JP2016005845A - Resistance spot weld method and production method of weld joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resistance spot weld method capable of performing weld of plural weld points at short time and stably.SOLUTION: A resistance spot weld method of the invention is configured so that, when two or more steel plates are subjected to resistance spot weld, and when two points in which distance between weld points is equal to or less than 50 mm, difference between weld start times of one weld point and the other weld point is equal to or more than 10 ms, and the time is time until weld of one weld point is finished.

Description

  The present invention relates to a resistance spot welding method in which two or more steel plates are overlapped and a method for manufacturing a welded joint using the same.

  Resistance spot welding is widely used for the assembly of automobile bodies. One car body performs several thousand resistance spot weldings.

  FIG. 1 is a diagram illustrating an example of general resistance spot welding. In resistance spot welding, two or more steel plates are overlapped (steel plates 1 and 2 in FIG. 1), sandwiched between a pair of upper and lower welding electrodes 4 and 5, and energized while being pressed, thereby welding the steel plates. A nugget 6 having a predetermined size is formed at (welding point) to obtain a welded joint.

  In recent years, in order to achieve both weight reduction of the car body and safety of passengers, in addition to studying the use of high-tensile steel plate and high-rigidity car body structure, investigations to increase rigidity by increasing the number of spot welding points have been promoted. It has been.

  For example, Patent Literature 1 discloses a technique for spot welding a plurality of welding points simultaneously. In Patent Document 1, a plurality of oscillating shanks for attaching electrodes are installed at the tip of the main body of one welding machine, and welding is performed simultaneously at a plurality of welding points by energizing the electrodes while simultaneously pressing and contacting the plurality of electrodes. (Claim 1, [0035]).

  In Patent Document 2, a step of performing series spot welding with a plurality of resistance welders and a welding electrode of one resistance welder among the plurality of resistance welders is used as an indirect welding electrode. There is disclosed a resistance welding method including a step of performing indirect spot welding by using a welding electrode as a ground electrode by bringing the welding electrode into contact with a spot previously welded by series spot welding.

JP 2010-179318 A Japanese Patent No. 4836515

  In multi-point welding, the increase in the number of welding points shortens the distance between the welding points, causing a shunt phenomenon in which the current branches to a welding point where welding has already been performed (already welded point). As a result, there is a problem in that a predetermined nugget diameter cannot be secured without sufficient current flowing at a welding point where new welding is performed.

  In response to such a problem, the inventors examined the influencing factors of the diversion phenomenon to the already welded point. When there is an already welded point, when a current is applied in resistance spot welding, an electric circuit in parallel with the already welded point and the weld point to be newly welded is formed. The current value to be diverted to the already welded point is determined by the relationship between the route to the already welded point and the resistance value of the already welded point itself and the resistance value of the point at which new welding is performed. Therefore, it is considered that the diversion can be suppressed by increasing the resistance value of the welded point.

  It is widely known that when the temperature of a steel plate rises, the resistance value of the steel plate increases. If the temperature of the welded point can be raised, it is considered that the shunt phenomenon can be suppressed and the nugget can be stably formed.

  Even if it is a case where it welds simultaneously with respect to several welding points like patent document 1, by simultaneously increasing the temperature of several welding points and raising resistance value simultaneously, several welding points The influence by mutual shunting can be suppressed. However, in the initial energization, the contact resistance between the steel plates is large, and the nugget formation may become unstable.

  In addition, the welding machine disclosed in Patent Document 1 uses a specially shaped electrode (two-forked electrode), which makes it difficult to manage.

  In the cited document 2, a step of bringing the ground electrode into contact with the already-welded point is necessary, and there is a problem that the work man-hour increases and the work time becomes long.

  The present invention has been made for such a problem, and provides a resistance spot welding method capable of forming a nugget stably in a short time and a method of manufacturing a welded joint using the same. Objective.

  The inventors of the present invention have studied welding conditions at two adjacent welding points. As a result of the examination, the welding start time at the two adjacent welding points is set to be different to perform the welding so that the temperature of the preceding welding point is raised and the preceding welding point is welded. We thought that it would be possible to stably form a nugget at the preceding welding point and the subsequent welding point while suppressing the diversion to the welding point and minimizing the increase in welding time.

The gist of the present invention is as follows.
[1] When two or more steel plates are overlapped and two adjacent points are resistance spot welded, the difference between the welding start time of one welding point and the welding start time of the other is set to 10 ms or more, and two points are welded. Resistance spot welding method that overlaps the welding time of points.
[2] The resistance spot welding method according to [1], wherein a difference in welding end time at two points is 0 ms or more and not more than a difference in welding start time.
[3] In the resistance spot welding method according to [1] or [2], when there is an existing weld point, a weld point close to the existing weld point is welded first, and a weld point far from the existing weld point A resistance spot welding method to weld after.
[4] A method for manufacturing a welded joint using the resistance spot welding method according to any one of [1] to [3].

  According to the present invention, a nugget can be formed at a welding point in a short time and stably.

It is a figure which shows the example of general resistance spot welding. It is a figure which shows the example of the resistance spot welding which concerns on this invention. It is the figure which showed the mode of resistance spot welding in an Example. It is a figure which shows the welding conditions in an Example, and is a figure which shows the electric current value of preceding welding and subsequent welding. It is a figure which shows the welding conditions in an Example.

  Hereinafter, a resistance spot welding method according to an embodiment of the present invention and a method for manufacturing a welded joint using the same will be described with reference to the accompanying drawings.

  The present invention is a resistance spot welding method for joining two or more of a total of two or more steel plates including one or more high-tensile steel plates by resistance spot welding, and a method for manufacturing a welded joint using the same. FIG. 2 is a diagram showing an example of resistance spot welding according to the present invention.

  First, two steel plates are overlapped. A steel plate disposed on the lower side is referred to as a lower steel plate 1, and a steel plate disposed on the upper side is referred to as an upper steel plate 2.

  The superposed steel plates 1 and 2 are sandwiched between an electrode pair consisting of an upper electrode A and a lower electrode B and an electrode pair consisting of an upper electrode C and a lower electrode D, and are energized while being pressed. A time difference is provided for energization by the two electrode pairs. Specifically, energization of one electrode pair (electrodes A and B) is started prior to energization of the other electrode pair (electrodes C and D).

  In addition, the configuration for applying pressure using the electrodes A and B and the electrodes C and D and the configuration for controlling the applied pressure are not particularly limited, and a conventionally known device such as an air cylinder or a servo motor is used. Can do. The time for the electrodes A, B, C, and D to start welding does not matter. The configuration for supplying current when energizing and controlling the current value is not particularly limited, and conventionally known devices can be used. The current during energization may be direct current or alternating current.

  If the axes of electrodes A and B are P1 (corresponding to the welding center of the preceding welding point) and the axes of C and D are P2 (corresponding to the welding center of the following welding point), the axes P1 and P2 The distance L between is preferably 50 mm or less. If the distance L is larger than 50 mm, the effect of the diversion due to the presence of the first welding point is relatively small. However, the effect of the present invention can be obtained even when the distance L exceeds 50 mm. If L is set larger than the target nugget radius, the effect can be obtained. However, in consideration of mechanical constraints, it is desirable to set it to 5 mm or more in practice.

  The welding start time for the preceding electrodes A and B is set 10 ms or more earlier than the welding start time for the following electrodes C and D. If it is less than 10 ms, the heating at the first point is not sufficient and the effect of suppressing the diversion cannot be obtained. From the viewpoint of workability, it is more desirable to set the time difference between the welding start times within a range of 10 ms to 200 ms.

  The difference between the welding end time of one electrode pair (electrodes A and B) and the welding end time of the other electrode pair (electrodes C and D) is not less than 0 ms and not more than the difference in welding start time. Either the preceding welding time or the finishing time of the following welding may be first, but from the viewpoint of securing a sufficient welding time and obtaining a sufficient nugget diameter, welding is started later. It is preferable that the subsequent welding is finished after the preceding welding.

  When there is an existing weld point, it is preferable to weld the weld point close to the existing weld point first and then weld the weld point far from the existing weld point later. If the weld point to be welded after the welding is close to the weld point to be welded before, the weld point to be welded prior to the existing weld point when performing subsequent welding As a result, a sufficient nugget cannot be obtained. In addition, due to the shunting at the preceding welding, the heat generation at the existing welding point is reduced, and the effect of suppressing the shunting is reduced, so that a sufficient nugget diameter cannot be obtained at the subsequent welding point.

  In the present invention, the difference between the welding start time of one welding point and the welding start time of the other is set to 10 ms or more, and the other welding starts by the time when one welding is completed. That is, the welding time is overlapped. As a result, at the start of energization, the current is concentrated on the welding point that is energized in advance, and the resistance value of the welding point that is energized in advance is sufficiently increased so that the welding is energized later. At the time of spot welding, it is possible to reduce the current flowing to the welding spot that is energized in advance. Thereby, a welded joint in which the nugget diameter is sufficiently secured at two points can be manufactured.

  In addition, after the start of welding of the welding point that is energized in advance, the welding time of the welding point that is energized after the start is started from 10 ms to 200 ms, and the welding time is reduced by overlapping the welding time of the two points. It can be shortened.

  Furthermore, by making the difference between the welding end times of the two points not less than 0 ms and not more than the difference in the welding start time, when continuously welding the third and subsequent points, it is possible to suppress the apparatus restriction and efficiently Can be welded.

  In the above description, the case where welding is performed on two welding points has been described as an example, but the present invention can also be applied to the case where welding is performed on three or more welding points. In such a case, the effect of the present invention can be obtained if the difference between the welding start times at at least two points is within the above-specified range.

  As shown in FIG. 3, the lower steel plate 1 and the upper steel plate 2 were overlapped and resistance spot welding was performed. The nugget diameter d3 is 4 at a distance L1 in the direction opposite to the axis P2 of the electrodes C and D starting the welding from the axis P1 of the electrodes A and B starting the welding in advance. An already-welded point that is √t (t: plate thickness) was formed. The distance L1 is the distance between the axis P1 of the electrodes A and B that start welding in advance and the center P3 of the nugget diameter. The distance L2 is the distance between the axis P1 of the electrodes A and B and the axis P2 of the electrodes C and D.

  Electrodes A, B, C, and D were all DR-type electrodes made of alumina-dispersed copper with a tip diameter of 6 mm and a curvature radius of 40 mm.

  The pressure applied to the upper electrodes A and C was controlled by controlling a servo motor that drives the upper electrodes A and C. A single-phase alternating current with a frequency of 50 Hz was supplied during energization. The lower steel plate 1 and the upper steel plate 2 have the same thickness and the same steel type, and have a rectangular shape with a long side of 150 mm and a short side of 50 mm. As shown in FIG. 4, the current value in the preceding welding is Ia (kA), the energization time is Ta (ms), the current value in the subsequent welding is Ib (kA), and the energization time is Tb (ms). The difference between the welding start time of the preceding welding and the welding start time of the subsequent welding is T1 (ms). The welding end of the preceding welding is earlier than the welding end of the subsequent welding, and the difference between the welding end time of the preceding welding and the welding end time of the subsequent welding is Td (ms). Each setting condition is shown in Table 1.

比較例１は、先行溶接と後行溶接を一点一点別に溶接を行ったものであり、T1(ms)は200msより大きい。また、比較例２は、先行溶接と後行溶接を同時に行ったものであり、T1(ms)は0msである。

In Comparative Example 1, prior welding and subsequent welding are performed one by one, and T1 (ms) is larger than 200 ms. In Comparative Example 2, the preceding welding and the subsequent welding were performed simultaneously, and T1 (ms) was 0 ms.

  The weld cross section of the weld joint obtained under each setting condition was cut, and the nugget diameter d1 of the welded part of the preceding weld and the nugget diameter d2 of the welded part of the subsequent weld were compared with the reference diameter of 5.0 mm. The standard nugget diameter was a diameter of a welded portion where welding was performed under the welding conditions of the electrodes C and D in a state where no existing welding points were formed.

  The nugget diameter d1 of the welded part of the preceding weld and the nugget diameter d2 of the welded part of the subsequent weld have a reduction rate of 5% or less compared to the diameter of the reference welded part, or the reference welded part The case where it was larger than the nugget diameter was marked with ◯, and the case where it was not so was marked with ×. As a result, in the present invention example to which the present invention was applied, sufficient nugget formation was recognized as compared with the comparative example to which the present invention was not applied.

  As shown in FIG. 5, the lower steel plate 1 and the upper steel plate 2 were overlapped and resistance spot welding was performed. It is a joint in which two welding points exist before starting welding. Let L be the distance between the centers P3 and P4 of the nugget diameter of the two already welded points. The nugget diameters d3 and d4 of the already welded points are both 4√t (t: plate thickness). Axis P1 of electrodes A and B that start welding in advance is located at a distance of L1 from the welding point on one side, and an axis P2 of electrodes C and D that starts welding after a distance of L2 is further located Welded as follows.

  Electrodes A, B, C, and D were all DR-type electrodes made of alumina-dispersed copper with a tip diameter of 6 mm and a curvature radius of 40 mm.

  The pressure applied to the upper electrodes A and B was controlled by controlling a servo motor that drives the upper electrodes A and B. A single-phase alternating current with a frequency of 50 Hz was supplied during energization. The lower steel plate 1 and the upper steel plate 2 have the same plate thickness and the same steel type, and have a rectangular shape with a long side of 250 mm and a short side of 50 mm.

  As shown in FIG. 4, the current value in the preceding welding is Ia (kA), the energization time is Ta (ms), the current value in the subsequent welding is Ib (kA), and the energization time is Tb (ms). The difference between the welding start time of the preceding welding and the welding start time of the subsequent welding is T1 (ms). The welding end of the preceding welding is earlier than the welding end of the subsequent welding, and the difference between the welding end time of the preceding welding and the welding end time of the subsequent welding is Td (ms). Each setting condition is shown in Table 2.

  In Comparative Example 1, prior welding and subsequent welding are performed one by one, and T1 (ms) is larger than 200 ms. In Comparative Example 2, the preceding welding and the subsequent welding were performed simultaneously, and T1 (ms) was 0 ms.

  The welded cross section of the welded joint obtained under each setting condition was cut, and the nugget diameter d1 of the welded part of the preceding weld and the nugget diameter d2 of the welded part of the subsequent weld were compared with the reference diameter 4√t. The reference diameter was the nugget diameter of the welded portion where welding was performed under the welding conditions of the electrodes C and D in a state where no existing welding points were formed.

  The diameter d1 of the welded part of the preceding weld and the diameter d2 of the welded part of the subsequent weld have a reduction rate of 5% or less compared to the standard nugget diameter of the welded part. The case where it was large was evaluated as ○, and the case where it was not so was evaluated as ×. As a result, in the present invention example to which the present invention was applied, sufficient nugget formation was recognized as compared with the comparative example to which the present invention was not applied.

1 Lower steel plate 2 Upper steel plate 4 Lower electrode 5 Upper electrode 6 Nugget

Claims (4)

  When two or more steel plates are stacked and resistance spot welding is performed on two adjacent points, the difference between the welding start time of one welding point and the welding start time of the other is set to 10 ms or more, and welding of two welding points is performed. Resistance spot welding method that overlaps time.   The resistance spot welding method according to claim 1, wherein a difference in welding end time between two points is 0 ms or more and not more than a difference in welding start time.   The resistance spot welding method according to claim 1 or 2, wherein when there is an already-welded point, the weld point close to the already-welded point is welded first, and the weld point far from the already-welded point is later welded. Spot welding method.   The manufacturing method of the welded joint using the resistance spot welding method in any one of Claims 1 thru | or 3.

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