Resistance spot joining device and resistance spot joining method

Abstract

Provided is a resistance spot joining device that comprises a pair of pressurization shafts (100) and a pair of electrodes (200). Each pressurization shaft has a pressurization surface (110). At least one of the pair of pressurization surfaces (110) comprises: a protrusion-forming part (111) that forms a protrusion; a gap-forming part (112) that has a shape extending from a peripheral edge section of the protrusion-forming part in a separation direction that separates from the protrusion-forming part along a center axis (AX), and that forms a gap between a first workpiece and a second workpiece; an extrusion-tapered section (113) that has a shape that is inclined so as to gradually become oriented in a direction that separates from the center axis moving from the peripheral edge section of the gap-forming part in the separation direction, and that extrudes surface foreign matter of the first workpiece and the second workpiece in a direction that separates from the center axis; and a pressing section (114) that has a shape that projects from the peripheral edge section of the extrusion-tapered section in a direction that separates from the center axis, and that presses the surfaces newly formed on each workpiece.

Description

Resistance spot bonding device and resistance spot bonding method

[0001] The present disclosure relates to a resistance spot bonding apparatus and a resistance spot bonding method.

[0002] WO 2021 / 182444 discloses a solid-state spot joining device including a pair of central pressure shafts and a pair of electrodes, wherein the tip of the central pressure shaft has a flat portion formed in the center, a tapered portion connected to the peripheral portion of the flat portion, a step extending from the peripheral portion of the tapered portion along the axial direction of the central pressure shaft, and a flat portion extending from a base end of the step in a direction perpendicular to the axial direction.

[0003] International Publication No. 2021 / 182444

[0004] In the solid state spot joining apparatus described in WO 2021 / 182444, it is desirable to improve the joining quality.

[0005] An object of the present disclosure is to provide a resistance spot bonding apparatus and a resistance spot bonding method that can improve bonding quality.

[0006] A resistance spot joining device according to one aspect of the present disclosure is a resistance spot joining device that applies pressure to a first workpiece made of metal and a second workpiece made of metal from both sides in a thickness direction of the first workpiece and a second workpiece, and joins the first workpiece and the second workpiece to each other by passing an electric current through the first workpiece and the second workpiece. The resistance spot joining device includes a pair of pressure shafts that can apply pressure to the first workpiece and the second workpiece from both sides in the thickness direction of the first workpiece and the second workpiece, and a pair of electrodes that are arranged around each of the pair of pressure shafts and can pass an electric current through the first workpiece and the second workpiece, each of the pair of pressure shafts having a pressure surface that applies pressure to the first workpiece and the second workpiece, and at least one of the pair of pressure surfaces is configured to apply pressure to one of the first workpiece and the second workpiece. a gap forming portion having a shape extending from the peripheral portion of the protrusion forming portion in a separation direction away from the protrusion forming portion along the central axis of the pressurizing shaft, and forming a gap between the first workpiece and the second workpiece; an extrusion taper portion having a shape that gradually slopes away from the central axis as it extends from the peripheral portion of the gap forming portion in the separation direction, and extrudes foreign matter on the surfaces of the first workpiece and the second workpiece in a direction away from the central axis; and a pressing portion having a shape that protrudes from the peripheral portion of the extrusion taper portion in a direction away from the central axis, and pressing the newly formed surfaces formed on the first workpiece and the second workpiece against each other.

[0007] A resistance spot welding method according to one aspect of the present disclosure is a resistance spot welding method for joining a first workpiece made of metal and a second workpiece made of metal to each other by applying pressure to the first workpiece and the second workpiece from both sides in the thickness direction while passing an electric current through the first workpiece and the second workpiece, the method including: a protrusion forming process for forming a protrusion on each of the first workpiece and the second workpiece, the protrusion including a contact surface that comes into contact with the first workpiece and the second workpiece, and forming a gap between the first workpiece and the second workpiece; a new surface joining process for pressing the protrusion into the first workpiece and the second workpiece while passing an electric current through the first workpiece and the second workpiece, thereby causing plastic flow at the contact surface and expelling surface foreign matter present on the contact surface of the protrusion toward the outside in a direction perpendicular to the pressure direction, thereby causing a new surface to appear; and a final joining process for joining the new surfaces to each other by pressing the new surfaces together from both sides in the thickness direction.

[0008] According to the present disclosure, it is possible to provide a resistance spot bonding apparatus and a resistance spot bonding method that can improve bonding quality.

[0009] Fig. 1 is a cross-sectional view schematically showing a resistance spot welding device according to an embodiment of the present disclosure; Fig. 2 is an enlarged view of a pressure shaft; Fig. 3 is a cross-sectional view schematically showing a state in which a protrusion forming portion of each pressure shaft is in contact with a workpiece; Fig. 4 is a cross-sectional view schematically showing a state after a protrusion forming step; Fig. 5 is a cross-sectional view schematically showing a state in which electricity is being applied to each workpiece; Fig. 6 is a cross-sectional view schematically showing a new surface joining step; Fig. 7 is a cross-sectional view schematically showing a final joining step; Fig. 8 is a cross-sectional view schematically showing a modified example of the pressure shaft;

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present disclosure will be described with reference to the accompanying drawings, in which the same or corresponding elements are designated by the same reference numerals.

[0011] 1 is a cross-sectional view schematically illustrating a resistance spot welding apparatus according to an embodiment of the present disclosure. The resistance spot welding apparatus 1 is an apparatus for welding multiple workpieces stacked on top of each other while maintaining the workpieces in a solid state by passing an electric current through the multiple workpieces to form softened regions in the multiple workpieces and plastically deforming the softened regions.

[0012] In this embodiment, the plurality of workpieces include a first workpiece W10 and a second workpiece W20. Each of the workpieces W10 and W20 is made of a metal such as iron or aluminum. Each of the workpieces W10 and W20 is formed, for example, in a flat plate shape.

[0013] As shown in FIG. 1 , the resistance spot welding device 1 includes a pair of pressure shafts 100 and a pair of electrodes 200 .

[0014] The pair of pressure applying shafts 100 can apply pressure to the first workpiece W10 and the second workpiece W20 from both sides in the thickness direction thereof. The pair of pressure applying shafts 100 are driven by a drive source (such as a servo press) not shown. The pair of pressure applying shafts 100 includes a first pressure applying shaft 101 and a second pressure applying shaft 102. In this embodiment, the first pressure applying shaft 101 and the second pressure applying shaft 102 have the same shape. Therefore, the following description will mainly focus on the first pressure applying shaft 101.

[0015] The first pressure applying shaft 101 has a shape that extends long in one direction (the vertical direction in FIG. 1 ). In this embodiment, the first pressure applying shaft 101 is formed in a cylindrical shape. However, the first pressure applying shaft 101 is not limited to a cylindrical shape. The first pressure applying shaft 101 is capable of pressing the first workpiece W10 so as to plastically deform the first workpiece W10. The first pressure applying shaft 101 is made of, for example, tungsten carbide.

[0016] The first pressure applying shaft 101 has a pressure applying surface 110 that applies pressure to the first workpiece W10. The pressure applying surface 110 is formed by the tip surface of the first pressure applying shaft 101. As shown in Fig. 2, the pressure applying surface 110 has a protrusion forming portion 111, a gap forming portion 112, an extrusion tapered portion 113, and a pressing portion 114.

[0017] The protrusion forming portion 111 forms a protrusion W11 (see FIG. 4, etc.) on the first workpiece W10 that protrudes toward the second workpiece W20. The protrusion forming portion 111 has a shape that applies a load to the first workpiece W10 that includes a component in a direction perpendicular to the central axis AX of the first pressure applying shaft 101. The protrusion forming portion 111 preferably has a shape that is curved so as to be convex toward the tip side (lower side in FIG. 2) of the first pressure applying shaft 101. The outer shape of the protrusion forming portion 111 when viewed from a direction parallel to the central axis AX is circular. The curvature of the protrusion forming portion 111 may be constant throughout the entire protrusion forming portion 111, or may be gradually changed from the center toward the periphery of the protrusion forming portion 111.

[0018] The gap forming portion 112 has a shape that extends from the peripheral edge of the protrusion forming portion 111 in a direction away from the protrusion forming portion 111 (upward in FIG. 2 ) along the central axis AX. The gap forming portion 112 forms a gap S (see FIG. 4 , etc.) between the first workpiece W10 and the second workpiece W20. The lengths of the protrusion forming portion 111 and the gap forming portion 112 in a direction parallel to the central axis AX are set depending on the material, thickness, etc. of each workpiece W10, W20.

[0019] The extrusion tapered portion 113 has a shape that gradually slopes away from the central axis AX as it moves away from the peripheral edge of the gap forming portion 112. The extrusion tapered portion 113 extrudes surface foreign matter 10 (see FIG. 6 ) of the first workpiece W10 and the second workpiece W20 in the direction away from the central axis AX. The extrusion tapered portion 113 is formed in a truncated cone shape. In the cross section shown in FIG. 2 , the angle between the extension line of the extrusion tapered portion 113 and the central axis AX is preferably set to approximately 70 to 85 degrees, and more preferably set to 80 degrees. The surface foreign matter 10 includes a plating layer, an oxide film on the base material, etc.

[0020] The pressing portion 114 has a shape that protrudes from the peripheral edge of the extrusion tapered portion 113 in a direction away from the central axis AX. The pressing portion 114 presses the newly formed surfaces formed on the first workpiece W10 and the second workpiece W20 against each other. It is preferable that the pressing portion 114 is perpendicular to the central axis AX. However, the pressing portion 114 does not have to be perpendicular to the central axis AX. The pressing portion 114 is formed in an annular shape.

[0021] 2, the length L4 of the pressing portion 114 in the orthogonal direction (radial direction of the first pressure shaft 101) perpendicular to the central axis AX is smaller than the length L3 of the extrusion tapered portion 113 in the orthogonal direction. The length L3 is preferably set to be between two and eight times the length L4.

[0022] The second pressure applying shaft 102 has the same configuration as the first pressure applying shaft 101. The second pressure applying shaft 102 is disposed in such a position that the central axis of the second pressure applying shaft 102 is located on an extension of the central axis AX of the first pressure applying shaft 101, and the pressure applying surface 110 of the second pressure applying shaft 102 faces the pressure applying surface 110 of the first pressure applying shaft 101.

[0023] The pair of electrodes 200 are arranged around each of the pair of pressure shafts 100. The pair of electrodes 200 can pass electricity through the first workpiece W10 and the second workpiece W20 while in contact with the first workpiece W10 and the second workpiece W20. A voltage is applied to the pair of electrodes 200 from a power supply unit (not shown). The pair of electrodes 200 includes a first electrode 201 and a second electrode 202.

[0024] The first electrode 201 can come into contact with a portion of the first workpiece W10 surrounding the portion that is pressed by the first pressing shaft 101. In this embodiment, the first electrode 201 is formed in a cylindrical shape that surrounds the first pressing shaft 101. A gap is provided between the inner circumferential surface of the first electrode 201 and the outer circumferential surface of the first pressing shaft 101. The first electrode 201 is made of, for example, copper.

[0025] The second electrode 202 has the same configuration as the first electrode 201. The second electrode 202 can come into contact with a portion of the second workpiece W20 surrounding the portion that is pressurized by the second pressure shaft 102. The second electrode 202 is disposed in such a position that the central axis of the second electrode 202 is located on an extension of the central axis of the first electrode 201, and the tip surface of the second electrode 202 faces the tip surface of the first electrode 201.

[0026] Next, a description will be given of a resistance spot welding method using the resistance spot welding apparatus 1. This welding method includes a protrusion forming step, a new surface welding step, and a final welding step.

[0027] In the protrusion forming process, as shown in FIG. 4 , protrusions W11, W21 including contact surfaces that come into contact with each other are formed on the first workpiece W10 and the second workpiece W20, respectively, and a gap S is formed between the first workpiece W10 and the second workpiece W20. Specifically, as shown in FIG. 3 , first, the protrusion forming portion 111 of the first pressure shaft 101 is brought into contact with the first workpiece W10, and the protrusion forming portion 111 of the second pressure shaft 102 is brought into contact with the second workpiece W20. Then, as shown by the arrows in FIG. 4 , the first workpiece W10 and the second workpiece W20 are pressed down by the protrusion forming portions 111. As a result, a gap S is formed between the first workpiece W10 and the second workpiece W20 because each pressure surface 110 has a gap forming portion 112.

[0028] In the new surface joining process, the protrusions W11, W21 are pressed against the first workpiece W10 and the second workpiece W20 while current is applied to them, causing plastic flow at the contact surfaces of the protrusions W11, W21. Surface foreign matter 10 present at the contact surfaces of the protrusions W11, W21 is expelled outward in a direction perpendicular to the pressure direction, thereby creating new surfaces. Specifically, as shown in FIG. 5 , a voltage is first applied between a pair of electrodes 200 to energize the protrusions W11, W21. This effectively heats and softens the protrusions W11, W21 (the shaded areas in FIG. 5 ). Then, as shown in FIG. 6 , the first workpiece W10 and the second workpiece W20 are pressed against each other by a pair of pressure shafts 100. As a result, a load as indicated by arrow AR61 acts on each workpiece W10, W20 by the protrusion forming portion 111 and the extrusion taper portion 113, and surface foreign matter 10 present on the contact surface of each protrusion W11, W21 is expelled outward in a direction perpendicular to the pressure direction as indicated by arrow AR62, while new surfaces appear on the contact surfaces of each protrusion W11, W21, and the joining of these new surfaces progresses.

[0029] In the final joining process, the newly formed surfaces are joined by pressing the newly formed surfaces together from both sides in the thickness direction of each workpiece W10, W20. Specifically, as shown by arrows AR71 in Fig. 7, the pressing portions 114 of the pressure surfaces 110 press the newly formed surfaces together so that they come into close contact with each other. This joins the newly formed surfaces together.

[0030] As described above, in the resistance spot welding apparatus 1 of this embodiment, when each workpiece W10, W20 is pressed by a pair of pressure shafts 100, protrusions W11, W21 are formed on each workpiece W10, W20 by the protrusion forming portion 111, and then the surface foreign matter 10 is pushed out in a direction away from the central axis AX by the extrusion taper portion 113, while the newly formed surfaces formed on each workpiece W10, W20 are joined together by the pressing portion 114, thereby improving the welding quality.

[0031] Furthermore, since the gap S is formed between the first workpiece W10 and the second workpiece W20 by the gap forming portion 112 when the protrusions W11, W21 are formed by the protrusion forming portion 111, plastic deformation at the contact interface between the first workpiece W10 and the second workpiece W20 is promoted compared to when the gap S is not formed between the first workpiece W10 and the second workpiece W20. As a result, the time required to join the first workpiece W10 and the second workpiece W20 together is shortened.

[0032] In the above embodiment, an example of joining a first workpiece W10 and a second workpiece W20 to each other is shown, but the above resistance spot joining device 1 can also be applied to joining three or more workpieces to each other.

[0033] 8, the pressure surface 120 of the second pressure shaft 102 may be formed as a flat surface perpendicular to the central axis AX. In this configuration, the formation of welding marks on the second workpiece W20 is suppressed, improving the appearance. However, as in the above embodiment, each pressure surface 110 has the protrusion-forming portion 111, the gap-forming portion 112, the extrusion tapered portion 113, and the pressing portion 114, which increases the amount of deformation of each workpiece W10, W20, thereby increasing the welding strength.

[0034] It will be appreciated by those skilled in the art that the exemplary embodiments described above are examples of the following aspects.

[0035] [Aspect 1] A resistance spot joining device that joins a first workpiece made of metal and a second workpiece made of metal to each other by applying pressure to both sides in a thickness direction of the first workpiece and the second workpiece and passing a current through the first workpiece and the second workpiece, the resistance spot joining device comprising: a pair of pressure shafts that can apply pressure to the first workpiece and the second workpiece from both sides in the thickness direction of the first workpiece and the second workpiece; and a pair of electrodes that are arranged around each of the pair of pressure shafts and can pass a current through the first workpiece and the second workpiece, each of the pair of pressure shafts having a pressure surface that applies pressure to the first workpiece and the second workpiece, at least one of the pair of pressure surfaces having: a protrusion forming portion that forms a protrusion on one of the first workpiece and the second workpiece that protrudes toward the other of the first workpiece and the second workpiece; and a gap forming portion that has a shape that extends from a peripheral portion of the protrusion forming portion in a separation direction along the central axis of the pressure shaft away from the protrusion forming portion, and forms a gap between the first workpiece and the second workpiece. a pressing portion having a shape that protrudes from the peripheral edge of the extrusion tapered portion in the direction away from the central axis and that presses newly formed surfaces formed on the first workpiece and the second workpiece against each other, the pressing portion having a shape that protrudes from the peripheral edge of the extrusion tapered portion in the direction away from the central axis and that presses newly formed surfaces formed on the first workpiece and the second workpiece against each other.

[0036] In this resistance spot welding device, when the workpieces are pressed by the pair of pressure shafts, the protrusion forming portion forms a protrusion on each workpiece, and then the extrusion tapered portion pushes surface foreign matter away from the central axis of the pressure shaft while the pressing portion joins the newly formed surfaces of the workpieces together, thereby improving welding quality. Furthermore, because a gap is formed between the first and second workpieces by the gap forming portion when the protrusion forming portion forms the protrusion, plastic deformation at the contact interface between the first and second workpieces is promoted compared to when no gap is formed between the first and second workpieces. This shortens the time required to join the first and second workpieces.

[0037] [Aspect 2] The resistance spot welding device according to Aspect 1, wherein the protrusion forming portion has a shape that applies a load to the one workpiece that includes a component in a direction perpendicular to the central axis.

[0038] In this embodiment, the surface foreign matter is more effectively pushed out in the direction away from the central axis. [Embodiment 3] The resistance spot welding device according to embodiment 2, wherein the protrusion forming portion has a shape that is curved so as to be convex toward the tip side of the pressure shaft.

[0039] [Aspect 4] The resistance spot joining device according to any one of Aspects 1 to 3, wherein the pressing portion is perpendicular to the central axis.

[0040] In this embodiment, the newly formed surfaces of the workpieces are pressed together more effectively, improving the joining quality.

[0041] [Aspect 5] The resistance spot joining device according to any one of Aspects 1 to 4, wherein a length of the pressing portion in a direction perpendicular to the central axis is smaller than a length of the extrusion tapered portion in the direction perpendicular to the central axis.

[0042] In this embodiment, the surface foreign matter is pushed out further to the outside of the region to be joined, thereby further improving the joining quality.

[0043] [Aspect 6] A resistance spot joining method for joining a first workpiece made of metal and a second workpiece made of metal to each other by applying pressure to the first workpiece and the second workpiece from both sides in a thickness direction thereof while passing an electric current through the first workpiece and the second workpiece, the resistance spot joining method comprising: a protrusion forming step for forming protrusions on each of the first workpiece and the second workpiece, the protrusions including contact surfaces that come into contact with each other, and forming a gap between the first workpiece and the second workpiece; a new surface joining step for causing plastic flow at the contact surfaces by pressing the protrusions into the first workpiece and the second workpiece while passing an electric current through them, and for causing surface foreign matter present on the contact surfaces of the protrusions to be expelled outward in a direction perpendicular to the pressure application direction, thereby causing a new surface to appear; and a final joining step for joining the new surfaces to each other by pressing the new surfaces together from both sides in the thickness direction.

[0044] It should be noted that the embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the description of the above embodiments, and further includes all modifications within the meaning and scope of the claims.

[0045] 1 Resistance spot welding device, 10 Surface foreign matter, 100 Pressure shaft, 101 First pressure shaft, 102 Second pressure shaft, 110 Pressure surface, 111 Protrusion forming portion, 112 Gap forming portion, 113 Extrusion taper portion, 114 Pressing portion, 120 Pressure surface, 200 Electrode, 201 First electrode, 202 Second electrode, W10 First workpiece, W11 Protrusion, W20 Second workpiece, W21 Protrusion.

Claims

1. A resistance spot joining device that applies pressure to a first workpiece made of metal and a second workpiece made of metal from both sides in the thickness direction of the first workpiece and the second workpiece, and joins the first workpiece and the second workpiece to each other by passing an electric current through the first workpiece and the second workpiece, the device comprising: a pair of pressure shafts that can apply pressure to the first workpiece and the second workpiece from both sides in the thickness direction; and a pair of electrodes that are arranged around each of the pair of pressure shafts and can pass an electric current through the first workpiece and the second workpiece, each of the pair of pressure shafts having a pressure surface that applies pressure to the first workpiece and the second workpiece, at least one of the pair of pressure surfaces having: a protrusion forming portion that forms a protrusion on one of the first workpiece and the second workpiece, the protrusion protruding toward the other of the first workpiece and the second workpiece; and a gap forming portion that has a shape that extends from the periphery of the protrusion forming portion in a separation direction along the central axis of the pressure shaft, away from the protrusion forming portion, and forms a gap between the first workpiece and the second workpiece. a pressing portion having a shape that protrudes from the peripheral edge of the extrusion tapered portion in the direction away from the central axis and that presses newly formed surfaces formed on the first workpiece and the second workpiece against each other, the pressing portion having a shape that protrudes from the peripheral edge of the extrusion tapered portion in the direction away from the central axis and that presses newly formed surfaces formed on the first workpiece and the second workpiece against each other.

2. The resistance spot welding device according to claim 1, wherein the protrusion forming portion has a shape that applies a load to the one workpiece that includes a component in a direction perpendicular to the central axis.

3. The resistance spot welding device according to claim 2, wherein the protrusion forming portion has a shape that is curved so as to be convex toward the tip end of the pressure shaft.

4. The resistance spot joining device according to claim 1, wherein the pressing portion is perpendicular to the central axis.

5. The resistance spot joining device according to claim 1, wherein the length of the pressing portion in a direction perpendicular to the central axis is smaller than the length of the extrusion taper portion in the direction perpendicular to the central axis.

6. A resistance spot joining method for joining a first workpiece made of metal and a second workpiece made of metal to each other by applying pressure to the first workpiece and the second workpiece from both sides in the thickness direction while passing an electric current through the first workpiece and the second workpiece, comprising: a protrusion forming process for forming protrusions on each of the first workpiece and the second workpiece, including contact surfaces that come into contact with each other, and forming a gap between the first workpiece and the second workpiece; a new surface joining process for causing plastic flow at the contact surface by pressing the protrusions into the first workpiece and the second workpiece while passing an electric current through them, and expelling surface foreign matter present on the contact surface of the protrusions outward in a direction perpendicular to the pressure direction, thereby causing a new surface to appear; and a final joining process for joining the new surfaces by pressing the new surfaces together from both sides in the thickness direction.

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