JP2007229752A - Overlap laser welding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent solidification cracking in overlap laser welding. <P>SOLUTION: In the laser welding method where a plurality of steel materials in which at least one is made of high tensile strength steel are overlapped, as laser light is emitted to the vicinities of the edge parts of the overlapped sheet materials from the overlapped direction in such a manner that melting is caused to the back face of the sheet material on the lower side to be overlapped, the laser light is moved along the edge parts, so as to form a weld zone in which the content of carbon in the weld metal satisfies 0.05≤C≤0.08%; thus the overlapped sheet materials are welded each other, the width of the overlapped parts in the sheet materials is controlled to ≤8 mm, and also, the weld zone is formed at a position far by ≥3.5 mm from the edges of the sheet materials. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention superimposes a plurality of plate materials, irradiates laser light in the vicinity of the end portion of the overlapped plate material from the superimposition direction, moves the laser light along the end portion, The present invention relates to a lap laser welding method for welding to each other.

As a body panel of an automobile, a cross section having a flange portion 2 and a bent portion 3 formed of a thin plate material made of high-strength steel, as shown in FIG. A frame member in which the overlapped portion is joined by spot welding or the like, and the flange portion 2 and the plate member 4 or the plate member 4 interposed between the flange portions as shown in FIGS. A frame member in which they are similarly joined, and a frame member in which a plurality of structural members 1 are stacked in the same direction as shown in FIG. 1d are used.
When laser welding is used to join the above-mentioned overlapping parts, the joint strength is high by continuous welding and the bead width is narrow. Therefore, the design of the joints is free compared to spot welding and arc welding used in the past. There are advantages such that the degree is large, the width of the flange portion is narrowed, and the structural member can be reduced in size and weight.

Conventionally, in laser welding of lap weld joints of plate materials, if the gap between the plate materials in the overlapped portion varies, the welding quality deteriorates, and therefore, the focus has been on optimizing the gap between the plate materials.
For example, pressing the roller from the laser irradiation side to the overlapping part, moving the roller together with the laser beam, pressing one plate against the other plate and adjusting the distance between them, or welding the plates together Patent Document 1 discloses that the flange portions are sandwiched from both sides by a pair of rollers and welded in the same manner.

  However, in structural members made of high-strength steel, the width of the flange portion is shortened to reduce the weight of the member, and the vicinity of the end of the overlapped portion is welded so as to melt to the back side of the lower plate material to further increase the joint strength. If it tried to do so, it turned out that the weld solidification crack becomes a problem in the research of the present inventors.

That is, as shown in FIG. 2a, the laser beam is irradiated from the overlapping direction, that is, the direction intersecting the flange, to the flange portion of the frame member in which the both side flange portions of the structural member having a hat-shaped cross section are overlapped with each other. When starting welding from the longitudinal end of the flange while welding so as to melt up to the lower plate material back, as shown in FIG. Will occur.
Further, as shown in FIG. 3, even when the welding start point 5 is not the longitudinal end portion of the flange and the point separated from the end portion by a predetermined distance is the welding start point, the central portion of the welded portion 6 is not welded after welding. Swelling and cracks 7 may occur. In the figure, 8 is a laser welding head.

  This is because when welding is performed by irradiating a laser beam so as to melt to the back surface of the stacked lower plate material, the flange on the end side from the melted portion is solidified until the melted portion formed by the laser beam irradiation is solidified. The part is separated from the flange body. At this time, if the width of the part is small, it is considered that the part expands due to heat conduction from the welded portion, the part is deformed, the weld bead in the middle of solidification is pulled, and a crack occurs during solidification.

Conventionally, Patent Literature 2 and Patent Literature 3 are known as techniques for preventing cracking and deformation of a welded portion in laser welding.
In Patent Document 2, when laser welding a lap joint of a member made of high carbon steel and a member made of stainless steel or the like, shrinkage cracking occurs due to shrinkage stress generated at the time of melt solidification, and the cracking, It describes that the position of the joint portion is devised to prevent the tensile stress from being applied to the melted portion.

Further, in Patent Document 3, when one plate member is abutted with the other narrow plate member and the butt portion is laser-welded, the narrower plate member is deformed by heat and the butt portion is deformed. Since the interval is widened, it is described that the butt portions of both plate materials are temporarily attached to prevent deformation of the plate materials.
However, these documents do not mention at all the above solidification cracks and solutions for the same.

As described above, in laser welding of a thin plate made of high-strength steel, the width of the flange portion is shortened in order to reduce the weight of the member, and the vicinity of the end of the overlapped portion is melted to the lower surface of the lower plate material. In the past, it has not been known that weld solidification cracking occurs when welding is performed so as to increase the joint strength.
JP-A-8-90264 Japanese Patent Laid-Open No. 11-245065 JP 59-215288 A

  Therefore, in the present invention, in view of the situation as described above, at least one plate material is formed by superimposing a plurality of plate materials made of high-strength steel, and in the vicinity of the end portion of the superimposed plate material, Laser welding without solidification cracks as described above when laser beams are moved along the end portion while irradiating laser beams from the overlapping direction so as to melt to the back surface and the stacked plate materials are welded together. It is an object to provide a method.

In order to solve the above problems, the present invention is characterized as follows.
The invention of the overlap laser welding method according to claim 1 is characterized in that at least one of the plate members is made by superimposing a plurality of plate members made of high-strength steel, and the back surface of the lower plate member is overlapped in the vicinity of the end of the overlapped plate member. The laser beam is moved along the end portion while irradiating the laser beam from the overlapping direction so as to melt up to 0.05% C ≦ 0.08%, or C <0.05%. , P + S ≧ 0.03%, a laser welding method in which the overlapped plate members are welded to each other, the width of the overlapped portion of the plate members being within 8 mm, and from the end of the plate member A welded portion is formed at a position separated by 3.5 mm or more. In the following, the element content% is mass%.

  The invention of the laser beam welding method according to claim 2 is characterized in that at least one of the plate materials is made by superimposing a plurality of plate materials made of high-strength steel, and the back surface of the laminated lower plate material is arranged in the vicinity of the end of the superposed plate material. The laser beam is moved along the end portion while irradiating the laser beam from the overlapping direction so as to melt up to 0.05% C ≦ 0.08%, or C <0.05%. , P + S ≧ 0.03%, a laser welding method in which the overlapped plate members are welded to each other, wherein one plate member is overlapped so as to protrude 5 mm or more from the other plate member, The width of the overlapped portion is within 8 mm, and a welded portion is formed at a position 1.5 mm or more away from the end of the other plate material.

The invention of the lap laser welding method according to claim 3 is characterized in that, as described in the claim, welding is started at a position away from an end portion in the welding direction of the overlapped plate members.
According to the invention of the lap laser welding method of claim 4, as described in the claim, welding is started from an end portion in the welding direction of the overlapped plate member, and 2.5 mm from the end of the other plate member. A welded portion is formed at a position apart from the above.

The invention of the lap laser welding method according to claim 5 is a structure in which at least one of the plurality of plate members has a bent portion and a flange portion subsequent thereto on at least one side of the plurality of plate materials. It is a member, The overlapping part of a board | plate material is what overlapped the flange and other board | plate material of the said structural member mutually, It is characterized by the above-mentioned.
The invention of the lap laser welding method according to claim 6 is that the at least one plate member is a hat-shaped structural member having a bent portion and a flange portion on both sides as described in the claim. It is characterized by.

  According to the first and second aspects of the invention, at least one plate material is a case where a structural member made of high-strength steel is overlapped and laser-welded, and the weld metal of the welded portion has a component composition in which solidification cracking is likely to occur. In such a case, laser welding can be performed without causing solidification cracks in the welded portion even if the lower surface of the laminated plate is sufficiently melted, so that the width of the overlapped portion is narrow. However, a high-strength weld can be formed, and the structural member can be reduced in size and weight.

According to the third and fourth aspects of the invention, the laser welding method of the first and second aspects of the invention can be more effectively implemented in a form corresponding to the shape of the lap joint.
According to the fifth and sixth aspects of the invention, the structural member having the flange can be further reduced in size and weight.

Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS.
A plate-like member made of high-strength steel and having a flange at the end, such as a hat-shaped structural member shown in FIG. 4, is overlapped with a similar flange or plate member, and laser-welded between the two to form a frame When manufacturing a member, using a structural member with a narrower flange width (width over which plate materials overlap) A, such as within 8 mm, to reduce the weight of the entire frame member, from the welded portion to the flange end The distance B must be shorter than the range of 1.5 mm or more, and under such conditions, welding is started at a position away from the flange longitudinal end as shown in FIG. Even if it did, as mentioned above, the site | part deform | transformed by the heat conduction from a welding part pulled the weld bead in the middle of solidification, and the solidification crack might generate | occur | produce.

  In order to reduce the weight of the structural member, it is more effective to make the flange width within 8 mm. In such a flange width, the distance from the weld bead center of the welded portion to the flange end is 1.5 mm. The reason for the above is that if the length is less than 1.5 mm, the flange end side melts to the flange end and is easily melted down.

Therefore, the present inventors investigated the cause of the occurrence of solidification cracks, and examined the relationship between the position from the flange end of the welded part and the weld metal component and the occurrence of the solidification cracks.
FIG. 5 shows the relationship between the temperature of the solidification process in the laminating laser welding of thin plates and the strain generated around the weld. The figure shows a steel plate with a tensile strength of 590 MPa with a plate thickness of 1.2 mm consisting of 0.06% carbon, 0.5% silicon, and 1.5% manganese. It was obtained by using a sample obtained by laser welding at a speed of 2 m / min.
According to FIG. 5, a tensile force acts on the welded portion immediately below the liquidus temperature, and a compressive force acts on the welded portion when the temperature is sufficiently lowered from the liquidus temperature. In the region (2) in the solidification process behind the laser light irradiation position, a large strain in the tensile direction is generated, which can be said to lead to solidification cracking.

The relationship between the occurrence of strain and solidification cracking can be explained from the relationship between the generally known solidification temperature brittleness range (BTR) and shrinkage displacement (P) as shown in FIG.
That is, there is an embrittlement region (D) having a high solidification cracking sensitivity indicated by hatching in the figure between the temperature of the weld and the displacement amount of the member accompanying solidification shrinkage, and the solidification shrinkage displacement (P) as the temperature decreases. ) Increases, and it is believed that solidification cracking occurs when it passes through the embrittled region. Also, just below the liquidus temperature, the minimum ductility value (Dmin) is small and the embrittlement region is wide, but the liquidus ratio is high, so even if solidification cracks occur between columnar crystals, they are filled by the liquid phase and solidification cracks are Does not occur.

In general, one of the factors affecting solidification cracking is the solidification temperature range between the liquid phase and the solid phase. In the binary system for Fe, C, P, and S are known as elements that widen the solidification temperature range even when a small amount is added (for example, Matsuda, “Welding Metallurgy”, published by Nikkan Kogyo Shimbun, 1972, No. 158 Page).
Further, C, P, and S have a small equilibrium partition coefficient, and the solute is discharged into the molten metal and remains between the columnar crystals. Therefore, the temperature at the final solidification position from the apparent solid phase temperature is as shown by the bold broken line in FIG. It is considered that it is an element that tends to expand to a BTR and easily cause solidification cracking.
Furthermore, it is considered that there is a component range that is particularly sensitive to cracking, such that the grain boundary strength of the solidification process is low in that component range, and the component range is determined by the range of the approximate C amount and P + S amount. Conceivable.

Therefore, the range of the amount of C and P + S in which solidification cracking occurred was examined.
In the experiment, steel sheets having various C amounts and P + S amounts and tensile strengths in the range of 270 MPa to 1470 MPa were used, and the same type or different types were combined to form a hat-shaped structural member and plate as shown in FIG. The shaped members were overlapped so that the flange width A was 8 mm.
The distance B from the weld bead center to the end of the plate material is 3.0 mm, the distance C from the longitudinal end of the flange portion to the welding start point is 5 mm, the laser processing point output is 3.5 kW, and the welding speed is 2 m / min. Laser welding was performed under the conditions.
FIG. 7 shows the result of arranging the occurrence of cracks after welding according to the C content and P + S amount of the weld metal. In FIG. 7, (1) and (3) are regions where solidification cracks do not occur, and (2) is a region where solidification cracks occur.

  From this result, a steel plate having a tensile strength in the range of 270 MPa to 1470 MPa, in particular, at least one plate member is overlapped with a plurality of plate members made of high-tensile steel plate of 440 MPa or more, and is overlapped in the vicinity of the end of the overlapped plate member. When welding the overlapped plate materials by moving the laser light along the end portion while irradiating laser light so as to melt from the direction to the back surface of the overlapped lower plate material, welding of the welded portion When the distance from the bead center to the flange end is shorter than 1.5 mm, the carbon content of the weld metal in the weld zone is 0.05 ≦ C ≦ 0.08% regardless of the P + S amount. It was found that solidification cracking occurred. Further, it was found that when C <0.05%, solidification cracking occurred in the range of P + S ≧ 0.03%.

Therefore, further examination was made on the construction conditions that do not cause solidification cracking even in such a range of C and P + S.
As a means for reducing the solidification shrinkage displacement amount P that causes cracks as described above, welding is started from a position away from the end portion in the welding direction of the overlapped plate materials, and the welded portion and the overlapped portion of the plate material (Flange portion) If the distance from the end portion is increased, the strength of the portion is further increased after both ends are constrained, so that the amount of displacement can be reduced.

Therefore, the conditions under which solidification cracks do not occur were examined depending on whether the ends of the overlapped portion were aligned or not.
As a result, when they are aligned as shown in FIG. 4, even if the flange width A is within 8 mm, welding is started from a position away from the end portion in the welding direction of the stacked plate members, and the aligned end portions If the weld is formed so that the distance B is 3.5 mm or more from the position, that is, the distance B is 3.5 mm or more, welding can be performed without causing solidification cracks that bulge in the middle as shown in FIG. I found out.

  In addition, in the above, when the flange width is within 8 mm and the welded portion is formed at a position 3.5 mm or more away from the end, welding as shown in FIG. 4 is due to interference between the bent portion and the laser welding head. Although difficult cases arise, in the case of FIGS. 1b and 1d, the welded portion can be formed at a position sufficiently away from the end portion by irradiating the laser from the side opposite to the bent portion.

Also, as shown in FIG. 8a, one plate member 4 is overlaid so as to protrude from the other plate member 1, and when the end portions of the overlapped portions are not aligned, By setting the distance D protruding from the plate material 1 to 5 mm or more, if welding is started from a position away from the end portion in the welding direction of the stacked plate materials, the distance B from the end portion of the plate material 1 to the welded portion is set to 1. It was found that welding can be performed without causing solidification cracks even when the thickness is 5 mm or more.
Further, when the distance D is set to 5 mm or more and the distance B from the end portion of the other plate material 1 to the welded portion is set to 2.5 mm or more, as shown in FIG. It was also found that welding can be performed without generating solidification cracks even if welding is started from the direction end.

In the above case, when welding is started from a position away from the end in the welding direction of the stacked plate members, the distance C from the end to the welding start point is from the center of the weld bead of the weld to the end in the flange width direction. It is preferable that the distance is equal to or longer than the distance B.
In addition, even when welding cannot be started from the end portion of the overlapped plate materials in the welding direction, the above condition should be adopted if the end portion is constrained by a clamp jig so that the end portion does not open as shown in FIG. As shown in FIG. 3, welding can be performed without swelling in the middle.

  As described above, the weld metal of the welded portion is in the range of 0.05 ≦ C ≦ 0.08%, or C <0.05%, and P + S depending on the combination of the component compositions of the high-tensile steel plate to be welded. Even in the case of ≧ 0.03%, if laser welding is performed under the above conditions, welding can be performed without causing solidification cracks.

The material of the plate material targeted by the present invention may be either a case where all of the plurality of plate materials are high-tensile steel or a case where at least one of the plate materials is high-tensile steel, depending on the combination of the plate materials, A steel combination in which the weld metal is 0.05 ≦ C ≦ 0.08% or C <0.05% and P + S ≧ 0.03% is targeted. Here, the range of high-tensile steel is 440 MPa or more in terms of tensile strength.
In addition, since the solidification cracking easily occurs when the amount of P + S becomes high, the upper limit of P + S in the weld metal targeted by the present invention is desirably 0.05%.

  In laser welding, the weld metal component is an average component calculated from the base material component value of each overlapped plate and the plate thickness unless a filler material such as a filler is added separately (three sheets) When the above plate materials are overlapped, they may be expressed by the average component calculated from the base material component value and the plate thickness in all the combinations of two adjacent sheets.) When the value of C in the weld metal calculated from the material of the member is in the range of 0.05 ≦ C ≦ 0.08%, the values of C and P + S are C <0.05%, and P + S ≧ When it is in the range of 0.03%, laser welding can be performed without causing solidification cracks by applying the present invention.

  Examples of the present invention will be described below, but the conditions adopted in the examples are one example of conditions for confirming the feasibility and effects of the present invention, and the present invention is limited to this one example of conditions. It is not something. This invention is prescribed | regulated only by the matter described in a claim, Embodiment other than the above can also be implemented. As long as the object of the present invention is achieved without departing from the present invention, various conditions can be adopted.

  As a test material, a cross-sectional hat-shaped structural member made of high-strength steel (SPFC590) having a thickness of 1.2 mm and a tensile strength of 590 MPa or more is converted into a flat plate material made of high-tensile steel, partly at the end. The other parts were overlapped so that the flat plate on the lower side protruded and the other part aligned. The width of each overlapped part was 8 mm. Further, the protruding amount D of the lower plate material was 3 mm and 6 mm. As high-tensile steel, samples having different amounts of C and P + S were used. The overlapped portion was laser welded under the following conditions.

In laser welding, a YAG laser was used, the processing point output was 3.5 kW, and the welding speed was 2.0 m / min. The laser beam was focused on the steel plate and the focused spot was 0.6 mm in diameter. The distance B from the flange width direction end to the laser irradiation position was set to 2.5 to 4 mm, and the point separated by 5.0 mm from the flange longitudinal direction end was set as the start position. With respect to the lower plate member having a protruding amount D of 6 mm, welding with the flange longitudinal end as a starting position was also performed.
The obtained results are shown in Table 1. It can be seen from Table 1 that welding can be performed without causing cracks when the conditions of the present invention are satisfied.

It is a figure which shows the example of the member which has a lap joint. It is a figure which shows one example of a solidification crack. It is a figure which shows the other example of a solidification crack. It is a figure explaining a flange width and a welding part position. It is a figure which shows the relationship between the temperature of the solidification process after welding, and distortion. It is a figure which shows the relationship between a solidification brittle range and shrinkage displacement. It is a figure which shows the relationship between generation | occurrence | production of a solidification crack, and a component. It is a figure explaining the flange width and welding part position in another example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Structural member of hat-shaped cross section 2 Flange part of structural member 3 Bending part of structural member 4 Plate material 5 Welding start point 6 Welded part (weld bead)
7 Solidification crack 8 Laser welding head A Flange width B Distance from weld to flange end C Distance from flange longitudinal end to welding start point D Distance from which one plate protrudes from the other plate

Claims (6)

  At least one of the plate materials is made by superimposing a plurality of plate materials made of high-strength steel, and a laser beam is applied from the superposition direction so as to melt up to the back surface of the lower plate material that has been piled up in the vicinity of the end of the laminated plate material. While irradiating, the laser beam is moved along the end portion, and the weld metal is 0.05 ≦ C ≦ 0.08 mass%, or C <0.05 mass%, P + S ≧ 0.03% mass. A laser welding method in which a welded portion is formed and the stacked plate materials are welded to each other, wherein the width of the overlapped portion of the plate materials is within 8 mm and is welded to a position at least 3.5 mm away from the edge of the plate material A lap laser welding method characterized by forming a portion.   At least one of the plate materials is made by superimposing a plurality of plate materials made of high-strength steel, and a laser beam is applied from the superposition direction so as to melt up to the back surface of the lower plate material that has been piled up in the vicinity of the end of the laminated plate material. While irradiating, the laser beam is moved along the end portion, and the weld metal is 0.05 ≦ C ≦ 0.08 mass%, or C <0.05 mass%, P + S ≧ 0.03% mass. A laser welding method in which welded portions are formed and the stacked plate materials are welded to each other, wherein one plate material is overlaid so that it protrudes 5 mm or more from the other plate material, and the width of the overlap portion of the plate materials is within 8 mm And a welded portion is formed at a position 1.5 mm or more away from the end of the other plate member.   3. The lap laser welding method according to claim 1, wherein welding is started at a position away from an end portion in the welding direction of the overlapped plate members.   The overlap laser according to claim 2, wherein welding is started from an end portion in the welding direction of the overlapped plate members, and a weld portion is formed at a position 2.5 mm or more away from the end of the other plate member. Welding method.   Among the plurality of plate members, at least one plate member is a structural member having at least one bent portion and a flange portion subsequent thereto, and the overlapping portion of the plate members mutually connects the flange of the structural member and another plate member. The overlapping laser welding method according to any one of claims 1 to 4, wherein the overlapping laser welding method is performed.   6. The lap laser welding method according to claim 5, wherein the at least one plate member is a structural member having a hat-shaped cross section having a bent portion and a flange portion on both sides.

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