JP2011206802A - Seam welding method of fuel tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize welding quality in a lap welding region between a welding start position and a welding end position, in forming a fuel tank by seam welding.SOLUTION: With flanges 203a, 203b superimposed, pressurization/energization is applied to the superimposed flange 203 with disk electrodes 115a, 115b from the upper and the lower side, thereby seam welding is performed along the circumferential direction of the flange 203. In such event, the seam welding starts from a welding start position S and after it returns to the welding start position S via an intermediate position C, seam welding is again performed on a region where the seam welding has already been performed, and is completed at the welding end position E. From the welding start position S to the intermediate position C, the seam welding is performed with a starting current Iwhich is 0.5-0.7 times as large as the regular current I. From the intermediate position C to the welding end position E, the seam welding is performed with the regular current I.

Description

  The present invention relates to a method for seam welding of a fuel tank, and is particularly suitable for use in forming a fuel tank by performing seam welding.

When manufacturing a metal fuel tank such as an automobile fuel tank, a flange formed along the lower outer peripheral edge of the upper member and a flange formed along the upper outer peripheral edge of the lower member are overlapped. In addition, it is necessary to perform seam welding on the flange continuously without any defects.
As a technique for performing such seam welding, there is a technique described in Patent Document 1. In the technique described in Patent Document 1, the energization time, cooling time, and welding current values for the base material are arbitrarily set by an inverter control device that switches a switching element of an inverter circuit that drives a welding transformer that supplies a welding current to the base material. It is disclosed that the setting can be made.

JP 11-300479 A

By the way, when seam welding is performed to form a fuel tank, welding is started so that an unwelded region does not occur between the welding start position and the welding end position in order to ensure the sealing performance of the fuel tank. Welding is terminated after welding is performed at the position.
However, in the prior art, generally, welding is performed with a constant steady current from the welding start position to the welding end position. For this reason, there is a problem that a welding defect such as a pit or a hole is generated in a region where welding is performed repeatedly between the welding start position and the welding end position.

In view of this, it is conceivable to reduce the welding current from a position before the welding start position when performing welding while overlapping the welding start position. However, in this case, it becomes difficult to control the timing for reducing the welding current with high accuracy. Therefore, there is a possibility that the weld nugget formed when the welding current is reduced and the weld nugget formed at the welding start position are not sufficiently connected. If it does so, there exists a possibility that the welding in the area | region where welding will be overlapped between a welding start position and a welding end position may become incomplete, and a fuel tank may not be sealed.
The present invention has been made in view of the above-described problems. When seam welding is performed to form a fuel tank, welding is performed in an overlap between a welding start position and a welding end position. The purpose is to stabilize the welding quality in the region.

  The fuel tank seam welding method according to the present invention includes a flange formed along a lower outer peripheral end of an upper member that is a part of a metal fuel tank, and an upper outer periphery of the lower member that is a part of the fuel tank. The flanges formed along the ends are overlapped with each other, and the overlapped flanges are pressurized and energized by disk electrodes from above and below, so that the seams are formed along the circumferential direction of the flanges. When performing welding, seam welding is started from the welding start position, and after the welding position returns to the welding start position via the intermediate position, seam welding is performed on the area where seam welding has already been performed, and the intermediate position is A seam welding method for a fuel tank in which seam welding is terminated at a welding end position after passing through the seam from the welding start position to the intermediate position with a first welding current. From the intermediate position to the welding end position, seam welding is performed with a second welding current having a magnitude exceeding the first welding current, and the magnitude at the start of the first welding current is The second welding current is 0.5 times or more and 0.7 times or less.

  According to the present invention, when seam welding is performed along the circumferential direction of the flange by pressing and energizing the overlapped flange from above and below with the disk electrodes, seam welding is started from the welding start position. After the welding position returns to the welding start position via the intermediate position, seam welding is performed on the area where seam welding has already been performed, and after passing through the intermediate position, the seam welding is terminated at the welding end position. Like that. At this time, seam welding is performed with the first welding current from the welding start position to the intermediate position. From the intermediate position to the welding end position, seam welding is performed with a second welding current having a magnitude exceeding the first welding current. At this time, the magnitude | size at the time of the start of 1st welding current shall be 0.5 times or more and 0.7 times or less of the magnitude | size of 2nd welding current. Therefore, when the disk electrode returns to the welding start position, the step generated at the welding start position can be made gentle. Therefore, the calorific value in this portion can be suppressed. Thereby, when performing a seam welding and forming a fuel tank, the welding quality in the area | region where welding is carried out in piles between a welding start position and a welding end position can be stabilized.

It is a figure which shows notionally an example of the mode of a welding state when seam welding is performed with a fixed steady current from a welding start position to a welding end position. It is a figure which shows embodiment of this invention and shows an example of schematic structure of a seam welding system. It is a figure which shows embodiment of this invention and shows the positional relationship of a fuel tank (upper member and lower member) and a disk electrode. It is a figure which shows the 1st Embodiment of this invention and demonstrates an example of the method of controlling the magnitude | size of a welding current. 1 shows a first embodiment of the present invention, and conceptually shows an example of a state of welding when seam welding is performed with a starting current from a welding start position to an intermediate position and then seam welding is performed with the current. FIG. It is a figure which shows embodiment of this invention and shows an example of the relationship between a nugget width and welding current. It is a figure which shows embodiment of this invention and demonstrates a nugget width | variety. It is a figure which shows the 1st Embodiment of this invention and shows an example of the relationship between this electric current, starting current, starting current / main current, and a defect incidence. It is a figure which shows the 2nd Embodiment of this invention and demonstrates an example of the method of controlling the magnitude | size of a welding current. 2 shows a second embodiment of the present invention, in which seam welding is performed with a starting current from the welding start position to the first intermediate position, and seam welding is performed with an intermediate current from the first intermediate position to the second intermediate position. FIG. 5 is a diagram conceptually illustrating an example of a state of welding when seam welding is performed with the current. It is a figure which shows the 2nd Embodiment of this invention and shows the 1st example of the relationship between this electric current, start current, intermediate current, start current / main current, and defect occurrence rate. It is a figure which shows the 2nd Embodiment of this invention and shows the 2nd example of the relationship between this electric current, starting current, intermediate current, starting current / main current, and defect occurrence rate. It is a figure which shows the 2nd Embodiment of this invention and shows the 3rd example of the relationship between this electric current, start current, intermediate current, start current / main current, and defect occurrence rate. It is a figure which shows the 3rd Embodiment of this invention and demonstrates an example of the method of controlling the magnitude | size of a welding current. In the third embodiment of the present invention, seam welding is performed with a starting current at a welding start position, and seam welding is performed while increasing the welding current linearly so as to be the current at an intermediate position, and thereafter with this current. It is a figure which shows notionally an example of the mode of the welding state when performing seam welding. It is a figure which shows the 3rd Embodiment of this invention and shows the 1st example of the relationship between this electric current, start current, intermediate current, start current / main current, and defect occurrence rate. It is a figure which shows the 3rd Embodiment of this invention and shows the 2nd example of the relationship between this electric current, starting current, intermediate current, starting current / main current, and a defect incidence. It is a figure which shows the 3rd Embodiment of this invention and shows the 3rd example of the relationship between this electric current, start current, intermediate current, start current / main current, and defect occurrence rate.

(Elucidation of welding mechanism)
When seam welding is performed with a constant steady current from the welding start position to the welding end position, the inventors have performed a pit or a pit in an area where welding is performed between the welding start position and the welding end position. We investigated the mechanism of weld defects such as holes. As a result, the present inventors obtained the following knowledge.
FIG. 1 is a diagram conceptually illustrating an example of a welding state when seam welding is performed with a constant steady current from a welding start position to a welding end position. Specifically, FIG. 1A shows an example of a welding state from when seam welding is started at the welding start position to when the welding position returns to the welding start position. Moreover, FIG.1 (b) shows an example of a welding state when a welding position returns to a welding start position. FIG. 1 shows a cross section in which the flange portion of the fuel tank is cut in the plate thickness direction along the direction of travel of the disc electrode (the direction of the arrow from the left to the right in the drawing). In each figure, only the portions necessary for explanation are shown in a simplified manner.

  In seam welding, an overlapping portion of metal plates 11 and 12 such as a steel plate having a plating treatment applied thereto is pressurized and energized by a rotating disk electrode 13. When the metal plates 11 and 12 are energized in this way, the metal plates 11 and 12 are heated and softened by resistance heat generation. For this reason, when the disk electrode 13 pressurizes the metal plate 11, the surface of the metal plate 11 is recessed. The nugget 14a already formed by seam welding has a smaller electric resistance than the region where no nugget is formed. Therefore, as shown in FIG. 1A, a part of the planned welding current Ia flows toward the nugget 14a as an invalid shunt, and welding is performed with the remaining welding current Ib (new nugget). Will be formed). In this case, since the metal plate 11 is energized and heated while maintaining a constant contact length with the disk electrode 13, constant welding is performed.

  On the other hand, as shown in FIG. 1B, when the welding position (disc electrode 13) returns to the welding start position, the welding current Ia as the ineffective diversion mentioned above hardly flows and is planned. Most of the welding current contributes to welding as the welding current Ib. That is, a recess having a depth of ΔL is formed in the metal plate 11 by a recess generated when welding is started at the welding start position. For this reason, compared with the state shown to Fig.1 (a), the contact length of the disc electrode 13 and the metal plate 11 becomes short, and the current density of the electric current which flows into the metal plate 11 becomes large. In particular, a spark is generated in the vicinity of the contact end point 15 between the welding start position (position where the depression starts) and the disc electrode 13, and the vicinity of the contact end point 15 generates heat intensively. For this reason, compared with the state shown to Fig.1 (a), the emitted-heat amount of the contact area of the disc electrode 13 and the metal plate 11 becomes large, and becomes high temperature. Further, in the vicinity of the contact end point 15 between the welding start position and the disk electrode 13, since the surface of the metal plate 11 is in a molten state, so-called scattering is ejected. Further, when the disc electrode 13 passes through the contact end point 15 that is at a high temperature, the molten metal adheres to the disc electrode 13. The present inventors have obtained the knowledge that, due to the above factors, welding defects such as pits and holes are generated in a region where welding is performed in an overlapping manner between the welding start position and the welding end position. The same applies to the metal plate 12.

  The following embodiment of the present invention has been made on the basis of such knowledge that the present inventors have elucidated for the first time. That is, the inventors of the present invention have a weld defect such as a pit or a hole in a region where welding is performed between the welding start position and the welding end position when welding is started at the welding start position. It was found that the formation of dents was a factor. Based on this knowledge, the present inventors have come up with the idea that the amount of heat generated in the vicinity of the contact end point 15 between the welding start position and the disc electrode 13 can be reduced by reducing the depth of the recess. Hereinafter, embodiments of the present invention will be described.

(First embodiment)
First, a first embodiment of the present invention will be described.
[System configuration]
FIG. 2 is a diagram illustrating an example of a schematic configuration of the seam welding system.
In FIG. 2, the seam welding system 100 includes a seam welding device 110, a welding transformer 120, an inverter circuit 130, an inverter control device 140, and a seam welding control device 150.
The seam welding device 110 includes a multi-axis robot 111, a fuel tank gripping mechanism 112, a rotation drive device 113, a rotation angle detector 114, disk electrodes 115a and 115b, and electrode drive devices 116a and 116b. is doing.

A fuel tank gripping mechanism 112 is attached to the tip of the arm 111 a of the multi-axis robot 111. The multi-axis robot 111 operates the fuel tank gripping mechanism 112 according to the control by the seam welding control device 150. The multi-axis robot 111 detects the position of the fuel tank gripping mechanism 112.
The fuel tank gripping mechanism 112 has a C-shaped frame 112a and rotating shafts 112b and 112c. Rotating shafts 112b and 112c are rotatably attached to the C-shaped frame 112a so as to sandwich the upper member 201 and the lower member 202 of the fuel tank 200 to be seam welded from above and below. The rotation shafts 112b and 112c support the upper surface of the upper member 201 and the lower surface of the lower member 202, and the upper member 201 and the lower member 202 can rotate about the Y axis as a rotation axis. The rotation drive device 113 is for rotating the rotation shafts 112b and 112c in accordance with the control by the seam welding control device 150. The rotation angle detector 114 is for detecting the rotation angle of the upper member 201 and the lower member 202 accompanying rotation of the rotating shafts 112b and 112c.

FIG. 3 is a diagram showing a positional relationship between the fuel tank 200 (upper member 201 and lower member 202) and the disk electrodes 115a and 115b.
The disk electrodes 115a and 115b are rotatably attached to the arms of the electrode driving devices 116a and 116b, respectively. The electrode driving devices 116a and 116b rotate and drive the disk electrodes 115a and 115b with the X1 axis and the X2 axis as the rotation axes, respectively, according to the control by the seam welding control device 150.
In the example shown in FIGS. 2 and 3, the flange 203 a formed along the lower outer peripheral end of the upper member 201 of the fuel tank 200 and the flange 203 b formed along the upper outer peripheral end of the lower member 202 are overlapped. The combined flange 203 is pressed and energized by the disk electrodes 115a and 115b from above and below. Further, the rotation of the fuel tank 200 by the rotation driving device 113 described above causes the flange 203 to be fed into the disk electrodes 115a and 115b along the circumferential direction of the upper member 201 and the lower member 202.

  Here, in this embodiment, the fuel tank 200 (the upper member 201 and the lower member 202) includes an aluminum plated steel plate, a Sn—Zn plated steel plate, a Zn plated steel plate, It is formed using any one of a Pb—Sn plated steel plate, a Zn—Al—Mg plated steel plate, and a Zn—Al—Mg—Si plated steel plate. Incidentally, these plated steel sheets are disclosed in, for example, JP-A-10-137681, JP-A-10-272582, JP-A-2001-279470, JP-A-2002-29271, JP-A-2004-360019, As described in JP-A-2005-336574, JP-A-2008-254053, and the like, it can be realized by a known technique, and thus detailed description thereof is omitted here.

  The inverter control device 140 controls a welding current and the like for seam welding the upper member 201 and the lower member 202. The inverter circuit 130 is configured using a semiconductor switching element such as an IGBT (Insulated Gate Bipolar Transistor). The inverter control device 140 controls the welding current by controlling the on / off timing of the semiconductor switching element in the inverter circuit 130. The current output from the inverter circuit 130 is converted into a welding current by the welding transformer 120 and supplied to the disk electrodes 115a and 115b.

  The seam welding control device 150 performs overall control of the entire seam welding system 100. Specifically, the seam welding control device 150 includes pressure applied by the disk electrodes 115a and 115b, rotation operation of the disk electrodes 115a and 115b, operation of the multi-axis robot 111, and a fuel tank (upper member) by the rotation drive device 113. 201 and the lower member 202), the magnitude of the welding current, and the like are controlled. In particular, in the present embodiment, the seam welding control device 150 controls the magnitude of the welding current according to the welding positions of the upper member 201 and the lower member 202. Therefore, the seam welding control device 150 needs to recognize the current welding positions of the upper member 201 and the lower member 202.

In the present embodiment, the seam welding control device 150 stores in advance information on the circumferential lengths of the flanges 203a and 201b of the upper member 201 and the lower member 202 to be welded and information on the welding start position. Yes. And the seam welding control apparatus 150 performs control for seam welding according to a predetermined schedule. For example, the seam welding control device 150 can recognize the current welding positions of the upper member 201 and the lower member 202 based on the elapsed time since the start of seam welding. However, such a method is not necessarily adopted as long as the current welding positions of the upper member 201 and the lower member 202 can be recognized. For example, the information stored in advance, the information on the rotation angles of the upper member 201 and the lower member 202 detected by the rotation angle detector 114, and the fuel tank gripping mechanism 112 detected by the multi-axis robot 111. Based on the position information, the current welding positions of the upper member 201 and the lower member 202 can be recognized.
In addition, the seam welding control apparatus 150 is realizable by using the computer provided with CPU, ROM, RAM, HDD, and various interfaces, for example.

[Overview of welding current control]
FIG. 4 is a diagram for explaining an example of a method for controlling the magnitude of the welding current. Specifically, FIG. 4A is a diagram conceptually illustrating an example of a welding path viewed from the flange 203a side of the upper member 201. FIG. As shown in FIG. 4A, here, it is assumed that seam welding is continuously performed counterclockwise toward the figure. FIG. 4B is a diagram showing the relationship between the welding current at the start of welding and the energization position, and FIG. 4C is a diagram showing the relationship between the welding current at the end of welding and the energization position. is there. In the following description, the magnitude of the current is an effective value (see FIG. 8 and the like).

In the present embodiment, as shown in FIG. 4 (b), when starting the seam welding, from welding start position S to the intermediate position C, and seam welding in starting current I _s having a size of less than the current I _o Do. Although the distance from the welding start position S to the intermediate position C depends on the length of the diameter of the disc electrode 115, it is, for example, 10 [mm] to 20 [mm]. The details about the current I _o and starting current I _s to be described later.
As shown in FIGS. 4B and 4C, the magnitude of the welding current is changed from the starting current I _s to the main current I _o at the intermediate position C, and then the magnitude of the welding current is The magnitude of the current I _o is maintained. Then, when seam welding is performed along the flanges 203a and 203b of the upper member 201 and the lower member 202 and the welding position returns to the welding start position S, seam welding is performed to the welding end position E ahead of the intermediate position C. To finish seam welding. The distance from the welding start position S to the welding end position E (in a region where welding is performed in an overlapping manner) is to ensure the sealing performance of the fuel tank 200 (stable fuel tank 200 with the sealing performance secured). For mass production, for example, it is desirable to set it to 30 [mm] or more. Moreover, when the area | region which overlaps and welds is too long, there exists a possibility that the molten metal may adhere to the disc electrode 13. FIG. Moreover, when the area | region which overlaps and welds is too long, the distance of the full length of welding will increase, welding time will become excessive, and there exists a possibility that production efficiency may fall. Therefore, the distance from the welding start position S to the welding end position E is more preferably, for example, 30 [mm] to 50 [mm].

5, the welding start position S to the intermediate position C performs seam welding in starting current I _s, schematically illustrates an example of a subsequently state of welding conditions when performing seam welding in this current I _o It is. Specifically, FIG. 5 shows an example of a welding state when the welding position returns to the welding start position. 5 shows a cross section in which the flange 203 is cut in the plate thickness direction along the traveling direction of the disc electrode 115 (the direction of the arrow from the left to the right in the drawing).
As described above, from the welding start position S to the intermediate position C, performing seam welding in starting current I _s having a size of less than the current I _o. As described later, in the present embodiment, the magnitude of the starting current I _s because it below 0.7 times 0.5 times the size of the current I _o, at the start welding, the welding start position S No nugget is formed in the region up to the intermediate position C (even if formed, it becomes an incomplete nugget). Thereafter, when the welding position reaches the intermediate position C, the welding current is changed to the main current I _o , so that the nugget 502 is formed in a region ahead of the intermediate position C.

Further, since the magnitude of the welding current is small from the welding start position S to the intermediate position C at the start of welding, the depth ΔL1 of the recess generated at the start of welding is compared with the depth ΔL of the recess shown in FIG. Become smaller. Thereafter, when the welding position reaches the intermediate position C, the magnitude of the welding current is set to the main current I _o , so that the depression (depth ΔL2) is deeper than the depression formed from the welding start position S to the intermediate position C. ) Is formed. Thus, since the magnitude of the welding current is finally the magnitude of the main current I _o , the sum of the depths of these two depressions (= ΔL1 + ΔL2) is the depth of the depression shown in FIG. It becomes substantially equal to ΔL. Thus, in the present embodiment, the surface of the flange 203 is recessed stepwise at the start of welding.

  When two depressions are formed as described above and the welding position returns to the welding start position S, the gap between the disc electrode 115a and the flange 203a is narrower than that shown in FIG. To. Therefore, when the welding position returns to the welding start position S, it is possible to suppress a spark generated in the vicinity of the contact end point 501 between the welding start position S (position where the depression starts) and the disc electrode 115a. It is possible to suppress the vicinity from generating heat intensively. Thereby, it can suppress that the flange 203a will be in a molten state to the surface, and can suppress that what is called a scattering spout and adhesion of the molten metal to the disc electrode 115a.

When the welding position returns to the welding start position S, the seam welding is performed with the current _Io , and the seam welding is finished at a position ahead of the intermediate position C. Therefore, a nugget (not shown) is formed so as to be connected to both the nugget 503 formed before the welding start position S and the nugget 502 formed in a region ahead of the intermediate position C. Thereby, it can prevent that a nugget becomes discontinuous in the circumferential direction of the flange 203a.

[Current]
FIG. 6 is a diagram illustrating an example of the relationship between the nugget width and the welding current. FIG. 7 is a diagram for explaining the nugget width. Specifically, FIG. 7 shows a cross section of the flange 203a of the upper member 201 and the flange 203b of the lower member 202 cut from the plate thickness direction. As shown in FIG. 7, the nugget width W is the length of the nugget in a direction perpendicular to the advancing direction of seam welding among the directions parallel to the plate surfaces of the two metal plates to be welded.
FIG. 6 shows the results of the test conducted under the following conditions. The white circle indicates that no welding defect occurred, and the black circle indicates that a welding defect (scattering) occurred. It shows that.
<Welding conditions>
Diameter of disk electrode: 250 [mm]
Disc electrode tip width; 3.0 [mm] (wire seam)
Pressure applied by disk electrode; 6.37 [kN]
Welding speed: 6.0 [m / min]
Welding power source: Inverter type DC energization method: Continuous energization
Stacked two aluminum-plated steel plates (plating amount: 40 [g / m ² ] on both sides, thickness 0.8 [mm] before plating) <Test method>
A welding current corresponding to the plot shown in FIG. 6 is applied to the <test material>, and the <test material> is continuously seam welded according to the <welding conditions>. However, here, there is no overlap between the welding start position and the welding end position.

In the present embodiment, a nugget having a nugget width W that is twice the plate thickness at the time of non-surface treatment (non-plating treatment) of one metal plate to be welded is set as the lower limit of the magnitude of the current I _o. Let the magnitude of the welding current to be obtained. On the other hand, the upper limit value of the range of the current I _o is set to 0.95 times the lower limit welding current at which a welding defect occurs in a region where welding is not performed repeatedly.
In the example shown in FIG. 6, the thickness of the aluminum-plated steel plate before plating is 0.8 [mm]. Therefore, the welding current for obtaining a nugget with a nugget width W of 1.6 [mm] is 17 [KA]. Therefore, the lower limit of the magnitude of the current I _o is 17 [kA]. By setting the lower limit value of the magnitude of the current I _o in this way, a nugget having an appropriate magnitude can be obtained. On the other hand, the value of the upper limit welding current at which a welding defect occurs is 21.3 [kA]. Therefore, the upper limit value of the magnitude of the current I _o is 20.3 [kA] (with a margin). By setting the upper limit value of the magnitude of the current I _o in this manner, it is possible to prevent welding defects (scattering) from occurring in a region where welding is not performed repeatedly.

[Starting current]
Figure 8 is a diagram showing the present current I _o, the starting current I _s, a starting current / present current, an example of the relationship between the defect rate.
FIG. 8 shows the results of testing under the following conditions. Here, the defect occurrence rate is obtained as follows. First, under the following conditions, by flowing the current I _o and starting current I _s shown in FIG. 8 to the test material performing 15-20 tests. And it is confirmed in each test whether the welding defect generate | occur | produced in the area | region where the welding between the welding start position S and the welding end position E is overlapped. Then, the number of occurrences of weld defects in all tests is counted, and the number of occurrences of weld defects counted is divided by the number of tests to obtain the percentage of defect occurrence.
<Welding conditions>
Diameter of disk electrode: 250 [mm]
Disc electrode tip width; 3.0 [mm] (wire seam)
Pressure applied by disk electrode; 6.37 [kN]
Welding speed: 6.0 [m / min]
Welding power source: Inverter type DC energization method: Continuous energization

<Test material>
Stacked two aluminum-plated steel plates (plating amount: 40 [g / m ² ] on both sides, thickness 0.8 [mm] before plating) <Test method>
From the welding start position S, and the position apart 10 [mm] in the direction to perform the seam welding an intermediate position C, passing a starting current I _s shown in FIG. 8 from the welding start position S to the intermediate position C to the test material seam Weld. Then, to change the welding current from the starting current I _s to the current I _o, from the intermediate position C to a welding end position E, perform seam welding by flowing the current I _o to the test material. Here, as shown in FIG. 4, after returning from the welding start position S to the welding start position S via the intermediate position C, seam welding is performed on the area where seam welding has already been performed, and the intermediate position C is set. The seam welding is terminated at the welding end position E. Further, the flow rate in the direction in which the seam welding is performed in the region where the welding is performed repeatedly is set to 30 [mm].

As shown in FIG. 8, the magnitude of the starting current I _s is the current I _o of the magnitude of 0.5 times or more, if it is 0.7 times or less, the welding end position E and the welding start position S It can be seen that no weld defect occurs in the region where the welding is performed in the middle. Therefore, in this embodiment, the magnitude of the welding current is determined so as to satisfy the following expression (1).
I _o × 0.5 ≦ I _s ≦ I _o × 0.7 (1)

[Control method]
Seam welding controller 150, when starting the seam welding, according to the schedule stored in advance, to indicate that flow starting current I _s to the inverter control device 140. Thereafter, when the seam welding control device 150 determines that the current welding position first reaches the intermediate position C based on the elapsed time from the start of welding, the inverter control device 140 indicates that the current _Io is allowed to flow. To instruct. As size information of the starting current I _s and the current I _o, information satisfies current value described above is previously stored in a storage medium such as an HDD provided in the seam welding control apparatus 150. In addition, information on the welding start position S, the intermediate position C, and the welding end position E is also stored in advance in a storage medium such as an HDD provided in the seam welding control device 150.

[Summary]
As described above, in the present embodiment, the flange 203a formed along the lower outer peripheral end of the upper member 201 of the fuel tank 200 and the flange 203b formed along the upper outer peripheral end of the lower member 202 are mutually connected. The overlapped flange 203 is subjected to seam welding along the circumferential direction of the flange 203 by pressing and energizing the overlapped flange 203 from above and below by the disk electrodes 115a and 115b. At this time, seam welding is started from the welding start position S, and after returning to the welding start position S via the intermediate position C, seam welding is performed on the area where seam welding has already been performed, and the intermediate position C is passed. Then, the seam welding is ended at the welding end position E. From welding start position S to the intermediate position C, subjected to seam welding in starting current I _s of the current I 0.5 times 0.7 times the size of the _o, from the intermediate position C to a welding end position E is Then, seam welding is performed with the current _Io . Accordingly, the depth of the step formed on the surfaces of the flanges 203a and 203b at the start of seam welding can be increased stepwise, and the deep step at the welding start position S can be prevented. As a result, when the welding position returns to the welding start position S, it is possible to suppress a spark generated in the vicinity of the contact end point 501 between the welding start position S (position where the depression starts) and the disc electrode 115a. Concentrated heat generation near 501 can be suppressed. Therefore, the flange 203 can be prevented from being melted to the surface, so-called scattering can be ejected, and the molten metal can be prevented from adhering to the disk electrode 115. From the above, it is possible to stabilize the welding quality in the region where the welding is performed repeatedly between the welding start position and the welding end position.
In the present embodiment, the start current I _s corresponds to the first welding current, the current I _o corresponds to the second welding current.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. In the first embodiment described above, after starting the seam welding, a case was described in which change once the welding current from the starting current I _s to the current I _o. On the other hand, this embodiment demonstrates the case where the frequency | count of change of welding current is set to 2 times. As described above, the number of times of changing the welding current is mainly different between the present embodiment and the first embodiment described above. Therefore, in the description of the present embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals as those in FIGS.

[Overview of welding current control]
FIG. 9 is a diagram illustrating an example of a method for controlling the magnitude of the welding current. Specifically, FIG. 9A is a diagram conceptually illustrating an example of a welding path viewed from the flange 203a side of the upper member 201. FIG. FIG. 9B is a diagram showing the relationship between the welding current at the start of welding and the energization position, and FIG. 9C is a diagram showing the relationship between the welding current at the end of welding and the energization position. is there.
In the present embodiment, as shown in FIG. 9B, when seam welding is started, the start current I _s having a magnitude less than the main current I _o from the welding start position S to the first intermediate position C1. Perform seam welding. Then, from the first intermediate position C1 to a second intermediate position C2, magnitude, but it exceeds the starting current I _s performing seam welding in the intermediate current I _c which is less than the current I _o. The distance from the welding start position S to the first intermediate position C1 depends on the length of the diameter of the disc electrode 115, and is, for example, 10 [mm] to 20 [mm]. However, the distance from the welding start position S to the first intermediate position C1 is preferably 10 [mm] or more in order to stably form the depression at the initial stage of the welding start. Further, the distance from the welding start position S to the first intermediate position C1, the ratio of the distance from the first intermediate position C1 to a second intermediate position C2, for example, the magnitude of the starting current I _s, the intermediate It can be proportional to the ratio of the current I _c or can be fixed in a one-to-one relationship.

As shown in FIGS. 9B and 9C, the welding current is changed from the intermediate current I _c to the main current I _o at the second intermediate position C2, and then the magnitude of the welding current is The magnitude of the current I _o is maintained. Then, when seam welding is performed along the flanges 203a and 203b of the upper member 201 and the lower member 202 and the welding position returns to the welding start position S, the seam is reached to the welding end position E ahead of the second intermediate position C2. Perform welding and finish seam welding. As described in the first embodiment, for example, the distance from the welding start position S to the welding end position E is preferably 30 [mm] or more, and is 30 [mm] to 50 [mm]. Is more preferable.

10, from the welding start position S to the first intermediate position C1 performs seam welding in starting current I _s, a seam welding in the intermediate current I _c from the first intermediate position C1 to a second intermediate position C2 performed, then is a diagram conceptually illustrating an example of a state of the welding conditions when performing seam welding in this current I _o. Specifically, FIG. 10 shows an example of a welding state when the welding position returns to the welding start position. 10 shows a cross section in which the flange 203 is cut in the plate thickness direction along the traveling direction of the disc electrode 115 (the direction of the arrow from the left to the right in the drawing).
As described above, from the welding start position S to the first intermediate position C1, performing seam welding in starting current I _s having a size of less than the current I _o. As described later, in the present embodiment, the magnitude of the starting current I _s because it below 0.7 times 0.5 times the size of the current I _o, at the start welding, the welding start position S Nuggets are not formed in the region up to the first intermediate position C1 (even if formed, it becomes an incomplete nugget). Thereafter, when the first intermediate position C1 circularly plate electrode 115a is reached to change the welding current to an intermediate current I _c. Since the magnitude of the intermediate current I _c exceeds the start current I _s but is less than the main current I _o , the nugget 1001 is formed in the region between the first intermediate position C1 and the second intermediate position C2. (However, depending on the magnitude of the intermediate current I _c , a nugget may not be formed in this region). Thereafter, when the disc electrode 115a reaches the second intermediate position C2, the welding current is changed to the main current _Io , so that the nugget 1001 is (continuously) formed in the region beyond the second intermediate position C2. The

  At the start of welding, the magnitude of the welding current is increased stepwise at two locations, the first intermediate position C1 and the second intermediate position C2, so that a step is formed at three locations and three depressions are formed. Is formed. Further, the depth ΔL3 of the first depression and the depth ΔL4 of the second depression are both shallower than the depth ΔL1 of the depression shown in FIG. Further, the sum of the depths of the three recesses (= ΔL3 + ΔL4 + ΔL5) is substantially equal to the sum of the depths of the two recesses shown in FIG. 5 (= ΔL1 + ΔL2). Therefore, the level difference formed by each depression shown in FIG. 10 is smaller than the level difference formed by the depression shown in FIG.

  As described above, in this embodiment, when the three recesses are formed and the welding position returns to the welding start position S, the gap between the disk electrode 115a and the flange 203a is shown in FIG. Try to be narrower than things. Therefore, when the welding position returns to the welding start position S, the spark generated near the contact end point 1002 between the welding start position S (position where the depression starts) and the disc electrode 115a can be further suppressed. Concentrated heat generation near the end point 1002 can be further suppressed. Thereby, it can suppress further that the flange 203a will be in a molten state to the surface, and can further suppress that what is called scattering spouts and adhesion of the molten metal to the disc electrode 115a. .

When the welding position returns to the welding start position S, the seam welding is performed with the current _Io , and the seam welding is finished at a position ahead of the second intermediate position C2. Therefore, both the nugget 1003 formed before the welding start position S and the nugget 1001 formed in the area ahead of the first intermediate position C1 (or the second intermediate position C2) are connected. In addition, a nugget (not shown) is formed. Thereby, it can prevent that a nugget becomes discontinuous in the circumferential direction of the flange 203a.

[Starting current, intermediate current]
11 to 13, and the current I _o, a diagram illustrating the starting current I _s, the intermediate current I _c, and a starting current / present current, an example of the relationship between the defect rate. The current _Io is as described in the first embodiment.
11 to 13 show the results of tests performed under the following conditions.
<Welding conditions>
Diameter of disk electrode: 250 [mm]
Disc electrode tip width; 3.0 [mm] (wire seam)
Pressure applied by disk electrode; 6.37 [kN]
Welding speed: 6.0 [m / min]
Welding power source: Inverter type DC energization method: Continuous energization

<Test material>
Stacked two aluminum-plated steel plates (plating amount: 40 [g / m ² ] on both sides, thickness 0.8 [mm] before plating) <Test method>
A position that is 10 mm away from the welding start position S in the direction in which seam welding is performed is defined as a first intermediate position C1, and the start current shown in FIGS. 11 to 13 from the welding start position S to the first intermediate position C1. performing seam welding by flowing a I _s to the test material. Then, the starting current I _s, to change the intermediate current I _c to the welding current shown in FIGS. 11 to 13, from the first intermediate position C1 to a second intermediate position C2, the intermediate current I _c to the test material Flow and perform seam welding. Here, a position separated by 6 [mm] from the first intermediate position C1 in the direction in which seam welding is performed is defined as a second intermediate position C2. Then, the welding current was changed from the intermediate current I _c to the main current I _o , and from the second intermediate position C2 to the welding end position E, the main current I _o was passed through the test material to perform seam welding. Here, as shown in FIG. 9, after returning from the welding start position S to the welding start position S via the first and second intermediate positions C <b> 1 and C <b> 2, the seam is overlapped on the area where seam welding has already been performed. Welding is performed, and the seam welding is terminated at the welding end position E through the first and second intermediate positions C1 and C2. Further, the flow rate in the direction in which the seam welding is performed in the region where the welding is performed repeatedly is set to 30 [mm].

As shown in FIGS. 11 to 13, start the magnitude of the current I _s it is 0.5 times or more the size of the current I _o, When it is 0.7 times or less, the welding end position and the welding start position S It can be seen that no welding defect occurs in the area between E and the area where welding is performed in an overlapping manner. Therefore, in this embodiment as well, as in the first embodiment, the magnitude of the welding current is determined so as to satisfy the above-described equation (1).

[Control method]
Seam welding controller 150, when starting the seam welding, according to the schedule stored in advance, to indicate that flow starting current I _s to the inverter control device 140. After that, when the current welding position first reaches the first intermediate position C1 based on the elapsed time from the start of welding, the seam welding control device 150 performs the intermediate current I _c according to the contents stored in advance. Is sent to the inverter control device 140. Thereafter, when the seam welding control device 150 determines that the current welding position first reaches the second intermediate position C2 based on the elapsed time from the start of welding, the seam welding control device 150 determines that the current _Io is allowed to flow. The controller 140 is instructed. As information on the magnitudes of the start current I _s , the intermediate current I _c , and the main current I _o , current value information that satisfies the above-described conditions is stored in advance in a storage medium such as an HDD provided in the seam welding control device 150. Yes. In addition, information on the welding start position S, the first intermediate position C1, the second intermediate position C2, and the welding end position E is also stored in advance in a storage medium such as an HDD provided in the seam welding control device 150.

[Summary]
The above in this embodiment, as described, from the welding start position S to the first intermediate position C1, seam welding in starting current I _s of 0.5 times to 0.7 times the magnitude of the current I _o From the first intermediate position C1 to the second intermediate position C2, seam welding is performed with an intermediate current I _c that exceeds the start current I _s and less than the main current I _o , and the second intermediate position C2 From seam to welding end position E, seam welding is performed with this current _Io . Therefore, the depth of the step formed on the surfaces of the flanges 203a and 203b at the start of seam welding can be divided into more stages and deepened step by step, and the deep step at the welding start position S is more reliably generated. Can be prevented. Therefore, it is possible to further stabilize the welding quality in the region where the welding is performed repeatedly between the welding start position and the welding end position.
In addition, the frequency | count of changing a welding current is not limited to 2 times, You may be 3 times or more. Further, in the present embodiment, the start current I _s and the intermediate current I _c corresponds to the first welding current, the current I _o corresponds to the second welding current.

(Third embodiment)
Next, a third embodiment of the present invention will be described. In the first embodiment described above, the case where the magnitude of the welding current is increased stepwise (stepwise) has been described. On the other hand, this embodiment demonstrates the case where the magnitude | size of a welding current is made to raise continuously (linearly). Therefore, in the description of this embodiment, the same parts as those in the first and second embodiments are denoted by the same reference numerals as those in FIGS.

[Overview of welding current control]
FIG. 14 is a diagram illustrating an example of a method for controlling the magnitude of the welding current. Specifically, FIG. 14A is a diagram conceptually illustrating an example of a welding path viewed from the flange 203a side of the upper member 201. FIG. FIG. 14B is a diagram showing the relationship between the welding current at the start of welding and the energization position, and FIG. 14C is a diagram showing the relationship between the welding current at the end of welding and the energization position. is there.
In the present embodiment, as shown in FIG. 14 (b), when starting the seam welding, from welding start position S to the intermediate position C, so that the welding current is present current I _o at the intermediate position C, starting current perform seam welding while gradually increasing the welding current linearly from I _s, then performs seam welding in the current I _o. Although the distance from the welding start position S to the intermediate position C depends on the length of the diameter of the disc electrode 115, it is, for example, 10 [mm] to 20 [mm].
As shown in FIGS. 14B and 14C, the magnitude of the welding current is that the main current _Io flows at the intermediate position C, and then the magnitude of the welding current is the magnitude of the main current _Io . Maintained. Then, seam welding is performed along the flanges 203a and 203b of the upper member 201 and the lower member 202, and when the welding position returns to the welding start position S, the seam welding is performed to the welding end position E ahead of the intermediate position C. Finish seam welding. As described in the first embodiment, for example, the distance from the welding start position S to the welding end position E is preferably 30 [mm] or more, and is 30 [mm] to 50 [mm]. Is more preferable.

FIG. 15 shows a case in which seam welding is performed at the welding start position at the starting current, seam welding is performed while increasing the welding current linearly so as to become the current at the intermediate position, and then seam welding is performed at the current. It is a figure which shows notionally an example of the mode of a welding state. Specifically, FIG. 15 shows an example of a welding state when the welding position returns to the welding start position. FIG. 15 shows a cross section in which the flange 203 is cut in the plate thickness direction along the traveling direction of the disc electrode 115 (the direction of the arrow from the left to the right in the drawing).
As described above, from the welding start position S to the intermediate position C, and seam welding begins at starting current I _s having a size of less than the current I _o, the magnitude of the welding current from the starting current I _s to the linear Seam welding is performed up to the intermediate position C while increasing. As described later, in the present embodiment, the magnitude of the starting current I _s because it below 0.7 times 0.5 times the size of the current I _o, at the start welding, the welding start position S No nugget is formed in the region up to the intermediate position C (even if formed, it becomes an incomplete nugget). Thereafter, when the disc electrode 115a reaches the intermediate position C, the welding current becomes the main current _Io . Accordingly, the nugget 1501 is formed at least in a region ahead of the intermediate position C.

Moreover, since the magnitude | size of welding current is small from the welding start position S to the intermediate position C, the hollow which has a gentler gradient than the hollow shown in FIG. 1 is formed. Finally, since the magnitude of the welding current is the magnitude of the current I _o , the final depth ΔL6 of the recess is substantially equal to the depth ΔL of the recess shown in FIG. Thus, in the present embodiment, at the start of welding, the surface of the flange 203 is depressed more gently than when the current _Io is first applied.

  As described above, in the present embodiment, a gentler depression than that shown in FIG. 1 is formed, and when the welding position returns to the welding start position S, the gap between the disk electrode 115a and the flange 203a. The gap is made narrower than that shown in FIG. Therefore, when the welding position returns to the welding start position S, it is possible to suppress a spark generated in the vicinity of the contact end point 1502 between the welding start position S (position where the depression starts) and the disc electrode 115a. It is possible to suppress the vicinity from generating heat intensively. Thereby, it can suppress further that the flange 203a will be in a molten state to the surface, and can suppress what is called a scatter and the fusion | melting metal adhering to the disc electrode 115a.

When the welding position returns to the welding start position S, the seam welding is performed with the current _Io , and the seam welding is finished at a position ahead of the intermediate position C. Therefore, a nugget (not shown) is formed so as to be connected to both the nugget 1503 formed in front of the welding start position S and the nugget 1501 formed in a region ahead of the intermediate position C. Thereby, it can prevent that a nugget becomes discontinuous in the circumferential direction of the flange 203a.

[Starting current, intermediate current]
16 to 18, and the current I _o, a diagram illustrating the starting current I _s, the intermediate current I _c, and a starting current / present current, an example of the relationship between the defect rate. The current _Io is as described in the first embodiment.
In FIGS. 16-18, the result of having conducted the test on the following conditions is shown.
<Welding conditions>
Diameter of disk electrode: 250 [mm]
Disc electrode tip width; 3.0 [mm] (wire seam)
Pressure applied by disk electrode; 6.37 [kN]
Welding speed: 6.0 [m / min]
Welding power source: Inverter type DC energization method: Continuous energization

<Test material>
Stacked two aluminum-plated steel plates (plating amount: 40 [g / m ² ] on both sides, thickness 0.8 [mm] before plating) <Test method>
From the welding start position S, the position separated by 15 [mm] in the direction to perform the seam welding an intermediate position C, as the current I _o shown in FIGS. 16 to 18 in the intermediate position C flows, FIGS. 16 from the start current I _s shown in 18 linearly while increasing the magnitude of the welding current (linear with respect to time), and seam welding. From the intermediate position C to the welding end position E, seam welding was performed by flowing the current _Io through the test material. Here, as shown in FIG. 14, after returning from the welding start position S to the welding start position S via the intermediate position C, seam welding is performed on the area where seam welding has already been performed, and the intermediate position C is set. The seam welding is terminated at the welding end position E. Further, the flow rate in the direction in which the seam welding is performed in the region where the welding is performed repeatedly is set to 30 [mm].

As shown in FIGS. 16 to 18, start the magnitude of the current I _s it is 0.5 times or more the size of the current I _o, When it is 0.7 times or less, the welding end position and the welding start position S It can be seen that no welding defect occurs in the area between E and the area where welding is performed in an overlapping manner. Therefore, in this embodiment as well, as in the first embodiment, the magnitude of the welding current is determined so as to satisfy the above-described equation (1).

[Control method]
Seam welding controller 150, when starting the seam welding, according to the schedule stored in advance, passing a welding current magnitude of the starting current I _s at welding start position S, then the linear magnitude of the welding current The inverter controller 140 is instructed to cause the welding current having the magnitude of the current _{Io to} flow at the intermediate position C. Thereafter, when the seam welding control device 150 determines that the current welding position has reached the intermediate position C based on the elapsed time from the start of welding, the seam welding control device 150 instructs the inverter control device 140 to flow the current _Io. To do. As information on the magnitudes of the starting current I _s and the main current I _o , current value information that satisfies the above-described conditions is stored in advance in a storage medium such as an HDD provided in the seam welding control device 150. In addition, information on the welding start position S, the intermediate position C, and the welding end position E is also stored in advance in a storage medium such as an HDD provided in the seam welding control device 150.

[Summary]
As described above, in the present embodiment, as described, at welding start position S, flowing starting current I _s of 0.5 times to 0.7 times the magnitude of the current I _o, then the current I at an intermediate position C Seam welding is performed while linearly increasing the magnitude of the welding current so that a welding current of the magnitude _o flows, and seam welding is performed with the current I _o from the intermediate position C to the welding end position E. Therefore, the slope of the step generated on the surfaces of the flanges 203a and 203b at the start of seam welding can be smoothed, and a deep step at the welding start position S can be more reliably prevented. Therefore, it is possible to stabilize the welding quality in the region where the welding is performed repeatedly between the welding start position and the welding end position.
Even in the case of the second embodiment, the present embodiment can be applied. That is, when the seam welding is started, the start current I _s is from the welding start position S to the first intermediate position C1 so that the welding current becomes the intermediate current I _c at the first intermediate position C1. From the first intermediate position C1 to the second intermediate position C2, the magnitude of the welding current is the current current I _o at the second intermediate position C2. It is also possible to perform seam welding while linearly increasing the welding current from the intermediate current I _c so that the current current I _c becomes larger, and then perform seam welding with the current I _o . Further, the number of intermediate positions is not limited to 2, and may be 3 or more.

In the embodiment of the present invention described above, the process of the seam welding control device 150 for changing the welding current can be realized by a computer executing a program. Further, a means for supplying the program to the computer, for example, a computer-readable recording medium such as a CD-ROM recording such a program, or a transmission medium for transmitting such a program may be applied as an embodiment of the present invention. it can. A program product such as a computer-readable recording medium that records the program can also be applied as an embodiment of the present invention. The programs, computer-readable recording media, transmission media, and program products are included in the scope of the present invention.
In addition, the embodiments of the present invention described above are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. Is. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

DESCRIPTION OF SYMBOLS 100 Seam welding system 110 Seam welding apparatus 111 Multi-axis robot 112 Fuel tank holding mechanism 113 Rotation drive device 114 Rotation angle detector 115 Disc electrode 116 Electrode drive device 120 Welding transformer 130 Inverter circuit 140 Inverter control device 150 Seam welding control device 200 Fuel tank 201 Upper member 202 Lower member 203 Flange 501, 1002, 1502 Contact end point 502, 503, 1001, 1003, 1501, 1503 Nugget S Welding start position C Intermediate position C1 First intermediate position C2 Second intermediate position E Welding End position

Claims (4)

A flange formed along the lower outer peripheral edge of the upper member, which is a part of the metal fuel tank, and a flange formed along the upper outer peripheral edge of the lower member, which is a part of the fuel tank, When the seam welding is performed along the circumferential direction of the flange by applying pressure and electricity to the overlapped flange from above and below with the disc electrode, the seam welding is started from the welding start position. After the welding position returns to the welding start position via the intermediate position, seam welding is performed on the area where seam welding has already been performed, and after passing through the intermediate position, seam welding is performed at the welding end position. A seam welding method for a fuel tank,
From the welding start position to the intermediate position, seam welding is performed with a first welding current,
From the intermediate position to the welding end position, seam welding is performed with a second welding current having a magnitude exceeding the first welding current,
The method for seam welding a fuel tank, wherein the magnitude of the first welding current at the start is 0.5 to 0.7 times the magnitude of the second welding current. The lower limit value of the magnitude of the second welding current is the magnitude of the welding current at which a nugget having a nugget width that is twice the thickness of one metal plate constituting the flange at the time of non-surface treatment is obtained. And
The upper limit value of the magnitude of the second welding current is 0.95 times the magnitude of the lower limit welding current at which a welding defect occurs in the region where the welding is not performed in an overlapping manner. Item 2. A method for seam welding a fuel tank according to Item 1.   The magnitude of the first welding current is increased stepwise so that the magnitude of the welding current at the intermediate position becomes the magnitude of the second welding current. The method for seam welding of a fuel tank as described.   The magnitude of the first welding current is continuously increased linearly so that the magnitude of the welding current at the intermediate position becomes the magnitude of the second welding current. 3. A seam welding method for a fuel tank according to 2.

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