JPH03210977A - Resistance welding machine control method - Google Patents

Abstract

PURPOSE:To automatically control welding conditions during welding and to form welding nuggets in proper quantities by detecting the surface temperature of materials to be welded corresponding to the peripheries of welding electrodes, comparing it with the preset reference temperature and stopping a welding current when the detected temperature coincides with the reference temperature. CONSTITUTION:The nuggest diameters formed on the materials 2a and 2b to be welded are always monitored by a temperature detector 4 even if the conditions of a weld zone such as the welding electrodes 1a and 1b, the materials 2a and 2b to be welded and the pressurizing force are changed. Since welding is completed when a signal of the temperature detector 4 attains a reference temperature signal and the nugget diameters attain desired values, the welding current is not impressed for a long time by setting the welding time excessively, dust is not also generated, safe and pertinent welding is performed and satisfactory welding quality is assured. In addition, since welding is completed in the shortest time automatically, the number of times of welding per the same time also increases and efficiency is also improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a control method for a resistance welding machine that automatically guarantees the quality of a welded part during resistance welding.

BACKGROUND OF THE INVENTION In conventional resistance welding machines, the welding condition of the welded material varies greatly depending on the shape of the welding electrode tip, the electrode pressure, the surface treatment state of the welded material, the shape and processing state of the welded material, and so on. Therefore, even if the welding current, welding time, and electrode pressure are kept constant, the welding quality of the welded part cannot be made constant, and the current situation is that a sampling destructive test is performed after welding is completed.

In addition, in order to cope with such problems, various quality assurance methods such as an inter-electrode voltage method, an inter-electrode resistance method, and an ultrasonic method have been considered as methods for monitoring the quality of a welded part.

Problems to be Solved by the Invention However, in the conventional method of controlling a resistance welding machine, in which the welding current, welding time, and electrode pressure are kept constant, as described above, the shape of the welding electrode tip, the electrode pressure, It is difficult to maintain a constant welding quality because the surface treatment state of the welded material, the shape and processing state of the welded material, etc. change greatly. For this reason, it is common practice to weld by setting the welding conditions to a level higher than necessary. However, this creates depressions on the surface of the weld nugget, which deteriorates the appearance of the welded area, generates dust, and prevents input. There are also problems from a safety and economic perspective, such as an increase in power and welding time, and a decrease in electrode life due to deformation of the tip of the welding electrode.

In addition, the above-mentioned monitoring method cannot be put to practical use depending on the shape of the welding electrode tip and the surface treatment state of the welded material, and has limitations such as being able to be applied only after welding is completed, so the quality of the welded part can always be guaranteed. There is a problem that cannot be done.

The present invention solves the above problems, and provides a resistance welding machine control method that can automatically control welding conditions during welding to ensure welding quality and form just the right amount of weld nugget. The purpose is to

Means for Solving the Problems In order to achieve the above object, the present invention detects the surface temperature of the material to be welded corresponding to the peripheral part of the welding electrode at a position separated by a predetermined distance from the center of the welding electrode. The detected temperature is compared with a preset reference temperature, and when the surface temperature of the welded material matches this reference temperature, the welding current applied from the welding electrode to the welded material is stopped. .

According to the present invention, the size of the weld nugget formed on the welding material can be detected by detecting the temperature change conducted to the surface of the welding material, and the size of the weld nugget formed on the welding material can be detected by detecting the temperature change conducted to the surface of the welding material. Since the welding current is controlled to stop when there is no difference between the welding temperature and the corresponding reference temperature, it is possible to control the size of the weld nugget formed on the welded material to the desired size. This has the effect that welding quality can always be guaranteed.

Embodiment FIG. 1 shows the structure of an embodiment of the present invention. In Fig. 1, la and lb are welding electrodes, 2a and 2b are the materials to be welded, 3 is a power supply circuit, 4 is a temperature detector, 5 is an error amplification circuit, 6 is a welding condition setting circuit, 7 is an arithmetic circuit, and 8 9 is a memory circuit, 9 is a reference temperature signal generation circuit, 10 is a current control circuit,
11 is a current detector, and 12 is an amplifier circuit.

The welding electrodes la and lb are pressurized across the materials to be welded 2a and 2b, and a power supply circuit 3 consisting of a transformer and a semiconductor element is connected.
Welding current is supplied from The temperature detector 4 is a non-contact type temperature detector that detects the temperature generated in the materials to be welded 2a, 2b, converts the temperature signal into an electric signal, and converts the temperature signal into an electric signal.
output to one end of the input. The welding condition setting circuit 6 receives inputs such as the plate thickness and material of the welded materials 2a and 2b, the required diameter of the nugget, etc. The arithmetic circuit 7 is a logic arithmetic circuit including a microcomputer, and calls reference temperature value data stored in the memory circuit 8 according to the output value of the welding condition circuit 6. The reference temperature signal generation circuit 9 outputs a reference temperature signal from the reference temperature value data and inputs it to the other end of the error amplification circuit 5 . The current control circuit 10 controls the output of the power supply circuit 3 to be substantially constant based on a signal from the arithmetic circuit 7. The current detector 11 detects the welding current and inputs it to the amplifier circuit 12, and the signal amplified by the amplifier circuit 12 is fed back to the arithmetic circuit 7.

Next, the operation of the above embodiment will be explained. First, when welding is started and the materials to be welded 2a and 2b begin to be electrically heated, the surface temperatures of the materials to be welded 2a and 2b begin to increase. Conditions for obtaining a desired welding result are input in advance to the welding condition setting circuit 6, and the arithmetic circuit 7 selects one of the reference temperature value data stored in the memory circuit 8 according to these conditions. , is input to the reference temperature signal generation circuit 9. The reference temperature signal generation circuit 9 generates a reference temperature signal and inputs it to the error amplification circuit 5. The error amplification circuit 5 is connected to the temperature detector 4
The signal from the controller is compared with the reference temperature signal, and an error signal is input to the arithmetic circuit 7. The arithmetic circuit 7 connects the materials to be welded 2a and 2b.
When the surface temperature is lower than the reference temperature signal, the welding current flowing through the power supply circuit 3 is kept substantially constant and output via the current control circuit 10. When the value of the error amplification signal output from the error amplification circuit 5 becomes zero, the arithmetic circuit 7 stops the current flowing through the power supply circuit 3 via the current control circuit 1o. The current detector 11 and the amplifier circuit 12 detect the welding current and feed back the state of the welding current to the arithmetic circuit 7.
Keeping the welding current constant Figure 2 shows a typical example of the relationship between the nugget diameter formed in the weld and the welding current in spot welding, which is one method of resistance welding. Further, FIG. 3 shows a typical example of the relationship between the nugget diameter and the welding current application time. Furthermore, FIG. 4 shows a typical example of the nugget diameter and the tensile shear strength of the weld.

The quality of a weld zone refers to the nugget formed in the weld zone and the resulting tensile shear strength of the weld zone.The quality of the weld zone is guaranteed by the diameter of the nugget formed in the weld zone. This means controlling the size to be determined by the material to be welded. Further, for this purpose, the relationship shown in FIGS. 2 and 3 shows that when the welding current is set to be substantially constant, controlling the welding current application time is an effective means.

Therefore, according to the embodiment, the materials to be welded 2a, 2
The diameter of the nugget formed at the welding electrode 1"11b% is constantly monitored by the temperature detector 4 even if the conditions of the welding part such as the welding electrode 1" 11b% and the welding force change. Welding ends when the signal reaches the reference temperature signal and the nugget diameter reaches the desired value, so setting the welding time excessively and applying welding current for a long time may adversely affect the electrode life. Safe and appropriate welding is performed without any dust generation, and good welding quality is guaranteed.Also, since welding is automatically completed in the shortest time, the number of welds per same time can be reduced. In addition, there is no need to consume unnecessary power, and welding costs can be reduced.

Effects of the Invention As is clear from the above embodiments, according to the present invention, the surface temperature of the material to be welded corresponding to the surrounding area of the welding electrode is detected, and the detected temperature is compared with a preset reference temperature. ,
Since the welding current applied to the welding electrode is stopped when the temperatures match, the quality of the weld can always be guaranteed, and the resistance welding machine control method improves safety, work efficiency, and economy. can be provided.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a resistance welding machine control method according to an embodiment of the present invention, FIG. 2 is a graph showing the relationship between nugget diameter and welding current in spot welding, which is a type of resistance welding machine, and FIG. The figure is a graph showing the relationship between the nugget diameter and the welding current application time in the same welding method, and FIG. 4 is a graph showing the relationship between the tensile shear strength and the nugget diameter in the same welding method. la, lb... Welding electrode, 2a, 2b... Welded material, 3... Power supply circuit, 4... Temperature detector, 5... Error amplification circuit, 6... Welding condition setting circuit , 7... Arithmetic circuit, 8... Memory circuit, 9... Reference temperature signal generation circuit, 10... Current control circuit, 11... Current detector,
12...Amplification circuit.

Claims (1)

[Claims] Detecting the surface temperature of the material to be welded corresponding to the surrounding area of the welding electrode at a position a predetermined distance away from the center of the welding electrode, comparing the detected temperature with a preset reference temperature, A method for controlling a resistance welding machine, comprising: stopping a welding current applied from the welding electrode to the material to be welded when the surface temperature of the material to be welded matches the reference temperature.