Welding method

Abstract

To provide a welding method capable of simply performing stacked joining of plate materials of different kinds with joining strength maintained.SOLUTION: A welding method is performed by holding and pressurizing a plurality of plate-like workpieces of different kinds in a stacked state between a pair of opposing welding electrodes 3, 4, and by applying a welding current between the welding electrodes 3, 4. At least one of the pair of welding electrodes 3, 4 is rotated in a prescribed period including at least part of the application period of the welding current.SELECTED DRAWING: Figure 10

Description

Technical Field

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[0001] The present invention relates to a welding method. More specifically, it relates to a welding method in which a plurality of plate-shaped workpieces to be welded are stacked and pressure-held between a pair of opposing electrodes, and an electric current is passed between the pair of electrodes to join the plurality of plate-shaped workpieces to be welded.

Background Art

[0002] This type of welding method is called spot welding, and as shown in, for example, Patent Document 1, it is performed using a welding gun having a pair of welding electrodes facing each other, and has conventionally been suitably used for lap joining of steel plates.

[0003] In recent years, for example, in the field of vehicle manufacturing, due to requirements such as weight reduction, there are cases where plates of different materials are stacked and joined. For example, in the lap joining of a steel plate and an aluminum alloy plate, when a conventional general spot welding method is used, there is a problem that brittle intermetallic compounds are formed at the interface and stable joint strength cannot be maintained.

[0004] As a method for joining a steel plate and an aluminum alloy plate while obtaining the required joint strength, for example, there is a laser welding method. However, when using the laser welding method, special equipment for laser oscillation and a huge amount of electric power are required, and it is impossible to meet the demand for cost reduction.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] This invention was conceived under the circumstances described above, and its objective is to provide a welding method that can easily perform overlapping and joining of dissimilar plate materials while maintaining joint strength. [Means for solving the problem]

[0007] To solve the above problems, the present invention employs the following technical means.

[0008] In other words, the welding method provided by the present invention is a welding method in which a plurality of different plate-shaped workpieces to be welded are pressed and clamped in an overlapping state between a pair of welding electrodes facing each other, and a welding current is passed between the two welding electrodes, characterized in that at least one of the pair of welding electrodes is rotated for a predetermined period of time that includes at least a part of the period during which the welding current is passed. [Effects of the Invention]

[0009] According to the welding method of the present invention, the molten or semi-molten material and intermetallic compound generated near the interface of dissimilar plate-shaped workpieces by the application of welding current are stirred by the rotation of the welding electrode, thereby forming a joint in which the influence of the brittleness of the intermetallic compound is eliminated or reduced. As a result, overlapping joints of dissimilar plate-shaped workpieces can be performed at a low cost while maintaining the required welding strength, using simple equipment for spot welding.

[0010] Other features and advantages of the present invention will become more apparent from the detailed description below with reference to the drawings. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of a welding apparatus for carrying out the method of the present invention. [Figure 2] This is a front view of the upper electrode. [Figure 3] This is a bottom view of the upper electrode. [Figure 4] This is a longitudinal cross-sectional view of the lower electrode. [Figure 5]This is a plan view of the lower electrode (viewed in the direction of the VV arrow in Figure 4). [Figure 6] This is a plan view showing another form of the lower electrode. [Figure 7] This is an explanatory diagram of the operation of the method of the present invention. [Figure 8] This is an explanatory diagram of the operation of the method of the present invention. [Figure 9] This is an explanatory diagram of the operation of the method of the present invention. [Figure 10] This is an explanatory diagram of the operation of the method of the present invention. [Modes for carrying out the invention]

[0012] Preferred embodiments of the present invention will be described in detail below with reference to the drawings.

[0013] Figures 1 to 4 show an overview of a spot welding machine 1 for carrying out the welding method according to the present invention.

[0014] As shown in Figure 1, the spot welding machine 1 has a welding gun 2 whose position is controlled in three dimensions by a robot (not shown). The welding gun 2 has an upper electrode 3 and a lower electrode 4. The upper electrode 3 and the lower electrode 4 are arranged opposite each other on the same axis L. The upper electrode 3 is made to move forward and backward in the direction of axis L by a pressurizing actuator such as a cylinder 21, and is also made to be rotatable around axis L by a rotation mechanism 31. The lower electrode 4 is also made to be rotatable around axis L by a rotation mechanism 41. The rotational drive direction of the upper electrode 3 is in the opposite direction to the rotational drive direction of the lower electrode 4. As a result, the spot welding machine 1 can advance the upper electrode 3 to clamp a stack of multiple plates to be welded 5 (Figures 7 and 8) between it and the lower electrode 4 with a predetermined pressure, then pass a predetermined welding current between the two electrodes 3 and 4, and rotate either or both of the upper electrode 3 and the lower electrode 4 around the axis L.

[0015] In the embodiment shown in the figure, the tip form of the upper electrode 3 is different from the tip form of the lower electrode 4. This is, as shown in Fig. 7, a tip form suitable for the assumption that a steel plate 51 is overlapped on the upper electrode 3 side (upper side) and an aluminum alloy plate 52 is overlapped on the lower electrode 4 side (lower side) and they are welded together.

[0016] Specifically, the tip form of the upper electrode 3 has a form in which a plurality of ridges 34 extending in a spiral radial direction are formed on the normal plane 33 of the substantially conical tip surface 32, as well represented in Figs. 2 and 3. The inclination angle θ of the normal plane 33 is, for example, 15.5°.

[0017] On the other hand, the tip shape of the lower electrode 4 has an outer diameter slightly larger than the outer diameter of the upper electrode 3, and has a gentle convex portion 42 protruding in the axial direction near the outer periphery, and a gentle convex portion 43 having a smaller protrusion amount than the convex portion 42 near the outer periphery at the central portion, as well represented in Figs. 4 and 5. The convex portion 42 near the outer periphery may be an annular convex portion 42 as shown in Fig. 5, or may be a plurality of convex portions 42 spaced apart in the circumferential direction as shown in Fig. 6.

[0018] In the case of this embodiment, the polarities of the upper electrode 3 and the lower electrode 4 are preferably such that the upper electrode is the - (minus) pole and the lower electrode is the + (plus) pole.

[0019] Next, referring to Figs. 7 to 10, one form of the welding method according to the present invention will be described.

[0020] A superimposed body 5, with a steel plate 51 positioned on top and an aluminum alloy plate 52 on the bottom, is placed between the upper electrode 3 and the lower electrode 4 (Figure 7). The upper electrode 3 is moved downward to sandwich the superimposed body 5 between the two electrodes 3 and 4, and the upper electrode 3 is pressed against the surface of the steel plate 51 with constant pressure (Figure 8). As a result, the conical tip surface 32 of the upper electrode 3 is embedded into the surface of the steel plate 51 (at the same time, the convex portion 42 near the outer circumference of the lower electrode 4 is also embedded into the lower surface of the aluminum alloy plate 52). When a welding current is passed between the upper electrode 3 and the lower electrode 4 at a predetermined timing, a molten portion 6 is created inside the superimposed body 5 in the thickness direction, and this molten portion 6 grows in the entire thickness direction of the superimposed body 5 (Figure 9). In this embodiment, the lower aluminum alloy plate 52 has superior heat dissipation compared to the upper steel plate 51, and the electron path E tends to converge from the protrusion 42 near the periphery of the lower electrode 4 towards the top of the conical tip surface 32 of the upper electrode 3. As a result, the molten portion 6 grows from the inside of the steel plate 51 in the thickness direction to the entire thickness direction of the superimposed body 5. At this time, a brittle intermetallic compound 7 is formed at the interface between the steel plate 51 and the aluminum alloy plate 52.

[0021] Next, as the molten portion 6 grows and the surface of the steel plate 51 turns red with heat, reaching a semi-molten state, the upper electrode 3 is rotated around the axis L (Figure 10). This rotational force reaches the interior of the molten portion 6, causing it to twist and stir in a spiral manner together with the intermetallic compound 7. This disperses the intermetallic compound 7, forming a joint 6a that eliminates or reduces the effects of its brittleness. As a result, it is possible to perform overlapping joining of the steel plate 51 and the aluminum alloy plate 52 at a low cost while maintaining the required weld strength, using simple equipment for spot welding. In this embodiment, the tip surface 32 of the upper electrode 3 is conical, and radial protrusions 34 are provided on the slope surface, so that the rotational force of the upper electrode 3 is effectively transmitted, and the twisting and stirring of the molten portion 6 can be effectively performed.

[0022] In the welding method described above, the period during which the upper electrode 3 is rotated is started within the period during which the welding current is applied, but it may also be ended within the application period, or the rotation may be continued for a while after the application period has ended.

[0023] Furthermore, although only the upper electrode 3 was rotated in the welding method described above, both the upper electrode 3 and the lower electrode 4 may be rotated. In this case, the rotation directions of the upper electrode 3 and the lower electrode 4 are opposite to each other.

[0024] Of course, the present invention is not limited to the embodiments described above, and any modifications within the scope of the claims are included within the scope of the present invention.

[0025] For example, in the above embodiment, a steel plate 51 and an aluminum alloy plate 52 were joined by overlapping them, but the method of the present invention can be applied to joining various dissimilar plate materials, such as a steel plate and a conductive resin plate, or an aluminum alloy plate and a conductive resin plate. [Explanation of Symbols]

[0026] L axis E electronic path 1 Spot welding machine 2. Welding gun 21 Cylinders 3 Upper electrode 31 Rotation mechanism 32 Tip surface 33 Slope 34 Convex Strip 4 Lower electrode 41 Rotation mechanism 42. Convex portion (near the outer edge) 43. Convex part (center) 5 Superposition 51 Steel plate 52 Aluminum alloy plate 6. Molten part 6a Joint 7 Intermetallic compounds

Claims

[Claim 1] A welding method in which multiple dissimilar plate-shaped workpieces are stacked and pressed together along the axis between a pair of welding electrodes facing each other in the axial direction, and a welding current is passed between the two welding electrodes, A welding method characterized in that, for a predetermined period including at least a portion of the energizing period of the welding current, at least one of the pair of welding electrodes is rotated around the axis, and the tip of the welding electrode rotated around the axis is substantially conical.

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