Resistance spot welding method

Abstract

This allows for the reduction of residual stress during resistance spot welding, thereby suppressing delayed fracture. [Solution] The resistance spot welding method involves overlapping 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, and performing resistance spot welding on the pair of plate-shaped members. In the resistance spot welding method, after overlapping the top plates of the pair of plate-shaped members and resistance spot welding the top plates, the steps include detecting the contact load necessary to bring into contact the portion where the gap between the pair of vertical wall portions, caused by the part tolerances of the plate-shaped members, is largest, and setting the pressure of the electrodes that sandwich the pair of vertical wall portions when performing resistance spot welding on the overlapping pair of vertical wall portions, such that the pressure of the electrodes is greater than half of the contact load and less than the contact load, and performing resistance spot welding on the pair of vertical wall portions with that pressure of the electrodes.

Description

Technical Field

[0001] The present disclosure relates to a resistance spot welding method.

Background Art

[0002] A resistance spot welding method is known in which a pair of overlapped plate-like members are sandwiched between a pair of electrodes, and each electrode is pressed to deform the plate-like members so that the gap between the pair of plate-like members becomes smaller (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, for example, there are cases where a pair of plate-like members having a hat-shaped cross-section are overlapped and resistance spot welding is performed on the overlapped pair of plate-like members. In this case, as described above, when resistance spot welding is performed while deforming the member having a hat-shaped cross-section, stress concentrates on the welded portion of the top plate portion of the hat-shaped cross-section, and there is a risk of delayed fracture occurring.

[0005] The present disclosure has been made in view of such problems, and the main object thereof is to provide a resistance spot welding method capable of relaxing residual stress during resistance spot welding and suppressing the occurrence of delayed fracture.

Means for Solving the Problems

[0006] One aspect of the present invention for achieving the above object is a resistance spot welding method in which a pair of plate-like members having a hat-shaped cross-section, having a top plate portion and a pair of vertical wall portions respectively extending from both ends of the top plate portion, are overlapped, and resistance spot welding is performed on the overlapped pair of plate-like members, The steps include overlapping the top plates of the pair of plate-shaped members and applying resistance spot welding to the top plates, The steps include: after resistance spot welding the top plate portion, detecting the contact load necessary to bring the portion where the gap between a pair of vertical wall portions, caused by the component tolerances of the plate-shaped member, is largest, The steps include setting the pressure applied by the pair of electrodes that sandwich the pair of vertical wall portions when performing resistance spot welding on the pair of overlapping vertical wall portions such that the pressure applied by the pair of electrodes is greater than half of the contact load and less than the contact load, The steps include performing resistance spot welding on the pair of vertical wall portions using the set pressure of the electrodes, A resistance spot welding method, including the following. In this embodiment, the pair of plate-like members may be made of high-tensile strength material with a tensile strength of 1100 MPa or more. In this embodiment, one of the pair of plate-shaped members may be a reinforcement component, and the other plate-shaped member may be a reinforcement component. [Effects of the Invention]

[0007] According to this disclosure, it is possible to provide a resistance spot welding method that can alleviate residual stress during resistance spot welding and suppress delayed fracture. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows an example of a vehicle component according to this embodiment. [Figure 2] This is a schematic cross-sectional view of a pair of plate-like members. [Figure 3] This flowchart shows the flow of the resistance spot welding method according to this embodiment. [Modes for carrying out the invention]

[0009] This embodiment will be described below with reference to the drawings. Figure 1 is a diagram showing an example of a vehicle part according to this embodiment.

[0010] The resistance spot welding method according to this embodiment involves overlapping a pair of plate-shaped members 10 and 11 and performing resistance spot welding on the overlapped pair of plate-shaped members 10 and 11 to manufacture, for example, a vehicle part 12 as shown in Figure 1.

[0011] One plate-shaped member 10 is a reinforcement component made of high-strength steel, for example, the outer B-pillar of a vehicle. The other plate-shaped member 11 is a reinforcement component made of high-strength steel, for example, the outer B-pillar hinge reinforcement of a vehicle. The plate-shaped members 10 and 11 are, for example, high-tensile steel with a tensile strength of 1100 MPa or more.

[0012] Incidentally, in the resistance spot welding of reinforcement and its reinforcing parts using high-strength steel of 1100 MPa or more, as described above, a gap may occur between a pair of plate-shaped members 10 and 11 due to part tolerances, and the two may be joined by resistance spot welding.

[0013] When such components are exposed to corrosive environments, stress concentration can occur starting from the weld, potentially leading to delayed fracture. This is thought to be partly due to increased susceptibility to fracture caused by residual stress generated by the pressure applied to the electrodes during resistance spot welding and the increased hardness of the nugget.

[0014] In particular, when resistance spot welding the top portions of a pair of plate-like members 10 and 11 having a hat-shaped cross-section, and then resistance spot welding the vertical wall portions, the gap between the vertical wall portions becomes maximum due to the component tolerances of the plate-like members 10 and 11. In this case, the stress concentration that occurs at the welded portion becomes maximum.

[0015] The resistance spot welding method according to this embodiment can effectively alleviate the stress concentration described above and suppress the occurrence of delayed fracture, as described below.

[0016] In addition, when one and the other plate-shaped members 10 and 11 are high-tensile steel materials with a tensile strength of 1100 MPa or more as described above, the stress concentration becomes greater. Therefore, the problem of delayed fracture becomes more significant. However, according to the resistance spot welding method according to the present embodiment, the above-described stress concentration can be further alleviated, so that the occurrence of delayed fracture can be more effectively suppressed.

[0017] FIG. 2 is a schematic cross-sectional view of the pair of plate-shaped members described above. In FIG. 2, the shape is simplified for easier understanding in the following description.

[0018] As shown in FIG. 2, the resistance spot welding method according to the present embodiment overlaps a pair of plate-shaped members 10 and 11 having a hat-shaped cross section, sandwiches the overlapped pair of plate-shaped members 10 and 11 with a pair of electrodes 13 and 13, and passes a large current welding current between the electrodes 13 and 13 for a short time to perform resistance spot welding on the pair of plate-shaped members 10 and 11.

[0019] One of the plate-shaped members 10 with a hat-shaped cross section has a top plate portion 101 and a pair of vertical wall portions 102 and 102 extending from both ends of the top plate portion 101, respectively. The other plate-shaped member 11 with a hat-shaped cross section has a top plate portion 111 and a pair of vertical wall portions 112 and 112 extending from both ends of the top plate portion 111, respectively.

[0020] Subsequently, the resistance spot welding method according to the present embodiment will be described. FIG. 3 is a flowchart showing the flow of the resistance spot welding method according to the present embodiment.

[0021] The top plate portions 101 and 111 of the pair of plate-shaped members 10 and 11 are overlapped, and with the pressing force of the pair of electrodes 13 and 13 as the standard pressing force, resistance spot welding is performed in a state where the pair of top plate portions 101 and 111 are sandwiched (step S101). In this state, the gap between the pair of top plate portions 101 and 111 is in a small state.

[0022] After resistance spot welding the top plate portions 101 and 111, the contact load F required to bring the portion where the gap between the pair of vertical wall portions 102 and 112 is largest, caused by the component tolerances (component precision, component assembly precision, etc.) of the plate-shaped members 10 and 11, into contact with each other is detected (step S102).

[0023] For example, the required contact load F can be detected by actually bringing the portion where the gap between the vertical wall sections 102 and 112 is largest into contact with each other and measuring the contact load F. Alternatively, the required contact load F can be detected by detecting the maximum value of the gap between the pair of vertical wall sections 102 and 112 and calculating the contact load F required for the mutual contact based on the detected maximum value of the gap.

[0024] When resistance spot welding is performed on a pair of overlapping vertical wall sections 102 and 112, the pressing force P of the pair of electrodes 13, 13 that sandwich the pair of vertical wall sections 102 and 112 is set so that the pressing force P is greater than half of the contact load F and less than the contact load F (step S103). Contact load F / 2 < Electrode pressure P < Contact load F

[0025] Resistance spot welding is performed on the pair of vertical wall sections 102 and 112 with the applied pressure P set above (step S104).

[0026] Furthermore, as mentioned above, the reason for setting the pressure P of electrode 13 < contact load F is as follows.

[0027] When the gap between a pair of vertical wall portions 102 and 112 becomes maximum due to the component tolerances of the plate-shaped members 10 and 11, the pressure P applied by the pair of electrodes 13 and 13 that sandwich the pair of vertical wall portions 102 and 112 is set to less than or equal to the contact load F required to bring those portions into contact with each other, thereby preventing contact between those portions.

[0028] Through the gap created by this non-contact process, the molten material from the resistance spot welding flows out, raising the surrounding temperature. This promotes plastic deformation of the surrounding material. As a result, the gap between the pair of vertical wall sections 102 and 112 can be substantially reduced, thereby easing residual stress and suppressing delayed fracture. Therefore, as described above, it is preferable to set the pressure P of the electrode 13 to be less than the contact load F.

[0029] Furthermore, in order to perform resistance spot welding effectively on a pair of vertical wall sections 102 and 112, the pressure P applied by the pair of electrodes 13, 13 that sandwich the pair of vertical wall sections 102 and 112 must be above a certain value.

[0030] Therefore, in this embodiment, as described above, the contact load F / 2 is set to < the pressure P of electrode 13. The reason for setting the pressure P of electrode 13 is as follows. First, experiments were conducted under the following conditions.

[0031] The pair of plate-like members 10 and 11 were made of hot-stamped steel plates with a tensile strength of 1500 MPa and a thickness of 2.0 mm. Resistance spot welding was performed on the top plate portions 101 and 111 and the vertical wall portions 102 and 112 of the plate-like members 10 and 11. The required contact load F was set to 5000 N, and the pressure P of the electrode 13 was set to 3000 N, with contact load F / 2 < pressure P of electrode 13.

[0032] As a result, resistance spot welding could be successfully performed on the pair of vertical wall sections 102 and 112 while simultaneously relieving residual stress. Therefore, as described above, it is preferable to set the contact load F / 2 < the applied pressure P of the electrode 13 < the contact load F.

[0033] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of symbols]

[0034] 10 Plate-shaped member 11 Plate-shaped member 12 Vehicle parts 13 electrodes 101 Top panel 102 Vertical wall section 111 Top panel 112 Vertical wall section

Claims

1. A resistance spot welding method comprising overlapping a pair of plate-like members having a hat-shaped cross-section, each having a top plate portion and a pair of vertical wall portions extending from both ends of the top plate portion, and performing resistance spot welding on the overlapped pair of plate-like members, The steps include overlapping the top plates of the pair of plate-shaped members and applying resistance spot welding to the top plates, The steps include: after resistance spot welding the top plate portion, detecting the contact load necessary to bring the portion where the gap between a pair of vertical wall portions, caused by the component tolerances of the plate-shaped member, is largest, The steps include setting the pressure applied by the pair of electrodes that sandwich the pair of vertical wall portions when performing resistance spot welding on the pair of overlapping vertical wall portions such that the pressure applied by the pair of electrodes is greater than half of the contact load and less than the contact load, The steps include performing resistance spot welding on the pair of vertical wall portions using the set electrode pressure, A resistance spot welding method, including the following.

2. A resistance spot welding method according to claim 1, The pair of plate-like members are made of high-tensile steel with a tensile strength of 1100 MPa or more. Resistance spot welding method.

3. A resistance spot welding method according to claim 1, Of the pair of plate-shaped members, one is a reinforcement component, and the other is a reinforcement component. Resistance spot welding method.

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