Method for welding resistance spot and welding object

Abstract

To suppress degradation of a welding object that spot-welds outer edges of overlaid two aluminum alloy materials to each other.SOLUTION: When outer edges of overlaid two aluminum alloy materials 24, 25 are spot-welded to each other by energization while being held and pressed by a first electrode 12 and a second electrode 14 that are opposite to each other, the spot-welding is performed while a contact area of the first electrode 12 to the aluminum alloy material 24 becomes larger than a contact area of the second electrode 14 to the aluminum alloy material 25.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a resistance spot welding method and to a workpiece welded by the resistance spot welding method. [Background technology]

[0002] Patent Document 1 below discloses a resistance spot welding method in which two metal plates are sandwiched between a first electrode and a second electrode facing each other, and spot-welded by passing current while applying pressure. The technology described in Patent Document 1 is a method for resistance spot welding a steel material (a material to be welded) and an aluminum or aluminum alloy material (a material to be welded), and at least one of the electrodes has a diameter d of a portion (electrode tip) that contacts the material to be welded, which is smaller than the electrode diameter D and is set to 3.6 mm to 7.5 mm. Normally, when welding aluminum-based materials, a high-current welding power source is required, but the method described in Patent Document 1 below discloses that resistance spot welding is possible using a low-current power source for steel materials. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-224148 A Summary of the Invention [Problem to be solved by the invention]

[0004] There are also cases where two sheets of aluminum alloy material are resistance spot welded together, and problems arise in such cases as well. More specifically, when spot welding the outer edges of two overlapping sheets of aluminum alloy material, the molten aluminum alloy may protrude from between the two sheets of aluminum alloy material and solidify in that state. The presence of this protruding portion (splash) is often unacceptable in terms of quality as a welded body.

[0005] The present invention has been made in consideration of such circumstances, and has an object to suppress deterioration in the quality of a welded body formed by spot welding the outer edges of two overlapping aluminum alloy materials. [Means for solving the problem]

[0006] In order to solve the above problems, the resistance spot welding method disclosed in the present application has the following configuration. (1) A resistance spot welding method in which outer edges of two overlapping aluminum alloy materials are clamped between a first electrode and a second electrode facing each other, and spot welded by passing current through the electrodes while applying pressure, a contact area of ​​the first electrode with the aluminum alloy material being larger than a contact area of ​​the second electrode with the aluminum alloy material;

[0007] In the resistance spot welding method disclosed in the present application (hereinafter, sometimes simply referred to as "welding method"), the contact area of ​​the first electrode with the aluminum alloy material is made larger than the contact area of ​​the second electrode with the aluminum alloy material, so that the area through which a current flows between the first electrode and the second electrode changes, that is, the area through which a current flows in the aluminum alloy material changes. In other words, the current density differs in the sheet thickness direction, and the current density is relatively low on the first electrode side and high on the second electrode side. The higher the current density, the higher the resistance value becomes, and the easier it is to generate heat. In other words, according to the welding method disclosed in the present application, a temperature gradient can be created in the sheet thickness direction of the aluminum alloy material, and it is possible to prevent the aluminum alloy material from melting too much due to heat concentration at a specific location, and to prevent the molten aluminum alloy from protruding from between two sheets of aluminum alloy material and solidifying, i.e., to prevent the so-called generation of dust.

[0008] In the welding method disclosed in the present application, the electrode may have a flat portion at the tip that fits the surface of the aluminum alloy material, or may be formed in a curved (convex) shape. When the tip of the electrode is curved, before pressure is applied, the electrode is in contact with the aluminum alloy material at almost a point, and by applying pressure and passing current, the aluminum alloy material is recessed, and the contact area gradually increases. In consideration of this point, the welding method disclosed in the present application desirably maintains a state in which the contact area of ​​the first electrode is larger than the contact area of ​​the second electrode from the start to the completion of spot welding. For example, by making the first electrode have a flat portion and making the second electrode have a curved shape or a flat portion smaller than the flat portion of the first electrode, the contact area of ​​the first electrode can be made larger than the contact area of ​​the second electrode from the start to the completion of spot welding.

[0009] The resistance spot welding method having the above-described configuration can be modified in various ways as shown below. Note that the present invention is not limited to the following aspects, and can be embodied in various aspects that are modified and improved based on the knowledge of those skilled in the art.

[0010] (2) The first electrode and the second electrode each have a flat portion at a tip thereof, the flat portion being formed flat along a surface of the aluminum alloy material, 2. The resistance spot welding method according to claim 1, wherein the spot welding is started in a state in which a ratio of a contact area of ​​the flat portion of the first electrode to a contact area of ​​the flat portion of the second electrode is 1.4 or more and 10.0 or less.

[0011] According to the welding method of this configuration, the contact area of ​​the first electrode is always larger than the contact area of ​​the second electrode. When both the first electrode and the second electrode are in contact with the aluminum alloy material over the entire area of ​​the flat portion, the contact area before the start of spot welding is the surface area of ​​the flat portion, and if the surface area ratio of the flat portion is within this range, good spot welding can be performed. Incidentally, if the surface area ratio of the flat portion is smaller than 1.4, the generation of spatter cannot be sufficiently suppressed, and if it exceeds 10.0, the temperature gradient is too high, making it difficult to increase the temperature between the two aluminum alloy materials, and sufficient spot welding cannot be performed. In addition, the welding method disclosed in the present application can also perform spot welding in a state in which a part of the flat portion of the first electrode protrudes outward from the outer edge of the aluminum alloy material. In this case, good spot welding can be performed by using the contact area of ​​the flat portion of the first electrode with the aluminum alloy material instead of the surface area of ​​the flat portion, and setting the contact area within the above range.

[0012] In the welding method having this configuration, the contact area ratio before the start of welding is preferably 1.6 to 8.0, and more preferably 1.6 to 3.0. By setting it in this range, no dust is discharged to the end, and a joint state with a good appearance can be obtained, and the nugget on the electrode side with the larger contact area is shallower than the nugget on the other electrode side, making the nugget less noticeable and resulting in a joint state with a better appearance.

[0013] (3) The resistance spot welding method according to (1), wherein the spot welding is performed such that when the spot welding is completed, a ratio of a contact area of ​​the first electrode to a contact area of ​​the second electrode is 1.05 or more and 8.0 or less.

[0014] As described above, the welding method disclosed in the present application can have the tip of the electrode curved. In addition, when welding is performed with an electrode having a relatively small contact area, the electrode bites into the aluminum alloy material during spot welding, as in the case of the tip of the electrode having a curved surface. In other words, the contact area between the electrode and the aluminum alloy material may be larger at the end of welding than at the start of welding. In such a case, good spot welding is performed by making the contact area ratio of the two electrodes at the end of spot welding 1.05 or more and 8.0 or less. In this configuration, the contact area ratio of the two electrodes at the end of spot welding is preferably 1.1 or more and 5.0 or less, and more preferably 1.1 or more and 2.0 or less. By setting it in this range, dust is not discharged to the end, and a good joint state in appearance is obtained, and the nugget on the electrode side with the larger contact area is shallower than the nugget on the other electrode side, so the nugget is less noticeable and a more good joint state in appearance can be obtained.

[0015] (4) The resistance spot welding method according to any one of (1) to (3), wherein the first electrode is a positive electrode and the second electrode is a negative electrode.

[0016] The resistance value is more likely to increase between the positive electrode and the surface of the aluminum alloy material than between the negative electrode and the surface of the aluminum alloy material. According to the welding method having this configuration, the contact area on the positive electrode side is made larger than the contact area on the negative electrode side, so that a temperature gradient is easily generated in the plate thickness direction of the aluminum alloy material, and heat concentration can be effectively suppressed.

[0017] (5) The resistance spot welding method according to any one of (1) to (4), wherein a central axis of the first electrode and a central axis of the second electrode are arranged on the same line.

[0018] According to the welding method having this configuration, no twisting force is applied to the aluminum alloy material when pressure is applied during spot welding, so that it is possible to avoid a situation in which the aluminum alloy material is deformed.

[0019] In order to solve the above problems, the welded body disclosed in the present application has the following configuration. (6) A welded body in which the outer edges of two aluminum alloy materials are welded together by resistance spot welding, In the nugget portion formed by the resistance spot welding, an area of ​​a depression formed in one of the two aluminum alloy materials is larger than an area of ​​a depression formed in the other of the two aluminum alloy materials, A welded body, wherein the area ratio of the one depression to the other depression is 1.05 or more and 8.0 or less.

[0020] Whether or not the welding method disclosed in the present application was used can be determined based on the shape of the nugget portion formed by resistance spot welding. In other words, if the area ratio of the depressions is within the above range, as in the case of the welded body disclosed in the present application, it can be determined that the welded body was welded using the welding method disclosed in the present application. Effect of the Invention

[0021] According to the present invention, it is possible to suppress deterioration in the quality of a welded body formed by spot welding the outer edges of two overlapping aluminum alloy materials. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic diagram of a resistance spot welding machine used in a resistance spot welding method according to an embodiment of the present invention. [Diagram 2] Diagram showing where resistance spot welding is used on an automobile side door [Diagram 3] FIG. 1 is a side cross-sectional view showing a state in which spot welding is being performed in Example 1. [Figure 4] FIG. 1 is a plan view showing a contact portion between a first electrode and a second electrode on an aluminum alloy material in Example 1. [Diagram 5] Thermal analysis results in Example 1 [Figure 6] FIG. 1 is a side cross-sectional view showing a state in which spot welding is being performed in Comparative Example 1. [Figure 7] Thermal analysis results for comparison 1 [Figure 8] FIG. 11 is a side cross-sectional view showing a state in which spot welding is being performed in Example 2. [Figure 9] FIG. 11 is a plan view showing a contact portion between a first electrode and a second electrode on an aluminum alloy material in Example 2. [Figure 10] FIG. 11 is a side cross-sectional view showing a state where spot welding is being performed in Example 3. [Figure 11] FIG. 11 is a plan view showing a contact portion between a first electrode and a second electrode on an aluminum alloy material in Example 3. [Figure 12] Thermal analysis results in Example 2 [Figure 13] Thermal analysis results in Example 3 [Figure 14] Comparison table of Examples 1 to 3 and Comparative Examples 1 and 2 [Figure 15] Thermal analysis results for Comparative Example 2 [Figure 16] FIG. 1 is an enlarged cross-sectional side view of a nugget portion of a welded body welded by a resistance spot welding method according to an embodiment (Comparative Example 1). [Figure 17] FIG. 1 is an enlarged plan view of a nugget portion of a welded body; [Figure 18] FIG. 11 is a side cross-sectional view showing a state in which spot welding is being performed in the resistance spot welding machine of the modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] A resistance spot welding method according to an embodiment of the present invention will be described with reference to Figs. 1 to 17. The resistance spot welding method according to the present embodiment is performed using a resistance spot welding machine 10, the schematic configuration of which is shown in Fig. 1. The resistance spot welding machine 10 includes a pair of electrodes, a first electrode 12 and a second electrode 14, and a welding power source 16 for applying current to the first electrode 12 and the second electrode 14. The first electrode 12 and the second electrode 14 are axially shaped and are arranged coaxially with their tips facing each other. More specifically, the first electrode 12 and the second electrode 14 are arranged such that their central axes overlap on the same straight line. The first electrode 12 and the second electrode 14 are movable relative to each other in the axial direction. More specifically, the first electrode 12 can be moved toward or away from the second electrode 14, and pressure can be applied while the material to be welded is sandwiched between them. The resistance spot welding machine 10 clamps two overlapping workpieces between the first electrode 12 and the second electrode 14, and applies pressure while passing an electric current through them, thereby melting and joining the two workpieces together using heat generated by electrical resistance.

[0024] The resistance spot welding machine 10 according to the present embodiment is used, for example, in a manufacturing process for an automobile side door 20 shown in Fig. 2. Specifically, in a window frame 22 of the side door 20, a portion 22a forming the upper side of the window is made up of two overlapping aluminum alloy materials, and the resistance spot welding machine 10 according to the present embodiment is used, for example, when joining the outer edges of these two aluminum alloy materials 24, 25 (see Fig. 3). Generally, resistance spot welding machines are not good at joining the outer edges of these two aluminum alloy materials, but the resistance spot welding machine 10 according to the present embodiment is capable of joining the outer edges of these two aluminum alloy materials.

[0025] The resistance spot welder 10 according to this embodiment is characterized by the relationship between the pair of electrodes 12, 14, and the shapes of the pair of electrodes 12, 14 will be described first. As shown in Fig. 1, the first electrode 12 and the second electrode 14 each have a circular flat portion 13, 15 at the tip, which is formed flat along the surface of the aluminum alloy material 24, 25 that is the material to be welded. However, the first electrode flat portion 13, which is the flat portion of the first electrode 12 on the positive side, is larger than the second electrode flat portion 15, which is the flat portion of the second electrode 14 on the negative side. Specifically, the outer diameter r of the first electrode flat portion 13 is 1-1 The outer diameter r of the second electrode flat portion 15 2 The outer diameter ratio R r is set to be 1.2 or more and 3.2 or less. Incidentally, a first electrode 12C of Example 3 described later is shown in Fig. 1 as the first electrode.

[0026] In the spot welder 10A according to the first embodiment of the present invention, as shown in FIGS. 3 and 4, the outer diameter r 2 is 6 mm, whereas the outer diameter r 1-1 is set to 8 mm, and the outer diameter ratio R r is said to be 1.33.

[0027] Incidentally, in this embodiment, the flat portions 13, 15 of the first electrode 12 and the second electrode 14 are circular, but this is not limited thereto, and they may be rectangular or polygonal, or the first electrode and the second electrode may have different shapes.

[0028] Here, the problems of conventional resistance spot welding will be described. As shown in FIG. 6, in the resistance spot welding machine 100 of Comparative Example 1, the first electrode 102 and the second electrode 104 have a circular flat portion at the tip, as in the above embodiment. However, the first electrode flat portion 102a and the second electrode flat portion 104a have the same outer diameter (6 mm). When the outer edges of the two aluminum alloy materials 24, 25 are spot-welded by this resistance spot welding machine 100, as shown in FIG. 6 and FIG. 7, heat is concentrated on the portion where the current flows on the opposing surfaces of the two aluminum alloy materials 24, 25, so that the aluminum alloy materials 24, 25 are crushed and the outer edges are expanded, and the contact surface side of the two aluminum alloy materials 24, 25 melts too much, and the molten aluminum alloy protrudes from between the two aluminum alloy materials 24, 25 and resolidifies, which is a problem that so-called dust 106 is generated. The presence of this dust 106 is not acceptable in terms of quality as a window frame 22.

[0029] On the other hand, the resistance spot welder 10 according to the present embodiment has a contact area S 1-1 However, the contact area S of the second electrode 14 with the aluminum alloy material 25 2 Since the width of the first electrode 12 and the second electrode 14 is larger than the width of the first electrode 12, the area through which the current flows between the first electrode 12 and the second electrode 14 changes, that is, the area through which the current flows in the aluminum alloy materials 24, 25 changes. In other words, the current density differs in the thickness direction, and the current density is relatively low on the first electrode 12 side and high on the second electrode 14 side. The higher the current density, the higher the resistance value and the easier it is to generate heat. In other words, according to the resistance spot welding machine 10 of this embodiment, a temperature gradient can be created in the thickness direction of the aluminum alloy materials 24, 25, and it is possible to prevent the opposing surfaces of the aluminum alloy materials 24, 25 from melting too much due to heat concentration at a specific location (the center of the opposing surfaces), and to prevent the molten aluminum alloy from protruding from between the two aluminum alloy materials 24, 25 and solidifying, that is, the generation of so-called dust. Note that FIG. 5 shows the result of a thermal analysis of the resistance spot welding machine 10A of Example 1.

[0030] In addition, the first electrode flat portion 13 on the positive electrode side is larger than the second electrode flat portion 15 on the negative electrode side. As a result, the resistance value is more likely to increase between the first electrode 12 on the positive electrode side and the surface of the aluminum alloy material 24 than between the second electrode 14 on the negative electrode side and the surface of the aluminum alloy material 25. In other words, the contact area S between the first electrode 12 on the positive electrode side and the aluminum alloy material 24 is 1-1 However, the contact area S between the second electrode 14, which is the negative electrode, and the aluminum alloy material 25 is 2 By making the diameter larger, a temperature gradient is easily generated in the thickness direction of the aluminum alloy materials 24, 25, and heat concentration can be effectively suppressed.

[0031] Next, a resistance spot welder 10B according to a second embodiment and a resistance spot welder 10C according to a third embodiment will be described with reference to Figs. 8 to 13. In the resistance spot welder 10B according to the second embodiment and the resistance spot welder 10C according to the third embodiment, the second electrode 14 is the same as that of the resistance spot welder 10A according to the first embodiment, but the first electrodes 12B and 12C are different from the first electrode 12A in the resistance spot welder 10A according to the first embodiment. In detail, the first electrode 12B according to the second embodiment shown in Figs. 8 and 9 and the first electrode 12C according to the third embodiment shown in Figs. 10 and 11 have flat portions 13B and 13C at their tips, similar to the first electrode 12A according to the first embodiment, but the sizes of the flat portions 13B and 13C are different and larger than the first electrode flat portion 13A in the first embodiment. The first electrode flat portion 13C in the third embodiment is larger than the first electrode flat portion 13B in the second embodiment.

[0032] Specifically, the outer diameter r of the first electrode flat portion 13B in Example 2 1-2 The outer diameter r of the first electrode flat portion 13C in the third embodiment is 10 mm, and the outer diameter ratio Rr is 1.67. 1-3 In other words, the surface area ratio R in Example 2 is 19 mm, and the outer diameter ratio Rr is 3.17. S1 is set to 2.78, and the surface area ratio R S1is said to be 10.03.

[0033] However, when the resistance spot welder 10B of the second embodiment and the resistance spot welder 10C of the third embodiment are used, spot welding is performed in a state in which a part of the first electrode flat portion 13B, 13C protrudes outward from the outer edge of the aluminum alloy material 24, 25, as shown in Figs. 8 to 11. In other words, the contact area S between the first electrodes 12B, 12C and the aluminum alloy material 24 is 1-2 ,S 1-3 is different from the surface area of ​​the first electrode flat portions 13B and 13C, and is a contact area ratio R S2 is 2.61 for Example 2 and 7.64 for Example 3. As shown in Fig. 12 and Fig. 13, the thermal analysis confirmed that Example 2 and Example 3 also performed spot welding appropriately without generating any spatter.

[0034] As shown in the comparison table of FIG. 14, the resistance spot welding method of this embodiment uses a contact area ratio (contact area ratio before welding) R S2 However, if the contact area ratio before welding R is at least 1.78 to 7.64, spot welding can be performed appropriately. S2 It was confirmed that good spot welding can be performed when the contact area ratio before welding R is 1.40 or more and 10.00 or less. S2 is preferably 1.60 or more and 8.00 or less, and more preferably 1.60 or more and 3.00 or less. By setting it in this range, dust is not discharged to the end portion, and a bonding state with a good appearance can be achieved. In addition, the nugget of the aluminum alloy material 24 on the first electrode 12 side, which has a larger contact area, is shallower and less noticeable than the nugget of the aluminum alloy material 25 on the second electrode 14 side, and a bonding state with a better appearance can be achieved.

[0035] Even if the tip of the first electrodes 12, 14 is flat, the smaller the contact area before welding, the more the electrodes will bite into the aluminum alloy materials 24, 25 due to pressure and current application. In other words, the contact area between the electrodes 12, 14 and the aluminum alloy materials 24, 25 after welding becomes larger than the contact area before welding. Therefore, as shown in the comparison table of FIG. 14, the contact area ratio (contact area ratio after welding) R S3 If the contact area ratio after welding R is at least 1.14 or more and 4.89 or less, appropriate spot welding can be performed. S3 It was confirmed that good spot welding was performed when the contact area ratio after welding R was 1.05 or more and 8.00 or less. S3 is preferably 1.10 or more and 5.00 or less, and more preferably 1.10 or more and 2.00 or less. By performing spot welding so as to satisfy this range, no dust is discharged to the end portion, and a joint state with a good appearance can be achieved. In addition, the nugget of the aluminum alloy material 24 on the first electrode 12 side, which has a larger contact area, is shallower and less noticeable than the nugget of the aluminum alloy material 25 on the second electrode 14 side, and a joint state with a better appearance can be achieved.

[0036] In addition, when the contact area of ​​the first electrode is made too large (Comparative Example 2 in FIG. 14), specifically, the contact area ratio before welding R S2 If is greater than 10.00, the contact area ratio after welding R S3 When the thermal analysis result is larger than 8.00, as shown in FIG. 15, the temperature gradient is too large, making it difficult to increase the temperature between the two aluminum alloy materials 24, 25, and it was confirmed that sufficient spot welding cannot be performed.

[0037] 16 and 17, a welded body 70 welded using the resistance spot welding method of this embodiment (resistance spot welder 10A of Example 1) is formed by welding the outer edges of two aluminum alloy materials 24, 25 together, and in a nugget portion 72 formed by resistance spot welding, the area of ​​a depression 74 formed in one aluminum alloy material 24 is larger than the area of ​​a depression 75 formed in the other aluminum alloy material 25. If the area ratio of the depression 74 on one side to the depression 75 on the other side is 1.05 or more and 8.00 or less, it can be determined that the welded body has been joined by the resistance spot welding method of this embodiment.

[0038] <Other embodiments> The present invention is not limited to the above-described embodiment, and can be embodied in various forms with various modifications and improvements based on the knowledge of those skilled in the art. For example, the following embodiments are also included within the technical scope of the present invention.

[0039] In the resistance spot welding machine 10 of the above embodiment, the second electrode 14 has the flat portion 15 at the tip, but as shown in Fig. 18, the second electrode 120 may have an upwardly convex curved shape. In this case, when the second electrode 120 initially comes into contact with the aluminum alloy material 25, the contact is almost at a point, and spot welding can be performed in a state in which the contact area of ​​the first electrode 12 with the aluminum alloy material 24 is always larger than the contact area of ​​the second electrode 120 with the aluminum alloy material 25. In this configuration, good spot welding can be performed by setting the ratio of the contact area of ​​the first electrode 12 to the contact area of ​​the second electrode 120 to be 1.05 or more and 8.00 or less when the spot welding is completed.

[0040] In the above embodiment, the contact area of ​​the first electrode 12 on the positive side with the joined material is larger than the contact area of ​​the second electrode 14 on the negative side with the joined material, but the contact area of ​​the electrode on the negative side may be larger than the contact area of ​​the electrode on the positive side. [Explanation of symbols]

[0041] REFERENCE SIGNS LIST 10...resistance spot welding machine, 12...first electrode, 13...first electrode flat portion, 14...second electrode, 15...second electrode flat portion, 24, 25...aluminum alloy material, 70...workpiece to be welded, 72...nugget portion, 74...dent, 75...dent

Claims

1. A resistance spot welding method in which outer edges of two overlapping aluminum alloy materials are clamped between a first electrode and a second electrode opposed to each other, and spot welded by passing current through the electrodes while applying pressure, comprising the steps of: a contact area of ​​the first electrode with the aluminum alloy material being larger than a contact area of ​​the second electrode with the aluminum alloy material;

2. the first electrode and the second electrode have, at their tips, flat portions formed flat along the surfaces of the aluminum alloy material; 2. The resistance spot welding method according to claim 1, wherein the spot welding is started in a state in which a ratio of a contact area of ​​the flat portion of the first electrode to a contact area of ​​the flat portion of the second electrode is 1.4 or more and 10.0 or less.

3. 2. The resistance spot welding method according to claim 1, wherein the spot welding is performed such that when the spot welding is completed, a ratio of a contact area of ​​the first electrode to a contact area of ​​the second electrode is 1.05 or greater and 8.00 or less.

4. The resistance spot welding method according to claim 1 , wherein the first electrode is a positive electrode and the second electrode is a negative electrode.

5. The resistance spot welding method according to claim 1 , wherein a central axis of the first electrode and a central axis of the second electrode are aligned on the same line.

6. A welded body in which outer edges of two aluminum alloy materials are welded together by resistance spot welding, In the nugget portion formed by the resistance spot welding, an area of ​​a depression formed in one of the two aluminum alloy materials is larger than an area of ​​a depression formed in the other of the two aluminum alloy materials, A welded body, wherein the area ratio of the one depression to the other depression is 1.05 or more and 8.00 or less.

Images