SU1316769A1 - Method and apparatus for controlling the welding current in resistance welding - Google Patents

Abstract

During resistance welding the welding current is caused to rise gradually to a maximum value at which it is held constant. The weld resistance value is determined by a generator (11) connected, through a differentiator (12), and a comparator (13), having a reference signal input (19), to an input (20) of a trigger (14). The output of the trigger is connected to a stopping input (23) of a ramp generator (15) which, through electronic control means (16), varies the welding process (17). A command (26) for starting (24) the ramp in the electronic control means is also connected to a clearing input (22) of the trigger, through a delay circuit (18), to a clock input (21) of the trigger. <IMAGE>

Description

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The invention relates to methods for controlling the welding current in contact, namely, spot welding, with a gradual increase in the welding current and equipment for this method.

There is a known method for controlling welding current in contact welding, in which the welding voltage is measured during the welding process.

At the time of delivery and voltage deviations of a predetermined value, the frequency of the welding pulse generator is changed (see ed. no. 679354, cl. 23 K 11/24, 1976).

The known method finds application with the use of an increased frequency of welding pulses and cannot be used with welding frequency signals of an industrial network, which is its disadvantage.

The closest technical solution to the present invention is a method of controlling the welding current in contact welding, mainly point welding with a smooth increase in current,; in which the weld resistance is measured and the welding current is controlled by the measured resistance value (see Aut. St. No. 461816, class B 23 K 11/24, 1973).

The disadvantage of this method is that in it the process of control of the welding current does not affect the weld point at which a change in the specified mode was detected.

It is known that a welding process control device is used to change, for example, the voltage on the welds or heat input in the welds (see German Patent No. 2362520, class B 23 K 11/10, 1976).

The disadvantage is that it is not adapted to varying conditions for the formation of the weld, its own change of the parts to be welded, the geometry of the weld, the state of the surface and the electrodes and requires adjustment with changes in the thickness to be welded, material, number of layers, surface preparation.

The closest to the invention is a device for controlling the welding current in contact welding, mainly spot welding, with a smooth increase in current, containing a node for measuring the resistance of the weld

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associated with the welding circuit, a comparator, a generator and a control circuit for the parameters of the welding process (see aut. St. No. 450666, clause B 23 K 11/24, 1973).

However, the device does not provide high-quality welding, since the measurement is carried out in the pauses between the pulses, and the current is controlled by the subsequent welding pulse, during the formation of which the welding conditions may change.

The purpose of the invention is to improve the quality of welded joints.

This goal is achieved by the fact that according to the method of controlling the welding current during contact welding, mainly spot welding, with a smooth increase in current, in which the measured resistance of the weld and the measured resistance are controlled by the welding current, the extreme point is determined during the welding current rise. the maximum value of the resistance of the weld, fix it, then continue welding without changing the value

welding current i.

A device that implements the proposed method, comprising a weld resistance measurement assembly connected to a welding circuit, a comparator, a generator and a control circuit for welding process parameters, is equipped with a differentiating node, a trigger circuit with three inputs and a delay circuit. the weld, the differentiating unit, the comparator, the trigger circuit, the generator, the control circuit for the parameters of the welding process and the welding circuit form a series-connected circuit,

the input of the delay circuit is connected to the second input of the trigger circuit, to one of the generator inputs and to one of the outputs of the control circuit of the parameters of the welding process, and the output of the circuit

the delay is connected to the third input of the trigger circuit ..

Fig. 1 shows a typical curve of change in resistance of a weld (curve 1) and a type curve of increase in the diameter of a weld point with constant adjustment of the welding current (curve 2); 2 - change in the resistance of the weld (curve 4) and change in the diameter of the weld point

(curve 5) with a gradually increasing welding current (curve 3); on . Fig. 3 - explaining how the welding current is controlled by stopping its buildup (forward 6 and 9) as from a change in the resistance of the weld (curve 7) or its derivative (curve 8); figure 4 is a functional diagram of the device that implements the method.

At a constant setting of the welding current, a typical change in the weld R is shown by curve 1 (Fig. 1). Curve 2 (FIG. 2) shows how the diameter of the weld point increases at the same time. From the above graph it can be seen that approximately at the instant of max-max when the resistance of the weld R has reached its local maximum. A weld point begins to form and its diameter grows.

. When welding current I in the welding process stops gradual increase (curve 3), the resistance (curve 4) will again reach its maximum R / viatcc- With this maximum, the beginning of the formation of the weld point corresponds approximately to this maximum, but its diameter D (Fig. 2, curve 5) increases rapidly with increasing welding current I. The steepness of the growth of the diameter of the weld point at the same time (curve 5) is significantly higher than in the case of constant adjustment of the welding current I (figure 1, curve 1), so that / over time, the energy saturation of the weld and splash fused material from the weld.

It was experimentally determined that the faster the welding current I grows, the sooner the maximum change in weld resistance R reaches the maximum and the sooner the onset of the weld point growth begins. .

When external conditions change, such as increasing the thickness or number of sheets to be welded, changing the diameter of the electrodes, due to wear H, the maximum is reached later, which means at higher values of welding current I. The time PR of which the maximum resistance of the weld R is reached It is an invariant of the welding process, which determines that such a welding current value (curve 1) has been achieved, which corresponds to the energy requirements of this welded joint.

The method is carried out as follows.

The welding current I gradually increases in accordance with direct 6 (Fig. 3). The change in resistance of the weld R (curve 7) is measured and its derivative dR / dt (curve 8) is measured simultaneously. At time t, when the flow R reaches a local maximum, the change in the derivative dR / dt (curve 8) passes through zero. This state is detected and, based on the received signal, stops the further rise of the welding current (forward 6 and 7 of FIG. 3). Welding is finished at a constant value of welding current I (Fig.Z, Lr Ma 9). From the technical point of view of the design of the electronic part, it may be advantageous to detect the value 10 (Fig.Z) of the derivative dR / dt (curve 8) at a point fairly close to zero. In this case, the signal to stop the growth of the welding current I is formed for a time interval t before the maximum resistance R .. is reached. U. . The time interval fit can be

MO t -C /

comparable or less than one half-cycle of the mains frequency 50 N, i.e., 0.01 in the case of ordinary welding installations using the frequency of the industrial network.

A device implementing the method consists of a source 11 for measuring the resistance of a weld, a differentiating device 12, a comparator 13 with an input 19 of a trigger circuit 14 with an input 20, An output of a trigger circuit .14 is connected to the input 23 of a sawtooth generator 15 control the parameters of the welding process with the input 25 of the settings to the welding circuit 17. Output

26 circuit 16 is connected to the input 24 of the generator 15, to the input 22 of the reset trigger circuit 14 and to the input

27 chain delay 18, the output of which is connected to another input 21 of the trigger circuit 14.

The device works as follows.

The signal from the source 11 measures the resistance of the weld is supplied to the differentiating device 12

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the input of which is connected to the comparator 13. The comparator 13 is triggered when the maximum resistance R is reached and generates a signal to the trigger circuit 14, which changes its state and, acting on the generator .15, stops the formation of a sawtooth voltage. This also stops the growth of the welding current, which is caused by the connection of the output of the sawtooth generator 15 through the electronic control circuit 16 of the parameters of the welding process. The connection of the circuit 16 to the input of the generator 15 and to the reset input of the trigger circuit 14 to its initial position allows changing the state of the trigger circuit and eliminating the increase in welding current at the extreme point of resistance resistance R. At the same time, the output of the circuit 16 is connected via delay 18 to the input of the delay circuit 18 , the output of which blocks the trigger circuit 14 during the first two to five periods.

The invention can be used to automatically control the process of resistance spot welding.

Claims (2)

1. The method of controlling the welding current in contact welding, mainly spot welding, with a smooth increase in current, at which 67696 the resistance of the weld and the measured resistance are controlled by the welding current, characterized in that, in order to improve the quality of the welds, the extreme point of the maximum value of the resistance of the weld is determined in the process of increasing the welding current, after 10 which continue the welding without changing the value of the welding current. 2.-Device for controlling welding current in contact welding, comprising a node for measuring the resistance of a weld or a weld, associated with a welding circuit, a comparator, a generator and a control circuit for parameters of the welding process, characterized in that it is equipped with a differentiating node, a trigger circuit with three inputs and a delay circuit, whereby the weld resistance measurement node, the differentiating node, the comparator, the trigger circuit, the generator 25, the welding process parameter control circuit and the welding circuit form connected in series circuit, the delay circuit input is connected to the second input trigger- e n hydrochloric circuit 30, to one of the inputs of the generator and one of the outputs of the control circuit of the welding process parameters, and the output of the delay circuit is connected to the third input of flip-flop 35 schemes. / matse cpue.f Fie.2 6 .- .9 TO yvvKS tfit at (fruf.y Editor M.Tovtin Compiled by L.Nazarova Tehred L.Oliynyk Order 2383/10 Circulation 975 Subscription VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow., Zh-35 Raushsk nab, 4/5 Production and printing company, Uzhgorod, st. Project, 4 . .. .. J Proofreader A.Ilyin