Low-temperature welding method and low-temperature welding apparatus

Abstract

To provide a pressure welding method and a pressure welding apparatus that can improve the bonding strength of two overlapping materials to be joined. [Solution] One aspect of the present disclosure is a pressing method in which a first material to be joined 11 and a second material to be joined 12 are placed on top of each other and pressed together by a punch 24 from the side of the first material to be joined 11, wherein the punch 24 comprises a convex portion 30 and a stepped portion 40 formed on the base portion 31 side of the convex portion 30 and protruding outward from the convex portion 30 in a direction intersecting the direction of movement of the punch 24, and when pressing together the first material to be joined 11 and the second material to be joined 12, the first material to be joined 11 is pressed by the convex portion 30 and pressed by the stepped portion 40, thereby pressing and causing to flow a portion of the first material to be joined 11 that is pressed by the convex portion 30 and is about to flow in a direction different from that of the second material to be joined 12 in the direction toward the second material to be joined 12 by the stepped portion 40.

Description

[Technical Field]

[0001] The present disclosure relates to a pressure welding method and a pressure welding apparatus for pressure welding a first workpiece to be joined and a second workpiece to be joined. [Background Art]

[0002] Patent Documents 1 and 2 disclose a pressure welding method in which two workpieces to be joined are overlapped and pressed from one workpiece side with a punch. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2006-150416 [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2013-99776 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] In the pressure welding method of overlapping two workpieces to be joined and pressing the overlapping workpieces with a punch, pressing one of the workpieces with the punch causes oxide films adhering to the joint surfaces of the workpieces to be crushed as the surface area of the joint surfaces increases, as shown in FIG. 30. The newly exposed surfaces brought about thereby are in close contact with each other, so that the two workpieces to be joined are joined together.

[0005] However, when pressing is performed from one workpiece side with a punch, there occurs a portion of the one workpiece that flows in a direction different from the direction toward the other workpiece (for example, when the punch is moved downward, the portion flows upward or in a radial direction (left-right direction)). When such a flowing portion occurs, even if the surface area of the joint surfaces of the workpieces to be joined increases, the material of the one workpiece flows in a direction different from the direction toward the other workpiece. This reduces the adhesion of the newly exposed surfaces exposed on the joint surfaces, weakens the joining force at the joint surfaces of the two workpieces to be joined, and may lower the joint strength between the two workpieces to be joined.

[0006] In Patent Document 2, the area around the portion pressed by the convex part of the punch is held down by the shoulder of the punch, but this shoulder only contacts the material to be joined to the extent that it does not obstruct the flow of the material. Furthermore, the punch is pressed in while leaving a gap around the convex part of the punch. Therefore, the shoulder does not cause a portion of one material to flow in a different direction from the other material to flow in the direction of the other material. Consequently, the adhesion of the newly exposed surface on the joining surface of the materials to be joined may decrease, weakening the joining force at the joining surface of the two materials and potentially lowering the joint strength of the two materials.

[0007] Therefore, this disclosure has been made to solve the above-mentioned problems, and aims to provide a pressure welding method and a pressure welding apparatus that can improve the bonding strength of two overlapping materials to be joined. [Means for solving the problem]

[0008] One embodiment of the present disclosure made to solve the above problems is a pressing method in which a first material to be joined and a second material to be joined are placed on top of each other and pressed together by pressing with a punch from the side of the first material to be joined, wherein the punch comprises a convex portion and a stepped portion formed on the base side of the convex portion and protruding outward from the convex portion in a direction intersecting the direction of movement of the punch, and when pressing together the first material to be joined and the second material to be joined, the first material to be joined is pressed with the convex portion while the stepped portion is pressed, thereby pressing with the stepped portion in the direction toward the second material to cause the portion of the first material to be joined that is pressed with the convex portion and tends to flow in a direction different from that of the second material to be joined to flow.

[0009] According to this embodiment, in the first material to be joined, not only the portion that flows toward the second material when pressed by the protrusion of the punch, but also the portion that would otherwise flow in a different direction when pressed by the protrusion of the punch, can be made to flow toward the second material by the stepped portion. Therefore, the portion of the first material that is pressed by the protrusion of the punch can be made to flow toward the second material throughout its entirety. Consequently, the surface area of ​​the joining surface of the first material to be joined and the joining surface of the second material to be joined is increased, improving the adhesion of the newly exposed surface at this joining surface. As a result, the joining force between the joining surface of the first material to be joined and the joining surface of the second material to be joined is increased, improving the joining strength between the first material to be joined and the second material to be joined (i.e., the two materials to be joined).

[0010] In the above embodiment, it is preferable that, when the punch is viewed from its tip side, the outer shape of the protrusion is circular and the outer shape of the stepped portion is circular.

[0011] According to this embodiment, the stepped portion can evenly and uniformly press the first material to be joined in the circumferential direction around the protrusion. As a result, the bonding strength between the first material to be joined and the second material to be joined is improved more effectively.

[0012] In the above embodiment, it is preferable that, when the punch is viewed from its tip side, the outer shape of the protrusion is circular and the outer shape of the stepped portion is square.

[0013] According to this embodiment, the area of ​​the stepped portion changes in the circumferential direction around the convex portion, thereby creating a flow in the material of the first material to be joined that is pressed against the stepped portion, while the first material to be joined can be pressed by the stepped portion. As a result, the bonding strength between the first material to be joined and the second material to be joined is improved more effectively.

[0014] In the above embodiment, it is preferable that the stepped portion is formed in a tapered shape that is inclined toward the opposite side of the convex portion with respect to the direction of movement of the punch.

[0015] In this embodiment, when a portion of the first joined material that is pressed by a protrusion and is about to flow in a direction different from that of the second joined material is pressed by the stepped portion in the direction toward the second joined material and forced to flow, the component force generated at the tapered stepped portion increases the surface pressure at the joint surface of the first joined material and the joint surface of the second joined material. As a result, the bonding force at the joint surface of the first joined material and the joint surface of the second joined material increases, improving the bonding strength between the first joined material and the second joined material.

[0016] In the above embodiment, it is preferable that the stepped portion is formed perpendicular to the direction of movement of the punch.

[0017] According to this embodiment, the step portion in the first material to be joined can increase the pressing force toward the second material to be joined. As a result, the joint strength between the first material to be joined and the second material to be joined is improved more effectively.

[0018] In the above embodiment, it is preferable that the surface of the protrusion is formed by a planar tip surface perpendicular to the direction of movement of the punch, and a side surface formed from the edge of the tip surface toward the base side of the protrusion along the direction of movement of the punch.

[0019] According to this embodiment, by pressing with the planar tip surface, the first and second materials to be joined are pressed together, and the surface pressure acting between the joining surface of the first material and the joining surface of the second material can be increased. As a result, the joint strength between the first and second materials to be joined is improved more effectively.

[0020] In the above embodiment, it is preferable that the surface of the protrusion is spherical or curved overall.

[0021] According to this aspect, when pressing with a punch from the first workpiece side, the bonding surface of the first workpiece and the bonding surface of the second workpiece are each changed from a flat surface to a spherical surface, whereby the surface area thereof can be increased. Therefore, exposure of a new surface on the bonding surface of the first workpiece and the bonding surface of the second workpiece (for example, splitting an oxide film adhering to the bonding surface to expose the new surface) can be promoted. Accordingly, the bonding strength between the first workpiece and the second workpiece is more effectively improved.

[0022] In the above aspect, it is preferable that a plurality of the step portions are formed side by side in the moving direction of the punch.

[0023] According to this aspect, a portion that is pressed by the convex portion of the punch and tends to flow in a direction different from the direction toward the second workpiece can be caused to flow in the direction toward the second workpiece over multiple stages. Therefore, the bonding strength between the first workpiece and the second workpiece is more effectively improved.

[0024] Another aspect of the present disclosure, which has been made to solve the above problems, relates to a pressure welding apparatus that overlaps a first workpiece and a second workpiece, presses the overlapping workpieces with a punch from the first workpiece side, and press-welds the first workpiece and the second workpiece, wherein the punch includes a convex portion and a step portion formed on a base side of the convex portion and projecting outward in a direction intersecting the moving direction of the punch more than the convex portion, and when press-welding the first workpiece and the second workpiece, the first workpiece is pressed by the step portion while being pressed by the convex portion, whereby a portion of the first workpiece that is pressed by the convex portion and tends to flow in a direction different from the direction toward the second workpiece is pressed by the step portion in the direction toward the second workpiece to flow. This is characterized by the above.

Effects of the Invention

[0025] According to the pressure welding method and the pressure welding apparatus of the present disclosure, the bonding strength of two overlapping workpieces can be improved. [BRIEF DESCRIPTION OF THE DRAWINGS]

[0026] [Figure 1] It is a schematic diagram schematically showing the cold pressure welding apparatus of the present embodiment. [Figure 2] It is a perspective view of the tip end of the punch according to the first example. [Figure 3] It is a side view of the tip end of the punch according to the first example. [Figure 4] It is a view of the punch according to the first example as seen from the tip end thereof. [Figure 5] It is a cross-sectional view showing a state where pressure welding is performed by the punch according to the first example. [Figure 6] It is a diagram summarizing the evaluation results of bonding strength. [Figure 7] It is a diagram showing the evaluation results of conduction resistance. [Figure 8] It is a diagram showing the evaluation results of peel strength. [Figure 9] It is a perspective view of the tip end of the punch according to the first modification of the first example. [Figure 10] It is a side view of the tip end of the punch according to the first modification of the first example. [Figure 11] It is a side view of the tip end of the punch according to the second modification of the first example (specifically, a modification of FIG. 3). [Figure 12] It is a side view of the tip end of the punch according to the second modification of the first example (specifically, a modification of FIG. 10). [Figure 13] It is a cross-sectional view showing a state where pressure welding is performed by the punch according to the first example in a case where concavo-convex portions are formed in advance on a first workpiece to be bonded and a second workpiece to be bonded. [Figure 14] It is a perspective view of the tip end of the punch according to the second example. [Figure 15] It is a side view of the tip end of the punch according to the second example. [Figure 16] It is a view of the punch according to the second example as seen from the tip end thereof. [Figure 17] It is a cross-sectional view showing a state where pressure welding is performed by the punch according to the second example. [Figure 18] It is a perspective view of the tip end of the punch according to the first modification of the second example. [Figure 19] This is a side view of the tip of the punch in the first modified example of the second embodiment. [Figure 20] This is a side view of the tip of the punch in the second modified example of the second embodiment (more specifically, the modified example in Figure 15). [Figure 21] This is a side view of the tip of the punch in the second modified example of the second embodiment (more specifically, the modified example in Figure 19). [Figure 22] This is a perspective view of the tip of the punch in the third embodiment. [Figure 23] This is a view of the punch of the third embodiment from the tip. [Figure 24] This is a perspective view of the tip of the punch in the first modified example of the third embodiment. [Figure 25] This is a view of the punch from the tip of the second modified example of the third embodiment (specifically, the case where the outer shape of the first stepped portion is circular). [Figure 26] This is a view of the punch from the tip of the second modified example of the third embodiment (specifically, the case where the outer shape of the first stepped portion is rectangular). [Figure 27] This is a cross-sectional view showing the case where the first and second materials to be joined are rods, and they are pressed together using the punches of the first to third embodiments. [Figure 28] This is a perspective view of the tip of a conventional punch. [Figure 29] This is a cross-sectional view showing the process when the material is pressed together using a conventional punch. [Figure 30] This is an explanatory diagram regarding pressure welding by overlapping two materials to be joined and pressing them together with a punch. [Modes for carrying out the invention]

[0027] This document describes a cold welding apparatus 1, which is an example of an embodiment of the welding method and welding apparatus of this disclosure, and a cold welding method using this cold welding apparatus 1.

[0028] <Overview of Cold Welding Equipment> The cold welding apparatus 1 of this embodiment is a device that performs cold welding (including low-temperature forging) to press two materials to be joined (i.e., a first material to be joined 11 and a second material to be joined 12) together at room temperature. As shown in Figure 1, the cold welding apparatus 1 includes a lifting section 21, a die mounting base 22, a die 23, a punch 24, a material holding plate 25, and a spring 26.

[0029] The lifting section 21 has a punch 24 attached to it and moves up and down by a drive device (not shown). A die 23 that receives the compressive load from the punch 24 is provided on the die mounting base 22. The first material to be joined 11 and the second material to be joined 12 are placed on top of each other on the die 23.

[0030] The first material to be joined 11 is, for example, a copper plate (a copper alloy plate). The second material to be joined 12 is, for example, an aluminum plate (aluminum alloy plate).

[0031] The punch 24 is attached to the lifting mechanism 21 and moves up and down together with the lifting mechanism 21. The material of the punch 24 is, for example, tool steel or cemented carbide. Further details of the punch 24 will be described later.

[0032] The material holding plate 25 is used to hold down the first and second materials to be joined, which are stacked on top of each other before pressure welding, with the biasing force of the spring 26, and to separate (detach) the punch 24 from the joint formed by the first and second materials to be joined after pressure welding.

[0033] The cold welding apparatus 1 with this configuration press-welds the first workpiece 11 and the second workpiece 12 together, as described below.

[0034] First, the first material to be joined 11 is placed on top of the second material to be joined 12 on the die 23. The joining surfaces of the first material to be joined 11 and the joining surfaces of the second material to be joined 12 are subjected to an oxide film removal treatment beforehand. Next, the first material to be joined 11 and the second material to be joined 12, which are stacked in this manner, are pressed down by the material holding plate 25 using the biasing force of the spring 26.

[0035] Next, the punch 24 is lowered by the lifting mechanism 21, and the punch 24 presses against the first material to be joined 11 from the side, thereby pressing the first material to be joined 11 and the second material to be joined 12 together to form a press-fitted body of the first material to be joined 11 and the second material to be joined 12.

[0036] After pressure welding, the material holding plate 25 holds down the joint between the first material to be joined 11 and the second material to be joined 12, and the punch 24 is raised by the lifting unit 21 to separate the punch 24 from the joint between the first material to be joined 11 and the second material to be joined 12.

[0037] <Punch Explanation> Conventional punches 124, for example, were formed in a straight cylindrical shape with a nearly constant outer diameter at the tip, as shown in Figure 28. When such a conventional punch 124 is used to overlap the first material to be joined 11 and the second material to be joined 12, and the conventional punch 124 is pressed from the first material to be joined 11 side, a portion of the first material to be joined 11 flows in a direction different from the direction toward the second material to be joined 12 (for example, upward or radially (left-right direction) when the punch 124 is moved downward), as shown by the arrow in Figure 29.

[0038] Consequently, even if the surface area of ​​the joint surface of the first material to be joined 11 and the joint surface of the second material to be joined 12 is increased by the pressing of the punch 124, the adhesion of the newly exposed surface on the joint surface decreases, weakening the bonding force at the joint surface, which may reduce the bonding strength between the first material to be joined 11 and the second material to be joined 12. When the bonding strength between the first material to be joined 11 and the second material to be joined 12 decreases, the conductive resistance of the joint between the first material to be joined 11 and the second material to be joined 12 increases, and the peel strength decreases.

[0039] Therefore, in this embodiment, the shape of the punch 24 is modified to improve the bonding strength between the first material to be joined 11 and the second material to be joined 12.

[0040] (First embodiment) First, the first embodiment will be described. In this embodiment, as shown in Figures 2 and 3, the punch 24 comprises, in order from its tip side, a protrusion 30, a stepped portion 40, and a base portion 50.

[0041] As shown in Figure 2, the protrusion 30 is formed by a planar tip surface 32 perpendicular to the direction of movement of the punch 24, a curved (R-shaped) edge 33 provided on the edge of the tip surface 32, and a side surface 34 formed from the edge 33 toward the base 31 along the direction of movement of the punch 24. In this way, as shown in Figure 3, when the tip of the punch 24 is viewed from its side, the outer shape of the protrusion 30 is formed in a roughly U-shape that opens upwards. Note that the edge 33 may be right-angled instead of curved (R-shaped).

[0042] As shown in Figure 3, the stepped portion 40 is formed on the base 31 side of the convex portion 30 and protrudes outward from the convex portion 30 in a direction intersecting the direction of movement of the punch 24 (left-right direction in Figure 3). When the tip of the punch 24 is viewed from its side, the stepped portion 40 is formed in a tapered shape that slopes toward the opposite side of the convex portion 30 with respect to the direction of movement of the punch 24. The angle θ (i.e., the angle between the outer circumference of the base portion 50 and the stepped portion 40) is preferably as large as possible, within 90°.

[0043] Furthermore, as shown in Figure 4, when the punch 24 is viewed from its tip side, the outer shape of the convex portion 30 (i.e., the edge 33 of the tip surface 32) is formed in a circular shape, and the outer shape of the stepped portion 40 (i.e., the boundary portion 41 between the stepped portion 40 and the main body 50) is also formed in a circular shape.

[0044] When pressing the first workpiece 11 and the second workpiece 12 together using a punch 24 of this shape, as shown in Figure 5, the first workpiece 11 is pressed by the convex portion 30 and then further pressed by the stepped portion 40. This causes the portion of the first workpiece 11 that is pressed by the convex portion 30 and is about to flow in a different direction from the second workpiece 12 (for example, upward or radially), as shown by arrow A, to flow towards the second workpiece 12 by being pressed by the stepped portion 40, as shown by arrow B.

[0045] More specifically, in the first material to be joined 11, there is a portion that flows when pressed in the direction toward the second material to be joined 12 by the tip surface 32 of the protrusion 30 of the punch 24, while at the same time, there is a portion that is pressed by the edge 33 of the protrusion 30 and tends to flow in a direction different from the second material to be joined 12, as shown by arrow A. Therefore, in order to prevent this portion that tends to flow in a direction different from the second material to be joined 12 from continuing to flow in a direction different from the second material to be joined 12, the stepped portion 40 is used to press and flow it in the direction toward the second material to be joined 12, as shown by arrow B.

[0046] In this embodiment, the punch 24 includes a convex portion 30 and a stepped portion 40 that protrudes outward from the convex portion 30. When pressing the first material to be joined 11 and the second material to be joined 12 together, the first material to be joined 11 is pressed by the convex portion 30 while simultaneously being pressed by the stepped portion 40. This causes the portion of the first material to be joined 11 that is pressed by the convex portion 30 and tends to flow in a direction different from that of the second material to be joined 12 to flow in the direction toward the second material to be joined 12 by the stepped portion 40.

[0047] As a result, in the first workpiece 11, not only the portion that flows toward the second workpiece 12 when pressed by the protrusion 30 of the punch 24, but also the portion that would otherwise flow toward the second workpiece 12 when pressed by the protrusion 30 of the punch 24, can be made to flow toward the second workpiece 12 by the stepped portion 40. Furthermore, even in cold pressure welding, the fluidity is improved.

[0048] Therefore, the portion of the first material to be joined 11 that is pressed by the protrusion 30 of the punch 24 can be made to flow in a direction toward the second material to be joined 12 throughout its entirety. Consequently, the pressing of the punch 24 increases the surface area of ​​the joining surface of the first material to be joined 11 and the joining surface of the second material to be joined 12, thereby improving the adhesion of the newly exposed surface at this joining surface. Thus, the bonding force at the joining surface of the first material to be joined 11 and the joining surface of the second material to be joined 12 is increased, improving the bonding strength between the first material to be joined 11 and the second material to be joined 12.

[0049] Here, the applicant performed an evaluation to verify the bonding strength between the first material to be joined 11 and the second material to be joined 12. As a result of this evaluation, the results shown in Figures 6 to 8 were obtained. As shown in Figures 6 to 8, the punch 24 of the first embodiment showed lower conductivity resistance and higher peel strength compared to the conventional punch 124.

[0050] Specifically, with the conventional punch 124, the conductivity resistance significantly exceeded the target value (0.030 mΩ), while with the punch 24 of the first embodiment, the conductivity resistance dropped to approximately the target value of 0.030 mΩ. Furthermore, the peel strength of the first workpiece 11 and the second workpiece 12 when pressed together with the punch 24 of the first embodiment was approximately 3 to 5 times greater than the peel strength of the first workpiece 11 and the second workpiece 12 when pressed together with the conventional punch 124.

[0051] Furthermore, according to this embodiment, when the punch 24 is viewed from its tip side (i.e., the tip surface 32 side), the outer shape of the convex portion 30 is formed in a circular shape, and the outer shape of the stepped portion 40 is also formed in a circular shape.

[0052] This allows the stepped portion 40 to evenly press the first material to be joined 11 in the circumferential direction around the protrusion 30 of the punch 24. As a result, the bonding strength between the first material to be joined 11 and the second material to be joined 12 is improved more effectively.

[0053] Furthermore, according to this embodiment, the stepped portion 40 is formed in a tapered shape such that, when viewed from the side of the punch 24, it is inclined toward the opposite side of the convex portion 30 with respect to the direction of movement of the punch 24.

[0054] As a result, when the portion of the first material to be joined 11 that is pressed by the convex portion 30 of the punch 24 and is about to flow in a direction different from that of the second material to be joined 12 is pressed and forced to flow in the direction toward the second material to be joined 12 by the stepped portion 40, the component force generated at the tapered stepped portion 40 spreads and acts on the first material to be joined 11, thereby increasing the surface pressure at the joint surface of the first material to be joined 11 and the joint surface of the second material to be joined 12. Therefore, the joining force at the joint surface of the first material to be joined 11 and the joint surface of the second material to be joined 12 is increased, and the joint strength between the first material to be joined 11 and the second material to be joined 12 is improved.

[0055] Furthermore, according to this embodiment, the surface of the protrusion 30 is formed by a planar tip surface 32 perpendicular to the direction of movement of the punch 24, and a side surface 34 formed from the edge 33 of the tip surface 32 toward the base 31 side of the protrusion 30 along the direction of movement of the punch 24.

[0056] As a result, by pressing the first material to be joined 11 with the flat tip surface 32 of the convex portion 30 of the punch 24, the first material to be joined 11 and the second material to be joined 12 are pressed together, and the surface pressure acting between the joining surface of the first material to be joined 11 and the joining surface of the second material to be joined 12 can be increased. Therefore, the bonding strength between the first material to be joined 11 and the second material to be joined 12 is improved more effectively.

[0057] Furthermore, as a first modification, as shown in Figure 9, the surface of the protrusion 30 of the punch 24 may be formed in a spherical shape. That is, as shown in Figure 10, when the tip of the punch 24 is viewed from the side, the outer shape of the protrusion 30 may be formed in an arc shape. Note that even if the surface of the protrusion 30 is not spherical, the entire surface may be formed in a curved shape.

[0058] As a result, when pressing with the punch 24 from the first material to be joined 11, the surface area of ​​the joining surfaces of the first material to be joined 11 and the second material to be joined 12 can be increased by changing them from flat surfaces to spherical or curved surfaces. Therefore, the exposure of new surface material (for example, by dividing the oxide film attached to the joining surface and exposing the new surface) can be promoted at the joining surfaces of the first material to be joined 11 and the second material to be joined 12. Consequently, the bonding strength between the first material to be joined 11 and the second material to be joined 12 is improved more effectively.

[0059] Furthermore, as a second modification, as shown in Figures 11 and 12, when the tip of the punch 24 is viewed from its side, a plurality (i.e., two) stepped portions 40 (i.e., a first stepped portion 40A and a second stepped portion 40B) may be formed in the direction of movement of the punch 24, with the intermediate portion 60 in between.

[0060] In this case, the angle θ1 of the first stepped portion 40A and the angle θ2 of the second stepped portion 40B are preferably larger than 90°. Note that angles θ1 and θ2 may be different from each other. Furthermore, three or more stepped portions 40 may be formed in the direction of movement of the punch 24.

[0061] This allows the portion that would otherwise flow in a direction different from the direction toward the second material to be joined 12 when pressed by the protrusion 30 of the punch 24 to flow toward the second material to be joined 12 in multiple stages. As a result, the bonding strength between the first material to be joined 11 and the second material to be joined 12 is improved more effectively.

[0062] As a third modification, as shown in Figure 13, the first material to be joined 11 and the second material to be joined 12 may have protrusions and indentations 70 formed in advance. In this case, when the punch 24 presses from the first material to be joined 11 side, the second material to be joined 12 is restrained by the first material to be joined 11 by the protrusions and indentations 70, so the pressure applied at the joint surface of the first material to be joined 11 and the joint surface of the second material to be joined 12 increases, and the joint strength between the first material to be joined 11 and the second material to be joined 12 is improved.

[0063] (Second example) Next, we will describe the second embodiment, explaining the differences from the first embodiment, and omitting the explanation of the points that are common to both embodiments.

[0064] In this embodiment, as shown in Figure 14, the stepped portion 40 of the punch 24 is formed perpendicular to the direction of movement of the punch 24. That is, as shown in Figure 15, when the tip of the punch 24 is viewed from its side, the stepped portion 40 is formed in a straight line perpendicular to the direction of movement of the punch 24 (left-right direction in the figure).

[0065] Furthermore, as shown in Figure 16, when the punch 24 is viewed from its tip side, the outer shape of the convex portion 30 (i.e., the shape of the base portion 31) is formed in a circular shape, and the outer shape of the stepped portion 40 (i.e., the shape of the boundary portion 41 between the stepped portion 40 and the main body 50) is also formed in a circular shape.

[0066] When pressing the first workpiece 11 and the second workpiece 12 together using a punch 24 of this shape, the first workpiece 11 is pressed by the protrusion 30 and the stepped portion 40, as shown in Figure 17. Then, as shown by arrow C in Figure 17, the portion that is pressed by the protrusion 30 and tends to flow in a direction different from the second workpiece 12 (for example, upward or radially) can be pressed by the stepped portion 40 in the direction toward the second workpiece 12, thereby causing it to flow.

[0067] More specifically, in the first material to be joined 11, there is a portion that flows when pressed by the tip surface 32 of the protrusion 30 of the punch 24 in the direction toward the second material to be joined 12, while as shown by arrow C, there is also a portion that tends to flow in a different direction from the second material to be joined 12 when pressed by the protrusion 30. Therefore, the stepped portion 40 can be used to press and flow this portion that tends to flow in a different direction from the second material to be joined 12 in the direction toward the second material to be joined 12, as shown by arrow D.

[0068] In this embodiment, the stepped portion 40 of the punch 24 is formed perpendicular to the direction of movement of the punch 24. Therefore, the force applied to the first material to be joined 11 toward the second material to be joined 12 by the stepped portion 40 can be increased. As a result, the bonding strength between the first material to be joined 11 and the second material to be joined 12 is improved more effectively.

[0069] Furthermore, as shown in Figures 6 to 8 above, the punch 24 of this second embodiment also exhibits lower conductivity resistance and higher peel strength compared to the conventional punch 124.

[0070] Furthermore, as a first modified example, as shown in Figures 18 and 19, the protrusion 30 of the punch 24 may have a spherical surface. Note that even if the surface of the protrusion 30 is not spherical, it may be formed with a curved surface overall.

[0071] As a second modification, as shown in Figures 20 and 21, when the tip of the punch 24 is viewed from its side, two stepped portions 40 (i.e., a first stepped portion 40A and a second stepped portion 40B) may be formed side by side in the direction of movement of the punch 24 (up and down in the figures), with the intermediate portion 60 in between.

[0072] (Third embodiment) Next, we will describe the third embodiment, explaining the differences from the first and second embodiments, and omitting the explanation of the points that are common to the first and second embodiments.

[0073] In this embodiment, as shown in Figure 22, the base 50 of the punch 24 is formed in the shape of a rectangular parallelepiped, and the outer shape of the cross section perpendicular to the direction of movement of the punch 24 is formed as a rectangle. Thus, as shown in Figure 23, when the punch 24 is viewed from its tip side, the outer shape of the convex portion 30 is formed as a circle, while the outer shape of the stepped portion 40 is formed as a rectangle. The outer shape of the stepped portion 40 may be formed as a polygon other than a rectangle.

[0074] Then, when pressing the first material to be joined 11 and the second material to be joined 12 together using a punch 24 of this shape, as in Figure 17, the portion that is pressed by the convex portion 30 as shown by arrow C and is about to flow in a direction different from the second material to be joined 12 is pressed by the stepped portion 40 as shown by arrow D and made to flow in the direction toward the second material to be joined 12.

[0075] At this time, the portion of the first material to be joined 11 that is pressed by the punch 24 flows as shown by the arrow in Figure 23. That is, the material of the first material to be joined 11 flows from the larger area portion of the stepped portion 40 to the smaller area portion, while the first material to be joined 11 is pressed by the stepped portion 40. As a result, the material of the first material to be joined 11 becomes fluid, so that the portion of the first material to be joined 11 that is pressed by the convex portion 30 and tries to flow in a direction different from that of the second material to be joined 12 can be smoothly pressed and flowed toward the second material to be joined 12 by the stepped portion 40. Therefore, the bonding strength between the first material to be joined 11 and the second material to be joined 12 is improved more effectively.

[0076] Furthermore, as shown in Figures 6 to 8 above, the punch 24 of this third embodiment also exhibits lower conductivity resistance and higher peel strength compared to the conventional punch 124.

[0077] Furthermore, as a first modified example, as shown in Figure 24, the surface of the protrusion 30 of the punch 24 may be formed in a spherical shape. Note that even if the surface of the protrusion 30 is not spherical, the entire surface may be curved.

[0078] As a second modification, similar to Figures 20 and 21, when the tip of the punch 24 is viewed from its side, two stepped portions 40 (i.e., the first stepped portion 40A and the second stepped portion 40B) may be formed side by side in the direction of movement of the punch 24 (up and down in the figure), with the intermediate portion 60 in between.

[0079] In this case, as shown in Figure 25, the outer shape of the first step portion 40A, which is the first step from the convex portion 30 side, may be formed in a circular shape, while the outer shape of the second step portion 40B, which is the second step from the convex portion 30 side, may be formed in a rectangular shape. Alternatively, as shown in Figure 26, the outer shape of the first step portion 40A may be formed in a rectangular shape, and the outer shape of the second step portion 40B may also be formed in a rectangular shape.

[0080] It should be noted that the embodiments described above are merely illustrative examples and do not limit this disclosure in any way. Various improvements and modifications are possible without departing from the gist of the disclosure.

[0081] For example, as shown in Figure 27, the first joined material 11 and the second joined material 12 may be rod-shaped joining materials, and the portion of the first joined material 11 that is pressed by the convex portion 30 and is about to flow in a direction different from that of the second joined material 12 can be pressed by the stepped portion 40 in the direction toward the second joined material 12 and made to flow.

[0082] Furthermore, in the third embodiment, the stepped portion 40 may be formed in a tapered shape such that, when viewed from the side of the punch 24, it is inclined toward the opposite side of the convex portion 30 with respect to the direction of movement of the punch 24.

[0083] Furthermore, the press-fitted body formed by press-fitting the first material to be joined 11 and the second material to be joined 12 can be used for a variety of applications, such as battery terminals (for example, the negative terminal of a secondary battery).

[0084] Furthermore, the materials of the first material to be joined 11 and the second material to be joined 12 are not particularly limited. For example, the materials of the first material to be joined 11 and the second material to be joined 12 may be pure aluminum (A1000 series), aluminum alloys (e.g., A2000 series, A5000 series, 6000 series), pure iron, iron alloys (e.g., S10C~45C, SUS304, SUS316, SUS430), pure titanium (e.g., TB340C), titanium alloys, pure copper (e.g., oxygen-free copper), copper alloys, or other metals.

[0085] The combination of materials for the first material to be joined 11 and the second material to be joined 12 may be a combination of the same type of metal, such as aluminum alloys or iron alloys. Alternatively, the combination of materials for the first material to be joined 11 and the second material to be joined 12 may be a combination of dissimilar metals, such as pure iron and iron alloys (e.g., SUS304, SU316, SUS430, etc.), iron-based metals (pure iron or iron alloys) and aluminum-based metals (pure aluminum or aluminum alloys), titanium-based metals (pure titanium or titanium alloys) and iron-based metals (pure iron or iron alloys), titanium-based metals (pure titanium or titanium alloys) and aluminum-based metals (pure aluminum or aluminum alloys), copper-based metals (pure copper or copper alloys) and iron-based metals (pure iron or iron alloys), or copper-based metals (pure copper or copper alloys) and aluminum-based metals (pure aluminum or aluminum alloys). [Explanation of Symbols]

[0086] 1. Cold welding apparatus 11. First material to be joined 12. Second material to be joined 21 Lifting section 22 Die mounting base 23 Die 24 Punch 25 Material holding plate 26 Springs 30 Convex part 31 Base 32 Tip surface 33 Edge 34 Side view 40 Step section 40A First step section 40B Second step section 41 Boundary 50 Core 60 Middle section 70 Uneven part 124 Punch θ angle θ1 angle θ2 angle A Arrow B Arrow C arrow D arrow

Claims

1. In a pressure welding method in which a first material to be joined and a second material to be joined are placed on top of each other and pressed together with a punch from the side of the first material to be joined, The punch comprises a convex portion and a stepped portion formed on the base side of the convex portion and extending outward from the convex portion in a direction intersecting the direction of movement of the punch, When pressing the first member to be joined and the second member to be joined together, By pressing the first material to be joined with the protrusion and then with the stepped portion, The portion of the first material to be joined that is pressed by the protrusion and is about to flow in a direction different from the second material to be joined is pressed by the stepped portion in a direction toward the second material to be joined and made to flow. A pressure welding method characterized by the following.

2. In the pressure welding method of claim 1, When the punch is viewed from its tip side, The outer shape of the aforementioned protrusion is formed to be circular, Furthermore, the outer shape of the stepped portion is formed in a circular shape. A pressure welding method characterized by the following.

3. In the pressure welding method of claim 1, When the punch is viewed from its tip side, The outer shape of the aforementioned protrusion is formed to be circular, Furthermore, the outer shape of the stepped portion is formed in a rectangular shape. A pressure welding method characterized by the following.

4. In any one of claims 1 to 3, The stepped portion is formed in a tapered shape that is inclined on the opposite side of the convex portion with respect to the direction of movement of the punch. A pressure welding method characterized by the following.

5. In any one of claims 1 to 3, The stepped portion is formed so as to be perpendicular to the direction of movement of the punch. A pressure welding method characterized by the following.

6. In any one of claims 1 to 3, The surface of the aforementioned protrusion is A planar tip surface perpendicular to the direction of movement of the punch, A side surface formed from the edge of the tip surface toward the base side of the protrusion along the direction of movement of the punch, It is formed by A pressure welding method characterized by the following.

7. In any one of claims 1 to 3, The surface of the aforementioned protrusion is formed to be spherical or curved overall. A pressure welding method characterized by the following.

8. In any one of claims 1 to 3, Multiple stepped portions are formed in the direction of movement of the punch. A pressure welding method characterized by the following.

9. In a pressure welding device in which a first material to be joined and a second material to be joined are placed on top of each other and pressed together by a punch from the side of the first material to be joined, The punch comprises a convex portion and a stepped portion formed on the base side of the convex portion and extending outward from the convex portion in a direction intersecting the direction of movement of the punch, When pressing the first member to be joined and the second member to be joined together, By pressing the first material to be joined with the protrusion and then with the stepped portion, The portion of the first material to be joined that is pressed by the protrusion and is about to flow in a direction different from the second material to be joined is pressed by the stepped portion in a direction toward the second material to be joined and made to flow. A pressure welding device characterized by the following.

Images