directed on search ways raise of strength a welded joint are executed. .... Use of a welding method «on the fixed settlement» assumes the certain deformation of ...
1 MEASUREMENT PARAMETERS OF ULTRASONIC OSCILLATORY SYSTEM DURING WELDING THERMOPLASTICS
Measurement Parameters of Ultrasonic Oscillatory System during Welding Thermoplastics Alexey N.Slivin, Alexey D. Abramov, Denis S.Abramenko, Student Member, IEEE Biysk Technological Institute (branch) of Altay State Technical University after I.I. Polzunov, Biysk, Russia Abstract - In the article the basic problems interfering evolution of automatic-control systems by process ultrasonic welding are analysed, measurements electric parameters of ultrasonic oscillatory system during welding thermoplastics, directed on search ways raise of strength a welded joint are executed.
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I. INTRODUCTION
LTRASONIC welding in modern conditions of manufacture allows to solve many problems connected with reception of the qualitative joint of any thermoplastic materials. Ultrasonic welding, in most cases in practice has successfully replaced thermal, highfrequency, frictional and other known ways of welding [1]. Wide application of ultrasonic welding speaks that at sampling optimum production engineering and the necessary equipment development engineers and industrial engineers are based on widely known advantages and advantages of ultrasonic welding [5]: 1. An opportunity to carry out welding at temperatures smaller temperatures of smelting welded thermoplastic materials. 2. High quality of a welded joint. 3. An opportunity to carry out welding without preliminary clearing welded surfaces of various pollution. 4. Exclusion of excessive heating welded thermoplastic materials, through local allocation of heat in a weld zone. 5. To get a welded joint thermoplastic materials at welding at a great distance from a point of feeding into of energy that allows to carry out joints in remote places. 6. Absence of auxiliary glutinous components. 7. Durability of a welded joint to dissolvents, etc.
Listed above advantage of ultrasonic welding have led to that at creation of new materials and products there is no any more a question on sampling a way of their welding. However, there is a some of problems which are connected with automation process of ultrasonic welding. Thus the main problem is definition of a time interval of the ultrasonic affecting necessary for formation a welded joint in thermoplastic polymeric materials.
The basic purpose now is development of automatic ways of welding and improvement of quality of a welded joint of products from thermoplastic polymeric materials. II. PRODUCTION OF THE PROBLEM During ultrasonic welding properties thermoplastic materials (there is a softening and transition in a is viscous-plastic condition) as a result of sorbtion of energy of ultrasonic oscillations change. It leads to decrease welding force, to warming up oscillatory system that cause decrease of its Q-factor and to an error signal of the oscillatory circuit. As a result, the resonant frequency and an amplitude of oscillation of ultrasonic oscillatory system (UOS) changes [1,4]. As a result of these destabilizing factors stability of a process of ultrasonic welding and reception of a qualitative welded joint gets special value. Change of following parameters is usually made for reception of a qualitative welded joint thermoplastic materials at ultrasonic welding: amplitudes oscillation of radiating surface UOS, magnitudes welding force and durations of ultrasonic affecting. The variation in last parameter has gained most a wide circulation. At the automated ultrasonic welding limitation of a time ultrasonic affecting is carried out by next ways: 1. Method «on the fixed time» assumes use of ultrasonic affecting of constant duration at welding the same products. Duration of ultrasonic affecting is from preliminary experiments and is set on all weld cycles equal, is usual by means of the electronic time relay [1]. 2. Method «on the fixed settlement» at which magnitude of deepening UOS in a welded detail or deformation of a weld zone is saved by constant. At achievement of the set deformation there is an automatic termination of ultrasonic affecting and restriction of moving UOS. Duration of a time of welding at this method in each separate case can be various [8,11,14]. 3. Method «under the kinetic characteristic» at which is installed interconnection between an amplitude oscillation of working end face UOS and change of properties thermoplastic materials as a result sorbtion of energy ultrasonic oscillations [9, 10, 12, 13]. Duration of ultrasonic affecting proceeds till the moment of equality
2 MEASUREMENT PARAMETERS OF ULTRASONIC OSCILLATORY SYSTEM DURING WELDING THERMOPLASTICS of voltages and currents flowing through UOS with a reference quantity certain by practical consideration. At use of the circuit diagram of welding «on the fixed time» the probability formation of a poor-quality welded joint is defined by following parameters: 1. Instability of a resonant frequency and amplitude of oscillation UOS; 2. Deviation of initial thickness of welded materials from optimum; 3. Instability of weld conditions (temperature of a waveguide and magnitude welding force). 4. Impurity of welded surfaces. Not large changes of parameters of a welding regime, geometry of details and properties of materials can lead to that the demanded time of welding will appear more or less time installed by the relay. Thus in the first case will be observed skin weld, in second - burn weld. It instability of the results gained at welding on the fixed time speaks. Improvement of quality in this case are aimed to attain due to maintenance of a constancy of parameters of a welding regime, however it considerably complicates a design of the equipment. Unlike the circuit diagram of welding «on the fixed time» at which sampling of duration of a welding time is not connected absolutely not with education of a welded joint, the circuit design of welding «on the fixed settlement» is partially connected with kinetics of education of a welded joint. In this case the probability of implementation of a poor-quality welded joint is defined by instability of initial thickness of welded materials. Use of a welding method «on the fixed settlement» assumes the certain deformation of a zone of a seam, that sometimes happens is inadmissible owing to a decline of a packaging of a product. The basic deficiencies of a way of management process of ultrasonic welding («on the fixed settlement») [8,11,14] is necessity of recustomizing of the equipment for realization of welded joints from various on properties and thickness of materials, and also presence of various sensors (end switch, optical, end-of-stroke sensors). At ultrasonic welding with a batching of energy under the kinetic characteristic the information on a physicomechanical condition of welded materials is used [1]. During ultrasonic welding there is a softening and transition of a material in a plastic condition, magnitude of a static compression pressure changes. Therefore the square of contact of a welded material and welding tool UOS changes. There is a change of an amplitude of oscillation of oscillatory system and as consequence change of a current, a voltage, a phase angle between them, the power consumed UOS during welding. The publications of authors [6,7,9,10,12] connected with measurements on the electric side of the generator of voltages and currents flowing through UOS, matching speed or amplitude of ultrasonic oscillations in a material, to a sign on a speed-up of a straining [8,11,14] materials under a waveguide and the high-frequency energy [12]
consumed UOS are known. In the specified ways measurement of the signal proportional to an amplitude of oscillation and management of process of welding make by comparison of signals with a reference quantity. Thus a batching of energy carry out with high repeatability of process. The basic deficiencies of these ways of management is that the offered criterion of definition of transition of a material in a plastic condition during ultrasonic welding is not to constants. Application of big static pressures during ultrasonic welding lead to a damping of working tool UOS, decrease of an amplitude of oscillation and impossibility of the control of process ultrasonic welding. Besides during welding there is a nonlinear change properties of polymeric materials, heating UOS, decrease of its resonant frequency and an amplitude of oscillation during welding. Because any of ways of management used now process of ultrasonic welding to the full does not consider change of parameters UOS, it is necessary to solve following problems: 1. To execute measurements of electric parameters UOS during ultrasonic welding. 2. To define the effect, changing properties of welded materials on parameters UOS. 3. To research effect welding pressure on electric parameters UOS.
III. RESULTS OF MEASUREMENT OF ELECTRIC PARAMETERS UOS DURING WELDING At research of process of ultrasonic welding it was used UOS for welding thermoplastic, operating at a frequency of 22 kHz, polypropylene weld specimens by thickness of 1,1 mm, lapped combined. The measuring complex is developed for measurement of electric parameters UOS during ultrasonic welding. In figure 1 the block diagram of the measuring complex of electric parameters UOS is presented. The measuring complex is connected to a diagnostic connector of the ultrasonic generator, and as in "rupture" of a cable of UOS. Such connection provides an
foс, foп Generator
U, I, f, ϕ (I,U)
Measuring complex
U, I, f, ϕ (I,U)
UOS
Control Control
Data
Computer Fig. 1. Block diagram of measurement of parameters UOS.
opportunity of measurement of parameters following signals:
3 MEASUREMENT PARAMETERS OF ULTRASONIC OSCILLATORY SYSTEM DURING WELDING THERMOPLASTICS 1. Signal of basic frequency from the setting generator sets working frequency UOS. 2. Feedback signal. Primary transformation of a signal is carried out by the internal circuit diagram of the generator. This signal is used in system of Automatic Frequency control (AFC). 3. Voltage on oscillatory system. 4. Strength of current on oscillatory system.
ϕ (U,Os)
ϕ (I,U) U I
0 0
t, s
1
Fig. 2. Electric parameters UOS during welding without taking into account effect of properties of materials (radiation in air).
ϕ (U,Os)
U I ϕ (I,U)
ϕ (U,Op) 0
0
Phase 1
Phase 2
Phase 3
1
t, s
Fig. 3. Electric parameters UOS during welding at constant pressure. Ι 5 kg 0 kg 8 kg
10 kg
15 kg
0 1
t, s
Fig. 4. Dependence of amplitude of the current flowing through piezoceramic elements UOS during welding at various weld pressure.
By means of these signals it is possible to compute following parameters UOS: 1. Value of a voltage on oscillatory system.
4 MEASUREMENT PARAMETERS OF ULTRASONIC OSCILLATORY SYSTEM DURING WELDING THERMOPLASTICS 2. Value of a current on oscillatory system. 3. Oscilation frequency UOS. 4. A phase difference of a voltage and a current on oscillatory system. 5. A phase difference between two any periodic signals (from the basic generator, a feedback, a current or a voltage on oscillatory system). For management of job of the measuring complex and as recordings and processings of the measured information the personal computer is used. Communication is carried out by means of protocol RS232. During ultrasonic welding continuous measurement of amplitude current of mechanical branch UOS I, amplitudes of electric voltage U, a phase angle between a voltage and current φ(I, U), a phase angle between a voltage on oscillatory system and feedback signal φ(I, Os), a phase angle between a voltage and a signal basic frequencies φ(I, Op) was made (figure 2). In figure 2 dependences of electric parameters UOS at an absent material are presented (radiation to air). During welding at an absent material value of current I, voltage U and phase angles φ (I, U), φ (I, Op), φ (I, Os) are saved by constants during all period of ultrasonic affecting. In this case parameters UOS remain to constants, because of absence of effect on oscillatory system, changing properties of a welded material during welding. Dependences presented in figure 3 illustrate effect of changing properties of a welded material in a weld zone (a softening of a polymeric material and transition in a is viscous-plastic condition) on electric parameters oscillatory system. There is a change of following magnitudes: I, U, φ(I, U), φ(I, Os) and φ(I,Op). From dependences presented in figure 3 follows that process of welding can be broken into 3 stages: 1. Change of a welded material from a solid condition in is viscous-plastic. At this stage there is a decrease of value of current I and voltage U on oscillatory system, increase in a phase angle between a voltage and a current φ(I,U), and values of phase angles φ(I,Os) and φ(I,Op) remain practically constant. 2. The Is viscous-plastic condition. At this stage there is maximum damping oscillatory system. Values of current I and voltage U attain the minimal value, and magnitude of a phase angle between a voltage and a current φ(I,U) o n oscillatory system attains the maximum value. 3. Change of a welded material from a is viscousplastic condition in is viscous-fluid. At this stage there is an intensive smelting a material in a weld zone. Excesses of the fused material start to be extruded from a weld zone that reduces welding pressure on oscillatory system. There is an increase in value of current I and voltage U on oscillatory system, decrease of a phase angle between a voltage and current φ(I, U).
One of key parameters of ultrasonic welding is welding pressure. In figure 4 some dependences of the current flowing through piezoceramic elements oscillatory system at welding of equal specimens on thickness from polypropylene at changing welding pressure on a material are presented. From the presented dependences follows, that, at welding equal specimens on thickness, curves of a current can differ essentially from each other. It is connected, first of all, with various force of welding pressures on welded materials, both during the initial moment, and during all process of welding. Carried out researches have shown, that at effect of big welding pressures there is strong damping UOS owing to what it is not formed a qualitative welded joint. On the other hand at small welding pressure also it is not formed a qualitative welded joint, owing to insufficient energy forwarded in a weld zone. Thus, for implementation of the qualitative joint of materials it is necessary to expel effect of instability welding pressures at ultrasonic welding, i.e. to expel distortions of curves of a current. From the gained results necessity of search optimum welding pressures during ultrasonic welding follows. The further jobs will be directed on search of optimum parameters of ultrasonic welding thermoplastic materials. IV. CONCLUSION As a result of the spent researches have been solved following individual problems: 1. Measurements of electric parameters UOS during ultrasonic welding are carried out; 2. Effect, changing properties of welded materials on parameters UOS is determine; 3. Eeffect welding pressures on electric parameters UOS Is researched; 4. Optimum regimes for implementation of ultrasonic welding with the maximum effect are installed. 5. Criteria of automatic determination of optimum regimes of ultrasonic welding of various materials in various conditions are determined.
REFERENCES [1] Volkov S.S., Cherniak B.J. Welding of plastic using ultrasound, Chemistry. [2] Volkov S.S., Orlov U.N., Astahova R.N. Welding and agglutination of plastic. М., «Machinery», 1972, 128 с . [3] Zaysev K.I., Matsuk L.N. Welding plastic. М., «Machinery», 1978. [4] Holopov JU.V. Ultrasonic welding of plastic and metals. "Mechanical engineering", 1988. [5] Khmelev V.N., Slivin A.N., Barsukov R.V., Tsyganok S.N., Savin I.I., Shalunov A.V., Levin S.V., Abramov A.D. "Development of the New
5 MEASUREMENT PARAMETERS OF ULTRASONIC OSCILLATORY SYSTEM DURING WELDING THERMOPLASTICS Principle of Batching of Energy at Ultrasonic Welding and Creation of the Equipment for Connection of Thermoplastic Materials", Intrnational Workshops and Tutorials on Electron Devices and Materials EDM'2006: Workshop Proceedings. Novosibirsk: NSTU, 2006. [6] Patent the USSR №1315341 Control mode of a ultrasonic welding. [7] Patent the USSR №1627413 Control mode of a ultrasonic welding. [8] Patent the USSR №176381 Device for ultrasound welding plastic. [9] Patent the USSR №550225 Device of a proportioning of energy at a ultrasonic welding. [10] Patent the USSR №719835 Way of management of process of a ultrasonic welding. [11] Patent the USSR №753664 Device for ultrasonic welding plastic. / Cherniak B.J., Bokov V.A., Lyashko F.E, Zvezdin G.A., Tizengauzen А.М.. [12] Patent the USSR №996140 Control mode of a ultrasonic welding / Kozich А.А.. [13] RU, patent, 2220917 kl. В 29с 65/08. Method of ultrasound welding thermoplastic / Lyashko F.E., Sokolova O.F. [14] RU, patent, 2229382 kl. В 29 С 65/08. Method of ultrasound welding thermoplastic / Lyashko F.E., Sokolova O.F. [15] RU, patent, 2247544 kl. A 61 B 18/00. A mode of steering of process ultrasonic liposaction / Khmelev V.N., Barsukov R.V., Tsyganok S.N., Slivin A.N., Rascals А.В. Alexey N Slivin was born in Biysk, Russia, 1976 He received degree on information measuring engineering and technologies from Altay State Technical University, key specialist of electronics. His main research interest are development of high-power electronic generators for ultrasonic technological welding.
Alexey D. Abramov was born in Biysk, Russia, 1984. Post graduated student of BTI. He is received engineer’s degree from BTI AltSTU at 2006. IEEE Student Member. His main research interest are development of high-power electronic generators for ultrasonic technological welding.
Denis S. Abramenko – post graduated student of BTI. He is received engineer’s degree from BTI AltSTU at 2005. IEEE Student Member.
