JPS58112673A - 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 increment of the accumulated value of integral values of an interchip voltage for a half cylce. 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. The increment of the accumulated value is compared with the value of a feeding cut set value circuit 7 and when the former is less than the latter, an input voltage variation compensating timer 9 cuts feeding by a feeding cut signal from the computer 8. Further, 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 its entire purpose is to improve and make uniform the quality of resistance welding, particularly spot welding.

Conventionally, measures to improve the welding quality of spot welding include (1) stabilization control of welding conditions, (trans)detecting the formation of weld nuggets using some physical quantity, and controlling the welding so that the diameter of these nuggets is uniform. Two methods of controlling the process have been considered. Method (1) is a method to stably control the three major conditions of resistance welding, such as welding current 9 energization time and applied 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 due to pressure fluctuations, 9 branch currents, chip deformation, or the shape of the workpiece (object to be welded) 9 and surface conditions.

There is no function to compensate for variations in the degree of contact, etc., and it is difficult to maintain constant welding quality.

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 (Vp) is detected,
Welding quality can be maintained even when the above-mentioned pressure fluctuations occur by cutting off the current at the moment when the inter-chip voltage decreases by a preset percentage relative to vp (when it reaches the Vc value). The purpose is to make the material uniform during welding, that is, in-process.
Publication No. 1).

However, the disadvantage of this method is that it controls only the current state of energization, 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. Become. Here, t, I) in Fig. 2 is the envelope of the peak value of the inter-chip voltage when sufficient nuggets are obtained, and (II) is the envelope when nuggets are insufficiently formed. However, it 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,
This is because the envelope of the wave height values mentioned above does not necessarily have a maximum value.
Threshold level (Tri)
Attempts have also been made to cut off the energization at the time when the above-mentioned E signal is detected. This is especially useful when detecting the large nuggets associated with the generation of medium dust during welding, and considering that sufficient nuggets have been formed by the time medium dust occurs, and the current is cut off at that point. It is something.

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 beam X 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.
Energization is cut off when the cumulative increase in the rectified value of the integrated value obtained by integrating the inter-chip voltage corresponding to energization for half a cycle of the power supply over the energization range for half a cycle exceeds a preset value. The most important point of the energization control method is that energization is carried out at the standard welding current for the workpiece for a certain period of time from the start of energization, and then the welding current is sequentially increased at a substantially constant rate for each cycle. The reason lies in the method adopted.

First, a method for monitoring chip-to-chip voltage will be explained. When detecting the chip-to-chip voltage, there are two methods: detecting the peak value at the peak as shown in Figure 3 (&), and detecting the chip-to-chip voltage corresponding to half a cycle of energization as shown in Figure 3 (&). In some cases, it is detected as a value integrated over a cycle.

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 detection group is placed along the edge of the spot welder. This has the advantage of improving accuracy. Now, the temporal change in the inter-chip voltage after the start of energization is as shown in FIG. Here, the vicinity of the peak value of the envelope of the chip opening pressure in Figure 2 is said to be the peak period of nugget growth, and the reason why the envelope curve declines after that is because the resistance value decreases due to the expansion of the nugget, and therefore the inter-chip This is because the voltage drop decreases. This tendency is approximately the same in the case of the method according to the present invention in which the welding current is increased after the start of energization or after a certain period of time. Therefore, the inter-chip voltage for half-cycle energization of the inter-chip voltage is integrated over the energization range for the half-cycle, and the values are sequentially rectified and further accumulated, and the changes in the cumulative value are monitored. When the amount of change (increase) becomes less than a preset value, the current is cut off to obtain an appropriate nugget. In addition, this can also prevent ramming. 'The basis of the waveform in FIG. 3 (IL) will be explained here.

The inter-chip voltage (e) is normally measured by detecting the voltage between the upper and lower tips using a full voltage detection probe, but at this time, the inter-tip voltage (6) is measured by welding between the tips. The resistance drop voltage (R1) due to the current flowing and the welding current are detected by closing the detection group.

That is, 1 e = iR + - t (K: induced voltage coefficient, 1: welding current, R: resistance between steps) What is shown in Fig. 4 (&), (b) e
(C).

Next, the setting of welding current will be explained.

The welding current is set to standard bath welding current conditions at the start of energization. During a certain period of time after electricity 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 preset and programmed to one value for each cycle in advance, and as welding progresses, the preset value can be changed by switching as shown in Figure 6. Multiple variable resistors VR1, VB2, 'iR5,-
・・VRH(!:, Analog switch S<, M82. S3... as a switch to select the variable resistance.
. . . can be easily constructed by using a shift register SR having a clock input as a pulse clock 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, VB2 is a variable resistor for setting the welding current for the second cycle, and VRHrri is a variable resistor for setting the welding current for the nth cycle. . The MND is a MND gate at the previous stage of the shift register SR, and a power frequency pulse and an energization time limit signal are both applied to the input side of the MND gate from a timer. 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 bath electrode (electrode tip), 2 is a workpiece (object to be welded), 3 is a filter circuit, 4 is an AC integrating circuit, 6 is a rectifier circuit, and 6 is a mu/
A D conversion circuit, 7 an energization cut setting value circuit, 8 a microcomputer, 9 an input voltage fluctuation compensation timer, and 10 a 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 M/D conversion, a conversion start pulse is generated at the time when the welding current for each half cycle finishes flowing, and the conversion is performed. Next, this integrating 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.

The "0" path 7 is constituted by a digital switch, and the increase in the cumulative value of the inter-chip voltage from the start of energization, which is taken into the microcomputer 8, is compared with the value of the set value circuit 7, respectively.

Here, if the increase in the cumulative value of the inter-chip voltage accumulated in the microcomputer 8 is smaller than the set value of the set value circuit 7, the microcomputer 8 sends an instruction to the timer 9 to cut off the current. Output a signal.

When the timer 9 receives this signal, it immediately cuts off the current. Regarding the welding current setting of timer 9, t/'i,
This is done 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: 35KV single phase spot welding machine Control device: No. 6
Equipment welding conditions shown in the figure: Initial welding current 8100 μm upper limit energization cycle value 15 cycles Current increase start cycle 5 cycles current increase value 300 μm/1 cycle energization cut cumulative voltage between tips 4.6 V Dust detection voltage between tips 0・261 Regarding the above, welding was carried out by changing the pressing force from 170 to 260 kg and the diameter of the tip (CF tip) from 6.8 to 7.0 mm. 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 increase in the cumulative value of the integral value every half cycle of voltage, prevents tip deformation, pressure fluctuations, current fluctuations, workpiece surface conditions, and contact. Even if there are variations in welding conditions such as welding conditions, it is possible to always guarantee good and uniform welding quality, and its industrial efficiency is outstanding.

[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 (
SL), (b) is a diagram for explaining the cycle inter-chip voltage waveform that halves the inter-chip voltage, Fig. 6 is a circuit diagram of a welding current setting circuit that sequentially switches the welding current, Fig. 6 is a diagram of the present invention. 1 is a block diagram of an apparatus for implementing the method of FIG. 1... Welding electrode, 2... Work to be welded, 3
... Filter circuit, 4 ... AC integration circuit, 6 ... Rectifier circuit, 6 ... Mu/D conversion circuit, 7 ... Energization cut setting value circuit, 8...
...Microcomputer, 9...Input voltage fluctuation compensation timer, 1o...Welding current setting circuit. Name of agent: Patent attorney Toshio Nakao and 1 other group
l Figure 3 Figure 4 Figure 5 AND SR

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 an increase in the cumulative value of integral values integrated over a energization range becomes equal to or less than a preset value.