JP5514505B2 - Resistance welding power supply apparatus, resistance welding apparatus using the power supply, and power supply control method - Google Patents

Description

  The present invention relates to a resistance welding power supply apparatus, a resistance welding apparatus using the power supply, and a power supply control method.

Seam welding, which is a type of resistance welding, is resistance welding performed continuously along the welded joints of the superposed base metal. It uses two disc-shaped welding electrodes and continuously sandwiches the workpiece. This is a welding method in which electric current is intermittently rotated while welding is performed.
Conventionally, a seam welder is heavy and large, and can only perform two-dimensional welding, and it has been difficult to mount it on a welding robot and perform three-dimensional welding.

  However, the inventor of the present application discloses a technology that enables a three-dimensional seam welding to a workpiece by mounting a miniaturized seam welding machine on a multi-axis robot (Patent Document 1). Thereby, the welding efficiency with respect to the workpiece | work which has a large-sized and three-dimensional curve was able to be improved significantly.

  Furthermore, this inventor invented and disclosed the welding transformer core cooling case (patent document 2). This enables the cooling of the transformer core efficiently, realizing a larger capacity, lighter weight and smaller size of the transformer, and can be installed on the welding head of the robot.

On the other hand, the welding speed that can be realized with the seam welding machine at present is a linear workpiece, even if it is fast, it is 3-5 m / min with a steel plate thickness of 1 mm, and even slower in actual welding workpieces with curved parts. It has become.
These are overwhelmingly faster than arc welding (30 to 40 cm / min with a steel plate thickness of 1 mm), but due to the need for cost reduction and improved efficiency in the manufacturing industry in recent years, there is a need for further improvement in welding speed. Is growing.

Therefore, in order to increase the welding speed, it is necessary to increase the response of the welding current and the welding voltage by increasing the frequency and to improve the performance of the power source. At present, the power supply apparatus mainly used is an inverter DC type. Since these power supplies are high and use a frequency of about 1000 Hz and change the call balance at a constant frequency, the current waveform is particularly disturbed and wasteful especially at the start-up.
Specifically, the concept of current change in the conventional power supply (at a constant 1000 Hz) (see FIG. 1) is high when the target current value is small compared to when the target current value (average current value) is high. This will reduce the time for the current to flow effectively in order to maintain the frequency, and an unnecessary large amount of current flows in each time unit, resulting in a lot of waste, and there has been a certain limit to increasing the frequency. .

Utility Model Registration No. 3124033 JP 2008-1112775 A

  Therefore, an object of the present invention is to provide a resistance welding power supply device that improves the response of welding current and welding voltage at a higher frequency, particularly an inverter type resistance welding power supply device used for seam welding, and further It is to provide a seam welding machine that achieves a high welding speed.

In order to solve the above-described problem, the power supply device of the present invention uses two disc-shaped welding electrodes, and in a seam welding device that performs welding by intermittently rotating a current while sandwiching a workpiece, It consists of performing seam welding at 8 m / min to 30 m / min by using an inverter type resistance welding power supply device having a variable frequency according to the actual (actually flowing) current value.
Specifically, an inverter type resistance welding power supply device, means for setting a predetermined target current value, means for detecting an actual current value (primary current and / or secondary current) in a predetermined time unit, Means for comparing the actual current value with a predetermined target current value, and means for stopping the current by switching control when the actual current value exceeds the target current value as a result of the comparison, and starting the next current Providing a variable frequency. Therefore, for example, the frequency is varied in a range up to 1000 to 10000 Hz or higher. The target current value is appropriately set to be a current value having an ideal rise as time elapses.

That is, at the rise and fall of the welding current, the required target current is low, and when the target current value is reached, the current is turned off and immediately rises again, so the frequency is increased and high-speed response is ensured. . On the other hand, during constant current welding during welding, the frequency decreases and the amount of wasted power is reduced. As a result, high frequency is realized and high-speed response is ensured, and seam welding at a high speed of 8 m / min to 30 m / min with a steel plate thickness of 1 mm becomes possible.
Further, when the above-described welding transformer core cooling case invented by the present inventor is used after using the above power source, even if a larger capacity welding transformer is used, the heat generation of the transformer can be sufficiently suppressed. It is possible to perform seam welding at a high speed up to 8 m / min to 30 m / min or more.

  On the other hand, the power supply apparatus / method of the present invention can be widely applied to resistance welding other than seam welding. For example, even when a thin plate is welded by spot welding, high-speed response can be ensured without waste, so that it is possible to perform good welding with less spatter. Thus, the power supply apparatus / method of the present invention is useful not only for improving the speed of seam welding but also for improving the quality of various resistance welding.

  Here, the welding transformer core cooling case is a welding transformer core cooling case described in Japanese Patent Application Laid-Open No. 2008-112775, and is an insulating heat conduction case (preferably an insulation-coated aluminum case) having fixing means. A cooling pipe having one end serving as a cooling medium (preferably water) introduction portion and the other end serving as a cooling medium discharge portion is provided inside the case.

This makes it possible to use a large-capacity welding transformer that is lightweight, small and low-cost, and can withstand welding at a higher speed, so that the synergistic effect with the power source is very high.
Furthermore, when a welding transformer is mounted on a seam welding robot and the power source or the power source and the welding transformer core cooling case are used, seam welding can be performed on various workpieces at high speed.

According to the above configuration of the present invention, it is possible to provide a resistance welding power source in which the frequency changes in a range reaching a high frequency and high frequency and high-speed response are ensured. As a result, high-speed seam welding is realized. Further, the current waveform is smooth, the ripple of the secondary current is reduced, and the welding failure can be reduced by reducing the applied pressure and reducing the generation of dust.
Furthermore, it can be used in combination with a large-capacity welding transformer, and speeding up to 8 m / min to 30 m / min or more is possible.
Furthermore, by using in combination with a welding robot, high-speed seam welding can be performed regardless of the workpiece shape.

Conceptual diagram of frequency change of conventional power supply Conceptual diagram of frequency change of power supply according to the present invention Configuration diagram of the power source of the present invention Current waveform using a conventional power supply Current waveform using a conventional power supply Current waveform using power supply according to the present invention Current waveform using power supply according to the present invention Diagram showing the configuration of the transformer core cooling case Diagram showing the configuration of the transformer core cooling case

An example of an embodiment of the present invention will be described with reference to the drawings.
FIG. 2 is a conceptual diagram showing changes in current and frequency output when the power supply device of the present invention is used. The graph on the left in FIG. 2 shows the case where the target current value is high. On the other hand, the graphs in the center and the right are cases where the target current value is lower than that on the left.
That is, in the present invention, a means for setting a predetermined target current value, a means for detecting an actual current value (primary current value and / or secondary current value) in a predetermined time unit, an actual current value, Since a means for comparing with a predetermined target current value and a means for switching control (current off) when the actual current value exceeds the target current value as a result of the comparison, the current is reduced when the target current value is low. Reaches the target value immediately after rising. When the target current value is exceeded, switching control is performed and the next output rises immediately after the output is turned off. As a result, the frequency changes according to the target current value and the actual current value.
Thus, it is clear that there is less waste and higher frequency is possible compared to the conventional control as seen in FIG.

An example of a specific power supply configuration is shown in FIG.
The input terminal of the rectifier circuit 2 is connected to the three-phase commercial AC power supply terminal 1, and direct current is obtained at the output terminal of the rectifier circuit 2. The direct current is smoothed by a smoothing circuit including a capacitor 3 and the like and then input to the inverter control circuit 4. The inverter control circuit 4 has a switching element 5 made of GTR (Giant Transistor), IGBT (Insulated Gate Bipolar Transistor), or the like, and converts input direct current into pulsed high-frequency alternating current by a high-frequency switching operation. Switching control is performed via a control circuit 6 that performs PWM control and the like.

The high-frequency alternating current output from the inverter control circuit 4 is supplied to the primary coil of the welding transformer 7 (primary current), and the stepped-down high-frequency alternating current is obtained in the secondary coil. This high-frequency alternating current is converted into direct current by a rectifier circuit including a pair of diodes 8, and direct current (secondary current) is supplied to the seam welding welding electrode 9.
The sensor position of the primary current can be installed at an appropriate position, but can be detected as a DC value in front of the inverter control circuit 4. The current sensor 10 detects the primary current and sends the current value to the control circuit 6. On the other hand, the current sensor 11 detects the secondary current and sends the current value to the control circuit 6. At this time, if necessary, the integration circuit 15 and the A-D converter 16 may be used, and the voltage detection 17 may be performed.

  The control circuit 6 is connected to an input unit including a display 12, a panel switch 13, and the like, and a target current value change is recorded with a time change. In addition, various types of data delivery are performed mutually with the outside via the interface circuit 14.

  When the detected primary current value and / or secondary current value reaches the target current value, the control circuit 6 immediately performs switching control and raises the next current. By repeating this operation, the output frequency is varied according to the primary current value and / or the secondary current value.

4 and 5 are current waveforms (5KA, 12KA) using a conventional power supply (Company M power supply), and FIGS. 6 and 7 are current waveforms (5KA, 12KA) using the power supply according to the present invention. It is.
When a conventional power source is used, the waveform is clearly rough and the response is poor, there are many ripples, a large primary current flows at the rise, and this is wasteful. On the other hand, in the power supply of the present invention, the primary current waveform is ideally smooth, and as a result, the secondary current waveform is also ideally smooth and has few ripples. In addition, the feedback to the resistance change during welding is also performed with a response that is 3 to 10 times faster than the conventional one because the frequency is high, so that the generation of dust and the like can be reduced.

FIG. 8 is a view showing a state in which the transformer core cooling cases 102 and 103 are attached to the welding transformer 101. When used in combination with the power supply apparatus / method of the present invention, the maximum synergistic effect can be achieved, and a high speed of 30 m / min or more can be achieved.
A specific example will be described with reference to FIG. 8. The secondary coil 102 of the welding transformer 101 is cooled by flowing a cooling medium through the coil cooling pipe 13. Two transformer core cooling cases 102 and 103 are used as a pair. That is, the transformer core cooling cases 102 and 103 are installed so as to sandwich the transformer core 104. The pair of transformer core cooling cases 102 and 103 are pressed and fixed to the transformer core 4 by applying a force so as to approach each other using screws or bolts 105.

  FIG. 9 is a front view of the transformer core cooling cases 102 and 103. A cooling pipe 106 is built in the transformer core cooling cases 102 and 103. One end of the cooling pipe 106 is a cooling medium introduction unit 107 and the other end is a cooling medium discharge unit 108. A valve 109 is provided at the end for connection and flow rate adjustment.

  When a cooling medium such as water flows through the cooling pipe 106, the transformer core cooling cases 102 and 103 are kept at a temperature lower than that of the transformer core 4. Since the transformer core cooling cases 102 and 103 are in contact with the transformer core 104, the transformer core 104 can be cooled. With this structure, the transformer can be increased in capacity and reduced in size and weight. Yes, by using it together with the power source of the present invention, the seam welding machine can achieve high frequency, high responsiveness, large current, small size and light weight, enabling high-speed seam welding. It is.

  Also, for example, by using the power supply and welding transformer core cooling case of the present invention in a multi-axis robot seam welding machine with a welding transformer attached to the welding head, it is possible to handle various workpieces at high speed. It is. The power supply apparatus / method of the present invention can be used not only for seam welding but also for various resistance welding apparatuses.

DESCRIPTION OF SYMBOLS 1 Commercial alternating current power supply terminal 2 Rectifier circuit 3 Capacitor 4 Inverter control circuit 5 Switching element 6 Control circuit 7 Welding transformer 8 Diode 9 Welding electrode 10 Current sensor 11 Current sensor 12 Display 13 Panel switch 14 Interface circuit 15 Integration circuit 16 AD conversion 17 Voltage detection 101 Welding transformer 102, 103 Transformer core cooling case 104 Transformer core 105 Screw or bolt 106 Cooling pipe 107 Cooling medium introduction section 108 Cooling medium discharge section 109 Valve

Claims (5)

Inverter direct current with variable frequency according to the actual current value in a seam welding device that uses two disk-shaped welding electrodes, and continuously welds the workpiece while rotating it with the workpiece sandwiched between them. shea over beam welding using a resistance welding power supply apparatus a row bovine chromatography beam welding method,
The inverter DC resistance welding power supply apparatus compares a means for setting a predetermined target current value, a means for detecting an actual current value in a predetermined time unit, and the actual current value and the predetermined target current value. A seam welding method comprising: switching means for switching control when an actual current value exceeds a target current value as a result of comparison, and raising a next current. This is a seam welding device that uses two disk-shaped welding electrodes and continuously turns the workpiece while rotating it across the workpiece to perform welding. The inverter has a variable frequency according to the actual current value. a sheet over beam welder capable of welding using the equation dc resistance welding power supply apparatus,
The inverter DC resistance welding power supply apparatus compares a means for setting a predetermined target current value, a means for detecting an actual current value in a predetermined time unit, and the actual current value and the predetermined target current value. A seam welding machine comprising: a means for switching control when an actual current value exceeds a target current value as a result of comparison; The seam welding machine according to claim 2, wherein the frequency of the inverter DC resistance welding power supply device is variable within a range of 1000 to 10000 Hz. A seam welding machine comprising the inverter DC resistance welding power supply device according to claim 2 or 3, wherein the insulation heat conduction case has a fixing means, and one end serves as a cooling medium introducing portion and the other end. A seam welder characterized in that a transformer core cooling case provided with a cooling pipe serving as a cooling medium discharge part inside the case is mounted on the transformer. 6. The seam welder according to claim 3, wherein the seam welder is a robot seam welder.

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