JP3226204B2 - Controller for resistance spot welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a resistance spot welding machine for sandwiching a work to be welded between a pair of positive and negative electrodes and performing welding by applying a pressure to the work. Control for resistance spot welding that aims to always obtain appropriate welding quality while supplying the welding current of the shape and preventing the surface indentation and deformation of the work to be welded, the welding of the electrodes, and the occurrence of deviation and scattering of the nugget. Related to the device.

[0002]

2. Description of the Related Art Conventional resistance spot welding control devices are roughly classified into single-phase AC, single-phase rectification, three-phase rectification, inverters, and capacitor systems.

However, single-phase alternating current, when the single-phase rectifier and three-phase rectification is not obtained performs only current control at regular intervals synchronized with the power frequency of 50H _Z to 60H _Z, if the inverter also controls time although the unit consists of hundreds to kH _Z and fast, no still it remains a constant interval.

In the single-phase AC type, the positive and negative currents are generated with the same value. In the single-phase rectification and the three-phase rectification type, the welding current controlled to the same positive and negative values is converted to DC on the secondary side of the welding transformer. Was.

In the capacitor type, welding conditions are set by adjusting the charging voltage of the capacitor group. Therefore, the energization time is determined by the capacity of the capacitor and the impedance of the secondary circuit of the welding machine, and can be adjusted arbitrarily. Could not.

As described below, these restrictions reduce the indentation and deformation of an object to be welded, in particular, to a workpiece having a different plate thickness or a material having a low specific resistance, at a low pressure and in a short time. This has been a problem when welding while suppressing the occurrence of welding and scattering of objects.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the drawbacks of the conventional control apparatus for resistance spot welding.

[0008] In other words, the present invention (claim 1) is a control device for a resistance spot welding machine in which an object to be welded is sandwiched between a pair of positive and negative electrodes and welding is performed by applying pressure and conducting. A power transformer for electrically insulating a voltage welding power source and stepping down to a predetermined low voltage, a charging circuit corresponding to a positive electrode and a negative electrode of the electrode for storing power from the power transformer, and the charging circuit. A capacitor group charged to a voltage value that can be set arbitrarily, and the electric power stored in the capacitor group are individually switched in the current direction corresponding to each of the positive and negative electrodes, and are set for the energizing time and the pause time. And a discharge circuit for supplying the workpiece to the workpiece n times .

In some cases, depending on the work to be welded, it is sufficient to apply only DC current. In this case, the charging circuit, the capacitor bank and the discharging circuit on the negative electrode side are omitted, and only the positive electrode side is used to simplify the apparatus. it can.

[0010] Still another aspect of the present invention (claim 2) is a control device for a resistance spot welding machine that sandwiches an object to be welded between a pair of positive and negative electrodes and conducts welding by applying a pressure to the electrode side. While electrically insulating the voltage welding power source,
A power transformer for stepping down to a predetermined low voltage, a rectifier circuit for converting a current from the power transformer into a direct current, and setting of the converted direct current in a current direction individually corresponding to the positive and negative electrodes of the electrodes, respectively. And an energization circuit for supplying the workpiece to the workpiece n times during the energization time and the pause time.

By using two DC stabilized power supplies instead of the welding transformer and the rectifier circuit, it is also possible to adopt a configuration in which a change in welding current due to a power supply fluctuation is compensated. In the same manner as in the preceding paragraph, if only DC energization is sufficient depending on the object to be welded, the charging circuit and the energizing circuit on the negative electrode side can be omitted and only the positive electrode side can be used to simplify the apparatus.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As an embodiment of the present invention, an example in which the present invention is applied to a resistance spot welding machine will be described below. FIG. 1 is an electric block circuit diagram of the present invention (claim 1). The welding power source 1 is stepped down through the power source transformer 2 and the charging circuit 3
And supplied to the charging circuit 4. The microcomputer 5 controls the charging circuit 3 and the charging circuit 4 to charge up to the voltage set in the presetter 14 through the capacitor bank 6 and the capacitor bank 7, respectively.

The microcomputer 5 controls the discharge circuit 9 and the discharge circuit 10 to energize the workpiece by an arbitrary number of times during an arbitrarily set energization time and a pause time, and to start the energization from the outside. This is performed when the switch 8 is input. At this time, if the discharge circuit 9 is driven, FIG.
Is supplied from the upper electrode E1 to the lower electrode E2. According to the discharge circuit 10, the positive and negative polarities are switched.
The current flows from the lower electrode E2 to the upper electrode E1. Current sensor 1 detects the welding current flowing through the secondary conductor of the welding machine during welding.
1 and is compared with the upper limit value or the lower limit value previously input to the setting unit 14 by the microcomputer 5 through the monitor circuit 12.

The level of the upper limit value is a set value based on a current value which does not cause scatter and crushing, which is obtained according to welding conditions such as the material of the workpiece and the plate thickness. As the lower limit, a reference level corresponding to a current value that does not cause unwelded or incomplete welding is set.

When the current value compared and determined by the microcomputer 5 exceeds a preset upper limit value or lower limit value, an alarm output is issued via the input / output circuit 15 and the transition to the next step is stopped. Has become. Note that the above determination result is output to the display 13 which displays input / output data to each device and the detected value is displayed.

FIG. 2 is an electric block circuit diagram showing an embodiment of the present invention (claim 2). The embodiment will be described. The same reference numerals as those in FIG. 1 indicate the same components.

The welding power source 4 is stepped down through the power source transformer 2 and supplied to the rectifier circuits 16 and 17 corresponding to the positive and negative electrodes, respectively.

When the start switch 8 is inputted from outside,
The microcomputer 5 controls the energizing circuit 18 and the energizing circuit 19 to energize the workpiece by an arbitrarily set number of times with an arbitrarily set energizing time and a pause time. At this time, when the energizing circuit 18 is driven, energization is performed from the upper electrode E1 to the lower electrode E2 in FIG. 2, and according to the energizing circuit 19, the positive and negative polarities are switched, and the welding current is changed from the lower electrode E2 to the upper electrode E1. To the power supply. The current value is detected by the current sensor 11 and determined by the microcomputer 5 through the monitor circuit 12, and an alarm is output when the current value exceeds a predetermined upper and lower limit value.

In the embodiment of the present invention, a continuous power supply can be used by using the rectifier circuit. Although a welding power source capacity is required, there is a feature that the length of current supply time is not restricted and the circuit configuration can be simplified.

FIG. 3 shows a phenomenon called a polarity effect when direct current welding is performed in the direct spot welding method and FIG. 4 is a series spot welding method. When the welding current flows from the positive electrode to the negative electrode, the electron current flows in the opposite direction to the current.
In this case, the nugget is displaced (biased) toward the positive electrode side, and the heat generation on the positive electrode side increases, so that the electrode on the positive electrode side is greatly worn and welded easily.

In addition to single-phase rectification and three-phase rectification, DC welding power sources such as the inverter type shown in FIG. 6 and the capacitor type shown in FIG. 7 all have this disadvantage. Such a phenomenon is not observed in the AC welding power source shown in FIG. 5 in which the direction of the current is alternately changed. However, when the two workpieces have significantly different plate thicknesses, that is, when the heat capacities of the positive and negative electrodes are significantly different. Is
Similar phenomena may occur due to different thermal time constants. Also, the electrode on the thin plate side is closer to the weld,
From this point, it is easier to overheat.

In the present invention, as described above, in order to correct this phenomenon, the magnitude of the current in both the positive and negative directions can be arbitrarily adjusted, and the direction of the current flow is switched, that is, the timing of changing the polarity of the upper and lower electrodes is changed. Can be performed any number of times in any energization time and pause time,
Even when welding workpieces with different plate thicknesses, the deviation of the nugget and the wear of both electrodes can be optimally balanced.
Accordingly, welding of the electrode to the workpiece can be prevented.

Further, in the present invention, compared with a conventional method of installing a welding transformer between a discharge circuit and an electrode instead of a power supply transformer, such as a single-phase AC, an inverter, a capacitor type, etc. There is no influence of the inductance, the rise of the current waveform is steep, and the switching pause time in the direction of the positive or negative current can be adjusted in a short time, so that the nugget formation can be started earlier. If a welding transformer is present after the discharge circuit as in the past, the rise of the current waveform will be delayed due to the influence of this inductance. Due to the pressure contact, the contact resistance between the plates sharply decreases. As a result, Joule heat is less likely to be generated in the welded portion, and the subsequent nugget growth rate will be reduced.

According to the present invention, a large amount of energy can be supplied to the welded portion before the contact resistance between the two workpieces is reduced, so that the nugget can be formed early.
The energization time can be short. That is, not only energy saving, but also welding can be completed before the crushing deformation of the workpiece is small. Further, there is an effect that the weldability to a material having low specific resistance such as copper and aluminum is also improved.

(Up slope) On the other hand, in the conventional case,
If the current rises steeply, the welded portion will be rapidly heated, and there is a problem that the welded portion is often exploded. To avoid this problem, perform initial up-slope control of the welding current used in single-phase rectification, three-phase rectification, inverter type, etc., or increase the pressing force to improve the familiarity of the welded material. The only option was to keep the inter-resistance low to suppress the generation of Joule heat in the weld. However, if the pressing force is increased and the inter-plate resistance is reduced, the welding current must be further increased and the energizing time must be prolonged. In combination with the high pressure, the crushing of the welded material is further promoted. Would.

According to the present invention, each pulse width of the current waveform can be freely adjusted, so that an effect equivalent to an appropriate upslope can be equivalently obtained, and even if the rise of the current is steep. Regardless, the blast of the weld can be suppressed while keeping the pressing force low.

(Polarity Effect) FIG. 8 is an example of a welding current waveform based on this embodiment. In the figure, the upper current waveform is due to the discharge circuit 9, and the lower current waveform is due to the discharge circuit 10. Here, the charging voltage of the capacitor bank 7 for supplying the power of the discharging circuit 10 is set slightly higher. First, the first pulse on the relatively short discharge circuit 9 side improves the conformity of the work to be welded to prevent explosion, and thereafter, welding is performed with three pulses contributing to welding. The lower pulse is made slightly larger to correct the nugget deviation due to the polarity effect.

(Polarity Effect and Tempering) FIG. 9 shows another example of a welding current waveform according to the present invention in which a tempering action is added to the embodiment of FIG. As shown in this figure, the discharge circuit 9 and the discharge circuit 10 are not necessarily driven alternately, and one side may be driven continuously depending on welding conditions. In FIG. 9, first, the first pulse for preventing explosion is supplied to the discharge circuit 9 side to improve the conformity of the work to be welded, and then a welding current having a large pulse width is applied in the same direction. The energization is performed on the side with a small pulse that serves both for correcting the polarity effect and for tempering.

FIG. 10 shows another example of a welding current waveform based on the embodiment of the present invention. FIG. 3A shows the positive and negative side rectangular waveforms when the discharge circuit 9 is continuously driven at the same time and when the discharge circuit 10 is driven intermittently. When a current having a long width is supplied and a pulse having a small current value is intermittently supplied from the discharge circuit 10 for a short period of time, the positive and negative pulse side rectangular waves are canceled. Therefore, the welding current substantially flowing to the electrode side as shown in the current waveform (B) of FIG.

By doing so, the rise of the welding current in accordance with the welding conditions of the work to be welded can be accelerated to generate heat before the resistance between the work plates is reduced, and a nugget can be generated in a short time. This can deepen the penetration. In addition, since the welding current can be set to any desired time and number of times, rapid heat generation can deepen the penetration, and the molten portion immediately before the explosion has a reduced time so that overheating can be intermittently diffused. Even in a mechanism with a slow pressing force following force, the explosion of the weld can be suppressed while keeping the pressing force low.

(Prevention of Scattering) FIG. 11 shows another example of a welding current waveform based on this embodiment. In this case, as in FIG. 10, pulse-shaped rectangular waves on the positive and negative sides when the discharge circuit 9 and the discharge circuit 10 are simultaneously driven intermittently are superimposed. As shown, the discharge circuit 9
When the currents having different magnitudes and the pulse widths from the discharge circuit 10 and the pulse width are simultaneously supplied, the positive-side pulse waveform and the negative-side pulse waveform cancel each other out, and as shown in FIG. A welding current having a superimposed pulse waveform can be supplied between the electrodes.

Therefore, according to this current waveform control,
Heat generation control according to the welding conditions of the workpiece can be quickly performed, and the penetration can be deepened by generating a nugget in a short time. In addition, since the welding current can be set to any desired pause time and the number of times of energization, rapid heat generation can deepen the penetration and provide a pause time for the molten zone immediately before the explosion, thereby dispersing the overheating intermittently and making it more polar. This prevents the explosion of the welded portion while keeping the applied pressure low even in a mechanism having a slow ability to follow the applied force to the welded portion.

[0033]

According to the present invention (claims 1 and 2), the magnitude and pulse width of the pulse waveform of the welding current in both the positive and negative directions can be arbitrarily adjusted. Since the welding can be performed at an arbitrary number of times during the pause time, even when welding workpieces having different plate thicknesses, the deviation of the nugget and the wear of both electrodes can be optimally balanced. Can also be prevented from welding to the workpiece. In addition, since the rising of the current waveform is steep and the switching pause time in the direction of the positive or negative current can be adjusted in a short time, the start of the nugget formation can be hastened.

Furthermore, if the present invention is applied, it is still 2
Since a large amount of energy can be supplied to the welded portion before the contact resistance between the workpieces is reduced, a nugget is formed early and the energization time can be reduced. That is, not only energy saving, but also welding can be completed before the crushing deformation of the workpiece is small. Further, the weldability to a material having low specific resistance such as copper and aluminum can be improved.

Further, according to the present invention, since each pulse width of the current waveform can be freely adjusted, the same effect as that of an appropriate up-slope control can be equivalently obtained. Regardless, the blast of the weld can be suppressed while keeping the pressing force low.

In the case of the present invention (claim 2), a continuous power supply can be used by using a rectifier circuit or a DC stabilized power supply circuit. , And a larger welding power source capacity is required. However, there is no restriction on the length of energization time, and the circuit configuration can be simplified.

[Brief description of the drawings]

FIG. 1 is an electric block circuit diagram showing an embodiment of the present invention.

FIG. 2 is an electric block circuit diagram showing another embodiment of the present invention.

FIG. 3 is a schematic explanatory view showing a polarity effect depending on a direction of a welding current in a direct spot welding method.

FIG. 4 is a schematic explanatory view showing a polarity effect depending on a direction of a welding current in a series spot welding method.

FIG. 5 is a current waveform diagram in a single-phase AC system.

FIG. 6 is a current waveform diagram in an inverter type.

FIG. 7 is a current waveform diagram in a capacitor system.

FIG. 8 is a current waveform diagram in the example of the present invention.

FIG. 9 is a current waveform diagram in another embodiment of the present invention.

FIG. 10 is a superimposed current waveform diagram of an upper discharge and a lower discharge in an example of the present invention.

FIG. 11 is a superimposed current waveform diagram of an upper discharge and a lower discharge in another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Welding power supply 2 ... Power supply transformer 3 ... Charging circuit 4 ... Charging circuit 5 ... Microcomputer 6 ... Capacitor bank 7 ... Capacitor bank 8 ... Start switch 9 discharge circuit 10 discharge circuit 11 current sensor 12 monitor 13 display device 14 setting device 15 input / output circuit 16 rectifier circuit 17 .. Rectifier circuit 18 ... energizing circuit 19 ... energizing circuit E1 ... upper electrode E2 ... lower electrode

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shoji Sanpeira 1-23-1 Masugata, Tama-ku, Kawasaki City, Kanagawa Prefecture Examiner at Dengensha Seisakusho Co., Ltd. Takayuki Kanzaki (56) References JP 3-285777 ( JP, A) JP-A-4-167981 (JP, A) JP-A-58-100984 (JP, A) JP-A-59-218284 (JP, A) JP-B-48-24625 (JP, B1) (58 ) Surveyed field (Int.Cl. ⁷ , DB name) B23K 11/26

Claims (2)

(57) [Claims] In a control apparatus for a resistance spot welding machine for performing welding by sandwiching an object to be welded between a pair of positive and negative electrodes and applying a current by applying a pressure, a high-voltage welding power source is electrically insulated from the electrode side. A power transformer for stepping down to a predetermined low voltage, a charging circuit corresponding to the positive and negative electrodes of the electrodes for storing power from the power transformer, and charging to a voltage value which can be set arbitrarily by the charging circuit. And the power stored in the capacitor group
Switching of current direction individually for positive and negative electrodes
Arbitrarily set n times for energization time and pause time
A control device for resistance spot welding, comprising: a discharge circuit for supplying only to a workpiece. 2. A control device for a resistance spot welding machine in which a work to be welded is sandwiched between a pair of positive and negative electrodes and welding is performed by applying a pressure and electrically welding a high-voltage welding power source to said electrode side. A power transformer for stepping down to a predetermined low voltage, a rectifier circuit for converting a current from the power transformer to a direct current, and converting the converted direct current individually in a current direction corresponding to a positive electrode and a negative electrode of the electrode . And a power supply circuit for supplying the workpiece to the workpiece by an arbitrary number of times set during the power-on time and the pause time after switching .