JPS6040955B2 - Spot welding monitoring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for monitoring welding quality by detecting displacement of an electrode tip and an electrode support rod during spot welding.

There are various types of quality control devices for spot welding, but the typical ones are those that judge welding quality by voltage fluctuations and current fluctuations between electrodes, and those that judge welding quality by checking the temperature rise or transformation of the weld zone. There is a type that uses the volume expansion to determine quality.

The former has a relatively simple device, but the judgment is not accurate due to error factors caused by external conditions such as the surface condition of the workpiece, induced voltage, and invalid shunt, and the latter has a high reliability of judgment. Although this method is excellent, it has the inconvenience of being a complicated device and difficult to easily attach to currently commercially available welding machines. It is an object of the present invention to improve this problem and provide a monitoring device that can be easily attached to an existing spot welding machine and that can accurately determine quality. The present invention attaches an acceleration sensor to the electrode tip support rod of a spot welding machine, double-integrates the acceleration signal from this acceleration sensor, converts it into a signal corresponding to the displacement of the electrode tip and the electrode support rod, and calculates the When the maximum amplitude of the corresponding signal is smaller than a predetermined lower limit set value, a welding defect signal is transmitted, and when it is larger than a predetermined upper limit set value, a spatter occurrence signal is transmitted. .

Next, embodiments of the present invention will be described with reference to the drawings.

In spot welding, two plates 3 to be welded sandwiched between an upper electrode tip 1 and a lower electrode tip 2 as shown in FIG.
When the flow passes through the lower electrode tip 2 and is properly welded, the plate 3 to be welded thermally expands due to the heat generated by energization, as shown in Figure b, and the area near the joint between the two plates expands. It softens and becomes molten to form a nugget 4, and at this time, the upper electrode tip 1 and the lower electrode tip 2 bite into the plate to be welded 3 due to the pressure applied between them.
In this state, it is cooled and spot welding is completed. At this time, if for some reason the generated heat is insufficient and the nugget 4 is not generated, welding will be defective, and in this case, the amount that the upper electrode tip 1 and the lower electrode tip 2 will bite into the welded plate 3 will be It will be smaller than if it were welded normally.

In addition, if the so-called "splatter" phenomenon occurs, in which the generated heat becomes excessive and the welded part explodes outward,
The amount by which the upper electrode tip 1 and the lower electrode tip 2 bite into the plate 3 to be welded becomes larger than in the case of normal welding. The present invention utilizes this phenomenon to monitor welded parts, and as shown in the embodiment shown in FIG. 2, an acceleration sensor 6 is attached to the upper movable electrode support rod 5 by adhesive, and a circuit shown in FIG. Performs signal processing.

In FIG. 4, the signal from the acceleration sensor 6 is transmitted to the amplifier 8.
After being amplified by the gain adjustment variable resistor 9, the
It enters the multiple integration circuit 10 and the trigger circuit 11.

The trigger circuit 11 starts the gate timer AI2 at the rising edge of the displacement signal at the timing shown in FIG. 3, and the gate timer AI2 starts the gate timer B13 after T seconds have elapsed.
Start. The gate timer B13 acts on the gate circuit 14, and the gate circuit 14 acts on the gate timer B13.
The displacement signal output from the double integration circuit 10 is sent to the maximum amplitude calculation circuit 15 only during the L seconds during which the double integration circuit 10 is activated. That is, as shown in FIG. 3, before welding is performed, the upper movable electrode support rod 5 descends, and the displacement waveform caused by the collision when the upper electrode tip 1 hits the plate 3 to be welded is stored in the maximum amplitude calculation circuit 15. Gate timer AI2 to prevent
, a gate timer B13, and a trigger circuit 11. The maximum amplitude value signal output from the maximum amplitude calculation circuit 15 (
(see FIG. 3) is determined by the determination circuit 16. That is, in the determination circuit 16, the maximum amplitude value is determined by the upper limit value setter 17.
If the value is larger than the value set by the lower limit value setter 18, a "splash occurrence" signal is sent to the external device, and if it is 4 points higher than the value set by the lower limit value setting device 18, a "defective welding" signal is sent.
A signal is sent to the external device, otherwise a "good weld" signal is sent to the external device. Note that a reset timer 19 is activated by the trigger circuit 11, and functions to reset the double integration circuit 10, maximum amplitude calculation circuit 15, and determination circuit 16 to return to the initial state after a certain period of time has elapsed. In the displacement waveform shown in Fig. 3, after the vibration waveform of the displacement signal at the time of electrode collision decreases, the displacement waveform first rises because the plate to be welded 3 is stretched by hot air due to the generated heat and the upper part It shows the process in which the electrode tip 1 is pushed upward, and the displacement waveform decreases thereafter due to the upper electrode tip 1.
The maximum amplitude is equivalent to the sum of the amount of expansion of the welding plate 3 and the amount by which the upper electrode tip 1 bites into the welding plate 3. It is.

As explained above, by using the device of the present invention, it is possible to accurately monitor welding quality by simply gluing an acceleration sensor to the upper movable electrode support rod with adhesive. It has the advantage that it can be easily installed on common spot welding machines.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the general operation of spot welding, FIG. 2 is a side view of the welding head portion of an embodiment of the present invention, FIG. 3 is an explanatory diagram of the operation of the present invention, and FIG. 4 is an explanatory diagram of the present invention. FIG. 2 is a block diagram showing the circuit configuration of FIG. DESCRIPTION OF SYMBOLS 1... Upper electrode chip, 5... Upper movable electrode support rod, 6... Acceleration sensor, 10...
Double integration circuit, 15... Maximum amplitude calculation circuit, 16.
...Judgment circuit. Figure 4 Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. An acceleration sensor attached to an electrode tip support rod of a spot welding machine, and a device that double-integrates the acceleration signal obtained by the acceleration sensor and converts it into a signal corresponding to the displacement of the electrode tip and electrode support rod; A determination circuit is provided that transmits a welding defect signal when the maximum amplitude of the signal corresponding to the displacement is smaller than a predetermined lower limit set value, and transmits a splintering occurrence signal when it is larger than a predetermined upper limit set value. A spot welding monitoring device characterized by: