Boom Box Structure Fatigue Strength via Segmented Plate Welding
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Solution Overview
Problem
The durability of box-shaped structural bodies in construction machines, such as hydraulic excavators, is compromised due to low fatigue strength in welded portions, particularly when plate materials of different thicknesses are joined using one-side welding with a backing material.
Innovation Solution
The implementation of a boom structure with a box-shaped cross-section, where the first and second front lower plates are fully welded to form a single different-thickness plate, and then one-side welded with a backing material, while the second front lower plate is similarly treated, enhancing fatigue strength and workability by optimizing plate thicknesses and welding methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If one-side welding with backing material is used to join plate materials of different thicknesses, then ease of manufacture is improved, but fatigue strength of the welded portion deteriorates
Solution Approach 1:
The lower plate is segmented into multiple plate materials (first lower plate, second lower plate, third lower plate) with different thicknesses arranged in sequence. This segmentation allows each weld joint to connect plates of similar thickness, improving fatigue strength while maintaining ease of manufacture through one-side welding with backing material.
Solution Approach 2:
Different thicknesses of plate materials are assigned to different locations of the lower plate based on local strength requirements. The first lower plate has greater thickness than the second lower plate, which in turn has greater thickness than the third lower plate, optimizing both manufacturing ease and structural strength.
2Weight of moving object
If plate thickness is reduced to minimize weight, then weight of the boom is reduced, but fatigue strength of welded portions deteriorates
Solution Approach 1:
The plate thickness is optimized locally at each position rather than using uniform thickness throughout. The first lower plate uses greater thickness where higher strength is needed, while the second and third lower plates use smaller thicknesses where less strength is required, achieving weight reduction without compromising fatigue strength.
Solution Approach 2:
The lower plate is constructed as a composite structure using multiple plate materials with different thicknesses joined together. This composite approach allows the boom to achieve both lightweight design and high fatigue strength by strategically combining plates of different thicknesses.
Data Source
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AI summary
A single different-thickness plate (18) is formed by performing double-side welding from both sides in a plate thickness direction of a first front lower plate (17A) having a plate thickness equal to a plate thickness of a lower joining plate (33F) of an arm-side mounting member (33) and a second front lower plate (17B) having a plate thickness equal to a plate thickness of a third front lower plate (17C). As a result, one-side welding can be performed by using a backing material (23) from an outer side of a box-shaped structural body (12) to the lower joining plate (33F) of the arm-side mounting member (33) and to the first front lower plate (17A) constituting the different-thickness plate (18). On the other hand, one-side welding can be performed by using a backing material (26) from the outer side of the box-shaped structural body (12) to the third front lower plate (17C) joined on lower end sides of left and right side plates (13), (13'), and to the second front lower plate (17B) constituting the different-thickness plate (18).