JPH0716758A - Monitoring device of resistance welding - Google Patents

Abstract

PURPOSE:To improve welding efficiency and welding quality in the resistance welding by resistance between electrodes increasing method. CONSTITUTION:CPU100 is provided function-wise with a timing control part 102, resistance value arithmetic part 104, resistance value memory part 106, DELTAr arithmetic part 108, setting value memory part 110, decision part 112 and output part 114. Based on the resistance between electrodes measured values r1, r2, r3 obtained by the resistance value arithmetic part 104 at every half cycle or one cycle, DELTAr (rMAX-rMIN) is operated by DELTAr arithmetic part 108, DELTAr from DELTAr arithmetic part 108 is compared to a base value DELTAR from the setting value memory part 110 by the decision part 112, making decision on a normal or defective of welding result. The decision obtained from the decision part 112 is delivered to a display part and other outside devices from the output part 114 as the prescribed signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for monitoring resistance welding performed by interposing an electric resistance increasing substance between materials to be welded.

[0002]

2. Description of the Related Art The present inventors have previously proposed a method of resistance welding by interposing an electric resistance increasing substance between galvanized steel sheets to be joined. In galvanized steel sheet, the galvanized layer on the surface of the steel sheet is a relatively soft material with relatively high conductivity, so if the applied pressure is applied during welding, the steel sheets will become familiar with each other In addition, there is a problem that zinc melts, the electric resistance of the mating surfaces is low, and sufficient resistance heat generation cannot be obtained. Therefore, in the past, for galvanized steel sheet, the welding current was set to 25 to 50% and the energization time was set to 50 to 100% larger values than in the case of a normal bare steel sheet having no plating layer. However, not only the power consumption is inevitably increased, but also the welding electrode is easily worn, and the welding electrode must be frequently dressed or replaced, which makes maintenance difficult.

The above resistance welding method solves this problem. According to this method, the resistance-increasing substance is present between the galvanized steel sheets, so that the electrical resistance of the mating surfaces increases and the resistance heat generation amount at the bonding site increases. Since it is formed, the power consumption is low, the welding electrode is less likely to wear, and the resistance heat is concentrated on the joining site, so that the dents and deformations associated with welding are reduced, and further, the loss of the zinc layer in the indented part is reduced. Since the amount is small, deterioration of rust prevention performance is avoided.

[0004]

According to the above-mentioned method of increasing the resistance between electrodes, a proper nugget is usually formed in a current-flowing time of 2 to 3 cycles. Due to the variation depending on various conditions such as the inter-plate interposition state, welding pressure, welding current, etc., an appropriate nugget is not always formed in the set energization time. Generally, in this type of resistance welding, the constant current control method is used to control the welding current to a constant value. It may not grow well, resulting in poor welding.

The present invention has been made in view of the above problems, and monitors the growth condition of the nugget or the welding result in resistance welding performed by interposing a resistance-increasing substance between the materials to be welded. An object of the present invention is to provide a resistance welding monitoring device that improves the reliability of welding quality.

[0006]

In order to achieve the above object, the resistance welding monitoring apparatus of the present invention is a welding for resistance welding performed by interposing an electric resistance increasing substance between the materials to be welded. In the resistance welding monitoring device that monitors the results,
Inter-electrode resistance measuring means for measuring the resistance between the welding electrodes sandwiching the material to be welded during the energizing time at predetermined intervals, and a predetermined value immediately after the start of energization based on the resistance measurement value obtained from the inter-electrode resistance measuring means. Inter-electrode resistance change detection means for detecting a change in the welding inter-electrode resistance during the monitoring period, and determining the quality of the welding result based on the characteristics of the change in the welding inter-electrode resistance obtained by the inter-electrode resistance change detection means Determination means,
It is configured to include a determination output unit that outputs the determination result obtained from the determination unit.

[0007]

[Function] In resistance welding in which a resistance-increasing substance is interposed between the materials to be welded, a nugget is usually generated immediately after the start of energization due to the action of the resistance-increasing substance. It is reflected in the resistance value between the welding electrodes immediately after.

According to the present invention, based on the inter-electrode resistance measurement value obtained by the inter-electrode resistance value measuring means at predetermined intervals, the inter-electrode resistance change detecting means detects the welding inter-electrode resistance in a predetermined monitoring period immediately after the start of energization. The change is detected, the judging means recognizes the growth condition of the nugget from the characteristic of the change in the resistance between the welding electrodes, and judges whether the welding result is good or bad. The result of this determination is output by the determination output means and displayed on, for example, a display device.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a circuit configuration of a resistance welding monitoring apparatus according to an embodiment of the present invention. FIG. 2 shows the signal waveform of each part of FIG.

First, in the resistance welding machine, during energization,
The commercial frequency AC power supply voltage E ((A) in FIG. 2) input to the input terminals 10 and 12 is applied to the pair of thyristors 14 and 16.
Is supplied to the primary coil of the welding transformer 18 via a contactor composed of. The AC induced electromotive force (secondary voltage) generated in the secondary coil of the welding transformer 18 is passed through the secondary conductor and the pair of welding electrodes 20 and 22 to be welded materials 24 and 26.
And a welding current i ((B) in FIG. 2) flows through the secondary circuit. The welding current i is controlled by adjusting the firing timing of the pair of thyristors 14 and 16 by the resistance welding control device 28.

The materials 24 and 26 to be welded are galvanized steel sheets, respectively, and the resistance increasing substance 30 made of, for example, ceramic powder is previously sprayed, applied or attached to their mating surfaces. When the materials to be welded 24 and 26 are pressed against each other by a pressure device (not shown) during welding,
The resistance-increasing substance 30 prevents the mating surfaces of the materials to be welded 24 and 26 from adhering to each other or getting familiar with them, thereby increasing the resistance between electrodes. When the welding current i flows there, resistance heat is generated intensively and efficiently at the joint, and a small current or a nugget is formed in a short time.

In the resistance welding monitoring apparatus of this embodiment used in such a resistance welding machine, the toroidal coil 32 is attached to the secondary circuit of the welding machine in order to detect the welding current i. The toroidal coil 32 outputs a signal di representing a differential waveform of the welding current i. The toroidal coil output signal di is input to the waveform restoring circuit 34 including an integrating circuit, and the welding current detection signal qi ((B) in FIG. 2) representing the waveform or the instantaneous value of the welding current i is output from the output terminal of the waveform restoring circuit 34.
) Is obtained. Based on the welding current detection signal qi, the zero current detection circuit 36 gives the timing signal Tz ((D) in FIG. 2) to the CPU 100 and the timing control circuit 38.

The zero current detection circuit 36 is based on the phenomenon that when the current flows, the thyristor voltage drops, and when the current stops, the thyristor voltage rises. Detect the end point. In response to the timing signal Tz from the zero current detection circuit 36, the timing control circuit 38 causes a timing signal TSH for sampling and holding ((G) in FIG. 2) and a timing for integration reset to The signal TR ((H) in FIG. 2) is generated.

The welding current detection signal qi obtained from the waveform restoration circuit 34 is also input to the current integration circuit 40. The current integration circuit 40 responds to the timing signal TR from the timing control circuit 38 to time-integrate the positive welding current detection signal qi for each cycle, and outputs a current integration value signal Si representing the time integration value. ((E) in Figure 2).
The sample hold circuit 44 includes a timing control circuit 38.
The value [Sin] (n = 1, 2, ...) Of the current integration value signal Si when the positive welding current i stops in each cycle in response to the timing signal TSH from (E) in Fig. 2). The current sampling hold value [Sin] is converted into a digital signal [DSin] by the A / D converter 46 and then input to the CPU 100.

The welding electrodes 20 and 22 are voltage detection lines 45 and 4, respectively.
It is connected to the input terminal of the voltage integration circuit 46 via 7. As a result, the voltage v ((C) in FIG. 2) between the welding electrodes 20 and 22 is input to the voltage integrating circuit 46 during energization.
The voltage integration circuit 46 responds to the timing signal TR from the timing control circuit 38 to time-integrate the welding electrode voltage v over the time during which the positive welding current detection signal qi is flowing for each cycle, and at that time. The voltage integrated value signal Sv representing the integrated value is output ((F) in FIG. 2). The sample hold circuit 48 responds to the timing signal TSH from the timing control circuit 38, and the value [Sv] of the current integral value signal Sv when the positive welding current i stops in each cycle.
n] (n = 1, 2, ...) Is sampled and held ((F) in FIG. 2). The voltage sampling hold value [Svn] is converted into a digital signal [DSvn] by the A / D converter 50 and then input to the CPU 100.

The polarity of the inter-electrode voltage v is reversed in the latter half of each half-wave energization cycle due to the induced electromotive force due to the inductance of the resistance welding machine. This induced electromotive force is almost evenly generated in both polarities. Therefore, by integrating the components of opposite polarities, as a result, the inductive component is canceled in both polarities, and the voltage sampling hold value [S
vn] is a value corresponding to the net voltage between the electrodes.

The CPU 100 performs necessary calculations and controls in accordance with a control program stored in the memory 52. Functionally, as shown in FIG. 3, the timing control section 102, the resistance value calculation section 104, and the resistance are calculated. Value storage unit 1
06, a Δr calculation unit 108, a set value storage unit 110, a determination unit 112, and an output unit 114. FIG. 4 is a flowchart showing the processing operation of the CPU 100 in the resistance welding monitoring apparatus of this embodiment.

In FIG. 3, the timing control unit 102
Is a timing signal Tz from the timing control circuit 38.
In response to the internal timing signal T0,
T1 is given to each part (step 200 in FIG. 4). The set value storage unit 110 holds the energization time set value SC and the resistance change set value ΔR input from the setting unit 54, gives the energization time set value SC to the Δr calculation unit 108, and the determination unit 112 to the resistance change set value. Give ΔR.

The resistance value calculation unit 104 includes an A / D converter 44.
The current sampling hold value [DSin] is received from the A / D converter 50, and the voltage sampling hold value [DSvn] is received from the A / D converter 50.
Sin] to obtain the interelectrode resistance value (measured value) rn for each cycle (step 202). Inter-electrode resistance value rn for each cycle obtained from the resistance value calculation unit 104
Is stored in the resistance value storage unit 106 (step 20).
4).

In the present embodiment, resistance welding is performed with the resistance increasing substance 30 interposed between the materials to be welded 24, 26, so the energization time set value EC is selected to be a short energization cycle, for example, 3 cycles.

In this case, the time point when the first half cycle of the third cycle is finished is judged (step 206), and immediately after the inter-electrode resistance measurement value r3 for the third cycle is obtained, Δr
The calculation unit 108 measures the inter-electrode resistance value r1 for the first cycle.
And the inter-electrode resistance measurement value r3 for the third cycle are calculated (step 208), and the magnitude relationship between the two is checked (step 210). As a result, when r1> r3, it is temporarily judged to be normal, and then Δr is calculated (step 212).
When r1≤r3, it is determined that an abnormality has occurred and an abnormality detection signal AR is given to the output section 114 (step 216). In the latter case, that is, when the abnormality detection signal AR is generated by the Δr calculation unit 108, the output unit 114 sends a display signal notifying the abnormal state to the display unit 56. As a result, the abnormality notification is displayed on the lamp or screen of the display unit 56. Further, if necessary, an abnormality notification signal from the output unit 114 may be sent to an external alarm device (not shown), and the alarm device may output an alarm sound or a voice message. Further, for recording, an abnormality notification signal from the output unit 114 may be sent to an external recording device (not shown).

Here, FIGS. 5 and 6 show various patterns (characteristics) of inter-electrode resistance change in three cycles immediately after the start of energization. FIG. 5 shows a normal case (r1> r3), and FIG. 6 shows an abnormal case (r1≤r3). In resistance welding,
The resistance between electrodes generally decreases as the nugget grows at the welding site, and in resistance welding performed by the resistance increasing method between electrodes as in the present embodiment, the nugget is formed immediately after the start of energization due to the action of the resistance increasing substance. It is usually generated. Therefore, when r1> r3, it may be determined that the nugget has grown for the time being, and when r1≤r3, it may be determined that the nugget has not grown substantially.

The Δr calculated in step 212 after it is determined that it is normal (r1> r3) is obtained by the following equation. Δr = rMAX −rMIN Here, rMAX and rMIN are the maximum and minimum values of r1, r2 and r3. That is, Δr is the amount (drop) that the inter-electrode resistance changes from the maximum value rMAX to the minimum value rMIN during the monitoring period, and is a parameter indicating the growth condition of the nugget. For example, in the pattern of (a) of FIG.
r1 is rMAX, r3 is rMIN, and Δr = r1-r3
Is. In this case, the nugget grows over the first to third cycles, and the growth condition is reflected in the size of (r1-r3). In the pattern of FIG. 5C, r
2 is rMAX, r3 is rMIN, and Δr = r2-r3
Is. In this case, the nugget grows over the second to third cycles, and the growth condition is reflected in the size of (r2-r3). Therefore, the larger the growth of the nugget, the larger the value of Δr, and the smaller the growth of the nugget, the smaller the value of Δr.

The Δr calculated by the Δr calculation unit 108 is given to the determination unit 112. The determination unit 112 includes a setting unit 11
A set value or reference value ΔR corresponding to the lower limit value of the interelectrode resistance change (drop) for forming a nugget more appropriate than 0
Is given. The determination unit 112 includes the Δr calculation unit 108.
The received Δr is compared with the reference value ΔR (step 21
4), when Δr ≧ ΔR, set energization time (3 cycles)
It was determined that a proper nugget was formed (welding was good) (step 218), and when Δr <ΔR, it was determined that the nugget growth was not sufficient for the set energizing time (3 cycles) (insufficient energizing). (Step 220).

The determination by the determination unit 112 as described above is given to the output unit 114 as a determination result signal OK / SH.
The output unit 114 sends a predetermined display signal to the display unit 56 according to the result of the determination that welding is good (OK) and the result of determination that the current is insufficient (SH), and causes the display unit 56 to display the determination result. Further, for recording, the determination result output signal or data from the output unit 114 may be sent to the recording device.

As described above, in this embodiment, the growth condition of the nugget in the resistance welding of the short-time energization is monitored during the energization time, and whether or not the proper nugget is formed within the set energization time (3 cycles). The judgment result is issued immediately after the end of energization, and the goodness / defectiveness of the welding result at each welding point is immediately found, so it is appropriate to sort good products and defective products, take measures for defective products, and continue / stop the work properly. Can be made. Therefore, it is possible to improve the reliability of resistance welding by the inter-electrode resistance increasing method and further increase its practical value.

In the above-mentioned embodiment, the set energization time is explained as 3 cycles, but this is an example, and an arbitrary number of cycles can be set according to the welding conditions of the materials 24 and 26 to be welded and other welding conditions. it can.

Further, in the above-described embodiment, when the set energization time is set to 3 cycles, the time from the start of energization to the end of the first half cycle of the third cycle is set as the monitoring period. As described above, when the monitoring period extends to immediately before the set energization time, it is generally possible to determine the degree of growth of the nugget with higher accuracy. However, the temporal position and range of the monitoring period with respect to the set energization time can be set to arbitrary values, and are not limited to the above examples.

Further, the integrating circuits 40, 46 and the like can be configured by digital circuits or software.

If the current flowing immediately after the start of energization (first half cycle of the first cycle) is so small that it does not contribute to resistance heating, the monitoring period may be started from the second cycle.

Further, in the above-mentioned embodiment, the inter-electrode resistance in the first half cycle of each cycle is detected in one cycle period. However, as shown in FIG. 7, the inter-electrode resistance in the first half cycle and the second half cycle of each cycle is reduced to half. It is also possible to detect the cycle period. The half cycle period can more accurately monitor the change in the interelectrode resistance, and even when the set energization time is set to 2 cycles, for example, the first half and second half cycles of the first cycle and the first half cycle of the second cycle can be Since a total of three inter-electrode resistance values can be obtained, highly reliable determination can be performed.

Further, although the above embodiment relates to the resistance welding monitoring device for the single-phase AC resistance welding machine, the present invention is the resistance welding for the three-phase rectification resistance welding machine and the inverter resistance welding machine. It is also applicable to monitoring devices.

[0034]

As described above, according to the resistance welding monitoring apparatus of the present invention, in the resistance welding of the inter-electrode resistance increasing method performed by interposing the resistance increasing substance between the materials to be welded to be joined. , The change in the resistance between the welding electrodes immediately after the start of energization, which reflects the growth of the nugget, is monitored to obtain reliable monitoring results for good and defective welding results. , Measures for defective products,
It is possible to appropriately continue or stop the work, and improve the welding efficiency and the reliability of welding quality. Therefore, the utility value of the inter-electrode resistance increasing method can be increased, and its practical application and spread can be achieved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration of a resistance welding monitoring apparatus according to an embodiment of the present invention and a circuit configuration of a single-phase AC resistance welding machine to which the monitoring apparatus is applied.

FIG. 2 is a timing diagram showing waveforms of signals at various parts in the resistance welding machine and the resistance welding monitoring apparatus of the embodiment.

FIG. 3 is a block diagram showing a functional configuration in a CPU in the resistance welding monitoring apparatus of the embodiment.

FIG. 4 is a flowchart showing a processing operation of a CPU relating to energization time control in the resistance welding monitoring apparatus of the embodiment.

FIG. 5 is a diagram showing an example of a pattern (characteristic) of inter-electrode resistance value under normal conditions.

FIG. 6 is a diagram showing an example of a pattern (characteristic) of inter-electrode resistance value at the time of abnormality.

FIG. 7 is a timing diagram showing waveforms of signals of respective portions in the resistance welding machine and the resistance welding monitoring device of the modified example.

[Explanation of symbols]

 14,16 Thyristor (contactor) 20,22 Welding electrode 24,26 Welding material 28 Resistance increasing substance 30 Toroidal coil 32 Waveform restoration circuit 38 Setting part 44 Current integration circuit 46 Voltage integration circuit 48,50 Sample hold circuit 52,54 A / D converter 56 memory 58 display unit 100 CPU 104 resistance value calculation unit 106 resistance value storage unit 108 Δr calculation unit 110 set value storage unit 112 determination unit 114 output unit

Front page continuation (72) Inventor Sobue Nao 2-chome, Toyota-cho, Kariya city, Aichi stock company Toyota Industries Corporation (72) Inventor Yasushi Kotetsu 2-chome, Toyota-cho, Kariya city, Aichi stock company Toyota Inside the automatic loom mill (72) Inventor Hiroaki Yoshihara 2-chome Toyota-cho, Kariya city, Aichi Stock company Toyota automatic loom mill (72) Inventor Toruichi Watanabe 4-chome Aoyamadai, Suita-shi, Osaka (72) ) Inventor Sakae Ishikawa, 3 Miyachi Technos Co., Ltd., 95-3 Futatsuka, Noda City, Chiba Prefecture

Claims (1)

[Claims] 1. A resistance welding monitoring apparatus for monitoring a welding result of resistance welding performed by interposing a resistance increasing substance between the materials to be welded, wherein a welding electrode sandwiching the materials to be welded during energization time. Inter-electrode resistance measuring means for measuring the resistance between the electrodes every predetermined time, and based on the resistance measurement value obtained by the inter-electrode resistance measuring means, detects a change in the welding inter-electrode resistance in a predetermined monitoring period immediately after the start of energization. Inter-electrode resistance change detection means, a determination means for determining the quality of the welding result based on the characteristics of the change in the welding inter-electrode resistance obtained by the inter-electrode resistance change detection means, and the determination obtained by the determination means A resistance welding monitoring device, comprising: a determination output unit that outputs a result.