Variable-Rake Orbital Drilling Cutter for Fatigue-Resistant Holes
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Solution Overview
Problem
Orbital drilling methods fail to induce residual stresses in the sidewall of holes, leading to inferior fatigue life compared to reaming processes, which also create burrs requiring labor-intensive removal, making them time-consuming and inefficient in multi-layered assemblies like aircraft fuselages.
Innovation Solution
A cutting tool with two distinct portions, one featuring a positive radial rake angle for efficient material removal and another with a negative radial rake angle to impart residual stresses in the sidewall, improving fatigue life without creating burrs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reaming process is used to create holes, then beneficial residual stresses are induced in the hole wall improving fatigue life, but burrs are created around the drilled hole requiring time-consuming and labor-intensive removal
Solution Approach 1:
The cutting tool is divided into two distinct portions: a first portion with a first radial rake angle for initial hole creation, and a second portion with a second radial rake angle for inducing residual stresses. This segmentation allows each portion to perform its specific function independently, achieving both fatigue life improvement and burr-free finishing in a single orbital drilling operation
Solution Approach 2:
Different radial rake angles are applied at different locations along the cutting tool. The first portion has a first radial rake angle optimized for material removal, while the second portion has a second radial rake angle optimized for inducing compressive residual stresses. This local differentiation of cutting parameters enables the tool to perform multiple functions sequentially during orbital drilling
2Productivity
If orbital drilling is used to create holes without removing material layers, then manufacturing efficiency is improved, but fatigue life is reduced due to neutral stress state in the machined surface
Solution Approach 1:
The radial rake angle parameter is changed between the two portions of the cutting tool. The first portion uses a first radial rake angle for efficient material removal, while the second portion uses a different second radial rake angle to induce compressive residual stresses in the hole wall, thereby improving fatigue life while maintaining the efficiency of orbital drilling
3Ease of manufacture
If conventional single-rake-angle cutting tool is used, then tool design is simple, but it cannot simultaneously achieve efficient material removal and induce beneficial residual stresses
Solution Approach 1:
The cutting tool body is segmented into two distinct portions along its length, with each portion having a different radial rake angle. This segmentation enables the tool to perform dual functions: the first portion removes material efficiently while the second portion induces compressive residual stresses, achieving both productivity and reliability improvements
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 tool effectively enhances the fatigue life of orbital drilled holes by inducing beneficial residual stresses, reducing the need for burr removal and minimizing labor and time in large structures, while maintaining efficient material removal.
Implementation Method 1
A first portion of a cutting tool removes a portion of the material from the at least one layer to form a hole
Implementation Method 2
A second portion of the cutting tool imparts residual stresses in a sidewall of the hole
Data Source
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AI summary
A cutting tool (110) for forming a hole by means of orbital drilling is provided. The cutting tool includes a body (112) having a first portion (118), which has a first diameter and a first radial rake angle (124: Fig. 2), and a second portion (120) adjacent the first portion (118), the second portion (120) having a second diameter and a second radial rake angle (126: Fig. 3). The second diameter is different from the first diameter and the second radial rake angle (128) is different from than the first radial rake angle (124). In preferred embodiments the second diameter is larger than the first diameter and the first radial rake angle (124) is positive, whilst the second radial rake angle (128) is negative, such that residual stresses may be imparted to the wall of the orbitally drilled hole. A system (110: Fig. 7) for, and a method (300: Fig. 9) of, orbitally drilling a hole are also provided, wherein the system includes the cutting tool (110).