JP2015199111A - Manufacturing method of welded structure - Google Patents

Abstract

In manufacturing a welded structure in which a metal plate member, for example, a hat-shaped member flange is overlapped with another metal plate member to perform laser welding, even if the flange width is reduced or the welding speed is increased, To provide a welded structure that is less prone to solidification cracking. A method of manufacturing a welded structure in which a plurality of metal plate members are overlapped and laser welding is performed at the overlapped portion, and a metal having an energy that melts the metal plate member is irradiated while moving the metal. In welding the plate member, welding is performed while performing auxiliary heating in which at least a part of the portion of the metal plate member other than the portion irradiated with the laser is heated with energy that does not melt the metal plate member. [Selection] Figure 3

Description

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

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 generated by the deformation of the steel plate end portion (in the above-described hat-shaped member, the flange) by the heat of fusion exceeds the strain required for crack generation (limit strain). ,it is conceivable that. In view of this, methods for preventing solidification cracking include reduction of the width of the BTR by controlling the components of the weld metal, control of the limit strain, and suppression of strain generated at the end of the steel plate. However, regarding the reduction of the BTR width 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 (jig) for suppressing the expansion of the end of the steel plate during welding, and it 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. This is because cracks occur 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. This is a method of preventing the occurrence of cracks by suppressing the occurrence of strain by suppressing expansion and contraction.
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, which may increase the number of work steps.

  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 amount of strain increase occurring in the BTR exceeds a certain threshold. In laser welding of the flange of the hat-shaped member, it is considered that there are the following two main factors affecting 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 larger 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, so that the plate 1 has an arrow C with the front P of the molten pool Y as a fulcrum. Rotational deformation occurs in the direction of. 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. Thereafter, when the welding proceeds, the molten pool Y also proceeds as shown in FIG. 6B, and the fulcrum of the rotational deformation follows and moves to 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.

  In view of the above problems, the present invention provides a metal plate member, for example, a hat-shaped member flange, which is overlapped with another metal plate member to manufacture a welded structure 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 even when the speed is increased.

  The present invention is as follows.

  The invention according to claim 1 is a method for manufacturing a welded structure in which a plurality of metal plate members are overlapped and laser-welded at the overlapped portion, and a laser having energy for melting the metal plate members is moved. When welding the metal plate member by irradiation, welding is performed while performing auxiliary heating in which at least a part of the metal plate member other than the portion irradiated with the laser is heated with energy that does not melt the metal plate member. A method for manufacturing a welded structure.

  According to a second aspect of the present invention, in the method for manufacturing a welded structure according to the first aspect, auxiliary heating is performed while moving.

  According to a third aspect of the present invention, in the method for manufacturing a welded structure according to the second aspect, the auxiliary heating is performed by a laser, and the auxiliary heating is performed while moving at the same speed as the laser welding.

  According to a fourth aspect of the present invention, in the method for manufacturing a welded structure according to any one of the first to third aspects, at least one of the metal plate members is a long member having a hat-shaped cross section, and the member The other flange and another 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, the welded portion is formed linearly along the longitudinal direction of the flange in an area of 10 mm or less from the end of the flange.

  According to a sixth aspect of the present invention, in the method for manufacturing a welded structure according to the fifth aspect, the portion heated by the auxiliary heating is more along the longitudinal direction of the flange than the portion irradiated with the laser. This is the end side of the flange.

  According to the present invention, 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 and laser-welded, the flange width is reduced or the welding speed is increased. However, 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 the method of welding. It is a figure explaining the preferable range of auxiliary heating. It is a figure explaining the evaluation method of 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 one embodiment, and is a perspective view showing an appearance of a hat-type welded structure 10 that is one mode 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.

The hat-type welded structure 10 includes a hat-type member 11 and a closing plate 12.
The hat-shaped member 11 is a metal plate member formed of a steel plate, and is provided at the end of the web piece 11a, the wall piece 11b extending from both ends of the web piece, and the end of the wall piece 11b in a cross section orthogonal to the longitudinal direction. It has a flange 11c and is formed in a so-called hat shape.
On the other hand, the closing plate 12 is also a metal plate member and is a substantially smooth steel plate.

And the closing plate 12 is arrange | positioned so that it may pass between the two flanges 11c of the hat-shaped member 11, and this closing plate 12 and the flange 11c are piled up. A welded portion 13 is provided at the overlapped portion, and both are joined at 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. In other words, in the welding method for forming the welded portion 13, the present invention cracks even if welding is performed at a high speed while shortening the distance from the flange end surface 11 d shown by IIa in FIG. 2 to the welded portion 13. As a result, the width of the flange indicated by IIb in FIG. 2 can be made smaller than the width required for conventional spot welding. For example, the width IIb of the flange can be suppressed to about 10 mm or less, more preferably about 8 mm or less. The lower limit of the flange width may be a width that does not cause solidification cracking, but if it is smaller than 1.5 mm, the flange end may melt and melt, so it is set to, for example, 1.5 mm or more. Is preferred.

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 zinc-type plating and aluminum-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 this invention is applicable also to manufacture of the welding structure which piles up and welds three or more metal plate members.

  Next, an example of a method for producing the hat-type welded structure 10 as described above will be described. In this example, for the sake of convenience, the example of producing the hat-type welded structure 10 described so far will be described. However, the method can be applied to other scenes in which the stacked metal plate members are laser-welded.

  First, at least two metal plate members to be welded are overlapped at the welding site. In the hat-type welded structure 10, the hat-type member 11 and the closing plate 12 are arranged so as to have the same form as in FIG. 1.

Next, the overlapped portion to be welded is laser welded. In the hat-type welded structure 10, the flange 11 c and the closing plate 12 stacked on the flange 11 c are welded so as to penetrate in the plate thickness direction. FIG. 3 shows an explanatory diagram. FIG. 3 is a view from the same viewpoint as FIG.
As can be seen from FIG. 3, in the laser welding of this embodiment, the main heating portion 20 is formed by laser irradiation (hereinafter also referred to as “main heating” in contrast to the auxiliary heating) for forming the welded portion 13 in the conventional manner. At the same time, the auxiliary heating is performed so as to run in parallel with the main heating unit 20, and welding is performed while forming the auxiliary heating unit 21. Therefore, the main heating part 20 moves in the direction along the welding line as shown by the arrow IIIa, and the auxiliary heating part 21 is also welded while moving in the direction shown by the arrow IIIb in parallel therewith.

  The main heating has energy for melting the metal plate member under the same conditions as usual, and a molten pool is formed in the main heating unit 20.

  On the other hand, in the auxiliary heating, the steel material cannot be melted alone by the auxiliary heating. Accordingly, the amount of heat for forming the auxiliary heating unit 21 is smaller than that of the main heating unit 20 to be welded, and the auxiliary heating unit 21 cannot be melted alone. The preferable amount of heat for auxiliary heating is 5% or more and 30% or less with respect to the amount of heat for main heating.

Moreover, if the position of the auxiliary heating part 21 with respect to the main heating part 20 is too close, the main heating part 20 will be affected too much to inhibit appropriate welding, and if too far, the influence of the auxiliary heating part 21 may be too small. is there. From this viewpoint, it is preferable that the auxiliary heating unit 21 is disposed in a range of 0 mm or more and less than 6 mm from the molten pool of the main heating unit 20 and the outer peripheral portion of the solidification brittle temperature region (BTR). However, at this time, it is more preferable to avoid the movement path of the main heating unit. Therefore, preferably, conceptually, it is preferable to form the auxiliary heating part 21 in the hatched area shown by IV in FIG.
Among these, it is preferable to perform auxiliary heating on the side with a smaller volume (in this embodiment, the end surface 11d side of the flange 11c) across the trajectory of movement of the main heating (that is, the portion that becomes the weld line).

  However, the auxiliary heating part 21 does not necessarily need to be one, and may be formed over a plurality. Further, the auxiliary heating unit 21 may extend over a wide range to some extent, and does not necessarily need to be a spot-like heating unit in a narrow range. Therefore, in the present embodiment, the auxiliary heating unit 21 has been described as running parallel to the main heating unit 20. However, the auxiliary heating unit 21 is formed at a predetermined position fixed without parallel running, and a plurality or a wide range is heated to provide the auxiliary heating unit. It may be formed.

As a main heating apparatus, a known laser welding apparatus can be exemplified. The type of laser is not particularly limited as long as it is a laser that is usually used for laser welding of steel, and examples thereof include a CO ₂ laser, a YAG laser, and a fiber laser. The spot diameter (laser irradiation diameter of the steel material) in laser welding is not particularly limited, but is preferably 0.5 mm or more and 1.0 mm or less, and the weld width obtained is usually about 1 mm.

On the other hand, as an apparatus for performing auxiliary heating, a laser welding apparatus similar to the main heating can be exemplified. However, the amount of heat and the irradiation position are adjusted as described above.
However, the apparatus for performing auxiliary heating is not limited to the laser welding apparatus described above. In addition, an arc welding apparatus, a gas burner, a high-frequency induction heating apparatus, an infrared heater for performing TIG (Tungsten Inert Gas) welding or plasma welding. Etc.

  The welding method as described above does not require a jig for restraining or contacting the metal plate member, so that welding can be performed easily. Furthermore, for example, solidification cracking can be suppressed even when the welding speed is increased at a portion where the distance from the end surface is small.

  In the above description, as an example of laser welding at the overlapping portion of the metal plate members, welding is performed by penetrating the welded portion from the surface of one of the metal plate members (flange 11c of the hat-shaped member 11) to the other (closing plate 12). An example of through welding is described. If the required welding strength is obtained, the welded portion may not penetrate the other member. Further, as another example of laser welding at the overlapping portion, the present invention can also be applied to the case where fillet welding of the overlapping portion is performed by laser welding.

  In the examples, auxiliary heating was performed for welding under conditions where solidification cracks were generated by a normal welding method, and the presence or absence of solidification cracks was evaluated.

  In the example, as shown in FIG. 5, main heating and auxiliary heating were performed on one 1 mm thick steel plate 30. And it evaluated whether the solidification crack generate | occur | produced in the site | part which the main heating part passed. In this evaluation, two or more steel plates were not overlapped and welded, so this is not an “Example” in a strict sense, but this result is in comparison with welding where two or more steel plates are overlapped. Has a similar tendency.

Main heating was performed by a laser emitted from a laser welding machine, and the irradiated portion was moved 3 mm from the end face 31 of the steel plate 30 in parallel with the end face 31. The moving speed is three conditions of 20 mm / s, 30 mm / s, and 40 mm / s.
On the other hand, the auxiliary heating is also performed by the laser emitted from the laser welding machine, the amount of heat is 10% of the main heating, and the auxiliary heating part is formed 2 mm away from the main heating part on the end face 31 side. Parallel to the main heating section.

  The comparative examples were all set to the same conditions except that auxiliary heating was not performed for the above-described examples.

  As a result, in the comparative example, intermittent cracking (solidification cracking) occurred in the part where the main heating part passed in all cases where the moving speed was 20 mm / s, 30 mm / s, and 40 mm / s. On the other hand, cracks did not occur in the examples where the moving speed was 20 mm / s or 30 mm / s. On the other hand, some cracks occurred in the examples where the moving speed was 40 mm / s, but the cracks could be greatly reduced as compared with the comparative example. Furthermore, when the amount of heat for auxiliary heating was 20% of the amount of heat for main heating under the condition of a moving speed of 40 mm / s, no cracking occurred.

  As described above, it was found that cracking can be suppressed by laser welding in which auxiliary heating is performed in addition to main heating.

10 Hat-type welded structure (welded structure)
11 Hat-shaped member (metal plate member)
12 Closing plate (metal plate member)
13 welding part 20 main heating part 21 auxiliary heating part

Claims (6)

A method for manufacturing a welded structure in which a plurality of metal plate members are overlapped and laser-welded at the overlapped portion,
In welding the metal plate member by irradiating while moving the laser having energy that melts the metal plate member, at least a part of the portion of the metal plate member other than the portion irradiated with the laser, The manufacturing method of the welding structure which performs the said welding, performing the auxiliary heating which heats with the energy which a metal plate member does not fuse | melt.   The method for manufacturing a welded structure according to claim 1, wherein the auxiliary heating is performed while moving.   The method for manufacturing a welded structure according to claim 2, wherein the auxiliary heating is performed by a laser, and the auxiliary heating is performed while moving at the same speed as the welding by the laser.   4. 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 overlapped and laser-welded. Method for manufacturing a welded structure.   The manufacturing method of the welding structure of Claim 4 which forms a welding part linearly in the area | region of 10 mm or less from the edge part of the said flange along the longitudinal direction of a flange.   The method for manufacturing a welded structure according to claim 5, wherein the portion heated by the auxiliary heating is closer to the end of the flange along the longitudinal direction of the flange than the portion irradiated with the laser. .

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