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Torque development process for threaded fasteners

March 23, 2024

a. Calculation of preload force. According to the product fastening occasions, design requirements, working load and connection requirements and other comprehensive factors (or CAE simulation analysis) to calculate the theoretical preload value.


b. Selection of standard parts. Reasonable selection of standard parts specifications, try to choose national standard parts, reduce the use of non-standard parts.


c. Tighten the space check. Check whether the connection occasions meet the assembly of standard parts.


d. Calculation of tightening torque. The tightening torque is calculated according to the parameters of pre-tightening force, fastener specification, thread coupling state and so on. The matching of friction coefficient, strength, tightening precision, tightening grade, connection stiffness and torque were analyzed.


e. Test verification. On the one hand, through the laboratory test project, through the test data of the relevant parameters to verify the rationality of the setting of tightening torque. On the other hand, the qualification and reliability of torque are verified by outdoor road test and durability test.


f. Select a tightening policy. Select the corresponding tightening method, tightening tool and tightening method according to the connection occasion, output and cost, tightening torque, tightening grade and tightening accuracy.


Analyze the fasteners in the torque list provided by each design department, compile the qualified analysis results into the vehicle torque list, countersign with each design department and manufacturing department after approval, and then release to the manufacturing department as an important process index document for final assembly to guide production. The manufacturing department reasonably selects tightening tools, tightening methods, assembly processes and torque quality detection methods according to the tightening grade, tightening accuracy, torque value and other parameters in the vehicle torque list.