JP5267320B2 - Steel plate lap welding method and steel plate lap weld joint - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lap welding method for steel sheets for lap-welding a plurality of steel sheets including a steel sheet having relatively small sheet thickness with high joining strength, and to provide a lap-welded joint for steel sheets. <P>SOLUTION: The lap welding method for steel sheets comprises: a spot welding stage where in a state that a surface side steel sheet 1a and high sheet thickness steel sheets 1b, 1c having sheet thickness higher than that of the surface side steel sheet 1a are lapped in such a manner that the surface side steel sheet 1a is arranged at a surface side, the steel sheets 1a to 1c are spot-welded while being pressurized from the sheet thickness direction so as to provide the steel sheets 1a to 1c with a spot weld zone 5; and a laser welding stage where the spot weld zone 5 or the circumference of the spot weld zone 5 is irradiated with a laser beam L, and the surface side steel sheet 1a and the high sheet thickness steel sheet 1b are laser-welded. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a steel plate lap welding method and a steel plate lap weld joint, and more particularly to a steel plate lap welding method using both laser welding and spot welding and a steel plate lap weld joint.

  In recent years, in the automobile field, as a means for reducing the weight of a vehicle body for the purpose of reducing fuel consumption or reducing CO2 emissions, the use of high-strength steel plates for vehicle bodies and parts has been promoted. Further, as means for improving the collision safety of an automobile body, a structure in which a reinforcement is sandwiched between an outer plate panel and an inner plate constituting the vehicle body is employed. In such a structure, it is necessary to weld three or more steel plates on top of each other. For example, a panel made of a thin steel plate with a plate thickness of 1 mm or less is arranged on the outside of the vehicle body, and a reinforcement and a member or an inner plate with a plate thickness of more than 1 mm are arranged on the inside, and the panel, the reinforcement and the member or Therefore, it is necessary to spot weld a set of plates combined with the inner plate.

  By the way, the spot welding method has a property that when a plurality of steel plates are overlapped and welded, a nugget is formed at a substantially central portion in the total thickness direction. For this reason, when a steel plate having a thickness of 1 mm or less is used as the outer panel, and the reinforcement and inner plate are overlapped on the outer panel and spot welding is performed, a nugget is formed between the reinforcement and the member or inner plate. However, nuggets are not formed on the outer panel, and there is a problem that the reinforcement and the inner panel and the outer panel cannot be welded together.

  Therefore, in Patent Document 1, when spot welding is performed by superposing two or more thick plates and thin plates, an electrode having a relatively small radius of curvature at the tip is disposed on the thin plate side, and two pressures are applied. A technique for performing spot welding while increasing the height in stages is disclosed. In Patent Document 1, the current density between the thin plate and the thick plate is increased to effectively form a nugget by increasing the applied pressure in the second stage welding to the applied pressure in the first stage welding. ing.

  Further, the welding of the vehicle body is not limited to the spot welding method, and a laser welding method may be used. The laser welding method is a welding method using a high-energy beam, and can continuously weld a long part at a higher speed than spot welding, and is effective as a welding method for a vehicle body. However, in lap laser welding of galvanized steel sheets, low boiling point zinc instantly evaporates and blows up the molten pool, making it difficult to obtain a good continuous bead. Further, if the gap between the steel plates becomes too large, good welding cannot be obtained. With respect to such a problem, in Patent Document 2, when a galvanized steel sheet is overlapped and laser-welded, a porous sheet is sandwiched between the galvanized steel sheets to secure a minute gap between the galvanized steel sheets. A method is disclosed in which zinc vapor generated by heating with a laser is allowed to pass through the inside of a porous sheet and escape to the outside.

  Patent Document 3 discloses a method of spot welding by superposing three or more steel plates. In Patent Document 3, a phosphate-treated film, a chromate-treated film, an organic film, or an inorganic film is formed on the overlap surface of the thinnest steel sheet in contact with the welding electrode among three or more steel sheets, and the contact resistance value is The plate is assembled so as to be 50 to 500 mΩ. By spot welding in this state, a nugget is formed on a thin plate that is most easily cooled by the electrode.

  Patent Document 4 discloses a laser welding method in which a member to be bonded and a base material covered with a low-melting-point coating material are overlapped. In this Patent Document 4, series welding is performed from one side to evaporate and remove the coating material in the welding region, and then the laser beam is irradiated to the welding region to evaporate and remove the coating material from the welding region and its periphery. A method for laser welding in an area is disclosed.

  Furthermore, in Patent Document 5, when performing lap laser welding, the bead shape immediately after welding is measured in parallel with the welding operation, and by controlling the welding conditions such as the supply amount of the filler wire according to the measurement result, A method for obtaining a good weld bead even when the gap between the steel plates fluctuates is disclosed.

JP 2006-55898 A JP-A-4-288986 JP 2008-161878 A JP 2006-110565 A JP 2006-136904 A

However, in the technique described in Patent Document 1, since heat is concentrated on the thin plate side, the electrode on the thin plate side is particularly worn out, the number of dots that can be continuously welded is reduced, and frequent electrode dressing is required. There was a problem inferior workability.
Moreover, in the technique described in Patent Document 2, there is a problem that a process of inserting a porous sheet is required and the process becomes complicated. Further, in the subsequent painting process of the welding process, there is a problem in that the porous sheet remaining between the steel sheets hinders the coating around the steel sheets.
Furthermore, the technique described in Patent Document 3 has a problem that it lacks versatility because it requires a steel plate obtained by subjecting a thin plate to a special surface treatment.
Furthermore, in the technique described in Patent Document 4, for example, when removing a coating material made of galvanizing by irradiating a laser beam, the laser beam is irradiated without applying a pressure between the steel plates. Even when the zinc is evaporated by irradiation, the zinc vapor often stays in place, so that the galvanizing cannot be completely removed and the welding strength may vary.
Furthermore, in the technique described in Patent Document 5, a means for measuring the bead shape immediately after welding and a means for adjusting the welding conditions such as the supply amount of the filler wire according to the measurement result are required, and the apparatus is large. There was a problem.

  The present invention has been made in view of the above circumstances, and in the case of lap welding a plurality of steel plates including a steel plate having a relatively small plate thickness, a lap welding method for steel plates and a lap welding of steel plates capable of lap welding with high joint strength. An object is to provide a welded joint.

The present invention adopts the following configuration in order to solve the above problems.
(1) A lap welding method for steel plates in which three or more steel plates are overlapped and welded, wherein the three or more steel plates include a surface side steel plate having a thickness of 0.3 to 1 mm and a surface side steel plate. And the ratio of the plate thickness of the surface side steel plate to the total plate thickness of the surface side steel plate and the one or more high plate thickness steel plates (total plate thickness / surface). the thickness of the side steel plates) was 5 or more, in a state where said surface side steel sheet was superposed the three or more steel plates to place on the surface side, while pressing spot welding the three or more steel sheet thickness direction By performing a spot welding step in which a spot weld is provided on at least the one or more high-thick steel plates, and irradiating a laser beam around the spot weld or the spot weld in an annular shape with a diameter of 2 mm or more , The high plate thickness adjacent to the surface side steel plate Lap welding method for steel sheet characterized by being provided with a laser welding step for laser welding the said surface side steel and plate, the.
(2) The steel plate lap welding method according to (1), wherein in the laser welding step, an annular weld bead is formed so as to overlap the spot weld.
(3) The steel plate lap welding method according to (1), wherein, in the laser welding step, an annular weld bead surrounding the spot welded portion is formed around the spot welded portion.
(4) The steel plate lap welding method according to (3), wherein a welding start end portion and a welding end portion of the weld bead are separated from each other.
(5) The depth of the weld bead is 1.2 times or more the plate thickness of the surface-side steel plate. The steel plate according to any one of (1) to (4), Lap welding method.
(6) In the spot welding step, the two sheets in the spot welding process in a state where the one surface-side steel sheet and the two high-thick steel sheets are overlapped so that the surface-side steel sheet is disposed on the surface side. Forming a spot weld on the high plate thickness steel plate and press-contacting the surface side steel plate and the high plate thickness steel plate, and in the laser welding step, the surface side steel plate and the high plate thickness steel plate in the press contact state. The steel plate lap welding method according to any one of (1) to (5), wherein laser welding is performed.
(7) A lap weld joint of steel plates in which three or more steel plates are overlapped and welded, wherein the three or more steel plates include a surface-side steel plate having a thickness of 0.3 to 1 mm, and the surface side One or more high-thickness steel plates having a thickness greater than that of the steel plate, and the ratio of the thickness of the surface-side steel plate to the total thickness of the surface-side steel plate and the one or more high-thickness steel plates (total thickness) / Thickness of the surface side steel plate) is 5 or more, the three or more steel plates are overlapped in a state where the surface side steel plate is disposed on the surface side, and at least the one or more high plate thickness steel plates include a nugget. A spot weld is provided, and a weld bead for welding the high-thick steel plate adjacent to the surface-side steel plate and the surface-side steel plate is provided around the spot weld or the spot weld. A lap welded joint for steel sheets.
(8) The steel plate lap weld joint according to (7), wherein the weld bead overlaps with the spot weld and is provided in an annular shape.
(9) The steel plate lap weld joint according to (7), wherein the weld bead is provided in an annular shape so as to surround the spot welded portion around the spot welded portion.
(10) The steel plate lap weld joint according to (9), wherein a weld start end portion and a weld end portion of the weld bead are spaced apart from each other.
(11) The steel plate according to any one of (7) to (10), wherein a depth of the weld bead is 1.2 times or more a plate thickness of the surface-side steel plate. Lap welded joints.
(12) One sheet of the surface side steel plate and two sheets of the high plate thickness steel plate are overlapped with the surface side steel plate disposed on the surface side, and at least the two high plate thicknesses are formed by the spot welded portion. Any of (7) to (11), wherein the steel plate is welded and at least the high plate thickness steel plate adjacent to the surface side steel plate and the surface side steel plate are welded by the weld bead. A lap weld joint for steel sheets according to claim 1.

According to the lap welding method of the steel sheet of the present invention, by sequentially performing the spot welding process and the laser welding process, among the three or more steel sheets, between the high thickness steel sheet adjacent to the surface side steel sheet and the surface side steel sheet Even if the spot welded portion is not formed, the surface-side steel plate and the high-thickness steel plate are welded by laser welding, so that three or more steel plates including the surface-side steel plate can be reliably lap welded. In addition, when laser welding is performed around the spot weld, laser welding can be performed with the gap between the high-thick steel plate adjacent to the surface-side steel plate and the surface-side steel plate controlled within a certain range. Thus, laser welding can be performed stably, and three or more steel plates including the surface-side steel plate can be reliably lap welded.
Moreover, since it is not necessary to provide a spot weld part over all the steel plates, the welding current and current application time in a spot welding process can be reduced, and the continuous spot performance of spot welding can be improved.

In addition, according to the lap welding method of the steel plate of the present invention, since the laser weld bead is formed in the spot welded portion, even if the surface side steel plate is thin, the surface side steel plate is pressed against the high plate thickness steel plate, A good laser weld bead can be formed without being affected by the gap. The laser weld bead can be a straight line, but by forming an annular laser weld bead that overlaps the spot weld, the area occupied by the weld can be reduced, and lap welding with excellent appearance A joint can be formed. Moreover, welding strength can be raised by forming a weld bead so that it may overlap with a spot welding part.
Furthermore, according to the lap welding method of the steel plate of the present invention, since the annular laser weld bead surrounding the spot weld is formed around the spot weld, the spot weld and the weld bead are separated from each other as designed. The welding strength can be expressed.
Furthermore, according to the lap welding method of the steel plate of the present invention, the metal vapor derived from the steel plate generated by overheating the steel plate is filled between the molten bead and the spot welded portion when forming the weld bead. Where there is a possibility, metal vapor can be released by separating the welding start end portion and the welding end portion of the weld bead, and laser welding can be performed stably.
Moreover, according to the lap welding method of the steel plate of the present invention, the depth of the weld bead is 1.2 times or more the plate thickness of the surface-side steel plate, thereby increasing the thickness of the plate adjacent to the surface-side steel plate. The steel plate and the surface-side steel plate can be reliably welded. In addition, by setting the depth of the weld bead to about 1.2 times the plate thickness of the surface side steel plate, the laser welding process can be realized with a small oscillator, and the initial equipment cost can be reduced.

  Next, according to the lap weld joint of the steel plate of the present invention, a spot welded portion is provided between two or more steel plates, and the high plate thickness steel plate adjacent to the surface side steel plate around the spot welded portion or the spot welded portion. Since the weld bead for welding the surface side steel plate and the surface side steel plate is provided, the surface side steel plate is included even if the spot weld is not formed between the high thickness steel plate adjacent to the surface side steel plate and the surface side steel plate. Two or more steel plates can be reliably lap welded.

Further, according to the lap weld joint of the steel plate of the present invention, since the laser weld bead is formed in the spot welded portion, even if the surface side steel plate is thin, the surface side steel plate is pressed against the high plate thickness steel plate, A good laser weld bead can be formed without being affected by the gap. The laser weld bead can be a straight line, but by providing an annular laser weld bead overlapping the spot weld, the area occupied by the welded portion can be reduced, and the appearance of the lap weld joint can be improved. In addition, the welding strength can be increased by providing an annular weld bead overlapping the spot weld.
Furthermore, according to the lap weld joint of the steel plate of the present invention, the spot welded portion and the weld bead are separated by providing an annular laser weld bead surrounding the spot welded portion around the spot welded portion. The designed welding strength can be achieved.
Furthermore, according to the lap weld joint of the steel plate of the present invention, by separating the start end portion and the end portion of the laser welding bead, metal vapor accompanying laser welding can be released, and a stable welding bead can be formed. Can do.
Moreover, according to the lap weld joint of the steel plate of the present invention, the depth of the weld bead is 1.2 times or more the plate thickness of the surface-side steel plate, thereby increasing the thickness of the plate adjacent to the surface-side steel plate. The steel plate and the surface-side steel plate can be reliably welded.

FIG. 1 is a process diagram illustrating a steel plate lap welding method according to a first embodiment of the present invention. FIG. 2 is a view for explaining the steel plate lap welding method according to the first embodiment of the present invention, and is a process diagram showing a spot welding process. Drawing 3 is a figure explaining the lap welding method of the steel plate which is the 1st embodiment of the present invention, and is a process figure showing a spot welding process. FIG. 4 is a diagram for explaining a lap welding method for steel sheets according to the first embodiment of the present invention, and is a process diagram showing a laser welding process. FIG. 5 is a view for explaining the steel plate lap welding method according to the second embodiment of the present invention, and is a plan view showing the surface-side steel plate after the laser welding process. FIG. 6 is a process diagram for explaining a steel sheet lap welding method according to a second embodiment of the present invention. FIG. 7 is a view for explaining the steel plate lap welding method according to the embodiment of the present invention, and is a plan view showing the surface-side steel plate after the laser welding process.

“First Embodiment”
Hereinafter, a steel plate lap welding method and a steel plate lap weld joint according to a first embodiment of the present invention will be described with reference to the drawings.
The steel plate lap welding method of the present embodiment includes a preparatory step in which two or more steel plates are overlapped and temporarily assembled, a spot welding step in which spot welding is performed while pressing two or more steel plates from the plate thickness direction, and a laser welding step. It is roughly composed.

  First, in a preparation process, as shown in FIG. 1, two or more steel plates 1 are piled up and temporarily assembled. The number of steel plates 1 to be subjected to lap welding may be two or more, preferably 2 to 4, and most preferably 3.

The form which can apply this invention suitably is a case where the steel plate which becomes the minimum board thickness among two or more steel plates 1 is distribute | arranged as the surface side steel plate 1a. Here, the surface side means a side that is disposed on the outermost side and is capable of laser welding when two or more steel plates 1 are overlapped.
As the steel plate other than the surface side steel plate 1a, one or two or more high plate thickness steel plates having a plate thickness larger than that of the surface side steel plate 1a can be used. In the present embodiment, two high plate steel plates 1b and 1c are used. The plate | board thickness of the surface side steel plate 1a has the preferable range of 0.3-1.0 mm. Moreover, the plate | board thickness of the high plate | board thick steel plates 1b and 1c should just be the range of about 0.8 mm-5 mm. In addition, a high plate | board thick steel plate is a term which means the steel plate whose plate | board thickness is larger than the surface side steel plate, and is not synonymous with what is called a thick plate.

Furthermore, the ratio of the plate thickness of the surface side steel plate 1a to the total plate thickness of the surface side steel plate 1a and the high plate thickness steel plates 1b, 1c (total plate thickness / plate thickness of the surface side steel plate (hereinafter referred to as plate thickness ratio)) is: 5 or more is preferable.
If the plate thickness ratio is less than 5, the ratio of the plate thickness of the surface-side steel plate 1a to the total plate thickness is sufficiently large, and in this case, it is possible to perform lap welding by ordinary spot welding. There is no need to use the lap welding method. Even if the plate thickness ratio is less than 5, the lap welding method according to the present invention can be applied, but it is economically disadvantageous in that laser welding is performed.
The upper limit of the plate thickness ratio is not particularly limited, but the upper limit of the plate thickness ratio is 10 because there are few application examples for combinations where the plate thickness ratio exceeds 10.

  As shown in FIG. 1, the stacking order of the steel plates 1 a to 1 c is preferably such that another high plate thickness steel plate 1 b is overlaid on the high plate thickness steel plate 1 c and further the surface side steel plate 1 a is overlaid thereon. The stacking order of the steel plates 1 may be the order opposite to the above order. In short, the surface-side steel plate 1a only needs to be arranged on the front side. In addition, although each steel plate 1a-1c is comparatively flat, since there exists some curvature, a clearance gap exists between each steel plate 1a-1c piled up mutually. Moreover, when each steel plate 1a-1c is shape | molded in advance, since distortion accompanying the shaping | molding process has arisen in each steel plate 1a-1c, in this case, it is somewhat between each steel plate 1a-1c. There will be a gap.

  In the lap welding method of this embodiment, there is no restriction | limiting in particular in the kind of steel plates 1a-1c. In ordinary laser welding, when laser-welding a plated steel sheet plated with a low-boiling point metal such as zinc, the low-boiling point metal constituting the plating component becomes steam and the molten steel is spattered as a spatter. In some cases, the lap welding method of this embodiment can use a plated steel plate without any problem. For example, even a galvanized steel plate can be suitably used.

  Next, in a spot welding process, as shown in FIG. 2, welding electrodes 2a and 2b are pressed against the steel plates 1a to 1c from the thickness direction. In this embodiment, direct spot welding is suitably applied as shown in FIG. The steel plates 1a to 1c are brought into close contact with each other by being pressed in the plate thickness direction by the welding electrodes 2a and 2b.

Next, as shown in FIG. 3, spot welding is performed by applying a welding current from the welding electrodes 2a and 2b. By spot welding, the nugget 3 is formed between the high thickness steel plates 1b and 1c.
Further, around the nugget 3, a corona bond portion 4 is formed in which the base metal of the high-thick steel plates 1b and 1c is solid-phase-welded. As described above, the spot welded portion 5 including the nugget 3 and the corona bond portion 4 is formed on the steel plate 1 to be subjected to lap welding.
Further, the corona bond portion 4 extends to one surface of the high-thick steel plate 1b, and the surface-side steel plate 1a is solid-phase welded at the previous contact portion 1d.
Although the strength of this solid phase welding is relatively weak, the strength is sufficient to temporarily fix the surface side steel plate 1a and the high thickness steel plate 1b.
At this time, a plate lifting phenomenon (hereinafter referred to as a sheet separation phenomenon) occurs around the pressure contact portion 1d between the surface side steel plate 1a and the high plate thickness steel plate 1b along with the plastic flow of the surface side steel plate 1a. Due to this sheet separation phenomenon, a gap G1 is provided between the front surface side steel plate 1a and the high plate thickness steel plate 1b. Since the gap G is a relatively uniform gap, it contributes to stabilization of welding conditions when laser welding is performed. Note that the sheet separation phenomenon is promoted not only by plastic flow but also by the expansion of the thermal expansion of the plate volume accompanying energization of the welding current between the steel plates.

  Further, a gap G2 is formed around the spot welded portion 5 and between the high thickness steel plates 1b and 1c. The gaps G1 and G2 are formed by the above-described sheet separation phenomenon. That is, the gap G1 is formed mainly by the plastic flow of the surface-side steel plate 1a due to the pressing of the welding electrodes 2a and 2b and the expansion of the plate volume due to thermal expansion caused by the energization of the welding current. The gap G1 is a gap when laser welding is performed around the spot welded portion 5. The gap G1 can be controlled by the radius of curvature R of the tip of the welding electrode, the pressure applied by the welding electrode, or the energization conditions.

  The welding conditions for spot welding are not particularly limited, and may be any conditions as long as at least the high plate steel plates 1b and 1c can be spot welded. For example, the tip diameter of the welding electrodes 2a and 2b is in the range of 6 to 8 mm, the curvature radius R of the tip of the welding electrodes 2a and 2b is, for example, 40 mm, and the pressure applied by the welding electrodes 2a and 2b is in the range of 3 to 5 kN. What is necessary is just to make the electric current value of welding current into the range of 7-9 kA, and to set the electricity supply time in the range of 12 / 50-30 / 50 second. The welding conditions are not limited to the exemplified conditions, and may be appropriately determined according to the type, thickness, etc. of the steel plate 1.

  Next, as shown in FIGS. 4 and 5, laser welding is performed by irradiating the spot welded portion 5 with laser light L from the surface side steel plate 1 a side. By laser welding, a weld bead 6 is formed across the high plate steel plate 1b and the surface side steel plate 1a, and the high plate steel plate 1b and the surface side steel plate 1a are welded. As shown in FIGS. 4 and 5, the weld bead 6 of the present embodiment is formed in a region inside the spot welded portion 5, that is, inside the corona bond portion 4 when the steel plate 1 is viewed in plan view. The weld bead 6 may be linear because it only needs to have a weld bead length that can bear the design load that the surface side steel plate 1a should transmit to the high thickness steel plate. However, if the weld bead 6 is arranged in an annular shape, the load is transmitted. It is preferable because the directionality can be eliminated. By scanning the laser beam L in an annular shape, the weld bead 6 can be formed in an annular shape. Moreover, when forming the weld bead 6, the welding start end part 6a and the welding termination | terminus part 6b may be accumulated, and the welding start end part 6a and the welding termination | terminus part 6b may be spaced apart. Furthermore, since it is only necessary that the weld bead length has such a length that the surface side steel plate 1a can bear the design load to be transmitted to the high thickness steel plate, the weld bead 6 may be one or a plurality of 1 / N yen may be sufficient. FIG. 5 shows an example in which the welding start end portion 6a and the welding end portion 6b are overlapped and welded.

As shown in FIG. 5, when the weld beads 6 are arranged in an annular shape, the shortest distance between the center position O of the annular weld beads 6 and the center line B in the width direction of the weld beads 6 is the radius of the weld beads 6. It is preferable that the diameter R1 of the weld bead 6 is 2 mm or more, where r1 is 2 and the radius R1 is twice the radius r1.
If the diameter R1 is less than 2 mm, it is not preferable because it melts by heat conduction to the inside of the annular weld bead 6 and solidification cracks are likely to occur.
The diameter R1 of the weld bead 6 is preferably about 1 mm shorter than the outer peripheral diameter R2 of the corona bond portion 4. This is a limitation for preventing the weld bead 6 from being formed outside the corona bond portion 4. When the weld bead 6 is formed outside the corona bond portion 4, it is necessary to separate the welding start end portion 6a and the welding end portion 6b as will be described later. The width direction center line B corresponds to the locus of the laser beam L when forming the weld bead 6.

The outer peripheral diameter R2 of the corona bond portion 4 needs to be determined by a peel test if it is a cross-sectional mirror or a mild steel from a joint that has been previously spot welded. This operation is necessary for confirming whether the high-thick steel plates 1b and 1c are appropriately welded and determining spot welding conditions.
Further, the outer peripheral diameter R2 of the corona bond portion 4 is not constant along the plate thickness direction as shown in FIG. 4, and becomes maximum between the high plate thickness steel plates 1b and 1c, and gradually decreases with increasing distance from the plate thickness direction. Yes. The outer diameter R2 of the corona bond portion 4 in this case may be the outer diameter of the corona bond portion 4 on the surface side steel plate 1 side of the high plate steel plate 1b.

  Further, the welding conditions are adjusted so that the depth d (penetration depth) of the weld bead 6 is at least 1.2 times greater than the thickness of the surface side steel plate 1a. The penetration depth d may be determined by performing a melt run with another steel plate, measuring the penetration depth in partial penetration, and determining the welding conditions in advance.

  In the laser welding process, it is preferable to irradiate the laser beam L from the surface side steel sheet 1a side. Although it is possible to irradiate the laser beam from the high-thick steel plate 1c side, in this case, it is necessary to cause the metal melted portion by the laser beam to reach the surface-side steel plate 1a, and a large laser output is required. That is, when irradiating a laser beam from the high-thickness steel plate 1c side, it is necessary to select a welding condition capable of through-welding the entire plate thickness, and the laser welding equipment becomes large.

In laser welding, a mirror disposed in the middle of light collection can be driven to scan with a laser beam for welding. In this case, the time required for the laser welding process can be greatly shortened.
Further, it is preferable to use nitrogen, carbon dioxide, argon, helium, or dry air as the shielding gas for laser welding. In particular, by using nitrogen or carbon dioxide gas, it is possible to suppress generation of pores in the weld bead 6 during non-penetrating welding in which the laser beam L is irradiated from the surface side steel plate 1a side.

  Moreover, the lap welding method of this embodiment is applied to the welding process of the vehicle body in a motor vehicle manufacturing process as an example. In a flow operation such as welding of a vehicle body, it is preferable that the spot welding process and the laser welding process are continuously performed without performing repositioning and re-clamping after positioning and clamping of the welded body. More preferably, laser welding is performed at the same station as the station where spot welding was performed, or laser welding is performed at a station close to the station where spot welding was performed. This is because, after spot welding to which the lap welding method of this embodiment is applied, if the number of hit points of other spot welding increases, a slight distortion occurs in the welded body, and the laser welding position needs to be repositioned. . If it is the same station or the next station, laser welding can be performed on the basis of position information on which spot welding has been performed.

In this way, the lap weld joint shown in FIGS. 4 and 5 is obtained. The lap weld joint shown in FIGS. 4 and 5 includes a surface side steel plate 1a having a plate thickness in the range of 0.3 to 1 mm, and two high plate steel plates 1b having a plate thickness larger than that of the surface side steel plate 1a. 1c is a joint obtained by lap welding. The ratio of the plate thickness of the surface side steel plate 1a to the total plate thickness of the surface side steel plate 1a and the high plate thickness steel plates 1b, 1c (total plate thickness / plate thickness of the surface side steel plate) is 5 or more. And each steel plate 1a-1b is piled up in the state by which the surface side steel plate 1a is arrange | positioned at the surface side. Moreover, the nugget 3 by resistance spot welding is provided over the high plate | board thick steel plates 1b and 1c. Around the nugget 3, a corona bond portion 4 in a solid phase bonded state is formed, and the corona bond portion 4 and the nugget 3 are integrated to form a spot weld portion 5. Further, a weld bead 6 by laser welding is provided on the spot welded portion 5 over the surface side steel plate 1a and the high plate steel plate 1b. Thus, the lap weld joint of this embodiment is comprised from the spot weld part 5 which welds the high plate steel plates 1b and 1c, and the weld bead 6 which welds the surface side steel plate 1a and the high plate steel plate 1b. Has been. Moreover, the press-contact part 1e is provided in the junction part of the surface side steel plate 1a and the high plate | board thick steel plate 1b, and the surface side steel plate 1a and the high plate | board thick steel plate 1b are in the state pressed. This pressure contact portion 1e is also included in the lap weld joint.
Moreover, in the lap weld joint of this embodiment, the bottom part of the weld bead 6 has penetrate | invaded the nugget 3, and the weld bead 6 and the spot weld part 5 are united.

  The weld bead 6 is provided in an annular shape so as to overlap the spot weld 5. This weld bead 6 is provided in the area | region inside the corona bond part 4 of the high thickness steel plates 1b and 1c. The diameter of the weld bead 6 is preferably 2 mm or more, and is preferably 1 mm smaller than the outer diameter of the corona bond portion 4. Furthermore, it is preferable that the depth of the weld bead 6 is 1.2 times or more the plate thickness of the surface-side steel plate 1a.

As described above, according to the lap welding method of the present embodiment, the spot welding process and the laser welding process are sequentially performed, so that a nugget by spot welding is generated between the surface-side steel plate 1a and the high-thick steel plate 1b. Even if it is not formed, since the surface side steel plate 1a and the high plate thickness steel plate 1b are welded by laser welding, two or more steel plates 1a to 1c including the surface side steel plate 1a can be surely lap welded.
Moreover, since it is not necessary to provide a spot welding part over all the steel plates 1a-1c, the welding current and current application time in a spot welding process can be decreased, and the continuous spot property of spot welding can be improved.
Moreover, by forming the annular weld bead 6 inside the corona bond portion 4, the area occupied by the welded portion can be reduced, and a lap weld joint excellent in appearance can be formed. Further, by forming an annular weld bead 6 inside the corona bond portion 4, the bottom of the weld bead 6 enters the nugget 3, and the weld bead 6 and the spot weld 5 are integrated, so that the welding strength Can be increased.
Moreover, the surface side steel plate 1a and the high plate steel plate 1b can be welded reliably by making the depth of the weld bead 6 1.2 times or more the plate thickness of the surface side steel plate 1a. Further, by setting the depth of the weld bead 6 to about 1.2 times the thickness of the surface side steel plate 1a, the laser welding process can be realized with a small oscillator, and the initial equipment cost can be reduced.

  Further, when galvanized steel sheets are used as the steel sheets 1a to 1c, since zinc is vaporized and scattered by the welding heat at the time of spot welding, almost no zinc remains in the press-contact part 1d immediately above the spot welded part 5. Disappear. In the present embodiment, since the molten bead 6 is formed by laser welding so as to overlap the spot welded portion 5, the phenomenon that the molten pool at the time of laser welding is scattered by the vapor of zinc can be avoided.

Next, according to the lap weld joint of the steel plate of the present embodiment, the spot welded portion 5 including the nugget 3 is provided across the high-thick steel plates 1b and 1c, and the surface-side steel plate 1a and Since the weld bead 6 for welding the high plate steel plate 1b is provided, even if the nugget 3 is not formed between the surface plate steel plate 1a and the high plate steel plate 1b, the surface bead plate 1a is formed by the weld bead 6. And the high-thick steel plate 1b are welded, so that two or more steel plates 1a to 1c including the surface-side steel plate 1a can be reliably lap welded.
Moreover, since the bottom part of the weld bead 6 penetrates into the nugget 3 and the weld bead 6 and the spot welded part 5 are integrated, the welding strength can be increased.

“Second Embodiment”
Next, a steel plate lap welding method and a steel plate lap weld joint according to a second embodiment of the present invention will be described with reference to the drawings.
The lap welding method of the present embodiment is different from the first embodiment in that a weld bead is formed outside the corona bond portion when forming a weld bead by laser welding.

  That is, as shown in FIG. 6, in this embodiment, laser welding is performed by irradiating the spot welded portion 5 with the laser beam L from the surface side steel plate 1a side. By laser welding, a weld bead 16 is formed across the high plate thickness steel plate 1b and the surface side steel plate 1a adjacent to the surface side steel plate 1a, and the high plate thickness steel plate 1b and the surface side steel plate 1a are welded. In the present embodiment, the weld bead 16 is formed so as to surround the spot welded portion 5 outside the spot welded portion 5, that is, outside the corona bond portion 4 when the steel plate 1 is viewed in plan view. The weld bead 16 is preferably formed in an annular shape, but does not necessarily have to be a full circle or close to a full circle, and may be one or a plurality of 1 / n circles such as a half circle. This is because the surface side steel plate 1a only needs to have a weld bead length capable of bearing a design load to be transmitted to the high plate steel plate. In the example illustrated in FIG. 6, laser welding is performed with the spot welding electrode retracted, but laser welding may be performed while the welding electrode is in contact with the steel plate 1. By keeping the welding electrode in contact, the spot welded portion 5 can be cooled by the weld electrode even during laser welding, and the spot welded portion 5 is not overheated.

  On the outside of the corona bond portion 4, a gap G1 is provided between the front surface side steel plate 1a and the high plate thickness steel plate 1b. The gap G1 is a gap due to a sheet separation phenomenon that occurs in the spot welding process. The gap G1 has a substantially constant size along the outer periphery of the corona bond portion 4. For this reason, when the molten bead 16 is provided in an annular shape along the outer periphery of the corona bond portion 4, the gap is always constant, so that welding conditions do not fluctuate and stable laser welding is possible. The gap G1 can be controlled by the radius of curvature R of the tip of the welding electrode, the pressure applied by the welding electrode, or the energization conditions.

  Moreover, when a galvanized steel plate is used as the steel plates 1a to 1c, the galvanization in the vicinity of the spot welded portion 5 is melted and vaporized due to the influence of welding heat accompanying the formation of the spot welded portion 5. Although the molten and vaporized zinc is released into the gaps G1 and G2, sheet separation is formed at the locations where laser welding is performed in the present embodiment, so that stable laser welding is possible.

  Moreover, the welding bead 16 in this embodiment needs to separate the welding start end part 16a and the welding terminal part 16b. This is caused by forming the weld bead 16 so as to surround the spot weld 5. The front surface side steel plate 1a and the high plate thickness steel plate 1b are press-contacted via a press-contact portion 1e in the vicinity of the spot welded portion 5. The weld bead 16 is formed so as to surround the press contact portion 1e. At this time, a space S surrounded by the weld bead 16, the surface side steel plate 1a, the high plate thickness steel plate 1b, and the press contact portion 1e is formed. If the welding start end portion 16a and the welding end portion 16b are overlapped, this space S becomes a completely sealed space. In the laser welding process, welding proceeds while the base metal of each of the steel plates 1a and 1b is melted by laser light, but the metal vapor generated at this time is also filled in the space S. When galvanized steel plates are used as the steel plates 1a to 1c, zinc vapor is also included in the generated metal vapor. When the space S is completely sealed by overlapping the welding start end portion 16a and the welding end portion 16b of the weld bead 16 in such a situation, the internal pressure in the space S is increased by the metal vapor left in the space S, and the weld bead 16 When forming the end portion of the steel, the molten steel is scattered to make a hole. Therefore, when the welding bead 16 is formed in an annular shape outside the spot welded portion 5, it is preferable to provide a metal vapor escape port by separating the welding start end portion 16a and the welding end portion 16b. Thereby, there is no possibility that the welding strength of the surface side steel plate 1a and the high thickness steel plate 1b may fall.

  When the shortest distance between the center position O of the annular weld bead 16 and the center line B in the width direction of the weld bead 16 is the radius r2 of the weld bead 16, and a multiple of the radius r2 is the diameter R3 of the weld bead 16. The diameter R3 of the weld bead 16 may be equal to or larger than the outer peripheral diameter R2 of the corona bond portion 4. The upper limit of the diameter R3 of the weld bead 16 may be 16 mm or less. Even if the diameter R3 of the weld bead 16 is made larger than this, there is no merit in terms of strength for welding the target surface side steel plate 1a. In addition, the diameter of a welding electrode for normal spot welding is 16 mm, and laser welding can be performed without any obstacle within this diameter range, but when welding with a diameter exceeding this is performed with a laser, It may occur that the laser beam cannot be irradiated due to interference with other members or jigs, and it is necessary to devise jigs and tools for laser welding.

  Also, the welding condition is such that the depth d (penetration depth) of the weld bead 16 is at least 1.2 times greater than the plate thickness of the surface-side steel plate 1a, as in the first embodiment. Can be adjusted.

Further, in laser welding, it is preferable to irradiate the laser beam L from the surface side steel plate 1a side, but as in the first embodiment, laser welding is performed by irradiating the laser beam from the high plate thickness steel plate 1c side. Is also possible.
Further, it is preferable to use nitrogen, carbon dioxide, argon, helium, or dry air as the shielding gas for laser welding. In particular, by using nitrogen or carbon dioxide gas, the generation of pores in the weld bead 16 can be suppressed during non-penetrating welding in which the laser beam L is irradiated from the surface-side steel plate 1a side.

  In this way, the lap weld joint shown in FIGS. 6 and 7 is obtained. The lap weld joint shown in FIGS. 6 and 7 includes a surface-side steel plate 1a having a minimum plate thickness in the range of 0.3 to 1 mm and two high plates having a plate thickness larger than that of the surface-side steel plate 1a. It is a joint obtained by lap welding thick steel plates 1b and 1c. In this lap joint, the nugget 3 is provided over the high steel plate 1b and 1c. Around the nugget 3, a corona bond portion 4 in a solid-phase pressure contact state is formed. And the corona bond part 4 and the nugget 3 are united and the spot welding part 5 is formed. Further, a weld bead 16 by laser welding is provided on the spot welded portion 5 over the surface side steel plate 1a and the high plate steel plate 1b. Thus, the lap weld joint of this embodiment is comprised from the spot weld part 5 which welds the high plate steel plates 1b and 1c, and the weld bead 16 which welds the surface side steel plate 1a and the high plate steel plate 1b. Has been. Moreover, the press-contact part 1e is provided in the junction part of the surface side steel plate 1a and the high plate | board thick steel plate 1b, and the surface side steel plate 1a and the high plate | board thick steel plate 1b are in the state pressed. This pressure contact portion 1e is also included in the lap weld joint.

The weld bead 16 is provided in an annular shape so as to surround the spot weld 5. The weld bead 16 is provided on the outside of the corona bond portion 4 of the high plate thickness steel plates 1b and 1c. The diameter of the weld bead 16 is preferably equal to or greater than the outer diameter of the corona bond portion 4 and is preferably 16 mm or less. Furthermore, it is preferable that the depth d of the weld bead 16 is 1.2 times or more the plate thickness of the surface-side steel plate 1a.
Further, by providing the annular weld bead 16 around the spot welded portion 5, the spot welded portion 5 and the weld bead 16 are always separated from each other.

According to the lap welding method of the present embodiment, in addition to the same effects as the lap welding method of the first embodiment, the following effects can be obtained.
That is, according to the lap welding method of this embodiment, since laser welding is performed around the spot welded portion 5, the gap G1 between the surface side steel plate 1a and the high plate steel plate 1b is controlled within a certain range. Laser welding can be performed, laser welding can be performed stably, and the steel plate 1 including the surface-side steel plate 1a can be reliably lap welded. Since this gap G1 can be controlled by the curvature radius R of the tip of the welding electrode, the pressure applied by the welding electrode, or the energization conditions, it is possible to avoid a situation in which laser welding is impossible because the gap G1 is too large. In addition, since the gap G1 is stabilized, a complicated mechanism for feeding a necessary amount of filler as in the prior art becomes unnecessary.

  In addition, since the spot welded portion 5 and the weld bead 16 are separated from each other, the designed welding strength can be exhibited in each of spot welding and laser welding. Even when a galvanized steel sheet is used as the steel sheet 1, laser welding is performed on the portion where the gap is formed by sheet separation, so that laser welding can be performed stably.

  Further, when the laser weld bead 16 is formed, the metal vapor derived from the steel plate 1 may fill up the space S between the molten bead 16 and the press contact portion, so that the start end portion 16a and the end end portion 16b of the weld bead 16 are formed. By separating, the filled metal vapor can be released, and laser welding can be performed stably.

  Moreover, according to the lap weld joint of the steel plate of this embodiment, the spot welded portion 5 and the weld bead 16 are provided by providing the annular weld bead 16 surrounding the spot welded portion 5 around the spot welded portion 5. Since they are spaced apart from each other, the designed weld strength can be expressed for each of the spot welds 5 and the weld beads 16.

  Further, by separating the welding start end portion 16a and the welding end portion 16b without overlapping each other, the welding start end portion 16a is not reheated and weld cracking can be prevented in advance.

  In the present invention, even when three or more lap welds having a plate thickness ratio exceeding 5.0 are used, if the steel plate having the minimum plate thickness can be sandwiched between the high plate steel plates, it is easy to spot. Since welding is possible, the present invention is not applicable.

Various steel plates shown in Table 1 were prepared, and the surface side steel plate, the second high plate thickness steel plate, the third high plate thickness steel plate, and the fourth high plate thickness steel plate were superposed in order of A to H. Board assembly. Next, spot welding was performed under the conditions shown in Table 2 while pressing these steel plates from the thickness direction. The squeeze time during spot welding was fixed at 25 cycles. Next, laser welding was performed under the conditions shown in Table 2 by irradiating a laser beam from the surface side steel plate side toward the spot welded portion, the outer periphery of the spot welded portion, or the periphery of the spot welded portion. In this way, a lap weld joint was manufactured.
The appearance of the weld bead by laser welding was observed for the obtained lap weld joint. In addition, a cross tension test was performed according to the cross tension test method for welded joints defined in JIS Z 3137. Moreover, in the cross tension test, when the number of stacked steel sheets was 3, the steel sheet was pulled between the surface side steel sheet and the second high-thick steel sheet. In addition, when the number of stacked steel sheets was 4, the steel sheet was pulled between the front-side steel sheet and the second high-thick steel sheet. Table 3 shows the observation results of the appearance of the weld beads and the results of the cross tension test. In addition, in the case where the number of steel plates is three, the tensile test between the second high-thick steel plate and the third high-thick steel plate, and when the number of steel plates is four, A good joint strength was obtained in the tensile test between the high-thick steel plates.

  In addition, the steel grade description in Table 1 is based on Japan Iron and Steel Federation standards JFS A 2001 (2008) and JFS A 3011 (2008). Further, “4 mm nugget” and “3.5 mm nugget” in Table 2 mean that a nugget having a diameter of 4 mm and 3.5 mm was formed across the surface-side steel plate and the second high plate steel plate. . Further, in the column of the start and end processing in Table 2, “overlap” is an example in which the welding start end and the welding end are overlapped. For example, 30 ° non-welding refers to a region at an angle of 30 ° at the center position of the weld bead. This means that no weld bead is formed. Moreover, in the column of the welding position of Table 2, the “pressure contact portion” is an example in which a weld bead is formed so as to overlap the spot weld portion (example shown in FIG. 4), and “on the outer periphery of the pressure contact portion” This is an example in which a weld bead is formed on the outer periphery of the corona bond portion of the welded portion, and the “sheet separation portion” is an example in which a weld bead is formed around the spot welded portion so as to surround the spot welded portion (FIG. 6). Example).

As shown in Tables 1 to 3, in Test Example 1, the thickness of the surface-side steel plate was too thin at 0.2 mm. Therefore, it was necessary to perform laser welding because the plug was broken and exhibited good strength even in the pressure contact state. There wasn't.
In Test Example 5, the thickness of the surface-side steel plate was as thick as 1.2 mm, and nuggets were also formed on the surface-side steel plate. In this example, it was not necessary to perform laser welding.
In Test Example 6, the plate thickness ratio was as low as 4.7, and nuggets were also formed on the surface-side steel plate. In this example, it was not necessary to perform laser welding.
In Test Example 8, laser welding was not applied as a comparison with Test Example 7, and interface fracture occurred and sufficient joint strength was not obtained.
In Test Example 10, laser welding was not applied as a comparison with Test Example 9, and interface fracture occurred and sufficient joint strength was not obtained.
Test Example 21 is an example in which a weld bead is formed on the outer periphery of the corona bond portion of the spot welded portion, and in the present invention, a gap (non-welded portion) should be provided without overlapping the start and end points, and welding is intentionally performed. This is an example in which a pit (a hole in the weld bead due to scattering of molten steel) occurs at the end, affecting the joint strength.
In Test Example 25, a weld bead was provided around the spot weld, but since the weld start end and the weld end of the weld bead were overlapped, pits were generated near the weld start end of the weld bead, resulting in poor appearance, The strength has been reduced.
In Test Example 27, laser welding was not applied as a comparison with Test Example 26, and interface fracture occurred partially, and sufficient joint strength was not obtained.
In Test Example 29, laser welding was not applied as a comparison with Test Example 28, interface fracture occurred, and sufficient joint strength was not obtained.

  DESCRIPTION OF SYMBOLS 1 ... Steel plate, 1a ... Surface side steel plate, 1b ... Thick steel plate, 3 ... Nugget, 4 ... Corona bond part, 5 ... Spot weld part, 6, 16 ... Weld bead, 6a, 16a ... Welding start end part, 6b, 16b ... welding end, d ... depth of weld bead, L ... laser beam.

Claims (12)

A lap welding method for steel plates in which three or more steel plates are stacked and welded,
The three or more steel plates include a surface side steel plate having a plate thickness in the range of 0.3 to 1 mm and one or more high plate thickness steel plates having a plate thickness larger than the surface side steel plate. And the ratio of the plate thickness of the surface side steel plate to the total plate thickness of the one or more high plate steel plates (total plate thickness / plate thickness of the surface side steel plate) is 5 or more, and the surface side steel plate is arranged on the surface side. In a state where the three or more steel plates are overlapped,
Spot welding step of providing a spot welded portion on at least the one or more high plate thickness steel plates by spot welding while pressing the three or more steel plates from the plate thickness direction;
Laser welding in which the high-thick steel plate adjacent to the surface-side steel plate and the surface-side steel plate are laser-welded by irradiating a laser beam around the spot welded portion or the spot welded portion in an annular shape having a diameter of 2 mm or more. Process,
A lap welding method for steel sheets, comprising:   2. The steel plate lap welding method according to claim 1, wherein in the laser welding step, an annular weld bead is formed so as to overlap the spot welded portion.   2. The steel plate lap welding method according to claim 1, wherein, in the laser welding step, an annular weld bead surrounding the spot welded portion is formed around the spot welded portion.   The steel plate lap welding method according to claim 3, wherein a welding start end portion and a welding end portion of the weld bead are separated from each other.   The steel plate lap welding method according to any one of claims 1 to 4, wherein a depth of the weld bead is 1.2 times or more a plate thickness of the surface-side steel plate. . In a state where the one surface side steel plate and the two high plate thickness steel plates are superposed such that the surface side steel plate is arranged on the surface side,
In the spot welding step, a spot weld is formed on the two high plate steel plates, and the surface side steel plate and the high plate steel plates are pressure-welded,
The steel plate lap welding method according to any one of claims 1 to 5, wherein, in the laser welding step, the surface-side steel plate and the high-thick steel plate in a press-contact state are laser-welded. It is a lap weld joint of steel plates in which three or more steel plates are stacked and welded,
The three or more steel plates include a surface-side steel plate having a thickness of 0.3 to 1 mm and one or more high-thick steel plates having a plate thickness larger than that of the surface-side steel plate. And the ratio of the plate thickness of the surface side steel plate to the total plate thickness of the one or more high plate steel plates (total plate thickness / plate thickness of the surface side steel plate) is 5 or more, and the surface side steel plate is arranged on the surface side The three or more steel plates are overlaid in a state where
At least the one or more high plate steel plates are provided with spot welds including nuggets,
An annular weld bead having a diameter of 2 mm or more for welding the high-thick steel plate adjacent to the surface-side steel plate and the surface-side steel plate is provided around the spot welded portion or the spot welded portion. A lap welded joint for steel sheets.   The steel plate lap weld joint according to claim 7, wherein the weld bead is provided in an annular shape so as to overlap the spot welded portion.   The steel plate lap weld joint according to claim 7, wherein the weld bead is provided in an annular shape so as to surround the spot welded portion around the spot welded portion.   The steel plate lap weld joint according to claim 9, wherein a welding start end portion and a welding end portion of the weld bead are spaced apart from each other.   11. The steel sheet lap welding according to claim 7, wherein the depth of the weld bead is 1.2 times or more the plate thickness of the surface-side steel plate. Fittings. One surface side steel plate and two high plate thickness steel plates are overlaid in a state where the surface side steel plate is disposed on the surface side,
The two high plate steel plates are welded at least by the spot welded portion, and the high plate steel plates and the surface side steel plates adjacent to the surface side steel plates are welded by at least the weld bead. The lap-welded joint for steel plates according to any one of claims 7 to 11, wherein

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