Impact Tool Anvil Neck Geometry for Fatigue-Resistant Torque Transfer
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Solution Overview
Problem
Rotary impact tools experience failures due to fatigue and contact stress on the anvil surfaces, particularly the lugs, drive surfaces, and shoulders, leading to reduced durability and efficiency.
Innovation Solution
The anvil design incorporates features such as necked portions, asymmetric lugs, and strategically positioned rings and depressions to reduce torsional stiffness, distribute impact forces, and ensure planar contact, thereby enhancing durability and service life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the anvil is designed with high torsional stiffness to withstand impact forces, then strength is improved, but stress concentrations occur at critical locations leading to fatigue failure
Solution Approach 1:
The patent applies local quality by creating a necked portion with reduced diameter at a specific location in the shank, between the drive portion and impact receiving portion. This localized geometric modification reduces torsional stiffness in that specific region to lower stress concentrations and prevent fatigue failure, while maintaining overall structural strength through the hardened surface layer applied to critical areas.
Solution Approach 2:
The patent employs composite materials by combining a base anvil material with a hardened surface layer applied to critical areas. This composite structure provides both the overall strength and toughness of the base material and the enhanced wear and fatigue resistance of the hardened surface, allowing the anvil to withstand high impact forces while resisting fatigue failure.
2Strength
If the anvil surfaces are hardened to increase durability, then hardness is improved, but the anvil becomes more susceptible to fatigue failure
Solution Approach 1:
The patent applies local quality by selectively hardening only the critical surfaces (impact receiving portion and drive portion) while leaving the interior and non-critical areas with different properties. This localized hardening provides durability where needed while the necked portion in the shank maintains lower hardness to absorb stress and prevent fatigue failure.
Solution Approach 2:
The patent changes material parameters by applying a hardened surface layer with different mechanical properties than the base material. This parameter change increases surface hardness and wear resistance on critical areas while the necked portion's geometric parameter changes (reduced diameter) create a stress-relieving effect that prevents fatigue propagation.
3Stress or pressure
If the anvil is designed with asymmetric lugs to optimize impact force distribution, then stress distribution is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies asymmetry by designing lugs with non-uniform geometry and positioning, where the lug profiles and spacing are specifically configured to distribute impact forces more evenly across the anvil body. This asymmetric design optimizes stress distribution during impact operations, and while it increases manufacturing complexity, the complexity is managed through standard machining operations and modular construction.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The improved anvil design reduces stress concentrations and fatigue, allowing for increased torque delivery and extended service life by absorbing and distributing impact forces more effectively.
Implementation Method 1
The shank includes a necked portion having a reduced diameter. The necked portion is located adjacent the drive portion and between the impact receiving portion and the drive portion.
Implementation Method 2
In another embodiment, the anvil includes a hardened surface layer on the impact receiving portion and the drive portion.
Data Source
AI summary
An anvil is for use with an impact tool. The anvil includes an impact receiving portion having a lug configured to be impacted to rotate the anvil about an axis, a drive portion opposite the impact receiving portion, and a shank extending between the impact receiving portion and the drive portion. The drive portion is configured for coupling to a tool bit. The shank includes a necked portion having a reduced diameter. The necked portion is located adjacent the drive portion and between the impact receiving portion and the drive portion.