Joint Preload Calibration Using Tightening and Removal Torque
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Solution Overview
Problem
Existing methods for achieving joint preload in bolted structures using tightening torque are uncertain, with uncertainties ranging from +/−35% for unlubricated fasteners and +/−25% for lubricated fasteners, due to variations in geometrical, frictional conditions, tools, technique, and technicians.
Innovation Solution
A method that determines the required tightening torque by measuring thread pitch, trial tightening torque, and trial removal torque, using equations to calculate the necessary torque for achieving a target joint preload, eliminating the need for previous torque-tension data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If tightening torque control is used to achieve preload, then the method is easy to implement, but the uncertainty in achieving target preload is significant (+/−35% for unlubricated, +/−25% for lubricated fasteners)
Solution Approach 1:
The patent uses feedback by measuring both tightening torque and removal torque, then using these measurements to calculate the actual preload achieved. This feedback loop allows determination of the relationship between torque and preload for the specific fastener and joint combination, enabling more accurate preload control than traditional torque-only methods.
Solution Approach 2:
The patent changes the approach from using a single parameter (tightening torque) to using multiple parameters (tightening torque, removal torque, and thread pitch) to calculate preload. This multi-parameter approach compensates for variations in friction conditions and geometry, reducing uncertainty in achieving target preload.
2Measurement precision
If torque-tension test data is used for specific fasteners and joints, then preload can be determined, but significant uncertainty remains due to differences between actual and test fasteners in geometry, friction conditions, tools, technique, and technicians
Solution Approach 1:
The patent enables the specific fastener and joint combination to determine its own torque-preload relationship through actual measurements of tightening and removal torques. This self-service approach eliminates the need to rely on test data from other fasteners or conditions, ensuring that the determined parameters are specific to the actual components being used.
Solution Approach 2:
The patent performs preliminary measurements of tightening torque and removal torque on the actual fastener and joint combination before final assembly. This preliminary action establishes the specific torque-preload relationship for the actual components, eliminating uncertainties that would arise from using test data from different fasteners or conditions.
3Device complexity
If traditional torque control methods are used, then the process is simple, but friction variations in thread and nut conditions create significant uncertainty in preload achievement
Solution Approach 1:
The patent extracts the friction effect from the torque measurement by measuring both tightening torque (which includes friction) and removal torque (which excludes friction). By taking the difference or using both measurements, the friction component is isolated and accounted for, allowing more accurate determination of the preload-related torque component.
Data Source
AI summary
A method for achieving a target joint preload can include applying a tightening torque to the second fastener element and measuring that torque as a trial tightening torque. The method can further include applying a loosening torque to the second fastener element and measuring that torque as a trial removal torque. Additionally, the method can include calculating a required tightening torque that is required to be applied to the second fastener element to achieve the target joint preload using only the thread pitch, the trial tightening torque, the trial removal torque, and the target joint preload.