JPS6040957B2 - How to control the quality of resistance welding - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for controlling the quality of resistance welding.

Conventionally, the quality of resistance welding has been controlled by monitoring the voltage between the welding electrodes during resistance welding, detecting and holding the peak voltage between the welding electrodes, and monitoring the subsequent drop in the voltage between the electrodes. The ratio of the peak voltage held is at least 2
A method has been proposed for controlling the quality of resistance welding by terminating the welding when the percentage decreases by at least 20% (1939 Chi-O Patent Publication No. 60).
No. 37). In this method of controlling the quality of resistance welding, welding is terminated based on the ratio of the voltage between the electrodes to the peak value.

Therefore, in this conventional method, the detected peak voltage differs depending on the position at which the inter-electrode voltage is detected, and therefore, there is a drawback that the ratio used as a reference for terminating welding fluctuates. The disadvantage of this is that in the case of resistance welding robots used in the automobile industry, etc., the welding electrode makes complex movements, so it may not always be possible to connect the lead wire to the electrode to detect the voltage between the electrodes. There was a drawback that the quality control device had to be adjusted each time depending on the connection position of the lead wire. Therefore, an object of the present invention is to provide a method for controlling the quality of resistance welding in which the measurement results do not differ depending on the connection position of the interelectrode voltage detection lead wire. Embodiments of the invention will be described based on the drawings. First, the resistance welding quality control device used in the embodiment will be described based on FIG. 1. 20 is a welding control device, 24
is a welding transformer, 21 and 22 are primary lead wires of the welding transformer, 25 and 26 are secondary lead wires of the welding transformer,
27 is a current transformer that detects the current in the secondary lead wire of the welding transformer, 3 and 4 are electrodes for resistance welding, 2 is the object to be welded, and 31 is a current transformer that detects fluctuations in the welding current detected by the welding transformer. This constant current circuit 31, which is a constant current circuit for removing the current, converts the fluctuation of the current detected by the current transformer 27 into a constant current within a half cycle response speed. 23
is arranged on the primary side lead wire 22 of the welding transformer, a constant current circuit 3 is a thyristor that is driven by the iron and controls the welding current at a constant level, and 32 and 33 are lead wires for detecting the voltage between the electrodes. , 34 is an input adjustment circuit, 35 is an induced electromotive force removal circuit that removes the induced electromotive force caused by the welding current generated in the lead wires 32 and 33 that detects the voltage between the electrodes, and 36 is an absolute value conversion circuit using Kinpa current. Reference numerals 37 and 38 are sample and hold circuits, to which sample signals are alternately applied from the constant current circuit 31 every half cycle immediately after half-cycle energization.39 is a sample and hold circuit that alternately applies sample signals to the sample and hold circuit 37. , 38; 40 is a comparator circuit that outputs the larger tortoise pressure signal among the voltage signals applied from the sample and hold circuits 37 and 38; 41 is a peak value that stores the maximum value of the voltage signal; A hold circuit 42 compares the peak value of the voltage signal with the detected voltage signal and detects the amount of change △V between the peak value and the subsequent voltage signal; 44 indicates the end of resistance welding in advance; A variable resistor 43 is used to set the amount of fin pressure drop △V that performs When the drop amount ΔV reaches a preset value, the output signal from the comparison circuit 43 controls the welding control device 20 to stop or reduce the welding current.

Next, Fig. 2 shows the main body of the resistance welding machine, 2 is the object to be welded, 3 and 4 are welding electrodes that hold the object to be welded, 5 and 6 are rams that hold the welding electrodes, and 7 is a cylinder that moves the upper ram up and down. ,8,
9 shows a connection piece for connecting the welding current to the ram.

Next, referring to the waveform of the interelectrode voltage shown in FIG. 3, FIG.
The voltage between the electrodes was detected between a and the maximum voltage value was 2.
8. The voltage between the electrodes just before splashing is 2.2
V, the voltage drop amount is 0.6V, and the voltage drop ratio is 2
It was 1%.

Figure 3B shows the voltage between the electrodes detected between the rising parts 5a and 6a of the rams 5 and 6 in Figure 2, and the maximum voltage value is 3.6V.
The voltage between the electrodes just before the splash occurs is 2.9V, the voltage drop is 0.7V, and the voltage drop ratio is 19%.
Met. FIG. 3C shows the voltage detected between the electrodes between the rear ends 8a and 9a of the connecting pieces 8 and 9 shown in FIG. The voltage between them was 3.9V, the amount of voltage drop was 0.7V, and the ratio of voltage drop was 15%.

As a result, even under the same welding conditions, the drop rate was 21% between A and A', 19% between B and B', and 19% between C and C' due to the difference in the position at which the interelectrode voltage was detected. varies as 15%, and the method of controlling the quality of resistance welding using this voltage drop ratio has the drawback that the setting of the voltage drop ratio must be changed depending on the detection position of the interelectrode voltage. However, as shown in FIG. 3, the voltage drop between A and A' is 0.
6V, 0.7V between B and B', and 0.7V between C and C', and this voltage drop does not vary depending on the detection position of the interelectrode voltage, and is almost the same. If the quality of resistance welding is controlled by the quantity, it becomes possible to use it without adjusting the control device depending on the detection position of the inter-electrode voltage.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a quality control device for resistance welding, FIG. 2 is a side view of a resistance welding machine, and FIG. 3 is a waveform diagram showing the detection voltage of the interelectrode voltage. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1 Quality of resistance welding in which the voltage between welding voltages is monitored during resistance welding, the peak value of this monitored voltage is detected, and resistance welding is terminated immediately when a preset voltage drop occurs from this peak value. control method.