Impact Tool Output Shaft Segmentation to Reduce Stress Concentration
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Solution Overview
Problem
Impact tools, such as impact wrenches, experience premature failure due to stress concentration at the square shaft of the output shaft, leading to reduced tool life.
Innovation Solution
The impact tool design includes a first output shaft with a partially nested second output shaft, where the nested region is greater than or equal to 3 mm, and the front end surface of the first output shaft forms a polygonal opening to accommodate the rear end of the second output shaft, enhancing structural integrity and distributing impact forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the output shaft is integrated with a square shaft at the front end, then the tool can be manufactured as a single piece, but stress concentration occurs at the square shaft causing premature breakage
Solution Approach 1:
The output shaft is divided into two separate components: a first output shaft and a second output shaft. The first output shaft is integrated with the impact member, while the second output shaft is separately formed with the square cross-section at its front end. This segmentation eliminates the stress concentration point that would occur at the junction of an integrated square shaft and circular shaft, thereby improving reliability while maintaining manufacturing simplicity through modular assembly.
2Device complexity
If the square shaft is integrated into the output shaft, then structural compactness is achieved, but the square shaft is prone to break off reducing tool life
Solution Approach 1:
The output shaft system is segmented into two separate shafts instead of one integrated shaft. The first output shaft maintains a circular cross-section for compact integration with the impact member, while the second output shaft is separately formed with a square cross-section at its front end for tool accessory attachment. This segmentation prevents stress concentration at junctions, extending tool service life while keeping the overall structure compact through modular design.
Solution Approach 2:
The second output shaft is partially nested within the first output shaft, with the front end of the first output shaft forming a polygonal opening that accommodates the rear end of the second output shaft. This nesting arrangement maintains structural compactness while allowing each shaft to be optimized independently - the first shaft for impact force transmission and the second shaft for tool accessory mounting - thereby preventing stress concentration and extending tool life.
3Device complexity
If a single integrated output shaft is used, then the device structure is simplified, but stress concentration occurs at the square shaft front end
Solution Approach 1:
The output shaft is segmented into two separate shafts: a first output shaft with a circular cross-section that integrates with the impact member, and a second output shaft with a square cross-section at its front end for tool accessory attachment. By separating these functions into different shafts, the design eliminates the stress concentration point that would occur at the junction of an integrated square and circular shaft, while maintaining simplified device structure through modular assembly.
Solution Approach 2:
Each shaft is designed with local quality optimization: the first output shaft has a circular cross-section optimized for transmitting impact forces from the impact member, while the second output shaft has a square cross-section optimized for attaching tool accessories. This local quality differentiation eliminates stress concentration at junctions while maintaining overall structural simplicity through modular design.
Data Source
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AI summary
An impact tool includes: an electric motor including a drive shaft rotating about a first axis; an impact member configured to be driven by the electric motor; an output mechanism configured to be provided with an impact force by the impact member; a transmission mechanism disposed between the electric motor and the impact member and transmitting torque outputted by the drive shaft to the impact member; and a power supply configured to supply electrical energy to the impact tool. The output mechanism includes: a first output shaft driven by an impact member to rotate, a second output shaft connected to the first output shaft and retained at the front-most end of the impact tool to be mounted with a tool accessory. The front end surface of the first output shaft is configured as a force-bearing region bearing an impact reaction force from the tool accessory.