SU996135A1 - Method of automatic control of resistance welding process - Google Patents

Description

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The invention relates to resistance welding, and specifically to methods for automatically controlling the resistance welding process and may find application in welding parts of small thickness.

There is a known method of automatic regulation of the spot welding process, according to which, in order to improve the quality of welding, the density of the welded current is continuously monitored and at a density less than the maximum allowed, the current is changed in proportion to the positive conductivity of the welding zone, and when the maximum allowable density value is reached proportional to the square of the voltage on the welding electrodes 1.

The disadvantage of this method is the low quality of regulation, which is caused by the incomplete correspondence of the measured and adjustable parameters.

There is also known a method for automatically controlling the thermal cycle of resistance welding, in which the thermopower is measured in the pauses between welding current pulses, the measured value is compared with

given and according to the error signal regulate the welding current 2.

The disadvantage of this method is that when welding parts of small thickness due to their low thermal inertia, the curve of temperature change actually coincides with the curve of change of the welding current of industrial frequency, therefore reducing the length of the back front of the current pulse does not exclude the possibility of formation of burnings and splashes of metal during welding if the temperature before the measurement was higher than the allowable .I

The closest to the invention according to the technical solution is the method of automatic control of the process of resistance welding, mainly of small thickness parts vTOKOM of the frequency of the industrial network, at which the specified welding current is switched on, its value is automatically controlled and current is turned off (3.

The disadvantage of this method is the low quality of welding.

The purpose of the invention is to improve the quality of welding by reducing overheating

connected parts and splash elimination.

This goal is achieved by the fact that according to the method of automatic control of the resistance welding process, mainly parts of small thickness of the industrial network frequency, at which the set value of the welding current is switched on, its value is automatically controlled and the current is turned off after the welding network has a welding current half-period periodically decreasing by 10-50% from a predetermined value with a frequency 4-20 times higher than the frequency of the industrial network.

Reducing the welding current by 10-50% eliminates overheating of parts and stabilizes the adjustable parameter (its maximum value), and the frequency of reduction with a frequency of 4-20 times more than the frequency of the supply network stabilizes the temperature in the welding zone, as in this case the curve of the temperature change already does not coincide with the curve of change in welding current.

The drawing shows a block diagram of a device that implements the proposed method.

The device contains welding electrodes 1 and 2, the source 3 of the welding current, the commutating valve 4, the device 5 for measuring (calculating) the control parameter, the source 6 of the reference voltage, the device 7 for comparing the magnitude of the voltages coming from the device 5 and the source b, reference voltage 6, driver 8 for control pulses of switching valve 4, sensor 9 for starting a welding cycle.

In the initial state, the welding electrodes 1 and 2 are open, the constant voltage from the source 6 of the reference voltage, determined depending on the desired value of the control parameter, is supplied to the comparison device 7.

According to the signal from the sensor 9 at the beginning of the welding cycle, the pulse shaper 8 generates a signal for switching on the switching valve 4 at the beginning of the half-period of the supply voltage. In the welding circuit current begins to flow. The input of the comparator device 7 begins to receive a voltage from the device 5 for measuring the control parameters. When the preset value of the control parameter is reached, the comparison device 7 generates a signal to the driver of 8 pulses for the forced locking of the switching valve 4. After

This causes a decrease in the welding current in the circuit and when the set value of the control parameter is reached, the comparison device 7 sends a signal to the driver 8 pulses to turn the switching valve 4 on. Later, the device's operation cycle repeats.

Example. For resistance spot welding of parts of small thickness, for example, NP-2 nickel 0.1 mm thick (soft, unannealed) with NP-2 nickel with a diameter of 0.5 mm (hard), a cycle is formed on the mounting and welding table SS-2 from one half cycle of power frequency current. Upon reaching an instantaneous welding current of 1400 A, by means of a forced shutdown of the switching thyristor valve, the welding current is reduced by 30% and then the thyristor is switched on again. At the same time, the welding current is reduced periodically with a frequency 10 times greater than the frequency of the supply network, i.e. 500 Hz.

As a result of the implementation of the proposed method, the welding quality is improved, namely, the strength of the welded joint is stabilized by 5.5 times and the precipitation value is 2.6 times.

Claims (1)

Invention Formula The method of automatic control of the resistance welding process, mainly of parts of small thickness by the current of the frequency of the industrial network, at which the switching-on value of the welding current is switched on, its value is automatically controlled, and the current is turned off, in order to improve the quality of welding by reducing overheating of the connected details and exclusion of splashes, after switching on, the welding current during a half-period of the frequency of the industrial network is periodically reduced by 10-50% of the set value with a frequency 4-20 times the frequency of the industrial network. Sources of information taken into account in the examination 1. USSR author's certificate number 503673, cl. At 23 K 11/10, 1975. 2. USSR author's certificate No. 706212, cl. In 23 K P / S, 1978. 3. USSR author's certificate No. 789257, cl. In 23 K 11/24, 1979 (prototype).