JP2008178905A - Laser welding method for structure composed of steel plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser welding method for preventing delayed fracture of a weld zone in laser welding of an overlapped part of a structure composed of steel plates. <P>SOLUTION: Laser welding is performed by irradiating the upper face of the uppermost steel plate in the overlapped part which is formed by superimposing a plurality of steel plates in the structure composed of steel plates, with a laser beam to fuse the overlapped part to the lower face of the lowermost steel plate and to weld the overlapped part, wherein tack welding is applied to a range within 30 mm from the starting/completing end on the extension of a planned laser weld bead of the overlapped part, this overlapped part is then welded by laser. Desirably, the tack welding is applied to the starting/completing end of the planned laser weld bead and, desirably, the tack welding is further applied to the intermediate part of the staring/completing end of the planned laser weld bead, in such a manner that an interval between the adjacent tack welding parts is within 100 mm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a laser welding method for a structure formed of steel plates, and more particularly, to a method for laminating a steel plate or a flange of a formed steel plate and laser welding the overlapped portion when manufacturing the structure.

Since laser welding uses laser light as a heat source, control of heat input is easier and more reliable than arc welding such as TIG welding and MIG welding. For this reason, it is a welding method that can form a good weld with little thermal deformation and little segregation by appropriately setting welding conditions such as welding speed, laser beam irradiation output, and shielding gas flow rate. Yes, suitable for welding thin steel plates and the like.
For example, in the automobile industry, the electrical equipment industry, and other fields, it has been adopted for welding a member formed by processing a thin steel plate, and related improvement techniques have been proposed.
For example, in Patent Document 1, when a thin steel plate is abutted and laser welding is performed along the abutting surface, welding is advanced in one direction from one end of the welding surface to the other end. In order to solve the problem that the butted part is expanded and welding becomes difficult, after laser beam welding is performed by pulse laser welding at a plurality of positions that are separated from each other, the laser is welded over the entire length of the planned welding part. It is disclosed to perform main welding by welding.
In Patent Document 2, two panel members having flange portions are welded with a laser beam in a state where the flange portions are opposed to and in contact with each other, and a structure for an automobile called a closed joint is manufactured. In order to secure an appropriate penetration depth due to the gap variation of the flange part that comes into contact, through holes are formed at appropriate intervals on the laser irradiation planned surface of the overlapped part, and an auxiliary plate having a pin part is fitted into this. A method of welding by irradiating a laser beam after wearing is proposed.

JP 59-215288 A Japanese Patent Laid-Open No. 9-10773

  Laser welding is suitable for welding thin steel sheets and the like, and its application range has been expanded to welding automobile structures. Furthermore, in recent years, in order to meet demands such as improvement in fuel ratio and safety, high strength (high-tensile) thin steel plates with a tensile strength of 440 MPa or more are often used. Are required to be welded by laser welding.

FIGS. 8A to 8D show examples of a vehicle body panel structure of an automobile, and these structures are formed of a thin plate material made of high-tensile steel as described above.
In FIG. 8, (a) shows two members 2 and 3 having a flange portion 4 and a bent portion 5 following the flange portion 4 and a cross-sectional shape perpendicular to the axial direction formed into a hat shape, and the flange portions 4 and 6 face each other. The flanges 4 and 6 are arranged so as to overlap each other, and the overlapping parts are welded to form a structure. (B) shows the flatness of the flange 4 of the hat-shaped member 2 described above. The steel plate members 8 are arranged so as to face each other, overlapped, and the overlapped portion is welded to form a structure. (C) shows the two hat-shaped members 2 and 3 as described above. The flange portions 4 and 6 are arranged so as to be opposed to each other with the flat steel plate member 8 therebetween, and the structure is formed by welding the overlapping portions. Further, (d) is as described above. Multiple hat-shaped members (2 in the figure, 2 and 3) Superimposed in the same direction, it is obtained by forming a structure by welding the overlapped portion.
In this way, by using a member having a flange portion, a member having a flange portion, or a member having a flange portion and a plate member are overlapped and welded at least at the overlapping portion of the flange portion, thereby producing a structure. Has been.
However, in the laser welding of the overlapping portion of the structure composed of such a high-strength thin steel plate, the welded portion after the welding may be cracked or broken.

The inventors investigated the state of breakage in laser welding of the above-described steel plate overlap by taking as an example a structure composed of steel plates used in automobiles. That is, FIGS. 7A and 7B show examples of structures. FIG. 7A shows an I shape when viewed from above, and FIG. 7B shows an H shape when viewed from above.
A thin steel plate having a tensile strength of 980 MPa and a thickness of 1.2 mm has flanges 4 and 6 and subsequent bent portions 5 and 7 as shown in FIG. Two molded members 2 and 3 were manufactured, the flange portions 4 and 6 of each molded member were opposed to each other, and the overlapped portions 6 of the flanges were welded with a laser beam to manufacture the structure 1.
The length of the structure was 600 mm, and the length of the laser weld bead was 580 mm. 10 mm at the front and rear ends in the longitudinal direction of the molded member was a non-welded part.
The laser welding conditions were as follows: bead width target: plate thickness mm × 1.0, beam waist 0.6 mm, defocusing: +2 mm, processing point output: 3.5 kw, welding speed: 2 m / min, tip diameter: 5 mmφ The shielding method was a coaxial center shield (no backside shield), and the shielding gas was Ar at 25 l / min.
Prior to laser welding, both surfaces of the flange part, which becomes the welded part of the molded member, are wiped with a waste cloth and cleaned, and the overlapping part of the flange is clamped from above and below with a clamping jig (not shown). Fixed.
The welding method in the case of FIG. 7B is also the same as that in the case of FIG. 7A except that the shape of the molded member in the top view is an H shape, and thus detailed description is omitted.

  Shortly after the laser welding is finished, the clamp jig is removed, that is, depending on the thickness of the thin steel plate, after the end of welding (within 8 hours after the end of welding), in FIG. 7A and FIG. Admitted.

  The inventors conducted a T peel strength test in order to confirm the cause of the crack in the laser weld as described above in more detail, and examined the influence of the elapsed time after welding, the steel type, etc. in more detail. . In this T peel strength test, as shown in FIG. 5, two test pieces 14 and 14 bent in an L shape are overlapped with one end of each short side facing each other, and the overlapped portion is laser welded. After forming the test body 15 (T peel test body), the other end side (non-welded end side) of the short sides of the two test pieces 14 and 14 of the test body 15 are pulled in opposite directions, and the welded portion breaks. The maximum tensile load (N / mm) at the time is evaluated as T peel strength.

First, a thin steel plate having a thickness of 1.2 mm for 980 MPa class steel is used as the steel type, and the shape and dimensions of the test specimen and the test piece are as shown in FIG. A weld bead having a length of 30 mm was formed on the overlapping portion.
The laser welding conditions are the same as above, aiming at the bead width: plate thickness mm × 1.0, beam waist 0.6 mm, defocusing: +2 mm, processing point output: 3.5 kW, welding speed: 2 m / min, tip Diameter: 5 mmφ, shield method: coaxial center shield (no back shield), shield gas Ar: 25 l / min.
Prior to laser welding, both surfaces of each flange part to be the welded part of the molded member are wiped with a waste cloth and cleaned, and the overlapping part of the flange is clamped with a clamping jig (not shown). Fixed.
In this test, the T peel specimen 15 when the elapsed time from the end of welding was changed to 30 minutes, 1 hour, 5 hours, 8 hours, 50 hours immediately after the end of welding (within 6 minutes from the end). Each was subjected to a tensile test apparatus and a tensile test was performed to determine the maximum tensile load (N / mm), that is, the T peel strength. The tensile speed was 10 mm / min. At this time, the fracture site of the test specimen was also confirmed.

  As a result, the T peel strength was extremely low immediately after the end of welding, but increased with the passage of time from the end of welding, and it was found that a substantially constant strength was obtained when 8 hours or more had elapsed after the end of welding. The T peel strength immediately after the end of welding was 25% or less of the T peel strength after 8 hours from the end of welding.

In the above test, the T-peel specimen 15 immediately after the end of welding was fractured at the weld metal part, but when it was 8 hours or more after the end of welding, the fracture occurred near the bond part (melting boundary) or HAZ. From this, it was found that joint strength comparable to that of the base material can be obtained. On the other hand, the fracture position of the T-peel specimen 15 immediately after the end of welding is a weld metal, and the fracture surface form is mainly a pseudo-cleavage fracture surface. It was confirmed that the crack was caused by.
FIG. 6 is a schematic cross-sectional view perpendicular to the welding direction of the weld bead showing the fracture state of the laser welded portion in a pattern, where (a) is a fracture at the weld metal 17 and (b) is a heat affected zone ( HAZ) or a break near the bond portion 18 (melting boundary), and (c) shows a break at the base material 16, respectively.

The inventors further investigated other high-strength steels having a tensile strength of 440 MPa class, 590 MPa class, and 780 MPa class as the specimens, welding conditions, test conditions, etc., similar to the above 980 MPa class steel types. went. As a result, the T peel strength of high strength steels having a tensile strength of 440 MPa or more is also very low immediately after the end of welding, but increases as time elapses and reaches a substantially constant T peel strength level after 8 to 10 hours. It was confirmed.
That is, immediately after the end of welding, it was found that there was only a sufficient time after the end of welding, for example, about 25% of the strength level after 8 hours or more, and the weld metal part was broken.
On the other hand, a similar test was performed with a steel type having a tensile strength of 270 MPa. However, when the tensile strength was 270 MPa, the T peel strength immediately after welding (about 6 minutes after welding) did not decrease, and the welding was completed. Although it passed 8 hours or more, it was almost equivalent to the T peel strength. Such destruction did not occur.

  From these results, it was considered that the fracture of the weld metal immediately after the welding was caused by delayed fracture due to hydrogen embrittlement of the weld metal. In other words, moisture in the atmosphere around the welded part or moisture or hydrocarbons adhering to the surface of the molded part is decomposed by the laser beam during laser welding to become atomic hydrogen, and the molten metal in the welded part Invade and spread inside. In particular, it tends to diffuse and accumulate in hardened structures such as martensite. In addition, when a thin and long bead is formed by laser welding, tensile residual stress or strain is generated due to shrinkage in the longitudinal direction of the bead during cooling. Further, not only welding deformation but also tensile stress from the outside such as a spring back of the molded member may act. Although these residual stresses and strains depend on the size and shape of the structure, they tend to concentrate at the beginning and end of the bead. Thus, hydrogen accumulates locally at a site where a large stress or strain is concentrated, leading to the occurrence of cracks or breakage.

The above-mentioned Patent Documents 1 and 2 do not prevent such delayed fracture in the laser welding of the overlapped portion of the structure made of a steel plate, but delay the welded portion in the laser welding of the overlapped portion of the structure made of the steel plate. No method has been proposed for preventing destruction.
Therefore, this invention makes it a subject to provide the laser welding method which can prevent the delayed fracture of the welding part in the laser welding of the overlap part of the structure which consists of a steel plate.

The present invention has been made to solve the above-described problems, and the gist thereof is as follows.
(1) A laser beam is irradiated from the upper surface of the uppermost steel plate of the overlapped portion formed by overlapping a plurality of steel plates of a structure composed of steel plates to melt the lower surface of the lower steel plate to the overlapped portion. In the laser welding of the overlapped portion of the steel sheets to be welded, the temporary overlap is applied to the range within 30 mm from the start and end on the extension line of the laser welding bead scheduled for the overlapped portion, and then the overlapped portion is laser welded. Laser welding method for the overlapping part of steel plates of the structure to be performed.
(2) The laser welding method for the overlapped portion of steel plates of the structure according to (1), wherein the tacking is performed on a start and end of a planned laser welding bead.
(3) The overlapping portion is formed by irradiating a laser beam from the upper surface of the uppermost steel plate of the overlapping portion formed by overlapping a plurality of steel plates of a structure composed of steel plates to melt the lower surface of the lowermost steel plate. In the laser welding of the overlapped portion of the steel plates to be welded, temporary attachment is performed at the intermediate portion of the start and end of the laser weld bead scheduled for the overlapped portion so that the interval between adjacent temporary attachments is within 100 mm. The laser welding method of the overlap part of the steel plate of the structure as described in (1).
(4) The laser welding method for the overlapped portion of steel plates of the structure according to any one of (1) to (3), wherein the diameter of the tack is larger than the bead width.
(5) The laser welding method for overlapping portions of steel plates of the structure according to any one of (1) to (4), wherein the tacking is performed by spot welding.
(6) The laser welding method for overlapping portions of steel plates of a structure according to any one of (1) to (5), wherein the tacking is performed by mechanical fastening means.

(7) The overlapping portion of the steel plates of the structure is a steel plate in which one steel plate has a bent portion on at least one side and a flange portion subsequent thereto, and the bent portion on one side of the steel plate has a bent portion and continues on at least one side thereof. The overlapping portion of the steel plate of the structural body according to any one of (1) to (6), wherein the flange portion of another steel plate having a flange portion is formed so as to oppose each other. Laser welding method.
(8) The overlapping portion of the steel plates of the structure is a steel plate in which one steel plate has a bent portion and a flange portion following the at least one side, and a flat portion of another flat steel plate on the flange portion of the one steel plate. (1) to (6), the method of laser welding of the overlapped portion of the steel sheets of the structure according to any one of (1) to (6).
(9) The overlapping portion of the steel plates of the structure is a steel plate in which one steel plate has a bent portion at least on one side and a flange portion subsequent thereto, and the bent portion at least on one side follows the flange portion of the one steel plate. Any one of (1) to (6), wherein the flange portion of another steel plate having a flange portion is formed so as to be opposed to each other through a flat portion of another steel plate that is flat. A method for laser welding of the overlapped portion of steel plates of the structure according to claim 1.
(10) The overlapping portion of the steel plates of the structure is a steel plate in which one steel plate has a bent portion at least on one side and a flange portion following the one, and the bent portion at least on one side follows the flange portion of the one steel plate. The overlapping portion of the steel plate of the structure according to any one of (1) to (6), wherein the flange portion of another steel plate having a flange portion is formed by overlapping in the same direction. Laser welding method.
(11) The method for laser welding a steel plate overlap portion according to any one of (1) to (10), wherein the steel sheet of the structure has a tensile strength of 440 MPa or more.

According to the present invention, the position of the joint portion is fixed by temporary attachment before performing laser welding. For this reason, at least immediately after laser welding (within about 8 hours after welding), it is possible to relieve stress applied to the laser welded portion due to deformation accompanying welding, springback of the molded member, and the like. For this reason, even if hydrogen penetrates into the welded part during welding, cracks in the welded part or breakage, that is, delayed fracture can be prevented.
Since the hydrogen that has entered during welding is dissipated into the atmosphere over time, the risk of delayed fracture is mitigated over time. Therefore, stress applied to the welded portion can be relaxed at least immediately after welding (within about 8 hours after welding), and delayed fracture can be prevented.

Hereinafter, the method of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a perspective view showing a structural material according to an embodiment of the laser welding method of the present invention. In this embodiment, a structure having an I shape in top view is illustrated.
As shown in FIG. 1, the structure 1 includes formed members 2 and 3 whose axial cross-sectional shape is formed into a hat shape. Each formed member is formed by pressing a thin steel plate with flanges 4, 6 and Bending portions 5 and 7 following this are formed. These forming members 2 and 3 are overlapped so that the flange portions 4 and 6 face each other, and the temporary attachment D is Ds, De, and D2 along the planned welding line of the formed overlapping portion 9 of the flange. It is given as D4. In addition, in the example of FIG. 1, the upper and lower steel plates of the overlapped portion are temporarily fixed by spot welding.
Thereafter, the overlapping portion 9 is welded by a laser torch 10 to form a laser weld bead 11.

FIG. 2 is a partial plan view of the upper surface showing the welding situation of the structure of one embodiment of the laser welding method of the present invention, showing the positional relationship between the welded part and the tacking.
On the extension line 13 of the planned line 12 where the laser welding bead of the flange overlapping portion 9 is formed, the temporary stop Ds near the start end and the vicinity of the end within a distance G1 or G2 from the start end S and end E of the bead In addition, temporary welding of D2 to D4 is applied to a planned weld bead (also referred to as an intermediate part of the weld bead) other than the start and end.

As described above, the tack D is for fixing the upper and lower steel plates at least in the flange portion in order to reduce or disperse the influence of stress on the laser weld bead (welded portion). As long as it has, the position where temporary attachment is performed, the number of temporary attachment parts, the form of temporary attachment, etc. are not particularly limited. That is, the tacking can be provided on the planned welding position (line) where the welding bead is to be formed, on the extension (line), or in the vicinity thereof.
In addition, since the vicinity part including the start end (S, E) of a weld bead and the extension line of a weld bead is a part where stress tends to concentrate, in this invention, the extension line 13 of the laser welding bead 12 planned. In the above, at least temporary attachment is performed within a range of 30 mm from the start and end.
This is because if the distance between the start and end points is 30 mm or more on the extension line of the planned weld bead, the welding start and end points are too far apart from each other, and the effect of the tacking on the start and end points is reduced. It is more preferable to tack on the start and end of the planned weld bead.
That is, as shown in FIG. 2, the temporary attachments Ds and De are applied within the range from the start and end S and E to G1 and G2 on the expected extension line of the laser weld bead 12, and G1 and G2 are , Within 30 mm. Moreover, it is also preferable to set Ds and De on the starting end S and the end of the planned weld bead.
In the present invention, when a part of the tacking portion is on the extension line or the weld bead, the tacking is on the extension line or the weld bead.

  Further, the number of places to be tacked is not particularly limited, and can be determined according to the planned length L of the weld bead. That is, if the number of temporary attachment points is large, it is advantageous in that the influence of stress on the planned weld bead can be suppressed or dispersed, but the work for temporary attachment increases, which is not preferable in terms of cost and efficiency. On the other hand, if the number of temporary attachment points is too small with respect to the planned length of the weld bead, the temporary attachment interval will be increased, and the effect of suppressing and dispersing the stress on the weld bead will be insufficient. Therefore, temporary attachment is also performed at the intermediate portion of the start and end of the planned weld bead, and the number of temporary attachment points and / or the temporary attachment interval is adjusted so that the interval between adjacent temporary attachments is within 100 mm. It is preferable. This is because, if the interval between the adjacent tacks is more than 100 mm, the effect of suppressing and dispersing the stress that affects the weld bead (welded part) becomes insufficient.

As shown in FIG. 2, in addition to the temporary attachments Ds and De in the vicinity of the start and end on the extended line of the planned line 12 of the laser weld bead, in D2 to D4 applied to the intermediate part of the planned weld bead 12, The intervals F1 to F4 between the adjacent tacks (Ds to D2, D2 to D3, D3 to D4, and the distances D4 to De are F1, F2, F3, and F4, respectively) are 100 mm or less as described above. Preferably there is.
Needless to say, if the length of the planned weld bead is short and the interval between adjacent tacks does not exceed 100 mm, it is only necessary to perform tacking in the vicinity of the start and end as described above.

The size of the tacking (for example, the diameter d of the tacking portion D) is not particularly limited, but if it is too small, the effect of suppressing and dispersing the stress on the planned weld bead becomes insufficient. Therefore, it is preferable that the width be at least the expected width t of the weld bead, that is, the length in a direction perpendicular to the welding direction of the bead.
That is, FIG. 3 is a schematic plan view in which the vicinity of the tacking portion in the welding method of the present invention is enlarged, and illustrates the size of the tacking D. In other words, the diameter d of the tack D is preferably equal to or greater than the planned weld bead width t (d ≧ t). This is because if the diameter d of the tack is too smaller than the width of the weld bead (the width in the direction perpendicular to the welding direction), the stress affecting the weld bead (welded portion) is suppressed and the effect of dispersing becomes insufficient. . Preferably, d is 1.5t to 3.0t.

The method for performing the tacking is not particularly limited as long as the tacking sufficiently suppresses the influence of the stress on the weld bead and obtains an effect of dispersing, and the welding or mechanical method is appropriately selected. Can do.
As a mechanical method, a clamp jig can be used for temporary attachment so as to sandwich the overlapping portion of the flange. However, in laser welding, it is necessary to avoid movement of the laser device to avoid interference with the clamp jig. In particular, when the number of temporary attachment points is large and the distance between adjacent temporary attachment points is small, the number of clamp jigs to be attached is large and the operation becomes complicated. However, when it is necessary to enlarge one tacking range, it is preferable that a tacking with a large range can be easily obtained by appropriately selecting the size of the clamp jig.

  On the other hand, unlike the mechanical method described above, the welding method does not require the movement of the laser device to avoid interference with the clamp jig during laser welding, and the number of temporary attachments is small. Even when there are many cases, it is possible to perform temporary attachment efficiently. Moreover, it is suitable when forming a small structure or a small range of tacks. However, when laser welding a large structure or when forming a large range of tacks, the spot size is limited. Thus, the means for forming the tack can be appropriately selected according to the conditions such as the properties of the structure to be laser welded, the number of tack positions, the interval, and the size of the tack range.

  4 (a) and 4 (b) show examples of structures according to other embodiments of the laser welding method of the present invention. In the example of the structure having an H shape when viewed from the top, the overlapping part of the flange of the molded member is shown. A laser weld bead is formed. In (a), temporary attachment is performed by spot welding on the start and end portions of the weld bead, and in (b), a plurality of temporary attachments are applied between the start and end portions of the weld bead and the start and end portions. Also in these examples, since the position where the temporary attachment is performed, the number of temporary attachment parts, the form of the temporary attachment, and the like are as described above, detailed description thereof is omitted.

  The laser welding method of the present invention is not limited to the structure, and can be widely applied when superposing thin steel plates and laser welding the overlapped portion, and the scope thereof is not limited. As described above, in FIG. 8, (a) shows two members 2 and 3 having a flange portion 4 and a bent portion 5 following the flange portion 4 and a sectional shape perpendicular to the axial direction formed into a hat shape. 4 and 6 are arranged so as to face each other, the flange portions 4 and 6 are overlapped, and the overlapped portion is welded to form a structure, and (b) shows the above-described hat-shaped member 2. The flange portion 4 is arranged so as to face the flat steel plate member 8 and overlapped, and the overlapped portion is welded to form a structure, and (c) shows the two hat shapes as described above. The flange portions 4 and 6 of the members 2 and 3 are arranged so as to oppose each other with a flat steel plate member 8 interposed therebetween, and the overlapped portions are welded to form a structure. ) A plurality of the hat-shaped members as described above (in the figure, Two 2,3) superimposed in the same direction, is obtained by forming a structure by welding the overlapped portion. In laser welding of such a structure, stress concentration due to springback of the molded member is present, so that the effects of the present invention can be obtained more suitably.

  Although the laser welding method of the present invention is not particularly limited to the steel type, as described above, delayed fracture did not occur in steel with a tensile strength of 270 MPa class, and thus high strength steel sheets, particularly delayed fracture. It is preferable to apply in the case of a structure using a steel material of a steel type having a tensile strength of 440 MPa or more where the above problem becomes significant.

Hereinafter, the present invention will be specifically described based on examples.
High-strength thin steel plate having a thickness of 1 to 1.2 mm (steel component having a tensile strength of 440 MPa is in mass%, C: 0.10%, Si: 0.11%, Mn: 0.95%, 980 MPa steel. The components were, by mass, C: 0.13%, Si: 1.00%, Mn: 2.20%.) Two molded members having the shape shown in FIG. Then, a structure was created by laser welding of the overlapped portion of the flange. The axial length of the molded member was 700 mm, and the length of the weld bead was 50 to 600 mm.
Prior to laser welding, temporary attachment was applied to the overlapped portion of the flange in various forms, and the presence or absence of delayed fracture after laser welding was confirmed. Table 1 shows the positions of the tacking, the spacing of the tacking, and the size (diameter) of the tacking. The laser welding conditions are the same as described above, aiming at the bead width: plate thickness mm × 1.0, beam waist 0.6 mm, defocusing: +2 mm, processing point output: 3.5 kW, welding speed: 2 m / min, tip The diameter was set to 5 mmφ, the shielding method was a coaxial center shield (no back shield), and the shielding gas was Ar of 25 l / min.

表１から判るように、予定される溶接ビード延長線上において始終端部の近傍に仮付けを施さなかった比較例１、２および、始終端部から３０ｍｍを超えた位置に仮付けを施した比較例３では、遅れ破壊が発生した。これに対して、予定される溶接ビードの延長線上で、始終端から３０ｍｍ以内に仮付けを施した本発明の実施例では、いずれも遅れ破壊は発生しなかった。また、実施例４から判るように、溶接ビードの始終端部の近傍のみに仮付けを施した場合でも、遅れ破壊の発生を抑制できることが判った。

As can be seen from Table 1, Comparative Examples 1 and 2 in which temporary attachment was not performed in the vicinity of the start / end portion on the planned weld bead extension line, and comparison in which temporary attachment was applied to a position exceeding 30 mm from the start / end portion In Example 3, delayed fracture occurred. On the other hand, no delayed fracture occurred in any of the examples of the present invention in which temporary attachment was performed within 30 mm from the start and end points on the planned extension line of the weld bead. Further, as can be seen from Example 4, it was found that the occurrence of delayed fracture can be suppressed even when provisional attachment is performed only in the vicinity of the start / end portion of the weld bead.

It is a perspective view which shows the structure by one Embodiment of the laser welding method of this invention. It is a partial top view of the upper surface which shows the welding condition of the structure by one Embodiment of the laser welding method of this invention. It is a plane schematic diagram explaining the magnitude | size of the temporary attachment in the laser welding method of this invention. It is a perspective view which shows the example of the structure by other embodiment of the laser welding method of this invention, (a) is the state which gave temporary attachment only to the start terminal part of a weld bead, (b) is the beginning and end of a weld bead The state which gave temporary attachment to the edge part and the intermediate part is each shown. It is a figure which shows the condition of the test body for a T peel strength test. It is a cross-sectional schematic diagram which shows the rupture situation of the laser welding part in a T peel strength test in a pattern, (a) is a rupture at the weld metal, (b) is a rupture near the HAZ or bond part, and (c). Indicates breakage in the base material. It is a schematic diagram which shows the generation | occurrence | production location of the delayed fracture in the laser welding of a structure material, (a) shows the case where a top view is an I-shaped structure, (b) shows the case where a top view is an H-shaped structure. . It is a schematic diagram which shows the structure of a flange and the cross-sectional shape of a structure, (a) is what overlapped the flange part facing the flange part of another member, (b) is another flat board. (C) is the same as the flange part of the other member of the flange part, and (c) is the same as the flange part of the other part of the flange part. Each is shown superimposed in the direction.

Explanation of symbols

1 Structure 2 Molded Member (Steel)
3 Molded parts (steel plate)
DESCRIPTION OF SYMBOLS 4 Flange part 5 Bending part 6 Flange part 7 Bending part 8 Flat steel plate member 9 Overlapping part 10 Laser torch 11 Laser welding bead 12 Expected laser welding bead line 13 Extension line of expected laser welding bead line 14 T peel test Piece 15 T peel specimen 16 Base material 17 Weld metal 18 Bond or heat-affected zone 19 Crack or fractured portion D Temporary attachment S Bead start end E Bead end portion Ds Temporary attachment near bead end portion Temporary near Dead end portion Attachment D1 to Dn Temporary attachment of intermediate part G1 Interval from bead start end to temporary attachment near bead start end G2 Interval from bead end to temporary attachment near bead end F1 to Fn Interval between adjacent temporary attachments L Expected bead length d Tacking diameter t Laser weld width

Claims (11)

  A laser beam is applied from the upper surface of the uppermost steel plate of the overlapped portion formed by overlapping a plurality of steel plates of a structure composed of steel plates to melt the lower surface of the lowermost steel plate and weld the overlapped portion. In laser welding of overlapped portions of steel sheets, a structure is provided in which tacking is applied to a range within 30 mm from the start and end on the extension line of the laser welding bead where the overlapped portions are planned, and then the overlapped portions are laser welded Laser welding method for the overlap of steel plates.   2. The laser welding method for a steel plate overlapping portion of a structure according to claim 1, wherein the tacking is performed on a start and end of a laser welding bead to be planned.   A laser beam is applied from the upper surface of the uppermost steel plate of the overlapped portion formed by overlapping a plurality of steel plates of a structure composed of steel plates to melt the lower surface of the lowermost steel plate and weld the overlapped portion. In the laser welding of the overlapped portion of the steel plates, temporary attachment is performed at the intermediate portion of the start and end of the laser welding bead scheduled for the overlapped portion so that the interval between adjacent temporary attachments is within 100 mm. The laser welding method of the overlap part of the steel plate of the structure of Claim 1.   The laser welding method for the overlapped portion of steel plates of a structure according to any one of claims 1 to 3, wherein the diameter of the tack is larger than the bead width.   The laser welding method for the overlapped portion of steel plates of a structure according to any one of claims 1 to 4, wherein the tacking is performed by spot welding.   6. The laser welding method for overlapping portions of steel plates of a structure according to any one of claims 1 to 5, wherein the tacking is performed by mechanical fastening means.   The overlap portion of the steel plates of the structure is a steel plate in which one steel plate has a bent portion and a flange portion subsequent to at least one side, and a bent portion and a subsequent flange portion are provided at least on one side of the flange portion of the one steel plate. The method of laser welding of the overlapped portion of the steel plates of the structure according to any one of claims 1 to 6, wherein the flange portions of the other steel plates are overlapped with each other.   The overlapping portion of the steel plates of the structure is a steel plate in which one steel plate has a bent portion and a flange portion following at least one side, and a flat portion of another flat steel plate is overlapped on the flange portion of the one steel plate. The method for laser welding of the overlapped portion of the steel plates of the structure according to any one of claims 1 to 6, wherein the method is a laser welding method.   The overlap portion of the steel plates of the structure is a steel plate in which one steel plate has a bent portion and a flange portion subsequent to at least one side, and a bent portion and a subsequent flange portion are provided at least on one side of the flange portion of the one steel plate. The flange part of the other steel plate which has it is made to oppose through the flat part of the further another steel plate, and it overlaps and formed, It is any one of Claims 1-6 characterized by the above-mentioned. Laser welding method for the overlapped part of steel plates of the structure.   The overlap portion of the steel plates of the structure is a steel plate in which one steel plate has a bent portion and a flange portion subsequent to at least one side, and a bent portion and a subsequent flange portion are provided at least on one side of the flange portion of the one steel plate. The method of laser welding of the overlapped portion of steel plates of a structure according to any one of claims 1 to 6, wherein the flange portion of another steel plate is formed by overlapping in the same direction.   The method for laser welding a steel plate overlap portion according to any one of claims 1 to 10, wherein the steel sheet of the structure has a tensile strength of 440 MPa or more.

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