Anvil Assembly Stress Reduction via Segmented Sleeve
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Solution Overview
Problem
Anvil assemblies in power tools, particularly impact wrenches, face high stress due to small fillet radii, which can lead to failure under high torsional loads, as they attempt to transfer significant torque to the tool element and workpiece.
Innovation Solution
The anvil assembly design includes a body with a head featuring large radii fillets and corners to reduce stress concentrations, along with a sleeve that shifts the shoulder function from the anvil to the sleeve, allowing for increased fillet radii and improved stress distribution, and optionally includes radially-extending lugs to enhance structural support.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a small fillet radius is used in the anvil head to maintain compact dimensions, then the anvil can transfer high torque to the tool element, but stress concentrations occur at the base of the head leading to potential failure
Solution Approach 1:
The anvil assembly is divided into two separate components: the anvil body and the sleeve. The sleeve is a separate component that can be independently designed with optimized geometry, allowing it to bear the shoulder load without requiring the anvil head to have large fillet radii. This segmentation enables the anvil head to maintain compact dimensions while the sleeve provides the necessary stress distribution.
Solution Approach 2:
The sleeve acts as an intermediary component between the anvil head and the tool element. It provides the shoulder surface that contacts the tool element, mediating the force transfer. This intermediary structure allows the anvil head to have reduced fillet radii while still maintaining adequate stress distribution, as the sleeve absorbs and distributes the loads.
2Strength
If the fillet radius at the anvil head is increased to reduce stress concentrations, then stress distribution improves, but the anvil assembly dimensions increase
Solution Approach 1:
By segmenting the anvil assembly into the anvil body and the sleeve, the design allows the fillet radius to be optimized independently in each component. The anvil head can have smaller fillet radii to maintain compact dimensions, while the sleeve provides the necessary stress distribution through its own geometry and material properties.
Solution Approach 2:
The sleeve serves as an intermediary that provides the shoulder function, allowing the anvil head to have reduced fillet radii. The sleeve's geometry and material properties enable it to distribute stresses effectively, compensating for the smaller fillet radii in the anvil head and maintaining overall stress distribution without increasing dimensions.
3Reliability
If a continuous shoulder surface is used on the anvil, then the tool element can be reliably abutted, but manufacturing complexity and material usage increase
Solution Approach 1:
The continuous shoulder surface is segmented and transferred to the separate sleeve component. The sleeve can be manufactured as a separate part with the shoulder surface, allowing for simplified manufacturing of the anvil body while maintaining the reliability of the tool element coupling through the sleeve's shoulder surface.
Solution Approach 2:
The sleeve acts as an intermediary that provides the continuous shoulder surface needed for reliable tool element coupling. This allows the anvil body to be manufactured simpler without compromising the reliability of the connection, as the sleeve's geometry ensures proper abutment and coupling of the tool element.
Data Source
AI summary
An anvil assembly for a tool includes an anvil having a body with an outer periphery and a head formed on a distal end of the body. The anvil assembly also includes a sleeve surrounding at least a portion of the outer periphery of the body. The sleeve has a distal end against which a tool element is abutted when the tool element is coupled to the head.