JP2016068153A - Welding structure manufacturing method and welding structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a welding structure manufacturing method capable of making difficult the occurence of solidification cracking even when a flange width is smaller than that of spot welding regarding the manufacturing of a welding structure in which a metal plate member, for example, the flange of a hat-shaped member is stacked on the other metal plate member to be welded by laser.SOLUTION: The welding structure manufacturing method for stacking together a plurality of metal plate members to weld the stacked parts by laser is characterized in that for at least one of the stacked metal plate members, the initial residual plastic strain of the end of one side having a short distance from a line to an end surface among the parts of one side and the other side sandwiching the line which is a welding line is increased, and laser is applied along the line to carry out welding.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for manufacturing a welded structure and a welded structure. More specifically, the present invention relates to a method for manufacturing a welded structure and a welded structure obtained by laser welding an overlapping portion of metal plate members. The “metal plate member” is used to mean a member formed and / or cut into a predetermined shape from a metal plate.

In an automobile, a long member having a cross-sectional hat shape (hereinafter simply referred to as a “hat type”), which is one embodiment of a metal plate member manufactured from a metal plate (typically, a steel plate and will be described below as a steel plate). A number of "members" are used. Such a hat-shaped member is usually overlapped with a steel plate member (for example, a closing plate or another hat-shaped member) that is another metal plate member by a flange, and is joined at the overlapping portion. The most commonly used method for joining in this case is resistance spot welding (hereinafter referred to as spot welding).
Recently, studies have been made to reduce the weight of the member by narrowing the flange width of the hat-shaped member by applying laser welding instead of spot welding. Specifically, it is as follows.

  In spot welding, it is necessary to sandwich and pressurize the welded portion with an electrode. Further, if the welding position is too close to the end face of the flange, the molten metal is scattered (chile). Therefore, in spot welding, it is necessary to secure the width of the flange with a size of about 15 mm or more. On the other hand, according to laser welding, it is not necessary to apply pressure unlike spot welding, and the melt width can be suppressed to about 1 mm. Therefore, in laser welding, there is a possibility that the width of the flange can be made narrower.

However, generally, when laser welding is performed near the end face of the flange (generally, an area less than 10 mm from the end face), there is a high risk of solidification cracking in the weld. Accordingly, there is a need for a welding method that does not cause solidification cracks even when the flange width is shortened.
For example, “Hirohira Ando,“ Evaluation Method for Hot Cracking Progression Mechanism and Hot Cracking Susceptibility by Rotational Deformation-Hot Cracking Phenomenon of Thin Aluminum Alloy (2nd Report) ”, Journal of Welding Society, Vol. 42, No. 9 Pp. 37-47 (1973) "indicates that solidification cracking during welding is a solidification brittle temperature region (Brittens Temperature region) in which the ductility in which a solid phase and a liquid phase coexist is reduced in the process of melting a molten metal. In the Range (BTR)), the increase in strain caused by the deformation of the steel plate edge (in the case of a hat-shaped member) by the heat of fusion exceeds the strain required for cracking (hereinafter referred to as “limit strain”). It is thought that it occurs in. In view of this, methods for preventing solidification cracking include reduction of BTR and control of limit strain by optimization of the components of the weld metal, and suppression of strain generated at the end of the steel plate. However, regarding the reduction of the BTR and the control of the limit strain by optimizing the components of the weld metal, it is necessary to adjust the material of the steel plate itself. The adjustment of the material of the steel sheet itself may affect other performances, so there is a limit as a countermeasure.

  Therefore, for example, the following techniques have been proposed for suppressing the distortion generated at the end (flange) of the steel plate.

In Patent Documents 1 and 2, when the composition of the weld metal can cause cracking, the plate is pressed against the steel plate end near the irradiation position of the laser beam, and welding is performed while suppressing the expansion of the steel plate end. An invention for preventing solidification cracking is disclosed. That is, it is restrained by a jig.
However, when a jig is used in this way, it is necessary to arrange a device (a jig) that suppresses expansion of the steel plate end during welding, and cannot be used for a welded portion of a small member or a member having a complicated shape. At the same time, the number of welding man-hours increases and becomes complicated.

Patent Document 2 discloses a method of welding while cooling the end face of the flange. Here, it is considered that cracking occurs due to the strain caused by the difference in thermal expansion between the base metal side and the end face side that is at a higher temperature than the base metal side, and the ultimate temperature on the flange end face side is lowered to reduce the plate width direction. By suppressing expansion and contraction, the generation of cracks is suppressed by suppressing the generation of strain.
However, when the flange end surface is cooled, the temperature difference from the weld line increases, and the rotational deformation driving force increases, so that depending on the welding conditions, distortion may increase and cracking may be promoted. Furthermore, in this method, it is necessary to pay attention to the arrangement of the cooling device in the same manner as described above, and there is a possibility that the number of work steps may increase.

  Patent Document 3 describes that the presence or absence of solidification cracking depends on the distance (L) from the end, the welding speed (V), and the plate thickness (h). However, when the flange width is small, the welding speed cannot be increased, and the solution is not clearly described in Patent Document 3.

JP 2008-18450 A JP 2009-56483 A JP 2009-285722 A

  As described above, solidification cracking is considered to occur when the incremental amount of strain generated in the BTR exceeds a certain threshold. In laser welding of hat-shaped member flanges, it is considered that there are the following two main factors that affect the strain increment in the BTR.

(1) Member rigidity determined by the size of the distance (flange width) of the welding position from the flange end face:
The greater the flange width and the greater the distance from the flange end to the welding position, the higher the rigidity, and the deformation (rotational deformation) of the flange and the strain received thereby are suppressed. However, simply increasing the flange width is contrary to the weight reduction of the member as described above.

(2) Temperature distribution in the plate width direction due to heat input:
It is well known that when the temperature distribution is non-uniform in the sheet width direction of the steel sheet, the driving force of rotational deformation works, but this rotational deformation is considered to cause cracking. That is, when welding from A to B of the plate 1 as shown in FIG. 6A, a non-uniform temperature distribution is generated in the plate width direction. Rotational deformation occurs in the direction of C. Since the strength of the embrittled region of the weld is extremely small, the weld metal in the embrittled region can hardly suppress this rotational deformation. Cracks occur when the amount of strain applied to the embrittled region due to this rotational deformation exceeds the limit strain. When welding proceeds thereafter, the weld pool Y also advances as shown in FIG. 6B, and the fulcrum of the rotational deformation follows the same and moves to the point P ′. At this time, if the temperature distribution is in a quasi-steady state, the amount of strain applied to the embrittled region is considered to be constant over time, and in this case, cracks propagate along the weld line as shown in FIG. To do.
On the other hand, when the welding speed is low, the temperature distribution in the plate width direction is easily uniformized, and the driving force for rotational deformation becomes small. However, if the welding speed is simply lowered, the productivity of the member is deteriorated, and if the plate width is reduced, the rigidity is lowered, so that the generated strain cannot be suppressed and the possibility of occurrence of solidification cracks increases.

  Therefore, in view of the above problems, the present invention reduces the flange width in comparison with spot welding when manufacturing a welded structure in which a metal plate member, for example, a flange of a hat-shaped member is overlapped with another metal plate member for laser welding. It is an object of the present invention to provide a method for manufacturing a welded structure that hardly causes solidification cracks. A welded structure is also provided.

The present invention is as follows.

  The invention according to claim 1 is a method of manufacturing a welded structure in which a plurality of metal plate members are overlapped and laser-welded at the overlapped portion, and at least one metal plate among the overlapped metal plate members About the member, increase the initial residual plastic strain at the end of the one side part where the distance from the line to the end surface is short among the parts on one side and the other side across the line to be the welding line, This is a method of laser welding of steel plates, in which welding is performed by irradiating a laser along.

  The invention according to claim 2 increases the initial residual plastic strain of the other side part in the laser welding method of the steel sheet according to claim 1.

  According to a third aspect of the present invention, in the laser welding method for a steel sheet according to the first or second aspect, the portion that increases the initial residual plastic strain is 20% or more of the residual strain that does not increase the initial residual plastic strain. Increase.

  Invention of Claim 4 includes the process of carrying out laser welding by the laser welding method of the steel plate in any one of Claim 1 thru | or 3, At least one of the metal plate members is a long member whose section is a hat type In this method, the initial residual plastic strain at the end of the flange of the member is increased, and the flange and the other metal plate member are overlapped and laser welded.

  According to a fifth aspect of the present invention, in the method for manufacturing a welded structure according to the fourth aspect, a weld line is formed along the longitudinal direction of the flange in a region of 10 mm or less from the range in which the initial residual plastic strain is increased.

  The invention according to claim 6 is a welded structure in which a plurality of metal plate members are overlapped and laser-welded at the overlapped portion, and at least one metal plate member of the overlapped metal plate members, A welded structure in which the initial residual plastic strain is larger at the end of one side of the one side and the other side across the weld line than the other flat part where the distance from the weld line to the end surface is short It is.

  According to a seventh aspect of the present invention, in the welded structure according to the sixth aspect, at least one of the metal plate members is a long member having a hat-shaped cross section, and the flange of the member and another metal plate member Are superimposed and laser welded.

  According to the present invention, in manufacturing a welded structure in which a metal plate member, for example, a flange of a hat-shaped member is overlapped with another metal plate member and laser-welded, even if the flange width is reduced compared to spot welding, The occurrence of solidification cracks can be suppressed.

1 is an external perspective view showing an outline of a hat-type welded structure 10. FIG. It is the figure which expanded and represented a part of flange 11c and the welding part 13. FIG. It is a figure explaining one scene of the process of a welding method. It is a figure explaining one scene of welding. It is a figure explaining the evaluation method by an Example. FIG. 6A is one explanatory diagram schematically showing the mechanism of solidification cracking, and FIG. 6B is another explanatory diagram schematically showing the mechanism of solidification cracking.

  FIG. 1 is a diagram for explaining a first embodiment, and is a perspective view showing an appearance of a hat-type welded structure 10 which is one form of a welded structure obtained by the method for manufacturing a welded structure of the present invention. FIG. 2 is an enlarged view of a part of the flange 11c. In FIG. 1 and FIG. 2, the width direction, the longitudinal direction, and the height direction are shown together as necessary.

The hat-type welded structure 10 includes a hat-type member 11 and a closing plate 12.
The hat-shaped member 11 is formed of a steel plate and is one of metal plate members. The hat-shaped member 11 has a web piece 11a, a wall piece 11b extending from both ends of the web piece 11a, and a flange 11c provided at the end of the wall piece 11b in a cross section orthogonal to the longitudinal direction, and is formed into a so-called hat shape. Has been. Further, the flange 11c is provided with an initial residual plastic strain increasing portion 11d whose initial residual plastic strain is greater (increased) than other portions (flat portions) at the end in the width direction (FIG. 2). (The part shown by hatching.)
Here, “residual plastic strain” means the plastic strain remaining in the material when no external force (load) is applied to the material, and “initial residual plastic strain” is the residual plastic strain before welding. Is the residual plastic strain present in

In the initial residual strain increasing portion 11d, it is preferable that the amount of the initial residual strain is increased by 20% or more compared to other portions where the initial residual strain is not increased. Thereby, the effect by this invention can be made more reliable. In addition, since the effect increases as the initial residual plastic strain increase increases, the upper limit is not particularly limited, but if it is too high, the material may break, so the material used may not cause the break. This is the upper limit for increasing the initial residual plastic strain.
Further, the initial residual strain increasing portion 11d has an initial residual plastic strain increasing portion 11d when the distance in the width direction (the size of IIa in FIG. 2) from a welded portion 13 described later to the end of the flange 11c is 100%. It is preferable to occupy in the range of 60% or more and 100% or less.
Here, the residual plastic strain can be specified by measurement by a known method. This includes, for example, hardness measurement method and X-ray diffraction method. In the case of the hardness measurement method, a relationship between hardness and residual plastic strain is obtained in advance, and the residual plastic strain is specified based on this relationship. The kind of hardness measurement is not particularly limited, and examples thereof include Vickers hardness measurement, Brinell hardness measurement, and Rockwell hardness measurement.

  Depending on the actual application, the hat-shaped member 11 may be straight in the longitudinal direction, or may be curved, or the cross-section may be widened or narrowed.

  On the other hand, the closing plate 12 is one of metal plate members, and is a substantially smooth steel plate that overlaps the initial residual plastic strain increasing portion 11d. Further, the width direction end portion of the closing plate 12 is also made to have a larger initial residual plastic strain at the width direction end portion than other flat portions in accordance with the example of the hat-shaped member 11, and a part of the initial residual plastic strain increasing portion 11d. It is preferable that it is comprised as.

Then, the closing plate 12 is disposed so as to pass between the two flanges 11c of the hat-shaped member 11 and overlap the initial residual plastic strain increasing portion 11d of the hat-shaped member 11, and the closing plate 12 and the flange 11c are overlapped. ing. Among the overlapped portions, a welded portion 13 is provided on the inner side (opposite to the end face) of the initial residual plastic strain increasing portion 11d, and both are joined by the welded portion 13. In this embodiment, the welded portion 13 is a welded portion by penetration welding that penetrates the flange 11c and the closing plate 12 in the plate thickness direction.
The welded portion 13 is formed by laser welding and extends along the longitudinal direction of the flange 11c. The present invention is a welding method for forming the welded portion 13 and is welded at a high speed while shortening the distance from the end of the flange 11c shown by IIa in FIG. 2 to the welded portion 13 as compared with the conventional laser welding. However, cracking can be suppressed, and as a result, the width of the flange 11c shown by IIb in FIG. 2 can be made smaller than in the case of spot welding. Although not particularly limited, as shown in FIG. 2, the width IIb of the flange 11c can be suppressed to about 15 mm or less, and can be suppressed to about 10 mm or less except for the initial residual plastic strain increasing portion 11d.

Here, the steel plate used for the hat-shaped member 11 is not particularly limited, and is not particularly limited as long as it has a composition and a thickness that can be overlapped and laser-welded. For example, the thickness is preferably 0.5 mm or more and 3.2 mm or less. Moreover, you may equip the surface with the aluminum type plating which carried out the zinc type plating. Further, instead of a steel plate, another metal plate such as an aluminum alloy plate can be used.
Depending on the actual application, the shape of the hat-shaped member 11 may be straight in the longitudinal direction, may be curved, or may have a cross-sectional shape changing in the longitudinal direction. The present invention may be applied to any of them. Moreover, it may replace with the closing plate 12 and may weld with another hat-type member and other shape metal plate members. Or it is applicable also to the welding structure which piles up and welds three or more metal plate members.

  Next, the hat-type welded structure 10 as described above can be manufactured, for example, as follows. FIG. 3 shows an explanatory diagram. FIG. 3 is a view from the same viewpoint as FIG. 1, and shows the width direction, the longitudinal direction, and the height direction together.

  First, a hat-shaped member 11 'for welding is prepared. The welding hat-type member 11 ′ is a member in which the welded portion 13 is not yet formed with respect to the hat-type member 11 described above. Here, an initial residual plastic strain increasing portion 11d is formed in the welding hat-shaped member 11 '. The formation method of the initial residual plastic strain increasing portion 11d is not particularly limited as long as it can be formed at the above-described position and strain amount. For example, by cold working such as forging, peening, rolling, and the like, work hardening is performed. A method for increasing the residual plastic strain amount can be mentioned.

  As shown in FIG. 3, the closing plate 12 is disposed so as to pass between the two flanges 11c of the welding hat panel 11 ′ as shown in FIG. 12 and the flange 11c are overlapped, whereby the initial residual plastic strain increasing portion 11d and the end of the closing plate 12 (in this embodiment, the portion where the initial residual plastic strain is increased at the end of the closing plate 12) are overlapped. .

Next, as shown in FIG. 4, the flange 11c and the closing plate 12 stacked on the flange 11c are welded so as to penetrate in the thickness direction. That is, laser irradiation is performed, and the irradiated portion is moved in the longitudinal direction as indicated by an arrow IVa in FIG. 4 to perform welding. A known laser welding apparatus can be used as an apparatus for welding. The type of laser is not particularly limited as long as it is a laser that is usually used for laser welding of a steel plate, and examples thereof include a CO ₂ laser, a YAG laser, and a fiber laser. In addition, the spot diameter (laser irradiation diameter of the steel plate) in laser welding is not particularly limited, but is preferably 0.5 mm or more and 1.0 mm or less, and the obtained weld width is usually about 1 mm.

  With the above welding method, the rotational deformation of the steel sheet can be suppressed, and it is not necessary to restrain the steel sheet or to contact the jig, so that welding can be easily performed. Further, for example, solidification cracking can be suppressed even when the welding speed is increased at a portion where the distance from the end face is small.

  In this embodiment, since it is a hat-type welded structure, a wall piece 11b is formed on the opposite side of the end of the flange 11c across the weld line (welded portion 13), which increases the initial residual plastic strain. The same function as the part (suppresses rotational deformation of the steel sheet). Therefore, even if it is a form which is not a hat-type welded structure or a hat-type welded structure, an initial residual plastic strain increasing part may be provided at both ends of the weld line depending on circumstances. However, the present invention is not limited to this, and it is only necessary that the initial residual plastic strain increasing portion is formed at the end of the portion on the side where the distance to the end face is short among the one and the other portions delimited by the weld line.

  As a form of the present invention other than this, it is not always necessary that the initial residual plastic strain is increased with respect to all the members at the overlapping end portion within a range in which solidification cracking can be prevented. For example, the case where the width | variety of one metal plate member overlaid is sufficiently wide, or the case where it is a steel component which hardly produces a solidification crack, etc. are assumed.

  In the examples, the initial residual plastic strain increasing portion was formed and welded to the conditions under which solidification cracks were generated by a normal welding method, and the presence or absence of the occurrence of solidification cracks was evaluated. In this example, evaluation was performed by irradiating a single steel plate with a laser. Therefore, although strictly different from welding, this evaluation is also applied to welding when a plurality of metal plate members are stacked. It is possible. In the embodiment, as shown in FIG. 5, an initial residual plastic strain increasing portion 31 having a strain of 20% to 30% higher than other flat portions is formed on a single 1 mm-thick steel plate 30 as described later. did. Then, it was evaluated whether or not solidification cracking occurred at a site through which a heating part by laser light irradiation assuming laser welding passed.

Heating was performed by a laser emitted from a laser welding machine, and the irradiated portion was moved 6 mm from the end face of the steel plate 30 in parallel with the end face. The moving speed is 10 mm / s.
The initial residual plastic strain increasing portion 31 has the shape shown in FIG. 2 and is formed in a range of 4 mm from the end portion as compared with other portions. More specifically, an initial residual plastic strain increasing portion in which the initial residual strain is 30% higher in the region 2 mm wide from the end and the initial residual strain is 20% higher in the remaining 2 mm wide region.
On the other hand, the comparative example had the same shape as the example, but the initial residual plastic strain increasing portion was not formed.

  As a result, in the comparative example, intermittent cracks (solidification cracks) occurred in the part through which the heating unit passed. In contrast, no cracks occurred in the examples. Thus, it was found that cracking can be suppressed by increasing (applying) the initial residual plastic strain to the end portion and performing laser welding.

10 Hat-type welded structure (welded structure)
11 Hat-shaped member (metal plate member)
11c Flange 11d Initial residual plastic strain increasing part 12 Closing plate (metal plate member)
13 Welded part

Claims (7)

A method for manufacturing a welded structure in which a plurality of metal plate members are overlapped and laser welded at the overlapped portion,
Of at least one metal plate member among the stacked metal plate members, one of the portions on one side where the distance from the line to the end surface is short among the portions on one side and the other side across the line to be a welding line. A method for laser welding of steel plates, wherein welding is performed by increasing the initial residual plastic strain at an end and irradiating a laser along the line.   The method of laser welding a steel sheet according to claim 1, wherein the initial residual plastic strain at the other side portion is also increased.   The method of laser welding a steel sheet according to claim 1 or 2, wherein the portion that increases the initial residual plastic strain increases the residual strain by 20% or more relative to the portion that does not increase the initial residual plastic strain.   A step of laser welding by the laser welding method for a steel sheet according to any one of claims 1 to 3, wherein at least one of the metal plate members is a long member having a hat-shaped cross section, and a flange of the member is formed. A method for manufacturing a welded structure, wherein an initial residual plastic strain at an end is increased, and the flange and another metal plate member are overlapped and laser-welded.   The method for manufacturing a welded structure according to claim 4, wherein the weld line is formed along the longitudinal direction of the flange in a region of 10 mm or less from the range in which the initial residual plastic strain is increased.   A welded structure in which a plurality of metal plate members are overlapped and laser-welded at the overlapping portion, and at least one metal plate member of the overlapped metal plate members is sandwiched between one side and a welding line The welded structure in which the initial residual plastic strain is larger at the end of the one side portion where the distance from the weld line to the end face is shorter than the other flat portion among the other side portions.   The welding structure according to claim 6, wherein at least one of the metal plate members is a long member having a hat-shaped cross section, and a flange of the member and another metal plate member are overlapped and laser-welded. body.

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