Construction Machine Arm Weight Reduction via Local Quality
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Solution Overview
Problem
The arm of construction machines, particularly hydraulic excavators, faces issues with weight reduction and fatigue strength due to stress concentration at non-welded parts in the closed sectional structure, leading to potential fatigue cracks when using high tensile steel materials.
Innovation Solution
The arm is designed with a combination of thick and thin plates made from soft and high tensile steel materials, respectively, with strategic welding to minimize non-welded areas and distribute stress, using both-side and one-side welding techniques to enhance structural integrity and reduce weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If high tensile steel material is used to reduce plate thickness and weight, then weight reduction is achieved, but fatigue strength deteriorates due to stress concentration at non-welded parts
Solution Approach 1:
The patent applies local quality by using high tensile steel material specifically at the front side plate where weight reduction is prioritized, while using soft steel material at the rear side plate where welding connections are located to ensure fatigue strength. This localized material selection allows the arm to achieve overall weight reduction while maintaining reliability at critical stress concentration points.
2Strength
If high tensile steel material is used, then plate thickness can be reduced, but stress concentration at non-welded parts increases leading to fatigue cracks
Solution Approach 1:
The patent implements local quality by strategically selecting high tensile steel material for the front side plate to maximize strength-to-weight ratio, while using soft steel material for the rear side plate that contains welding connections. This localized differentiation ensures that areas subject to cyclic loading and stress concentration maintain adequate fatigue strength, while other areas achieve optimal weight reduction.
3Reliability
If soft steel material is used throughout the arm, then fatigue strength is maintained, but weight reduction cannot be achieved
Solution Approach 1:
The patent applies local quality by using soft steel material specifically at the rear side plate where welding connections are located to maintain fatigue strength, while using high tensile steel material at the front side plate to achieve weight reduction. This localized material selection allows the arm to achieve overall weight reduction while maintaining reliability at critical stress concentration points.
4Weight of moving object
If high tensile steel material is used, then weight reduction is achieved, but the arm becomes more susceptible to fatigue cracks under large external forces
Solution Approach 1:
The patent implements local quality by strategically selecting high tensile steel material for the front side plate to maximize weight reduction, while using soft steel material for the rear side plate that contains welding connections to reduce susceptibility to fatigue cracks. This localized differentiation ensures that areas subject to cyclic loading and stress concentration maintain adequate fatigue resistance, while other areas achieve optimal weight reduction.
Data Source
AI summary
In an arm for a construction machine formed as a box-shaped structural body by left and right side plates, an upper plate, a lower plate, and a rear plate, a left rear thick side plate constituting the left side plate, a right rear thick side plate constituting the right side plate, a rear thick upper plate constituting the upper plate, and a rear thick lower plate constituting the lower plate are formed by using a soft steel material having a large plate thickness. A left front thin side plate constituting the left side plate, a right front thin side plate constituting the right side plate, a front thin upper plate constituting the upper plate, and a front thin lower plate constituting the lower plate are formed by using a high tensile steel material having a small plate thickness. As a result, the weight of the entire arm can be reduced.