JP2017070977A - Welded joint, welded structure, construction machine and welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a welded joint, a welded structure, a construction machine and a welding method capable of suppressing fatigue failure starting from un-welded part between base material and backing metal.SOLUTION: A welded joint includes a first base material 31, a second base material 32 opposed to the first base material 31 by butting bevels 34 to each other and a backing metal 33 attached to the first and second base materials 31, 32 while striding over a root gap 34a of the bevels 34. Therein, the base material 31 is inclined with respect to the base material 32 by setting the bevels 34 as a boundary such that a neutral surface P1 of the base material 31 is separated to the side opposite to the backing metal 33 from a surface P2' containing a neutral surface P2 of the base material 32 as going away from the bevels 34.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a welded joint using a backing metal, a welded structure and a construction machine including the welded joint, and a welding method.

  Since butt welding with a backing metal can be welded from one side of a base material, it is often used in structures where welding on the back side is difficult. However, a notch-shaped unwelded portion remains between the base material and the backing metal, and when external force is repeatedly applied to the base material, there is a problem that stress is concentrated on the unwelded portion and fatigue failure is likely to occur. .

  On the other hand, a technique for improving the joint strength by bending the base material end and omitting the backing metal with a special shape of the groove, or using a special backing metal has been proposed ( (See Patent Documents 1 and 2).

Japanese Patent Laid-Open No. 9-16496 JP 09-253890 A

  However, the technique of Patent Document 1 requires advanced welding technology for back wave welding, and since the degree of welding difficulty is high, the number of man-hours is increased because of limited welding. Above all, it takes time to form the groove. On the other hand, in the technique of Patent Document 2, man-hours are required for manufacturing a special backing metal made of two kinds of materials having different elastic coefficients and linear expansion coefficients.

  Therefore, the present invention does not require a special groove or backing metal, a welded joint that can suppress fatigue fracture starting from an unwelded portion between the base material and the backing metal, a welded structure, An object is to provide a construction machine and a welding method.

  In order to achieve the above object, a welded joint according to the present invention includes a first base material, a second base material that faces the first base material with the groove facing each other, and the root of the groove. Backing metal attached to the first and second base materials across the gap, and the first base material from a surface including a neutral surface of the second base material as the distance from the groove increases. The first base material is inclined with respect to the second base material with the groove as a boundary so that a neutral surface of the material is away from the backing metal. .

  According to the present invention, fatigue failure starting from an unwelded portion between the base material and the backing metal can be suppressed without requiring a special groove or backing metal.

It is the figure which looked at the welded joint which concerns on one Embodiment of this invention from the direction orthogonal to a weld line. It is the figure which looked at the welded structure which concerns on one Embodiment of this invention from the direction orthogonal to a weld line. It is a figure explaining the effect | action of one Embodiment of this invention. 1 is a side view of a hydraulic excavator that is an example of a construction machine that can be an application target of a welded joint according to the present invention. It is the side view which extracted and represented the boom of the hydraulic shovel shown in FIG. It is a figure which shows one Example which applied the welded joint which concerns on one Embodiment of this invention to the boom shown in FIG. 5, and is a figure equivalent to the arrow directional cross-sectional view in the iii-iii line in FIG. It is a schematic diagram of the welded structure which concerns on a comparative example.

  Embodiments of the present invention will be described below with reference to the drawings.

1. 1 is a view of a welded joint according to an embodiment of the present invention as viewed from a direction orthogonal to the weld line. The weld joint shown in this figure includes a first base material 31 (hereinafter simply referred to as base material 31), a second base material 32 (hereinafter simply referred to as base material 32), and a backing metal 33. I have. The base materials 31 and 32 are flat members, and are butt joints that face each other with the groove 34 butted. The groove 34 does not need to have a special shape, and may be a V-shaped one that narrows from the front side to the back side of the base materials 31 and 32, for example. The groove 34 is formed by forming at least one end face of the base materials 31 and 32 obliquely. The front side of the base materials 31 and 32 is the side where welding is performed, and the back side is the opposite side. The backing metal 33 is attached (temporarily fixed) to at least one back side of the base materials 31 and 32 across the route gap 34a of the groove 34 by spot welding or the like. The backing metal 33 does not have to be special in material or shape, and may be a general flat plate shape conventionally used in butt welding with a backing metal.

  The base materials 31 and 32 are arranged such that the neutral surface P1 of the base material 31 is separated from the surface P2 ′ including the neutral surface P2 of the base material 32 toward the opposite side to the backing metal 33 as the base material 31 is separated from the groove 34. The base material 32 is inclined with respect to the base material 31 with the groove 34 as a boundary. Thereby, the neutral surface P1 of the base material 31 is not included in the surface P2 'including the neutral surface P2 of the base material 32 (the neutral surface P1 is deviated from the surface P2'). In the portion of the root gap 34a, the root tips (lower end portions in the drawing) of the base materials 31 and 32 face each other, and at least one of the tip tips of the base materials 31 and 32 faces the backing metal 33. In contact or close proximity.

2. Welded Structure FIG. 2 is a view of a welded structure according to an embodiment of the present invention as viewed from a direction orthogonal to the weld line. The welded structure shown in this figure includes a weld metal 35 and the weld joint shown in FIG. The weld metal 35 is formed on the groove 34 by welding from the side opposite to the backing metal 33. By forming the weld metal 35 along the groove 34, the base materials 31 and 32 are joined to each other. The welding operation at this time is the same as the ordinary butt welding with a backing metal because the backing metal 33 is on the root side of the groove 34, and does not require a high level of skill like back wave welding.

  This welding method (manufacturing method of the welded structure) is as follows. First, the base materials 31 and 32 are made to face each other with the groove 34 abutted so that the neutral surface P1 of the base material 31 is not included in the surface P2 'including the neutral surface P2 of the base material 32. Specifically, as described above, as the neutral surface P1 of the base material 31 moves away from the groove 34, the base materials 31 and 32 move away from the surface P2 ′ including the neutral surface P2 of the base material 32. The grooves 34 are opposed to each other in a state where they are inclined with respect to each other. Then, a backing metal 33 is attached to the base materials 31 and 32 across the root gap 34 a of the groove 34, and a weld metal 35 is formed on the groove 34 from the side opposite to the backing metal 33.

3. Comparative Example FIG. 7 is a schematic view of a welded structure according to a comparative example and corresponds to FIG. In the welded structure shown in this figure, flat base materials A and B having the same thickness are joined by butt welding with a backing metal. The neutral surfaces of the base materials A and B are included in the same plane. In the weld metal D, an unwelded portion E exists between the backing metal C and the base materials A and B. For example, when a tensile load repeatedly acts on the welded structure in the surface direction of the base materials A and B as indicated by arrows in FIG.

4). Effect FIG. 3 is a diagram for explaining the operation of the present embodiment. In the welded structure of the present embodiment, when a tensile load is applied in the direction in which the base materials 31 and 32 are separated from each other as indicated by thick arrows in FIG. 3, the neutral surface P <b> 1 of the base material 31 is neutral. Deformation that approaches the surface P2 ′ including the surface P2 occurs. When tensile stress is generated in the direction in which the base materials 31 and 32 are separated from the entire weld metal 35, the tensile stress is generated on the front side of the weld metal 35 and the backing metal 33 side is accompanied by the previous deformation. Stress is applied in the compression direction. Therefore, the tensile stress on the front side of the weld metal 35 increases and the tensile stress on the back side decreases. By reducing the tensile stress acting on the back side of the weld metal 35 in this way, the tension on the backing metal side that tends to cause fatigue failure in a butt welded joint with a backing metal, without requiring a special groove or backing metal. Stress can be reduced and fatigue failure can be suppressed.

  In addition, on the front side of the weld metal 35 where the tensile stress increases, the fatigue strength is improved by post-processing, for example, by performing a grinder process to smooth the surface shape or applying compressive residual stress by shot peening or the like. Can do.

5. Embodiment (1) Construction Machine FIG. 4 is a side view of a hydraulic excavator that is an example of a construction machine that can be applied to a welded joint according to the present invention. When there is no notice in the following description, the front of the driver's seat (the left direction in the figure) is the front of the aircraft. The illustration of the hydraulic excavator does not limit the application target of the welded joint according to the present invention, and the welded joint according to the present invention is necessary even for other types of construction machines such as wheel loaders, cranes, and bulldozers. Can be applied accordingly.

  The hydraulic excavator shown in FIG. 4 includes a traveling body 4 for traveling and a revolving body 5 that is mounted on the upper portion of the traveling body 4 so as to be rotatable. The revolving structure 5 is provided on the engine room 7 installed on the revolving structure frame, the cab 6 provided on the front left side of the engine room 7, the front working machine extending forward from the right side of the cab 6, and the rear of the engine room 7. Counter weight 8 is provided. Although not particularly illustrated, the engine room 7 houses various devices such as an engine, a heat exchanger, and a battery.

  The front work machine includes a boom 9 whose base is rotatably connected to the revolving body frame, an arm 2 rotatably connected to the tip of the boom 9, and a bucket 12 rotatably connected to the tip of the arm 2. ing. The boom 9, the arm 2, and the bucket 12 operate in a vertical plane extending in the front-rear direction by a hydraulically driven boom cylinder 10, arm cylinder 11, and bucket cylinder 13, respectively.

(2) Boom FIG. 5 is a side view of the boom 9 extracted. As shown in FIG. 5, the boom 9 is formed hollow by joining the side plates 19, 20, the upper plate 27 and the lower plate 28 by welding, and is curved so as to be convex upward when viewed from the side. It is formed in the shape. A bracket 14 for connecting the arm cylinder 11, a boss 15 for connecting the boom cylinder 10, a boss 16 for connecting the boom 9 and the swing body 5, and the boom 9 and the arm 2 are connected to the boom 9. A boss 17 is provided. The left side surface of the boom 9 is formed by joining a plurality of plate members. For example, even when a portion from the curved portion to the base side is seen, the side plate 19 on the base side provided with the boss 16 and the curved portion provided with the boss 15 The side plate 20 is joined by a butt weld portion 21. Further, a bent portion 18 is provided on the side plate 19 on the base side. By providing the bent portion 18, the base portion of the boom 9 (the portion on the boss 16 side) is thicker than the portion on the front side as viewed from above, which is sufficient to support the moment load of the entire front work machine. Rigidity is given. The right side surface of the boom 9 has the same configuration as the left side surface.

  However, in the case where the butt weld portion 21 and the bent portion 18 are separately provided, the side plate 19 is bent and the side plates 19 and 20 are joined in the process of manufacturing the boom 9.

  6 is a view showing an example in which the welded joint according to the embodiment of the present invention is applied to the boom 9, and corresponds to a cross-sectional view taken along line iii-iii in FIG. As shown in FIG. 6, the butt welding portion 21 is made to coincide with the position of the bending portion 18, and the neutral surfaces of the side plates 19 and 20 are bent to the bending portion 18 as in the above-described embodiment (example of FIGS. 1 to 3). The butt welding with backing metal is applied at the same angle. Thereby, the board | plate material without the bending part 18 can be used for the side plate 19, and the process of a bending process can be skipped. Accordingly, the manufacturing efficiency of the boom 9 and thus the hydraulic excavator can be improved. As described above, the tensile stress acting on the portion of the weld metal on the backing metal 22 side, and hence the fatigue failure, can be suppressed.

  In this embodiment, the boom 9 is illustrated as a particularly suitable application location, but this is not intended to limit the application location of the invention to the boom 9, but other locations such as the arm 2 and the frame of the traveling body 4, for example. In addition, the present invention can be applied as necessary.

19 ... side plate (first base material), 20 ... side plate (second base material), 21 ... butt weld, 22 ... backing metal, 31 ... first base material, 32 ... second base material, 33 ... backing metal, 34 ... groove, 34a ... root gap, 35 ... weld metal, P1 ... neutral surface of the first base material, P2 ... neutral surface of the second base material, P2 '... second Surface including the neutral surface of the base material

Claims (4)

A first base material;
A second base material that faces the first base material by facing a groove;
A backing metal attached to the first and second base materials across the root gap of the groove,
As the distance from the groove increases, the neutral surface of the first base material moves away from the surface including the neutral surface of the second base material to the side opposite to the backing metal. The first base material is inclined with respect to the second base material. A welded joint according to claim 1;
A welded structure comprising a weld metal formed on the groove from the side opposite to the backing metal.   A construction machine comprising the welded structure according to claim 2. A welding method for joining the first and second base materials facing each other by facing a groove,
As the distance from the groove increases, the neutral surface of the first base material separates from the surface including the neutral surface of the second base material away from the backing metal. Tilting the first base material with respect to the second base material,
Attaching a backing metal to the first and second base materials across the root gap of the groove,
A welding method comprising forming a weld metal on the groove from a side opposite to the backing metal.

Images