Work Arm Boss Structure for Weld Fatigue Reduction
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Solution Overview
Problem
Existing work arm designs for machines like hydraulic excavators face fatigue issues due to stress concentration at welds between bosses and side plates, leading to premature fatigue cracks, especially under bending deformations.
Innovation Solution
A work arm design featuring a pair of bosses with a cylindrical boss coupling member, where the outer diameter of the inner body portion is smaller than the outer body portion, reducing flexural rigidity and bending stress on the welds, thereby enhancing the fatigue life of the welds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the thickness of the weld between the flange portion of the boss and the side plate is made equal to the plate thickness of the side plate, then the magnitude of stress exerted on the weld is made equal to the magnitude of stress exerted on the side plate, but a fatigue crack initiates from the weld because the welding material has lower fatigue strength than the base material
Solution Approach 1:
The invention applies local quality by creating a groove-shaped thick adjustment portion at the specific welding position of the flange portion, making the thickness locally greater than the plate thickness. This localized thickness increase reduces stress concentration at the weld, allowing the weld to have lower stress magnitude than the side plate, thereby preventing fatigue crack initiation while maintaining overall structural integrity.
2Reliability
If groove-shaped thick adjustment portions are formed on the flange portions to make the thickness of the side plate equal to the thickness of the flange portion at the welding position, then stress concentration at welds is prevented, but the device complexity increases
Solution Approach 1:
The invention merges the thick adjustment portion with the flange portion, making them an integrated structure rather than separate components. The groove-shaped thick adjustment portion is formed as part of the flange portion itself, combining the load-bearing function of the flange with the stress-distribution function of the thick portion, thereby reducing device complexity while maintaining reliability.
Data Source
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Figure 5
AI summary
A work arm of a work machine includes a box-shaped structure 21 including multiple plate members, a pair of bosses 30 attached to opposing plate members 22, and a cylindrical boss coupling member 42 coupling the pair of bosses 30 together. Each boss 30 includes a boss body section 31 having a pin insertion hole 31a through which a coupling pin 48 is inserted and extending in an arrangement direction of the plate members 22, and a flange section 32 extending outward from an outer circumferential portion of the boss body section 31 and joined to a corresponding one of the plate members 22 via a first weld 44. The boss body section 31 includes a cylindrical outer body portion 33 on an outer surface side of the box-shaped structure 21 and a cylindrical inner body portion 34 on an inner surface side of the box-shaped structure 21. The boss coupling member 42 is joined, at both axial ends thereof, to respective ends of the inner body portions 34 via second welds 45. The inner body portion 34 is configured such that an outer diameter D2 at a flange section-side part thereof is smaller than an outer diameter D1 at an axial end of the outer body portion 33. This allows improvement of fatigue life of the weld 44 joining the boss 30 and the plate member 22.