JP3169175B2 - Inverter resistance seam welding machine for fuel tank - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance seam welding machine. More specifically, it relates to a resistance seam welding machine for a fuel tank of an automobile using a plated steel sheet.

[0002]

2. Description of the Related Art A shell-shaped metal fuel tank of an automobile is housed in a narrow space of a vehicle body, and furthermore, an upper tank body and a lower tank which are pressed into complicated shapes to secure a large fuel capacity. The body is assembled in a shell shape, and the overlap of the flange portion formed on the outer periphery of the container combined in the shell shape is airtightly joined by a seam welding machine.

Heretofore, lead-tin (Pb-Sn) alloy-plated steel sheets have been generally used as materials for metal fuel tanks of automobiles. Recently, the harmfulness of lead contained in the plating of this type of steel sheet has become a major social problem, and as an alternative, the development of fuel tank manufacturing technology using aluminum alloy coated steel sheet (hereinafter referred to as aluminum alloy coated steel sheet) is being promoted. .

[0004] When seam welding an aluminum alloy-plated steel sheet, the number of blowholes generated has become much larger than that of a lead / tin alloy-plated steel sheet. There are several possible causes of blowholes, such as spatter generation, heat / cool timing, welding of electrodes and plating, and the like.

[0005]

Conventionally, when intermittent current is applied as in the case of general seam welding in the manner of setting the timing of heat / cool, blow holes are easily generated. Also, if the cool time is shortened, the number of blowholes will gradually decrease. In addition, blow current hardly occurs in continuous energization without cooling time, but when continuous energization is performed in an actual line, if there is contamination on the electrodes, overheating will occur in that part, resulting in poor welding and poor welding. Becomes

On the other hand, if wire seam welding is used, the electrode is always clean and can be used in the field, but continuous energization cannot be used in general seam welding. In addition, since wire seam welding requires a wire supply device and wire consumables, there has been a problem that the cost increases.

[0007]

SUMMARY OF THE INVENTION The present invention has been developed to improve the seam weldability of plated steel sheets used for materials such as fuel tanks of automobiles. is there. A resistance seam welding machine for pressurizing a flange portion of an automotive fuel tank using a plated steel plate via a seam electrode, repeating heat and cooling, intermittently energizing, and rotating and driving the electrode wheel to perform seam welding. Is converted to direct current by a forward converter to generate a half or full bridge low-order high-frequency current using the power as a power source. The current required for welding is supplied to the seam electrode wheel through a welding transformer, and the In an inverter type seam welding machine for seam welding a flange portion, a circuit for constantly generating a higher-order triangular wave higher than the frequency of an inverter output current supplied to the transformer, and a pulse width for detecting the output current and comparing the two. A modulation circuit (PWM) for turning on / off a switching element of an inverter main circuit by a modulation wave of the modulation circuit; Higher frequency components reactor or directly to a filter, a sine wave, triangle wave, square wave, necessary for welding through the welding transformer
A current control unit that forms a welding current waveform that is faithful to a set signal waveform including a trapezoidal wave or a form close to these waveforms; Millisec (m
A continuous high and low current waveform is generated by falling to within the range of s) and seam welding is performed.

[0008]

According to the resistance seam welding machine of the present invention, a flange portion of an automobile fuel tank using a plated steel sheet is sandwiched between seam electrodes and pressurized, and heat and cooling are repeatedly intermittently conducted to rotate the electrode wheels. In the case of seam welding, continuous high and low current waveforms are alternately flown by an inverter control with a pause time of 2 ms after a conduction time of 20 ms. As a result, blowholes generated in the seam weld can be suppressed, and the seam welding speed can be increased. Also, compared to a wire seam welding machine, there is no need for a wire supply device or wire consumables, so no equipment cost is required.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a resistance seam welding machine according to the present invention will be described below based on data obtained by experiments using current waveforms shown in FIGS. In intermittent energization in general seam welding as shown in FIG. 1, if the cool time is lengthened, blow holes are likely to occur. With continuous energization without the cool time as shown in FIG. 2, the occurrence of blowholes is almost eliminated. However, if there is disturbance such as contamination of the electrodes, holes are formed due to overheating, resulting in poor welding.

[0010] In the turn sheet, the occurrence of blowholes was hardly a problem. Although there is no particular problem with the presence of blowholes (for example, a blowhole with a length of about half the nugget diameter also has a problem with strength, but such a large one does not generally occur). I have never done it.

Next, in the case where an aluminum alloy-plated steel sheet is welded by a seam welding machine using DC inverter control, FIG.
As shown in Fig. 1, when welding an aluminum alloy coated steel plate with an energization time of 20 msec (ms) and a pause time of 20 msec (ms), a nugget diameter of 1.5 mm or more is obtained as shown in Fig. 4. Although there is a width, the average number of blow holes is 10 mm for a length of 100 mm.
It has been confirmed that the ke position occurs.

The inverter type resistance seam welding machine according to the present invention converts alternating current of commercial frequency into direct current by a forward converter,
This is an inverter type seam welding machine that generates a half- or full-bridge low-order high-frequency current using this power as a power source, supplies the current necessary for welding to the seam electrode wheel through a welding transformer, and seams the workpiece. A circuit that constantly generates a triangular wave having a higher frequency than the frequency of the inverter output current supplied to the welding transformer, and a pulse width modulation circuit (PWM) that detects the output current and compares the two. A reactor for turning on / off the switching element of the inverter main circuit by the modulated wave and filtering high-order high-frequency components, or a sine wave, a triangular wave, a rectangular wave, a trapezoidal wave required for resistance seam welding directly via a welding transformer. Alternatively, a current control device that forms a welding current waveform that is faithful to a setting signal waveform including a form close to these waveforms is incorporated.

Next, using DC inverter control, FIG.
When current was continuously applied with the current waveform shown in Fig. 5, since there was no cool time, as shown in Fig. 5, holes were generated due to abnormal heat generation between the electrode and the work, and it was confirmed that the welding condition width was extremely narrow.

On the other hand, when the cool time is set to 2 milliseconds (ms) after the heat time of 20 milliseconds (ms) using the DC inverter control as shown in FIG. 3, the DC current continues without dropping completely to zero. A high-low current waveform is obtained. When such continuous high-low waveform inverter current waveform is generated and seam-welded, the high-low waveform welding current flows alternately in one direction, which reduces the cooling time which causes blowholes. As shown, the occurrence of blowholes in the nugget was hardly a problem, and the seam weldability was improved.

According to an experiment, the lower limit of the cool time is less than 1 millisecond (ms) and the upper limit of the cool time is 6 ms.
In the case of milliseconds (ms) or more, blow holes were easily formed, and no remarkable improvement effect was obtained.

[0016]

As described above, according to the inverter type seam welding machine for manufacturing an automobile fuel tank using a plated steel sheet, the cool time of the heat / cool timing at the time of seam welding is 1 to 5 milliseconds ( ms), and high and low currents without cooling time are alternately flowed.
Moreover, by generating a current waveform of an arbitrary shape in accordance with welding conditions, it is possible to prevent internal defects such as blowholes generated in a seam welded portion of the fuel tank, and to increase the seam welding speed of the tank. In addition, it can be manufactured in each stage at low cost without using expensive accessories as compared with wire seam welding machines.

[Brief description of the drawings]

FIG. 1 shows a current waveform due to intermittent energization in an experiment of the seam welding method of the present invention.

FIG. 2 shows a current waveform by continuous energization in an experiment of the seam welding method of the present invention.

FIG. 3 shows a current waveform for realizing the seam welding method of the present invention.

FIG. 4 shows the relationship among the welding current, the number of blowholes (BH), and the weld bead width when seam welding aluminum alloy plated steel sheets with a heat time of 20 msec and a cool time of 20 msec in the seam welding method.

FIG. 5 shows that when an aluminum alloy plated steel sheet is seam-welded by continuous energization by the seam welding method, holes are formed due to abnormal heat generation between the electrode and the work, and there is no welding condition width.

FIG. 6 shows that when the aluminum alloy plated steel sheet is seam-welded with a heat time of 20 msec and a cool time of 2 msec in the seam welding method of the present invention, the number of blow holes hardly increases even if the welding current is increased. This shows that the weld bead width has increased.

Claims (1)

(57) [Claims] 1. A resistance seam welding in which a flange portion of an automobile fuel tank using a plated steel sheet is sandwiched and pressurized by a seam electrode wheel, heat and cool are repeatedly intermittently energized, and the electrode wheel is rotated to drive seam welding. A commercial frequency alternating current is converted into a direct current by a forward converter to generate a half- or full-bridge low-order high-frequency current using the power as a power source, and the current required for welding is transmitted through a welding transformer to the seam. In an inverter type seam welding machine for seam welding the flange portion by supplying to an electrode wheel, a circuit for always generating a higher-order triangular wave of a higher frequency than the frequency of an inverter output current supplied to the transformer, and detecting the output current. And a pulse width modulation circuit (PWM) for comparing the two, and the switching element of the inverter main circuit is operated by the modulation wave of the modulation circuit. A setting signal including a sine wave, a triangular wave, a rectangular wave, a trapezoidal wave, or a form close to these waveforms necessary for welding via the welding transformer, or a reactor for turning on / off and further filtering high-order high-frequency components It has a current control device that forms a welding current waveform that is faithful to the waveform, and the control device allows the cool time of the heat / cool timing to be 1 to 5 msec (m
An inverter-type resistance seam welder that performs continuous seam welding by generating a continuous high and low current waveform by falling to within the range of s).