WO2024202315A1 - Boom for work machine, work machine, and method for manufacturing boom for work machine - Google Patents

Abstract

A boom (21) comprises: a pair of left and right lateral plates (53); an upper plate (51); and a lower plate (52). The upper plate (51) is joined to the upper ends of the pair of lateral plates (53). The lower plate (52) is joined to the lower ends of the pair of lateral plates (53). The upper plate (51) or the lower plate (52) has a welding line (81) or a welding line (82) formed in a section divided in the longitudinal direction. The welding line (81) or the welding line (82) includes inclined sections (811, 812) or inclined sections (821, 822) which are inclined with respect to a direction perpendicular to the longitudinal direction.

Description

Boom for work implement, work machine, and method for manufacturing boom for work implement

The present invention relates to a boom for a work machine, a work machine, and a method for manufacturing a boom for a work machine.

A hydraulic excavator, which is an example of a work machine, comprises a lower running body, an upper rotating body arranged above the lower running body, and a work implement attached to the upper rotating body so that it can rotate in the vertical direction. The work implement has a boom attached to the upper rotating body, an arm attached to the tip of the boom, and a bucket attached to the tip of the arm.

As a method for manufacturing such a boom, a method has been disclosed in which a tip member, a base member, and an intermediate member that have been bent into a U-shape are welded to a floor plate (see, for example, Patent Document 1).

In the boom shown in Patent Document 1, the top plate and a pair of side surfaces are divided into three parts in the longitudinal direction, and the divided parts are joined by welding.

Japanese Unexamined Patent Publication No. 58-164828

However, because the principal stress acting on the boom during operation is generally parallel to the longitudinal direction, durability is insufficient if the weld lines are formed perpendicular to the longitudinal direction, as in the configuration shown in Patent Document 1 above.

An object of the present disclosure is to provide a boom for a work machine, a work machine, and a method for manufacturing a work machine that are capable of improving durability.
(Means for solving the problem)

In order to achieve the above object, the boom for a work machine according to the first disclosure comprises a pair of left and right side plates, an upper plate, and a lower plate. The upper plate is joined to the upper ends of the pair of side plates. The lower plate is joined to the lower ends of the pair of side plates. The upper plate or the lower plate has a first weld line formed in a portion divided in the longitudinal direction. The first weld line has an inclined portion inclined with respect to a direction perpendicular to the longitudinal direction.

The boom for a work machine according to the second disclosure comprises a main body, an end, and a weld line. The main body has a pair of left and right side plates, an upper plate, and a lower plate. The upper plate is joined to the upper ends of the pair of side plates. The lower plate is joined to the lower ends of the pair of side plates. The weld line is formed by butt welding between the upper or lower plate of the main body and the end. The weld line is located at both ends and has a pair of third straight line portions inclined with respect to a direction perpendicular to the longitudinal direction.

The manufacturing method of a boom for a work machine according to the third disclosure is a manufacturing method of a boom for a work machine divided into two or more subunits in the longitudinal direction, and includes a subunit manufacturing process, an alignment process, and an inter-subunit joining process. The subunit manufacturing process manufactures subunits by joining a pair of left and right side plates, an upper plate, and a lower plate by welding. The alignment process aligns a predetermined subunit with other subunits by rotating or suspending the subunit. The inter-subunit joining process welds the predetermined subunit to the other subunits.
(Effects of the Invention)

This disclosure provides a boom for a work machine, a work machine, and a method for manufacturing a work machine that can improve durability.

1 is a perspective view showing a work machine according to an embodiment of the present disclosure. FIG. 2 is a perspective view of a boom according to an embodiment of the present disclosure, viewed from above the tip. FIG. 2 is a perspective view of a boom according to an embodiment of the present disclosure, viewed from above the base end. FIG. 2 is a perspective view of a boom according to an embodiment of the present disclosure viewed from below. FIG. 2C is a diagram showing the internal structure of the boom 21 in FIG. 2B. FIG. 2 is a side view of a boom according to an embodiment of the present disclosure. FIG. 2 is a top view of a boom according to an embodiment of the present disclosure. FIG. 2 is a bottom view of a boom according to an embodiment of the present disclosure. FIG. 2B is an exploded view of the boom shown in FIG. FIG. 2C is an exploded view of the boom shown in FIG. FIG. 3B is an exploded view of the boom shown in FIG. FIG. 2C is a perspective view showing a divided state before the boom main body base end portion and the boom main body intermediate portion are joined by welding at the dividing portion in FIG. 2B . FIG. 5B is a perspective view showing a state in which the boom main body base end portion and the boom main body intermediate portion shown in FIG. 5A are welded together. FIG. 2 is a diagram for explaining butt welding according to an embodiment of the present disclosure. FIG. An enlarged view of part V1 of FIG. 3B. An enlarged view of part V2 in FIG. 3C. An enlarged view of area V3 of FIG. 3A. FIG. 2C is a perspective view showing a separated state before the boom main body tip portion and the boom main body intermediate portion are joined by welding at the separation portion in FIG. 2B . FIG. 8B is a perspective view showing a state in which the tip portion of the boom main body and the intermediate portion of the boom main body in FIG. 8A are welded together. An enlarged view of part V4 in FIG. 3B. An enlarged view of part V5 in FIG. 3C. An enlarged view of part V6 in FIG. 3A. FIG. 4 is a perspective view showing a separated state before the base end and the boom main body base end are joined by welding. FIG. 10B is a perspective view showing a state in which the base end portion of FIG. 10A and the base end portion of the boom main body are welded together. An enlarged view of part V7 in FIG. 3B. An enlarged view of part V8 in FIG. 3C. An enlarged view of area V9 in FIG. 3A. FIG. 4 is a perspective view showing the separated state before the tip portion and the tip portion of the boom body are joined by welding. FIG. 11B is a perspective view showing the state in which the tip portion of FIG. 11A and the tip portion of the boom body are welded together. An enlarged view of part V10 in FIG. 3B. An enlarged view of part V11 in FIG. 3C. An enlarged view of part V12 in FIG. 3A. FIG. 2 illustrates a first subunit, a second subunit, and a third subunit of a boom according to an embodiment of the present disclosure. 6A and 6B are diagrams for explaining alignment of a first subunit and a second subunit in an embodiment according to the present disclosure. FIG. 13 is a diagram for explaining alignment of a second subunit and a third subunit in the embodiment according to the present disclosure.

Below, a hydraulic excavator and a boom for a work machine as an example of a work machine according to the present disclosure will be described with reference to the drawings.

(Overview of hydraulic excavator 10)
FIG. 1 is a diagram showing the appearance of a hydraulic excavator 10 according to the present embodiment.

As shown in FIG. 1, a hydraulic excavator 10 (an example of a work machine) includes a work machine body 1 and a work implement 4. The work machine body 1 includes a lower traveling body 2 and an upper rotating body 3.

The lower traveling body 2 has a pair of traveling devices 11, 12. Each traveling device 11, 12 has tracks 11a, 12a. The driving force from the engine rotates the traveling motor, driving the tracks 11a, 12a, causing the hydraulic excavator 10 to travel.

The upper rotating body 3 is disposed above the lower running body 2. The upper rotating body 3 is configured to be able to rotate relative to the lower running body 2 around an axis along the vertical direction by a rotating motor (not shown). A swing machinery is disposed on the upper rotating body 3. A swing circle is disposed on the lower running body 2 and engages with the output pinion of the swing machinery. The rotational drive of the swing motor is decelerated by the swing machinery (not shown) and output from the output pinion. As a result, the swing machinery rotates inside or outside the swing circle, causing the upper rotating body 3 to rotate relative to the lower running body 2.

The upper rotating body 3 has a rotating frame 13, a cab 14, and an engine room 15. The rotating frame 13 is disposed above the lower running body 2, and is a frame that can rotate relative to the lower running body 2. The cab 14 is provided at the front left side of the rotating frame 13. The cab 14 is provided as a driver's seat where an operator sits when driving. Inside the cab 14, the driver's seat, an operating device for operating the work machine 4, a display device, etc. are disposed.

In this embodiment, the front, rear, left and right of the hydraulic excavator 10 will be described based on the driver's seat in the cab 14. The direction in which the driver's seat faces directly ahead is the forward direction Xf, and the direction opposite the forward direction is the rear direction Xb. The right and left sides when the driver's seat faces directly ahead are the right direction Yr and the left direction Yl, respectively.

The work machine 4 is attached to the center of the front of the revolving frame 13. As shown in FIG. 1, the work machine 4 has a boom 21 (an example of a boom for a work machine), an arm 22, and a bucket 23. The base end of the boom 21 is rotatably connected to the revolving frame 13 via a boom pin 21a. The tip of the boom 21 is rotatably connected to the base end of the arm 22 via an arm pin 22a. The tip of the arm 22 is rotatably connected to the bucket 23. The bucket 23 is attached to the arm 22 so that its opening faces the cab 14 (rear). A hydraulic excavator 10 with the bucket 23 attached in this orientation is called a backhoe.

Hydraulic cylinders 24 to 26 (boom cylinder 24, arm cylinder 25 and bucket cylinder 26) are arranged to correspond to the boom 21, arm 22 and bucket 23, respectively. The work implement 4 is driven by driving these hydraulic cylinders 24 to 26. This allows work such as excavation to be carried out.

The engine room 15 is located behind the cab 14 of the upper rotating body 3. The engine room 15 houses the engine, an after-treatment device for the engine's exhaust gas, a cooling unit for cooling the engine, a hydraulic pump, etc.

(Boom 21)
Figures 2A to 2D are perspective views showing the boom 21. Figure 2A is a perspective view of the boom 21 viewed from above the tip end. Figure 2B is a perspective view of the boom 21 viewed from above the base end. Figure 2C is a perspective view of the boom 21 viewed from below. Figure 2D is a diagram showing the internal structure of the boom 21 in Figure 2B by dotted lines. Figure 3A is a side view of the boom 21. Figure 3B is a top view of the boom 21. Figure 3C is a bottom view of the boom 21. Figures 4A and 4B are exploded perspective views of the boom 21.

As shown in FIG. 2A, the boom 21 has a base end 31, a boom body 32, and a tip end 33. The base end 31 and the boom body 32 are joined by welding at a dividing portion 34. The tip end 33 and the boom body 32 are joined by welding at a dividing portion 35. The dividing portions 34 and 35 will be described later.

(Base end portion 31)
The base end 31 is disposed at the end of the base end side of the boom body 32. The base end 31 is rotatably supported by a bracket of the revolving frame 13 via a boom pin 21a (see FIG. 1). As shown in FIGS. 3A and 4C, the base end 31 is substantially triangular in side view. The base end 31 narrows in the vertical direction as it moves away from the boom body 32. As shown in FIGS. 2B and 2C, the base end 31 has an upper surface 41, a lower surface 42, and a pair of side surfaces 43. As shown in FIG. 3A, the widths of the upper surface 41 and the lower surface 42 narrow as it moves away from the boom body 32. The left side surface 43 is disposed between the left end of the upper surface 41 and the left end of the lower surface 42. The right side surface 43 is disposed between the right end of the upper surface 41 and the right end of the lower surface 42.

As shown in FIG. 2B, the base end 31 has a rotating body mounting part 44 that is attached to the upper rotating body 3 at the tip opposite the boom main body part 32. The rotating body mounting part 44 has a boom pin hole 44a into which the boom pin 21a is inserted. The boom pin hole 44a is provided on each of the pair of side surfaces 43. The boom pin hole 44a is formed along the left-right direction.

(Tip portion 33)
As shown in FIG. 2A, the tip portion 33 is disposed at the end of the tip side of the boom main body portion 32. The base end portion of the arm 22 is rotatably attached to the tip portion 33 via the arm pin 22a (see FIG. 1). As shown in FIG. 2A and FIG. 2C, the tip portion 33 has a main body portion 45 and a pair of plate-shaped protruding portions 46 protruding from the main body portion 45 toward the arm 22 side. The pair of protruding portions 46 are disposed on the left side surface and the right side surface of the main body portion 45. The pair of protruding portions 46 are disposed at a predetermined interval in the left-right direction. Each of the protruding portions 46 has an arm pin hole 46a into which the arm pin 22a is inserted along the left-right direction. The main body portion 45 is disposed between the pair of protruding portions 46. The upper surface 47 (FIG. 2A) and the lower surface 48 (FIG. 2C) are disposed substantially parallel to each other. The tip surface 49 is disposed between the end of the upper surface 47 opposite the boom main body portion 32 and the end of the lower surface 48 opposite the boom main body portion 32.

The base end of the arm 22 is positioned between the pair of protrusions 46. The arm pin 22a is inserted into the arm pin hole 46a of the left protrusion 46, the base end of the arm 22, and the arm pin hole 46a of the right protrusion 46. This allows the arm 22 to be rotatably attached to the boom 21.

(Boom main body 32)
As shown in Figs. 2A and 2C, the boom body 32 has an upper plate 51, a lower plate 52, and a pair of left and right side plates 53. The pair of side plates 53 are arranged at a predetermined interval in the left-right direction. The pair of side plates 53 are arranged to face each other. The left end of the upper plate 51 is joined by welding to the upper end of the left side plate 53. As a result, as shown in Fig. 2A, a left upper corner weld line 54 (an example of a weld line formed at a corner) is formed at the corner between the left end of the upper plate 51 and the upper end of the left side plate 53. The right end of the upper plate 51 is joined by welding to the upper end of the right side plate 53. As a result, a right upper corner weld line 55 (an example of a weld line formed at a corner) is formed at the corner between the right end of the upper plate 51 and the upper end of the right side plate 53. As shown in Fig. 2C, the left end of the lower plate 52 is joined by welding to the lower end of the left side plate 53. As a result, a left lower corner weld line 56 (an example of a weld line formed at a corner) is formed at the corner between the left end of the lower plate 52 and the lower end of the left side plate 53. The right end of the lower plate 52 is joined to the lower end of the right side plate 53 by welding. As a result, a right lower corner weld line 57 (an example of a weld line formed at a corner) is formed at the corner between the right end of the lower plate 52 and the lower end of the right side plate 53. In this way, the upper plate 51, the lower plate 52, and the pair of side plates 53 are arranged in a cylindrical shape. Note that fillet welding or V-groove welding is used for welding the above-mentioned corners.

As shown in FIG. 2A, the boom main body 32 further has a curved portion 61, a boom cylinder attachment portion 62, and an arm cylinder attachment portion 63. The curved portion 61 is disposed approximately in the center of both ends of the boom main body 32 in a side view. As shown in FIG. 3A, the boom main body 32 is curved so that the curved portion 61 protrudes upward in a side view.

As shown in FIG. 2A, the boom cylinder attachment portion 62 is provided on the curved portion 61 of the side plate 53. The boom cylinder attachment portion 62 has a through hole 62a formed along the left-right direction. The through hole 62a is formed in each of the pair of left and right side plates 53. A shaft 64 (see FIG. 1) is inserted into the through hole 62a, and the tip of the rod of the boom cylinder 24 is attached to the shaft 64.

The arm cylinder mounting portion 63 is disposed closer to the tip portion 33 than the curved portion 61. The arm cylinder mounting portion 63 is disposed on the upper plate 51. The arm cylinder mounting portion 63 has a pair of plate-shaped brackets 63a. The brackets 63a are disposed facing each other in the left-right direction. Each bracket 63a has a through hole 63b that penetrates in the left-right direction. The arm cylinder 25 is disposed between the pair of brackets 63a. The arm pin 22a (see Figure 1) is inserted into the through hole 63b of the left bracket 63a, the arm cylinder 25, and the through hole 63b of the right bracket 63a. This allows the arm cylinder 25 to be rotatably attached to the arm cylinder mounting portion 63.

As shown in Figures 4A to 4C, the boom main body 32 is configured by joining three divided sections in the longitudinal direction. The boom main body 32 has a boom main body base end 65 (an example of a second boom section), a boom main body intermediate section 66 (an example of a first boom section), and a boom main body tip section 67 (an example of a third boom section). The tip end 65a of the boom main body base end 65 and the base end end 66a of the boom main body intermediate section 66 are joined by welding at a dividing section 68. The tip end 66b of the boom main body intermediate section 66 and the base end end 67a of the boom main body tip section 67 are joined by welding at a dividing section 69.

As described above, the boom 21 is curved at the curved portion 61, so the longitudinal direction of the boom 21 is different before and after the curved portion 61 in the side view of FIG. 3A. In the side view, on the base end 31 side of the curved portion 61, the direction along the straight line connecting the boom pin hole 44a of the base end 31 and the through hole 62a of the boom main body 32 is the longitudinal direction La, and on the tip end 33 side of the curved portion 61, the direction along the straight line connecting the through hole 62a of the boom main body 32 and the arm pin hole 46a of the tip end 33 is the longitudinal direction Lb.

Since the boom body 32 is divided into three parts, the upper plate 51, lower plate 52 and pair of side plates 53 described above are also divided into three parts.

As shown in Figures 3B, 4A, and 4B, the upper plate 51 is formed by joining an upper plate portion 71 of the boom body base end 65, an upper plate portion 72 of the boom body middle portion 66, and an upper plate portion 73 of the boom body tip portion 67 by welding. As shown in Figure 3B, the upper plate 51 has a weld line 81 (an example of a first weld line) formed between the upper plate portions 71 and 72, and a weld line 84 (an example of a first weld line) formed between the upper plate portions 72 and 73.

As shown in Figures 3C and 4C, the lower plate 52 is formed by joining a lower plate portion 74 of the boom body base end 65, a lower plate portion 75 of the boom body middle portion 66, and a lower plate portion 76 of the boom body tip portion 67 by welding. The lower plate 52 has a weld line 82 (an example of a first weld line or an example of a second weld line) formed between the lower plate portion 74 and the lower plate portion 75, and a weld line 85 (an example of a first weld line or an example of a second weld line) formed between the lower plate portion 75 and the lower plate portion 76.

As shown in Figures 3A, 4A, and 4B, each of the pair of side plates 53 is formed by joining a side plate portion 77 of the boom body base end 65, a side plate portion 78 of the boom body middle portion 66, and a side plate portion 79 of the boom body tip portion 67 by welding. The side plate 53 has a weld line 83 (an example of a side plate weld line) formed between the side plate portions 77 and 78, and a weld line 86 (an example of a side plate weld line) formed between the side plate portions 78 and 79.

The boom main body 32 has reinforcing plates 101-104, as shown in FIG. 2D. The reinforcing plates 101-104 reinforce the rigidity of the boom 21. Each of the reinforcing plates 101-104 is rectangular. As shown in FIG. 2D, the reinforcing plates 101-104 are disposed in an internal space surrounded by the upper plate 51, lower plate 52, and pair of side plates 53 described above. The reinforcing plates 101-104 are welded to the upper plate 51, lower plate 52, and pair of side plates 53.

The reinforcing plate 101 is disposed near the dividing section 34. The reinforcing plate 101 is disposed in the internal space of the boom body base end 65. The reinforcing plate 102 is disposed near the dividing section 68, in the internal space of the boom body middle section 66. The reinforcing plate 103 is disposed near the dividing section 69, in the internal space of the boom body middle section 66. The reinforcing plate 104 is disposed near the dividing section 35. The reinforcing plate 104 is disposed in the internal space of the boom body tip section 67.

(Splitting unit 68)
Fig. 5A is a diagram showing a separated state before the boom main body base end portion 65 and the boom main body intermediate portion 66 are joined by welding at the separation portion 68 in Fig. 2B. Fig. 5B is a diagram showing a state in which the boom main body base end portion 65 and the boom main body intermediate portion 66 shown in Fig. 5A have been welded together.

At the dividing section 68, the end 65a of the boom body base end 65 and the end 66a of the boom body middle section 66 are welded by butt welding. As shown in FIG. 5A, the end 65a has an end 71a on the tip 33 side of the upper plate 71, an end 74a on the tip 33 side of the lower plate 74, ends 77a on the tip 33 side of the pair of side plate sections 77, ends 77e on the upper plate section 71 side at the end on the tip 33 side of the pair of side plate sections 77, and both ends 74e in the width direction of the end on the tip 33 side of the lower plate section 74.

The end 66a has an end 72a on the base end 31 side of the upper plate portion 72, an end 75a on the base end 31 side of the lower plate portion 75, ends 78a on the base end 31 side of the pair of side plate portions 78, ends 78e on the base end 31 side of the pair of side plate portions 78 on the lower plate portion 75 side, and both ends 72e in the width direction of the end of the upper plate portion 72 on the base end 31 side.

As shown in Figures 5A and 5B, the weld line 81 is formed by joining the end 71a of the upper plate portion 71 and the end 72a of the upper plate portion 72 by butt welding. The ends 71a and 72a are formed into shapes that correspond to each other so as to define the shape of the weld line 81, which will be described later.

As shown in Figures 5A and 5B, the weld line 82 is formed by joining the end 74a of the lower plate portion 74 and the end 75a of the lower plate portion 75 by butt welding. The ends 74a and 75a are formed into shapes that correspond to each other so as to define the shape of the weld line 82, which will be described later.

As shown in Figures 5A and 5B, each of the pair of weld lines 83 is formed by joining ends 77a of a pair of side plate portions 77 and ends 78a of a pair of side plate portions 78 by butt welding. Ends 77a and 78a are formed into shapes that correspond to each other so as to define the shape of weld line 83, which will be described later.

In addition, the ends 77e of the pair of side plate portions 77 are welded to both ends 72e of the upper plate portion 72. The ends 78e of the pair of side plate portions 78 are welded to both ends 74e of the lower plate portion 74.

As shown in FIG. 5A, before the boom body base end 65 and the boom body intermediate section 66 are welded together, a backing material 100 is placed on one of the ends. In the example shown in FIG. 5A, the backing material 100 is placed on the ends 71a, 77a of the boom body base end 65 and the end 75a of the boom body intermediate section 66. The backing material 100 is placed inside the ends 71a, 77a, 75a. The backing material 100 protrudes from each of the ends 71a, 77a, 75a toward the opposing ends 72a, 78a, 74a.

FIG. 6A is a diagram showing butt welding. In FIG. 6A, ends 71a and 72a are shown, but welding between the other ends is similar. As shown in FIG. 6A, end 72a is arranged on the backing material 100 protruding from end 71a with a predetermined distance between it and end 71a. Ends 71a and 72a are then welded together. This forms a weld line 81. Similarly, by welding between end 75a and end 74a, between left end 77a and end 78a, and between right end 77a and end 78a, the boom body base end 65 and the boom body middle portion 66 can be joined together as shown in FIG. 5A.

(weld line 81)
7A is an enlarged view of the V1 portion in FIG. 3B. The weld line 81 in the division portion 68 is formed symmetrically. The weld line 81 includes a pair of inclined portions 811, 812, a straight portion 813 (an example of a first straight portion), and a pair of curved portions 814, 815. The inclined portion 811 is formed from the upper left corner weld line 54 toward the right direction (inward in the width direction). The inclined portion 811 is linear. The inclined portion 811 is formed inclined with respect to the short direction (left-right direction, width direction) perpendicular to the longitudinal direction La. The inclined portion 811 is inclined toward the base end portion 31 as it moves toward the right direction. In this specification, the term "vertical" does not indicate a strict meaning, but includes an error and includes a range that is recognized as vertical in social terms.

The inclined portion 812 is formed from the upper right corner weld line 55 toward the left (inward in the width direction). The inclined portion 812 is linear. The inclined portion 812 is formed at an angle with respect to the short direction (left-right direction, width direction) perpendicular to the longitudinal direction La. The inclined portion 812 is inclined toward the base end portion 31 as it extends toward the left.

Straight portion 813 is disposed between inclined portion 811 and inclined portion 812. Straight portion 813 is disposed in the center between upper left corner weld line 54 and upper right corner weld line 55. Straight portion 813 is disposed perpendicular to the longitudinal direction La.

The curved portion 814 is disposed between the inclined portion 811 and the straight portion 813. The curved portion 814 connects the right end of the inclined portion 811 and the left end of the straight portion 813. The curved portion 814 is curved convexly toward the base end portion 31.

The curved portion 815 is disposed between the inclined portion 812 and the straight portion 813. The curved portion 815 connects the left end of the inclined portion 812 and the right end of the straight portion 813. The curved portion 815 is curved convexly toward the base end portion 31.

As described above, a weld line 81 is formed between the upper plate portion 71 and the upper plate portion 72.

(Weld line 82)
7B is an enlarged view of the V2 portion of FIG. 3C. The weld line 82 in the division portion 68 is formed symmetrically. The weld line 82 includes a pair of inclined portions 821, 822, a straight portion 823, and a pair of curved portions 824, 825. The inclined portion 821 is formed from the lower left corner weld line 56 toward the right (inward in the width direction). The inclined portion 821 is linear. The inclined portion 821 is formed at an incline with respect to the short direction (left-right direction, width direction) perpendicular to the longitudinal direction La. The inclined portion 821 is inclined toward the base end portion 31 as it goes rightward.

The inclined portion 822 is formed from the lower right corner weld line 57 toward the left (inward in the width direction). The inclined portion 822 is linear. The inclined portion 822 is formed at an angle with respect to the short direction (left-right direction, width direction) perpendicular to the longitudinal direction La. The inclined portion 822 is inclined toward the base end portion 31 as it extends toward the left.

Straight portion 823 is disposed between inclined portion 821 and inclined portion 822. Straight portion 823 is disposed in the center between upper left corner weld line 54 and upper right corner weld line 55. Straight portion 823 is disposed perpendicular to the longitudinal direction La.

The curved portion 824 is disposed between the inclined portion 821 and the straight portion 823. The curved portion 824 connects the right end of the inclined portion 821 and the left end of the straight portion 823. The curved portion 824 is curved convexly toward the base end portion 31.

The curved portion 825 is disposed between the inclined portion 822 and the straight portion 823. The curved portion 825 connects the left end of the inclined portion 822 and the right end of the straight portion 823. The curved portion 825 is curved convexly toward the base end portion 31.

As described above, a weld line 82 is formed between the lower plate portion 74 and the lower plate portion 75.

As shown in FIG. 5A, the end 72a of the upper plate portion 72 is positioned closer to the tip portion 33 than the end 75a of the lower plate portion 75, and therefore, as shown in FIG. 5B, the weld line 82 is located closer to the tip portion 33 than the weld line 81.

(weld line 83)
Fig. 7C is an enlarged view of part V3 in Fig. 3A. Fig. 7C shows the weld line 83 of the left side plate 53, but the weld line 83 of the right side plate 53 is formed in the same manner. The left weld line 83 and the right weld line 83 face each other in the width direction. The left weld line 83 and the right weld line 83 are formed symmetrically with respect to the central axis passing through the center in the width direction. The weld line 83 in the division portion 68 has a straight portion 831 (an example of a second straight portion), an inclined portion 832, and a curved portion 833.

The straight portion 831 is disposed from the lower left corner weld line 56 toward the upper left corner weld line 54. The straight portion 831 is disposed perpendicular to the longitudinal direction La. The inclined portion 832 is formed from the upper left corner weld line 54 toward the lower left corner weld line 56. The inclined portion 832 is inclined in a direction perpendicular to the longitudinal direction La. The inclined portion 832 is a straight line. The inclined portion 832 is inclined toward the tip portion 33 as it approaches the lower left corner weld line 56.

The curved portion 833 is disposed between the straight portion 831 and the inclined portion 832. The curved portion 833 connects the end of the straight portion 831 on the side of the upper left corner weld line 54 to the end of the inclined portion 832 on the side of the lower left corner weld line 56. The curved portion 833 is curved so as to protrude toward the tip portion 33.

As shown in FIG. 5B, if the position where the weld line 81 intersects with the upper left corner weld line 54 is P1, and the position where the left side weld line 83 intersects with the upper left corner weld line 54 is P2, then position P1 is offset from position P2. In the direction along the upper left corner weld line 54, position P1 is located closer to the base end 31 than position P2. If the position where the weld line 82 intersects with the lower left corner weld line 56 is P3, and the position where the weld line 83 intersects with the lower left corner weld line 56 is P4, then position P3 is offset from position P4. In the direction along the lower left corner weld line 56, position P3 is located closer to the tip end 33 than position P4.

If the position where the weld line 81 intersects with the upper right corner weld line 55 is P1', and the position where the right side weld line 83 intersects with the upper right corner weld line 55 is P2', then position P1' is offset from position P2'. In the direction along the upper right corner weld line 55, position P1' is located closer to the base end 31 than position P2'. If the position where the weld line 82 intersects with the lower right corner weld line 57 is P3', and the position where the weld line 83 intersects with the lower right corner weld line 57 is P4', then position P3' is offset from position P4'. In the direction along the lower right corner weld line 57, position P3' is located closer to the tip end 33 than position P4'.

Also, as shown in FIG. 7C, in the longitudinal direction La, the left weld line 83 is disposed between positions P1 and P3. Similarly, in the longitudinal direction La, the right weld line 83 is disposed between positions P1' and P3'.

(Dividing unit 69)
Fig. 8A is a diagram showing a separated state before the boom main body tip portion 67 and the boom main body intermediate portion 66 are joined by welding at the separation portion 69 in Fig. 2B. Fig. 8B is a diagram showing a state in which the boom main body tip portion 67 and the boom main body intermediate portion 66 shown in Fig. 8A have been welded together.

In the dividing section 69, the end 67a of the boom body tip 67 and the end 66b of the boom body middle section 66 are welded by butt welding. As shown in FIG. 8A, the end 65a has an end 72b on the tip 33 side of the upper plate 72, an end 75b on the tip 33 side of the lower plate 75, ends 78b on the tip 33 side of the pair of side plate sections 78, ends 78f on the upper plate section 72 side of the end on the tip 33 side of the pair of side plate sections 78, and both ends 75f in the width direction of the end on the tip 33 side of the lower plate section 75.

The end 67a has an end 73a on the base end 31 side of the upper plate portion 73, an end 76a on the base end 31 side of the lower plate portion 76, ends 79a on the base end 31 side of the pair of side plate portions 79, ends 79e on the base end 31 side of the pair of side plate portions 79 on the lower plate portion 76 side, and both ends 73e in the width direction of the end of the upper plate portion 73 on the base end 31 side.

As shown in Figures 8A and 8B, the weld line 84 is formed by joining the end 72b of the upper plate portion 72 and the end 73a of the upper plate portion 73 by butt welding. The ends 72b and 73a are formed into shapes that correspond to each other so as to define the shape of the weld line 84, which will be described later.

As shown in Figures 8A and 8B, the weld line 85 is formed by joining the end 75b of the lower plate portion 75 and the end 76a of the lower plate portion 76 by butt welding. The ends 75b and 76a are formed into shapes that correspond to each other so as to define the shape of the weld line 85, which will be described later.

As shown in Figures 8A and 8B, the pair of weld lines 86 are formed by joining ends 77b of a pair of side plate portions 77 and ends 79a of a pair of side plate portions 79 by butt welding. Ends 77a and 79a are formed into shapes that correspond to each other so as to define the shape of weld line 83, which will be described later.

In addition, ends 78f of the pair of side plate portions 77 are welded to both ends 73e of the upper plate portion 73. Ends 79e of the pair of side plate portions 79 are welded to both ends 75f of the lower plate portion 75.

In the example shown in FIG. 8A, a backing material 100 is disposed at end 72b of the boom body middle section 66, end 76a of the boom body tip section 67, and a pair of ends 79a. The backing material 100 is disposed inside ends 72b, 76a, and 79a. The backing material 100 protrudes from each of ends 72b, 76a, and 79a toward the opposing ends 73a, 75b, and 78a. Each butt weld is similar to the structure described in FIG. 6, so a description thereof will be omitted.

(Weld line 84)
9A is an enlarged view of the V4 portion in FIG. 3B. The weld line 84 in the division portion 69 is formed symmetrically. The weld line 84 includes a pair of inclined portions 841, 842, a straight portion 843, and a pair of curved portions 844, 845. The inclined portion 841 is formed from the upper left corner weld line 54 toward the right direction (inward in the width direction). The inclined portion 841 is linear. The inclined portion 841 is formed at an incline with respect to the short side direction (left-right direction) perpendicular to the longitudinal direction Lb. The inclined portion 841 is inclined toward the tip portion 33 as it goes rightward.

The inclined portion 842 is formed from the upper right corner weld line 55 toward the left (inward in the width direction). The inclined portion 842 is linear in plan view. The inclined portion 842 is formed at an angle with respect to the short direction (left-right direction) perpendicular to the longitudinal direction Lb. The inclined portion 842 is inclined toward the tip portion 33 as it extends toward the left.

Straight portion 843 is disposed between inclined portion 841 and inclined portion 842. Straight portion 843 is disposed in the center between upper left corner weld line 54 and upper right corner weld line 55. Straight portion 843 is disposed perpendicular to longitudinal direction Lb.

The curved portion 844 is disposed between the inclined portion 841 and the straight portion 843. The curved portion 844 connects the right end of the inclined portion 841 and the left end of the straight portion 843. The curved portion 844 is curved convexly toward the tip portion 33.

The curved portion 845 is disposed between the inclined portion 842 and the straight portion 843. The curved portion 845 connects the left end of the inclined portion 842 and the right end of the straight portion 843. The curved portion 845 is curved convexly toward the tip portion 33.

As described above, a weld line 84 is formed between the upper plate portion 72 and the upper plate portion 73.

(weld line 85)
Fig. 9B is an enlarged view of part V5 in Fig. 3C. The weld line 85 in the division part 69 is formed symmetrically. The weld line 85 includes a pair of inclined parts 851, 852, a straight part 853, and a pair of curved parts 854, 855. The inclined part 851 is formed from the lower left corner weld line 56 toward the right direction (inward in the width direction).

The inclined portion 851 is linear. The inclined portion 851 is formed at an incline in the short direction (left-right direction) perpendicular to the longitudinal direction Lb. The inclined portion 851 is inclined toward the tip portion 33 as it extends to the right.

The inclined portion 852 is formed from the lower right corner weld line 57 toward the left (inward in the width direction). The inclined portion 852 is linear. The inclined portion 852 is formed at an angle with respect to the short direction (left-right direction) perpendicular to the longitudinal direction Lb. The inclined portion 852 is inclined toward the tip portion 33 as it extends toward the left.

Straight portion 853 is disposed between inclined portion 851 and inclined portion 852. Straight portion 853 is disposed in the center between lower left corner weld line 56 and lower right corner weld line 57. Straight portion 853 is disposed perpendicular to the longitudinal direction Lb.

The curved portion 854 is disposed between the inclined portion 851 and the straight portion 853. The curved portion 854 connects the right end of the inclined portion 851 and the left end of the straight portion 853. The curved portion 854 is curved so as to protrude toward the tip portion 33.

The curved portion 855 is disposed between the inclined portion 852 and the straight portion 853. The curved portion 855 connects the left end of the inclined portion 852 and the right end of the straight portion 853. The curved portion 855 is curved convexly toward the tip portion 33.

As described above, a weld line 85 is formed between the lower plate portion 75 and the lower plate portion 76.

As shown in Figures 8A and 8B, the end 72b of the upper plate portion 72 is positioned closer to the base end portion 31 than the end 75b of the lower plate portion 75, so the weld line 84 is located closer to the base end portion 31 than the weld line 85.

(weld line 86)
Fig. 9C is an enlarged view of part V6 in Fig. 3A. Fig. 9C shows the weld line 86 of the left side plate 53, but the weld line 86 of the right side plate 53 is formed in the same manner. The weld line 86 of the left side and the weld line 86 of the right side face each other in the width direction. The weld line 86 of the left side and the weld line 86 of the right side are formed symmetrically with respect to the central axis passing through the center in the width direction. The weld line 86 in the division portion 69 has a straight portion 861, an inclined portion 862, and a curved portion 863.

The straight portion 861 is disposed from the upper left corner weld line 54 toward the lower left corner weld line 56. The straight portion 861 is disposed perpendicular to the longitudinal direction Lb. The inclined portion 862 is formed from the lower left corner weld line 56 toward the upper left corner weld line 54. The inclined portion 862 is inclined with respect to the direction perpendicular to the longitudinal direction Lb. The inclined portion 862 is a straight line. The inclined portion 862 is inclined toward the base end portion 31 as it approaches the lower left corner weld line 56.

The curved portion 863 is disposed between the straight portion 861 and the inclined portion 862. The curved portion 863 connects the end of the straight portion 861 on the side of the lower left corner weld line 56 to the end of the inclined portion 862 on the side of the upper left corner weld line 54. The curved portion 833 is curved so as to protrude toward the base end portion 31.

As shown in FIG. 8B, if the position where the weld line 84 intersects with the upper left corner weld line 54 is P5, and the position where the weld line 86 on the left side intersects with the upper left corner weld line 54 is P6, then position P5 is offset from position P6. In the direction along the upper left corner weld line 54, position P5 is located closer to the base end 31 than position P6. If the position where the weld line 85 intersects with the lower left corner weld line 56 is P7, and the position where the weld line 86 intersects with the lower left corner weld line 56 is P8, then position P7 is offset from position P8. In the direction along the lower left corner weld line 56, position P7 is located closer to the tip end 33 than position P8.

If the position where the weld line 84 intersects with the upper right corner weld line 55 is P5', and the position where the weld line 86 on the right side intersects with the upper right corner weld line 55 is P6', then position P5' is offset from position P6'. In the direction along the upper right corner weld line 55, position P5' is located closer to the base end 31 than position P6'. If the position where the weld line 85 intersects with the lower right corner weld line 57 is P7', and the position where the weld line 86 intersects with the lower right corner weld line 57 is P8', then position P7' is offset from position P8'. In the direction along the lower right corner weld line 57, position P7' is located closer to the tip end 33 than position P8'.

Also, as shown in FIG. 9C, in the longitudinal direction Lb, the weld line 86 on the left side surface is disposed between positions P5 and P7. Similarly, in the longitudinal direction Lb, the weld line 86 on the right side surface is disposed between positions P5' and P7'.

(Splitting unit 34)
Fig. 10A is a perspective view showing a separated state before the base end portion 31 and the boom main body base end portion 65 are joined by welding. Fig. 10B is a perspective view showing a state in which the base end portion 31 and the boom main body base end portion 65 shown in Fig. 10A are welded together.

By welding the base end 31 and the boom body base end 65 at the dividing section 34, weld lines 91, 92, and 93 are formed.

As shown in Figures 10A and 10B, the weld line 91 is formed by joining the end 71b of the upper plate portion 71 on the base end portion 31 side to the end 41a of the upper surface 41 of the base end portion 31 by butt welding. The ends 71b and 41a are formed into shapes that correspond to each other so as to define the shape of the weld line 91, which will be described later.

As shown in Figures 10A and 10B, the weld line 92 is formed by joining the end 74b on the base end 31 side of the lower plate portion 74 and the end 42a on the tip end 33 side of the lower surface 42 by butt welding. The ends 74b and 42a are formed into shapes that correspond to each other so as to define the shape of the weld line 92, which will be described later.

As shown in Figures 10A and 10B, each of the pair of weld lines 93 is formed by joining the end 77b on the base end 31 side of the side plate portion 77 and the end 43a on the tip end 33 side of the side surface 43 by butt welding. The ends 77b and 43a are formed into shapes that correspond to each other so as to define the shape of the weld line 93 described below.

In the example shown in FIG. 10A, a backing material 100 is disposed at ends 71b, 74b of the boom body 32. The backing material 100 is disposed inside ends 71b, 74b. The backing material 100 protrudes from each of ends 71b, 74b toward the opposing ends 41a, 42a. Each butt weld is similar to the structure described in FIG. 6, so a description thereof will be omitted.

(weld line 91)
Fig. 11A is an enlarged view of portion V7 in Fig. 3B. The weld line 91 in the dividing portion 34 is formed symmetrically. The weld line 91 includes a pair of inclined portions 911, 912, a straight portion 913 (an example of a fourth straight portion), and a pair of curved portions 914, 915.

The inclined portion 911 is formed from the end of the upper left corner weld line 54 on the base end 31 side toward the right (inward in the width direction). The inclined portion 911 is linear. The inclined portion 911 is formed at an angle with respect to the short direction (left-right direction) perpendicular to the longitudinal direction La. The inclined portion 911 is inclined toward the tip end 33 as it extends toward the right.

The inclined portion 912 is formed from the end of the upper right corner weld line 55 on the base end portion 31 side toward the left (inward in the width direction). The inclined portion 912 is linear. The inclined portion 912 is formed at an angle with respect to the short side direction (left-right direction) perpendicular to the longitudinal direction La. The inclined portion 912 is inclined toward the tip end portion 33 as it extends toward the left.

The straight portion 913 is disposed between the inclined portion 911 and the inclined portion 912. The straight portion 913 is disposed in the center between the upper left corner weld line 54 and the upper right corner weld line 55. The straight portion 913 is disposed perpendicular to the longitudinal direction La.

The curved portion 914 is disposed between the inclined portion 911 and the straight portion 913. The curved portion 914 connects the right end of the inclined portion 911 and the left end of the straight portion 913. The curved portion 914 is curved convexly toward the tip portion 33.

The curved portion 915 is disposed between the inclined portion 912 and the straight portion 913. The curved portion 915 connects the left end of the inclined portion 912 and the right end of the straight portion 913. The curved portion 915 is curved convexly toward the tip portion 33.

As described above, a weld line 91 is formed between the upper plate portion 71 and the upper surface 41.

(Weld line 92)
Fig. 11B is an enlarged view of portion V8 in Fig. 3C. The welding line 92 in the dividing portion 34 is formed symmetrically. The welding line 92 includes a pair of inclined portions 921, 922, a straight portion 923 (an example of a fourth straight portion), and a pair of curved portions 924, 925.

The inclined portion 921 is formed from the end of the lower left corner weld line 56 on the base end 31 side toward the right (inward in the width direction). The inclined portion 921 is linear. The inclined portion 921 is formed at an angle with respect to the short direction (left-right direction) perpendicular to the longitudinal direction La. The inclined portion 921 is inclined toward the tip end 33 as it extends toward the right.

The inclined portion 922 is formed from the end of the lower right corner weld line 57 on the base end 31 side toward the left (inward in the width direction). The inclined portion 922 is linear. The inclined portion 922 is formed at an angle with respect to the short direction (left-right direction) perpendicular to the longitudinal direction La. The inclined portion 922 is inclined toward the tip end 33 as it extends toward the left.

Straight portion 923 is disposed between inclined portion 921 and inclined portion 922. Straight portion 923 is disposed in the center between lower left corner weld line 56 and lower right corner weld line 57. Straight portion 923 is disposed perpendicular to the longitudinal direction La.

The curved portion 924 is disposed between the inclined portion 921 and the straight portion 923. The curved portion 924 connects the right end of the inclined portion 921 and the left end of the straight portion 923. The curved portion 924 is curved so as to protrude toward the tip portion 33.

The curved portion 925 is disposed between the inclined portion 922 and the straight portion 923. The curved portion 925 connects the left end of the inclined portion 922 and the right end of the straight portion 923. The curved portion 925 is curved convexly toward the tip portion 33.

As described above, a weld line 92 is formed between the lower plate portion 74 and the lower surface 42.

(weld line 93)
Fig. 11C is an enlarged view of part V9 in Fig. 3C. Fig. 11C shows the weld line 93 of the left side plate portion 77, but the weld line 93 of the right side plate portion 77 is formed in the same manner. The left weld line 93 and the right weld line 93 face each other in the width direction. The left weld line 93 and the right weld line 93 are formed symmetrically with respect to a central axis passing through the center in the width direction. The weld line 93 in the division portion 34 has a pair of curved portions 931, 932 and a straight portion 933.

The curved portion 931 is disposed from the end of the upper left corner weld line 54 on the base end 31 side toward the lower left corner weld line 56. The curved portion 931 is curved so as to protrude toward the base end 31 side. The curved portion 932 is disposed from the end of the lower left corner weld line 56 on the base end 31 side toward the upper left corner weld line 54. The curved portion 932 is curved so as to protrude toward the base end 31 side.

The straight portion 933 is disposed perpendicular to the longitudinal direction La. The straight portion 933 is disposed between the curved portion 931 and the curved portion 932. The straight portion 933 connects the end of the curved portion 931 on the side of the lower left corner weld line 56 and the end of the curved portion 932 on the side of the upper left corner weld line 54.

The left end of the weld line 91 is connected to the end of the left weld line 93 on the upper plate portion 71 side, and the end of the left weld line 93 on the lower plate portion 74 side is connected to the left end of the weld line 92. The right end of the weld line 91 is connected to the end of the right weld line 93 on the upper plate portion 71 side, and the end of the right weld line 93 on the lower plate portion 74 side is connected to the right end of the weld line 92.

(Splitting unit 35)
Fig. 12A is a perspective view showing a separated state before the tip portion 33 and the boom main body tip portion 67 are joined by welding. Fig. 12B is a perspective view showing a state in which the tip portion 33 and the boom main body tip portion 67 shown in Fig. 12A are welded together.

By welding the tip 33 and the boom body tip 67 at the dividing section 35, a weld line 94, a weld line 95, and a pair of weld lines 96 are formed.

As shown in Figures 12A and 12B, the weld line 94 is formed by joining the end 73b of the upper plate portion 73 on the tip portion 33 side to the end 47a of the upper surface 47 of the tip portion 33 by butt welding. The ends 73b and 47a are formed into shapes that correspond to each other so as to define the shape of the weld line 94, which will be described later.

As shown in Figures 12A and 12B, the weld line 95 is formed by butt welding the end 76b on the tip end 33 side of the lower plate portion 76 to the end 48a on the base end 31 side of the underside 48 of the tip end 33. The ends 76b and 48a are formed in shapes that correspond to each other so as to define the shape of the weld line 95, which will be described later.

As shown in Figures 12A and 12B, each of the pair of weld lines 96 is formed by joining the end 79b on the tip end 33 side of the side plate portion 79 and the end 46b on the base end 31 side of the protrusion 46 by butt welding. The ends 79b and 46b are formed into shapes that correspond to each other so as to define the shape of the weld line 96 described below.

In the example shown in FIG. 12A, a backing material 100 is disposed at ends 73b, 76b of the boom body 32. The backing material 100 is disposed inside ends 73b, 76b. The backing material 100 protrudes from each of ends 73b, 76b toward the opposing ends 47a, 48a. Each butt weld is similar to the structure described in FIG. 6, so a description thereof will be omitted.

(Weld line 94)
Fig. 13A is an enlarged view of portion V10 in Fig. 3B. The weld line 94 in the division portion 35 is formed symmetrically. The weld line 94 includes a pair of inclined portions 941, 942, a straight portion 943, and a pair of curved portions 944, 945.

The inclined portion 941 is formed from the end of the upper left corner weld line 54 on the tip end 33 side toward the right (inward in the width direction). The inclined portion 941 is linear in a plan view. The inclined portion 941 is formed at an angle with respect to the short direction (left-right direction) perpendicular to the longitudinal direction Lb. The inclined portion 941 is inclined toward the base end 31 as it extends toward the right.

The inclined portion 942 is formed from the end of the upper right corner weld line 55 on the tip end 33 side toward the left (inward in the width direction). The inclined portion 942 is linear in a plan view. The inclined portion 942 is formed at an angle with respect to the short direction (left-right direction) perpendicular to the longitudinal direction Lb. The inclined portion 942 is inclined toward the base end 31 as it extends toward the left.

The straight portion 943 is disposed between the inclined portion 941 and the inclined portion 942. The straight portion 943 is disposed in the center between the upper left corner weld line 54 and the upper right corner weld line 55. The straight portion 943 is disposed perpendicular to the longitudinal direction Lb.

The curved portion 944 is disposed between the inclined portion 941 and the straight portion 943. The curved portion 944 connects the right end of the inclined portion 941 and the left end of the straight portion 943. The curved portion 944 is curved convexly toward the base end portion 31.

The curved portion 945 is disposed between the inclined portion 942 and the straight portion 943. The curved portion 945 connects the left end of the inclined portion 942 and the right end of the straight portion 943. The curved portion 945 is curved convexly toward the base end portion 31.

As described above, a weld line 94 is formed between the upper plate portion 73 and the upper surface 47.

(weld line 95)
Fig. 13B is an enlarged view of portion V11 in Fig. 3C. The weld line 95 in the division portion 35 is formed symmetrically. The weld line 95 includes a pair of inclined portions 951, 952, a straight portion 953, and a pair of curved portions 954, 955.

The inclined portion 951 is formed from the end of the left lower corner weld line 56 on the tip end 33 side toward the right (inward in the width direction). The inclined portion 951 is linear. The inclined portion 951 is formed at an angle with respect to the short direction (left-right direction) perpendicular to the longitudinal direction Lb. The inclined portion 951 is inclined toward the base end 31 as it extends toward the right.

The inclined portion 952 is formed from the end of the lower right corner weld line 57 on the tip end 33 side toward the left (inward in the width direction). The inclined portion 952 is linear. The inclined portion 952 is formed at an angle with respect to the short direction (left-right direction) perpendicular to the longitudinal direction Lb. The inclined portion 952 is inclined toward the base end 31 as it extends toward the left.

The straight portion 953 is disposed between the inclined portion 951 and the inclined portion 952. The straight portion 953 is disposed in the center between the lower left corner weld line 56 and the lower right corner weld line 57. The straight portion 953 is disposed perpendicular to the longitudinal direction Lb.

The curved portion 954 is disposed between the inclined portion 951 and the straight portion 953. The curved portion 954 connects the right end of the inclined portion 951 and the left end of the straight portion 953. The curved portion 954 is curved so as to protrude toward the base end portion 31.

The curved portion 955 is disposed between the inclined portion 952 and the straight portion 953. The curved portion 955 connects the left end of the inclined portion 952 and the right end of the straight portion 953. The curved portion 955 is curved so as to protrude toward the base end portion 31.

As described above, a weld line 95 is formed between the lower plate portion 76 and the lower surface 48.

(Weld line 96)
Fig. 13C is an enlarged view of part V12 in Fig. 3A. Fig. 13C shows the weld line 96 of the left side plate 53, but the weld line 96 of the right side plate 53 is formed in the same manner. The weld line 96 of the left side and the weld line 96 of the right side face each other in the width direction. The weld line 96 of the left side and the weld line 96 of the right side are formed symmetrically with respect to the central axis passing through the center in the width direction. The weld line 96 in the division portion 35 has a pair of curved portions 961, 962 and a straight portion 963.

The curved portion 961 is disposed from the end of the upper left corner weld line 54 on the tip 33 side toward the lower left corner weld line 56. The curved portion 961 is curved so as to protrude toward the tip 33 side. The curved portion 962 is disposed from the end of the lower left corner weld line 56 on the tip 33 side toward the upper left corner weld line 54. The curved portion 962 is curved so as to protrude toward the tip 33 side.

The straight portion 963 is disposed perpendicular to the longitudinal direction Lb. The straight portion 963 is disposed between the curved portion 961 and the curved portion 962. The straight portion 963 connects the end of the curved portion 961 on the side of the lower left corner weld line 56 and the end of the curved portion 962 on the side of the upper left corner weld line 54.

As shown in FIG. 12B, the left end of weld line 94 is connected to the end of left weld line 96 on the upper plate portion 73 side, and the end of left weld line 96 on the lower plate portion 74 side is connected to the left end of weld line 95. The right end of weld line 94 is connected to the end of right weld line 96 on the upper plate portion 71 side, and the end of right weld line 96 on the lower plate portion 74 side is connected to the right end of weld line 95.

(Manufacturing method of the boom 21)
Next, a manufacturing method of the boom 21 will be described.

First, as shown in Figures 14(a) to (c), the first subunit 110, the second subunit 120, and the third subunit 130 are created. The first subunit 110 is formed by welding the boom body base end 65 and the base end 31 as shown in Figure 10B. As shown in Figure 10A, the reinforcing plate 101 is positioned near the opening formed by the ends 71b, 77b, 74b, and 77b, so that the reinforcing plate 101 can be welded to the upper plate portion 71, the lower plate portion 74, and the pair of side plate portions 77 through the opening.

The second subunit 120 is the boom body intermediate portion 66. As shown in FIG. 5A, the reinforcing plate 102 is disposed near the dividing portion 68, so that it can be welded to the upper plate portion 72, the lower plate portion 75, and the pair of side plate portions 78 through an opening formed in the end portion 66a. As shown in FIG. 8A, the reinforcing plate 103 is disposed near the dividing portion 69, so that it can be welded to the upper plate portion 72, the lower plate portion 75, and the pair of side plate portions 78 through an opening formed in the end portion 66b.

The third subunit 130 is formed by butt welding the boom body tip 67 to the tip 33 as shown in FIG. 12B. As shown in FIG. 12A, the reinforcing plate 104 is disposed near the dividing portion 35, so that the reinforcing plate 104 can be welded to the upper plate portion 73, the lower plate portion 76, and the pair of side plate portions 79 through the openings formed by the ends 73b, 79b, 76b, and 79b.

15A, the end 65a of the first subunit 110 is aligned with the end 66a of the second subunit 120. The first subunit 110 is moved upward relative to the second subunit 120 from below the second subunit 120. For example, with the second subunit 120 fixed, the end 65a of the first subunit 110 may be aligned with the end 66a of the second subunit 120 by rotating the end 65a side of the first subunit 110 upward around the boom pin hole 44a. Also, with the first subunit 110 fixed, the second subunit 120 may be hung and lowered toward the first subunit 110 to align the end 65a of the first subunit 110 with the end 66a of the second subunit 120. After the end 65a of the first subunit 110 and the end 66a of the second subunit 120 are aligned, the end 65a and the end 66a are butt-welded.

15B, the end 66b of the second subunit 120 and the end 67a of the third subunit 130 are aligned. The third subunit 130 is moved downward relative to the second subunit 120 from above the second subunit 120. For example, with the first subunit 110 and the second subunit 120 fixed, the end 67a of the third subunit 130 may be rotated downward around the arm pin hole 46a to align the end 67a of the third subunit 130 with the end 66b of the second subunit 120. Also, with the third subunit 130 fixed, the first subunit 110 and the second subunit 120 may be suspended and lifted toward the third subunit 130 to align the end 67a of the third subunit 130 with the end 66b of the second subunit 120. After the end 66b of the second subunit 120 and the end 67a of the third subunit 130 are aligned, the end 66b and the end 67a are butt-welded.

The boom 21 can be assembled as described above.

(Features, etc.)
In this embodiment, as shown in Fig. 7A, the weld line 81 has inclined portions 811 and 812 inclined with respect to a direction perpendicular to the longitudinal direction La, and as shown in Fig. 7B, the weld line 82 has inclined portions 821 and 822 inclined with respect to a direction perpendicular to the longitudinal direction La. As shown in Fig. 9A, the weld line 84 has inclined portions 841 and 842 inclined with respect to a direction perpendicular to the longitudinal direction Lb, and as shown in Fig. 9B, the weld line 85 has inclined portions 851 and 852 inclined with respect to a direction perpendicular to the longitudinal direction Lb.

The boom 21 is subjected to a principal stress parallel to the longitudinal direction, but the weld line of this embodiment has an inclined portion that is inclined relative to a direction perpendicular to the longitudinal direction, thereby improving durability. Fatigue cracks that occur in the boom 21 grow as fine cracks merge. Such fine cracks grow roughly perpendicular to the principal stress, but in this embodiment, the weld line is inclined relative to a direction perpendicular to the principal stress, which causes the fine cracks to shift and become less likely to merge. This makes it more difficult for fatigue cracks to grow, improving durability.

In this embodiment, weld line 81 has curved portions 814 and 815 as shown in FIG. 7A. Weld line 82 has curved portions 824 and 825 as shown in FIG. 7B. Weld line 84 has curved portions 844 and 845 as shown in FIG. 9A. Weld line 85 has curved portions 854 and 855 as shown in FIG. 9B.

By having a curved weld line like this, stress concentration is less likely to occur and durability can be improved.

In this embodiment, the weld lines 81 to 86 are formed by butt welding.

This improves durability. In this embodiment, as shown in FIG. 6A, the root S between the backing material 100 and the plate material (upper plate portion 71 and upper plate portion 72) is parallel to the direction in which the principal stress acts, and therefore does not act in the direction of opening the root S. On the other hand, as shown in FIG. 6B, in the case of fillet welding, the plate material 1001 and the plate material 1002 are joined via the member 1003, and therefore the root 1000S is perpendicular to the direction in which the principal stress acts. Therefore, the principal stress acts in the direction of opening the root 1000S. In this way, in the welding for joining the boom main body portion 32 in the longitudinal direction, the butt welding of this embodiment is advantageous in terms of durability.

In this embodiment, as shown in FIG. 7A, the inclined portion 811 is formed from the upper left corner weld line 54 formed at the corner between the upper plate 51 and the left side plate 53. The inclined portion 812 is formed from the upper right corner weld line 55 formed at the corner between the upper plate 51 and the right side plate 53. As shown in FIG. 7B, the inclined portion 821 is formed from the lower left corner weld line 56 formed at the corner between the lower plate 52 and the left side plate 53. The inclined portion 822 is formed from the lower right corner weld line 57 formed at the corner between the lower plate 52 and the right side plate 53. As shown in FIG. 9A, the inclined portion 841 is formed from the upper left corner weld line 54 formed at the corner between the upper plate 51 and the left side plate 53. The inclined portion 842 is formed from the upper right corner weld line 55 formed at the corner between the upper plate 51 and the right side plate 53. As shown in FIG. 9B, the inclined portion 851 is formed from a lower left corner weld line 56 formed at the corner between the lower plate 52 and the left side plate 53. The inclined portion 852 is formed from a lower right corner weld line 57 formed at the corner between the lower plate 52 and the right side plate 53.

This helps reduce stress at corners where cracks are likely to occur.

In this embodiment, as shown in FIG. 7A, the weld line 81 has a straight portion 813 perpendicular to the longitudinal direction La. As shown in FIG. 7B, the weld line 82 has a straight portion 823 perpendicular to the longitudinal direction La.

This allows the straight line portions 813 and 823 to be used as reference points, making it easy to align the end 65a of the first subunit 110 with the end 66a of the second subunit 120.

As shown in FIG. 9A, the weld line 84 has a straight portion 843 perpendicular to the longitudinal direction Lb. As shown in FIG. 9B, the weld line 85 has a straight portion 853 perpendicular to the longitudinal direction Lb.

This allows the straight line portions 843 and 853 to be used as reference points, making it easy to align the end 66b of the second subunit 120 with the end 67a of the third subunit 130.

In this embodiment, as shown in FIG. 5B, the position P1 where the weld line 81 intersects with the upper left corner weld line 54 is offset from the position P2 where the weld line 83 on the left side intersects with the upper left corner weld line 54 on the upper left corner weld line 54. The position P1' where the weld line 81 intersects with the upper right corner weld line 55 is offset from the position P2' where the weld line 81 intersects with the upper right corner weld line 55 on the right side weld line 83 on the upper right corner weld line 55. The position P3 where the weld line 82 intersects with the lower left corner weld line 56 is offset from the position P4 where the weld line 82 intersects with the lower left corner weld line 56 on the lower left corner weld line 56. The position P3' where the weld line 82 intersects with the lower right corner weld line 57 is offset from the position P4' where the weld line 82 intersects with the lower right corner weld line 57 on the right side weld line 83 on the lower right corner weld line 57.

In this embodiment, as shown in FIG. 8B, the position P5 where the weld line 84 intersects with the upper left corner weld line 54 is offset from the position P6 where the weld line 86 on the left side intersects with the upper left corner weld line 54 on the upper left corner weld line 54. The position P5' where the weld line 84 intersects with the upper right corner weld line 55 is offset from the position P6' where the weld line 84 intersects with the upper right corner weld line 55 on the right side intersects with the upper right corner weld line 55 on the upper right corner weld line 55. The position P7 where the weld line 85 intersects with the lower left corner weld line 56 is offset from the position P8 where the weld line 86 on the left side intersects with the lower left corner weld line 56 on the lower left corner weld line 56. The position P7' where the weld line 85 intersects with the lower right corner weld line 57 is offset from the position P8' where the weld line 86 on the right side intersects with the lower right corner weld line 57 on the lower right corner weld line 57.

In this way, by shifting the position of the weld line, stress concentration can be avoided.

In this embodiment, as shown in FIG. 4A, the boom 21 is divided between a boom body middle portion 66 (an example of a first boom) including a curved portion 61 and a boom body base end portion 65 (an example of a second boom), and as shown in FIG. 7C, the straight portion 831 of the weld line 83 on the left side surface is formed from a lower left corner weld line 56 formed at the corner between the lower plate 52 and the side plate 53. The straight portion 831 of the weld line 83 on the right side surface is formed from a lower right corner weld line 57 formed at the corner between the lower plate 52 and the side plate 53.

In the division section 68 on the base end side of the curved section 61, greater stress is generated on the upper plate 51 side than on the lower plate 52 side. Therefore, by providing a straight section 831 on the lower plate 52 side, the effect of stress caused by the formation of the straight section used as a reference for alignment can be suppressed.

In this embodiment, as shown in FIG. 4A, the boom 21 is divided between a boom body middle portion 66 (an example of a first boom) including a curved portion 61 and a boom body tip portion 67 (an example of a third boom), and as shown in FIG. 9C, the straight portion 861 of the weld line 86 on the left side surface is formed from an upper left corner weld line 54 formed at the corner between the top plate 51 and the side plate 53. The straight portion 861 of the weld line 86 on the right side surface is formed from an upper right corner weld line 55 formed at the corner between the top plate 51 and the side plate 53.

In the split section 69 located further towards the tip than the curved section 61, greater stress is generated on the lower plate 52 side than on the upper plate 51 side. Therefore, by providing a straight section 861 on the upper plate 51 side, the effect of stress caused by the formation of the straight section used as a reference for alignment can be suppressed.

In this embodiment, as shown in FIG. 2D, the boom 21 has reinforcing plates 101-104 in an internal space surrounded by a pair of side plates 53, an upper plate 51, and a lower plate 52. The reinforcing plates 101-104 are welded to the pair of side plates 53, the upper plate 51, and the lower plate 52.

This allows the thickness of the upper plate 51, the lower plate 52, and the side plate 53 to be reduced, and the weight can be reduced while maintaining rigidity. Furthermore, reinforcing plate 101 is positioned near dividing portion 34, reinforcing plate 102 is positioned near dividing portion 68, reinforcing plate 103 is positioned near dividing portion 69, and reinforcing plate 104 is positioned near dividing portion 35. Therefore, reinforcing plates 101 to 104 can be easily welded to the upper plate 51, the lower plate 52, and the pair of side plates 53 from the divided portions.

In this embodiment, as shown in FIG. 5B, the weld line 81 is positioned closer to the base end 31 in the longitudinal direction La than the weld line 82, and the weld line 83 on the left side is positioned between position P1 (an example of the first upper position) where the weld line 81 intersects with the upper left corner weld line 54 and position P3 (an example of the first lower position) where the weld line 82 intersects with the lower left corner weld line 56. Position P1 is positioned closer to the base end 31 in the longitudinal direction La than position P3. Position P2 (an example of the second upper position) where the weld line 83 on the left side intersects with the upper left corner weld line 54 is positioned closer to the base end 31 than position P4 (an example of the second lower position) where the weld line 83 on the left side intersects with the lower left corner weld line 56. The weld line 83 on the right side is located between position P1' (an example of a first upper position) where the weld line 81 intersects with the upper right corner weld line 55 and position P3' (an example of a lower position) where the weld line 82 intersects with the lower right corner weld line 57. Position P1' is located closer to the base end 31 in the longitudinal direction La than position P3'. Position P2' (an example of a second upper position) where the weld line 83 on the right side intersects with the upper right corner weld line 55 is located closer to the base end 31 than position P4' (an example of a second lower position) where the weld line 83 on the right side intersects with the lower right corner weld line 57.

As a result, as shown in FIG. 15A, it becomes possible to move the first subunit 110 relative to the second subunit 120 so as to approach it from below, making it easy to align the end 65a of the first subunit 110 with the end 66a of the second subunit 120.

In this embodiment, as shown in FIG. 8B, the weld line 84 is positioned closer to the base end 31 in the longitudinal direction Lb than the weld line 85 (an example of one direction side), and the weld line 86 on the left side is positioned between position P5 (an example of the first upper position) where the weld line 84 intersects with the upper left corner weld line 54 and position P7 (an example of the first lower position) where the weld line 85 intersects with the lower left corner weld line 56. Position P5 is positioned closer to the base end 31 in the longitudinal direction Lb than position P7. Position P6 (an example of the second upper position) where the weld line 86 on the left side intersects with the upper left corner weld line 54 is positioned closer to the base end 31 than position P8 (an example of the second lower position) where the weld line 86 on the left side intersects with the lower left corner weld line 56. The weld line 86 on the right side is located between position P5' (an example of the first upper position) where the weld line 84 intersects with the upper right corner weld line 55 and position P7' (an example of the first lower position) where the weld line 85 intersects with the lower right corner weld line 57. Position P5' is located closer to the base end 31 in the longitudinal direction Lb than position P7'. Position P6' (an example of the second upper position) where the weld line 86 on the right side intersects with the upper right corner weld line 55 is located closer to the base end 31 than position P8' (an example of the second lower position) where the weld line 86 on the right side intersects with the lower right corner weld line 57.

As a result, as shown in FIG. 15B, it becomes possible to move the third subunit 130 relative to the second subunit 120 so as to approach it from above, making it easy to align the end 66b of the second subunit 120 with the end 67a of the third subunit 130.

In this embodiment, as shown in FIG. 11A, a weld line 91 is formed by butt welding between the upper plate 51 and the base end 31 of the boom main body 32. The weld line 91 is located at both ends and has a pair of inclined portions 911, 912 inclined with respect to a direction perpendicular to the longitudinal direction La. As shown in FIG. 11B, a weld line 92 is formed by butt welding between the lower plate 52 and the base end 31 of the boom main body 32. The weld line 92 is located at both ends and has a pair of inclined portions 921, 922 inclined with respect to a direction perpendicular to the longitudinal direction La.

In this embodiment, as shown in FIG. 13A, a weld line 94 is formed by butt welding between the upper plate 51 and the tip 33 of the boom main body 32. The weld line 94 is located at both ends and has a pair of inclined portions 941, 942 inclined with respect to a direction perpendicular to the longitudinal direction Lb. As shown in FIG. 13B, a weld line 95 is formed by butt welding between the lower plate 52 and the tip 33 of the boom main body 32. The weld line 95 is located at both ends and has a pair of inclined portions 951, 952 inclined with respect to a direction perpendicular to the longitudinal direction Lb.

As a result, the weld line has parts that are not formed perpendicular to the principal stress, making it difficult for fatigue cracks to propagate and improving durability.

In this embodiment, as shown in FIG. 11A, the weld line 91 has a straight portion 913 perpendicular to the longitudinal direction La. As shown in FIG. 11B, the weld line 92 has a straight portion 923 perpendicular to the longitudinal direction La.

As a result, when attaching the base end 31 to the boom body base end 65, the straight section 913 can be used as a reference, making alignment easy.

In this embodiment, as shown in FIG. 13A, the weld line 94 has a straight portion 943 perpendicular to the longitudinal direction Lb. As shown in FIG. 13B, the weld line 95 has a straight portion 953 perpendicular to the longitudinal direction Lb.

As a result, when attaching the tip 33 to the boom body tip 67, the straight section 913 can be used as a reference, making alignment easy.

In this embodiment, as shown in FIG. 14, a first subunit 110, a second subunit 120, and a third subunit 130 are created. Next, the first subunit 110 is rotated or hung to align the first subunit 110 with the second subunit 120. The second subunit 120 may be rotated or hung instead of the first subunit 110. Next, the first subunit 110 and the second subunit 120 are welded together. Next, the third subunit 130 is rotated or hung to align the third subunit 130 with the second subunit 120. The second subunit 120 may be hung or rotated instead of the third subunit 130. Next, the third subunit 130 and the second subunit 120 are welded together.

This allows multiple subunits to be easily aligned and welded together to assemble the boom.

Other Embodiments
Although one embodiment of the present disclosure has been described above, the present disclosure is not limited to the above embodiment, and various modifications are possible without departing from the gist of the present disclosure.

(A)
In the above embodiment, the inclined portions 811, 812, 821, 822, 841, 842, 851, and 852 are formed in a straight line, but they may be curved instead of straight.

(B)
In the above embodiment, the boom main body portion 32 is divided into three parts: the boom main body base end portion 65, the boom main body middle portion 66, and the boom main body tip portion 67. However, this is not limited to three, and may be two or four or more.

(C)
In the above embodiment, the weld lines 81, 82, 84, 85, 91, 92, 94, and 95 are configured to be symmetrical on the left and right sides, but all or some of these do not necessarily have to be configured to be symmetrical on the left and right sides.

(D)
In the above embodiment, the dividing section 68 is provided with the straight line portion 813 and the straight line portion 823 that serve as a reference for alignment, but only one of them may be provided. Similarly, the dividing section 69 is provided with the straight line portion 843 and the straight line portion 853 that serve as a reference for alignment, but only one of them may be provided.

The boom for work machines of the present invention has the effect of improving durability, and is useful for work machines such as hydraulic excavators.

21 : Boom 51 : Upper plate 52 : Lower plate 53 : Side plate 81 : Weld line 82 : Weld line 811 : Inclined portion 812 : Inclined portion 821 : Inclined portion 822 : Inclined portion

Claims (18)

A pair of left and right side panels;
An upper plate joined to upper ends of the pair of side plates;
A lower plate joined to lower ends of the pair of side plates,
The upper plate or the lower plate has a first weld line formed in a portion divided in the longitudinal direction,
The first weld line has an inclined portion inclined with respect to a direction perpendicular to the longitudinal direction.
Boom for work equipment. The first weld line further has a curved portion.
The boom for a work implement according to claim 1. The first weld line is formed by butt welding.
The boom for a work implement according to claim 1. The inclined portion is formed by a weld line formed at a corner between the upper plate or the lower plate and the side plate where the first weld line is formed.
The boom for a work implement according to claim 1. The inclined portion includes a straight portion.
The boom for a work implement according to claim 1. The first weld line further has a first straight line portion perpendicular to the longitudinal direction.
The boom for a work implement according to claim 1. The inclined portions include straight portions and are disposed on both ends of the first weld line,
The first straight portion is disposed between the inclined portions in the width direction,
The first weld line further includes a curved portion connecting both ends of the first straight portion and an inner end of the inclined portion.
A boom for a work machine according to claim 6. Each of the pair of side plates has a side plate weld line at which divided portions in the longitudinal direction are joined by welding,
a position where the first weld line intersects with a weld line formed at a corner between the upper plate or the lower plate and the side plate, where the first weld line is formed, is shifted from a position where the side plate weld line intersects with a weld line formed at the corner, on the weld line formed at the corner;
The boom for a work implement according to claim 1. Each of the pair of side plates has a side plate weld line at which divided portions in the longitudinal direction are joined by welding,
The side plate weld line has a second straight portion perpendicular to the longitudinal direction,
The second straight portion is formed by a weld line formed at a corner between the upper plate or the lower plate and the side plate.
The boom for a work implement according to claim 1. The work machine boom is divided between a first boom section including a curved portion and a second boom section located closer to the base end than the first boom section,
The weld line formed at the corner is formed at the corner between the lower plate and the side plate.
The boom for a work implement according to claim 9. The work machine boom is divided between a first boom section including a curved section and a third boom section located closer to the tip end than the first boom section,
The weld line formed at the corner is formed at the corner between the top plate and the side plate.
The boom for a work implement according to claim 9. a backing material disposed along the first weld line;
The upper plate or the lower plate on which the first weld line is formed is welded by butt welding using the backing material.
The boom for a work implement according to claim 1. The housing further includes a reinforcing plate disposed in an internal space surrounded by the pair of side plates, the upper plate, and the lower plate,
The reinforcing plate is welded to the pair of side plates, the upper plate, and the lower plate.
The boom for a work implement according to claim 1. The first weld line is formed on the upper plate;
The lower plate has a second weld line formed in a portion divided in the longitudinal direction,
Each of the pair of side plates has a side plate weld line formed in a portion divided in the longitudinal direction,
The first weld line is disposed on one side of the second weld line in the longitudinal direction,
the side plate weld line is disposed between a first upper position where the first weld line intersects with an upper corner weld line formed at a corner between the upper plate and the side plate, and a first lower position where the second weld line intersects with a lower corner weld line formed at a corner between the lower plate and the side plate;
a second upper position where the side plate weld line intersects with the upper corner weld line is disposed on the one side of a second lower position where the side plate weld line intersects with the lower corner weld line;
The boom for a work implement according to claim 1. a boom main body including a pair of left and right side plates, an upper plate joined to upper ends of the pair of side plates, and a lower plate joined to lower ends of the pair of side plates;
An end portion joined to an end of the boom body portion;
a weld line formed by butt welding between the upper plate or the lower plate of the boom main body and the end portion,
The weld line has a pair of third straight line portions disposed at both ends and inclined with respect to a direction perpendicular to the longitudinal direction.
Boom for work equipment. The weld line further has a fourth straight portion perpendicular to the longitudinal direction.
A boom for a work implement according to claim 15. A work machine body,
A work machine having a work machine boom according to any one of claims 1 to 16, which is attached to the work machine body.
Working machinery. A method for manufacturing a boom for a work machine, the boom being divided into two or more subunits in a longitudinal direction, comprising the steps of:
a subunit manufacturing process for manufacturing the subunit by joining a pair of left and right side plates, an upper plate, and a lower plate by welding;
an alignment step of aligning a predetermined subunit with another subunit by rotating or suspending the subunit;
and a subunit joining step of welding the predetermined subunit and the other subunit.
A method for manufacturing a boom for a work machine.

Images