JPS5913584A - Method and device for controlling resistance welding - Google Patents

Abstract

PURPOSE:To enable the formation of a welding nugget having stable quality by increasing successively an electrical welding current together with conduction time and stopping the current application upon completion of the formation of the prescribed welding nugget thereby making the device easily adaptable to various kinds of disturbances. CONSTITUTION:The output of a nugget detector 1 which monitors the formation of the welding nugget in spot welding by resistance welding is converted to quantity of electricity with a converter 2. Said quantity of electricity is compared with the quantity of electricity upon completion of an adequate nugget applied from a setter 3 in a comparator 4, and when both quantities of electricity attain equal, a stop signal for current application is transmitted to a conduction time controller 5, which interrupts the power feed to a welding transformer 7 with an electronic switch 6, thereby stopping the conduction of the welding current. On the other hand, a current controller 8 servocontrols the welding current by the feedback input from a current detector 10 and a function voltage curve including a straight line to increase the welding current upon lapse of the weld time obtained from a function voltage transmitter 9.

Description

DETAILED DESCRIPTION OF THE INVENTION The object of the present invention is to always obtain weld nuggets of a predetermined quality by monitoring the weld nuggets and adjusting the welding current application time in resistance welding such as spot welding. The present invention relates to flow waveform control of welding current in an adaptive control device.

Currently, as an adaptive control device for lap resistance welding, the voltage or resistance between the electrode tips, the expansion reduction between the electrode tips and the
Possible detection methods include the temperature rise at the tip of the electrode tip, the ultrasonic transmittance between the electrode tips, and the precise acoustic emission generated from the welding nugget. Various methods have been studied for controlling welding parameters, etc. based on the correlation characteristics of

The majority of these control methods are of the so-called energization time adjustment type, which stops the flow of welding current when the detected amount of electricity reaches a predetermined value. Generally, the current is a constant value as shown in Figure 1, that is, the current is basically a rectangular waveform, although a slight upslope waveform may sometimes be added to the rise. be.

However, with such a current waveform, the first waveform will not respond to disturbances such as when spot welding points get closer together and a so-called shunt occurs, or when the pressure applied to the electrode increases for some reason. It has been found that JJ & response control by simply extending the energization time as shown in Figures (B) to (C) is extremely ineffective.

That is, in such a case, the welded part rj! If E is kept constant, securing the nugget quality by extending the energizing time will quickly reach its limit, and from then on, even if the energizing time is extended to twice or three times the normal time. It has also been found that there are cases in which the desired nugget cannot be obtained.

The present invention provides a simple f method that eliminates these problems.

FIG. 2 shows an example of a current waveform when the welding current is increased linearly, and FIG. 3 shows an electrical block diagram of an example for spot welding.

As shown in Figure 2, if the welding current increases linearly with the welding time, the heat input required by the weld nugget increases compared to the case where only the welding time increases at the same current value. It has been proven from the results of numerous welding experiments that extremely effective compensation control is possible because it can deal with problems in a cumulative manner.

In other words, even in response to a disturbance such as an increase in electrode pressure, the waveform from (b) to (c) in Figure 2 shows that
If the welding current itself increases with the energization time, it will always reach a current range that corresponds to the increased electrode pressurizing force, so it is possible to obtain a weld nugget of a predetermined size only under appropriate welding conditions. It is.

If a specified nugget is obtained, the welding current is automatically cut off by a signal from the nugget detector, so if the current increase rate is adjusted to an appropriate value, excessive heat input to the weld can be prevented. It is possible to prevent dangers such as "deflection" and "blind welding" caused by being thrown in.

On the other hand, if the welding nugget is completed early due to thin workpiece plate thickness, for example, the welding time shown in Fig. 2 (a) is better than simply reducing the energization time as shown in Fig. 1 (a). It is easy to understand that it is more effective to control the welding current by simultaneously decreasing it as shown in b).

FIG. 3 is a block diagram of an embodiment for spot welding.

The nugget detector (1) shown in the figure may be of a type that detects changes in the voltage between electrode tips or resistance (n:i) as described above, or of any other type.

The output of this detector (1) is converted into an appropriate amount of electricity by a converter (2), and compared with a pre-obtained appropriate amount of electricity when the nugget is completed in a setting device (3) and a comparator (4). Ru.

When the electrical quantities of the converter (2) and the setting device (3) become equal, the comparator (4) sends a energization stop signal to the energization time regulator (5), and an electronic switch (6) such as a thyristor or contactor is activated. As a result, the supply of core force to the welding transformer (7) is cut off, and the flow of welding current is also stopped.

On the other hand, the current controller (8) is operated in conjunction with the current feedback input from the current detector (1) to follow the rising command voltage from the functional voltage transmitter (9) at the same time as the start of the energization time. The current will be servo controlled.

The welding current waveform controlled by this current controller (8) may be linear, exponential, or other curved with respect to the energization time, but as mentioned above, in order to complete adaptive control, an appropriate ratio should be set. It is necessary to have a rising current waveform with .

The welding current waveform obtained in this way not only has the function of automatically compensating to always maintain the same waveform against fluctuations in the power supply voltage or changes in the secondary circuit impedance of the welding machine, but also has the function of automatically compensating to maintain the same waveform at all times. As mentioned above, in response to the output of the energization time regulator (5), when welding nuggets are difficult to form and a longer energization time is required, the welding current is automatically increased IJI + Φ control is performed. Therefore, compared to similar conventional control devices that only adjust the energization time, we have established a stable adaptive control device with a much wider adaptability range to various anticipated disturbances using a simple and practical control method. It is something that can be done.

FIG. 2 is an example of the welding current waveform of the present invention.

FIG. 3 is an electrical block diagram for one embodiment of the present invention.

[Explanation of symbols]

Claims (1)

[Claims] 1. An adaptive control device for resistance welding that monitors the generation of weld nuggets and adjusts the flow time of welding current to always form weld nuggets of a predetermined quality, A control method for resistance welding, characterized in that the welding current uses a current waveform that gradually increases according to a straight line or a predetermined function curve as the energization time passes. 2. A device that detects the state of weld nugget formation during resistance welding, a device that converts the detection signal into an appropriate amount of electricity, and a device that detects the amount of electricity when the detected amount of electricity matches the amount of electricity when an appropriate weld nugget is completed. An energization time adjustment device that stops the flow of the welding current, a functional voltage generator that includes a straight line to control the waveform of the welding current, and a current that servo-controls the welding current so that the effective value of the current matches the voltage signal. 1. A control device for resistance welding, characterized in that the effective value of the welding current gradually increases in accordance with a predetermined functional voltage signal as the welding current energization time passes.