JPS5940550B2 - Spot welding strength monitoring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention can detect the strength of spot welding with high accuracy even if the detection mechanism is installed far away from the workpiece, and can eliminate power fluctuations and spatter that occur frequently at welding sites. This invention relates to a welding strength monitoring device for spot welding that is not affected by

Spot welding is often used for a variety of products using steel plates, but in recent years the number of welding defects has been increasing.

In other words, in the past, mild steel plates were generally used as materials to be welded, making it difficult for conduction failures to occur, and the number of failures was decreasing year by year due to advances in technology.However, new materials are being used to replace mild steel plates. As a result, there has been a tendency for the incidence of welding defects to increase. As a new material,
There are galvanized steel sheets and high-tensile steel sheets.

When spot welding these materials, welding defects will occur unless the current is monitored more severely than with conventional mild steel plates. Therefore, it is necessary to monitor the welding current, but the causes of welding defects include insufficient current (causing approximately 50% of welding defects), poor electrode angle (causing approximately 15% of welding defects), and poor electrode fitting (causing approximately 50% of welding defects). approximately 15%), others (approximately 2%
0%), and detection of welding defects by welding current monitoring is 5%.
There was a problem in that it stopped at 0% and I couldn't hope for anything more. Therefore, there was a desire for an advanced monitoring device that does not simply detect the welding current, and the development of a welding strength monitoring device to ensure that all welded products are of good quality has been delayed.

The following methods have been developed for this purpose: 1. A device that detects the voltage between the welding electrodes, 2. A device that detects the expansion dimension of the welded part, 3. A device that detects the exothermic temperature, and 4. A device that transmits ultrasonic waves between the materials to be welded. There are 5 types that transmit magnetic flux between materials to be welded and detect the amount of permeation, and 6) types that detect welding current.

When these various methods were compared and examined from the viewpoints of technical difficulty, accuracy, ease of monitoring during welding, ease of use on the line, cost, etc., method 1 yielded almost satisfactory results. However, it is recognized that method 6, which yields the following results, has some difficulty in terms of accuracy.

The remaining methods 2 to 5 appear to have room for improvement in terms of technical difficulty, ease of use on the line, cost, etc. Under these circumstances, the present invention aims to provide a more accurate, simpler, and cost-effective welding strength monitoring device.

Next, this invention will be explained theoretically. The strength of spot welding increases as the area of the melted part of the two welded materials, that is, the nugget diameter, increases, but the nugget diameter should be increased as the voltage that effectively acts on the welded materials becomes higher. is known to be possible. As shown in FIG. 1, the voltage applied between the welding electrodes includes a true interelectrode voltage waveform W, an effective component VR, an induced noise component VN, and a component Vt equivalent to heat dissipation. Components of welding gun electrode Vr
and are included.

That is, there is the following relationship.

This invention removes an induced noise component N, a component Vt equivalent to heat dissipation, and a component Vr of the welding gun electrode from the voltage applied between the welding electrodes, integrates the remaining effective component, and calculates its value. It compares the value with a preset standard setting value and displays whether it is good or bad.

The induced noise N is expressed as follows, where I is the welding current.

Therefore, if the voltage is detected at the timing of DI/Dt=0 (N=0), the result will be as shown in FIG. This will be removed by a circuit described later. In this case, in order to increase the number of samplings, it is preferable to partially invert as shown by the arrow in the figure. Next, the component t equivalent to heat dissipation can be considered as follows. That is, when the welding current is 11, the resistance between the materials to be welded is R1, and the heat dissipation energy is ET, the input energy Ei is Ei=2RT=I-V-T, and when Ei>ET, a nugget is generated, and Ei =
The lower limit of nugget generation is when ET=I-VT-T.

Specifically, spot welding is performed while the electrode pressure, current application time, and plate thickness of the welded material are kept constant, and the current is gradually lowered.The voltage is measured each time, and the lower limit at which nuggets are generated is determined. Find the voltage VT.

The energy ET due to this voltage is an ineffective component that is dissipated into the air as heat without contributing to nugget generation, that is, welding, and this voltage VT is a component equivalent to heat dissipation. Note that the voltage VT is measured instantaneously at DI/Dt-0, where the current does not change to remove induced voltage, that is, at zero cross timing. The component Vr of the welding gun electrode is as follows.

That is, as shown in FIG. 3, when the welding gun electrodes 2 and 3 are connected to the welding transformer 1 and the welding current 1 is applied with the materials to be welded 6 and 7 sandwiched between the tips 4 and 5 at the tips of the welding gun electrodes 2 and 3, DeRl
, r2 are the resistance values from the voltage application point to the tip of the welding gun electrodes 2 and 3, and R is the resistance value between the tips 4 and 5.

Therefore, the generated voltage when there are no materials to be welded 6, 7 (R=0) is V=r2(r1+R2)1.

Therefore, if -r is read and adjusted using a zero regulator (not shown), the voltage detection cables can be attached to the welding gun electrodes 2 and 3 at any position. However, = r
changes with the current 1, so it is necessary to constantly compensate for voltage fluctuations within the device. As shown in Figure 6, the method for correcting current fluctuations in the gun electrode component Vr is to detect the current during welding, amplify it, pass through one filter circuit, then full-wave rectify it, and sample it at the zero cross timing. The current obtained is multiplied by the specific resistance of the gun and electrode. The timing of the correction is preferably the same as the time of removing the induced noise component VN (d1/DtO) described above. FIG. 4 shows a circuit diagram of an embodiment of the present invention, and 8 is a voltage detection circuit that detects the voltage applied between the welding gun electrodes 2 and 3.

The output side of this voltage detection circuit 8 includes an inductive noise removal circuit 9, a heat dissipation component removal circuit 10, and a gun electrode component removal circuit 1.
1 are connected in series. Inductive noise removal circuit 9
As shown in FIG. 5, the circuit includes an amplification circuit for amplifying the detected voltage, a full-wave rectification circuit for rectifying the detected voltage, and a full-wave rectification circuit for rectifying the detected voltage.
It consists of a sample and hold circuit that outputs a voltage from which induced noise has been removed by detecting it at the same zero cross timing as the measurement of the voltage value t described above. Then, at the next stage of the gun electrode component removal circuit 11, an active component integration circuit 1 is provided.
2 is connected, and a comparison measurement circuit 14 that compares and measures the output voltage of the integrating circuit 12 with the output voltage of the setting circuit 13 is connected at the next stage. The setting circuit 13 is set to match the integrated voltage of the effective component, which has been determined in advance through experiments to ensure good welding depending on the material to be welded. Differential voltage, maximum voltage, voltage drop rate, time when voltage exceeds a reference value, etc. can also be considered as monitoring parameters.

A display device 15 is connected to the output side of the comparison measurement circuit 14.

This display device 15 displays the output voltage of the comparison measurement circuit 14 to determine whether it is good or bad. 16 in FIG. 4 is a current detection circuit, 17 and 18 each calculate the (DI/Dt) value,
a detection circuit for determining the value at which this becomes zero and causing the inductive noise removal circuit 9 to perform voltage detection at that point;
19 is a circuit for setting the voltage Vt by a digital switch, and 20 is a circuit for setting the voltage Vr. In this device configured in this way, the induction noise removal circuit 9 removes induced components other than the true inter-electrode voltage from the voltage V between the welding gun electrodes 2 and 3 detected by the voltage detection circuit 8. Noise components are removed, heat dissipation components unrelated to nugget generation are removed by a heat dissipation component removal circuit 10, and losses caused by the welding gun electrodes 2 and 3 are removed by a subsequent gun electrode component removal circuit 11. Considerable voltages will be removed and the effective components from which they have been removed will be provided to the integrating circuit 12. Therefore, the voltage applied to the integrating circuit 12 can be said to have a value equivalent to the voltage that is actually supplied to the material to be welded and is useful for generating nuggets in spot welding.

Therefore, after this voltage is integrated by the integrating circuit 12, a comparative measurement circuit 14 performs comparison measurement with a preset value, and the display device 15 displays whether the voltage is good or bad. The reason for performing the integration is to avoid being affected by power fluctuations and spatter during energization, which tend to occur at welding sites. Since the present invention is constructed as described above, there is an advantage that the strength of spot welding can be detected with high accuracy even if the detection mechanism is installed at a position far away from the materials to be welded 6, 7. It also has the advantage of being able to perform the above detection without being affected by power fluctuations and spatter, which are common in welding sites.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between voltage and time to theoretically explain this invention, Fig. 2 is a diagram to explain the induced noise component, and Fig. 3 is a perspective view showing the gun electrode. , FIG. 4 is a block diagram of an embodiment of the present invention, FIG. 5 is a block diagram of an example of an inductive noise removal circuit, and FIG. 6 is a block diagram of an example of a gun/electrode component removal circuit. 1... Welding transformer, 2, 3... Welding gun electrode, 4, 5... Chip, 6, 7...
... Material to be welded, 8... Voltage detection circuit, 9...
... Inductive noise removal circuit, 10 ... Heat dissipation component removal circuit, 11 ... Gun electrode component removal circuit,
12...Integrator circuit, 13...Setting circuit, 14...Comparison measurement circuit, 15...Display circuit.

Claims (1)

[Claims] 1. A voltage detection circuit that detects the voltage applied to the welding gun electrode, an inductive noise removal circuit, a heat dissipation component removal circuit, a gun electrode component removal circuit, and these circuits that are sequentially connected to the output side of the voltage detection circuit. an integrating circuit that integrates the welding voltage after ineffective components have been removed; a comparison measuring circuit that compares and measures the output voltage of the integrating circuit with a preset reference value; and determining whether the output voltage of the comparing measuring circuit is good or bad. A welding strength monitoring device for spot welding, characterized by comprising a display device for displaying information.