JP5836248B2 - Spot welding method - Google Patents

Description

  The present invention relates to a spot welding method, and in particular, a thin steel plate is further superposed on one of two superposed thick steel plates, and these steel plates are sandwiched between a pair of electrodes and energized under pressure to spot these steel plates. It relates to a method of welding.

  In general, spot welding is used for welding the stacked steel plates. This welding method uses the resistance heating of the steel plate that is generated by passing the welding current in the plate thickness direction while directly pressing the two stacked steel plates between the upper and lower electrode tips and applying pressure. Have gained a part. That is, when an electric current is passed, a melted portion of both steel plates called a welding nugget (hereinafter referred to as “nugget”) is formed at the contact point of both steel plates, and both steel plates are welded in a spot shape by this nugget.

  However, when spot welding is performed by further superimposing a thin steel plate on one of the two thick steel plates, the ratio of the total thickness of the thin steel plate and the two thick steel plates to the thin steel plate is about 4 times or more. As a result, there is a problem that the nugget is not sufficiently formed between the thin steel plate and the thick steel plate adjacent to the thin steel plate, and a predetermined welding strength cannot be obtained.

  In Patent Document 1, in order to solve this problem, a hollow frustoconical convex portion having a seat surface that is one step higher than the general portion is formed at a portion to be welded of a thin steel plate, and the thin electrode of the pair of electrodes is thin. The electrode facing the steel plate is formed with a spherical tip, and at the initial stage of welding, the thin steel plate and the adjacent thick steel plate are welded by crushing the convex portion of the thin steel plate with low pressure, and then with high pressure. A method of welding two thick steel plates is disclosed.

JP 2003-71569 A

  However, the spot welding described in Patent Document 1 has a problem that unevenness remains on the surface of a thin steel plate after welding because the convex portion having a hollow truncated cone shape is crushed by a spherical electrode.

  Therefore, an object of the present invention is to provide a spot welding method capable of forming a good nugget between a thin steel plate and an adjacent thick steel plate and finishing the surface of the thin steel plate after welding flat.

In the spot welding method of the present invention, a thin steel plate is further superposed on one of two superposed thick steel plates, and these steel plates are sandwiched between a pair of welding electrodes and are energized under pressure to spot weld these steel plates. In the method, a concave portion is formed on one surface of a thick steel plate, and a convex portion is formed on the other surface. The thin steel plate is overlapped on two thick steel plates so that the convex portion is in contact with the thin steel plate. A thin steel plate and an adjacent thick steel plate are welded by energizing with a low pressure while the steel plate is sandwiched between a pair of welding electrodes so as to cover the entire concave and convex portions of the thick steel plate. The method is characterized in that two thick steel plates are welded to each other by energizing with high pressure.

  According to the present invention, when a thin steel plate is further superposed on one of two superposed thick steel plates, and these steel plates are spot welded, a good nugget is formed between the thin steel plate and the adjacent thick steel plate. In addition, sufficient welding strength can be obtained, and the surface of the thin steel plate after welding can be finished flat.

It is a figure which shows the spot welding method by the 1st Embodiment of this invention. It is a top view which shows the arrangement | positioning relationship between the welding electrode 11 and the thin steel plate Wa. It is sectional drawing corresponding to the XX line of FIG. 2 when welding the thin steel plate Wa and the adjacent thick steel plate Wb. It is sectional drawing corresponding to the XX line of FIG. 2 when welding the two thick steel plates Wb and Wc. It is a figure which shows the spot welding method by the 2nd Embodiment of this invention. It is a top view which shows the arrangement | positioning relationship between the welding electrode 11 and the thick steel plate Wb. It is sectional drawing corresponding to the XX line of FIG. 6 when welding the thin steel plate Wa and the adjacent thick steel plate Wb.

<First Embodiment>
Hereinafter, an embodiment of a spot welding method according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a welding apparatus 10 used in the spot welding method of the present embodiment, and a thin steel plate Wa and thick steel plates Wb and Wc which are members to be welded.

  The welding apparatus 10 includes a pair of welding electrodes 11 and 12, a cylinder 13 that supports one welding electrode 12 and can pressurize a member to be welded with the welding electrodes 11 and 12, and pressure of air supplied to the cylinder 13. A pressure switching device 14 capable of switching the pressure by adjusting the pressure, a commercial AC power supply 15 of 50 Hz, for example, a welding transformer 16 capable of supplying a welding current to the welding electrodes 11 and 12 using the commercial AC power supply 15 as a power source, A welding current control device 17 capable of arbitrarily controlling the welding current supplied to the welding electrodes 11 and 12 is configured.

  The pair of welding electrodes 11 and 12 are positioned so as to face each other with a predetermined interval, one welding electrode 11 is supported by a cylinder 13 so as to be movable, and the other welding electrode 12 is fixed. . The welding electrodes 11 and 12 are preferably formed with flat or spherical tip surfaces 11a and 12a, respectively, in order to finish the surface of a thin steel plate flat.

  The cylinder 13 has a movable part that can be moved in the direction of the other welding electrode 12 by pressurized air, and is configured to be able to support the one welding electrode 11 in this movable part. Thereby, when the movable part is moved by the pressurized air supplied from the air source, the welding electrode 11 can be moved in the direction of the welding electrode 12.

  The welding current control device 17 is configured to be able to control the value of the welding current supplied to the pair of welding electrodes 11 and 12 in synchronization with the change in the pressing force of the pressing force switching device 14. In this embodiment, the thin steel plate Wa and the adjacent thick steel plate Wb are welded by supplying a welding current of, for example, 8000 to 10000 A to the welding electrodes 11 and 12 with a low pressurizing force. For example, two thick steel plates Wb and Wc are welded to each other by supplying a welding current of 8000 to 10000 A to the welding electrodes 11 and 12. By configuring the welding device 10 in this way, a thin steel plate Wa, thick steel plates Wb and Wc can be sandwiched between the pair of welding electrodes 11 and 12, and can be energized under pressure. A predetermined welding current can be passed.

  Next, the structure of the thin steel plate Wa will be described with reference to FIGS. A portion to be welded of the thin steel plate Wa is formed with a recess 20 on one surface by hitting the tip of the punch against one surface of the thin steel plate Wa by, for example, a punching method, and a recess on the other surface. The convex part 21 corresponding to 20 is formed.

  Then, the thin steel plate Wa is superposed on the two thick steel plates Wb and Wc so that the convex portion 21 of the thin steel plate Wa is in contact with the adjacent thick steel plate Wb, and the concave portion 20 and the convex portion of the thin steel plate Wa are the welding electrodes 11. These steel plates are sandwiched between a pair of welding electrodes 11 and 12 so as to cover the entire area 21. In this case, as shown in FIG. 2, the distal end surface 11 a of the welding electrode 11 has a diameter that covers the entire recess 20 and projection 21.

  Then, the pressure of the air supplied to the cylinder 13 is adjusted to a low pressure by the pressurizing force switching device 14, a low pressurizing force (for example, 0.7 to 1.0 KN) is applied to the welding electrode 11, and the current is thin. The first welding for welding the steel plate Wa and the adjacent thick steel plate Wb is performed. The energization time at this time is, for example, 5 cycles.

  At this time, the two thick steel plates Wb and Wc are brought into close contact with each other by the pressure of the welding electrode 11, and the thick steel plate Wb adjacent to the thin steel plate Wa is brought into contact with high resistance via the convex portion 21 of the thin steel plate Wa. become. For this reason, a welding current concentrates on the contact part of this convex part 21 and the thick steel plate Wb, and this contact part and its peripheral part melt and solidify, thereby forming a good nugget 22 as shown in FIG. Sufficient weld strength can be obtained.

  Since the convex portion 21 of the thin steel plate Wa exists at the initial stage of welding, a gap is generated between the thin steel plate Wa and the adjacent thick steel plate Wb. However, since the convex portion 21 is then melted, the thin steel plate Wa is finally formed. And the thick steel plate Wb adjacent to each other without any gap. Further, the concave portion 20 of the thin steel plate Wa is flattened to some extent by the applied pressure of the welding electrode 11.

Thereafter, the pressure of the air supplied to the cylinder 13 is adjusted to a high pressure by the pressure switching device 14, a high pressure (for example, 3.0 to 5.0 KN) is applied to the welding electrode 11, and the current 2 is applied. A second welding for welding the thick steel plates Wb and Wc is performed. The energization time at this time is set longer than the first energization time in order to ensure the welding strength between the two thick steel plates Wb and Wc, and is, for example, 20 cycles.
As a result of the second welding, as shown in FIG. 4, a nugget 23 is formed at the contact point between the two thick steel plates Wb and Wc. If the nugget 23 is large, the nugget 22 is brought into contact with the nugget 22 formed by the first welding, and both are integrated. In the second welding, since a high pressing force is applied to the welding electrode 11, the concave portion 20 of the thin steel plate Wa is almost completely flattened. In this case, in order to flatten the concave portion 20 of the thin steel plate Wa, it is preferable that the tip surfaces 11a and 12a of the welding electrodes 11 and 12 are each formed as a flat surface or a spherical surface as described above.

  In order to form the nugget 23 large in a short time, it is preferable that the welding current control device 17 sets the welding current for the second welding to be larger than the welding current for the first welding.

  As described above, according to the spot welding method according to the first embodiment of the present invention, the thin steel plate Wa is further superposed on one of the two superposed thick steel plates Wb and Wc, and these steel plates are spot welded. In this case, a good nugget 22 can be formed between the thin steel plate Wa and the adjacent thick steel plates Wb and Wc to obtain sufficient welding strength, and the surface of the thin steel plate Wa after welding can be finished flat.

<Second Embodiment>
In the spot welding method according to the first embodiment, the concave portion 20 and the convex portion 21 are formed on the thin steel plate Wa. However, in the spot welding method according to the present embodiment, the concave portion 24 is not formed on the thick steel plate Wb but on the thick steel plate Wb. And the point which forms the convex part 25 differs. Other configurations are the same as those of the first embodiment.

  The configuration of the thick steel plate Wb will be described with reference to FIGS. 5 and 6. For example, by punching a portion of the thick steel plate Wb against one surface of the thick steel plate Wb by a punching method. The concave portion 24 is formed on one surface, and the convex portion 25 corresponding to the concave portion 24 is formed on the other surface.

  Then, the thin steel plate Wa is superposed on the two thick steel plates Wb and Wc so that the convex portion 25 of the thick steel plate Wb comes into contact with the thin steel plate Wa, and the concave portions 24 and the convex portions 25 of the thick steel plate Wa are formed. These steel plates are sandwiched between a pair of welding electrodes 11 and 12 so as to cover the whole. In this case, as shown in FIG. 6, the front end surface 11a of the welding electrode 11 has a diameter that covers the entire recess 24 and projection 25 as viewed from the upper surface of the thin steel plate Wa.

  Then, similarly to the first embodiment, the pressure of the air supplied to the cylinder 13 is adjusted to a low pressure by the pressure switching device 14, and a low pressure (for example, 0.7 to 1.0 KN) is applied to the welding electrode 11. ) And applying current, the first welding for welding the thin steel plate Wa and the adjacent thick steel plate Wb is performed. The energization time at this time is, for example, 5 cycles.

  At this time, the two thick steel plates Wb and Wc are in close contact by the pressure of the welding electrode 11 except for the concave portion 24 of the thick steel plate Wb, and the thick steel plate Wb adjacent to the thin steel plate Wa is a convex portion of the thick steel plate Wb. It will contact with high resistance via 25. For this reason, the welding current concentrates on the contact portion between the convex portion 25 and the thin steel plate Wa, and the contact portion and its peripheral portion melt and solidify, thereby forming a good nugget 22 as shown in FIG. Sufficient weld strength can be obtained.

  Since the convex portion 25 of the thick steel plate Wb exists at the initial stage of welding, a gap is generated between the thin steel plate Wa and the adjacent thick steel plate Wb, but the convex portion 25 is then melted. And the thick steel plate Wb adjacent to each other without any gap. Further, the concave portion 24 of the thick steel plate Wb is flattened to some extent by the applied pressure of the welding electrode 11.

  Thereafter, the pressure of the air supplied to the cylinder 13 is adjusted to a high pressure by the pressure switching device 14, a high pressure (for example, 3.0 to 5.0 KN) is applied to the welding electrode 11, and the current 2 is applied. A second welding for welding the thick steel plates Wb and Wc is performed. The energization time at this time is set longer than the first energization time in order to ensure the welding strength between the two thick steel plates Wb and Wc, and is, for example, 20 cycles.

  As a result of the second welding, as in the first embodiment, as shown in FIG. 4, a nugget 23 is formed at the contact point between the two thick steel plates Wb and Wc. At this time, the concave portion 24 of the thick steel plate Wb is absorbed into the nugget 23 and disappears. If the nugget 23 is large, the nugget 22 is brought into contact with the nugget 22 formed by the first welding, and both are integrated.

  According to this embodiment, the uneven | corrugated | grooved part is not formed in the thin steel plate Wa, but the surface is originally flat. In order to maintain the flatness of the thin steel plate Wa even after welding, it is preferable that the welding electrodes 11 and 12 have their tip surfaces 11a and 12a formed as a flat surface or a spherical surface, respectively.

  In order to form the nugget 23 large in a short time, it is preferable that the welding current control device 17 sets the welding current for the second welding to be larger than the welding current for the first welding.

  As described above, according to the spot welding method according to the second embodiment of the present invention, the thin steel plate Wa is further superposed on one of the two superposed thick steel plates Wb and Wc, and these steel plates are spot-welded. In this case, a good nugget 22 can be formed between the thin steel plate Wa and the adjacent thick steel plates Wb and Wc to obtain sufficient welding strength, and the surface of the thin steel plate Wa after welding can be finished flat.

  The spot welding method of the present invention can be applied to both the case where the thin steel plate Wa and the thick steel plates Wb, Wc are plated steel plates (aluminum plated steel plates, galvanized steel plates, etc.) or non-plated steel plates. it can.

  In addition, a welding gun such as a robot gun or a servo spot gun can be used in place of the welding apparatus 10 for carrying out the spot welding method of the present invention.

DESCRIPTION OF SYMBOLS 10 Welding apparatuses 11 and 12 Welding electrode 13 Cylinder 14 Force-switching apparatus 15 Commercial alternating current power supply 16 Welding transformer 17 Welding current control apparatus 20 Concave part 21 of thin steel plate Wa Convex part 22, 23 of thin steel plate Wa Nugget 24 Concave part of thick steel plate Wb 25 Convex portion Wa of thick steel plate Wb Thin steel plate Wb, Wc Thick steel plate

Claims (3)

In a method of spot welding these steel plates by further superimposing a thin steel plate on one of the two thick steel plates superimposed, and sandwiching these steel plates with a pair of welding electrodes and applying energization under pressure,
A thick steel plate is formed with a concave portion on one surface and a convex portion on the other surface, and the thin steel plate is superposed on two thick steel plates so that the convex portion is in contact with the thin steel plate. With these steel plates sandwiched between a pair of welding electrodes so as to cover the entire concave and convex portions, a thin steel plate and an adjacent thick steel plate are welded by energizing with a low pressure, and after the welding, A spot welding method characterized in that two thick steel plates are welded together by energizing with pressure. The spot welding method according to claim 1 , wherein, of the pair of welding electrodes, a tip surface of the welding electrode facing a thin steel plate is formed as a flat surface or a spherical surface. 3. The spot welding method according to claim 1 or 2 , wherein a convex portion is formed on one surface of the thick steel plate and a concave portion is formed on the other surface by punching the thick steel plate.

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