| 摘要 |
PROBLEM TO BE SOLVED: To reduce a welding joining part, to reduce weight, and to reduce a manufacturing cost by forming a work arm having a box-shaped structure as a tubular body by joining the respective bending ends by bending a plate member. SOLUTION: An arm 8 is integrally formed by mutually welding various steel members. An arm main body 8a of this arm 8 is formed by bending a single plate member as a tubular body of a triangular cross section, the other two sides of a triangle are formed by bending both sides of a base, and the respective bending ends being end parts of the other two sides are butted to be welded and joined. The arm main body 8a has a shape of linearly changing the triangular cross section to the small end from the large end in the lengthwise direction. A connecting bracket 8b to be connected with a bucket is installed on the small end side of the arm main body 8a, a connecting bracket 8c to be connected with a boom is installed on the base of a triangular cross section on the large end side, respectively, and an actuator installing bracket 8d is installed in a welding joining part of a triangular cross section.
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