanks to the national grants: VEGA 1/009/08 Optimalized systems and processes of performance ultrasound

5. REFERENCES

Dillinger, J.; Tolnay, M. & Mihalcak, P. (1997). Rezonancne systemy priecnej transformacie vykonoveho ultrazvuku (Rezonance systems of cross transformation of power ultrasound.), Proceedings of Zbornik inzinierstvo 1997, SjF STU Bratislava, 1997, Strojnicka fakulta STU, Bratislava

Mankova, I. (2000). Progreslvne metody obrdbania. (Progresive methods of machining), Vienala, ISBN 80-7099-430, Kosice

Melo, S.; Bigos J. & Mihalcak, P. (1997). Analyza a optimalizacia ultrazvukovych koncentratorov. (Analysis and optimation of ultrasonic concentrators) Proceedings of Zbornik vedeckych prac 1997, pp. 105-121, MtF STU Trnava, 1997, Strojnicka fakulta STU, Bratislava

Tolnay, M.; Gregus--Kollar, J. & Mihalcak, P. (2000). Konstrukcia nastrojov pre ultrazvukove obrabanie. (Ultrasonic tool design) Proceedings of Zbornik Naradie 2000, pp. 185-188, Trencin, 2000, SOPK, Trencin

Wilk, W. & Tota, J. (2007). Modern ultrasonic machines in shaping of materials. Proceedings of Zbornik International Congress on Precision Machining 2007, pp. 314-320, 2007, Praha