JPS58112674A - Resistance welding control method - Google Patents

Abstract

PURPOSE:To improve and uniform the quality of spot welding by increasing a welding current gradually after a specific time limit from the starting of feeding and detecting nugget formation on the basis of the decrement of the integral value of an interchip voltage for every half cycle. CONSTITUTION:The voltage between chips 1 and 1 which clamp a work 2 is passed through a filter circuit 3 and integrated by an AC integrating circuit 4, whose output is supplied to a rectifying circuit 5. Once a welding current of each half cycle flows, an A/D converting circuit 6 generates a conversion starting pulse to perform conversion. By a conversion ending signal, the circuit 4 is reset and a microcomputer 8 accumulates and stores the interchip voltage of every half cycle. Then the fetched decrement of the interchip voltage of every half cycle is compared with the value of a dust generation detection value setting circuit 7 and when the former is greater than the latter, feeding is cut by an input voltage variation compensating timer 9 by a signal from the computer 8. The welding current setting of the timer 9 is carried out by a welding current setting circuit 10.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resistance welding control method, and an object thereof is to improve and make uniform the quality of resistance welding, particularly spot welding.

Traditional measures to improve the welding quality of spot welding include (1) stabilizing control of welding conditions, (2) detecting the formation of weld nuggets using some physical quantity, and controlling the welding so that the diameter of these nuggets is uniform. A dual energization method is being considered to control the process. Method (1) is a method to stably control the three major conditions of resistance welding, such as welding current 1 energization time and pressurizing force, so that there are few fluctuations. An example of this can be seen in the synchronous timer, which incorporates a constant current control circuit that controls the flow of a constant current even when the power factor varies. However, these are based on pressure fluctuation (1) branch flow, chip deformation, or shape (9) surface condition of the workpiece (object to be welded).

There is no function to compensate for variations in the contact level, etc., and it is difficult to make the quality of the welded product constant.

On the other hand, method (2) more directly detects the welding quality, that is, the state of nugget formation, using sound or voltage, and attempts to stabilize the quality by cutting off the current when the nuggets have grown sufficiently. . For example, the voltage between welding electrodes (hereinafter referred to as the voltage between tips) during welding is monitored, and as shown in Figure 1, the peak value of the voltage between tips is monitored for each cycle, and the maximum value By detecting (v) and cutting off the current when the inter-chip voltage decreases by a preset ratio with respect to Vp (when it reaches the Vc value), the above-mentioned pressure fluctuations, etc. Even if there is, the welding quality is made uniform during welding, that is, in-process (Japanese Patent Laid-Open No. 114541/1983).

However, the disadvantage of this method is that only the energization time is controlled, so if the welding current drops considerably for some reason, the energization time will be longer, but sufficient nugget growth cannot be expected, and the strength will therefore be low. . Here, (I) in FIG. 2 shows the envelope of the peak value of the inter-chip voltage when sufficient nuggets are obtained, and (It) shows the envelope when nuggets are insufficiently formed.

Furthermore, this method has the disadvantage that only materials with high resistivity, such as mild steel or stainless steel, can be used as the workpiece. This is because materials with low resistivity such as aluminum do not necessarily have a maximum value in the envelope of the wave height values.

On the other hand, acouste monitoring system that occurs from the welding part during welding,
MuX above threshold level (Vti)
Attempts have also been made to cut off the current when a signal is detected. This is especially useful because it detects a large warning signal associated with the occurrence of medium dust during welding, and cuts off the current flow based on the idea that sufficient nuggets have been formed at the time when medium dust occurs. It is.

However, like the tip-to-chip voltage method described above, this method only restricts the energization time and does not actively control the welding current. The 5E signal is also small, and only the energization time period becomes longer, making it impossible to obtain a uniform nugget diameter.

The present invention focuses on the fact that the inter-tip voltage is closely related to nugget growth, and monitors the inter-tip voltage during welding.
An energization control method that cuts energization when a decrease value of an integral value obtained by integrating the inter-chip voltage corresponding to energization for half a cycle of a power supply over a energization range for half a cycle exceeds a preset value, and The most important point is that the welding current is applied at the standard welding current for the workpiece for a certain period of time after the start of energization, and then the welding current is gradually increased at an approximately constant rate for each cycle. .

First, a method for monitoring chip-to-chip voltage will be explained. When detecting the chip-to-chip voltage, there are cases where the peak value is simply detected as shown in Figure 3 (a), and cases where the chip-to-chip voltage corresponding to half a cycle of current is detected as shown in Figure 3 (b). In some cases, it is detected as a value integrated over minutes.

Method (b) detects the inter-chip voltage because it can largely eliminate the superimposed induced voltage caused by the welding current, which is particularly noticeable when the probe is placed along the edge of the spot welder. This has the advantage of improving accuracy.

The power supply is cut off when dust occurs. In this case, the time change in the rectified value of the integral value of the chip-to-chip voltage for each half cycle shows a rapid drop as shown in FIG.

Therefore, monitor the decrease value of the rectified value of the integral value (ΔV in Figure 4) of the inter-chip voltage every half cycle, and if this value is larger than a predetermined value or If the degree of increase in the integral value becomes smaller than a preset value, it is assumed that dust has occurred and the energization is cut off.

The basis of the waveform shown in FIG. 3(a) will now be explained.

The inter-chip voltage (e) is normally measured by detecting the voltage between the upper and lower tips using a detection probe. Detected by resistance drop due to current flow.

That is, e = iR + t (K: induced voltage coefficient, 1: welding current, R: inter-chip resistance) This is illustrated in Figure 5 (a), (b),
(c).

Next, the setting of welding current will be explained.

The welding current is set to standard welding current conditions at the start of energization. For a certain period of time after energization is started, the temperature of the nugget forming part of the work increases, and finally reaches the melting point and the nugget begins to grow. During this time, it seems best to keep the welding current approximately constant or to slightly increase the slope.

Now, after this period, the welding current is increased one cycle at a time in the range of 2 to 20%. in particular,
The welding current setting voltage value of the constant current timer and input voltage fluctuation compensation timer is individually preset and programmed for each cycle, and as welding progresses, the preset value is selected with a switch.
For example, as shown in FIG. 6, a plurality of variable resistors v''+I vR21vRs +・'''' giving a preset value
・vR", analog switch S1 as a switch to select the variable resistance + S5...
... can be easily constructed by using a shift register i9R having as a clock input a pulse synchronized with the power supply frequency for controlling an analog switch. VR1 is a variable resistor for setting the welding current for the first cycle, vR2 is for setting the welding current for the second cycle, and vRn is for setting the welding current for the nth cycle. be. MND is shift register SR
This is a ND gate at the front stage of the ND gate, and a power supply frequency pulse and an energization time signal are both given from a timer to its input side. Note that the energization time limit is limited by the energization cut signal, but if this does not occur even after exceeding the upper limit energization cycle value set by the timer, it is cut by the upper limit energization cycle value.

Next, an example of a circuit for carrying out the method of the present invention will be described with reference to the drawing of FIG. In the figure, 1 is a welding electrode (electrode tip), 2 is a workpiece (object to be welded), 3 is a filter circuit, 4 is an AC integrating circuit, 5 is a rectifier circuit, and 6 is a mu/
D conversion circuit, 7 is a dust generation detection value setting circuit, 8 is a microcomputer, 9 is an input voltage fluctuation compensation timer, 1o
is the welding current setting circuit shown in FIG.

The inter-chip voltage is then input to an AC integrating circuit 4 via a filter circuit 3, subjected to integration processing, and then input to a rectifier circuit 5. In the system/D conversion, a conversion start pulse is generated at the time when the welding current for each half cycle has finished flowing, and the conversion is performed.

Next, this integration circuit 4 is reset by the M/D conversion end signal.

In this way, the inter-chip voltage for each half cycle is stored and accumulated in the memory of the microcomputer 8. circuit 7
is composed of digital switches, and if the reduction value of the inter-chip voltage calculated in the microcomputer 8 is larger than the set value of the circuit 7, then , the microcomputer 8 outputs a signal to the timer 9 to cut off the current. When the timer 9 receives this signal, it immediately turns on and off the current. Further, the welding current setting of the timer 9 is performed using the welding current setting circuit 1o.

Now, an example of a concrete implementation is as follows.

Workpiece; Mild steel plate (thickness 1mm) Welding machine; 3sKV single-phase spot welding machine control device;
Equipment welding conditions shown in Fig. 7: Initial welding current 81oOm Upper limit energization cycle value 15th cycle Current increase start cycle 5th cycle current increase value
300 μm/1 cycle energization cut cumulative voltage between chips 4.5 V Dust detection voltage between chips 0.25 V or more, pressurizing force is 170 to 2 sokg, diameter of tip (OF chip) is 6.8 Welding was performed by changing the temperature to 7 to OWin. As a result, the current application time was within 7 to 16 cycles, and the welding results (strength) were also very good.

As described above, according to the resistance welding control method of the present invention, after a certain time period has elapsed from the start of energization, the welding current is gradually increased within the range of 2 to 20% compared to the previous value, and the Effective combination with control that guarantees the growth of weld nuggets by monitoring the cumulative value of the integral value for every half cycle of the voltage, it is possible to control tip deformation, pressure fluctuations, current fluctuations, workpiece surface conditions, contact conditions, etc. Even when there are variations in welding conditions, it is possible to always guarantee good and uniform welding quality, and its industrial potential is great.

[Brief explanation of the drawing]

Figure 1 is a typical waveform diagram of inter-chip voltage, Figure 2 is a diagram showing an example of energization time control using inter-chip voltage, and Figure 3 (
a) and (b) are waveform diagrams of an example of the chip-to-chip voltage integrated every half cycle, FIG. 4 is a waveform diagram of the chip-to-chip voltage when dust occurs, and FIG. 5 (a). (b) and (c) are diagrams for explaining the inter-chip voltage waveform, Figure 6 is a circuit diagram of a welding current setting circuit that sequentially switches the welding current, and Figure 7 is a diagram for implementing the method of the present invention. FIG. 2 is a block diagram of a device for 1... Welding electrode, 2... Work to be welded, 3
... Filter circuit, 4 ... AC integration circuit, 5 ... Rectifier circuit, 6 ... Mu/D conversion circuit, 7 ... Dust generation detection value setting circuit, 8.
...Microcomputer, 9...Input voltage fluctuation compensation timer, 1o...Welding current setting circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
1!1 Figure 3 (α) Figure 5 Figure 6

Claims (1)

[Claims] The welding current is increased sequentially at a preset rate after a preset time period has elapsed from the start of energization in resistance welding, and the voltage between welding electrodes is monitored during welding to adjust the voltage between the welding electrodes for half a cycle of energization to the same value as that for the half cycle. 1. A resistance welding control method, characterized in that energization is cut off when a reduction value of an integral value integrated over a energization range reaches a preset value or more.