Coldworking Mandrel Speed Control for Fatigue Life
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Solution Overview
Problem
Existing coldworking methods for metal holes, such as those used in aircraft parts, result in substantial axial plastic flow of metal, which can lead to reduced fatigue life and increased risk of cracks, as they primarily induce axial plastic flow rather than non-axial (radial and tangential) flow, resulting in suboptimal residual stress distribution.
Innovation Solution
A method and system that control the speed of a mandrel engaging with metal holes to promote non-axial plastic flow by using multiple speeds during the coldworking process, specifically slowing down the mandrel retraction speed to increase the unit relevant retraction time, thereby reducing axial plastic flow and enhancing compressive residual stress creation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional coldworking methods are used with standard mandrel speeds, then the coldworking process is efficient and quick, but substantial axial plastic flow occurs which reduces fatigue life and increases crack risk
Solution Approach 1:
The mandrel speed is dynamically adjusted during the coldworking process. The system transitions from a constant high speed to a variable speed profile that includes acceleration, deceleration, and dwell phases. This dynamic speed control allows the mandrel to engage and disengage quickly (maintaining productivity) while slowing down during critical engagement periods to reduce axial plastic flow and enhance compressive residual stress (improving fatigue life).
Solution Approach 2:
The invention changes the speed parameter from a constant value to a time-varying parameter with specific phases. By modifying the speed parameter throughout the process - particularly by introducing deceleration and dwell phases during mandrel engagement - the system optimizes both productivity and fatigue life. The parameter change allows control over plastic flow direction and magnitude.
2Productivity
If the mandrel moves quickly through the aperture, then productivity is high, but axial plastic flow increases which creates suboptimal residual stress distribution
Solution Approach 1:
The mandrel speed is dynamically adjusted during the coldworking process. The system transitions from a constant high speed to a variable speed profile that includes acceleration, deceleration, and dwell phases. This dynamic speed control allows the mandrel to engage and disengage quickly (maintaining productivity) while slowing down during critical engagement periods to reduce axial plastic flow and enhance compressive residual stress (improving fatigue life).
Solution Approach 2:
The invention changes the speed parameter from a constant value to a time-varying parameter with specific phases. By modifying the speed parameter throughout the process - particularly by introducing deceleration and dwell phases during mandrel engagement - the system optimizes both productivity and fatigue life. The parameter change allows control over plastic flow direction and magnitude.
3Loss of time
If the mandrel engages the metal at high speed, then the process is fast, but non-axial plastic flow is insufficient which reduces compressive residual stress creation
Solution Approach 1:
The mandrel speed is dynamically adjusted during the coldworking process. The system transitions from a constant high speed to a variable speed profile that includes acceleration, deceleration, and dwell phases. This dynamic speed control allows the mandrel to engage and disengage quickly (maintaining productivity) while slowing down during critical engagement periods to reduce axial plastic flow and enhance compressive residual stress (improving fatigue life).
Solution Approach 2:
The invention changes the speed parameter from a constant value to a time-varying parameter with specific phases. By modifying the speed parameter throughout the process - particularly by introducing deceleration and dwell phases during mandrel engagement - the system optimizes both productivity and fatigue life. The parameter change allows control over plastic flow direction and magnitude.
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
This approach effectively reduces axial plastic flow while increasing non-axial plastic flow, leading to improved fatigue life and structural integrity of coldworked metal holes by enhancing the creation of beneficial compressive residual stress.
Implementation Method 1
These coldworking methods and systems result in substantial axial plastic flow of metal to the mandrel-exit side of a metal sheet
Data Source
AI summary
Systems and methods for coldworking metal are described that reduce the axial flow of metal and increase the radial/tangential flow, thereby improving the fatigue life at an aperture. A tool is inserted through an aperture and its travel speed is reduced when in contact with the metal to reduce axial plastic flow. A sensor as part of the motive system moving the mandrel can sense when the tool contacts the metal and reduces the speed of the tool. The tool may move more quickly when not in contact with the metal to reduce working time than when the mandrel is working the metal. The coldworking tool engages the metal at the aperture at a speed of less than the speed which results in the time duration for the mandrel engaging the metal at the aperture for 35 second per inch of metal thickness at the aperture.