JPS6319276B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resistance welding device that can automatically guarantee the quality of a welded location during resistance welding.

In general, in resistance welding, welding quality is determined by various electrical quantities: voltage, current, resistance which is the voltage divided by current, electric power which is the product of voltage and current,
Furthermore, it has been well known that this has a deep relationship with the value integrated over the energization time. Therefore, as methods for monitoring the quality of welded parts, methods such as an inter-electrode voltage method, an inter-electrode tip resistance method, and an ultrasonic method have been devised and are currently in use. However, although each of these monitoring methods has a different scope of application, all of them can only roughly judge the quality of the welded area after welding is completed, and cannot actively guarantee the quality of the welded area. It's not a thing. For this reason, even if conventional resistance welding methods and various monitoring methods are used together, quality defects occur in the welded parts, requiring rework and, in some cases, the product having to be discarded. There were flaws.

The purpose of the present invention is to automatically guarantee welding quality during the welding process by focusing on the size of the nugget that is most closely related to the quality of the welding location, and by detecting the size of the nugget. Our goal is to provide resistance welding equipment that can.

The resistance welding device according to the present invention can be used at the time when the integrated value of the voltage between the welding electrodes reaches a predetermined upper limit value, or when the resistance between the welding electrodes reaches a predetermined value, whichever comes first. energization time control means for stopping the welding current at , and alarm means for issuing an alarm when the integral value of the voltage between the welding electrodes does not reach a predetermined lower limit value after a predetermined energization time elapses. It is a feature.

Before explaining the present invention, the states of nuggets and current-carrying paths formed under various different welding conditions will be described. Figure 1 shows the plate thickness
This is a graph showing the current conduction path diameter between the welded materials and the nugget diameter when 0.8 mm mild steel plates are spot welded using a CF type (flat type) electrode. Now, the electrode tip diameter is De, the electrode pressure is P,
When welding current is I, curve a-1 is De=6.8
mm, P = 380Kg, I = 12000A, a-2 is the nugget diameter vs. time curve, curve c-1 is De = 4.8mm, P = 190Kg, I
=6000A, and c-2 is the nugget diameter versus time curve in that case. In addition,
Welding time is indicated by the number of cycles of alternating current. As is clear from this figure, when a nugget is formed, the diameter of the nugget and the area of the current-carrying path are closely related.

FIG. 2 shows the relationship between the diameter of the nugget and the integral value of the voltage between the electrodes. The welding conditions were as follows: an R type (curved type) with the same tip diameter as the electrode;
Using the CF type, we are trying to divide the pressure into low pressure (190Kg) and high pressure (380Kg). In the figure, curve A shows the case where welding is performed with a high welding force, and curve B shows the case where welding is carried out with a low welding force. From this figure, it can be seen that when the pressing force and the electrode tip diameter are constant, the nugget diameter and the integral value of the interelectrode voltage are closely related. This shows that the welding current can be cut off when the integral value of the voltage between the electrodes reaches a reference voltage integral value preset in accordance with the degree of formation of a necessary nugget while the welding current is being applied. .

Figure 3 shows the relationship between the interelectrode resistance during welding and the reciprocal 1/S of the energized path area over time under different welding conditions such as various electrode tip tip shapes and dimensions, electrode pressing force, and welding current. This shows the changes in As seen in the figure, the interelectrode resistance changes moment by moment during welding. Note that the direction of the arrow of each curve indicates the direction in which time passes. Looking at the relationship with the reciprocal of the energized path area, there is an almost proportional relationship at the time after the interelectrode resistance passes the maximum value, and under any welding conditions, the relationship is almost proportional to the reciprocal of the current-carrying path area. There is a similar relationship.

Figure 4 shows the relationship between the interelectrode resistance at the initial stage of energization and the reciprocal of the energized path area, 1/S, under various welding conditions. In this case, too, the proportional relationship is approximately along a single proportional straight line indicated by a broken line. It turns out that there is. As a result, the interelectrode resistance R is R=ρ・l/S
It is easily understood that the relationship is as follows: (ρ: specific resistance of material, l: distance between electrodes, S: area of energizing path between welded materials).

The facts shown in these graphs indicate that the current carrying path area between the materials to be welded can be easily estimated during welding by measuring the interelectrode resistance. Note that even if other welding points already exist in the vicinity of the welding point of interest, the area of the energized path based on the interelectrode resistance can be estimated within approximately the same error range. In addition, the interelectrode voltage and interelectrode resistance include the value between the electrode tip and the welded material in addition to the value between the welded materials, but the latter is generally compared to the former. It is small at about 20 to 30% and is almost constant over time, so it can be considered that the interelectrode voltage and resistance represent that between the materials to be welded.

The above facts always hold true regardless of the electrode tip shape, dimensions, type of material to be welded, etc., and even if the thickness, number, etc. of the material to be welded changes, the basic trends will change. There isn't. Therefore, by detecting the inter-electrode resistance during the welding process, it is possible to detect the current carrying path area between the materials to be welded during welding. Since the area of this current-carrying path is closely related to the size of the nugget to be formed, a reference resistance value is set in advance so that the area of the current-carrying path is such that the desired nugget diameter is obtained. By cutting off the welding current when the interelectrode resistance reaches its reference resistance value during welding, a desired nugget diameter can be obtained.

Next, a resistance welding apparatus according to the present invention will be explained with reference to the drawings.

FIG. 5 is a block diagram showing the structure of an embodiment according to the present invention. In the figure, 1
a, 1b are materials to be welded such as mild steel plates, 2a is a movable welding electrode connected to a piston or the like (not shown), 2
b is a fixed welding electrode. During the welding process, the materials to be welded 1a and 1b are sandwiched and pressurized by the electrodes 2a and 2b, and an AC power source 4 is connected to the welded materials via a transformer 3.
Welding current is applied from 10 is a welding current control circuit, which includes a phase control circuit 11, a thyristor trigger pulse generation circuit 12, and a switching element 13.
and SCR14. The phase control circuit 11 is provided with a welding current setting circuit (not shown), and at the beginning of welding, the welding current setting dial 11a controls the thyristor trigger pulse generation circuit 12 to set the welding current. The thyristor trigger pulse generation circuit 12 generates a trigger pulse during the operation period of the energization time control circuit 15. The output of the thyristor trigger pulse generation circuit 12 is applied to the SCR 14 via the switching element 13, and the SCR 14 adjusts the voltage supplied from the AC power source 4, and supplies the voltage to the welding electrodes 2a, 2b via the transformer 3. be done.

Reference numeral 20 denotes a first current application time control section, which integrates the voltage between the welding electrodes and controls the welding current to be stopped when the integrated value reaches a predetermined upper limit value. This first energization time control section 20 controls the electrodes 2a and 2b during welding current energization.
A voltage detection circuit 21 that momentarily detects the voltage between the electrodes (hereinafter referred to as the interelectrode voltage), a voltage integration circuit 22 that integrates this detected voltage over time, and an allowable range (diameter) of the nugget diameter that provides the desired welding strength. The output of the upper limit reference integral voltage generator 23 and the voltage integral circuit 22, which are determined in advance by experimenting with the upper limit voltage integral value of , is used as one input, and the output of the upper limit reference integral voltage generator 23 is used as the other input. As the input of
These two inputs are compared, and when the output of the voltage integration circuit 22 reaches the output of the upper limit reference integrated voltage generator 23, a logic "1" signal is output, and while the output does not reach the output, a logic "0" signal is output. When the inputs from the circuit 24 and the upper limit comparison circuit 24 are logic “1”, Q
A flip-flop 25 outputs a logic "1" signal from its terminal, and outputs a logic "1" signal from its terminal when the input is logic "0", and the output from the Q terminal of the flip-flop 25 is used as one input, and will be described later. It consists of a gate circuit 26 which uses the output from the Q terminal of the flip-flop 33 as the other input, and outputs a logic "1" signal to the energization time control circuit 15 when both inputs are logic "1" signals. ing.

Further, numeral 30 indicates an alarm section, in which control is performed to issue an alarm when the integral value of the voltage between the welding electrodes does not reach a value predetermined as a lower limit. This alarm unit 30 is connected to a lower limit reference integral voltage generator 31 which is preset by determining the lower limit voltage integral value in the allowable range (diameter) of the nugget diameter at which the desired welding strength can be obtained through experiments or the like; Using the output of the circuit 22 as one input and the output of the lower limit reference integral voltage generator 31 as the other input, these two inputs are compared, and the output of the voltage integral circuit 22 reaches the output of the lower limit reference integral voltage generator 31. A lower limit comparator circuit 32 outputs a logic "1" signal when the signal is reached, and outputs a logic "0" signal while it does not reach the lower limit comparator circuit 32, and when the input from the lower limit comparator circuit 32 is logic "1", the Q
A flip-flop 33 outputs a logic "1" signal from its terminal and outputs a logic "1" signal from its terminal when the input is logic "0"; A gate circuit 34 which takes the output from the terminal as the other input and outputs a logic "1" signal when both inputs are logic "1" signals, a switch 35 and a delay timer 36, It consists of, for example, a lamp 37 that issues an alarm based on the output of the gate circuit 34. Since the switch 35 is controlled to close its contacts by a signal output at the end of the operation of the energization time setting dial 15a attached to the energization time control circuit 15, the lamp 37 is closed when the energization time is completed. It will light up if the nugget has not grown to a predetermined size at the time. The delay timer 36 is for determining the lighting time of the lamp 37.

Furthermore, 40 indicates a second energization time control section,
Here, control is performed so that the welding current is stopped when the resistance between the welding electrodes reaches a predetermined value. This second energization time control section 40 has a current detection circuit 41 that detects the welding current moment by moment, the output of this current detection circuit 41 as one input, and the output of the voltage detection circuit 21 as the other input. A resistance value calculation circuit 42 detects the interelectrode resistance by dividing the voltage value by the current value, and the upper limit interelectrode resistance value within the allowable range (diameter) of the nugget diameter that provides the desired welding strength is determined through experiments or the like. The calculated and preset reference resistance value generator 43 and the output of the resistance value calculation circuit 42 are used as one input, and the output of the reference resistance value generator 43 is used as the other input, and these two inputs are compared to calculate the resistance value. When the output of the circuit 42 reaches the output of the reference resistance value generator 43, the resistance value comparison circuit 44 outputs a signal for cutting off the welding current to the energization time control circuit 15.

The operation of the embodiment configured as described above will be explained below. Now, welding electrodes 2a, 2b
When the materials to be welded 1a and 1b are sandwiched between them and welding current is applied from the AC power source 4, the voltage between the electrodes 2a and 2b is detected moment by moment by the voltage detection circuit 21, and at the same time the voltage between the two electrodes of the transformer 3 is detected. The welding current is detected momentarily by a current detection circuit 41 from the next conductor side. The interelectrode voltage detected by the voltage detection circuit 21 is time-integrated by the voltage integration circuit 22 and input to the upper limit comparison circuit 24 and the lower limit comparison circuit 32. The upper limit comparison circuit 24 compares the output of the voltage integration circuit 22 with the output of the upper limit reference integrated voltage generator 23, and outputs a logic "1" signal when the reference integrated voltage has been reached, and a logic "0" signal while the reference integrated voltage has not been reached. The signal is output to flip-flop 25. In addition, the lower limit comparison circuit 32 compares the output of the voltage integration circuit 22 with the output of the lower limit reference integrated voltage generator 31,
When the reference integrated voltage is reached, a logic "1" signal is output to the flip-flop 33, and while the reference integrated voltage is not reached, a logic "0" signal is output to the flip-flop 33. Therefore, when the interelectrode voltage integral value reaches the upper limit reference integral voltage value, a logic "1" signal is input from the Q terminals of the flip-flops 25 and 33 to the gate circuit 26, and a signal for stopping the current supply is input to the gate circuit 26. The signal is output from the circuit 26 to the energization time control circuit 15. When the interelectrode voltage integral value exceeds the lower limit reference integral voltage value and does not reach the upper limit reference integral voltage value, logic "1" signals are output from the terminals of the flip-flop 25 and the Q terminal of the flip-flop 33 to the gate circuits 26 and 3, respectively.
4, the gate circuits 26 and 34
No signal is output from.

Further, when the interelectrode voltage integral value does not reach the lower limit reference integral voltage value, a logic "1" signal is input from the terminals of the flip-flops 25 and 33 to the gate circuit 34, and the gate circuit 34 inputs the logic "1" signal to the lamp 34.
A signal for lighting 7 is output. but,
The lamp 37 is turned on via the delay timer 36 only when the energization time preset with the energization time setting dial 15a has elapsed and the switch 35 is closed. On the other hand, the welding current detected by the current detection circuit 41 is inputted to the resistance value calculation circuit 42 together with the interelectrode voltage of the voltage detection circuit 21, and is calculated and outputted to the resistance value comparison circuit 44 as an interelectrode resistance value. Then, the comparison circuit 44 generates the reference resistance value generator 4.
3, and when the reference resistance value is reached, a signal for stopping the energization is output to the energization time control circuit 15. Energization time control circuit 15
is the gate circuit 26 or the resistance value comparison circuit 44
When a signal is input from the thyristor, regardless of the energization time preset with the energization time setting dial 15a, a energization stop signal is output to the thyristor trigger pulse generation circuit 12, and the generation of trigger pulses is stopped. Stop energizing.

In the above-mentioned embodiment, a case has been described in which the warning is given by a lamp display, but the same effect can be obtained by switching off the main switch of the welding power source instead of using the lamp.

As is clear from the above explanation, the resistance welding apparatus according to the present invention detects the size of the nugget that is most closely related to the quality of the welded part, and when the size of the nugget reaches a desired value. Since the energization can be stopped regardless of the preset energization time, an optimal nugget can always be obtained without being affected by changes in the welding equipment, welding material, welding conditions, etc. In addition, since the allowable upper limit of the nugget diameter is monitored separately using the integral value of the voltage between the electrodes and the resistance value, for example, when the end of the material to be welded is welded, the material to be welded may suddenly melt. However, even in a case where the interelectrode voltage integral value does not reach the reference value, the interelectrode resistance value reaches the reference value and energization is stopped, so that damage to the electrodes due to excessive current does not occur. Furthermore, even if the nugget does not grow due to a break in the secondary cable, etc., this can be displayed with a lamp after the preset energization time has elapsed. The effect of improving reliability is significant.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the current conduction path diameter between the materials to be welded, the nugget diameter, and welding time when mild steel plates are spot welded, and Figure 2 is a graph showing the relationship between the welding time and the diameter of the current-carrying path between the materials to be welded.
A graph showing the relationship between the nugget diameter and the integral value of the voltage between the electrodes when welding is performed using a welding type and a CF type, and the welding force is divided into a low welding force and a high welding force. A graph showing the temporal change in the relationship between the interelectrode resistance and the reciprocal of the current carrying path area during welding under various conditions. A graph showing the relationship with the reciprocal number, and FIG. 5 is a block diagram showing the configuration of an embodiment of the resistance welding apparatus according to the present invention. Explanation of symbols: 1a and 1b are materials to be welded, 2a and 2
b is a welding electrode, 3 is a transformer, 4 is an AC power source, 10
15 is a current control circuit, 15 is an energization time control circuit, and 20 is a current control circuit.
21 is a first energization time control section; 21 is a voltage detection circuit;
22 is a voltage integration circuit, 23 is an upper limit reference integrated voltage generator, 24 is an upper limit comparison circuit, 25, 33 are flip-flops, 26, 34 are gate circuits, 30 is an alarm section, 31 is a lower limit reference integrated voltage generator, 32 is a Lower limit comparison circuit, 35 is a switch, 36 is a delay timer, 37 is a lamp, 40 is a second energization time control section, 41 is a current detection circuit, 42 is a resistance value calculation circuit, 43 is a reference resistance value generator, 44 is a This is a resistance value comparison circuit.

Claims (1)

[Claims] 1 Energization to stop the welding current at the time when the integral value of the voltage between welding electrodes reaches a predetermined upper limit value or when the resistance between welding electrodes reaches a predetermined value, whichever comes first. A resistance welding device comprising a time control means and an alarm means for issuing an alarm when the integral value of the voltage between welding electrodes does not reach a value predetermined as a lower limit after a predetermined energization time has elapsed.