Impact Tool Anvil Surface Hardening for Fatigue Crack Resistance
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Solution Overview
Problem
Impact tool anvils experience fatigue crack initiation, growth, and eventual fracture due to repeated striking by the hammer, necessitating a solution that balances high hardness for strength and wear resistance with toughness in different areas of the anvil.
Innovation Solution
The anvil is designed with localized hardened layers formed by heating processes, such as carburization or induction, and treated with peening processes like laser peening to introduce compressive residual stresses, targeting specific areas for enhanced strength and wear resistance while maintaining toughness in other regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the anvil is made with high hardness throughout to improve strength and wear resistance, then the anvil becomes more resistant to fatigue cracking, but the anvil becomes too brittle and loses toughness in areas that require impact absorption
Solution Approach 1:
The patent applies different hardness levels to different regions of the anvil by forming hardened layers selectively on specific surfaces (impact receiving surface, drive surfaces, or both) while leaving the core and other regions with lower hardness. This is achieved through localized heating processes that create a hardened外层 with a tougher core, allowing the anvil to have both wear-resistant surfaces and impact-absorbing interior.
2Reliability
If the entire anvil is hardened to increase durability, then the anvil resists wear and fatigue better, but the manufacturing complexity and cost increase
Solution Approach 1:
Instead of hardening the entire anvil, the patent applies hardening selectively to only the regions that require enhanced durability (impact receiving surface, drive surfaces). This partial action approach reduces manufacturing complexity and cost while still achieving the desired reliability improvement in the critical areas.
3Reliability
If localized hardened layers are formed on the anvil to reduce stress, then fatigue crack resistance improves by 12.2-30%, but the manufacturing process time and energy consumption increase
Solution Approach 1:
The patent applies energy-consuming hardening processes only to the specific regions that need fatigue crack resistance improvement, rather than treating the entire anvil. This localized approach achieves the 12.2-30% fatigue crack resistance improvement while minimizing the total energy consumption by limiting the treatment to critical areas only.
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 localized treatment significantly reduces maximum stress during operation, leading to a 12.2-30% decrease in stress, thereby improving the anvil's lifespan and resistance to fatigue cracking.
Implementation Method 1
The hardened layer is formed by a heating process
Implementation Method 2
the compressive residual stresses are added to the hardened layer by a peening process, wherein the peening process is a laser peening process
Data Source
AI summary
An anvil for an impact tool including an impact receiving portion at an end of the anvil, the impact receiving portion including a lug having an impact receiving surface that receives impact from a hammer of the rotary power tool, a shank portion extending from the impact receiving portion, a drive portion located at an end of the shank portion opposite from the impact receiving portion, the drive portion including a plurality of drive surfaces configured to engage a tool bit, and a hardened layer formed on at least one of the drive portion or the impact receiving surface, the hardened layer having a higher hardness than a remaining portion of the anvil. The hardened layer is formed by a heating process.