JP2019209360A - Spot weld joint and method for manufacturing the same - Google Patents

Abstract

To provide a spot weld joint that is excellent in static strength while having a structure capable of relaxing stress acting on a joint, and to provide a method for manufacturing the same.SOLUTION: A spot weld joint (1) includes a plurality of metal plates (21, 22) stacked in a thickness direction and has a groove part (9) formed so as to be recessed in the thickness direction from a surface of the metal plate (21) in a stress concentration zone.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a spot welded joint and a manufacturing method thereof.

  Various metal structural parts (for example, car body parts, etc.) are used in the field of transportation machines and industrial machines such as automobiles. For mounting and manufacturing of these metal structural parts, Resistance spot welding is often used.

As one of such metal structural parts, for example, a spot welded joint is known in which a plurality of steel plates stacked in the thickness direction are joined by spot welding. Here, FIG. 10 is an enlarged cross-sectional view of a main part of a conventional general spot welded joint 1 ′, and FIG. 6 is a steel sheet assuming a state when a tensile load in the peeling direction is applied to the spot welded joint. It is the stress distribution map which analyzed (namely, the steel plate which provided the tensile load of the peeling direction) by the finite element method.
In this specification, so as to be perpendicular to the planar direction D _P in which the metal plate extends, the cutting surface when cutting along the metal plate in the thickness direction D _T, called the cross In particular, in a welded member (joint) after spot welding, it passes through the center of indentation (hereinafter referred to as “welding center”) when viewed from the plate surface of the metal plate and is perpendicular to the plate surface. The cut surface when cut is called a cross section.

As shown in FIG. 10, a typical spot weld joint 1 ', two steel plates 21 superimposed in the thickness direction D _T', energizes the 'plate set 2 consisting of' 22 in the thickness direction D _T By melting a predetermined region in the plate assembly 2 ′ (specifically, the overlapping surface of the steel plates 21 ′ and 22 ′ adjacent to the thickness direction _DT and the vicinity thereof) by Joule heat due to electric resistance. The steel plates 21 'and 22' are joined to each other. Therefore, a welded portion 3 ′ (so-called nugget) formed by melting the steel plates 21 ′ and 22 ′ when energized is formed inside the spot welded joint 1 ′.

'In the sign S of the structure of the joint, since the stress from the weld end in the region spanning the periphery thereof is made tends to concentrate (6' such spot welded joint 1 reference area indicated _c. In Hereinafter, such a region where stress is likely to concentrate is referred to as a “stress concentration part”.) When used as a structural part such as a car body part of an automobile, the stress is particularly high among the stress concentration parts S ′ _c described above. Starting from the welded portion end portion (refer to the portion indicated by reference numeral S ′ _max in FIG. 6, the portion where such stress is most likely to be concentrated is referred to as “the most stress concentrated portion”). In particular, spot welded joints using high strength steel sheets with low toughness may cause cracks and fractures (hereinafter collectively referred to as “ruptures”). Strength reduction is regarded as a problem The If fracture occurs in the weld zone, the strength of the structural part (joint) will be reduced, which will have a great effect on the mechanical properties. It is strongly desired to improve the strength of spot welded joints using these steel plates.

  On the other hand, various techniques for reducing stress concentration and improving fatigue strength have been studied. For example, each of Patent Documents 1 and 2 includes a hat-shaped first member having a flange portion and the flange portion. With respect to a structural member formed by joining the overlapped flat plate-like second members with a plurality of point-like joints, between the adjacent point-like joints, from the outer edge of the flange part to the joint side (inward side) A technique is disclosed in which the stress concentration generated at the end portion of the point-like joint is relaxed by forming a slit or a recess cut away toward the surface.

JP 2012-219886 A US Patent Application Publication No. 2007/0187371

  However, in the techniques disclosed in Patent Documents 1 and 2, although a certain improvement in fatigue strength is expected due to stress relaxation by the slits or recesses described above, from the outer edge portion of the flange portion toward the joint portion side. Since the cut-out structure, that is, a structure in which a part of each member is completely lost in the thickness direction, the static strength of the joint itself may be lowered.

  Therefore, an object of the present invention is to provide a spot welded joint having an excellent static strength while having a structure that can relieve stress applied to the joint, and a method for manufacturing the spot welded joint.

One aspect (aspect 1) of the present invention is a spot welded joint composed of a plurality of metal plates stacked in the thickness direction,
The spot weld joint has a groove formed so as to be recessed in the thickness direction from the surface of the metal plate at a stress concentration site.

The spot welded joint of the present aspect 1 has a groove formed so as to be recessed in the thickness direction from the surface of the metal plate at the stress concentration portion, so that the metal plate has a predetermined flexibility in the peeling direction. However, when the joint is used as a structural part such as a car body part of an automobile, the stress applied to the joint is concentrated on the bottom of the groove and absorbed by the deformation of the metal plate. Can be relaxed.
Furthermore, the spot welded joint of this aspect 1 is formed so that the above-mentioned groove portion is recessed in the thickness direction and the plate thickness is relatively thin, that is, the metal plate is not completely lost in the thickness direction. Therefore, a predetermined static strength can be ensured while the metal plate on which the groove is formed is easily deformed in the peeling direction.
As described above, the spot welded joint according to the first aspect can maintain excellent quality in static strength while having a structure capable of relaxing the stress applied to the joint.

  In the present specification, the “stress concentration part” includes not only the end portion of the weld where the stress is most likely to be concentrated (the most stress concentration part) but also a peripheral part thereof and a part where the stress is likely to be relatively concentrated. As shown in FIG. 6 described above, a metal plate assuming a state when a tensile load in the peeling direction is applied to the spot welded joint (that is, a metal plate provided with a tensile load in the peeling direction) is used. From the stress distribution diagram analyzed by the finite element method, it can be specified as a portion having a relatively high stress.

  Further, in another aspect (aspect 2) of the present invention, in the spot welded joint according to aspect 1, the groove portion has a curvature radius of 0.1 mm or more and a plate thickness of the metal plate on which the groove portion is formed. And a maximum depth of ¼ or less.

  In the spot welded joint according to the second aspect, since the groove portion has the specific radius of curvature and the maximum depth, the metal plate on which the groove portion is formed is easily deformed in the peeling direction, and a predetermined static Strength can be ensured more reliably. Thereby, the spot welded joint of the present aspect 2 can more reliably exhibit excellent static strength while having a structure that can relieve stress applied to the joint.

  In still another aspect (Aspect 3) of the present invention, in the spot welded joint according to Aspect 1 or 2, the groove is formed so as to surround the center of the weld in plan view.

Since the spot welded joint of this aspect 3 is formed in an annular shape so that the groove portion surrounds the center of the welded portion in plan view, the stress can be relaxed regardless of the direction of the stress applied to the joint ( That is, the stress can be relaxed in response to a stress applied from an arbitrary plane direction (for example, a longitudinal direction, a short direction, etc.), and further, the static of the metal plate on which the above-described groove is formed. The strength is also less likely to decrease.
Therefore, the spot welded joint of the third aspect can exhibit excellent static strength more stably while having a structure that can relieve stress applied to the joint.

In still another aspect (Aspect 4) of the present invention, in the spot welded joint according to any one of the above aspects 1 to 3,
The groove is formed in at least one of the plurality of metal plates on at least one of the surface on one side and the surface on the other side of the metal plate,
Furthermore, when the surface on which the groove is formed is a non-overlapping surface that does not overlap with other metal plates in the plurality of metal plates, the groove is from the welded portion end to the welded portion in plan view. Formed in an area within 3 times the radius,
When the surface on which the groove is formed is an overlapping surface that overlaps with another metal plate in the plurality of metal plates, the groove is from the portion 1 mm away from the end of the welded portion in plan view. It is formed in a region within 3 times the weld radius.

In the spot welded joint of this aspect 4, the groove is formed in the specific region of the non-overlapping surface or the overlapping surface of the plurality of metal plates, and the stress is particularly concentrated in the specific region. Since the spot welded joint of this aspect 4 in which the above-mentioned groove is formed in such a specific region, the stress applied to the joint can be more accurately mitigated, and the above-mentioned groove is The static strength of the formed metal plate can also be made more difficult to decrease.
Therefore, the spot welded joint according to the fourth aspect can exhibit excellent static strength more reliably while having a structure capable of relaxing the stress applied to the joint.

Still another aspect (aspect 5) of the present invention is a method for manufacturing the spot welded joint according to any one of aspects 1 to 4,
Forming the groove at the stress concentration site in at least one metal plate of the plurality of metal plates;
A step of overlapping the plurality of metal plates in the thickness direction to form a plate set;
Joining a plurality of metal plates stacked in the thickness direction by energizing the plate assembly in the thickness direction.

The manufacturing method of the spot welded joint according to the fifth aspect easily includes the above-described steps to easily obtain a spot welded joint excellent in static strength while having a structure capable of relaxing the stress applied to the joint. be able to.
In addition, in the manufacturing method of the spot welded joint according to the fifth aspect, when the step of forming the groove is performed before the step of forming the plate assembly, the groove is formed of a plurality of metals. Since it can be formed on the overlapping surface of the metal plates in the plate, there is an advantage that it is possible to reduce restrictions on the appearance or structure of the joint, and the step of forming the groove portion described above includes a plurality of the steps described above. When implemented after the step of joining a single metal plate, since there are few restrictions on the joining position (welding part forming position) according to the forming position of the groove part, the positional relationship between the above groove part and the welding part is There is also an advantage that it can be controlled more accurately.

  ADVANTAGE OF THE INVENTION According to this invention, while having the structure which can relieve | moderate the stress concerning a joint, the spot welded joint which has the outstanding static strength, and its manufacturing method can be provided.

FIG. 1 is an enlarged cross-sectional view of a welding location in a spot welded joint 1 according to an embodiment of the present invention. FIG. 2 is an enlarged plan view of the welded spot in the spot welded joint 1 of FIG. 1 as viewed from the upper side in the thickness direction _DT . FIG. 3A is an enlarged cross-sectional view of the main part in the vicinity of the welding location in the spot welded joint 1 of FIG. 1, and FIG. 3B is a tensile load in the peeling direction applied to the spot welded joint 1 of FIG. It is a principal part expanded sectional view which shows typically a state when is provided. FIG. 4 is an enlarged plan view of the groove forming portion of the steel plate 21 used in the spot welded joint 1 as viewed in the thickness direction _DT from the overlapping surface 21b side. FIG. 5 is an enlarged cross-sectional view along the line VV of the groove forming portion in the steel plate 21 of FIG. FIG. 6 shows an analysis of a steel plate without a groove assuming a state in which a tensile load in the peeling direction is applied to a spot welded joint (that is, a steel plate without a groove provided with a tensile load in the peeling direction) by a finite element method. Specifically, FIG. 6A is a schematic cross-sectional view showing the structure of a steel sheet to which a tensile load in the peeling direction is applied, and FIG. 6B is a tensile load in the peeling direction. It is a stress distribution figure of the steel plate without the groove part which provided. FIG. 7 is a stress distribution diagram obtained by analyzing a steel plate having a groove portion assuming a state when a tensile load in the peeling direction is applied to the spot welded joint 1 according to an embodiment of the present invention by a finite element method. FIG. 8 is an enlarged cross-sectional view of the welding locations of spot welded joints 1a to 1d according to another embodiment of the present invention, in which the arrangement of the groove portions is different from the spot welded joint 1 described above. FIG. 9 is a plan view schematically showing spot welded joints according to Examples 1 and 4 and Comparative Example 1 of the present invention. FIG. 10 is an enlarged cross-sectional view of a main part of a conventional general spot welded joint 1 ′. Specifically, FIG. 10 (a) is a main part in the vicinity of a welding spot in a general spot welded joint 1 ′. FIG. 10B is an enlarged cross-sectional view, and FIG. 10B is an enlarged cross-sectional view of an essential part schematically showing a state when a tensile load in the peeling direction is applied to the spot welded joint 1 ′ of FIG.

  Hereinafter, a preferred embodiment of a spot welded joint according to the present invention will be described in detail with reference to the drawings.

The various directions used in the present specification are as follows unless otherwise specified.
In the present specification, the “thickness direction D _T ” of the metal plate is the thickness direction (plate thickness direction) of the overlapped portion of the metal plates, which becomes a joining target portion when a plurality of metal plates are overlapped and joined. Means. Therefore, for example, when the metal plate has a hat-type structure, the plate thickness direction of the flange portion serving as a joining target portion of the hat-type metal plate is the thickness direction _DT of the metal plate. In the present specification, the thickness direction _DT is similarly applied to a welded joint after a plurality of metal plates are joined.
In this specification, the “planar direction D _P ” in which the metal plate extends is a virtual plane parallel to the overlapping surface of the metal plate in the joining target portion when the plurality of metal plates are overlapped and joined. Means the extending direction, and the above-described thickness direction _DT is orthogonal to each other. Therefore, for example, when the metal plate has a hat-shaped structure, the extending direction of the virtual plane parallel to the overlapping surface of the metal plates in the flange portion to be joined to the hat-shaped metal plate is a planar direction _{D P.} In this specification, such a planar direction D _P, even in a welded joint after the plurality of metal plates are bonded, are similarly applicable.
In this specification, the metal plate or welded joint, in the planar direction D _P of the above, the length of the long in one direction (longitudinal direction) and the widthwise direction orthogonal to the longitudinal direction (width direction) In the case of having a vertically long outer shape, the direction in which the length of the metal plate or welded joint in the planar direction is simply referred to as the longitudinal direction _DP1, and the metal plate or welded joint in the planar direction is referred to for convenience of explanation. the lateral direction sometimes referred to simply as a transverse direction D _P2.
In the present specification, "object placed on a plane direction D _P and a horizontal plane parallel to (e.g., a metal plate, welded joints, etc.), seen in the thickness direction D _T of the object from the upper side in the vertical direction This is simply called “plan view”.

Furthermore, in this specification, the upper side and the lower side are relative positional relationships in the vertical direction (vertical direction) of an object (for example, a metal plate, a welded joint, etc.) (that is, positions including diagonally upward, diagonally downward, etc. Relationship), and not limited positional relationships such as directly above and directly below.
Further, in this specification, in the planar direction D _P of the welded joint in which a plurality of metal plates superimposed in the thickness direction D _T is formed by joining, "relatively distal to the welding center (nugget center) side "," outer side of the planar direction D _P "or simply referred to as" outer side ", the" relatively proximal side with respect to the welding center "," inner side in the planar direction D _P "or It is simply called “inward side”.
In the present specification, in the plurality of metal plates stacked in the thickness direction _DT , one surface and the other surface of each of the uppermost metal plate and the lowermost metal plate are arranged. Among the surfaces, a surface that does not overlap with another metal plate is referred to as a “non-overlapping surface”, and in the plurality of metal plates overlapped in the thickness direction _DT , one side surface and the other side of each metal plate Of the surface on the side, the surface that overlaps with another metal plate is referred to as an “overlapping surface”. Therefore, for example, when three or more metal plates are overlapped in the thickness direction _DT , a metal plate having no surface (non-overlapping surface) that does not overlap other metal plates (that is, one surface and the other) In the case of a metal plate in which both surfaces of the side surface overlap with other metal plates, the both surfaces are superposed surfaces.

Here, FIG. 1 is an enlarged cross-sectional view of a welded spot in the spot welded joint 1 according to an embodiment of the present invention, and FIG. 2 shows the thickness of the welded spot in the spot welded joint 1 of FIG. It is the enlarged plan view seen in direction _DT . 3 (a) is an enlarged cross-sectional view of the main part in the vicinity of the welding location in the spot welded joint 1 of FIG. 1, and FIG. 3 (b) is a cross-sectional view of the spot welded joint 1 of FIG. It is a principal part expanded sectional view which shows a state when a tensile load is provided typically.

As shown in FIGS. 1 and 2, a spot welded joint 1 according to an embodiment of the present invention includes two steel plates (the main steel plate 21 and a lower steel plate 22) that are superposed in the thickness direction _DT. It is an example of “a plurality of metal plates” in the invention.) In the stress concentration portion of the spot welded joint 1, from the lower surface (the overlapping surface 21b) of the upper steel plate 21 in the thickness direction _DT . It has the groove part 4 formed so that it might become depressed, and in this groove part 4, plate | board thickness is relatively thin.
In addition, as shown in FIG. 2, the spot welded joint 1 of this embodiment has a longitudinally long outer shape having a longitudinal direction D _P1 and a short direction D _P2 in a plan view.

The spot welded joint 1 of the present embodiment has the same structure as a conventional general spot welded joint except that the above-described groove portion 4 is formed, and is overlapped in the thickness direction _DT . The plate set 2 composed of the two steel plates 21 and 22 is energized in the thickness direction _DT , and a predetermined region in the plate set 2 (that is, the two steel plates 21 and 22 adjacent to each other in the thickness direction _DT are overlapped). The steel plates 21 and 22 are joined to each other by melting the mating surface and the vicinity thereof by Joule heat due to electric resistance. Therefore, also in the spot welded joint 1 of this embodiment, as shown in FIG.1 and FIG.2, the welding part 3 (what is called a nugget) formed by each steel plate 21 and 22 fuse | melting at the time of electricity supply is formed in a joint. ing. In FIG. 2, reference numeral 31 is a welding center located at the center of the welded part 3 in plan view, and reference numeral 32 is a welded part end along the outer edge of the welded part 3 in plan view.

  In the present embodiment, as shown in FIG. 2, the groove 4 surrounds the welded portion 3 in a peripheral portion of the welded portion 3 that is a fixed distance away from the welded end portion 32 in plan view. Are formed concentrically with the weld 3.

Thus, the spot welded joint 1 of this embodiment has the groove part 4 formed so that it may be depressed in thickness direction _DT from the overlapping surface 21b of the upper steel plate 21 in the above-mentioned stress concentration part. As shown in FIG. 3, the upper steel plate 21 has a predetermined flexibility in the peeling direction and is easily deformed. Therefore, the spot welded joint 1 according to this embodiment has a structure such as a body part of an automobile. When used as a part, the stress applied to the joint is concentrated on the bottom of the groove 4, and the stress can be absorbed by the deformation of the steel plate 21 and relaxed (that is, between the weld 3 and the groove 4. site between becomes the stress relaxation site R _s.).
Further, the groove 4 is formed so as to be recessed from the overlapping surface 21b of the upper steel plate 21 in the thickness direction _DT and relatively thin in thickness, that is, the steel plate 21 is formed in the thickness direction D _T. Therefore, a predetermined static strength can be ensured while making it easy to deform the steel plate 21 in which the groove 4 is formed in the peeling direction.
Therefore, the spot welded joint 1 of the present embodiment can maintain excellent quality in static strength while having a structure that can relieve stress applied to the joint.

  In addition, as above-mentioned, since the spot welded joint 1 of this embodiment has the structure similar to the conventional general spot welded joint except the groove part 4 being formed, it is structural or manufactured. There is an advantage that there are few restrictions on the above, and it is difficult for the application location of the joint to be limited or a special manufacturing process or manufacturing condition to be required.

Further, as shown in FIG. 2, the spot welded joint 1 of the present embodiment has a long and long outer shape in one direction having a longitudinal direction D _P1 and a short direction D _P2 in a plan view. The spot welded joint of the present invention is not limited to such an outer shape, and any outer shape according to various uses can be adopted as long as the effects of the present invention are not impaired.

  Hereinafter, various members constituting the spot welded joint of the present invention will be described in more detail using the spot welded joint 1 according to the above-described embodiment.

[Metal plate]
In the spot weld joint 1 of the present embodiment, the upper steel plate 21 and the lower steel plate 22 both have a flat plate-like structure, and as shown in FIG. having _P1 and lateral direction D _P2, and has a long elongated outer shape in one direction.

In addition, as shown in FIG. 1, the upper surface of the upper steel plate 21 is another metal plate (lower steel plate 22) among the upper surface and the lower surface facing the thickness direction _DT. A non-overlapping surface 21 a that does not overlap with the lower steel plate 22 is formed, while a lower surface forms an overlapping surface 21 b that overlaps with the lower steel plate 22. Similarly, as shown in FIG. 1, the lower steel plate 22 has an upper surface of another metal plate (upper steel plate 21) among the upper surface and the lower surface facing the thickness direction _DT. ) And the non-overlapping surface 22a that does not overlap the upper steel plate 21 is formed on the lower surface.

  In the present invention, the type of the metal plate used for the plurality of metal plates is not limited to the steel plate as in the above-described embodiment, but is a structural component to which the spot welded joint of the present invention is applied (for example, a vehicle body component of an automobile). Any metal plate can be adopted as long as it has the required characteristics. Examples of such a metal plate include a steel plate, an aluminum plate, a stainless steel plate and the like having a tensile strength of 270 MPa to 1500 MPa. When used as a base material for spot welded joints, the spot welded joint of the present invention is made of such a high-strength steel plate with high rigidity, since it tends to break starting from the welded end due to stress concentration on the welded part. It is particularly advantageous when used. In addition, when using such a high-tensile steel plate as a base material, the tensile strength of the steel plate is preferably 590 MPa or more, more preferably 780 MPa or more, from the viewpoint of joint strength, thin wall weight reduction, and the like.

Further, in the present invention, the plurality of metal plates are all the same even if all the metal plates are the same type of metal plate or only some of the metal plates are the same type of metal plate. Different types of metal plates may be used.
Furthermore, as long as the metal plate that can be used in the present invention does not impair the effects of the present invention, at least one surface may be plated with zinc or the like, or may be subjected to any other surface treatment. Good.

When using a plated metal plate as the metal plate, the type of plated metal that forms the metal plating layer of the plated metal plate is not particularly limited, and any plated metal such as a copper-based metal can be used in addition to a zinc-based metal such as zinc. Although it can be employed, it is preferable to use a zinc-based metal from the viewpoint of corrosion resistance. In addition, the coating amount in particular of a metal plating layer is not restrict | limited, The arbitrary coating amounts (For example, the coating amount of 130 g / m < ² > or less per single side | surface of a metal plate) according to various uses etc. are employable.

  In the present invention, the number of metal plates used for the spot welded joint is not particularly limited as long as the effects of the present invention are not hindered. In addition to the two metal plates as in the above-described embodiment, the welded joint after joining is not limited. Three or more metal plates may be used depending on the application to be applied. Furthermore, the plate thickness of each metal plate (that is, the plate thickness of one metal plate) is not particularly limited, and an arbitrary plate thickness can be adopted depending on the application to which the welded joint after joining is applied. it can. As such a plate thickness, for example, a plate thickness within a range of 0.5 mm to 5.0 mm can be mentioned. In this connection, the total plate thickness of the plurality of metal plates is not particularly limited. For example, the total plate thickness can be in the range of 1.0 mm to 8.0 mm, but the strength, weight reduction, etc. From this point, it is preferably within a range of 2.0 mm to 3.5 mm.

In the present invention, the overall shape of the metal plate (that is, the shape other than the groove) has a flat structure in which at least a portion to be joined is overlapped with a portion to be joined of another metal plate in the thickness direction. If it is a thing, it will not restrict | limit in particular, Even if it is what has a flat plate-like structure (for example, flat plate steel plate etc.) like the above-mentioned embodiment, a metal plate will have a joint object place. It may have a flat structure in some of the included portions and a bent structure or the like in the other portions (for example, L-shaped steel plate, hat-shaped steel plate, etc.).
In addition, the plate | board thickness of the above-mentioned metal plate is the plate | board thickness (namely, the distance between the one side surface in the thickness direction and the other side surface) of the part (except a groove part) which has a flat structure in a joining object location. Means.

And the spot welded joint of this invention has the groove part formed so that it might be depressed in thickness direction _DT from the surface of a metal plate in the stress concentration site | part as mentioned above.

[Groove]
As shown in FIG. 1, the spot welded joint 1 according to the above-described embodiment is formed so as to be recessed in the thickness direction _DT from the lower surface (overlapping surface 21 b) of the upper steel plate 21 at the stress concentration portion. Further, as shown in FIG. 2, the groove 4 is formed in the peripheral portion of the welded portion 3 that is a predetermined distance away from the welded end portion 32 in a plan view. It is formed concentrically with the welded part 3 so as to surround 3. Therefore, in the present embodiment, the welding center 31 of the welded portion 3 and the circular center 41 of the circular groove portion 4 overlap in the thickness direction _DT (that is, at the same position in plan view). ), A circular groove 4 is formed in plan view.
In the above-described embodiment, the groove portion 4 is formed in a peripheral portion of the welded portion 3 that is a fixed distance away from the welded portion end portion 32 in a plan view. If it is a stress concentration part, it is not limited to a position like the above-mentioned embodiment, for example, a groove part can be formed in the arbitrary positions outside the welding end.

Here, FIG. 4 is an enlarged plan view of the groove forming portion of the steel plate 21 used in the spot welded joint 1 as viewed in the thickness direction _DT from the overlapping surface 21b side, and FIG. 5 is the steel plate of FIG. 5 is an enlarged cross-sectional view taken along a line VV of a groove portion forming portion in FIG.
As shown in FIG. 4, the groove portion 4 in the present embodiment has a circular outer shape having a constant circular radius R around the above-described circle center 41 in plan view. The outer shape of the groove 4 is such that the outer end 44 of the groove 4 located on the distal side relative to the circle center 41 and the inner side of the groove 4 located on the proximal side relative to the circle center 41. The end portions 43 respectively extend concentrically around the circle center 41.
As shown in FIG. 4, the groove 4 has a constant width b (that is, a distance between the outer end 44 and the inner end 43 in a direction orthogonal to the direction in which the groove 4 extends). Further, the groove portion 4 is located in the middle of the outer end portion 44 and the inner end portion 43 of the groove portion 4 in the radial direction centered on the circle center 41 (that is, the groove portion). The deepest portion 42 (located at the center in the width direction of the groove portion). The deepest portion 42 also extends concentrically with the outer end portion 44 and the inner end portion 43 with the above-described circle center 41 as the center, and is a plan view from the circle center 41 to the deepest portion 42. Is the radius R of the groove 4 described above.

And the groove part 4 in this embodiment draws a circular-arc-shaped curve from the outer side edge part 44 and the inner side edge part 43 in the overlapping surface 21b of the steel plate 21, as shown in FIG. 5 (that is, predetermined curvature). It is recessed in the thickness direction _DT (in a semicircular shape having a radius ρ), and is formed so that the plate thickness gradually decreases toward the deepest portion 42.
Here, the deepest part 42 is the deepest part in the groove part 4 (in other words, the thinnest part in the groove part 4). As shown in FIG. The depth of the groove 4 in the portion corresponding to the direction _DT is the maximum depth h of the groove 4.
In the present embodiment, the cross-sectional shape along the width direction of the groove 4 is a radius of curvature of 0.1 mm or more (that is, ρ ≧ 0.1 mm) and the thickness t of the steel plate 21 on which the groove 4 is formed. On the other hand, it has a maximum depth h (that is, h ≦ t / 4) of ¼ or less.

  In the present invention, the cross-sectional shape along the width direction of the groove is not limited to such an aspect of the embodiment, and any cross-sectional shape (for example, a semicircular shape, a U-shape, A semi-rectangular shape, a V-shaped cross-sectional shape) can be employed, but in view of the static strength of the obtained welded joint and the stress relaxation effect due to the groove, a material having a predetermined radius of curvature is preferable. Particularly preferred are those having a radius of curvature of 0.1 mm or more and a maximum depth of 1/4 or less with respect to the thickness of the metal plate on which the groove is formed, as in the above-described embodiment. When the groove portion has such a radius of curvature and the maximum depth, the predetermined static strength can be more reliably ensured while easily deforming the metal plate on which the groove portion is formed in the peeling direction. Therefore, the obtained spot-welded joint can more reliably exhibit excellent static strength while having a structure that can relieve the stress applied to the joint.

As described above, the maximum depth of the groove is preferably ¼ or less of the thickness of the metal plate, but the maximum depth h (mm) of the groove is the thickness of the metal plate. It can set suitably according to t (mm) and tensile strength p (MPa). That is, assuming that the stress applied to the metal plate without the groove is 1, the stress applied to the deepest portion of the groove of the metal plate having the groove is t / (t−h), and the strength of the groove is p × (t−h). However, when the strength of the groove is higher than the joint strength f (p) (MPa), that is, when the following equation (1) is satisfied, the above-described effects of the present invention are more reliably exhibited. .
p × (t−h) / t> f (p) (1)
Using this equation (1) and the tensile strength p (MPa) and joint strength f (p) (MPa) of the actual metal plate (steel plate), the upper limit h _max (mm) of the maximum depth of the groove When calculated, the following equation (2) is obtained. Therefore, the maximum depth h (mm) of the groove is preferably set to be equal to or less than the upper limit value h _max of the equation (2).
h _max /t=0.00016×p+0.22-75/p

  The above-mentioned joint strength means the tensile strength when a tensile load in the peeling direction is applied, that is, the cross tensile strength (CTS), and the CTS is measured by a cross tensile test based on JIS Z 3137. be able to.

  In the above-described embodiment, the groove 4 is formed so as to surround the welded portion 3 (more specifically, the weld center 31 of the welded portion 3) in a plan view as shown in FIG. However, in the present invention, the planar shape of the groove portion is not limited to such an aspect, and the groove portion may have any planar shape (for example, a straight line extending continuously or intermittently) as long as the effect of the present invention is not impaired. Or a plurality of dots such as a circle or a rectangle). However, if the groove is formed in an annular shape so as to surround the center of the welded portion as in the above-described embodiment, the stress can be relaxed regardless of the direction of the stress applied to the joint (that is, The stress can be relaxed corresponding to the stress applied from any direction in the plane direction (for example, the longitudinal direction, the short direction, etc.), and the static strength of the metal plate on which the groove is formed. However, since the spot welded joint obtained has a structure that can relieve stress applied to the joint, excellent static strength can be more stably exhibited.

In the present invention, the stress concentration site of the spot welded joint in which the groove is formed is not only the weld end portion where the stress is most likely to concentrate (the most stress concentration site), but also the periphery from the weld end portion as described above. This is a region extending over a portion where stress is likely to concentrate, and in the above-described embodiment, a predetermined region over the peripheral portion of the welded portion 3 that is a fixed distance away from the welded end portion 32 in plan view. Is applicable. As described above, such a stress concentration part is a metal plate without a groove part assuming a state when a tensile load in the peeling direction is applied to the spot welded joint (that is, the groove part to which a tensile load in the peeling direction is applied). From a stress distribution diagram obtained by analyzing (non-metal plate) by a finite element method (FEM analysis), it can be specified as a portion having a relatively high stress.
Here, FIG. 6 shows a finite element for a steel plate without a groove portion (that is, a steel plate without a groove portion provided with a tensile load in the peeling direction) assuming a state when a tensile load in the peeling direction is applied to the spot welded joint. FIG. 6A is a schematic cross-sectional view showing the structure of a steel sheet to which a tensile load in the peeling direction is applied, and FIG. 6B is a drawing showing the direction of peeling. It is a stress distribution figure of the steel plate without the groove part which provided the tensile load of.

The stress distribution diagram shown in FIG. 6B is the length from the one side end where the virtual welded portion 3 _i is located to the other end in the longitudinal direction _DP1 shown in FIG. Using the virtual steel plate 21M having a direction D _P1 length) of 12 mm and a plate thickness of 1.6 mm, the other side end in the longitudinal direction D _P1 of the virtual steel plate 21M is set to a predetermined distance Δt _p (= 1 mm). The stress applied when it is pulled upward (in the peeling direction) is analyzed by the finite element method.
In addition, a peeling direction means the direction orthogonal to the overlapping surface of metal plates in a spot welded joint, and spaced apart from this overlapping surface.

As shown in FIG. 6 (b), the stress distribution of the virtual steel plate 21M ₀ states other end is pulled in the longitudinal direction D _P1, the stress is most at weld ends S _T of the virtual weld 3 _i concentrated and (i.e., weld ends S _T has become the most stress concentration sites S _'max), further, the peripheral portion of the other end side of the longitudinal direction D _P1 from the weld end S _T Since the stress is concentrated to a certain degree (that is, the peripheral portion is also the stress concentration site S ′ _c ), the stress concentration site S ′ _c (the above-mentioned stress concentration site S ′ _max is set as the above-mentioned stress concentration site S ′ _c ). Forming the above-described groove portion, the steel plate (metal plate) can be easily deformed in the peeling direction, and stress can be absorbed by the deformation of the steel plate and relaxed.

Here, FIG. 7 is a stress distribution diagram obtained by analyzing a steel plate having a groove portion assuming a state when a tensile load in the peeling direction is applied to the spot welded joint 1 according to the above-described embodiment by a finite element method. . In addition, the structure of the steel plate which gives the tensile load of a peeling direction is the same as that of the above-mentioned FIG.6 (a).
As shown in FIG. 7, in the virtual steel plate 21M ₁ having a groove 4, the stress concentration portion _{S c} is the other end side in the longitudinal direction _{D P1} of the virtual steel plate 21M ₀ shown in the above FIG. 6 (b) Although the stress is most easily concentrated on the bottom of the groove portion 4, the stress is relaxed by the deformation in the peeling direction of the virtual steel plate 21 M ₁ , and particularly at the welded portion end portion that tends to be the starting point of fracture. , stress applied to the virtual steel plate 21M ₁ are significantly reduced. In the results of the FEM analysis, the weld ends _{S T} virtual steel plate 21M ₀ no grooves shown in FIG. 6 (b), while the stress of 1373MPa is applied, the groove 4 shown in FIG. 7 the weld ends S _T virtual steel plate 21M ₁ having, not taken only 678MPa about stress, by the groove 4 described above are formed, the stress applied to the virtual steel plate 21M ₁ are significantly reduced I understand that.
In this way, the spot welded joint of the present invention makes it difficult for stress to concentrate on the welded portion end portion and its peripheral portion, thereby making it difficult to cause breakage starting from the welded portion end portion. In particular, the joint fatigue strength is also expected to improve.

As shown in FIG. 6B, the stress concentration site S ′ _c is the same not only on the lower surface (superimposed surface) of the virtual steel plate 21M ₀ but also on the upper surface (non-superimposed surface). Therefore, even if the above-mentioned groove is formed in the stress concentration part S ′ _c of such a non-overlapping surface, the same effect as described above can be obtained.
Therefore, in the present invention, the surface of the metal plate on which the groove portion is formed is not particularly limited, and the groove portion is a surface of one side of the metal plate in at least one metal plate of the plurality of metal plates and It can be formed on at least one of the other surfaces.

Furthermore, in the present invention, when the above-described groove portion is formed on a non-overlapping surface that does not overlap other metal plates in the plurality of metal plates, the groove portion is a welded portion in plan view. Preferably, the groove is formed in a region within 3 times the radius of the welded portion (that is, the radius of the nugget) from the end, and the above-mentioned groove portion overlaps with other metal plates in a plurality of metal plates. When formed on the mating surface, the groove is preferably formed in a region within 3 times the radius of the welded portion from a portion 1 mm away from the end of the welded portion in plan view.
In these specific regions of the non-overlapping surfaces and the overlapping surfaces of the plurality of metal plates, stresses are particularly likely to concentrate, so the above-described groove is formed in such specific regions. In addition, the stress applied to the joint can be more accurately mitigated, and the static strength of the metal plate on which the above-mentioned groove is formed can be made more difficult to decrease. Even though it has a structure that can relax the above, it is possible to more reliably exhibit excellent static strength.

  In addition, since the above-mentioned specific region of the non-overlapping surface and the overlapping surface in the plurality of metal plates also corresponds to the stress concentration part, the formation position of the groove portion without performing the above-described FEM analysis in advance. There is also an advantage that can be easily set.

In the present specification, the weld radius and the distance from the end of the weld mean the radius of the weld and the shortest distance from the end of the weld in plan view, for example, FIG. 1 and FIG. In the spot welded joint 1 shown in FIG. 2, the planar view distance between the weld center 31 and the welded portion end 32 corresponds to the welded portion radius, and the planar view from the welded portion end 32 and the welded portion end 32. The distance in plan view between the portion having the shortest distance corresponds to the distance from the end of the weld.
Furthermore, in this specification, the reference of the groove portion formation position is the deepest portion of the groove portion. For example, the meaning that the groove portion is formed in the predetermined region means that the deepest portion of the groove portion is in the predetermined region. That is, the outer end portion of the groove portion may not be located in the predetermined region.

Moreover, in the spot welded joint 1 which concerns on the above-mentioned embodiment, although the groove part 4 is formed only in the overlapping surface 21b of the upper steel plate 21, in the spot welded joint of this invention, it is a groove part as mentioned above. The surface of the metal plate on which the metal plate is formed is not particularly limited, and the groove can be formed on at least one surface of the overlapping surface and the non-overlapping surface of the metal plates in the plurality of metal plates. In addition, in the spot welded joint, when the above-mentioned groove is formed on the overlapping surface of the metal plates in a plurality of metal plates, there is an advantage that it is possible to reduce restrictions on the appearance or structure of the joint. In addition, when the above-described groove portion is formed on the non-overlapping surface of the metal plate in the plurality of metal plates, the groove portion can be formed after spot welding at the time of manufacturing, and the groove portion can be more accurately and more accurately There exists an advantage that it can form in a precise position.
Hereinafter, spot welded joints 1a to 1d according to another embodiment of the present invention, which are different from the spot welded joint 1 according to the above-described embodiment, will be described in detail with reference to the drawings.

  FIG. 8 is an enlarged cross-sectional view of the welding locations of spot welded joints 1a to 1d according to another embodiment of the present invention, in which the arrangement of the groove portions is different from the spot welded joint 1 described above. In these other embodiments, since the configuration other than the configuration different from the above-described embodiment (that is, the configuration related to the arrangement form of the groove portions) is basically the same as the above-described embodiment, The same reference numerals as those in the embodiment are attached and detailed description is omitted.

As shown to Fig.8 (a), the spot welded joint 1a which concerns on another embodiment of this invention is the stress concentration site | part of the spot welded joint 1a. the groove 4 formed to recessed in the thickness direction D _T from the upper surface (mating surfaces 22b) in the thickness direction D _T of the groove portion 4 in the thickness direction D opposite to the _T and the underside of the steel plate 22 And a groove portion 4a formed so as to be recessed. Similar to the spot welded joint 1 of the above-described embodiment, these groove portions 4 and groove portions 4a are also connected to the welded portion 3 in a peripheral portion of the welded portion 3 that is a fixed distance away from the welded portion end portion 32 in plan view. It is formed concentrically with the weld 3 so as to surround it.

Also in such a spot welded joint 1a, the above-described groove 4 and groove 4a are formed in the stress concentration portions of the upper steel plate 21 and the lower steel plate 22, respectively, so that the upper steel plate 21 and the lower steel plate 21 Since each of the steel plates 22 has a predetermined flexibility in the peeling direction and is easily deformed, the stress applied to the joint is concentrated on each bottom portion of the groove portion 4 and the groove portion 4a, and the stress is applied to the steel plate 21 and the steel plate. 22 can be absorbed and relaxed. In particular, since the spot welded joint 1a is formed not only in the upper steel plate 21 but also in the lower steel plate 22, the stress applied to the joint can be more reliably reduced.
Further, also in this spot welded joint 1a, each of the above-described groove portion 4 and groove portion 4a is formed so as to be recessed in the thickness direction _DT of each steel plate and relatively thin in plate thickness. Since the steel plate is formed so as not to be completely lost in the thickness direction _DT , a predetermined static strength is ensured while the steel plate 21 and the steel plate 22 formed with these grooves are easily deformed in the peeling direction. can do.

In addition, as shown in FIG. 8B, a spot welded joint 1b according to still another embodiment of the present invention has an upper surface (non-overlapping) of the upper steel plate 21 at the stress concentration portion of the spot welded joint 1b. The groove portion 4b is formed so as to be recessed from the surface 21a) in the thickness direction _DT . As with the spot welded joint 1 of the above-described embodiment, the groove 4b also surrounds the welded portion 3 in a peripheral portion of the welded portion 3 that is a fixed distance away from the welded portion end portion 32 in plan view. It is formed concentrically with the weld 3.

Also in this spot welded joint 1b, the above-mentioned groove 4b is formed in the stress concentration portion of the upper steel plate 21, so that the upper steel plate 21 has a predetermined flexibility in the peeling direction and is easily deformed. Therefore, the stress applied to the joint can be concentrated on the bottom of the groove 4b and absorbed by the deformation of the steel plate 21 to be relaxed.
Moreover, also in this spot welded joint 1b, since the above-mentioned groove part 4b is formed so that the steel plate 21 may not be completely lost in the thickness direction _DT , the steel plate 21 with the groove part 4b formed in the peeling direction. While facilitating deformation, a predetermined static strength can be ensured.
And in this spot welded joint 1b, since the groove part 4b is formed in the non-overlapping surface 21a of the upper steel plate 21, since the said groove part 4b can be formed after spot welding of each steel plate at the time of manufacture, There is also an advantage that the groove 4b can be formed in a more accurate position with higher accuracy. Thereby, the spot welded joint 1b can relieve | moderate the stress concerning a joint more exactly.

Further, as shown in FIG. 8C, a spot welded joint 1c according to still another embodiment of the present invention has an upper surface (non-overlapping) of the upper steel plate 21 at a stress concentration portion of the spot welded joint 1c. A groove portion 4b formed so as to be recessed from the surface 21a) in the thickness direction _DT , and the groove portion 4b overlapping the groove portion 4b in the thickness direction _DT and from the lower surface (non-overlapping surface 22a) of the lower steel plate 22 And a groove portion 4c formed so as to be recessed in the thickness direction _DT . Similar to the spot welded joint 1 of the above-described embodiment, the groove 4b and the groove 4c are also connected to the welded portion 3 in a peripheral portion of the welded portion 3 that is apart from the welded end portion 32 in a plan view. It is formed concentrically with the weld 3 so as to surround each other.

Also in this spot welded joint 1c, the upper steel plate 21 and the lower steel plate 22 are formed by forming the above-described groove 4b and groove 4c at the stress concentration portions of the upper steel plate 21 and the lower steel plate 22, respectively. Since each has a predetermined flexibility in the peeling direction and is easily deformed, the stress applied to the joint is concentrated on each bottom of the groove 4b and the groove 4c, and the stress is applied to the steel plate 21 and the steel plate 22. It can be absorbed and relieved by deformation. Further, since the groove portion of the spot welded joint 1c is formed not only on the upper steel plate 21 but also on the lower steel plate 22, the stress applied to the joint can be more reliably reduced.
Also in this spot welded joint 1c, the above-described groove 4b and groove 4c are formed so that each steel plate is not completely lost in the thickness direction _DT. Therefore, the steel plate on which these grooves are formed. A predetermined static strength can be ensured while making it easy to deform 21 and the steel plate 22 in the peeling direction.
And in this spot welded joint 1c, the above-mentioned groove part 4b and groove part 4c are formed in non-overlapping surface 21a of upper steel plate 21, and non-overlapping surface 22a of lower steel plate 22, respectively, Since these groove portions can be formed after spot welding of each steel plate, there is also an advantage that the above-described groove portions 4b and 4c can be formed more accurately and at more accurate positions. Thereby, the spot welding joint 1c can relieve | moderate the stress concerning a joint more exactly.

Further, as shown in FIG. 8D, a spot welded joint 1d according to still another embodiment of the present invention has a lower surface (overlapping) at the stress concentration portion of the spot welded joint 1d. Groove portion 4d ₁ formed so as to be recessed in the thickness direction _DT from the surface 21b), and in the longitudinal direction _DP1 , the groove portion 4d ₁ is disposed at a target position with respect to the weld center 31 of the weld portion 3 and the lower side 4 d ₂ formed so as to be recessed in the thickness direction _DT from the upper surface (overlapping surface 22 b) of the steel plate 22. Unlike the spot welded joint 1 of the above-described embodiment, the groove 4d ₁ and the groove 4d ₂ are the welded part in the peripheral part of the welded part 3 that is a fixed distance away from the welded part end part 32 in plan view. 3 extend respectively in the longitudinal direction D position to and transverse direction D _P2 so as to sandwich from both sides the _P1, which is constituted by a linear groove portion of the two.

In this spot welded joint 1d, by the groove 4d ₁ and the groove portion 4d ₂ described above to each stress concentration portions of the upper steel plate 21 and the lower steel plate 22 is formed, the upper steel plate 21 and the lower It has a predetermined flexibility, each in a peeling direction of the steel sheet 22, since that is easily deformed, while concentrating the stress applied to the joint on each bottom of the groove portion 4d ₁ and the groove portion 4d _2, the stress steel 21 It can be absorbed and relaxed by deformation of the steel plate 22. Further, since the groove portion of the spot welded joint 1d is formed not only on the upper steel plate 21, but also on the lower steel plate 22, the stress applied to the joint can be more reliably reduced.
Also in the spot welded joint 1d, groove 4d ₁ and the groove portion 4d ₂ described above, both because it is formed so as not to completely deficient in the thickness direction D _T is the steel plate, the formation of these grooves A predetermined static strength can be ensured while the steel plate 21 and the steel plate 22 are easily deformed in the peeling direction.

As a modification of this spot welded joint 1d, 2 this straight groove portion 4d ₁ and the groove portion 4d ₂ of the above, one of which is formed in the non-overlapping surfaces of the steel plate, the other is formed on the overlapping surface of the steel plate Or both may be formed on the non-overlapping surface of each steel plate. Also in these modified examples, the same operational effects as those of the above-described spot welded joint 1d can be achieved.
Furthermore, in such a linear groove part, unless the effect of this invention is inhibited, the number in particular is not restrict | limited, In addition to the above-mentioned two, one or three or more may be sufficient.

  In the present invention, the means for forming the groove in the metal plate is not particularly limited, and any known processing means (for example, cutting processing means, laser processing means, plasma processing means, etc.) can be employed.

[welded part]
Next, the welded portion in the spot welded joint will be described using the spot welded joint 1 according to the above-described embodiment.
In the spot welding joint 1 welded portion 3 energizes the plate assembly 2 consisting of two steel plates 21, 22 superimposed in the thickness direction D _T in the thickness direction D _T, a predetermined region within the plate pairs 2 1 to 3, as shown in FIGS. 1 to 3, in the spot welded joint 1, the overlapping surface of the two steel plates 21 and 22 adjacent to the thickness direction _DT. And in the vicinity thereof.

  Since the pair of electrodes used for energizing the plate assembly 2 is usually circular in cross section, the welded portion 3 formed after the energization has a substantially circular plan view shape as shown in FIG. have. In the present specification, the substantially circular center in plan view is referred to as a welding center 31, and the substantially circular outer edge line in plan view is referred to as a weld end 32.

In addition, the diameter of the welded portion 3 (so-called nugget diameter) is a factor that greatly affects the bonding strength of each steel plate, and thus the joint strength. The composition of each steel plate and the current-carrying conditions during spot welding (for example, current flow, The current can be appropriately controlled depending on the energization time, the applied pressure of the electrode, and the like.
In the present invention, the diameter of the welded portion is not particularly limited, and any size according to the desired joint strength and the like can be adopted. In addition, the size (diameter, radius, etc.) of the welded portion is determined by cutting the spot-welded steel plate in the thickness direction so as to pass through the above-mentioned welding center, polishing the cut surface, etching, and then further It can be measured by observing the cut surface with any magnifying observation means such as a magnifying glass.

(Production method)
Hereinafter, the manufacturing method of the spot welded joint of this invention is demonstrated.
The above-described spot welded joint of the present invention can be obtained by a manufacturing method including the following steps.
That is, the method for manufacturing a spot welded joint according to the present invention is referred to as a step of forming the groove at a stress concentration site in at least one of the plurality of metal plates (hereinafter referred to as “first step”). ), A step of stacking a plurality of metal plates in the thickness direction to form a plate set (hereinafter referred to as “second step”), and energizing the plate set in the thickness direction. And a step of joining a plurality of metal plates stacked in the thickness direction (hereinafter referred to as “third step”).

  In the method for manufacturing a spot welded joint according to the present invention, the second step is performed before the third step, but the timing of performing the first step is arbitrarily set according to the formation position of the desired groove. be able to. That is, the first step described above is performed at least one time before the second step, between the second step and the third step, and after the third step, depending on the formation position of the groove. be able to. For example, when forming a groove on each of the non-overlapping surface and the overlapping surface of the metal plate in a plurality of metal plates, the groove is formed on the surface of the metal plate that becomes the overlapping surface before the second step. The first step is performed, and the surface of the metal plate to be the non-overlapping surface (that is, the plate set is formed between the second step and the third step or after the third step). You may implement the 2nd 1st process of forming a groove part in the non-overlapping surface of the metal plate after or after joining.

In the first step described above, an arbitrary processing means such as a cutting means is used at a stress concentration site in at least one metal plate of the plurality of metal plates, and the groove portion (that is, from the surface of the metal plate). A groove formed so as to be recessed in the thickness direction). At this time, the groove is formed on the metal plate before the plate set is formed, the metal plate after the plate set is formed, and / or the metal plate after the plurality of metal plates are joined. The
In addition, about the stress concentration site | part of the metal plate which forms a groove part, you may specify the position by performing the above-mentioned FEM analysis before the 1st process, and when the position is already known, That position may be adopted.

  In the first step, the processing conditions and the like when forming the groove are not particularly limited as long as the effects of the present invention are not impaired, and arbitrary processing conditions and the like taking into account the desired ease of processing and processing accuracy are adopted. be able to.

  In the second step described above, a plurality of metal plates are overlapped in the thickness direction so that the portions to be joined of the metal plates overlap in the thickness direction, thereby forming a plate assembly composed of the plurality of metal plates. Form. In addition, the joining object location of a metal plate is a location where the above-mentioned welding part is formed after electricity supply.

  In the second step, the means for superimposing a plurality of metal plates in the thickness direction is not particularly limited, and any means (for example, a robot or a transfer device) that takes into account desired placement accuracy, workability, productivity, and the like. Etc.) can be employed.

  And in the above-mentioned 3rd process, a plurality of metal plates piled up are joined by energizing to a plate set formed at the 2nd process in the thickness direction. At this time, a predetermined current (energization current) and pressure are applied to the plate assembly by a pair of electrodes that sandwich the plate assembly in the thickness direction. In this way, when the plate assembly is energized, the overlapping surface of the metal plates adjacent in the thickness direction and the vicinity thereof are melted by Joule heat due to electric resistance in the plate assembly, and the above-mentioned welded portion (nugget) ) Are formed, and the metal plates are firmly joined to each other.

  In the third step, the energization conditions (for example, energization current, energization time, electrode pressure, etc.) are not particularly limited as long as they do not impair the effects of the present invention, and are arbitrary considering the desired joint strength and productivity. The energization conditions can be adopted.

  In addition, the manufacturing method of the spot welded joint of the present invention is within the range not impairing the effect of the present invention, before the first step, between the first step to the third step, and / or the third step. Later, an arbitrary processing step (for example, a surface treatment step of a metal plate) may be included.

  According to the manufacturing method of the present invention described above, a spot welded joint excellent in static strength can be easily obtained while having a structure capable of relaxing the stress applied to the joint. In addition, in the manufacturing method, when the first step described above is performed before the second step, the groove portion can be formed on the overlapping surface of the metal plates in the plurality of metal plates, There is an advantage that it is possible to reduce restrictions on the appearance or structure of the joint, and when the first step described above is performed after the third step, the bonding according to the formation position of the groove is performed. Since there are few restrictions of a position (welding part formation position), there exists an advantage that the positional relationship of the above-mentioned groove part and a welding part can be controlled more exactly.

  The spot welded joint of the present invention thus obtained includes various parts such as a structural part of a transport machine such as a railway vehicle, a structure of a building, and parts of various industrial machines in addition to a car body part of an automobile. In particular, it can be suitably used for structural parts of transportation machines such as automobiles and railway vehicles that require both fatigue strength and static strength. In addition, the spot welded joint of the present invention is not limited to the above-described embodiments or examples to be described later, and can be appropriately combined, substituted, changed, and the like within a scope that does not depart from the purpose and spirit of the present invention. It is. In this specification, ordinal numbers such as “first” and “second” are used to distinguish items with the ordinal numbers, and mean the order, priority, importance, etc. of each item. Not what you want.

  EXAMPLES Hereinafter, although an Example and a comparative example are illustrated and this invention is demonstrated more concretely, this invention is not limited only to such an Example. FIG. 9 is a plan view schematically showing spot welded joints according to Examples 1 and 4 and Comparative Example 1 of the present invention.

Example 1
As the metal plate, two steel plates (steel plate strength p = 1180 MPa) having a length in the longitudinal direction D _P1 of 150 mm, a length in the short direction D _P2 of 50 mm, and a plate thickness of 1.6 mm are prepared (FIG. 9A )), And the maximum depth h is only on one side of one steel plate 210 (one-side steel plate) (specifically, the surface that becomes the overlapping surface when two steel plates are overlapped). A groove portion 4 having a circular shape with a radius of 0.3 mm, a radius of curvature ρ of 0.3 mm, and a plan view shape of a radius of 5 mm was formed by cutting.
These two steel plates 210 and 220 are overlapped in the thickness direction _DT so that the surface on which the above-mentioned groove 4 is formed becomes an overlapping surface to form a cross-shaped plate set, and then a stationary spot The spot welded joint 10 of Example 1 as shown to Fig.9 (a) was produced by energizing a board assembly to thickness direction _DT using a welding apparatus. As shown in FIG. 9A, the groove 4 is formed at a position where the planar view distance from the welding center of the welded portion 3 to the inner end of the groove 4 is 4.7 mm in plan view. is there.
The spot weld joint 10 of Example 1 obtained in this manner had a nugget diameter (diameter of the weld zone 3) of 3.8 mm.

Example 2
Example 2 is the same as Example 1 except that the groove is formed only on the non-overlapping surface of the one-side steel plate and that the maximum depth h and the radius of curvature ρ of the groove are changed to 0.45 mm. A spot welded joint was produced.

Example 3
The structure of the steel plate and the groove portion was changed to the one shown in Table 1 below (with the change of the structure of the steel plate and the groove portion, the welding conditions were changed to the conditions corresponding to them), and the groove portion was changed to the one side steel plate. A spot welded joint of Example 3 was produced in the same manner as Example 1 except that it was formed only on the non-overlapping surface.
The spot weld joint of Example 3 obtained in this way had a nugget diameter of 3.3 mm.

Example 4
The steel plate is changed to a steel plate having a steel plate strength p of 590 MPa (see the steel plates 211 and 221 in FIG. 9B), and the groove has a maximum depth h of 0.2 mm and a curvature radius ρ of 0.2 mm. One side of one steel plate 211 (one-side steel plate) in the same manner as in Example 1 except that the shape in plan view is changed to two linear grooves 4 ′ having a length of 20 mm extending in the short direction _DP2. Specifically, the two linear grooves 4 ′ are formed only on the surface to be the overlapping surface, and the spot welded joint 11 of Example 4 as shown in FIG. 9B is manufactured. The two forming position of the straight groove 4 'of the present, as shown in FIG. 9 (b), in plan view, a position as to sandwich the welded portion 3 from both sides in the longitudinal direction D _P1, It is a position where the planar view distance from the welding center of the welding part 3 becomes 5 mm, respectively.
The spot weld joint 11 of Example 4 obtained in this way had a nugget diameter of 3.8 mm.

Comparative Example 1
The steel plate is changed to a steel plate having a steel plate strength p of 590 MPa (see the steel plates 212 and 222 in FIG. 9 (c)), and in addition to the above-described groove portion, the short side direction _DP2 outer edge portion of the steel plate leads to the short side direction. comprising notched inwardly side of the D _P2, most important lack depth 12.5 mm, the maximum notch width cutouts 5 of substantially semi elliptical shape 15 mm, only one of the steel sheet 212 (side steel) And the spot welded joint 12 of the comparative example 1 as shown in FIG.9 (c) is produced similarly to Example 1 except having formed in only four places of the peripheral part of the welding part 3 of the said steel plate 212. FIG. did. In addition, as for the formation position of the four notch parts 5 in the above-mentioned one side steel plate, as shown in FIG.9 (c), the planar view distance of the longitudinal direction _DP1 from the welding center of the welding part 3 becomes 17.5 mm, respectively. Position.
The spot welded joint 12 of Comparative Example 1 obtained in this way is formed so that the notch portion 5 is not formed in a stress concentration portion like the groove portion of the present invention and is recessed in the thickness direction of the steel plate. (That is, one steel plate 212 is formed to be completely missing in the thickness direction).

For the spot welded joints of Examples 1 to 4 and Comparative Example 1, the cross tensile strength (MPa) was measured by a cross tension test based on JIS Z 3137, and the measured values were measured for the groove or notch. The joint strength of each spot welded joint was evaluated by comparing with the measured value of the cross tensile strength of the spot welded joint that was not formed.
Specifically, after producing spot welded joints for comparison reference in the same manner as the spot welded joints of Examples 1 to 4 and Comparative Example 1 except that no grooves or notches are formed. The cross tension test was similarly performed on the spot welded joints for comparison. Then, using the measured values of the cross tensile strength (MPa) of the spot welded joints for comparison as reference values, the measured values of the cross tensile strengths of the spot welded joints of Examples 1 to 4 and Comparative Example 1 described above. The joint strength was evaluated.
In this joint strength evaluation, “○” (excellent static strength) indicates that the cross tensile strength is improved by 5% or more compared to the cross tensile strength of the spot welded joint for comparison. In the case where the cross tensile strength was not improved by 5% or more, “x” (static strength was not good) was evaluated.
The configuration of each spot welded joint of Examples 1 to 4 and Comparative Example 1 and the evaluation results of joint strength are as shown in Table 1 below.

  As shown in Table 1, the spot welded joints of Examples 1 to 4 in which specific groove portions in the present invention are formed have excellent joint strength (static strength), whereas It was found that the spot welded joint of Comparative Example 1 in which the notch was formed did not have sufficient joint strength.

According to the present invention, it is possible to obtain a spot welded joint having excellent static strength while having a structure that can relieve stress applied to the joint. The present invention can be applied to various structural parts such as structural parts of transportation machinery, structures of buildings, and parts of various industrial machines.
Therefore, the spot welded joint and the manufacturing method thereof of the present invention have high industrial applicability.

1 Spot welded joint 2 Plate assembly 21 Upper steel plate (metal plate)
21a Non-overlapping surface 21b Overlapping surface 22 Lower steel plate (metal plate)
22a Non-overlapping surface 22b Overlapping surface 3 Welded portion 31 Weld center 32 Welded portion end 4 Groove portion 41 Circle center 42 Deepest portion 43 Inner end portion 44 Outer end portion 5 Notch portion S _c Stress concentrated portion S _max Maximum stress concentrated portion

Claims (5)

A spot welded joint composed of a plurality of metal plates stacked in the thickness direction,
The spot welded joint has a groove formed so as to be recessed in the thickness direction from the surface of the metal plate at a stress concentration site.
The spot weld joint. The groove has a radius of curvature of 0.1 mm or more and a maximum depth of 1/4 or less with respect to the thickness of the metal plate on which the groove is formed.
The spot welded joint according to claim 1. The groove is formed so as to surround the center of the weld in plan view.
The spot welded joint according to claim 1 or 2. The groove is formed in at least one of the plurality of metal plates on at least one of the surface on one side and the surface on the other side of the metal plate,
Furthermore, when the surface on which the groove is formed is a non-overlapping surface that does not overlap with other metal plates in the plurality of metal plates, the groove is from the welded portion end to the welded portion in plan view. Formed in an area within 3 times the radius,
When the surface on which the groove is formed is an overlapping surface that overlaps with another metal plate in the plurality of metal plates, the groove is from the portion 1 mm away from the end of the welded portion in plan view. Formed in an area within 3 times the radius of the weld,
The spot welded joint according to any one of claims 1 to 3. It is a manufacturing method of the spot welded joint according to any one of claims 1 to 4,
Forming the groove at the stress concentration site in at least one metal plate of the plurality of metal plates;
A step of overlapping the plurality of metal plates in the thickness direction to form a plate set;
Joining a plurality of metal plates stacked in the thickness direction by energizing the plate assembly in the thickness direction,
A method for manufacturing the spot welded joint.