JP2861528B2 - Laser welding method for steel sheet for press forming - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser welding method for a steel sheet used for press forming, and more particularly to a laser welding method for enhancing stretch flange formability.

[0002]

2. Description of the Related Art In recent years, as a material for press forming in automobile factories, a joining material obtained by butt-welding thin steel plates with laser light is often used. Usually, the allowable amount of the butt gap in laser welding is said to be about 15 to 20% of the plate thickness, and when the welding line is long, it is difficult to maintain the butt gap within the allowable value. Therefore, a technique has been developed in which a filler wire is fed to the butt gap, and the filler wire and the material to be welded are irradiated with laser light to perform welding. As prior art related to this, for example, Japanese Patent Publication No. Sho 63-3
No. 2554 is known.

[0003] In butt laser welding of thin steel plates using filler wires, if welding conditions are not proper, poor welding tends to occur at the welding start end and the welding end end, causing problems in press forming. FIG. 9 and FIG. 10 show examples of poor welding at the welding start end.

In FIG. 9, a butting gap S is formed between the thin steel plate 1 and the thin steel plate 2, and the butting portion where the gap S is generated is joined by laser welding. The weld bead 3 at the butt portion is formed from a position advanced by a distance X from the welding start side end face of the thin steel plates 1 and 2,
A so-called sink mark 4 occurs in a portion corresponding to the distance X.

In FIG. 10, a thin steel plate 5 and a thin steel plate 6
The weld bead 7 at the butt portion is formed from the welding start side end surfaces of the thin steel plates 5 and 6, and a spherical molten deposit 7a is formed on the welding start side end surfaces. Before welding the thin steel plates 5 and 6, only the filler wire is melted by the laser beam and adheres to the welding start side end surfaces of the thin steel plates 5 and 6.

As shown in FIG. 9 and FIG. 10, the occurrence of sink marks 4 and the generation of spherical molten deposits 7a significantly reduce stretch flange formability during press forming and cause flange cracking. Here, the stretch flange forming refers to a forming form in which the panel wire length is increased in the draw forming or the bending forming as compared with before the forming. In stretch flange forming, for example, the outer edge of the panel is significantly elongated, so that a material having low ductility may be broken.

As a method of preventing a flange crack due to generation of sink marks and spherical molten deposits, for example, Japanese Utility Model Laid-Open No. 3-2
No. 4371 is known. This publication discloses that after welding with a steel plate by butt laser welding, welding defects such as insufficient welding such as sink marks are eliminated by notching a welding end. Further, a technique has been considered in which a notch is formed in advance in the butted portion of the steel sheet before welding to prevent the generation of a spherical melt at the joint end of the steel sheet.

[0008]

However, a method of forming a notch in a butt portion of a steel plate before laser welding,
In the case of the method in which the welded end is cut off after laser welding, the number of processing steps is increased, and the degree of freedom of the material shape is limited, which is problematic in terms of productivity. In addition, a press machine and a notch die are required to form the notch, and the die needs to be periodically polished to maintain the quality of the notch surface. In stretch flange forming, the quality of the notch surface is important, and if the burr of the notch surface is increased, the stretch flange formability is rather deteriorated. Therefore, in order to enhance the stretch flange formability, it is necessary to sufficiently suppress sink marks and molten deposits at the welding start end and the welding end end.

[0009] The present invention can sufficiently suppress the occurrence of sink marks and melt deposits at welding start end and the end of welding ends, provide a laser welding method of press-molding a steel sheet capable of enhancing the stretch flangeability The purpose is to do.

[0010]

In order to achieve the object of the present onset to achieve the above purpose
The light is as follows. Ends of the first steel plate and the second steel plate
While supplying filler wire to the butting part,
Laser welding of steel sheet for press forming to weld joint
The butt gap of the steel sheet is 0.1 mm or less,
Between the irradiation start position of the laser beam and the welding start side end face of the steel sheet
When the distance is 2 mm or more, the laser beam
The distance from the end surface on the contact end side is
The difference between the firing start time and the filler wire supply start time
−0.1 to 0.1 second, laser beam irradiation end time and filler
-The deviation from the wire supply end time is -0.1 to 0.1
A laser welding method for a steel sheet for press forming , wherein the laser welding is performed under welding conditions of seconds .

[0011]

According to the laser welding method for a steel sheet for press forming constituted as described above, the butt gap of the steel sheet is 0.1 mm.
Laser welding is started in the state set below . At the start of laser welding, the distance between the laser beam irradiation start position and the welding start end face of the steel plate is set to 2 mm or more , so that laser welding can be performed when the laser beam output reaches a stable state. Become. Also, at the start of laser welding, the difference between the start time of laser beam irradiation and the start time of filler wire supply is in the range of -0.1 to 0.1 seconds . The start of supply will not be significantly delayed. Therefore, the abutting portion is sufficiently melted by the laser light, and the occurrence of sink marks is prevented at the position irradiated with the laser light.

At the end of laser welding, the distance between the laser beam irradiation end position and the welding end surface of the steel plate is set to 2 mm or more, so that the laser beam output is stable. Light irradiation is terminated. At the end of laser welding, the difference between the end time of laser beam irradiation and the end time of filler wire supply is in the range of -0.1 to 0.1 seconds. The timing is not greatly advanced, and the occurrence of sink marks is prevented.

The prevention of the generation of spherical molten deposits in laser welding is performed by the following operation. At the start of laser welding, the difference between the laser beam irradiation start time and the filler wire supply start time is -0.1 to 0.1 seconds.
Since the range is set, the supply start time of the filler wire is not greatly advanced with respect to the laser irradiation start time. Therefore, only the filler wire is not melted by the laser beam before the steel sheet is welded, and the adhesion of the spherical molten material to the welding start side end face of the steel sheet is prevented.

[0014] At the laser welding completion, the deviation between the supply stop timing of the irradiation end timing and filler wire of the laser beam -
Since the time is in the range of 0.1 to 0.1 seconds, the supply end time of the filler wire does not significantly delay from the laser irradiation end time. Therefore, similarly to the above, only the filler wire is not melted by the laser beam, and the adhesion of the spherical melt to the end surface of the steel plate on the welding end side is prevented.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the laser welding method for a steel sheet for press forming according to the present invention will be described below with reference to the drawings.

FIGS. 1 to 8 show an embodiment of the present invention, particularly an example applied to a thin steel plate used for a body of an automobile. FIG. 1 shows an outline of a laser welding apparatus for carrying out the present invention. In FIG. 1, 11 indicates a thin steel plate as a steel plate, and 12 indicates a thin steel plate as a steel plate. The shear-cut end surface of the thin steel plate 11 and the shear-cut end surface of the thin steel plate 12 are butted. A butt gap S is formed between the end surface of the thin steel plate 11 and the end surface of the thin steel plate 12. The thin steel plates 11 and 12 both have a thickness T of 1.0 mm.
It is.

A torch (not shown) having a condenser lens 21 immediately above the butted portion of the thin steel plate 11 and the thin steel plate 12
Is located. Laser light L output from a laser oscillator (not shown) is converged by a condenser lens 21,
Its focus is adjusted to be at the abutment. At the time of welding, the filler wire 13 is automatically fed into the butting gap S between the thin steel plate 11 and the thin steel plate 12. A torch (not shown) having the condenser lens 21 and a feeding device (not shown) for feeding the filler wire 13 move integrally in the welding direction.

Next, a specific example of a laser welding method for a steel sheet for press forming will be described. As shown in FIG.
When 1 and the thin steel plate 12 are set at predetermined positions, laser light L is output from the laser oscillator, and the laser light L passes through the condenser lens 21 and irradiates the butted portion with the thin steel plates 11 and 12. . At the same time, the filler wire 13 is automatically fed to the portion irradiated with the laser beam L. In this state, the movement of the torch having the condenser lens 21 and the feeding device in the welding progress direction is started. When the irradiation of the laser beam L is started, the butted portions of the thin steel plates 11 and 12 are heated and melted, and the filler wire 13 is heated and melted. At the time of welding, the molten metal resulting from the melting of the filler wire 13 flows into the butt gap S between the thin steel plates 11, 12, and the butt gap S is filled with the molten metal.

In butt razor welding using a filler wire, if the welding conditions are not proper, sink marks and spherical molten deposits are generated at the welding start and end ends. The occurrence of sink marks and molten deposits significantly lowers stretch flange formability during press molding and causes flange cracking. The present invention enhances stretch flange formability by performing welding under welding conditions that can sufficiently suppress generation of sink marks and molten deposits, as described below. In each of the test examples described below, the thin steel plate 1 having a thickness of 1.0 mm was used.
1, 12 were used.

FIG. 4 shows the relationship between the butting gap S and the sink rate. Here, the sink is 0.4m long
m. As shown in FIG. 4, the sink rate is extremely low until the butt gap S is 0.1 mm.
It was found that when the butt gap S became 0.2 mm, the sink rate increased sharply.

FIG. 5 shows the distance P ₁ between the irradiation start position A of the laser beam L and the welding start side end face B of the thin steel plates 11 and 12, and the irradiation end position E of the laser beam L and the thin steel plate 1.
The relationship between the distance P ₂ between the welding end side end faces F of Nos. 1 and 12 and the sink rate is shown. As shown in FIG.
_1, if you set the P ₂ to zero, increased significantly the incidence of sink marks, the distance P _1, if you set the P ₂ from zero to a value between 2 mm, the distance P _1, P ₂ to zero The occurrence of sink marks was reduced to about 1/3 as compared with the case of setting. When the distances P ₁ and P ₂ were set to 2 mm or more, generation of sink marks could not be confirmed.

FIG. 6 shows the rate of occurrence of sink marks and molten deposits with respect to the difference between the irradiation time of the laser beam L and the supply time of the filler wire. In FIG. 6, the characteristic (a) shows a case where the supply time of the filler wire is earlier than the irradiation time of the laser beam L. That is, the characteristic (a)
This is the case where the supply of the filler wire is advanced by 0.3 to 0.1 second with respect to the start of the irradiation of the laser beam L. Under such welding conditions, a high ratio of spherical molten deposits is generated. This phenomenon occurs not only at the irradiation start time of the laser beam L but also at the irradiation end time.

The characteristic (c) in FIG. 6 shows a case where the supply time of the filler wire is delayed with respect to the irradiation time of the laser beam L. That is, the characteristic (c) is a case where the supply of the filler wire is delayed by 0.1 to 0.3 seconds with respect to the irradiation of the laser beam L, and a sink occurs at a high rate under such welding conditions. This phenomenon also occurs not only at the start of laser beam irradiation but also at the end of laser beam irradiation. The characteristic (b) is that the supply time of the filler wire is −
0.1 to 0.1 seconds, and in this state, sink marks and molten deposits did not occur.

FIG. 7 shows the relationship between the sink mark and the stretch flange ratio λ, and FIG. 8 shows the relationship between the size of the molten deposit and the stretch flange ratio λ. Here, stretch flange forming refers to a forming mode in which the panel wire length increases compared to before forming in draw forming or bending, and a high stretch flange ratio is required in draw forming or bending. .

FIGS. 2 and 3 show a forming process of bending flange forming. Figure 2 shows a thin steel plate 11, 12 butt laser welding, hole first diameter d ₀ is the butt weld of the steel sheet 11 and 12 (weld bead portion)
9 are formed. FIG. 3 shows the thin steel plates 11 and 1 of FIG.
2 shows the shape after flange forming. After the flange is formed, the diameter d ₀ of the hole 19 becomes the diameter d, and the diameter of the hole 19 is increased. The stretch flange ratio is λ = (d−d ₀ / d ₀ )
× 100%, and the larger the stretch flange ratio, the better the stretch flange formability.

As shown in FIG. 7, it was found that the larger the sink mark, the smaller the stretch flange ratio λ, and that when the sink mark length exceeds 0.4 mm, the stretch flange ratio λ sharply decreases. As shown in FIG. 8, it was found that the larger the size of the molten deposit, the smaller the stretch flange ratio λ, and when the size of the molten deposit exceeded 1 mm ³ , the stretch flange ratio λ rapidly decreased.

As described above, when butt laser welding thin steel plates having both thicknesses T of 1.0 mm, by performing the welding under the following welding conditions, the generation of sink marks and molten deposits can be sufficiently suppressed. Stretch flange formability can be improved. Butt gap S is suppressed to 0.1 mm or less. Distance P between the irradiation start position (irradiation end position) of laser beam L and the welding start side end surface (welding end side end surface) of the thin steel plate
_1, sets the P ₂ than 2 mm. Supply start time (supply end time) of filler wire 13 with respect to laser light L irradiation start time (irradiation end time)
Is set within -0.1 to 0.1 seconds.

Although the present embodiment has been described with respect to the case where the present invention is applied to butt laser welding of a thin steel plate having a thickness of 1.0 mm, if the composition or the thickness of the steel plate changes, the welding conditions described above are of course appropriately changed.

[0029]

According to the present invention, the butt gap of the steel sheet is reduced.
0.1mm or less, welding start position of laser beam and welding of steel plate
Laser light irradiation when the distance from the start side end surface is 2 mm or more
The distance between the end position and the end surface of the steel plate on the welding end side is 2 mm
The laser beam irradiation start time and filler wire supply
The deviation from the start time is -0.1 to 0.1 seconds,
The gap between the firing end time and the filler wire supply end time
Laser welding under welding conditions of -0.1 to 0.1 seconds
Since it is performed , generation of sink marks and molten deposits at the welding start end and the welding end end can be sufficiently suppressed.

Therefore, the stretch flange formability during press forming of the butt laser-welded steel sheet can be improved, and flange cracking can be prevented.
As a result, it is not necessary to cut out the weld end before or after laser welding, and the productivity in the press forming step can be increased.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of laser welding using the present invention.

FIG. 2 is a perspective view of a stretch-flanged steel plate.

FIG. 3 is a plan view of a steel sheet before stretch flange forming.

FIG. 4 is a characteristic diagram showing a relationship between a butt gap and a sink rate.

FIG. 5 is a characteristic diagram showing a relationship between a distance from a laser beam irradiation start position to a welding start side end face of a steel sheet or a distance from a laser beam irradiation end position to a welding end side end face of a steel sheet and a sink rate.

FIG. 6 is a characteristic diagram showing a relationship between a difference between a laser beam irradiation time and a filler wire supply time and an occurrence rate of sink marks or molten deposits.

FIG. 7 is a characteristic diagram showing a relationship between sink mark and stretch flange rate.

FIG. 8 is a characteristic diagram showing a relationship between a size of a molten deposit and a stretch flange ratio.

FIG. 9 is a perspective view showing a state in which sink marks have occurred at the welding start end of the steel plates joined by laser welding.

FIG. 10 is a perspective view showing a state in which a molten deposit is generated at a welding start end of a steel plate joined by laser welding.

[Explanation of symbols]

11, 12 Steel plate 13 Filler wire 21 Condenser lens L Laser light S Butt gap P ₁ Distance between laser light irradiation start position and welding start side end face of steel plate P ₂ Laser light irradiation end position and steel plate welding end Distance to side end face

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B23K 26/00 310

Claims (1)

(57) [Claims] An end of a first steel plate and a second steel plate are projected from each other.
While supplying filler wire to the butting part,
Laser welding method for press forming steel plate to be laser welded
Therefore, the butting gap of the steel sheet is 0.1 mm or less, between the laser beam irradiation start position and the welding start side end face of the steel sheet.
Distance of 2mm or more, the end position of laser beam irradiation and the steel plate
The distance from the end face on the welding end side is 2 mm or more, the laser beam irradiation start time and the filler wire supply start time
-0.1 to 0.1 second deviation from the end of the laser beam irradiation
The difference between the timing and the end time of the supply of the filler wire is -0.0.
A laser welding method for a steel sheet for press forming , wherein the laser welding is performed under welding conditions of 1 to 0.1 second .