No abstract

During the automated tightening process of bolted joints, the preload force can only be determined with greater effort. This is usually realized by using indirect methods, one of which is the torque‐controlled procedure. The dependency between the tightening torque and the preload force is deeply connected to the frictional conditions under the screw head and in the screw thread. Several methods exist to support the tightening process. Nonetheless, errors occur, which are, besides other reasons, due to friction‐induced vibrations. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The tightening process of bolted joints shows a highly dynamic behavior, which depends on numerous factors and can therefore be challenging to be adequately quantitatively reproduced. The presented model solves this problem by combining a multi-body model of the joint with the sophisticated LuGre friction model. This allows for a detailed simulation while simultaneously reducing the computational work in comparison to a standard finite element simulation. We demonstrate that, with a constant tightening angular velocity, the progression of the tightening torque and the preload force can be described by three constants. The model further allows to implement custom torque sources, screw types, and materials to further extend its capabilities. In this contribution, we focus on the basic relationships of acting torques on the joint and friction-induced vibrations during the tightening process. Furthermore, effects of typical geometric and material changes on the stick-slip frequency are demonstrated and discussed.

Bolted joints are one of the most used machine elements. Holding together structures of all sizes, the integrity rests on their shoulders. Thus, an accurate and reliable assembly of the joint is crucial. While it is the aim to not experience friction-induced vibrations at all, at some situations, it is unavoidable. These cases, however, have yet been out of the focus of control algorithms due to the volatile nature of the process. This contribution delivers analytical and experimental results for the occurrence of friction-induced vibrations during tightening of bolted joints. Previous findings of system characteristic constants could be validated, which can be used to monitor the tightening process even while strong vibrations during the tightening process occur. Additionally, a real-time algorithm is presented which allows for an advanced process monitoring and control by identifying process characteristics based on which predictions of the process can be made. These measures significantly improve the capabilities to reach the target values of the tightening process.

The assembly of bolted joints is often based on the assumption that the joint has been assembled as the design guidelines prescribe. However, during the tightening process, errors can occur, some of which can be affiliated with friction-induced vibrations. In order to improve the automated tightening process and reduce the influence of friction-induced vibrations, an additional high frequency torque is applied to the bearing of the bolted joint. This leads to a significant increase in tightening efficiency, lower tightening torque, and lower pretension force increments during the tightening process.