JP2013081973A - Lap fillet arc welded joint having excellent fatigue characteristic and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lap fillet arc welded joint having excellent fatigue characteristic, in which one or both fatigue fracture which is generated from the toe of weld at the welding starting point and fatigue fracture which is generated from the root at the welding finished point are suppressed when load acts on the lap fillet arc welded joint of steel plates, and to provide a method of manufacturing the lap fillet arc welded joint.SOLUTION: There is provided the lap fillet arc welded joint having excellent fatigue characteristic, in which a part of two steel plates are lapped and a fillet arc weld bead is formed by welding a corner of an upper steel plate and a lower steel plate. The lap fillet arc welded joint having excellent fatigue characteristic is characterized in that: an upper plate additional bead on the side of welding finished point where the upper steel plate and the lower steel plate are spot-welded is provided on the side of the upper steel plate which is the welding finished point of a fillet arc weld bead; and a lower plate additional bead on the side of the welding starting point which is partly superimposed with the toe of weld of the welding starting point of the fillet arc weld bead is provided on the lower steel plate.

Description

  The present invention relates to a thin fillet arc welded joint for thin steel sheets applied to automobile-related members, such as automobile undercarriage members, and a method for manufacturing the same, and particularly to the occurrence of fatigue cracks generated from the welding start and end points. The present invention relates to a lap fillet arc welded joint of thin steel sheets excellent in suppressed fatigue characteristics and a method for manufacturing the same.

  Until now, in the field of automobiles, from the viewpoint of global environmental conservation, there has been a demand for improved fuel efficiency by reducing the weight of the vehicle body, as well as improved collision safety. For this reason, various efforts have been made to achieve both weight reduction and improved collision safety by thinning and structural optimization by using high-strength steel sheets.

  However, it is known that the fatigue strength of a steel sheet itself increases in proportion to the strength of the steel sheet, whereas in a welded joint, the fatigue strength of the welded joint hardly increases even if the steel sheet strength increases. Thus, even if the design stress is increased by using a high-strength steel plate, the fatigue strength of the welded joint is hardly different from that of the low-strength steel plate.

  Among the components of automobiles, suspension members such as suspension arms and subframes are particularly difficult to reduce in weight due to the fatigue strength of welds. For these suspension members and the like, overlapped fillet arc welding is generally used.

  As shown in FIG. 1, in the case of overlapped fillet arc welding of steel plates, two steel plates (upper plate 1 and lower plate 2) are overlapped, and the end portion (the end face and the vicinity thereof) of one steel plate is used as the other steel plate. The weld bead 3 is formed by stacking on the surface and performing fillet arc welding. The steel plate which welds this edge part is called the upper board 1, and the steel plate which has the surface welded with an upper board edge part is called the lower board 2. In general, fillet welding (referred to fillet arc welding unless otherwise noted; the same shall apply hereinafter), two steel plates are placed horizontally, the upper plate is in the vertical direction, and the lower plate is in the lower direction. Thus, the fillet welding is performed because the fillet welding is performed with the welding wire approaching in the downward direction and the welding wire approaching downward. However, actual overlap fillet welding is not limited to the vertical direction, but defines the upper and lower plates based on the relative positional relationship of the steel plates that have been stacked as described above.

  When a lap fillet welded joint of steel plates is applied to a structure such as an automobile, its fatigue durability (fatigue strength) becomes a problem. In the case of a lap fillet welded joint, a fatigue crack is a weld toe on the lower plate side where stress is concentrated due to shape discontinuity (the weld toe is the welding wire supply side when making a weld joint, Thickness generated from the interface between the upper or lower plate and the weld metal) or the route (the side opposite to the welding wire supply side when making the welded joint, the interface between the upper plate (or lower plate) and the weld metal) Progress in the direction leading to destruction.

  The failure starting from the weld toe is due to the concentration of stress on the toe shape such as the radius of curvature or flank angle of the toe. On the other hand, in the fracture starting from the root, the remaining part of the upper plate and the lower plate that are not welded is a notch-like part starting from the root (hereinafter referred to as a notch-like part starting from the root). The root part of the weld metal (the root of the weld metal), because there is a strength non-uniformity in which the hardness of the upper and lower plates and the weld metal differs. This is because stress concentrates on the portion corresponding to the tip of the part.

  In general, since the degree of stress concentration is larger in the root portion than in the toe portion, a crack is easily generated from the root portion depending on how the load is applied. Therefore, the structural designer designs the arrangement of the welded parts in consideration of the arrangement of the joints and how to apply the load. However, the actual situation is that it is impossible to actually consider all parts of the welded part in practice.

  Up to now, as a technique for improving the fatigue characteristics of a lap fillet arc welded joint of a high-strength hot-rolled steel sheet, for example, in Patent Document 1, the fatigue characteristics of a lap-arc welded joint part of a high-strength hot-rolled steel sheet include Since the radius of curvature of the weld bead toe is a dominant factor, a chemical composition is disclosed in which the toe shape has a gentle shape with little stress concentration in order to improve fatigue characteristics. However, this technique is effective only for the steady portion where the weld bead is stable. An actual welding member has a welding start point and an end point. Since the weld metal rises at the welding start point, the stress concentration at the toe is larger than that at the steady part. It is not sufficient to suppress fatigue cracks generated from such locations. Further, depending on the load acting on the member, the fatigue crack does not occur from the toe portion and may occur from the root portion. At this time, even if the technique is applied, the root portion is not effective. That is, it cannot cope with fatigue fracture starting from the root portion.

  Further, in Patent Document 2, as a method for improving the fatigue strength of the welded joint by reducing the stress concentration by gently reducing the shape of the weld bead toe, the bead toe is formed on the steel surface prior to welding. A method is disclosed in which a material containing 30% by mass or more of Si is coated on a portion to be formed and welded. However, in this method, prior to welding, it is necessary to coat a material containing 30% by mass or more of Si on the steel surface in advance. This requires time for the covering work, which is very time-consuming and causes problems such as not only an increase in cost, but also a decrease in productivity due to the covering work during welding.

  Further, in Patent Document 3, the fatigue strength of the welded joint varies depending on the hardness of the weld bead toe on the lower plate surface that is the starting point of fatigue fracture. In addition, assuming the location where the toe portion of the overlapped fillet weld bead is formed, the portion is previously irradiated with high energy and melted to form a solidified portion, and a martensite structure is generated in the solidified portion. A method is disclosed in which, after the hardness rises higher than the hardness of the base material, the fillet arc welding is performed so that the toe portion overlaps the solidified portion. However, this method can also prevent the weld toe from becoming the starting point of fatigue failure, but it cannot effectively prevent the fatigue failure starting from the root portion.

  Further, in Patent Document 4, when forming an additional bead made of a low-temperature transformation melt at a weld toe where stress is concentrated, welding is performed to achieve high fatigue strength by applying an external force in advance so that tensile stress is generated. A method is disclosed. However, this method requires the use of a special low-temperature transformation melt as the welding material (welding wire), and does not relate to overlapped fillet arc welding, but discloses that it solves fatigue fracture starting from the root. It has not been.

  As described above, there have been many proposals for improving fatigue fracture from the weld bead toe in lap fillet arc welded joints of high-strength steel sheets, but fatigue starting from the root of the welding end point has been proposed. In fact, there has been no proposal for a lap fillet arc welded joint that effectively suppresses fracture (root cracking) and a method for manufacturing the same.

JP-A-6-340947 JP 2006-305630 A JP 2011-62718 A Japanese Patent Laid-Open No. 2002-113577

  In view of the above situation, the present invention is a method of fatigue fracture occurring from the toe portion at the welding start point and fatigue fracture occurring from the root portion at the welding end point when a load is applied to the lap fillet arc welded joint of the steel plate. It is an object of the present invention to provide a lap fillet arc welded joint excellent in fatigue characteristics in which one or both are suppressed and a method for manufacturing the same.

  The present inventor has investigated the cause of fatigue failure occurring from the root portion of the welding end point in the lap fillet arc welded joint, and since the welding end point lacks the weld metal, the cross-sectional area decreases and the root portion starts. It has been found that fatigue cracks are generated and that it is effective to prevent the root portion from opening in order to suppress fatigue cracks generated from the root portion. Therefore, in order to prevent the root portion from opening, a through hole is made in the upper plate on the welding end point side, and welding such as plug welding for filling the through hole is performed to form an additional bead on the welding end point side upper plate. It has been found that by joining the upper plate and the lower plate, stress can be prevented from concentrating on the root portion, and the occurrence of fatigue cracks from the root portion can be suppressed.

  In addition, the cause of fatigue failure from the toe portion at the welding start point is that the weld metal near the welding start point has a convex shape, and the flank angle tends to be smaller than the steady part, and the toe radius tends to be small, For this reason, when a load is applied to the welded portion, the stress is likely to be concentrated compared to the steady portion. Therefore, the welding start point toe part is spot welded to the weld start point bead toe part before or after the start of the main welding so that the weld start point side lower plate additional bead partially overlaps the weld bead toe part. It was found that the shape of the weld metal raised in the protrusion can be eliminated, stress can be prevented from concentrating on the toe, and the occurrence of fatigue cracks from the bead toe at the welding start point can be suppressed.

  The present invention has been completed based on the above findings, and the gist of the present invention is as follows.

  (1) In a lap fillet arc welded joint in which a fillet arc weld bead is formed by overlapping a part of two steel plates and welding the corners of the upper plate steel plate and the lower plate steel plate, Overlap fillet arc welded joint with excellent fatigue characteristics, characterized in that a welding end point side upper plate additional bead is provided by spot welding the upper plate steel plate and the lower plate steel plate to the upper plate steel plate side as the welding end point. .

  (2) In the overlapped fillet arc welded joint in which a part of two steel plates are overlapped and the fillet arc weld bead is formed by welding the corners of the upper plate steel plate and the lower plate steel plate, the fillet arc weld bead A laminated fillet arc welded joint excellent in fatigue characteristics, characterized in that a welding start point side lower plate additional bead that partially overlaps the welding start point toe is provided on the lower plate steel plate.

  (3) In a lap fillet arc welded joint in which a fillet arc weld bead is formed by overlapping a part of two steel plates and welding the corners of the upper plate steel plate and the lower plate steel plate, On the upper plate steel plate side, which is the welding end point, a welding end point side upper plate additional bead is formed by spot welding the upper plate steel plate and the lower plate steel plate, and the welding start point toe portion of the fillet arc welding bead is provided. A lap fillet arc welded joint with excellent fatigue characteristics, characterized in that a lower plate additional bead on the welding start point side that partially overlaps is provided on the lower plate steel plate.

  (4) The welding end point side upper plate additional bead has a distance from the upper plate side toe of the fillet arc welding bead to the solidification center of the welding end point side upper plate additional bead of 2 to 7 mm. The distance from the weld bead end on the welding end point side to the solidification center of the welding end point side upper plate additional bead is provided at a position where the distance is -3 to 8 mm. The lap fillet arc welded joint having excellent fatigue characteristics as described in (1) or (3) above.

  (5) The welding start point side lower plate additional bead has a distance from the lower plate side toe of the fillet arc welding bead farthest to the toe of the welding start point side lower plate additional bead. 2 to 5 mm, the distance from the end on the welding start point side parallel to the end of the upper plate to the toe end of the welding start point side lower plate additional bead farthest in the opposite direction to the welding end point side is 0 to 4 mm The lap fillet arc welded joint having excellent fatigue characteristics as described in (2) or (3) above, which is provided at a position where

  (6) The overlapped fillet arc welded joint having excellent fatigue characteristics according to any one of claims 1 to 5, wherein a gap between the superposed upper steel plate and lower steel plate is 0 to 2 mm. .

  (7) The plate thickness of the upper plate steel plate is 1.8 to 4 mm, and the plate thickness of the lower plate steel plate is 1.8 mm or more, according to any one of the above (1) to (6), Lap fillet arc welded joint with excellent fatigue characteristics.

  (8) In the method of manufacturing a lap fillet arc welded joint in which a part of two steel plates are overlapped and a fillet arc weld bead is formed by welding the corners of an upper plate steel plate and a lower plate steel plate, the welding end point A through hole is provided on the upper plate steel plate side, and the upper plate and the lower plate are overlapped, and spot welding is performed to fill the through hole before or after the start of overlapped fillet arc welding. A plate-added bead is formed to spot weld the upper plate and the lower plate to suppress fatigue fracture occurring from the root portion of the welding end point. Manufacturing method of meat arc welding joint.

  (9) In the method of manufacturing a lap fillet arc welded joint in which a part of two steel plates are overlapped and the fillet arc weld bead is formed by welding the corners of the upper plate steel plate and the lower plate steel plate, the welding start point Welding starts at the fillet arc weld bead toe before or after welding is started by spot-welding the lower plate so that a part of the weld bead-side lower plate additional bead overlaps the fillet arc welding bead. A layered fillet excellent in fatigue characteristics as described in (2) above, wherein a point side lower plate additional bead is formed, and the weld metal shape of the weld bead toe at the welding start point does not rise convexly Manufacturing method of arc welding joint.

  (10) In the method for manufacturing a lap fillet arc welded joint in which part of two steel plates are overlapped and the fillet arc weld bead is formed by welding the corners of the upper plate steel plate and the lower plate steel plate, the welding end point A through hole is provided on the upper plate side, and the upper plate steel plate and the lower plate steel plate are overlapped, and spot welding is performed to fill the through hole before or after the start of overlapped fillet arc welding. The welding end point side upper plate additional bead is spot welded to suppress fatigue failure that occurs from the root part of the welding end point, and welding is performed at the fillet arc weld bead toe at the welding start point. Before starting welding or after finishing welding, spot welding is performed on the lower plate steel plate so that a part of the welding start point side lower plate additional bead overlaps with the fillet arc welding bead to form the welding starting point side lower plate additional bead, and welding starts. The weld metal shape of the point bead toe is convex (3) method of manufacturing superior overlapped fillet arc welded joint fatigue properties according to reluctant not shape the fact characterized.

  (11) The through hole provided on the upper plate steel plate side is a through hole having a diameter of 3 to 8 mm and has excellent fatigue characteristics as described in (8) or (10) above Manufacturing method of fillet arc welded joint.

  According to the present invention, when a load is applied to a lap fillet arc welded joint of a steel sheet, fatigue fracture occurring from the toe portion at the welding start point and fatigue fracture occurring from the root portion at the welding end point are effectively prevented. A lap fillet arc welded joint that can be suppressed and has excellent fatigue characteristics can be obtained.

It is a figure for demonstrating a lap fillet arc welding. It is a figure which shows an example of the external view of a weld bead. 2 shows a cross-sectional photomicrograph of the welded portion of FIG. 2, FIG. 3 (a) is the position of FIG. 2 (a), which is the welding start point, FIG. 3 (b) is the position of FIG. 3 (c) is the position of FIG. 2 (c) which is a welding end portion, and FIG. 3 (d) is the position between the upper plate and the lower plate at the position of FIG. 2 (c) which is a welding end portion. It is a welding part cross-sectional microscope picture which shows an example in case there exists a gap. In overlap fillet arc welding, it is a figure which shows the state which provided the welding end point side upper board addition bead and the welding start point side lower board addition bead in the welding end point vicinity of a welding bead. It is a figure which shows the test piece shape used for the fatigue test, (a) is a top view, (b) is a side view. It is a photograph which shows the fatigue crack generation | occurrence | production from the toe part of a welding start point, and the fatigue crack generation | occurrence | production from the root part of a welding end point (crater). It is a photograph of the welding bead which shows the example which provided both the welding end point side upper board addition bead and the welding start point side lower board addition bead after this welding bead. It is a photograph of the welding bead which shows the example which provided both the welding end point side upper board addition bead and the welding start point side lower board addition bead ahead of this welding bead.

  The present invention will be described in detail below.

First, it will be described that in a lap fillet arc welded joint, a fatigue crack from the toe portion tends to occur near the welding start point, and a fatigue crack from the root portion tends to occur near the welding end point.
As shown in the cross-sectional view of FIG. 1, lap fillet arc welding is performed on two superposed upper steel plates 1 (hereinafter sometimes referred to as upper plates) and lower steel plates 2 (hereinafter also referred to as lower plates). In this welding, the bead (welded metal) 3 is formed by welding the corners of the overlapped portion.

  FIG. 2 is a diagram showing an example of an external view of a weld bead, FIG. 3 shows a cross-sectional micrograph of the welded portion, and FIG. 3A is a welded portion at the position of FIG. FIG. 3B is a cross-sectional micrograph, FIG. 3B is a cross-sectional micrograph of the welded portion at the position of FIG. 2B, which is a steady welding portion, and FIG. 3C is the end of welding in FIG. FIG. 3D is a welding micrograph showing a case where there is a gap between the upper plate and the lower plate at the position of FIG. 2C, which is the welding end portion. It is a cross-sectional micrograph.

  As shown in FIGS. 3 (a) and 3 (c), the shape of the welding start / end portion is different from the shape of the stable welded portion of the constant welding portion shown in FIG. 3 (b). As shown in FIG. 3A, the weld metal in the vicinity of the welding start point has a convex shape, and has a tendency that the flank angle is smaller and the toe radius is smaller than that in FIG. This convex shape is formed because the steel plate is not heated immediately after the start of welding, so that the familiarity between the steel plate and the weld metal is poor.

  On the other hand, the weld metal in the vicinity of the welding end point becomes flat or concave as shown in FIGS. 3C and 3D because of a recess called a crater 6 shown in FIG. The shape of the toe part is good because of the shape of the welded part, but it is good, but when the load is applied to the welded part because the effective cross-sectional area required for load transmission is small, the stress is higher than that of the steady part. It will increase. Therefore, a fatigue crack starting from the root portion 4 shown in FIG. 2 is likely to occur. Even after the welding torch is positioned at the welding end position, the effective cross-sectional area cannot be ensured as much as the steady portion even if the crater treatment for eliminating the crater depression is performed for a while. Furthermore, there is a problem that excessive crater treatment may cause the lower plate to melt.

When tensile forces F ₁ and F _{2 in the} vertical direction are applied to the weld line of such a welded joint portion, the root portion 4 and the corner portion 4 and the corner portion are displaced due to a shift between the central axis of the upper plate 1 and the central axis of the lower plate 2. A large bending moment is generated at the flesh toe 5 and the effective cross-sectional area required for load transmission and load transmission near the welding start point on the lower plate side where stress is likely to concentrate compared to the steady part due to discontinuous shape is small. A fatigue crack is generated from the root portion in the vicinity of the welding end point of the flat welded portion shape, and progresses in the plate thickness direction to cause fracture.

  FIG. 6 shows an example of a state of fatigue crack generation from the toe portion 5 at the welding start point and fatigue crack generation from the root portion 4 at the welding end point (crater).

  In view of this, the present inventor has intensively studied to prevent fatigue cracks generated from the weld toe near the welding start point and the root near the welding end point. As a result, it is effective to prevent the root portion from opening in order to suppress fatigue cracks generated from the root portion. To prevent the root portion from opening, the upper plate near the welding end point is effective. The upper plate and the lower plate are welded so as to fill the through hole by welding such as plug welding or slot welding, and the weld end point side upper plate additional bead is provided to concentrate stress on the root part. It has been found that this can prevent the occurrence of fatigue cracks from the root portion.

  In addition, the cause of fatigue failure from the weld bead toe at the welding start point is that the weld metal at the welding start point toe is convexly raised, and the flank angle is smaller and the toe radius is smaller than the steady part. This is because there is a tendency, and when a load is applied to the welded portion, the stress is likely to be concentrated compared to the steady portion. Therefore, the weld start point side lower plate additional bead is spot welded to the weld start point before or after the start of welding so that it partially overlaps the weld bead end. The present inventors have found that the shape of the weld metal that bulges up can be eliminated, stress can be prevented from concentrating at the toe, and the occurrence of fatigue cracks from the vicinity of the welding start point can be suppressed.

  First, a description will be given of providing a welding end point side upper plate additional bead for suppressing a fatigue crack generated from the root portion.

  FIG. 4 shows an additional bead (referred to as “welding end point side upper plate additional bead”) on the upper plate near the welding end point of the weld bead and the lower plate side of the welding start point toe end of the weld bead in lap fillet arc welding. It is a figure which shows the state which provided the additional bead (referred to as a welding start point side lower board additional bead).

  In the present invention, prior to the start of lap fillet arc welding (hereinafter sometimes referred to as main welding), as shown in FIG. 4, the welding end point 7 (the position of the welding torch is stopped at a position where the movement of the welding torch is stopped). A teaching hole is provided with a through hole 8 on the upper plate 1 side, the upper plate 1 and the lower plate 2 are overlapped, and spot welding such as plug welding or slot welding is performed to fill the through hole 8, and the welding end point side An upper plate additional bead 9 is formed and the upper plate 1 and the lower plate 2 are welded. Next, by carrying out the main welding for forming the main welding bead 3, the layered fillet excellent in fatigue characteristics that suppresses the fatigue fracture occurring from the root portion 4 at the welding end point 7 (which is the teaching position of the welding torch). It could be an arc welded joint.

  In overlapped fillet arc welding, the location of the fillet weld and the required weld length are determined by the design of the parts, so the welding torch starts to move to ensure the required weld length. The welding start position 10 (which becomes the teaching position of the welding torch), which is the position, and the welding end position 7 (which becomes the teaching position of the welding torch), which is the position where the movement of the welding torch ends, are determined. In addition, the aim position of this welding is implemented as usual aiming at the corner of the overlapping part of the upper plate 1 and the lower plate 2.

  Therefore, the center position of the through hole 8 provided on the upper plate 1 side can be set with reference to the welding end point 7 of the main welding bead. The center position is such that the distance 11 from the welding end point 7 to the center is 5 to 10 mm toward the upper plate 1 side of the main welding bead on the welding end point 7 side, and is parallel to the upper plate end (parallel to the welding line). ) Is preferably set to a center position within a range of -5 to 5 mm. As shown in FIG. 4, the positive direction of the distance here is a positive direction from the welding end point to the welding start point, and is based on the lead line.

  The center position of the through hole substantially coincides with the solidification center position of the welding end point side upper plate additional bead 9.

  Fatigue from the root portion of the main welding bead 3 by forming the welding end point side upper plate additional bead 9 and welding the upper plate 1 and the lower plate 2 by spot welding filling the through hole 8 on the upper plate side. Although crack generation can be effectively suppressed, fatigue from the root portion will occur even if the center position where the upper plate and the lower plate are spot welded is too far or too close to the welding end point 7. Since the effect of suppressing crack generation is reduced, the center position is preferable.

  The size of the through hole 8 on the upper plate side is not particularly limited as long as the upper plate 1 and the lower plate 2 can be welded. However, the lower limit is 3 mm in diameter for ease of welding. It is preferable to set the upper limit to 8 mm in diameter in order to prevent fear of coming off and melting and to prevent excessive heat input.

  It should be noted that welding for forming the welding end point side upper plate additional bead 9 has no difference in function and effect even before the start of the main welding or after the main welding, and may be arbitrarily selected and executed. .

  The welding end point side upper plate additional bead 9 is formed by welding to fill the through hole 8 on the upper plate 1 side. If the upper plate 1 and the lower plate 2 are welded, the object of the present invention is achieved. . Accordingly, the size of the upper plate additional bead is not particularly limited, but is preferably 6 to 16 mm in diameter, which is twice the diameter of the through hole. The positional relationship between the welding end point side upper plate additional bead 9 and the main welding bead 3 is such that the welding end point side upper plate additional bead 9 from the upper plate 1 side toe end of the main welding bead 3 on the welding end point 7 side. The distance 13 from the weld bead end 12 on the welding end point side parallel to the end of the upper plate steel plate to the solidification center of the welding end point side upper plate additional bead 9 is 2 to 7 mm. It is desirable to have a positional relationship of −3 to 8 mm.

  Therefore, a part of the welding end point side upper plate additional bead 9 and the main welding bead 3 may overlap.

  Thus, as a result of testing the 200,000 times fatigue life and the 2 million times fatigue life of the lap fillet arc welded joint provided with the welding end point side upper plate additional bead, improvement in fatigue characteristics was recognized in both cases.

  Next, providing a welding start point side lower plate additional bead for suppressing a fatigue crack generated from the welding start point will be described.

  In order to suppress fatigue failure from the toe at the welding start point, the bottom plate side toe of the main welding bead (welded metal) at the welding start point is shaped as shown in the cross-sectional photograph of FIG. Therefore, if this bulge is eliminated, stress does not concentrate at the toe portion at the welding start point, and fatigue failure can be suppressed.

  Therefore, in the present invention, a portion of the welding start point side lower plate additional bead 16 overlaps with the main weld bead toe at the position of the main weld bead toe at the welding start point 10 before or after the start of welding. The lower plate was spot welded to form the welding start point side lower plate additional bead 16 to eliminate the raised shape of the weld metal shape in the vicinity of the welding start point. The area ratio at which the welding start point side lower plate addition bead 16 overlaps with the main welding bead 3 is preferably 30 to 70% of the area of the welding start point side lower plate addition bead 16 projected from the vertical direction on the lower plate. . This is because if the overlapping area ratio is small or too large, it is impossible to correct the raised shape of the main weld bead (welded metal) at the toe at the welding start point.

  As shown in FIG. 4, the welding start point side lower plate addition bead 16 is a welding start point side lower plate addition bead 16 farthest from the toe portion on the lower plate 2 side of the welding start point 10 side of the main welding bead 3. The distance 17 to the end is 2 to 5 mm, parallel to the end of the upper plate 1, and not the end of welding 12 from the end 18 on the welding start point side where the upper plate and the lower plate are joined by the main welding bead. It is preferable to form an additional bead having a diameter of 6 to 16 mm so that the distance 21 to the toe end of the far welding starting point side lower plate additional bead 16 is 0 to 4 mm. The center position of the welding start point side lower plate additional bead 16 is such that the distance 19 from the end of the upper plate 1 to the teaching position of the welding start point side lower plate additional bead 16 is 3 to 8 mm. It is preferable that the distance 20 from the welding start point 10 to the teaching position of the welding start point side lower plate additional bead 16 is a central position that is -3 to 3 mm parallel to the portion.

  By setting the position and size of the welding start point side lower plate additional bead as described above, the main welding bead toe end portion (lower plate side) at the welding starting point overlaps with the welding start point side lower plate additional bead. Thus, fatigue cracks from the weld start point toe (lower plate side) could be suppressed.

  That is, 200,000 times fatigue life and 2 million times fatigue life were tested on the fillet arc welded joint provided so that the welding start toe of the main weld bead and the weld starting point side lower plate additional bead partially overlap each other. As a result, improvement in fatigue characteristics was recognized in all cases.

  Further, by providing both the welding end point side upper plate additional bead and the welding start point side lower plate additional bead, it was confirmed that the fatigue characteristics of the lap fillet arc welded joint were further improved.

  That is, as a result of testing the fatigue life of 200,000 times and the fatigue life of 2 million times for the lap fillet arc welded joint provided with the welding start point side lower plate additional bead, improvement in fatigue characteristics was recognized in both cases.

  The example which provided both the welding end point side upper board addition bead and the welding start point side lower board addition bead mentioned above was shown in FIG.7 and FIG.8. FIG. 7 is a photograph of a weld bead showing an example in which both additional beads are provided after the main weld bead, and FIG. 8 is a photograph of a weld bead showing an example in which both additional beads are provided before the main weld bead.

  In addition, it is preferable that there is no gap between the upper plate and the lower plate that are welded and overlapped, but there may be a gap between the upper plate and the lower plate from the viewpoint of welding work, but it is 2 mm or less. Even if there is such a gap, the function and effect of the present invention are not impaired.

  Further, as a component member of an automobile, generally, a steel plate having a thickness of an upper plate thickness of 1.8 to 4 mm and a lower plate thickness of 1.8 mm or more is overlapped and arc-welded and used in many cases. However, in the case of lap fillet arc welded joints, when there is a difference in plate thickness, if the lower plate thickness is large, it tends to cause fatigue failure from the root, and if the upper plate thickness is large, it tends to cause fatigue failure from the toe. According to the invention, it is possible to provide a lap fillet arc welded joint having excellent fatigue characteristics regardless of the thickness difference of the steel plates.

  Therefore, in the present invention, overlapped fillet arc welding is performed on a steel sheet having an upper plate thickness of 1.8 to 4 mm and a lower plate thickness of 1.8 mm or more, and the overlapped fillet arc welding excellent in fatigue characteristics is performed. It can be a joint. The upper limit of the thickness of the lower plate is not particularly limited, but about 12 mm is realistic.

  Next, based on an Example, this invention is demonstrated.

  In Examples, a fatigue test was performed on a test piece obtained by lap fillet welding of a thin steel plate, and the effect was verified. Table 1 shows the test steel sheets, and Table 2 shows the test welding wires.

  FIG. 5 shows the shape of a test piece subjected to a fatigue test. FIG. 5A is a plan view and FIG. 5B is a side view. That is, as shown in FIGS. 5 (a) and (b), two steel plates having a plate width of 60 mm are combined with the upper plate 1 and the lower plate 2 at a stacking allowance of 20 mm, and overlapped fillet arc welding is performed. Welding torch travel distance (teaching): Designed and tested at 40 mm (weld bead length is about 45 mm). The upper plate end of the overlapped fillet arc welded portion was set to the center of the test piece.

  Here, the welding start point side lower plate additional bead is welded from the welding start point when welding the main welding bead (the end of the upper plate 1 at the teaching position of the welding torch 10 mm away from the plate end). An additional bead having a diameter of 9 mm is formed with the lower plate position 5 mm away from the teaching position at a right angle to the center. The welding end point side upper plate additional bead is 7 mm on the upper plate side perpendicular to the welding line from the welding end point (which becomes the end of the upper plate 1 at the teaching position of the welding torch) when welding the main welding bead. A through hole having a diameter of 5.5 mm was provided at the position of the separated upper plate, and an additional bead having a diameter of 10 mm was formed by filling the through hole and spot welding the lower plate and the upper plate.

The welding conditions are as follows.
・ Welding method Consumable electrode welding / Welding power source DP350 (Daihen Co., Ltd.)
・ Welding mode DC-Pulse
・ Welding posture Horizontal downward ・ Distance between chip steel plates (extrusion length) 15mm
・ Shield gas type Ar + 20% CO ₂
・ Shielding gas flow rate 20L / min
<About welding sequence>
In order to ensure the necessary welding length, the welding start position (the teaching position of 10 welding torches in FIG. 4) and the welding end position (the teaching position of 7 welding torches in FIG. 4) are determined.

  The welding position of the additional bead is determined so that the positional relationship obtained after the additional bead welding falls within the specified range. The position is set on the basis of the position of the teaching point of this welding bead.

<Conditions during main welding>
・ Torch angle 55 ° raised from the lower plate, 0 ° forward angle
・ Target position Overlapping corner / Welding speed 40cm / min
-Wire feed speed As an example of setting a value that does not cause undercut on the upper plate side, it was set to 3.8 m / min (about 120 A, about 22 V) in the case of overlap fillet welding with an upper plate thickness of 2.6 mm.

<Conditions for welding start point additional beads>
・ Torch angle 90 °
・ Target position Lower plate position 8mm away from teaching position perpendicular to the welding line ・ Wire feed speed Same condition as in main welding ・ Welding time As an example, the time (0.8 seconds) when the diameter of the additional bead becomes 9 mm .

<Conditions for welding end point addition beads>
・ Torch angle 90 °
・ Target position Position of upper plate 7mm away from welding end point perpendicular to welding line to upper plate side ・ Wire feed speed Same condition as in main welding ・ Welding time Set time for welding metal to rise from upper plate surface

  As an example, a 5.5 mm hole was made in the upper plate by lap fillet welding with a plate thickness of 2.6 mm, and 1.0 second was set when there was no gap between the upper and lower plates. Similarly, when there was a 1 mm gap between the upper and lower plates, the time was 1.4 seconds.

  The weld specimen was subjected to an electrohydraulic fatigue test apparatus, subjected to an axial tension fatigue test with a constant load range (stress range constant) and a load ratio of 0.1, and the fatigue characteristics were measured. The fatigue life was evaluated based on the number of times the test piece was separated and fractured in a load range of 10 kN.

  Table 3 shows the welding conditions and fatigue property evaluation results.

  As shown in Table 3, all of the inventive examples had a good fatigue life, and it was confirmed that the fatigue life was improved as compared with the comparative example.

  In the above, according to the Example, the welded joint and the welding method which concern on this invention were demonstrated.

  The embodiments of the present invention are not limited to the embodiments described in the above examples. Those substantially satisfying the requirements of the invention fall within the scope of the invention.

  The present invention can be used not only in the machine industry but also in industries that can apply overlapped fillet welding of steel plates.

1: lower plate 2: upper plate 3: main welding bead 4: root portion 5: fillet toe portion 6: crater 7: welding end point when welding the main welding bead (the teaching position of the welding torch)
8: Through hole previously drilled in the upper plate for spot welding of the welding end point side upper plate additional bead 9: Welding end point side upper plate additional bead 10: Welding start point when welding the main welding bead (welding torch Teaching position)
11: Distance from the welding end point 7 to the center of the through hole 8 12: End portion on the welding end point side where the upper plate and the lower plate are joined by the main welding bead 13: Upper plate side on the welding end point side of the main welding bead 3 Distance 14 from the toe portion to the solidification center of the upper plate additional bead 9 on the welding end point side: parallel to the end portion of the upper plate 1 and distance 15 from the welding end point 7 to the center of the through hole 8: Distance from the end 12 of the welding end point parallel to the end to the solidification center of the welding end point side upper plate additional bead 9 16: welding start point side lower plate additional bead 17: welding start point side of the main welding bead 3 Distance 18 from the welding start point side lower plate additional bead 16 farthest from the lower plate side toe end: End 19 on the welding start point side where the upper plate and the lower plate are joined by the main welding bead 3: Distance 20 from the end of the upper plate 1 to the teaching position of the welding start point side lower plate additional bead 16: the end of the upper plate 1 Distance 21 from the welding start point 10 to the teaching position of the welding start point side lower plate additional bead 16 in parallel: parallel to the end of the lower plate 1 and not from the end 18 of the welding start point to the end 12 side of the welding end point Distance to the toe of the farthest welding start point side lower plate additional bead 16

Claims (11)

  In a lap fillet arc welded joint where a fillet arc weld bead is formed by overlapping a part of two steel plates and welding the corners of the upper and lower plate steel plates, the welding end point of the fillet arc weld bead A lap fillet arc welded joint excellent in fatigue characteristics, characterized in that a welding end point side upper plate additional bead is formed by spot welding the upper plate steel plate and the lower plate steel plate on the upper plate steel plate side.   In a lap fillet arc welded joint, in which a fillet arc weld bead is formed by overlapping a part of two steel plates and welding the corners of the upper and lower plate steel sheets, the welding of the fillet arc weld bead starts. A lap fillet arc welded joint excellent in fatigue characteristics, characterized in that a welding start point side lower plate additional bead that partially overlaps the point toe is provided on the lower plate steel plate.   In a lap fillet arc welded joint where a fillet arc weld bead is formed by overlapping a part of two steel plates and welding the corners of the upper and lower plate steel plates, the welding end point of the fillet arc weld bead On the upper plate steel plate side to be provided, a welding end point side upper plate additional bead is formed by spot welding the upper plate steel plate and the lower plate steel plate, and partially overlaps the welding start point toe of the fillet arc welding bead. A lap fillet arc welded joint excellent in fatigue characteristics, characterized in that a lower plate additional bead on the welding start point side is provided on the lower plate steel plate.   The welding end point side upper plate additional bead has a distance of 2 to 7 mm from the upper plate side toe of the fillet arc welding bead to the solidification center of the welding end point side upper plate additional bead. The distance from the weld bead end on the welding end point side to the solidification center of the upper plate additional bead on the welding end point side parallel to the end of the steel plate is provided at a position where the distance is -3 to 8 mm. Item 4. An overlapped fillet arc welded joint excellent in fatigue characteristics according to item 1 or 3.   The welding start point side lower plate additional bead is a distance from the end of the bottom plate steel plate side toe end of the fillet arc welding bead to the toe end of the welding start point side lower plate additional bead. 2 to 5 mm, the distance from the end on the welding start point side parallel to the end of the upper plate steel plate to the toe end of the welding start point side lower plate additional bead farthest in the opposite direction to the welding end point side is 0 The lap fillet arc welded joint excellent in fatigue characteristics according to claim 2 or 3, characterized in that it is provided at a position of -4 mm.   The overlapped fillet arc welded joint having excellent fatigue characteristics according to any one of claims 1 to 5, wherein a gap between the superposed upper steel plate and lower steel plate is 0 to 2 mm.   The plate thickness of the upper plate steel plate is 1.8 to 4 mm, and the plate thickness of the lower plate steel plate is 1.8 mm or more, excellent fatigue characteristics according to any one of claims 1 to 6 Lap fillet arc welded joint.   In the method of manufacturing a lap fillet arc welded joint, in which a fillet arc weld bead is formed by overlapping a part of two steel plates and welding the corners of the upper plate steel plate and the lower plate steel plate A through hole is provided on the steel plate side, the upper plate and the lower plate are overlapped, and spot welding is performed to fill the through hole before or after the start of overlapped fillet arc welding. The lap fillet arc welded joint having excellent fatigue characteristics according to claim 1, wherein the upper plate and the lower plate are spot welded to prevent fatigue fracture occurring from the root portion of the welding end point. Manufacturing method.   In the method for manufacturing a lap fillet arc welded joint, in which a fillet arc weld bead is formed by superposing a part of two steel plates and welding the corners of the upper plate steel plate and the lower plate steel plate, the fillet at the welding start point Spot welding to the bottom plate so that a part of the additional bead on the welding start point side lower plate overlaps the fillet arc welding bead at the position of the arc weld bead toe before or after the start of welding. 3. The lap fillet arc welded joint having excellent fatigue characteristics according to claim 2, wherein a plate-added bead is formed, and the weld metal shape of the weld bead toe at the welding start point is not convexly raised. Production method.   In the method of manufacturing a lap fillet arc welded joint, in which a fillet arc weld bead is formed by overlapping a part of two steel plates and welding the corners of the upper plate steel plate and the lower plate steel plate A through hole is provided on the plate side, and the upper plate and the lower plate are overlapped and spot welding is performed by spot welding to fill the through hole before or after overlapped fillet arc welding is started. The weld end point side upper plate additional bead is formed to suppress fatigue fracture occurring from the root portion of the welding end point, and before the start of welding at the fillet arc weld bead toe end position at the welding start point or After welding is completed, spot welding is performed on the lower plate steel plate so that a part of the weld starting point side lower plate additional bead overlaps with the fillet arc welding bead to form the welding starting point side lower plate additional bead, and the welding start point bead is stopped. The weld metal shape at the end does not rise Overlapping corners method for producing meat arc welded joint having excellent fatigue characteristics according to claim 3, characterized in that a shape.   11. The lap fillet arc welded joint having excellent fatigue characteristics according to claim 8, wherein the through hole provided on the upper plate steel plate side is a through hole having a diameter of 3 to 8 mm. Production method.