JPH1085947A - Method and device for controlling resistance welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate a simultaneous welding of plural places in series welding for example, for a nearly uniform welding strength in a short energizing time. SOLUTION: In the first half of an energizing time, a controller 56 continuously switches only the first set (positive electrode side) of switching elements 32, 36 through PWM control. As a result, the welding current I2 of straight polarity having a nearly trapezoidal current waveform flows in a path from the first welding electrode 48, to a material W1 to be welded, to a first welding place Pa , to a material W2 to be welded, to a second welding place Pa , to the material W1, and to a second welding electrode 50. In the second half of the energizing time, the controller continuously switches only the second set (negative electrode side) of switching elements 34, 38 through PWM control. As a result, the welding current I2 of negative polarity having a nearly trapezoidal current waveform flows in the path reverse to the above. Consequently, at the point of time when all energizing time is completed, a nugget in the first and the second welding places grows in a nearly identical size.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0010]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance welding method and apparatus for simultaneously joining workpieces at a plurality of welding locations by series welding or the like.

[0020]

2. Description of the Related Art In recent years, a resistance welding apparatus using an inverter for a power supply has been widely used. FIG. 7 shows a configuration of a conventional typical inverter type resistance welding apparatus. The inverter circuit 100 has a built-in switching element, and outputs a high-frequency AC pulse by chopping the DC input voltage E by high-frequency switching according to a control pulse CP from the inverter control unit 102. Inverter circuit 10
The AC pulse output from 0 is supplied to the primary coil of the welding transformer 104, and the secondary coil obtains an AC pulse similar to that of the primary coil. This secondary side AC pulse is supplied to a rectifier circuit 10 comprising a pair of diodes 106a and 106b.
The DC current is converted by DC 6 and the DC secondary current, that is, the welding current I2, is supplied to the workpieces (W1, W2) via the pair of welding electrodes 108, 110.

Conventionally, the above-mentioned inverter type resistance welding apparatus has been used for two-point simultaneous joining type resistance welding (series welding) mainly for small metals such as electronic parts (materials to be welded).
It is also used for

FIG. 8 shows an example of series welding. In this example, the two welding electrodes 108 and 112 abut against one side of the material to be welded (W1, W2) at positions separated from each other,
The material to be welded (W1, W2) is brought into pressurized contact with a pressurizing force from a pressurizing mechanism (not shown). During the energization time, the direct current welding current I2, as indicated by the dotted line,
8 → Workpiece W1 → First welding point Pa → Workpiece W2
→ The second welding point Pb → the material to be welded W1 → flows along the path of the second welding electrode 110. Thereby, the material to be welded (W1,
At the first and second welding points Pa and Pb on the contact surface (joining surface) of W2), the material to be welded (W1) is heated by Joule heat.
, W2) are melted, and the melted portion solidifies after energization, so that the materials to be welded (W1, W2) are metallurgically joined.

[0050]

However, in the series welding by the conventional inverter type resistance welding apparatus as described above, both welding portions Pa are affected by the Peltier effect.
, Pb, the nuggets (molten and solidified portions) Na and Nb are not uniform in size. Here, the Peltier effect is a phenomenon in which when a current flows through a contact between different types of conductors, heat is generated or absorbed in addition to Joule heat at the contact. There is a property of being opposite.

In the series welding, the material to be welded (conductor) W1
, W2, the directions of the welding currents I2 flowing through the two welding points (contact points) Pa and Pb are opposite to each other. That is, as shown in FIG. 8, at the first welding point Pa, the welding current I2
Flows from the material to be welded W1 to the material to be welded W2, whereas at the second welding point Pb, the welding current I2 is
It flows from the side 2 to the workpiece W1 side.

As described above, since the welding current I2 flows in the opposite directions at the two welding points Pa and Pb, even if the Joule heat is equal, for example, the Peltier effect of absorbing the heat occurs at the first welding point Pa. Then, the second welding point Pb
Then, a Peltier effect that generates heat occurs. As a result, FIG.
As shown in the figure, the nugget Na generated at the first welding point Pa is relatively small, and the nugget Nb generated at the second welding point Pb is relatively large. Since the strength of the resistance welding is proportional to the size of the nugget, if the size of the nugget is not uniform, the joining strength at the welding location will vary, and the welding quality is not good.

On the other hand, in the conventional single-phase AC resistance welding apparatus, since the welding current is alternately supplied in the positive polarity and the negative polarity, the Peltier effect as described above is compensated in series welding.
A uniform nugget can be obtained at the first and second welding points. However, the single-phase AC type has a drawback in that since the heat generation efficiency is low, the energization time for obtaining a desired nugget becomes long, and small parts such as electronic components are easily damaged.

The present invention has been made in view of the above-mentioned problems of the prior art, and has made it possible to simultaneously join a plurality of welding portions of a material to be welded to a substantially uniform welding strength in a short welding time in series welding or the like. An object of the present invention is to provide a resistance welding method and apparatus.

[0100]

In order to achieve the above object, according to the first aspect of the present invention, the first and second welding electrodes are applied to a material to be welded at positions separated from each other. Pressure contact, and applying a welding current to the material to be welded between the first and second welding electrodes, so that the material to be welded corresponds to the pressure contact position of the first and second welding electrodes, respectively. In the resistance welding method, the alternating current of the commercial frequency is converted into direct current by a rectifier circuit and input to the bidirectional current-type switching means, and the output of the switching means is output. Is supplied to a primary coil of a welding transformer, and a voltage obtained in a secondary coil of the welding transformer is applied to the first and second welding electrodes so that the welding current flows in a secondary circuit. , Energizing Continuously high-frequency switching of said switching means in one polarity in the first half portion between the in the second half of the weld time, characterized in that the continuous high-frequency switching of said switching means in the other polarity.

The invention described in claim 2 is the same as the claim 1.
Wherein the first half and the second half of the energization time are set to have substantially the same length of time.

The invention described in claim 3 is the same as the invention described in claim 2
In the resistance welding method according to the above, the waveform of the welding current in the first half and the waveform of the welding current in the second half are point-symmetric with respect to each other with respect to a predetermined point in the energization time as a center point. Is set.

Further, the invention according to claim 4 is a rectifier circuit for converting an alternating current of a commercial frequency into a direct current, a bidirectional current-type switching means for converting the direct current from the rectifier circuit into a high-frequency pulse, The output of the means is input to the primary side coil, and a welding transformer that outputs a high-frequency pulse voltage from the secondary side coil, and is connected to both ends of the secondary side coil of the welding transformer and separated from the workpiece to be welded. The first and second welding electrodes that are in pressure contact with each other at the position, and the switching means continuously performs high-frequency switching with one polarity in the first half of the energization time, and switches the switching means to the other in the second half of the energization time. Switching control means for continuously performing high-frequency switching with a polarity.

The invention described in claim 5 is the same as the invention described in claim 4.
In the resistance welding apparatus according to the above, the switching control means, for each switching cycle, current detection means for detecting the current on the primary side or the welding current on the secondary side of the welding transformer to obtain a current measurement value, Pulse width control means for comparing the measured current value from the current detection means with a desired set current value and calculating a pulse width of an output pulse of the switching means in a next switching cycle according to the comparison error. It is characterized by including.

The invention described in claim 6 is the same as claim 4
Or the resistance welding apparatus according to 5, wherein the rectifier circuit includes first and second diodes each having an anode terminal and a cathode terminal connected to one terminal of a single-phase AC power supply having a commercial frequency. The first terminal is connected to the cathode terminal of the first diode, is connected to one input terminal of the switching means, and the other terminal is connected to the other terminal of the single-phase AC power supply. A capacitor, one terminal connected to the other terminal of the single-phase AC power supply, and the other terminal connected to the anode terminal of the second diode and to the other input terminal of the switching means; And a second capacitor.

[0160]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows a circuit configuration of a resistance welding apparatus for series welding according to one embodiment of the present invention. This resistance welding apparatus uses, for example, a 100 V single-phase AC power supply 10 of a commercial frequency (50 Hz or 60 Hz). The bidirectional energizing type switching means 30 in this resistance welding apparatus is GT
It has four transistor switching elements 32, 34, 36, 38, such as R (Sianant Transistor) or IGBT (Insulated Gate High Wheel Transistor).

The four switching elements 32 to 38
Of the switching elements 32, 3 of the first set (positive electrode side)
6 is a first switching control signal F from the drive circuit 58.
a is simultaneously controlled on and off at a predetermined high frequency (for example, 8 kHz), and the switching elements 34 and 38 of the second pair (negative electrode side) are simultaneously controlled by the second switching control signal Fb from the driving circuit 58 to the predetermined high frequency. Frequency (8
(kHz).

The input terminals (La,
Lb) is connected to an output terminal of a rectifier circuit 28 described later, and the output terminals (Ma, Mb) are connected to both ends of the primary coil of the welding transformer 46, respectively. A pair of welding electrodes 4 are provided at both ends of the secondary coil of the welding transformer 46.
8, 50 are directly connected (that is, not via a rectifier circuit). At the time of welding, the two welding electrodes 48 and 50 are in contact with the workpieces (W1 and W2) apart from each other and are brought into pressurized contact with a pressing force from a pressurizing mechanism (not shown).

The rectifier circuit 28 mainly includes a pair of diodes 20 and 22 and a pair of capacitors 24 and 26. An anode terminal of the diode 20 and a cathode terminal of the diode 22 are connected to one terminal 10 a of the AC power supply 10. The cathode terminal of the diode 20 is connected to one terminal of the capacitor 24 and to one input terminal La of the switching means 30. The other terminal of the capacitor 24 is connected to one terminal of the
0 is connected to the other terminal 10b. Capacitor 2
The other terminal of 6 is connected to the anode terminal of the diode 22 and to the other input terminal Lb of the switching means 30.

In the rectifier circuit 28, in the positive half cycle of the commercial frequency, the commercial AC from the AC power supply 10 is half-wave rectified by the diode 20, and
Is charged. In the negative half cycle of the commercial frequency, the commercial alternating current from the
And the capacitor 26 is charged. Since the two capacitors 24 and 26 are connected in series with the same polarity, the DC voltage of the value obtained by adding the respective charging voltages is used as the output voltage of the rectifier circuit 28 as the input terminal (La, La) of the switching means 30. Lb).

A main power switch 12a, a choke coil 14, and a current limiting resistor 16 are inserted in series between one terminal 10a of AC power supply 10 and the anode terminal of diode 20 and the cathode terminal of diode 22. Further, a switch 18 for bypass (for removing the resistor) is connected in parallel with the current limiting resistor 16. A main power switch 12b is also inserted between the other terminal 10b of the AC power supply 10 and a connection point between the capacitors 24 and 26. The current limiting resistor 16 is connected to the main power switch 12a,
It operates at the time of start-up of charging immediately after the closing of 12b, and is removed from the circuit after the end of start-up.

According to the rectifier circuit 28 having such a configuration, the 100 V commercial AC from the single-phase AC power supply 10 is converted into DC, and the DC voltage boosted to, for example, about 280 V is charged in the capacitors (24, 26). Can be.

In the switching means 30, an input terminal L
a and Lb between the resistor 40 and the diode (42a, 4b).
2b) and a switching noise elimination circuit composed of capacitors (44a, 44b).

A current sensor 52 composed of, for example, a current transformer is provided between the output terminal of the switching means 30 and the primary coil of the welding transformer 46.
During welding power supply, a current detection signal representing the current value (instantaneous value) of the primary current I1 is output from the current sensor 52. Based on the current detection signal, the current detection circuit 54 outputs the primary current at predetermined switching cycles. A current measurement [I1] of I1 is obtained. The measured current value [I1] obtained from the current detection circuit 54 is supplied to the control unit 56.

The control unit 56 is composed of a microcomputer, and includes a CPU, a ROM (program memory), and a RAM.
(Data memory), a clock circuit, an interface circuit, and the like. In this embodiment, the control unit 56 performs a constant current control of a feedback system. For this constant current control, the control unit 56 uses the measured current value [I1] from the current detection circuit 54 as the set current value [I1] registered in the memory.
s], and calculates an output pulse of the switching means in the next switching cycle according to the comparison error, and determines a pulse width modulation (PW
M) The driving circuit 58 uses the signal as the switching control signal F.
Give to.

The control unit 56 operates the main power switch (1
2a, 12b) and the bypass switch 18 are also controlled. However, the main power switch (12a, 12b)
May be switched manually. Input unit 6
Reference numeral 0 denotes a keyboard or a pointing device such as a mouse, and is used for inputting various setting values. Other peripheral devices such as a display device (not shown) are also connected to the control unit 56.

Next, the operation of the resistance welding apparatus according to the present embodiment will be described with reference to FIGS.

Prior to conducting the welding current, the control unit 56
By closing the main power switches 12a and 12b, the rectifier circuit 28
Of the capacitors 24 and 26 of a predetermined voltage (for example, 280
V). At the time of starting the charging, the bypass switch 18 is turned off and the current limiting resistor 16 is turned off.
The charging current is passed through.

After charging the capacitors 24 and 26 to a predetermined voltage as described above, when an activation signal ST is sent from an external device (not shown) such as a welding robot, the control unit 56 responds to this. Starts welding current. For example, when seam welding is to be performed on the materials to be welded (W1, W2) as shown in FIG. 3, the control unit 56 determines the first set (the positive electrode side) of the switching elements (3) in the first half TF of the energization time.
Only the switching elements (2, 36) are continuously switched by PWM control, and only the switching elements (34, 38) of the second set (negative electrode side) are continuously switched by PWM control in the latter half of the energization time TL.

Therefore, as shown in FIG. 2, in the first half TF of the energization time, a positive output pulse is supplied from the switching means 30 to the primary coil of the welding transformer 46, and the substantially trapezoidal current is supplied to the secondary circuit. A positive welding current I2 having a waveform flows. In this case, as shown in FIG. 3 (A), the welding current I2 is changed from the first welding electrode 48 → the material to be welded W1 → the first welded portion Pa → the material to be welded W2 → the second welded portion Pb → the material to be welded. The welding material W1 flows along the path of the second welding electrode 50. That is, at the first welding point Pa, the welding current I2 flows from the workpiece W1 to the workpiece W2, and at the second welding location Pa, the welding current W1 starts from the workpiece W2.
Current I2 flows to the side. Thereby, for example, the first
A Peltier effect of absorbing heat is generated at the welding point Pa, while a Peltier effect of generating heat is generated at the second welding point Pb. Thus, in the first half TF of the energizing time,
The nugget Nb at the second welding point Pb grows larger than the nugget Na at the first welding point Pa.

However, as shown in FIG. 2, in the latter part TL of the energization time, a negative output pulse is supplied from the switching means 30 to the primary coil of the welding transformer 46, and the trapezoidal current is applied to the secondary circuit. A negative welding current I2 having a waveform flows. In this case, as shown in FIG. 3 (B), the welding current I2 is the second welding electrode 50 → the material to be welded W1 → the second welding location Pb → the material to be welded W2 → the first welding location Pa → The material to be welded W1 flows along the path of the first welding electrode 48. That is, at the first welding point Pa, the workpiece W
The welding current I2 flows from the side 2 to the workpiece W1, and at the second welding point Pa, the welding current I2 flows from the workpiece W1 to the workpiece W2. As a result, the Peltier effect of generating heat at the first welding point Pa is generated, while the Peltier effect of absorbing heat at the second welding point Pb is generated. For this reason, in the latter part TL of the energization time, the nugget Na at the first welding point Pa grows larger than the nugget Nb at the second welding point Pb.

As a result, at the time when the second half TL of the energizing time has ended, that is, when the entire energizing time has ended, the nugget Na and the second welding point P at the first welding point Pa are attained.
b has grown to approximately the same size as the nugget Nb. Therefore, substantially uniform welding strength can be obtained at the first welding point Pa and the second welding point Pb.

If the first half TF and the second half TL of the energization time are set to, for example, 5 ms each, the welding current I2 flows in a trapezoidal waveform, so that the material to be welded (W1,
In W2), the heat generation efficiency is high, and a sufficiently large nugget or welding strength can be obtained even with a short energization time of about 10 ms. However, according to the single-phase AC method, the shortest (one cycle) requires 20 ms (at 50 Hz), and in practice, the heat generation efficiency is low, so that two to three cycles (40 to 60 cycles) are required.
ms).

The current flow may differ between the positive electrode and the negative electrode due to the influence of the Peltier effect and the like. However, in the resistance welding apparatus of this embodiment, the first half of the energization time T
Constant direction (polarity) in each of F and the second half TL
Is controlled by the PWM control method, so that constant current control can be stably performed.

In the resistance welding apparatus of the present embodiment, even if the switching means 30 performs a switching operation at a high frequency such as 8 kHz, for example, the welding transformer 46 supplies the first half TF and the second half TL of the energization time. A current having a cycle defined by For this reason, it is possible to configure the welding transformer 46 as a single-phase AC (for commercial frequency) welding transformer instead of a high-frequency type.

When the switching frequency is increased,
Since the number of pulses per unit time increases, the energization time can be set with a more precise value. It is also possible to insert an energization suspension period (cooling time) between the first half TF and the second half TL of the energization time.

As shown in FIG. 4, the first half TF and the second half TL of the energization time can be set to different lengths positively. The example of FIG. 4 can be applied to, for example, series welding as shown in FIG.

In the example of FIG. 5, the material to be welded W2 having a U-shaped cross section is shown.
A relatively thick plate-like workpiece W1 and a relatively thin plate-like workpiece W1 'made of the same material on both outer surfaces opposed to each other.
And weld. In this case, the welding strength is such that the nugget Na formed at the welding point Pa on the relatively thick workpiece W1 is larger than the nugget Nb formed at the welding spot Pb on the relatively thin workpiece W1 '. Can be balanced. In FIG. 5, at the time of welding, the back bar electrode 6
2 is inserted.

FIG. 6 shows an example of setting the waveform of the welding current I2 in the input unit 60 and the control unit 56. In this example,
The welding current in the first half TF of the energization time is set to an up slope waveform IF, and the welding current in the second half TL is set to a down slope waveform ID.
, ID are set to be point-symmetric with respect to a predetermined time tc as a center point.

At the time of energization in this case, the set current value [Is] changes every moment in the control unit 56 in accordance with the up-slope waveform IF and the down-slope waveform IL. Will be flown in the waveform of

When the welding current waveform in the first half TF and the welding current waveform in the second half TL of the energization time are set to be point-symmetrical, only the welding current waveform in the first half TF is set and input by the input unit 60. Thus, the control section 56 automatically sets the welding current waveform in the second half TL, which facilitates the setting input. In addition, since the currents on the positive electrode side and the negative electrode side have the same magnitude, there is no need to worry about the magnetic polarization in the welding transformer.

According to the resistance welding apparatus of this embodiment,
Since the respective lengths or relative ratios of the first half TF and the second half TL of the energizing time can be arbitrarily selected, the welding portions Pa, Pb
The size and relative ratio of each of the nuggets Na and Nb generated in the above can be arbitrarily selected. However, when the first half TF and the second half TL of the energization time are positively unbalanced in this way, it is necessary to take into consideration the occurrence of the magnetic polarization phenomenon in the welding transformer 46. In order to prevent the magnetic polarization phenomenon, for example, a technology for preventing magnetic saturation disclosed by the present applicant in Japanese Patent Application Laid-Open No. 64-22477 may be used. According to this magnetic saturation prevention technology, the magnetic saturation of the intermediate portion between the rising portion and the falling portion of each pulse of the primary current is determined from the difference between the current change amount of the change portion of the intermediate portion and the reference change amount. The state and degree or degree are determined, and the pulse width is adjusted by controlling the switching operation of the switching means so that the difference between the two amounts of change becomes zero, so that the magnetic saturation state or the demagnetization state can be minutely and quickly suppressed. it can. Since this method can be realized by software, it may be incorporated in the control unit 56.

The resistance welding apparatus of the above embodiment has a rectifier circuit 28 for converting a single-phase alternating current to a direct current. As described above, according to the rectifier circuit 28, a high-voltage (for example, about 280V) DC voltage can be obtained from a 100V commercial AC. However, it is also possible to convert three-phase alternating current to direct current by using a three-phase rectifier circuit. The circuit configuration of the switching means 30 is also an example, and various modifications are possible. Further, instead of detecting the primary side current I1, the secondary side welding current I2 may be detected.

[0450]

As described above, according to the resistance welding method or apparatus of the present invention, in the first half of the energizing time, the bidirectional energizing type switching means continuously performs high-frequency switching with one polarity, so that the energizing time is reduced. In the latter half, the high frequency switching of the switching means is continuously performed with the other polarity, so that a plurality of welding portions of a material to be welded can be simultaneously joined to a substantially uniform welding strength in a short period of time in series welding or the like. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a circuit configuration of a resistance welding apparatus for series welding according to one embodiment of the present invention.

FIG. 2 is a waveform chart showing an example of the operation of the resistance welding apparatus according to the embodiment.

FIG. 3 is a partial cross-sectional view illustrating an example of an operation of the resistance welding apparatus according to the embodiment.

FIG. 4 is a waveform diagram showing another example of the operation of the resistance welding apparatus according to the embodiment.

FIG. 5 is a partial sectional view showing another example of the operation of the resistance welding apparatus according to the embodiment.

FIG. 6 is a diagram showing a setting example of a welding current waveform in the resistance welding apparatus according to the embodiment.

FIG. 7 is a diagram showing a circuit configuration of a conventional typical inverter type resistance welding apparatus.

FIG. 8 is a partial cross-sectional view showing a problem caused by a conventional inverter type resistance welding apparatus in series welding.

[Explanation of symbols]

 Reference Signs List 10 single-phase AC power supply 20, 26 diode 24, 26 capacitor 28 rectifier circuit 30 switching means 32, 34, 36, 38 switching element 46 welding transformer 48, 50 welding electrode W1, W2 welded material 52 current sensor 54 current detection circuit 56 Control unit 58 Drive circuit 60 Input unit

Claims (6)

[Claims] 1. A first and second welding electrodes are brought into pressure contact with a material to be welded at positions separated from each other, and said first and second welding electrodes are contacted with each other.
By passing a welding current to the material to be welded between the welding electrodes, the material to be welded is placed at first and second welding locations corresponding to the press contact positions of the first and second welding electrodes, respectively. In the resistance welding method, a commercial frequency alternating current is converted into a direct current by a rectifier circuit and input to a bidirectional current-type switching means, and an output of the switching means is supplied to a primary coil of a welding transformer. ,
The welding current flows in the secondary circuit by applying a voltage obtained to the secondary coil of the welding transformer to the first and second welding electrodes. A resistance welding method, wherein high frequency switching is continuously performed with one polarity, and the switching means is continuously high frequency switched with the other polarity in the latter half of the energization time. 2. The resistance welding method according to claim 1, wherein the first half and the second half of the energization time are set to have substantially the same length of time. 3. A welding current waveform is set such that a waveform of the welding current in the first half and a waveform of the welding current in the second half are point-symmetric with respect to a predetermined point in the energization time as a center point. The resistance welding method according to claim 2, wherein: 4. A rectifier circuit for converting alternating current of commercial frequency into direct current, a bidirectional current-type switching means for converting direct current from the rectifier circuit into high-frequency pulses, and an output of the switching means is input to a primary coil. And
A welding transformer that outputs a high-frequency pulse voltage from the secondary coil; first and second welding transformers that are respectively connected to both ends of the secondary coil of the welding transformer and that pressurize and contact the workpiece to be welded at a distance from each other. A switching control for continuously performing high frequency switching of the switching means with one polarity in the first half of the energizing time, and performing continuous high frequency switching of the switching means with the other polarity in the second half of the energizing time. And a means for resistance welding. 5. The switching control means detects a primary current or a secondary welding current of the welding transformer for each switching cycle and obtains a measured current value. Pulse width control means for comparing the measured current value from the means with a desired set current value and determining a pulse width of an output pulse of the switching means in a next switching cycle according to the comparison error. The resistance welding apparatus according to claim 4, wherein 6. A rectifier circuit comprising: first and second diodes each having an anode terminal and a cathode terminal connected to one terminal of a single-phase AC power supply having a commercial frequency; A first capacitor connected to the cathode terminal of one of the diodes and connected to one input terminal of the switching means, and the other terminal connected to the other terminal of the single-phase AC power supply; A second capacitor having a terminal connected to the other terminal of the single-phase AC power supply, and another terminal connected to an anode terminal of the second diode and connected to the other input terminal of the switching means; The resistance welding apparatus according to claim 4, further comprising: