VDA Volume 5.2 Inspection Process Capability for Static Torques on Bolted Joints, 2nd revised Edition, January 2025

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Bolted joints are of vital importance in the automotive industry, as they are frequently used (more than 100 million threaded fasteners are tightened in German automotive companies every workday). When it comes to producing bolted joints, a distinction can be made between the actual production and an inspection process carried that follows the production process. The production process is carried out using suitable tools selected according to tightening specifications.
This volume only covers the inspection process that is conducted after the production process. Some of the tightening tools include integrated functions that serve to monitor the process sequence. However, these monitoring functions are not covered in this VDA volume. The most frequently used type of inspection is based on determining static torques in order to use them as an auxiliary quantity for the relevant preload. Due to the complex relationship between preload and torque, the quality of the “torque” characteristic is not comparable to those that are directly measurable. Moreover, multiple measurements of this characteristic on the same object, which are actually common practice to quantify inspection process capability, are not possible when it comes to bolted joints: Any tightening or loosening changes the condition of the measured object irreversibly.
In this volume, the approach presented in VDA Volume 5 is therefore modified in such a way that it can be applied to bolted joints.