JP2017052006A - Lap joint coupler and method for manufacturing same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a joint coupler which has an excellent strength of joint and an enhanced reliability.SOLUTION: A lap joint coupler which is configured from plural metal plates which are lapped and has a junction of punctiform, in which the junction of punctiform has a melting coagulation part which bridges over the plural metal plates, and the melting coagulation part has a re-melting coagulation part and a coagulation re-heating part. When viewed in a plan of the melting coagulation part, the re-melting coagulation part bridges the plural metal plates in a punctiform including a circle equivalent central axis, and the coagulation re-heating part is positioned around the re-melting coagulation part, includes a melting boundary of the junction of punctiform, and is softened by the re-melting coagulation part.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a lap joint and a method for manufacturing the same, and more particularly to a lap joint for a high-strength steel sheet used for an automobile body and a method for manufacturing the same.

In recent years, in the automobile field, it has been required to reduce the weight of a vehicle body in order to reduce fuel consumption and reduce CO ₂ emissions, and to increase the strength of vehicle body members in order to improve collision safety. In order to satisfy these requirements, it is effective to use high-strength steel sheets for vehicle body members and various parts.

  In the process of assembling the body made of such a high-strength steel sheet and attaching parts, mainly spot-like fusion bonding using resistance heating is widely used, but in recent years, instead of this resistance spot bonding, Melt bonding (hereinafter simply referred to as “joining”) using light rays (hereinafter referred to as “light rays”) having a high power density in part has been used. Joining using light beams can be performed at high speed, and since there is no shunting of joining current to existing joints, the pitch interval of the joints can be shortened, and the rigidity of the vehicle body by multipoint joining can be reduced. Improvements are also possible.

  The joint strength, which is one of the quality indicators of joints formed by melt bonding (hereinafter referred to as “joined joints”), includes the tensile shear strength (TSS) measured by applying a tensile load in the shear direction, and the peel direction. There is a cross tensile strength (CTS) measured by applying a tensile load. In joints using light beams, CTS tends to be the same as or lower than conventional resistance spot bonding, and CTS may be particularly low in the case of high-strength steel sheets with a large amount of carbon. . For this reason, when joining using a light beam to a high-strength steel plate, the technique of improving joint strength, such as CTS, was desired.

  Under such circumstances, as a technique for improving joint strength in the joining using light rays, a technique for forming another joining part in the vicinity of the joining part (see Patent Document 1), A technique for forming another bead for the purpose of tempering the bead inside is known (see Patent Documents 2 and 3).

  On the other hand, in the assembly process of an automobile body, spot bonding is frequently used. However, a method for obtaining a shape similar to a point-like lap joint by planar bonding formed by this bonding method is disclosed in Patent Literature. 4. Spot lap joints using light rays have attracted attention as a technique that replaces spot joints in cases where electrodes cannot be sandwiched from both sides of the laminated steel sheets.

JP 2010-012504 A JP2012-240086A International Publication No. 2012/050097 JP 60-68185 A

  However, the point-like lap joints formed by the light beams have a problem that the cross tensile strength (CTS) cannot be sufficiently obtained, particularly in the case of lap joints of high-strength steel sheets, and improve joint strength. It was hoped that.

  In view of such circumstances, an object of the present invention is to provide a lap joint having excellent joint strength.

  Means for improving the toughness of the pointed joint near the melting boundary in order to improve the joint strength of the joint where the pointed joint has been formed by joining the metal plate with a light beam. We studied earnestly.

  The present inventors have conceived that heat treatment is performed on the spot-like joint, and have made various investigations regarding the heat treatment location and the heat treatment method. As a result, when the melt-solidified part of the dotted joint is viewed in plan from the irradiation side of the light beam, the light beam is irradiated to the inside of the melt-solidified part, the outer contour is substantially circular, and remelted to the center. The remelted and solidified part is formed by remelting and solidifying the substantially central part of the shape (hereinafter referred to as “spot-like”) across a plurality of metal plates, and in the vicinity of the melting boundary of the dotted joint It was found that CTS is improved by re-heating so as to temper and forming a coagulation re-heating part.

The present invention has been made based on the above findings, and the gist thereof is as follows.
(1) In a lap joint having a plurality of stacked metal plates and having a dotted joint,
The dotted joint has a melt-solidified part straddling the plurality of metal plates,
The molten and solidified part has a remelted and solidified part and a solidified and reheated part,
The remelted and solidified part is a point including a circle-equivalent center of the melted and solidified part when viewed in plan, and straddles the plurality of metal plates,
The lap joint joint is characterized in that the solidification reheating part is located around the remelt solidification part, includes a melting boundary of the dotted joint, and is softer than the remelt solidification part .
(2) The average value of the Vickers hardness in the range of 0.5 mm from the melting boundary of the overlapping surface of the metal plate to the remelted solidified portion in the solidified reheated portion is Hv390 or less. In addition, the lap joint according to (1), which is lower by Hv 70 or more than an average value of Vickers hardness of the remelted and solidified portion.
(3) The lap joint according to (1) or (2), wherein the plurality of metal plates include one or more metal plates having a surface treatment film.
(4) In a method for manufacturing a lap joint, in which a plurality of metal plates are superposed and irradiated by irradiation with light,
By irradiating one superimposed metal plate with a light beam, forming a spot joint having a melted and solidified part melted and solidified in a spot shape across the plurality of metal plates,
When the molten and solidified portion is viewed in plan from the irradiation side of the light beam, the light beam is re-irradiated on the inner side of the molten and solidified portion, and the plurality of metal plates are formed into dots including the circle-equivalent center of the molten and solidified portion. Remelted and solidified to form a remelted solidified portion, and further, a solidified reheated portion including the melting boundary of the dotted joint is formed around the remelted solidified portion, and reheating at that time A method for producing a lap joint, wherein the solidification reheat part is softened from the remelt solidification part by adjusting conditions.
(5) In the re-irradiation of the light beam, the distance from the outer end portion of the remelted and solidified remelted solidified portion to the melting boundary of the dotted joint is 1 in the cross section in the thickness direction of the plurality of metal plates. The method for producing a lap joint according to (4), wherein the method is performed so as to have a thickness of 0.0 to 3.0 mm.
(6) The method for manufacturing a lap joint according to (4) or (5), wherein at least one metal plate on which a surface treatment film is formed is used for the plurality of metal plates.

  According to the present invention, since the solidification reheat part having excellent toughness is provided in the vicinity of the melting boundary of the dotted joint, the joint strength of the lap joint, particularly the cross tensile strength (CTS) can be improved. it can. And the reliability of a motor vehicle component can be improved by applying the joint joint of this invention to a motor vehicle component.

It is a figure which shows the outline of the Vickers hardness distribution of the joint joint which has a dotted | punctate junction part. (A) shows the structure of the cross section of a joint joint typically, (b) shows the Vickers hardness distribution of a joint joint. It is a figure which shows the outline of the Vickers hardness distribution of the joint joint which irradiated the light beam to the center part of a dotted | punctate junction part. (A) shows the structure of the cross section of a joint joint typically, (b) shows the Vickers hardness distribution of a joint joint. It is a figure which shows typically the structure of the cross section of the joint joint of this invention. It is a perspective view which shows the outline | summary of formation of a dotted | punctate junction part. (A) shows a schematic diagram of irradiating a light beam with different irradiation diameters, (b) shows a schematic diagram of irradiating a light beam with a wide condensing area, and (c) shows a dot-like joint formed. A perspective view is shown. It is a perspective view which shows the outline | summary of the heat processing of a dotted | punctate junction part. (A) shows a schematic diagram of irradiating light beams with different irradiation diameters, (b) shows a schematic diagram of irradiating light beams with a wide condensing area, and (c) shows a remelting solidification part and a solidification reheating part. The perspective view of the dotted | punctate junction part which has these is shown.

  The lap joint of the present invention (hereinafter referred to as “joint joint of the present invention”) is a lap joint having a point-like joint formed by irradiating a plurality of metal plates with light rays. The joint portion has a melt-solidified portion, the melt-solidified portion is composed of a remelt-solidified portion and a solidification-reheated portion, and the solidification-reheated portion is softer than the remelt-solidified portion. It has the characteristics.

Hereinafter, the background of the examination that led to the joint joint of the present invention will be described, and the joint joint of the present invention will be described.
In a lap joint having a dotted joint, it has been desired to further improve the joint strength. Therefore, the present inventors examined heat treatment of the dotted joints, and investigated the heat treatment location and the heat treatment method of the dotted joints.

  In a lap joint, when a load is applied to the joint in the peeling direction, stress concentrates in the vicinity of the melting boundary and easily breaks. Therefore, when the molten and solidified portion of the spot-like joint having a diameter of about 6.0 mm is viewed in plan from the irradiation side of the light beam, a light beam having a light beam diameter of about 3.0 mm is re-irradiated to the inside of the molten and solidified portion. In addition to remelting and solidifying in the form of dots, heat treatment was performed on the melting boundary of the melt-solidified part, and the Vickers hardness distribution of the joint joint was investigated. As a result, the melting boundary was tempered by re-irradiation, and improvement in toughness was confirmed. This test will be described with reference to the drawings.

  In FIG. 1, the schematic of the Vickers hardness distribution of the joint joint which has a dotted | punctate junction part is shown. Fig.1 (a) shows the schematic diagram of the cross section of the joint joint which has a melt-solidification part, FIG.1 (b) shows the schematic diagram of the Vickers hardness distribution of the joint joint in a melt-solidification part and its vicinity. FIG. 2 shows a schematic diagram of a Vickers hardness distribution of a joint joint obtained by re-irradiating the central part of the spot-like joint part with light rays. Fig.2 (a) shows the schematic diagram of the cross section of a joining joint, FIG.2 (b) shows the schematic of the Vickers hardness distribution of a joining joint.

  First, the joint joint which investigated distribution of Vickers hardness is demonstrated using Fig.1 (a) and FIG. 2 (a). Fig.1 (a) and FIG.2 (a) have shown the schematic diagram of the cross section of the joint joint cut | disconnected in the plate | board thickness direction so that the fusion | melting solidification part of a dotted | punctate junction part may be included. The joint 1 is obtained by superposing and joining metal plates 2a and 2b. The metal plates 2a and 2b are hot stamped steel plates having a tensile strength of 1500 MPa, which are joined and joined by the melted and solidified portion 3 which is a dotted joint.

  A joint joint 1 shown in FIG. 1 (a) is the one before the heat treatment for re-irradiating light to the melt-solidified portion 3 of the dotted joint. The joint joint 1 shown in FIG. 2 (a) re-irradiates the inside of the melt-solidified portion 3 with a light beam and re-melts it in a spot shape when the melt-solidified portion of the spot-like joint portion is viewed from the light irradiation side. A solidified remelted solidified portion 3a and a solidified reheated portion 3b reheated thereby are provided.

  Next, the Vickers hardness distribution of these joints will be described with reference to FIGS. 1 (b) and 2 (b). 1 (b) and FIG. 2 (b) show the Vickers hardness distributions shown in FIG. 1 (a) and FIG. 2 (a), respectively, at the position of the dotted line X (measurement of Vickers hardness in the plate thickness direction). It is the schematic which calculated | required the position) over the measurement range L1 of the Vickers hardness of a parallel direction with the metal plate surface. The dotted line X is a position of 0.2 mm from the overlapping surface of the metal plates 2a and 2b to the metal plate 2a side in the plate thickness direction. L2 is the measurement range of the Vickers hardness of the melt-solidified part. L3 is a measurement range of the Vickers hardness of the remelted solidified part.

  As shown in FIG. 1 (b), the Vickers hardness of the joint joint 1 before the heat treatment for re-irradiating the melt-solidified portion 3 with light rays is as hard as about HV460 inside the melt-solidified portion 3 (L2). It is almost constant. Although the outer side of L2 is not a melt-solidified part, it is heated to a high temperature region and quenched, so that the hardness is large. In addition, there exists a site | part with low hardness further outside, but this is a HAZ softening part of the hot stamped steel plate which is a base material.

  On the other hand, as shown in FIG. 2 (b), the Vickers hardness of the joint 1 having the remelted solidified portion 3a and the solidified reheated portion 3b is remelted and solidified. On the inner side (L3) of the portion 3a, the value is as high as about 460 HV. The outer side of L3 is not the remelted solidified part 3a, but is heated to a high temperature region and quenched, and thus has a high hardness. Furthermore, the site | part with low Vickers hardness was formed in the outer side. The average hardness of the melt boundary (around a radius of about 3 mm) and the inner side of less than 1 mm decreased to about HV320. Note that the HAZ softened portion of the base material outside the melt-solidified portion 3 remains as it is.

  And when the cross tensile strength (CTS) of both joints was investigated, the cross tensile strength of the direction of the joint which has the solidification reheating part formed by re-irradiating a light beam inside the fusion | melting solidification part is shown. It turned out to be high. As a result, the one having the solidified reheated portion in which the dotted joint shown in FIG. 2 (a) is softer than the remelted solidified portion is tempered by the melting boundary to reduce hardness and improve toughness. I found out that Moreover, even if the combination of the metal plates was changed, the improvement of CTS was confirmed in the case of having a solidification reheating part in which the dotted joint is softer than the remelt solidification part.

  The present invention has reached the invention described in the above (1) through the examination process as described above, and the necessary and preferred requirements will be further described in order.

  Next, the joint joint of this invention is demonstrated using FIG. FIG. 3 shows a cross-sectional view of the joint joint of the present invention cut in the thickness direction so as to include the joint portion.

The joint joint 10 of the present invention overlaps a plurality of metal plates 20a and 20b, and irradiates a part of the surface of the metal plate 20a with light rays from the metal plate 20a side to form a dotted joint. A plurality of metal plates 20a and 20b are laminated and joined. The metal plates 20a and 20b are joined by a melt-solidified part 30 which is a dotted joint. When the molten and solidified part 30 is viewed in plan from the light irradiation side, the melted and solidified part 30 is a remelted and solidified part 30a that is a structure that has been melted and solidified at the center, and a solidified and reheated part 30b that is reheated after solidification. , 30c.
Hereinafter, it demonstrates in detail in order of a dotted | punctate junction part and a some metal plate.

<Dotted joint>
The dotted joint has a melted and solidified part 30 that is formed by superposing a plurality of metal plates 20a and 20b and melted and solidified by irradiation with light rays. As long as the melt-solidified portion 30 of the dotted joint is formed across the plurality of metal plates 20a, 20b, it may or may not penetrate through the plurality of metal plates.

  The dot shape means that when the molten and solidified portion is viewed in plan from the light irradiation side, the outer peripheral contour of the molten and solidified portion is circular or polygonal and melted and solidified to the center of the contour. The circular shape includes a combination of semi-circles and semi-ellipses having different diameters in addition to the case where the melt-solidified portion is circular or elliptical when the melt-solidified portion is viewed in plan from the light irradiation side. Moreover, the shape of the melt-solidified part formed by irradiating a metal plate with a light beam in a spiral shape from the outer peripheral side toward the central side or from the central side toward the outer peripheral side is also included in a dot shape.

  The width W (the equivalent circle diameter of the melt-solidified portion when the melt-solidified portion is viewed in plan from the light irradiation side) of the spot-like joined portion may be adjusted according to the joint strength, etc. Although not limited, 3-12 mm is illustrated. Preferably, it is 4-10 mm.

(Remelt solidification part)
The remelted and solidified portion 30a is a portion obtained by irradiating the inner side of the melted and solidified portion 30 of the point-like joint portion with light again and melted and solidified in a dotted shape, and has a structure that is melted and solidified. The dot shape means that when the remelted solidified part is viewed in plan from the light irradiation side, the outer peripheral outline of the remelted solidified part is circular or polygonal and melted and solidified to the center of the outline. The circular shape includes a combination of semi-circles and semi-ellipses having different diameters in addition to the case where the re-melt solidification part is circular or elliptical when the re-melt solidification part is viewed in plan from the light irradiation side. Further, the shape of the remelted and solidified portion formed by irradiating the metal plate with a light beam in a spiral shape and irradiating from the outer peripheral side to the central side or from the central side to the outer peripheral side is also included in a dot shape.

  The remelted and solidified portion 30a is formed so as to include the center corresponding to the circle of the melted and solidified portion and not include the melting boundary of the melted and solidified portion 30 when the melted and solidified portion is viewed in plan from the light irradiation side. However, when the melt-solidified portion is viewed in plan from the light irradiation side, the center corresponding to the circle of the melt-solidified portion does not need to coincide with the center corresponding to the circle of the re-melt-solidified portion 30a.

  Further, the remelted and solidified portion 30 a is formed across the plurality of metal plates 20 a and 20 b in the plate thickness direction of the joint joint 10. That is, as shown in FIG. 3, the remelted solidified portion 30a may or may not penetrate the metal plate 20b as long as it is formed across at least a plurality of metal plates.

  The upper limit of the width Wa of the remelted and solidified part 30a (equivalent circle diameter of the remelted and solidified part when the melted and solidified part is viewed in plan from the light irradiation side) is not particularly limited. It is determined by the relationship with the width Wb of the surrounding solidification reheating parts 30b, 30c.

(Coagulation reheating part)
The solidification reheating portions 30b and 30c are portions formed so as to include a melting boundary around the remelt solidification portion 30a by re-irradiating the melt solidification portion 30 of the spot-like joint portion with light. It includes a portion that is softer than the portion 30a. The solidification reheating part 30b adjacent to the remelting solidification part 30a is a part reheated below the melting point of the base material and above the Ac1 point temperature. The solidification reheating part 30c is a part reheated to a temperature below the Ac1 point temperature, has a tempered structure, and is formed at least around the melting boundary in the vicinity of the overlapping surface of the metal plates. When a load is applied to the joint joint 10 in the peeling direction, stress concentrates on the melting boundary in the vicinity of the overlapping surface of the metal plates, leading to breakage. Therefore, at least the toughness of the solidified reheat part 30c is improved.

  In addition, since the solidification reheating part 30c near the melting boundary of the overlapping surface of the metal plates tends to concentrate stress, the average value of the Vickers hardness is set to Hv390 or less, and the Vickers hardness of the remelting solidification part 30a. It is preferable to make it Hv70 or more lower than the average value. Moreover, the toughness in the vicinity of the melting boundary can be improved by setting the width Wc of the solidification reheating part 30c to at least 0.5 mm. In order to set the width Wc of the solidification reheating unit 30c to at least 0.5 mm, the width Wb of the solidification reheating units 30b and 30c is preferably set to 1.0 to 3.0 mm.

  In the measurement of the average value of the Vickers hardness of the remelted solidified part 30a and the solidified reheated part 30c, the melted solidified part 30 in contact with the overlapping surface of the metal plates in the cross section in the thickness direction including the central axis C is melted. Measure on the line connecting the boundaries. And in the remelting solidification part 30a and the solidification reheating part 30c, Vickers hardness is measured at equal intervals of 3 points or more including the center of each part and the vicinity of both ends, and an average value is obtained. As an example of specific measurement conditions, the hardness is measured at 0.15 mm pitch from both ends with a test force of 0.3 kg, and the average value of the hardness at 0.15 mm, 0.30 mm, and 0.45 mm is obtained. The vicinity of both ends means a range of 5 to 10% of the width from both ends. Further, when there are a plurality of overlapping surfaces of the metal plates, the measurement is performed on a line connecting melting boundaries of the melt-solidified portion 30 in contact with the overlapping surfaces of the respective metal plates. The remelted solidified part and the solidified reheated part can be distinguished from each other by observing the microstructure.

<Multiple metal plates>
Next, the several metal plate which comprises the joint joint of this invention is demonstrated.

(Type and composition of metal plate)
The metal plate is not particularly limited and may be a plate of various metals, but is preferably a steel plate. The component composition of the steel sheet is not particularly limited, and may be a steel sheet having a component composition that can provide mechanical properties and the like according to the application. Moreover, when a high-strength steel sheet having a carbon content of 0.10% by mass or more is applied to the joint joint of the present invention, the improvement in cross tensile strength is remarkable, and it is preferable to target such a steel sheet.

(Metal plate thickness)
The plate | board thickness of a metal plate is not specifically limited, It can be set as the range of 0.5-3.2 mm. Even if the plate thickness is less than 0.5 mm, the effect of improving the joint strength of the joint can be obtained, but since the joint strength affects the plate thickness, the effect of improving the strength of the entire joint joint is reduced, and the joint joint is reduced. The scope of application is limited. Moreover, even if the plate thickness is over 3.2 mm, an effect of improving the joint strength of the joint portion can be obtained, but the application range of the joint joint is limited from the viewpoint of reducing the weight of the member.

(Surface treatment film of metal plate)
The plurality of metal plates may include one or more metal plates in which a surface treatment film is formed on both surfaces or one surface of at least a joining portion. The surface treatment film includes a plating film, and may further include a coating film or the like. Examples of the plating film include zinc plating, aluminum plating, zinc / nickel plating, zinc / iron plating, and zinc / aluminum / magnesium plating. The plating production method includes hot dipping and electroplating. Hot stamped zinc plating or aluminum plating may also be used.

(Metal plate form)
As for the form of the metal plate, it suffices that at least the portion forming the joint joint is plate-like, and the whole may not be a plate. For example, it includes a flange portion of a member press-molded into a specific shape having a hat-shaped cross section, a flat portion of a pipe, and the like. The number of metal plates to be superimposed is not limited to two and may be three or more. Further, the types, component compositions, and plate thicknesses of the respective metal plates may all be the same or different from each other. Moreover, it is not limited to what is comprised from a separate metal plate, The lap | joint joint of what formed one metal plate in predetermined shapes, such as a tubular shape, and overlap | superposed the edge part may be sufficient.

Hereinafter, although not limited thereto, an example of a lap joint in an automobile will be shown.
In the case of A-pillar, a combination of 270 to 340 MPa class galvannealed steel sheet, 590 to 1800 MPa class non-plated steel sheet or hot stamped steel sheet, and 590 to 1800 MPa class non-plated steel sheet or hot stamped steel sheet A lap joint is illustrated.

  In the case of the B pillar, a combination of three layers of an alloyed hot-dip galvanized steel sheet having a tensile strength of 270 to 340 MPa, a 590 to 1800 MPa class non-plated steel sheet or a hot stamped steel sheet, and a 440 to 980 MPa class non-plated steel sheet A lap joint is illustrated.

  In the case of a side sill, a lap-jointed joint in a combination of three layers of a 270 to 340 MPa class galvannealed steel sheet, a 590 to 1800 MPa class galvannealed steel sheet, and a 590 to 1800 MPa class galvannealed steel sheet Is exemplified.

  In the case of a floor member, lap joining in a combination of two layers of a 270-590 MPa class alloyed hot dip galvanized steel floor panel and a 440-1800 MPa class non-plated steel sheet or an alloyed hot dip galvanized steel floor member A joint is illustrated.

Next, a method for producing a lap joint according to the present invention (hereinafter referred to as “the production method of the present invention”) will be described.
The production method of the present invention comprises:
(A) When a plurality of metal plates are overlapped, irradiated with light rays, and viewed in plan from the metal plate surface side, the outer contour is substantially circular, forming a point-like joint melted and solidified to the center; as well as,
(B) Re-irradiate the inside of the dotted joint with light rays, and when the molten and solidified portion is viewed in plan from the light irradiation side, the outer contour is substantially circular and re-melted into a shape that has been re-melted and solidified to the center. It includes solidifying and reheating the melting boundary so as to soften from the remelted solidified portion.

  First, (a) when a plurality of metal plates are overlapped, irradiated with light, and viewed in plan from the metal plate surface side, the outer contour is substantially circular, and a point-like joint is formed that melts and solidifies to the center. This will be described with reference to FIG.

  FIG. 4 is a perspective view showing an outline of the formation of the dotted joint. FIG. 4 (a) shows an outline of irradiating light rays with different irradiation diameters, FIG. 4 (b) shows an outline of irradiating light rays with a wide condensing area, and FIG. 4 (c) is formed. A dotted joint is shown.

  FIG. 4A shows an example of a method of irradiating the light beam 50. The light beam 50 is irradiated with different irradiation diameters. In this figure, the irradiation planned portion 60a of the light beam 50 is indicated by a dotted line, and three irradiation planned portions 60a having different irradiation diameters are shown.

  In the formation of the dotted joint, first, the plurality of metal plates 20a and 20b are overlapped, and the light beam 50 is irradiated from one metal plate 20a side to perform the joining. In the irradiation of the light beam 50, when the irradiation planned portion 60a is viewed in plan from the irradiation side of the light beam 50, the light beam is scanned in a substantially circular shape as indicated by a white arrow. At that time, the irradiation of the light beam 50 is performed on the outer irradiation scheduled portion 60a, and then performed on the inner irradiation planned portion 60a, and then on the inner irradiation planned portion 60a. You may go. The scanning direction of the light beam is not particularly limited, and may be either clockwise or counterclockwise.

  In addition, when the irradiation target portion 60a from the irradiation side of the light beam 50 is viewed in plan, the outer peripheral shape of the irradiation target portion 60a of the light beam 50 is a circle, but an elliptical shape, a polygonal shape, a semicircle or a half ellipse having different diameters are used. A combined shape or a spiral shape may be used. When the irradiation target portion 60a of the light beam 50 has a spiral shape, the irradiation of the light beam 50 is performed from the outer end portion of the spiral irradiation target portion 60b toward the inner end portion or the spiral irradiation. The scanning is performed in a spiral shape from the inner end of the planned location 60b toward the outer end. The direction of the spiral is not particularly limited, and may be either clockwise or counterclockwise.

  In FIG. 4 (a), three irradiation planned places with different diameters are illustrated, but the number of irradiation planned spots with different diameters may be increased or decreased according to the focal area of the light beam or the bonding area of the dotted joint. Can do.

  FIG. 4B shows another example of the method of irradiating the light beam 50, which irradiates the light beam 50 with a wide condensing area. In this figure, the irradiation planned portion 60b of the light beam 50 is indicated by a dotted line. The irradiation of the light beam 50 is performed once with the light beam condensing area widened.

  As shown in FIG. 4 (a) or 4 (b), by irradiating the light beam 50, the melted melted portion solidifies from the outside to the center side, and as shown in FIG. The melt-solidified part 30 can be formed.

  Moreover, when using one or more metal plates on which a surface treatment film is formed on a plurality of metal plates, the irradiation of the light beam 50 can be performed on the outer planned irradiation site 60a, and then performed on the inner planned irradiation site 60a. preferable. Thereby, it becomes easy to collect and stir and remove the film that has become a gas causing a defect in the joint in the vicinity of the center of the melted part. In addition, even if it irradiates the light ray 50 to the inner irradiation scheduled part 60a, and then performs it to the outer irradiation planned part 60a or widens the condensing area of the light ray 50, the film which became gas is applied. Since it can remove from a fusion | melting part, it does not exclude employ | adopting the irradiation method of these light rays.

  Next, (b) when the light beam is re-irradiated inside the dotted joint, and when the melt-solidified portion is viewed in plan from the light-irradiated side, the outer contour is substantially circular, and the shape is re-melt-solidified to the center. A description will be given of re-melting and solidifying (dots) and reheating the melting boundary so as to soften from the re-melting and solidifying part.

  In the heat treatment of the spot-like joint, the temperature of the melt-solidified part 30 of the spot-like joint obtained by the method shown in FIG. 4 is equal to or lower than a predetermined temperature, for example, Ms point-50 ° C. (Ms point: martense for a steel plate). It waits until it becomes below a site transformation start temperature), Then, it irradiates with the light ray 50 to the inner side of the fusion | melting solidification part 30 from the metal plate 20a side. The inner side means the inside of the melted and solidified part 30 excluding the melting boundary of the melted and solidified part 30.

  If the temperature of the melt-solidified portion 30 is Ms point −50 ° C. or lower, a certain amount or more of martensite is generated in the steel sheet. Is tempered and softened, improving the joint strength. Further, the lower limit of the temperature of the melt-solidified portion 30 when the heat treatment of the melt-solidified portion 30 of the dotted joint is started is not particularly limited, but is preferably set to Ms point −250 ° C. or less. This is because a general steel plate finishes the martensitic transformation at an Ms point of −250 ° C.

Next, scanning of the light beam 50 in the irradiation of the light beam 50 in the heat treatment of the dotted joint will be described with reference to FIG.
FIG. 5 is a perspective view showing an outline of the heat treatment of the dotted joint. FIG. 5 (a) shows an outline of irradiating light beams with different irradiation diameters, FIG. 5 (b) shows an outline of irradiating light beams with a wide condensing area, and FIG. 5 (c) shows remelting. The point-like junction which has a solidification part and a solidification reheating part is shown.

  FIG. 5A shows an example of a method of irradiating the re-melted portion with the light beam 50, and irradiates the light beam with different irradiation diameters. In this figure, the irradiation planned portion 70a of the light beam 50 is indicated by a dotted line, and two irradiation planned portions 70a having different irradiation diameters are shown inside the melt-solidified portion 30.

  In the irradiation of the light beam 50, the light beam is scanned in a substantially circular shape as indicated by an outline arrow. At that time, irradiation of the light beam 50 is performed on the inner irradiation scheduled portion 70a, and then performed on the outer irradiation planned portion 70a, and then on the outer irradiation planned portion 70a, and then on the inner irradiation planned portion 70a. You may go. The scanning direction of the light beam is not particularly limited, and may be either clockwise or counterclockwise.

  When the molten solidified portion 30 is viewed in plan from the irradiation side of the light beam 50, the planned irradiation location 70 a of the light beam 50 is remelted in a dot shape including the circle-equivalent center of the molten solidified portion 30. Set to be tempered.

  Further, when the joint portion is viewed in plan from the irradiation side of the light beam 50, the outer peripheral shape of the irradiation target portion 70a of the light beam 50 is a circle, but an elliptical shape, a polygonal shape, a shape combining a semicircle or a semi-ellipse with different diameters. Alternatively, a spiral shape may be used. In addition, although two irradiation planned locations with different diameters are illustrated, the number of irradiation planned locations with different diameters can be increased or decreased according to the focal area of the light beam or the area of the melt-solidified portion of the dotted joint. .

  FIG. 5B shows another example of the method of irradiating the re-melting planned portion with the light beam 50, and the light beam 50 is irradiated with the condensing area widened. In this figure, the irradiation planned portion 80b of the light beam 50 is indicated by a dotted line inside the melt-solidified portion 30. The irradiation of the light beam 50 is performed once with the light beam condensing area widened. Also in this example, when the melted and solidified portion 30 is viewed in plan from the irradiation side of the light beam 50, the planned irradiation portion 80 b of the light beam 50 is remelted into a dot shape including the circle-equivalent center of the melted and solidified portion 30. 30 melting boundaries are set to be tempered.

  By irradiating the light beam 50 as shown in FIGS. 5 (a) and 5 (b), as shown in FIG. The remelted and solidified part 30a is formed in a dot shape including the circle-equivalent center of the melted and solidified part, and the solidified and reheated parts 30b and 30c are formed around it. And the solidification reheating part 30c containing a fusion boundary is tempered and toughness improves.

  Further, in the formation of the dotted joint and the heat treatment at the melting boundary of the dotted joint, the light irradiation method may be the same irradiation method or different irradiation methods. For example, even if a light beam is irradiated with a different irradiation diameter to form a spot-like joint, and a light beam is irradiated with a different irradiation diameter to heat-treat the melting boundary of the spot-like joint, the condensing area is widened. Then, a light beam may be irradiated to form a dotted joint, and a light beam may be irradiated with a different irradiation diameter to heat-treat the melting boundary of the dotted joint.

Next, of the irradiation with the light beam 50, the heating temperature of the coagulation reheating units 30b and 30c will be described.
Of the melt-solidified portion 30 of the dotted joint, at least a region in the range of 0.5 mm from the melt boundary in the vicinity of the overlapping surface of the metal plates 20a, 20b is tempered (the solidification reheat portion 30c is obtained). Reheat).

  In order to temper a region in the range of 0.5 mm from the melting boundary in the vicinity of the overlapping surface, the maximum attained temperature in this range is a predetermined temperature below the Ac1 point (for example, 500 ° C. or more and 700 ° C. or less), A light beam 50 is applied to the inside of the melt-solidified portion 30. The temperature measured on the steel sheet surface can be used as a representative value for the temperature of the solidification reheating unit 30c. The temperature can be measured using a radiation thermometer or a thermocouple.

  In order to obtain such a temperature, the equivalent circle diameter of the remelting point (scheduled light irradiation point) or the width Wb of the solidified reheating part to be formed, and the temperature in the above range during the reirradiation of the light beam, , The relationship between the re-irradiation time of the light beam and the temperature in the above range, and the like, the equivalent circle diameter of the re-melting point (light beam irradiation point), the width Wb of the solidification reheating part, This can be done by adjusting the re-irradiation time or the like. Further, in order to set the coagulation reheating part 30c to 500 ° C. or more and 700 ° C. or less, it is exemplified that the irradiation of light rays is adjusted so that the width Wb of the coagulation reheating part is 1.0 to 3.0 mm. Preferably, it is 1.5 to 2.5 mm.

  Next, a description will be given of the light rays used in the formation of the dotted joint and the heat treatment of the dotted joint. A laser is generally used for the light beam, and the type is not particularly limited, but a remote bonding apparatus is preferable. The remote bonding apparatus moves a light beam between bonding points at high speed by a galvanometer mirror attached to the tip of a robot arm, and can greatly reduce the work time of bonding. As the oscillator, a gas excitation type, a solid excitation type, a semiconductor type, or the like can be used.

  Moreover, the conventional conditions can be employ | adopted for the conditions of joining. For example, it can be performed under the joining conditions of an output of 2 to 30 kW, a light beam diameter of the condensing surface of 0.1 to 8.0 mm, and a joining speed of 0.1 to 60 m / min.

  In addition, the assembly of automobiles consists of a plurality of joining processes, but when the manufacturing method of the present invention is carried out within one process, the joining and remelting by light irradiation is carried out for each joining point. However, in order to reduce the waiting time for cooling to an Ms point of −250 ° C. or lower, more preferably, a plurality of melt bonding is performed by light irradiation, and then a plurality of remelting is performed by light irradiation. Is preferred. Moreover, when implementing the manufacturing method of this invention in a some joining process, the waiting time of cooling can be eliminated by making the fusion | melting joining process by light irradiation, and the remelting process by light irradiation into a separate process.

  Next, examples of the present invention will be described. The conditions in the examples are one example of conditions used for confirming the feasibility and effects of the present invention, and the present invention is based on this one example of conditions. It is not limited. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

  Table 1 shows steel sheets to be joined.

  Two steel plates of the same type shown in Table 1 were overlapped and joined by a fiber laser using a remote joining device having a galvanometer mirror, to create a test piece having a dotted joint. Table 2 shows the conditions for forming the dotted joint. The light beam diameter is the diameter of the light beam on the condensing surface.

  Next, heat treatment was performed on the dotted joints of each test piece. This heat treatment is carried out by forming the remelted and solidified part so that the center of the melted and solidified part and the remelted and solidified part coincide with each other when the melted and solidified part is viewed in plan from the light irradiation side. It was. Table 3 shows the heat treatment conditions for the spot-like laser junction. The light beam diameter is the diameter of the light beam on the condensing surface. In the heat treatment, the same remote bonding apparatus as that for forming the dotted joints was used.

  Table 4 shows the test piece after the heat treatment, the width Wb of the solidification reheated part, the average Vickers hardness A (excluding the shrinkage nest) of the remelted solidified part, and the average of 0.5 mm from the melting boundary of the molten solidified part. The Vickers hardness B, the difference between the average Vickers hardness A and B, and the cross tensile strength (CTS) are shown.

  For CTS, a method described in JIS Z3137 as a strength test method for spot bonding was adopted. Further, after joining, the steel sheet was cut and polished perpendicularly to the plate surface through the center of the dotted joint, and the size of the shrinkage nest was observed, and the Vickers hardness was measured. The Vickers hardness A of Comparative Examples 1, 5, and 14 is the average Vickers hardness at the center of the melt-solidified portion.

  No. 2 to 4, 6 to 8, and 10 to 13 are heat-treated on the dotted joints, and satisfy the configuration defined by the joint joint of the present invention. Toughness is improved and cross tensile strength (CTS) is high.

  In contrast, no. 1, no. 5 and No. In No. 14, since the heat treatment is not performed on the spot-like joint portion, the toughness of the melt boundary of the melt-solidified portion is not improved, and the cross tensile strength (CTS) is low. No. In No. 9, since the entire melt-solidified part was heat-treated, the toughness of the melt boundary of the melt-solidified part was not improved, and the cross tensile strength (CTS) was low.

  According to the present invention, since the solidification reheat part having excellent toughness is provided in the vicinity of the melting boundary of the dotted joint, the joint strength of the lap joint, particularly the cross tensile strength (CTS) can be improved. It is possible to improve the reliability of the joint joint. And the reliability of a motor vehicle component can be improved by applying the joint joint of this invention to a motor vehicle component. Therefore, the present invention has high industrial applicability.

DESCRIPTION OF SYMBOLS 1 Junction joint 2a, 2b Metal plate 3 Melt-solidification part of a dotted joint part 3a Remelt-solidification part 3b Solidification reheating part 10 Joint joint 20a, 20b Metal plate 30 Melt-solidification part 30a of a point-like junction 30a Remelt solidification Part 30b Solidification reheating part 30c Solidification reheating part 50 Light beam 60a, 60b Planned irradiation part 70a, 70b Planned irradiation part X Measurement position of Vickers hardness in the plate thickness direction L1 Measurement range of Vickers hardness in the direction parallel to the metal plate surface L2 Measurement range of Vickers hardness of melt-solidified part L3 Measurement range of Vickers hardness of re-melted solidified part C Central axis W Width of melt-solidified part Wa Width of re-melted solidified part Wb Width of solidified reheat part Wc Near melting boundary Width of solidification reheating part

Claims (6)

In a lap joint with a plurality of metal plates stacked and having a dotted joint,
The dotted joint has a melt-solidified part straddling the plurality of metal plates,
The molten and solidified part has a remelted and solidified part and a solidified and reheated part,
The remelted and solidified part is a dot including the center of the melted and solidified part when the melted and solidified part is viewed in plan, and straddles the plurality of metal plates,
The lap joint joint is characterized in that the solidification reheating part is located around the remelt solidification part, includes a melting boundary of the dotted joint, and is softer than the remelt solidification part .   Of the solidification reheating part, the average value of the Vickers hardness in a range of 0.5 mm from the melting boundary of the overlapping surface of the metal plate toward the remelting solidification part is Hv390 or less, and 2. The lap joint according to claim 1, wherein Hv is 70 or more lower than an average value of Vickers hardness of the remelted solidified portion.   The lap joint according to claim 1 or 2, wherein the plurality of metal plates include one or more metal plates having a surface treatment film. In the method of manufacturing a lap joint where a plurality of metal plates are overlapped and bonded by irradiating a light beam having a high power density,
Irradiating a light beam having a high power density to one of the superimposed metal plates to form a point-like joint having a melt-solidified portion melted and solidified in a point-like manner across the plurality of metal plates,
When the molten and solidified portion is viewed in plan from the irradiation side of the light beam having the high power density, the light beam having the high power density is re-irradiated inside the molten and solidified portion, and includes the circle-equivalent center of the molten and solidified portion. A solidified and reheated portion that is re-melted and solidified across the plurality of metal plates to form a remelted and solidified portion, and further includes a melting boundary of the dotted joint around the remelted and solidified portion. And a reheat condition at that time is adjusted to soften the solidified reheated part from the remelted solidified part.   The re-irradiation of the light beam having a high power density is a distance from the outer end portion of the remelted and solidified remelted solidified portion to the melting boundary of the dotted joint in the thickness direction cross section of the plurality of metal plates. The method for producing a lap joint according to claim 4, wherein the lap joint is carried out so as to be 1.0 to 3.0 mm.   The method for manufacturing a lap joint according to claim 4 or 5, wherein at least one metal plate on which a surface treatment film is formed is used for the plurality of metal plates.

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