Welding method

Abstract

To provide a welding method capable of welding the peripheral edge parts of plate materials with high quality and obtaining high joining strength between the plate materials while suppressing the increase of equipment cost and the complication of equipment.SOLUTION: In the method for spot-welding a pair of mutually overlapped plate materials 1113,, an emboss 21 to be a circular shape on the plate surface of the plate material 11 is formed on the peripheral edge part of either one plate material 11 so that the 3R of the emboss is arranged in a region of the radius R or more and the center part or less of the emboss toward the inside of the plate surface from the outer edge of the peripheral edge part. One plate material 111 on which the emboss 21 is formed and the other plate material 13 are overlapped by arranging the emboss 21 between a pair of plate materials. Then, spot welding electrodes 27,29 are energized and welded while being pressed against the pair of plate materials 11,13 at the positions where the embossments 21 are formed.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a welding method. [Background technology]

[0002] There has been a demand for improved occupant safety in vehicles, and for this purpose, the strength of vehicle bodies has been improved. On the other hand, against the backdrop of worsening issues such as global warming, there has been an accelerating movement to improve the fuel efficiency of automobiles. It is known that reducing the weight of vehicle bodies is effective in improving fuel efficiency. Therefore, aluminum alloys are increasingly being used as structural materials for vehicle bodies, replacing conventional steel materials.

[0003] Resistance spot welding is widely used to join aluminum alloys. However, because aluminum alloys have high thermal and electrical conductivity, they require higher pressure and welding current, and shorter welding times, compared to steel. When welding the edges of the welding material (where the weld allowance is short), conventional spot welding causes deformation due to the application of pressure, reducing the current density. As a result, it is generally known that welding becomes impossible or that current shunting can cause unstable formation of the molten zone. The distance from the center of the weld point to the nearest edge of the material at the edge of such materials is defined as the edge distance (JIS Z 3001-6 (2013)).

[0004] Laser welding has generally been used to weld aluminum alloy plates with short edge distances (weld allowances). However, laser welding requires huge equipment costs, and the introduction of safety equipment places restrictions on factory layout.

[0005] Meanwhile, in recent years, it has been discovered that resistance spot welding can also be performed by employing a long, narrow, mountain-shaped embossed projection (see Patent Document 1). Furthermore, in this case, welding can be performed at a position closer to the outer edge of the aluminum alloy plate compared to general-purpose spot welding. When welding at a position closer to the outer edge, weld marks can be made smaller, and the complexity of finishing processing can be suppressed. Furthermore, long, narrow parts such as window frames (sashes) can be joined with a small welding allowance. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4708519 Summary of the Invention [Problem to be solved by the invention]

[0007] However, while resistance spot welding reduces the equipment costs and limitations mentioned above, it can deform the aluminum itself due to heat generated during welding, potentially damaging the aesthetic appearance. Furthermore, the deformation can cause the welding current to shunt, resulting in unstable nugget quality. Furthermore, the technique using emboss projection welding, such as that described in Patent Document 1, imparts an embossed shape to the aluminum plate using a high pressure, which places restrictions on the processing location of the embossed shape.

[0008] Therefore, an object of the present invention is to provide a welding method that can weld the peripheral edges of plate materials with high quality and obtain high joining strength between the plate materials while suppressing increases in equipment costs and the complexity of the equipment. [Means for solving the problem]

[0009] The present invention comprises the following configurations. A welding method for spot welding a pair of overlapping plate materials, comprising: a circular embossment is formed on the peripheral edge of one of the plates, the circular embossment being located on the surface of the plate from the outer edge of the peripheral edge toward the inside of the plate surface, with the emboss center being located in an area of ​​radius R or more and radius 3R or less of the embossment; one of the plate materials on which the embossment is formed and the other of the plate materials are superimposed on each other with the embossment disposed between the pair of plate materials; spot welding electrodes are applied to the embossed portions of the pair of plate materials while applying pressure thereto, thereby welding the plate materials; Welding method. [Effects of the Invention]

[0010] According to the present invention, the peripheral edges of plate materials can be welded with high quality while suppressing increases in equipment costs and the complexity of the equipment, and high joining strength between the plate materials can be obtained. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view showing a part of a joined body formed by spot welding a pair of plate materials. [Figure 2] FIG. 2 is a cross-sectional view of the bonded body taken along line II-II of FIG. [Figure 3] FIG. 3 is a cross-sectional view of the bonded body taken along line III-III shown in FIG. [Figure 4] FIG. 4 is a process explanatory diagram that schematically shows the procedure for spot welding a pair of plate materials together to obtain a joined body. [Figure 5] FIG. 5 is a cross-sectional view of a plate material and a punch and die for forming embossments on the plate material. [Figure 6] FIG. 6 is a plan view of the die as seen from above. [Figure 7] FIG. 7 is a cross-sectional view of a plate material, a punch, and a die showing the state in which the embossment is press-formed. [Figure 8] FIG. 8 is a photograph showing an example of embossment formation. [Figure 9] FIG. 9 is a cross-sectional view showing how one plate material on which an embossment is formed is overlapped with another plate material and spot-welded. [Figure 10] FIG. 10 is an external perspective view showing an example of a spot welding electrode. [Figure 11] FIG. 11 is an explanatory diagram that schematically shows an example of a pressure and current pattern for spot welding. [Figure 12] FIG. 12 is a cross-sectional photograph of the plate material taken along line XII-XII parallel to the outer edge of the plate material shown in FIG. [Figure 13] FIG. 13 shows the result of joining the plate materials corresponding to FIG. 3, and is a cross-sectional photograph of the plate materials cut in the direction from the outer edge of the plate materials toward the inside of the plate surfaces. [Figure 14] FIG. 14 is a photograph showing the appearance of a plate material on which one embossment has been formed. [Figure 15] FIG. 15 is an explanatory diagram showing a plate material on which the same embossing as in Example 1 and the elongated embossing as a comparative example are formed by applying the same pressure. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The welding method described here involves projection spot welding a pair of overlapping plate materials, but the shape, thickness, and other conditions of the plate materials can be changed as appropriate.

[0013] Fig. 1 is a perspective view showing a part of a joined body 100 formed by spot welding a pair of plate materials 11, 13. Fig. 2 is a cross-sectional view of the joined body 100 shown in Fig. 1 taken along line II-II. Fig. 3 is a cross-sectional view of the joined body 100 shown in Fig. 1 taken along line III-III.

[0014] As shown in Fig. 1, the joined body 100 is formed by spot welding a pair of overlapping plate materials 11, 13 at the peripheral portions near the outer edges of the plate surfaces. At the position of a spot weld mark (depression) 15 formed on the plate surfaces, a nugget 17 is formed between the plate materials 11 and 13, as shown in Figs. 2 and 3. The nugget 17 is formed by emboss projection welding, which will be described below, and the nugget center is located within a range W of a predetermined dimension extending from the outer edges of the plate materials 11, 13 toward the inside of the plate surfaces.

[0015] The plates 11 and 13 used here are wrought aluminum or aluminum alloys, and are preferably aluminum alloys of the 5000, 6000, or 7000 series defined by JIS or AA standards. The plates 11 and 13 can be suitably manufactured by an appropriate combination of tempering treatments such as homogenization heat treatment, hot extrusion, solution treatment and quenching, and artificial aging treatment.

[0016] As described above, by spot welding the peripheral edges of the plate materials 11 and 13, it becomes possible to join members having narrow widths together, and the degree of freedom in welding work can be improved.

[0017] 4 is a process explanatory diagram that schematically shows the procedure for spot welding a pair of plate materials 11, 13 together to obtain a joined body 100. First, an embossment 21 is formed on one plate material 11 of the pair of plate materials 11, 13 (St. 1). The embossment 21 can be formed by press molding (such as doweling), but protrusions may also be formed by other methods such as cutting.

[0018] Fig. 5 is a cross-sectional view of the sheet material 11 and the punch 23 and die 25 that form embosses on the sheet material 11. Fig. 6 is a plan view of the die 25 as viewed from above. Two protrusions 23a are formed on the punch 23, and recesses 25a are formed on the die 25 at positions corresponding to the protrusions 23a of the punch 23. Here, there are two pairs of protrusions 23a and recesses 25a, and the respective positions of the pairs are set so that they are located at positions separated from each other within the pressure region (electrode tip surface) of the spot welding electrode described below.

[0019] The flat plate material 11 is placed between the punch 23 and the die 25, and the punch 23 is pressed toward the die 25. As a result, embossments 21 corresponding to the shapes of the convex portions 23a and the concave portions 25a are formed in the plate material 11.

[0020] FIG. 7 is a cross-sectional view of the sheet material 11, punch 23, and die 25 showing the state in which the embossment 21 has been press-formed. The sheet material 11 is formed with the protrusion 23a of the punch 23 and the recess 25a of the die 25 by press-forming to form the embossment 21 protruding from one surface of the sheet material 11 (the lower surface in FIG. 7). While an example in which two embossments 21 are formed at once is shown here, the number of embossments 21 may be one or three or more. The protruding height of the embossment 21 from the sheet surface of the sheet material 11 on the protruding side of the embossment 21 is preferably 0.2 mm or more, more preferably 0.4 mm or more. Furthermore, it is preferably 1.0 mm or less, more preferably 0.8 mm or less. Having the protruding height of the embossment 21 within the above range ensures good nugget formation during spot welding.

[0021] FIG. 8 is a photograph showing an example of the formation of embossments 21. The embossments 21 are formed near the outer edge 11a of the peripheral portion of the sheet material 11, and each have a circular shape on the sheet material surface. Specifically, the centers of the embossments 21 on the sheet material surface (embossment centers) are arranged in an area from the outer edge 11a of the sheet material 11 toward the inside of the sheet material surface (arrow D1) that is equal to or greater than the radius R of the embossment 21 and equal to or less than 3R. The embossments 21 in the area indicated by arrow P1 in FIG. 8 are formed such that the embossment center O is located 1.3 times the radius R of the embossment 21 from the outer edge 11a of the sheet material 11 toward the inside of the sheet material surface. Furthermore, the embossments 21 in the area indicated by arrow P2 are formed such that the emboss center O is located approximately 2R from the outer edge 11a of the sheet material 11.

[0022] By locating the embossing center O of each embossment 21 in an area that is at least R and at most 3R from the outer edge 11a of the plate material 11, the embossment 21 can be positioned close to the outer edge 11a within a range in which the outer peripheral edge 21a of the embossment 21 does not protrude from the outer edge 11a of the plate material 11.

[0023] Furthermore, the distance between the centers of adjacent embossments 21 is preferably two to four times, and more preferably three times, the radius R of the embossments 21. In the case where the distance is two times, the embossments 21 may be adjacent. This makes it easier for the molten parts formed in the embossments 21 to connect with each other during spot welding, which will be described later. Moreover, since the nugget is formed extending along the direction in which the embossments 21 are arranged, the joining area is increased, and the joining strength between the plate materials can be improved.

[0024] 9 is a cross-sectional view showing how one plate material 11 having an embossment 21 formed thereon and the other plate material 13 are overlapped and spot-welded. One plate material 11 having the above-described embossment 21 formed thereon and the other plate material 13 are overlapped with the embossment 21 disposed between the plate materials. Then, the positions where the embossment 21 is formed on the overlapped plate materials 11, 13 are sandwiched between a pair of spot welding electrodes 27, 29, and the plate materials 11, 13 are pressed by the spot welding electrodes 27, 29 (St. 2).

[0025] 10 is an external perspective view showing an example of the spot welding electrodes 27, 29. The spot welding electrodes 27, 29 are "double-sided cut tips" and have an attachment portion 31 having an attachment hole 31a and an electrode tip portion 33 on the opposite side of the attachment portion 31.

[0026] The electrode tip portion 33 is formed by thinning its outer circumferential surface from one side in the diametric direction toward the inside in the radial direction, leaving the electrode center axis Ax. The electrode tip portion 33 has a pair of rectangular side surfaces 33a and a tip surface 33b formed in a substantially rectangular shape. The tip surface 33b is formed as a convex curved surface with a predetermined curvature. The pair of spot welding electrodes 27, 29 are fixed to a chuck mechanism (not shown) with the extension directions of the tip surfaces 33b parallel to each other. The sheet materials 11, 13 are arranged so that the arrangement direction of the two embossments 21 coincides with the extension direction of the tip surface 33b. In other words, the embossments 21 are formed side by side along the outer edge of the sheet material 11.

[0027] 11 is an explanatory diagram schematically illustrating an example of a pressure and current pattern for spot welding. To spot weld plate materials 11, 13, for example, pressure is started at time t0 with pressure P, and current value I is applied from time t1 after the squeeze time has elapsed while maintaining pressure (St. 3). Current (main current) is applied while maintaining pressure from time t1 to t2, and current application ends at time t2. Then, pressure P is continued from time t2 to time t3 after the hold time has elapsed, and pressure is released at time t3. Note that an upslope period may be provided before time t1.

[0028] According to the above-described pressure application and current application pattern, at time t1 in the early stage of welding (St. 3) shown in Fig. 4, the contact points between the tips of the two embossments 21 provided on the sheet material 11 and the sheet material 13 melt, forming two starting points for molten zones. Then, as current is applied toward the later stage of welding (St. 4), the two molten zones grow and expand, and the space between the embossments is filled with molten metal. In other words, the two molten zones merge into one, and at time t2 in the later stage of welding, the molten metal becomes a single lump. At the completion of welding (St. 5), the molten zone solidifies to form a nugget 17.

[0029] As described above, by simultaneously applying pressure and current to the two embossments 21, a single large nugget is formed that includes the positions of the embossments 21 and the area between them. This nugget, which has an expanded melting area, allows the sheet materials 11, 13 to be joined together with higher strength. Furthermore, since the nugget that is formed extends in the aligning direction of the two embossments 21, the joined portion extends along the outer edge 11a of the sheet material 11. Therefore, even when a tensile load is applied to the sheet materials 11, 13 in the thickness direction, peeling between the sheet materials 11, 13 at their peripheral portions can be suppressed, and the peel strength between the sheet materials 11, 13 (for example, lap joint cross tensile strength) can be increased. [Example]

[0030] Next, the results of spot welding when an embossed plate material is overlapped with another plate material will be described. Example 1 (sample material) Material: 6000 series aluminum wrought material Plate thickness: 1.6 mm (upper plate, embossed), 1.2 mm (lower plate, flat) (Embossed) Diameter of the embossing convex part of the punch: 2.57 mm Protruding height of the embossing part of the punch: 0.6 mm Embossing center distance: 3.8 mm (2-point embossing) (Welding conditions) The welding conditions are summarized in Table 1.

[0031] [Table 1]

[0032] Fig. 12 is a cross-sectional photograph of the plate materials 11 and 13 taken along line XII-XII, which is parallel to the outer edge 11a of the plate material 11 shown in Fig. 4. Fig. 13 is a cross-sectional photograph of the plate materials 11 and 13 cut in a direction from the outer edge 11a of the plate material 11 toward the inside of the plate surface, showing the joining result of the plate materials 11 and 13 corresponding to Fig. 3. Note that Figs. 12 and 13 have bold lines indicating the outer edge of the nugget 17.

[0033] As shown in Fig. 12, the nugget 17 was formed extending along the outer edge 11a, and a good melted state was obtained with the embossments 21 melted. Also, as shown in Fig. 13, the nugget 17 did not protrude from the outer edges 11a, 13a of the sheets 11, 13, and no spatter was generated. Furthermore, no surface melting or internal defects were observed on the sheet surface.

[0034] <Example 2> In Example 1, an example in which two embossments 21 are formed on the plate material 11 is shown, but in Example 2, an example in which one embossment 21 is formed on the plate material 11 under the same processing conditions as in Example 1 is shown. FIG. 14 is a photograph of the appearance of a sheet material 11 on which one embossment 21 is formed. Even when the outer peripheral edge 21a of the embossment 21 is arranged near the outer edge 11a of the peripheral portion of the sheet material 11 as in this example, the sheet material 11 does not undergo significant deformation. In both Examples 1 and 2, the emboss shape is circular in a plan view, and deformation during processing is isotropic. Therefore, deformation of the material is less likely to become distortion, and in particular, when the two embossments 21 in Example 1 are arranged closely to each other, this, combined with good weldability, makes it easier to achieve welding closer to the edge of the sheet material.

[0035] <Comparative Example> FIG. 15 is an explanatory diagram showing a plate material on which an embossment 21 similar to that in Example 1 and an elongated embossment 22 as a comparative example were formed by applying the same pressure. In the comparative example, an elongated embossment 22 was formed instead of the circular embossment 21 in Examples 1 and 2 described above. Each embossment 22 was formed so that the center of the embossment was located approximately 2 mm inward from the outer edge 11a of the plate material 11. Each embossment was formed by applying loads of 4 kN and 5 kN using a punch and die (not shown). When the embossment 22 of the comparative example was formed to have a predetermined protruding height, the outer edge 11a of the plate material 11 bulged outward significantly.

[0036] In the embossed shape of this comparative example, the outer edge 11a of the plate material 11 protrudes outward, so that the edges of the plate material 11 are not aligned in a straight line, making it impossible to reproduce the dimensional accuracy at the time of design.

[0037] On the other hand, it was confirmed that the circular embossment 21 similar to that of Example 1 suppressed the bulging of the outer edge 11a of the sheet material 11, and the protrusion height was also good, making it easier to obtain a nugget as designed. In Fig. 15, cases where large deformation of the outer edge 11a of the sheet material 11 was observed are indicated by "x", cases where it was within the allowable range are indicated by "o", and cases where the height of the embossed shape was within the allowable range are indicated by "o".

[0038] The present invention is not limited to the above-described embodiments, and it is also intended that the various components of the embodiments be combined with one another, and that modifications and applications be made by those skilled in the art based on the description in the specification and well-known techniques, and these modifications and applications are included in the scope of protection sought.

[0039] For example, in the above embodiment, an example was shown in which an embossment was formed on the outer peripheral edge of the plate material, but the embossment may also be formed on the inner peripheral edge of an opening formed in the plate material, or along a notch formed in the plate material. In other words, the embossment may be formed anywhere near the edge of the plate material. Furthermore, the number of overlapping plate materials is not limited to two, but may be three or more, and the thickness of each plate material may be the same or different.

[0040] As described above, the present specification discloses the following: (1) A welding method for spot welding a pair of overlapping plate materials, comprising: a circular embossment is formed on the peripheral edge of one of the plates, the circular embossment being located on the surface of the plate from the outer edge of the peripheral edge toward the inside of the plate surface, with the emboss center being located in an area of ​​radius R or more and radius 3R or less of the embossment; one of the plate materials on which the embossment is formed and the other of the plate materials are superimposed on each other with the embossment disposed between the pair of plate materials; spot welding electrodes are applied to the embossed portions of the pair of plate materials while applying pressure thereto, thereby welding the plate materials; Welding method. According to this welding method, since the embossments on the plate materials are circular, the molten portion formed during spot welding occurs and grows isotropically within the plate surface, and a good nugget is formed between the plate materials.

[0041] (2) The welding method according to (1), wherein a plurality of the embossments are formed at positions spaced apart from one another within a pressure region of one of the plate materials applied by the spot welding electrode. According to this welding method, a plurality of embossments are simultaneously pressed by a spot welding electrode, and when current is applied, a molten portion is formed by extending between the embossments.

[0042] (3) The welding method according to (2), wherein the plurality of embossments are two embossments arranged side by side along the outer edge of one of the plate materials. According to this welding method, a nugget is formed that extends in one direction along the outer edge of the plate material so as to connect the two embossments.

[0043] (4) The welding method according to (3), wherein the distance between the centers of adjacent embossments is set to be not less than two times but not more than four times the radius R of the embossment. According to this welding method, by maintaining an appropriate distance between the centers of adjacent embossments, the molten zones formed in each embossment during spot welding are easily connected. Moreover, because the nugget is formed extending along the direction in which the embossments are arranged, the joining area is increased, and the joining strength between the plate materials can be improved.

[0044] (5) The welding method according to any one of (1) to (4), wherein the embossment is formed to protrude from the surface of one of the plates by 0.2 mm to 1.0 mm. According to this welding method, by maintaining an appropriate amount of protrusion of the embossment, good nugget formation is achieved during spot welding. [Explanation of symbols]

[0045] 11,13 Board material 11a, 13a outer edge 15 Spot welding marks 17 Nuggets 21,22 Emboss 21a outer edge 23 Punch 23a Convex part 25 dice 25a Recess 27,29 Spot welding electrodes 31 Mounting part 31a Mounting hole 33 Electrode tip 33a rectangular side 33b Tip surface 100 zygote

Claims

1. A welding method for spot welding a pair of overlapping plate materials, comprising: a circular embossment is formed on the peripheral edge of one of the plates, the circular embossment being located on the surface of the plate from the outer edge of the peripheral edge toward the inside of the plate surface, with the emboss center being located in an area of ​​radius R or more and radius 3R or less of the emboss; one of the plate materials on which the embossment is formed and the other of the plate materials are superimposed on each other with the embossment disposed between the pair of plate materials; spot welding electrodes are applied to the embossed portions of the pair of plate materials while applying pressure thereto, thereby welding the plate materials; Welding method.

2. forming a plurality of the embossments at positions spaced apart from each other within a pressure region of one of the plate materials applied by the spot welding electrode; The welding method according to claim 1 .

3. The plurality of embossments are two embossments arranged side by side along the outer edge of one of the plate materials. The welding method according to claim 2.

4. The distance between the centers of adjacent embossments is set to be not less than two times and not more than four times the radius R of the embossment. The welding method according to claim 3.

5. The embossment is formed by protruding 0.2 mm to 1.0 mm from the plate surface of one of the plate materials. The welding method according to any one of claims 1 to 4.

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