JPH0225284A - Spot welding method for laminated steel plate - Google Patents

Abstract

PURPOSE:To prevent the generation of holding of a surface steel plate by suspending energization, regulating voltage to an adequate voltage, and executing welding by starting the energization when an abnormal voltage fluctuation is detected in spot welding with an inverter controlled DC power source, and returning the voltage to the initial voltage at the point of the time when the resistance value falls to a prescribed value or below. CONSTITUTION:A shorting circuit 4 is provided and the energization is executed for spot welding of the laminated steel plates 2 having an intermediate resin layer 2 which is an insulator. The inverter-controlled DC is used for the power source and the voltage between electrodes is detected. The energization is interrupted when the abnormal voltage fluctuation is detected. After the voltage is regulated to the adequate voltage, the welding is executed by starting the energization to prevent the holding of the surface steel plate. Further, the voltage is returned to the initial voltage and the welding is executed at an ordinary welding speed when the resin right under the electrodes is removed and the resistance value between the electrodes falls to the prescribed value or below. The generation of the holding in the surface steel plate is prevented in this way without lowering the productivity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for spot welding laminated steel plates used as vibration damping materials and the like.

[Conventional technology]

As shown in FIG. 7, a laminated steel plate 1 used as a damping material etc. is made by forming a viscoelastic resin layer 2 with a thickness of 0.4 nm to 1.0 m, for example, with a thickness of 0.03 a+ to 0.1 mm. It is constructed by being sandwiched between two skin steel plates 3. In this type of laminated steel plate 1, since the intermediate resin layer 2 is an electrical insulator, it is impossible to apply normal direct current to the laminated steel plate 1 when performing resistance spot welding. For this reason, during welding, a so-called shunt method is used in which a short circuit 4 is provided between the upper and lower skin steel plates 3 to supply current, as shown in FIG.

This method utilizes resistance heat generation between the skin steel plate 3 and a pair of electrodes 5 due to the current flowing through the path shown by the broken line A in FIG. In this method, after melting the resin M2 and removing the resin M2 in this part by pressurizing the electrode 5, welding is performed by using a current flowing through the path shown by 1sB in FIG. 8(b).

[Problem to be solved by the invention]

When performing spot welding of the laminated steel plates 1 by the above-mentioned shunting method, a spark-like discharge may unexpectedly occur in the vicinity of the weld, and holes may be formed in the skin steel plate 3.

The occurrence of such holes not only impairs the appearance, but also causes problems such as oil leakage in parts that require airtightness, such as oil pans.

The reason why such holes occur is that when manufacturing the laminated steel sheet 1, a high voltage is applied to conductive foreign matter such as iron powder mixed between the skin steel sheets 3, causing discharge. In order to prevent the formation of holes due to such discharge, it is necessary to perform welding without applying a high voltage between the electrodes 5. However, if welding is carried out at a low voltage that does not cause holes during all welding, only a low current can be passed when the resistance between the skin steel plates 3 before removing the resin/lF2 is high, and the time until the resin is removed will be longer. Therefore, the welding time after the resin is removed becomes significantly longer, and there is a problem in that productivity deteriorates in places such as automobile manufacturing lines where a large number of welds are required in a short period of time.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for spot welding laminated steel plates that can shorten welding time and improve productivity while preventing the occurrence of holes.

[Means to solve the problem]

To achieve the above object, the present invention provides a method for spot welding laminated steel plates, in which a member to be welded, including a laminated steel plate, is held between a pair of electrodes and spot welded using an inverter-controlled DC power source. , detecting the voltage between the pair of electrodes, and interrupting energization when abnormal voltage fluctuation is detected;
After the power source voltage is adjusted to an appropriate value, the power is turned on again to perform welding, and when the resistance value of the welded part becomes less than a predetermined value, the power source voltage is returned to the original voltage.

[Effect]

According to the above method, since an inverter-controlled DC power supply is used for the power supply, it is possible to complete the interruption of power supply in an extremely short time after detecting abnormal voltage fluctuations, and after detecting this abnormal voltage fluctuation, the voltage energizes to prevent holes from forming on the skin steel plate. Furthermore, by returning the power supply voltage to the initial high voltage when the resin directly under the electrode is removed and the resistance value between the electrodes becomes small, welding can be performed at normal welding speed and holes can be formed without reducing productivity. can be prevented.

〔Example〕

Hereinafter, one embodiment of the method for spot welding laminated steel plates according to the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. The voltage of the welding current supplied from the three-phase AC power supply 6 is adjusted to rA by an automatic voltage regulator (AVR) 7, converted to DC by a rectifier 8, and converted to high-frequency AC by an inverter section 9, which is then converted to a welding transformer 10. is applied to This transformer 1
The output of 0 is a high-frequency alternating current of low voltage and large current, which is rectified again by the rectifier 11 and sent as a welding current to the workpiece 12, at least one of which is the laminated steel plate 1, via the pair of electrodes 5.

On the other hand, the control unit 13 controls the electrode 5. AVR7, inverter section 9
Calculates the interelectrode type during energization, determines that there is an abnormality when v2 exceeds a predetermined value v2a, and issues a command signal to the inverter section 9 to interrupt the energization, and at the same time issues a command to the AVR 7. It has a function of outputting a signal to adjust the power supply voltage so that the secondary side no-load voltage V, reaches a predetermined value v, s, which is a safe value that does not cause discharge.

Next, to explain the spot welding method according to the present embodiment, holes occur in the skin steel plate 3 due to electrical discharge when a high voltage is applied between the electrodes 5 before removing the resin. Sometimes, as shown in FIG. 2, a waveform disturbance C occurs in the interelectrode voltage V□. Moreover, the curved line indicates the interelectrode voltage V□ after the resin is removed. During normal use without any abnormality occurring, the secondary side no-load voltage V is VxV as shown in FIG. 3, and does not change within the set welding time TV.

The secondary current at this time is the set welding current I, as shown in FIG.

A predetermined inter-electrode voltage change rate 728 that monitors the inter-electrode voltage V□ during energization, calculates the voltage change rate v2 in the control unit 13, and determines that the voltage change rate v2 is abnormal, which is a sign of the formation of holes due to discharge. If the above occurs, it is determined that there is an abnormality, and the control unit 13 issues a command signal to interrupt the energization to the inverter unit 9 before the perforation occurs. At this time, as shown in FIG. The required time T must be within a predetermined time Ts.

When an abnormality is detected, a command signal is issued from the control unit 13 to the AVR 7, and the power supply voltage is adjusted so that the secondary side no-load voltage V is set to a predetermined value v, s, which is a safe value at which no discharge occurs. After this adjustment is completed, the current is turned on again.The voltage V and s at this time are low, so if the current value Iw set as the welding condition cannot be obtained, adjust it as shown in Figure 6. The maximum current that can be flowed at the secondary no-load voltage V 3 s is applied. During this time, the interelectrode voltage v1 and the secondary current I are monitored, and the control unit 13 calculates the resistance value R of the welded part. When the resistance value becomes equal to or less than a predetermined resistance value Rs when continuity is obtained, the power supply voltage is returned to the initial voltage, and then a welding process is performed for a time Tv set as a welding condition.

Next, an example in which spot welding was performed using the method according to this example will be described.

N steel plate Thickness of skin steel plate 0.8 nm Thickness of resin layer 0.05 mm Steel plate to be welded Sep thickness 0.8 mV, a=1.
0X10'V/sec, v, 5=3vTs=1
/1000sec, Rs =150X10-'Ω
According to this embodiment, when an abnormal voltage fluctuation occurs, the energization is interrupted, the power supply voltage is adjusted by the AVR 7 to an appropriate value that does not cause perforation, and then the energization is resumed, and after the resin layer 2 directly under the electrode 3 is removed, the welding conditions are Since spot welding is performed using the power supply voltage and welding time set as follows, it is possible to prevent the formation of holes in the skin steel plate 3 without reducing productivity. At this time, by controlling the current between the electrodes 5 using high frequency using the inverter 9, high responsiveness of control can be obtained.

〔Effect of the invention〕

According to the present invention described above, the inter-electrode voltage applied by the inverter-type DC power supply is monitored, and when an abnormal voltage fluctuation is detected, the energization is interrupted, and after the power supply voltage is adjusted to an appropriate value by the AVR, the energization is resumed. Welding is carried out at the welding point, and the power supply voltage is returned to the original voltage when the resistance value of the welded part falls below a predetermined value, thereby preventing the formation of holes in the skin steel plate without reducing productivity. I can do it.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of the spot welding method for laminated steel plates according to the present invention, Fig. 2 is a graph showing inter-electrode voltage fluctuation when a hole occurs, and Figs. 3 and 4 are abnormalities, respectively. 2 is a graph showing temporal changes in secondary side no-load voltage and current when no load occurs. Figures 5 and 6 are two cases in which an abnormality is detected, respectively.
Graph showing temporal changes in next-side no-load voltage and current, No. 7
The figure is a side view showing the laminated steel plate, and Figure 8 is the product N obtained by the shunting method.
FIG. 3 is a side view showing a method of spot welding steel plates. DESCRIPTION OF SYMBOLS 1... Laminated steel plate, 5... Electrode, 6... 7... 9... 13... Substitute power source 5 Automatic voltage rAll regulator (AVR), inverter, control section. Buried Tetsuro Abe No. 30 Figure 5 Figure 6 Gi g-1

Claims (1)

[Claims] (1) A method for spot welding laminated steel plates, in which a workpiece to be welded, including a laminated steel plate, is held between a pair of electrodes and spot welded using an inverter-controlled DC power supply, wherein the voltage between the pair of electrodes is When an abnormal voltage fluctuation is detected, the power supply is interrupted, and after adjusting the power supply voltage to an appropriate value, the power supply is turned on again to perform welding, and when the resistance value of the welding part falls below a predetermined value, the power supply is turned off. A method for spot welding laminated steel plates characterized by returning the voltage to the original voltage.