JPH06344155A - Controller for spot welding machine - Google Patents

Abstract

PURPOSE:To suppress generation of expulsion and surfaces flash and to perform welding with the uniform welding nugget diameter by detecting the voltage between electrodes, comparing a voltage value or its increasing rate with a reference value to predict generation of expulsion and surface flash and taking a measure to meet the situation according to its predicted result. CONSTITUTION:The expulsion and surface flash generated from the interval between metallic sheet materials to be welded can be suppressed by supplying a current reduced by teh specified quantity than the usual current quantity only for a period of a specified period tw1 during welding energizing. Experiment confirms that the expulsion and surface flash are easily generated during the period of this period tw1. Further, since the presence or absence of generation of the expulsion and surface flash is predicted by whether or not the voltage between electrodes during welding exceeds the reference value, generation of the expulsion and surface flash can be suppressed surely and effectively. While the period tw1 is the period when an area of a current path between the materials to be welded is going to expand suddenly, a welding current Iw is reduced by DELTAIw1 and the area of the welding current path is expanded smoothly during this period, by which generation of expulsion and surface flash is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spot welding device for superposing and welding metal plate materials.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram of a control circuit of a conventional general spot welding machine for welding metal plate materials such as mild steel plate and galvanized steel plate. In the figure, I _a , I
_b is, for example, a welded machine of a metal plate having a material thickness of about 0.6 mm to 3.2 mm, which is sandwiched by electrodes 2a and 2b, and a secondary conductor of a welding transformer 30 is passed from the welding power source 21 through an electronic switch 29 to the electrode. It is connected. On the other hand, the initial pressurization time timer (T ₁ ) 22, the energization timer (T ₂ ) 23, and the electrode holding time timer (T ₃ ) 24 that have received the control power supply 20 operate in sequence to perform energization. During time, the welding current control circuit 26 activates the electronic switch 29 to supply the welding transformer 30 with welding power.

FIG. 8 is an example showing a state of welding current and electrode pressure when a DC welding transformer is used. The horizontal axis represents time, and the vertical axis represents electrode pressure (F) and welding current (I). _W) indicates respectively T ₁ by 3 types of timers 22, 23, 24 in FIG. 7,
It indicates that the sequence of T ₂ and T ₃ is in progress.

In a conventional welding machine, the nugget diameter increases as shown in FIG. 9 when welding is carried out by increasing the welding current only while keeping the electrode tip shape, the electrode pressing force, and the energization time constant, and eventually the scattering current exceeds the limit current. And the plate-to-plate of the material to be welded occurs, and the nugget diameter also decreases.

[0005] Automakers who use a lot of spot welding often work under welding conditions that produce a relatively large nugget diameter in order to increase the stability of the welding strength. Due to fluctuations in the pressing accuracy of the work piece, the plate-to-plate overlapping degree of the work material is not uniform, and spatter may occur even if the welding current is set below the spatter generation limit current.

[0006]

In order to obtain spot welding with a large nugget diameter by the conventional spot welding machine as described above, if the welding current is increased up to near the scattering current, welding conditions (electrode pressure, welding Dispersion may occur due to slight variations in the current, the flow passage area between the materials to be welded, etc.).

[0007] Even if an attempt is made to obtain a reliable spot with a large nugget diameter, if scattering occurs between the materials to be welded, the nugget diameter becomes extremely small and the welding strength is reduced. Furthermore, this scattering not only adheres to the equipment near the electrodes, but is not preferable from the viewpoint of the safety of the operator and has been a problem from the working environment.

In order to solve the above-mentioned problems, the control device of the present invention detects the voltage between electrodes during welding, incorporates this as a judgment element for predicting the occurrence of scattering, and when it is predicted that scattering will occur. An object of the present invention is to provide a spot welding machine control device capable of suppressing the occurrence of dust by taking measures to suppress the occurrence of dust during welding.

[0009]

[Means for Solving the Problems] As shown in FIG. 10 (A), the inter-electrode voltage when the dispersion occurs during welding is the inter-electrode voltage (V _E when a constant welding current (I _W ) is applied. ) Draws a waveform showing the maximum value at the initial stage of energization as shown in the figure. Even if the welding current (I _W ) is the same as in FIG. 10 (A), the inter-electrode voltage (V _E ) shown in FIG. 10 (B) and FIG. As shown in the figure (B), the initial rise is abrupt, and in the case of a high peak value, scattering often occurs in the time zone as shown. In the case of Fig. 10 (C),
There is no need to worry about scattering.

Therefore, in the spot welding machine control apparatus of the present invention, welding is performed with an inter-electrode voltage detector for detecting the inter-electrode voltage during welding and a current slightly smaller than the scattering occurrence limit current (I _ex ) shown in FIG. Determination by experimentally obtaining the inter-electrode voltage generated at the time of use, using this as a reference voltage, and comparing the voltage detected by the inter-electrode voltage detector with the reference voltage to determine whether or not the reference voltage is exceeded. And a welding current reduction circuit that reduces the welding current for a certain period when the inter-electrode voltage exceeds the reference voltage by the determination circuit.
This is characterized in that the welding current is supplied slightly before the occurrence of 10 (B) to reduce the current so as to suppress the occurrence of scattering.

[0011]

In the controller of the present invention, by supplying a current reduced by a predetermined amount from the normal current amount only during a predetermined period during welding energization, it is possible to suppress the scattering generated between the metal plate materials to be welded. it can. This predetermined period is a period of tw ₁ shown in FIG. 1 and is a period in which it is experimentally confirmed that scattering easily occurs. Further, in the control device of the present invention, the presence or absence of the scattering is predicted depending on whether or not the inter-electrode voltage during welding exceeds the reference value, so that the scattering can be reliably and effectively suppressed. The period of tw ₁ shown in FIG. 1 is a period in which the area of the current path between the materials to be welded is rapidly expanding, but during this period, the welding current is reduced by ΔI _W , and the area of the welding current path is moderate. The spread is suppressed by being expanded to. However, the reduction amount of welding current Δ
If I _W1 becomes excessively large, there is a risk that a second scattering occurs as shown by S in FIG. 2 (A). Therefore, even during this period, the inter-electrode voltage is detected and the change in the voltage is detected. When the change turns to increase, as shown in FIG. 2 (B), in order to suppress the occurrence of the second and third scattering, tw ₂ , ΔIw ₂
And tw ₃ and ΔIw ₃ are controlled.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a sequence operation when the control device of the present invention is operated in anticipation of occurrence of scattering, and the states of welding current, inter-electrode voltage and electrode pressure. 1 often occurs during the tw ₁ period of FIG. 1, and in this case, the risk of occurrence of scattering increases from the time when the inter-electrode voltage reaches the maximum value at the initial stage of welding current application, and is almost the same as in FIG. Of t
Concentrate on w ₁ period. Moreover, as shown in FIG. 3 (A) when the scattering occurs, when the scattering does not occur, as shown in FIG.
The maximum value is higher than that of (B). Therefore, the inter-electrode voltage V _{E at} t _C after the welding current is applied as shown in FIG. 1 is compared with the reference voltage E _C to determine and predict the occurrence or non-occurrence of scattering. When the inter-electrode voltage at t _C after energization exceeds the reference voltage E _C , it is determined that the dispersion occurs, and the welding current is reduced by ΔI _W1 for a period of tw ₁ after t _o from the start of energization.

The reason for sampling the inter-electrode voltage V _E at t _C after energization is that there are two inter-electrode voltages at the initial stage of energization as shown in FIG. 6 depending on the type of material to be welded. It is possible to avoid it and detect the maximum value of the inter-electrode voltage V _E as shown in FIG.
After detecting the voltage of _{O + e} and E _O , the time to the scattering occurrence part is comparatively short, so it is necessary to make the time between the occurrence of the scattering occurrence and the dispersion occurrence suppression measure as long as possible. Is that the control device can be easily manufactured.

FIG. 4 shows a block diagram of a control device which enables the control of the present invention. In the drawing, the material to be welded 1a, from to welding transformer 30 1b is the same as the block diagram of a conventional control system, inter-electrode voltage detection circuit expulsion generation suppression timer from 50 (t _o) 55 is established by the present invention Circuit.

The operation of this circuit will be described below. control
The power is received from 20, and the initial pressurization time timer (T₁) 22, through
Electric power timer (T ₂) 23, electrode hold time timer (T₃) 24 is
T shown in FIG.₁, T₂, T₃Sequence operation like
It

Now, when the welding is started and the welding current is counted up by the initial pressurization time timer (T ₁ ) 22, the energization is started. During this energizing time, the welding current control circuit 26
1 operates the electronic switch 29 for welding power source, and when the welding current supplied to the welding transformer 30 flows through the electrodes 2a, 2b to the objects to be welded 1a, 1b, it is shown in FIG. 1 between the electrodes 2a, 2b. An inter-electrode voltage V _E is generated. This V _E is detected by the inter-electrode voltage detector 50
In detected, the reference voltage has been set this V _E advance (E
_C ) 53 is compared with the comparison / discrimination circuit 52. Sampling the comparison determination circuit V _E of the t _c when in the inter-electrode voltage between electrodes voltage V _E at the time of lapse t _c from the start of energization when the comparison 5
Done in 2. The flow of this determination is as shown in FIG. 5, and there are a method of directly comparing each voltage (A) and a method of comparing the rate of change of voltage (B). As a result of the discrimination, the inter-electrode voltage is the reference voltage E _c.
If the value exceeds the value, the welding current reduction circuit 54 is Δt during t _w1 after t _o at the timer (t _o ) 55 for preventing dispersion from the start of energization.
Welding current control circuit 26 reduces the welding current by I _w1.
Command. After that, if the inter-electrode voltage does not shift in the increasing direction, the set welding current I _w flows until the end of welding, but it increases in the increasing direction while monitoring the voltage after the inter-electrode voltage shows the maximum value. the voltage decrease judgment circuit 51 if that Turning, second scattering suppression current as is issued command to the welding current reduction circuit 54 to the scattering prevention measures current view _{2 (B) (ΔI w1,} t w2 ), Depending on the case, the third dispersion suppressing current (ΔI _w3 , t _w3 ) is controlled.

[0017]

The controller for the spot welding machine of the present invention is
It is necessary to detect the voltage between electrodes and compare the voltage value or its increase rate with the reference value to predict the occurrence of scattering in the hot-welding of the metal plate material of the work piece, and take measures according to the prediction result. In order to suppress the occurrence of scatter, the welding device is capable of performing uniform welding of the welding nugget diameter in an environment in which the occurrence of scatter is suppressed as a whole. Material, electrode shape,
Stable inter-electrode voltage that does not cause scattering due to welding current, pressure, and other welding conditions is compared with the voltage at the electrode that is actually welding, and feedback control is performed to prevent the occurrence of scattering. Welding with a uniform weld nugget diameter can be achieved more effectively.

Further, since it is possible to suppress the occurrence of scattering, it is possible to prevent the equipment near the electrodes from being contaminated, ensure the safety of the operator, improve the working environment and improve the efficiency of the welding work. It is a spot welding device.

[Brief description of drawings]

FIG. 1 is a sequence diagram illustrating an operation of a control device according to the present invention.

FIG. 2 is a sequence diagram for explaining the operation of the control device according to the present invention, and is a sequence diagram when a situation occurs in which scattering occurs multiple times.

FIG. 3 is a diagram showing a voltage between electrodes when welding is performed using a general welding device, in which (A) shows a state in which dispersion occurs and (B) shows a state in which no dispersion occurs.

FIG. 4 shows a block diagram of a control device according to the invention.

5 is a diagram showing an operation flow of a control circuit that compares the inter-electrode voltage in FIG. 4 with a reference voltage to predict and determine whether or not dispersion occurs from the inter-electrode voltage during welding.

FIG. 6 is a diagram for explaining that there are two types of inter-electrode voltage at the initial stage of energization (A) and (B) depending on the material to be welded and the surface condition.

FIG. 7 shows a block diagram of a conventional control device.

FIG. 8 is an operation sequence diagram when welding is performed by the control device of FIG. 7.

FIG. 9 shows the relationship between nugget diameter and welding current.
In particular, it was shown that there is a current that causes scattering between the materials to be welded as the welding current is increased.

FIG. 10 is a diagram illustrating the states of the inter-electrode voltage when the scattering occurs and when the scattering does not occur.

[Explanation of symbols]

 1a, 1b Material to be welded 2a, 2b Electrodes holding the material to be welded 20 Control power supply receiving terminal 21 Welding power supply receiving terminal 22 Initial pressurization time timer 23 Energization time timer 24 Electrode holding time timer 26 Welding current control circuit 29 Electronic Switch 30 Welding transformer 50 Electrode voltage detector 51 Voltage increase / decrease judgment circuit 52 Comparison judgment circuit 53 Reference voltage setting circuit 54 Welding current reduction circuit with built-in timer 55 Timer until implementing measures to prevent scattering

Claims (1)

[Claims] 1. A spot welding machine in which materials to be welded are stacked, sandwiched between a pair of electrodes, a suitable pressure is applied between the electrodes, and a welding current is passed between the electrodes to perform welding. The welding current low-pass circuit that reduces the welding current for a certain period of time, the inter-electrode voltage detector that detects the inter-electrode voltage during welding, and the inter-electrode voltage generated when welding with a current slightly smaller than the dispersion limit current It is provided with a determination circuit that compares the reference inter-electrode voltage obtained during the experiment with the voltage detected by the inter-electrode voltage detector to determine whether or not the detected voltage exceeds this. In addition, when the inter-electrode voltage exceeds the reference voltage, the welding current reduction circuit operates to reduce the welding current for a certain period of time to suppress the occurrence of scattering, thereby controlling the spot welder.