Resistance spot welding method

Abstract

The present invention provides a resistance spot welding method that can alleviate residual stress during resistance spot welding and can suppress occurrence of delayed fracture. In the resistance spot welding method, a pair of plate-shaped members having a hat-shaped cross section with a top plate portion and a pair of vertical wall portions extending from both ends of the top plate portion are overlapped, and resistance spot welding is performed on the pair of plate-shaped members. In the resistance spot welding method, there are included a step of detecting a contact load required for mutual contact of a portion where a gap between the pair of vertical wall portions becomes the largest due to a part tolerance of the plate-shaped members after the top plate portions of the pair of plate-shaped members are overlapped and resistance spot welding is performed on the top plate portions; and a step of setting a pressing force of a pair of electrodes that sandwich the pair of vertical wall portions during resistance spot welding on the overlapped pair of vertical wall portions in such a manner that the pressing force of the electrodes is greater than half of the contact load and smaller than the contact load, and performing resistance spot welding on the pair of vertical wall portions with the pressing force of the electrodes.

Description

Technical Field

[0001] This invention relates to a resistance spot welding method. Background Technology

[0002] A resistance spot welding method is known in which a pair of plates are clamped together by a pair of electrodes and pressure is applied to each electrode to deform the plates, thereby reducing the gap between the pair of plates (for example, see Patent Document 1).

[0003] Patent Document 1: Japanese Patent Application Publication No. 2013-078806 Summary of the Invention

[0004] For example, sometimes a pair of plate-shaped components with a hat-shaped cross-section are overlapped, and the overlapping pair of plate-shaped components are resistance-spot welded. In this case, as described above, if resistance spot welding is performed while deforming the components with the hat-shaped cross-section, stress will concentrate on the welded portion of the top plate of the hat-shaped cross-section, which may lead to delayed fracture.

[0005] The present invention was made in view of these problems, and its main objective is to provide a resistance spot welding method that can alleviate residual stress during resistance spot welding and suppress the occurrence of delayed fracture.

[0006] To achieve the above objectives, one aspect of the present invention is a resistance spot welding method, which involves overlapping a pair of plate-shaped components having a top plate portion and a pair of vertical wall portions extending from both ends of the top plate portion in a cap-shaped cross-section, and performing resistance spot welding on the overlapping pair of plate-shaped components. The resistance spot welding method includes the following steps:

[0007] The top plates of the pair of plate-shaped components are overlapped, and the resistance spot welding is performed on the top plates.

[0008] After the resistance spot welding is performed on the top plate, the contact load required to maximize the contact between the two vertical wall portions caused by the part tolerances of the plate-shaped component is measured.

[0009] The electrode pressure is set such that, during resistance spot welding of the overlapping pair of vertical walls, the pressure applied to the pair of electrodes clamping the pair of vertical walls is greater than half of the contact load but less than the contact load; and

[0010] Resistance spot welding is performed on the pair of vertical wall sections using the pressure applied by the set electrodes.

[0011] In this approach, the pair of plate-shaped components can be high-strength steel with a tensile strength of 1100 MPa or higher.

[0012] In this approach, one of the pair of plate-shaped components may be a reinforcing member, and the other plate-shaped component may be a reinforcing reinforcement.

[0013] Invention Effects

[0014] According to the present invention, a resistance spot welding method is provided that can alleviate residual stress during resistance spot welding and suppress the occurrence of delayed fracture. Attached Figure Description

[0015] Figure 1 This is a diagram showing an example of a vehicle part involved in this embodiment.

[0016] Figure 2 It is a schematic cross-sectional view of a pair of plate-shaped components.

[0017] Figure 3 This is a flowchart illustrating the process of the resistance spot welding method described in this embodiment. Detailed Implementation

[0018] Hereinafter, this embodiment will be described with reference to the accompanying drawings. Figure 1 This is a diagram showing an example of a vehicle part involved in this embodiment.

[0019] The resistance spot welding method described in this embodiment involves overlapping a pair of plate-shaped components 10 and 11 and performing resistance spot welding on the overlapping pair of plate-shaped components 10 and 11, for example, manufacturing a... Figure 1 Vehicle part 12 shown.

[0020] One plate-shaped component 10 is a high-strength steel reinforcement, such as the outer B-pillar panel of a vehicle. The other plate-shaped component 11 is a high-strength steel reinforcing member, such as a hinge reinforcement for the outer B-pillar panel of a vehicle. One and the other plate-shaped components 10 and 11 are, for example, high-strength steel (HTSS) with a tensile strength of 1100 MPa or higher.

[0021] For example, in the resistance spot welding of reinforcing members and their reinforcing parts using high-strength steel of 1100 MPa or above as described above, sometimes resistance spot welding is performed on a pair of plate-shaped parts 10 and 11 to join them together when there is a gap between them due to part tolerances.

[0022] If such a component is exposed to a corrosive environment, stress concentration may occur starting from the weld, delaying fracture. This is believed to be due to the increased residual stress caused by the electrode pressure during resistance spot welding and the increased hardness of the weld nugget, thus increasing its susceptibility.

[0023] In particular, when the top plate portion of the pair of plate-shaped components 10 and 11 with a cap-shaped cross-section is resistance-spotted, and then the vertical wall portion is resistance-spotted, the gap between the vertical wall portions becomes the largest due to the part tolerances of the plate-shaped components 10 and 11. In this case, the stress concentration occurring at the aforementioned welded portion becomes the largest.

[0024] The resistance spot welding method described in this embodiment is as follows, which can effectively alleviate the stress concentration mentioned above, thereby suppressing the occurrence of delayed fracture.

[0025] Furthermore, as described above, when one and the other plate-shaped components 10 and 11 are made of high-strength steel with a tensile strength of 1100 MPa or higher, the stress concentration becomes even greater. Therefore, the problem of delayed fracture becomes more significant. However, according to the resistance spot welding method of this embodiment, the stress concentration can be further mitigated, and thus the occurrence of delayed fracture can be suppressed more effectively.

[0026] Figure 2 This is a schematic cross-sectional view of the aforementioned pair of plate-shaped components. Additionally, in Figure 2 In order to facilitate understanding of the following explanation, its shape has been simplified.

[0027] like Figure 2 As shown, in the resistance spot welding method of this embodiment, a pair of plate-shaped components 10 and 11 with cap-shaped cross sections are overlapped, and the overlapping pair of plate-shaped components 10 and 11 are clamped by a pair of electrodes 13 and 13. A large current welding current is applied between each electrode 13 and 13 for a short time, thereby performing resistance spot welding on the pair of plate-shaped components 10 and 11.

[0028] One plate-shaped component 10 of the hat-shaped cross-section has a top plate portion 101 and a pair of vertical wall portions 102, 102 extending from both ends of the top plate portion 101. The other plate-shaped component 11 of the hat-shaped cross-section has a top plate portion 111 and a pair of vertical wall portions 112, 112 extending from both ends of the top plate portion 111.

[0029] Next, the resistance spot welding method involved in this embodiment will be described. Figure 3 This is a flowchart illustrating the process of the resistance spot welding method described in this embodiment.

[0030] The top plate portions 101 and 111 of a pair of plate-shaped components 10 and 11 are overlapped, and the pressure applied to a pair of electrodes 13 and 13 is used as the standard pressure. Resistance spot welding is performed while the pair of top plate portions 101 and 111 are clamped (step S101). In this state, the gap between the pair of top plate portions 101 and 111 is small.

[0031] After resistance spot welding is performed on the top plate portions 101 and 111, the contact load F required for the gap between the pair of vertical wall portions 102 and 112, which is caused by the part tolerances (part accuracy, part assembly accuracy, etc.) of the plate components 10 and 11, to reach maximum contact with each other is measured (step S102).

[0032] For example, the required contact load F can be detected by measuring the contact load F when the gap between the vertical wall portions 102 and 112 is maximized and they actually come into contact with each other. Alternatively, the maximum value of the gap between a pair of vertical wall portions 102 and 112 can be detected, and the required contact load F for mutual contact can be calculated based on the detected maximum value of the gap, thereby detecting the required contact load F.

[0033] The pressure P is set such that the pressure P is greater than half of the contact load F but less than the contact load F, and is used as the pressure P for clamping the pair of electrodes 13, 13 of the pair of vertical wall portions 102, 112 when resistance spot welding is performed on the pair of overlapping vertical wall portions 102, 112 (step S103).

[0034] Contact load F / 2 < electrode pressure P < contact load F

[0035] With the pressure P set above, resistance spot welding is performed on a pair of vertical wall portions 102 and 112 (step S104).

[0036] Furthermore, as mentioned above, the reason for setting the applied pressure P of electrode 13 to be less than the contact load F is as follows.

[0037] When the gap between a pair of vertical wall portions 102 and 112 becomes the largest due to the part tolerances of the plate-shaped components 10 and 11, the pressure P applied to the pair of electrodes 13 and 13 that hold the pair of vertical wall portions 102 and 112 is set to be less than or equal to the contact load F required to make the portions come into contact with each other, so that the portions do not come into contact with each other.

[0038] The temperature rises around the gap that occurs without contact, due to the shunting flow of the molten component from the resistance spot welding. This promotes plastic deformation around the gap. Consequently, the gap between the pair of vertical wall portions 102 and 112 is substantially reduced, thus mitigating residual stress and suppressing delayed fracture. Therefore, as described above, it is preferable to set the applied pressure P of electrode 13 to be less than the contact load F.

[0039] Furthermore, when performing resistance spot welding on a pair of vertical wall portions 102 and 112, the pressure P applied to the pair of electrodes 13 and 13 that hold the pair of vertical wall portions 102 and 112 needs to be set to a certain specified value or higher.

[0040] Therefore, in this embodiment, as described above, the contact load F / 2 is set to be less than the applied pressure P of electrode 13. The applied pressure P of electrode 13 is set based on the following reasons. First, an experiment was conducted under the following conditions.

[0041] A pair of plate-shaped components 10 and 11 are hot-stamped steel plates with a tensile strength of 1500 MPa, and the plate thickness is set to 2.0 mm. Resistance spot welding is performed on the top plates 101 and 111 and the vertical walls 102 and 112 of the plate-shaped components 10 and 11. The required contact load F is set to 5000 N, and since the contact load F / 2 < the applied pressure P of electrode 13, the applied pressure P of electrode 13 is set to 3000 N.

[0042] As a result, resistance spot welding can be performed well on the pair of vertical wall portions 102 and 112, while mitigating their residual stress. Therefore, as described above, it is preferable to set the contact load F / 2 < the applied pressure P of electrode 13 < the contact load F.

[0043] Several embodiments of the present invention have been described, but these embodiments are presented by way of example and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are all included in the scope or spirit of the invention, and are included within the scope of the invention as described in the claims and their equivalents.

[0044] Symbol Explanation

[0045] 10-plate-shaped component, 11-plate-shaped component, 12-vehicle part, 13-electrode, 101-top plate, 102-vertical wall, 111-top plate, 112-vertical wall.

Claims

1. A resistance spot welding method comprising overlapping a pair of plate-shaped components having a top plate portion and a pair of vertical wall portions extending from both ends of the top plate portion in a cap-shaped cross-section, and performing resistance spot welding on the overlapping pair of plate-shaped components, the resistance spot welding method being characterized by comprising the following steps: The top plates of the pair of plate-shaped components are overlapped, and the resistance spot welding is performed on the top plates. After the resistance spot welding is performed on the top plate, the contact load required to maximize the contact between the two vertical wall portions caused by the part tolerances of the plate-shaped component is measured. The electrode pressure is set such that, during resistance spot welding of the overlapping pair of vertical walls, the pressure applied to the pair of electrodes clamping the pair of vertical walls is greater than half of the contact load but less than the contact load; and Resistance spot welding is performed on the pair of vertical wall sections using the pressure applied by the set electrodes.

2. The resistance spot welding method according to claim 1, characterized in that, The pair of plate-shaped components are made of high-strength steel with a tensile strength of 1100 MPa or higher.

3. The resistance spot welding method according to claim 1, characterized in that, One of the pair of plate-shaped components is a reinforcing member, and the other plate-shaped component is a reinforcing reinforcement.

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