Excavator Arm Cylinder Bracket Joint Strength via Localized Plate Thickness
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Solution Overview
Problem
Conventional construction machine arms are heavy due to uniform plate thickness, leading to excessive weight and reduced durability from stress concentrations at welding joints, particularly at the arm cylinder brackets.
Innovation Solution
The arm is designed with a box-shaped structural body featuring varying plate thicknesses and strategically positioned arm cylinder brackets with grooves for fillet welding, ensuring increased joint strength and reduced stress concentrations, while maintaining required strength and weight reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If uniform plate thickness is used throughout the arm, then manufacturing is simplified, but weight increases excessively and durability decreases due to stress concentrations
Solution Approach 1:
The patent applies different plate thicknesses to different regions of the arm based on local strength requirements. The rear side uses thicker plates (first and second plate thicknesses) to handle higher stresses from the arm cylinder bracket, while the front side uses thinner plates (third and fourth plate thicknesses) where less strength is needed, thereby reducing overall weight while maintaining manufacturing feasibility through standardized welding processes
2Ease of manufacture
If uniform plate thickness is used throughout the arm, then manufacturing is simplified, but durability decreases due to stress concentrations at welding joints
Solution Approach 1:
The patent strategically places arm cylinder brackets at positions where they can utilize the thicker rear plates to bear high stresses, while the transition regions are designed with appropriate thickness variations to distribute stress concentrations. This local differentiation of plate thicknesses improves durability by matching structural capacity to actual load requirements at each location
Solution Approach 2:
The arm cylinder brackets are pre-positioned at optimal locations on the rear side of the arm before final assembly, allowing the thicker plates to be strategically placed where maximum stress occurs during operation, thereby preventing stress concentrations and improving durability in advance
3Reliability
If thicker plates are used to increase strength, then durability improves, but weight increases excessively
Solution Approach 1:
The patent implements a non-uniform plate thickness design where thicker plates are used only in the rear region (first and second plate thicknesses) where the arm cylinder bracket generates high stresses, while thinner plates are used in the front region (third and fourth plate thicknesses) where less strength is required. This localized strengthening approach maintains durability at critical points while minimizing overall weight
4Strength
If arm cylinder brackets are positioned higher on the rear plate, then strength against load improves, but stress concentration at welding joints increases
Solution Approach 1:
The patent positions the arm cylinder brackets at optimized heights on the rear plate where they can effectively utilize the thicker first and second plates to bear vertical loads, while the rear plate design itself incorporates thickness variations that distribute stress concentrations away from the welding joints, thereby simultaneously achieving both bracket strength and welding joint durability
Data Source
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AI summary
An arm (11) of a hydraulic excavator (1) is formed as a box-shaped structural body surrounded by left and right side plates (12, 13), an upper plate (14), a lower plate (15), and a thick rear plate (16). An upper end (16A) of the thick rear plate (16) is protruded upward from an outer surface (14A3) of the upper plate (14). Upper ends (22B) of a pair of arm cylinder brackets (22) joined to an outer surface (16C) of the thick rear plate (16) are arranged higher than the outer surface (14A3) of the rear thick upper plate (14A) and lower than the upper end (16A) of the thick rear plate (16). As a result, in each of the arm cylinder brackets (22), a joint area with the thick rear plate (16) can be ensured large, and joint strength can be improved.