SU1744635A1 - Method of non-destructive testing of welded joints - Google Patents

Abstract

This invention relates to control technology and ultrasonic welding. The purpose of the invention is to improve the accuracy of control of the strength of the welded joint. According to the method, two signals are measured during welding: a current transducer and a voltage of the probe pulse generator. The dependence of the ratio of their values is recorded. The strength of the trial is based on the difference in the value of the obtained dependence at the end of welding and the extremum of this dependence. 2 Il.

Description

The invention relates to ultrasonic welding and can be used for real-time non-destructive testing of shear strength of welds made by ultrasonic welding.

Known methods of non-destructive testing of welded joints; electromagnetic, blown gas jet under pressure, X-ray television, ultrasound resonance, infrared radiometry, photoacoustic, etc.

The disadvantage of these methods is the great complexity of the apparatus for their implementation, which makes it difficult to use them directly on the welding machine, in some cases an additional effect on the already formed joint, the inability to obtain information in real time, during the welding process.

The closest to the invention is a method of non-destructive testing of the strength of welded joints, according to which a signal proportional to the amplitude of oscillations of an ultrasonic transducer is memorized when excited by a welding pulse at idle, a feedback signal is obtained that is proportional to the amplitude of vibrations of the ultrasonic transducer during welding, and form a difference signal by subtracting from the memorized signal proportional to the amplitude of the ultrasonic transducer zovatel in idle signal proportional to the amplitude of the ultrasound transducer during welding oscillation.

The resulting difference signal is used to evaluate the strength of the joints.

The disadvantage of this method is low control accuracy, due to the fact that

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This differential signal is influenced by a number of factors: the output impedance of the ultrasonic generator, the excitation voltage of the ultrasonic transducer, the initial conditions in the welding zone, the amount of deformation of the connected parts at the moment the tool of the ultrasonic converter leaves the welding position and the amount of compressive force of the connected parts,

The aim of the invention is to improve the accuracy of control,

This is achieved by the fact that in the method of controlling welded joints during welding, the product is probed by means of series-connected generator and ultrasonic converter, and the current value of the ultrasonic converter is measured, taking into account the strength of the welded connections, the dependence of the current ratio of the ultrasonic converter and the value generator excitation voltage from welding time, and the strength of a welded joint is judged by the difference between the extremum of this dependence and its point corresponding to the end of the weld.

FIG. Figure 1a shows the character of the change of the ratio signal during welding when the first feedback signal is divided by the second (curve 1) and the difference signal corresponding to the atom (curve 2); Fig. 16 shows the ratio signal from dividing the second feedback signal by the first (curve 3) and the difference signal corresponding to this (curve 4); FIG. 2 is a simplified equivalent circuit of the input circuit of an ultrasonic transducer.

The method is carried out as follows.

The theoretical basis of the method. To clarify the physical essence of the method, we turn to the simplified equivalent circuit of the input circuit of the ultrasonic transducer (see Fig. 2) when it is excited at the resonance frequency. This scheme was obtained by the electromechanical analogy method of force – voltage, oscillatory speed – current, neglecting radiation losses into air, and an acoustic separation node and nonlinear effects when converting electrical energy into mechanical energy. FIG. 2 is indicated: Ur is the amplitude of the voltage driving the ultrasonic transducer;

i is the amplitude of the current in the input circuit of the ultrasonic transducer;

R is the inherent impedance of the loss converter (resonant impedance0

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0

ultrasonic transducer in idle);

g - loss resistance in the weld zone (insertion resistance);

U is the amplitude of the voltage drop across the resistance (analogous to the force of resistance to movement of the tool).

Based on Ohm's law, U M if i const with, i.e. if the current in the input circuit is stabilized or the oscillating speed of the ultrasonic transducer, then

U gs g, (1)

those. the force of resistance to movement of the instrument is proportional to

If Ur is const with, i.e. excitation voltage is stabilized, then

U - Ur. g - sgo

  R + r1W

those. tool drag force is proportional

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0

five

0

five

five

g

I const

3 (YY „)

I const

R + r1

Since the value of r at the beginning of the welding process contains information about the initial state of the joined parts (initial deformation, loading force, initial state of the surfaces of the joined parts), then to form a signal S proportional to the strength of the joint per cut, it is necessary to subtract:

U- UH С (Г- ГН) (I -const

 c (r-rH) R ™ (fTf g))

where UH, nG are the corresponding parameters characterizing the initial state in the welding zone. From where

(Mr Mr) I

(K + rKR + J U const (3)

The main idea of the proposed method consists in forming the signal S in accordance with the expression (3), unlike the prototype method, which works according to the expression (2), which causes its low strength, and when stabilized, the prototype method does not work at all.

The essence of the method is as follows.

The prototype method and the proposed method work only when the ultrasonic transducer is excited at the resonance frequency. According to the proposed method for controlling the strength of the joint during welding tc (Fig. 1), a first feedback signal Ui is obtained, which is proportional to the oscillatory speed of the ultrasonic transducer. It is possible to receive the indicated signal, for the sensor, in the input

An ultrasonic transducer circuit, for example, based on a current transformer connected in series with an ultrasonic transducer, or with a special sensor of the vibrational speed of the ultrasonic transducer.

After receiving the first feedback signal Ui, a second feedback signal U2 is obtained, proportional to the voltage driving the ultrasonic transducer during welding.

Then, by arithmetic division, the ratio of the received feedback signals is determined, and the ratio signal is generated from the obtained value. When determining the value of the ratio, it is necessary to establish an unambiguous correspondence between the mode of operation of the ultrasonic generator and ultrasonic transducer and the purpose of the dividend and the divisor. If the ultrasonic generator-ultrasonic converter system operates in the stabilization mode of the oscillatory velocity or current in the input circuit of the ultrasonic transducer, it is necessary to determine the ratio of the second feedback signal Da to the first Ui - Ite / lb h to form the ratio n; 1 gear zonal resonant resistance of the input circuit of the ultrasonic transducer.

If the ultrasonic generator — an ultrasonic generator system — the converter works in the stabilization mode of the excitation voltage of the ultrasonic converter, then it is necessary to determine the ratio of the first feedback signal Ui to the second Ua - Ui / U2 and form, therefore, the ratio signal proportional to the resonant conductivity of the input circuit of the ultrasonic transducer.

After that, the extreme value of the generated signal is determined. For the mode of stabilization of the oscillatory velocity or current, this will be the minimum, for the mode of stabilization of the same, the maximum (see Fig. 1a and Fmg. 16, respectively). The specified extreme value will be the very original value in which c. Information on the initial conditions of welding. -j jЈ lc at the site At (ck fig 1), oo..n) py / ke1 / w lekum, neo6 /; c- for the end of the pen. ..- x processes in the auto-stand-up system of the ultrasound 1 transform, triggered by the t-sharp uvs WSHH-mc at the beginning of the call

ultrasonic transducer voltage; neither

The detected extreme value of the ratio signal is memorized for 5 to further determine the magnitude of the difference between the stored extreme value and the current value of the ratio signal. Based on the obtained value, a difference signal is formed (Figs. 1a and 16, curves 2 and A), according to which the strength of the joint is evaluated.

When operating in the mode with a stable oscillatory speed or current in the input circuit of the ultrasonic transducer 5 (Fig. 1a), the value of the difference signal is proportional to Hn - r, which coincides with expression (3) to within the sign.

When working in stable mode

excitation voltage (fig. 16) the value of the difference signal is proportional to

Mr. Mr.

/R . g / r O-g V WHAT WITH ACCURACY TO POSTYAN- (g t f) (r-g H)

coefficient of R during welding coincides with expression (3).

5 Consequently, the accuracy of determining the strength of a joint is not affected by a change in the amplitude of the voltage that excites the ultrasonic transducer, nor does it change in the input circuit of the ultrasonic transducer, the initial state of the connecting parts and the force of their compression, which increases the accuracy of controlling the strength 5 . PRI me R

5 The method was tested in laboratory conditions on a prototype of the UM-4170 automatic ultrasonic welding machine. We used ultrasonic transducer transient resonance at idle 69, 85 kHz and study a sound generator with systems for automatic tuning of frequency and stabilization of the excitation voltage or current in the input circuit of the ultrasonic transducer. In the mode of current stabilization as

5 of the first feedback signal, a digital signal was used, the code value of which from FGM to FFM set the value of the current to a / o, oi, egi and razvukovy transducer supported by a constant current stabilization system during welding.

As a second feedback signal, a signal was used, proportional to HEnsH. Fi, to the excitation voltage of the ultra sonic O over a preamplifier of amplitude about 1 i ds 10 V.

8 voltage stabilization mode as the first feedback signal used the signal from the output of the transform

The current torus in the input circuit of the ultrasonic transducer with amplitude up to 1 to 8 V, and the second feedback signal is a digital signal, the code value of which (from OFH to FFH) set the value of the voltage driving the ultrasonic transducer supported during welding voltage stabilization system. The ratio signal in both cases was formed using a multiplying digital-to-analog converter,

The search for the extreme value of the ratio signal, the storage of the extreme value and the formation of the difference signal were performed using a hardware-software complex consisting of an analog-digital converter, a specially designed controller based on a single-crystal microcomputer KP 1816BE39 and a control program.

Testing showed an increase in the control accuracy, as a result of which it was possible to assess the effect on the strength of the joint on the way to the welding position and welding conditions.

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Difference

Savings from the application of the proposed method can be achieved by increasing the actual performance and yield, associated with an increase in the accuracy of control, as well as by increasing the reliability of the products obtained,

Claims (1)

Claim Method Non-Destructive Testing strength of welded joints in the welding process, which consists in probing the product by means of series-connected generator and ultrasonic transducer and measuring the amount of current ultrasonic transducer, which is judged on the strength of welded joints, characterized in that, in order to improve the accuracy, the excitation voltage of the generator is measured, The dependence of the ratio of the magnitude of the current ultrasound of the transducer to the magnitude of the exciting voltage of the generator on the welding time, and the strength of the welded joint is judged by the difference between the extremum of this dependence and its point corresponding to the end of welding.  te / FIG. 2