Expert Hub: Mr. Laue, Atlas Copco Tools offers joint design with seating control. What does seating control mean precisely?
Michael Laue: In tightening technology, the seating point is the point where the underside of the screw or bolt head makes contact with the surface of the component to be joined as it is tightened. This point is the latest transition from the stage of screw insertion, thread tapping or thread forming to the joining stage. From this point onwards, the torque increases with increasing angle. Initially, this torque increase is non-linear as a result of leveling and relaxation processes in the affected components. Depending on the hardness of a tightening operation, this phase may be longer or shorter. The seating phase ends when the joining point is reached. Then, the joint is tightened until the specified final value is reached.
Expert Hub: Thank you for this interesting introduction. In practice, joints are often tightened with torque or angle control. What is the specific difference between these strategies and seating control?
Michael Laue: The difference between tightening strategies based on seating control and those based on torque control with angle monitoring is that torque control is only possible with a stable tightening process. Torque and angle control can only accommodate process fluctuations to a limited extent and do not take the clamping torque into consideration. In addition, this strategy entails a risk that NOK joints may not be detected. For example, with a self-forming joint, the tightening system may give an OK signal even though the joint has not been clamped and is loose. Seating control offers considerable advantages in this respect. With this strategy, it is possible to react more flexibly to the challenges faced and to reliably deliver OK joints.
This diagram illustrates a typical tightening process and the phases involved.
Expert Hub: If I understand you correctly, Mr. Laue, this tightening strategy is suitable for tightening joints that pose special challenges. When do you advise customers to use seating control?
Michael Laue: The use of seating control is especially beneficial if assembly is subject to fluctuations in process parameters which it is not feasible to eliminate or which can only be eliminated with considerable effort.
With seating control, users can detect process errors which have a direct impact on the quality of a tightening process. For example, these may include:
- Skewed tightening as a result of worker error (incorrect positioning of screw) or defects in the threaded hole.
- Use of incorrect screw – possibly as a result of the confusion if screws with different coatings or material grades and similar dimensions are available and no precautions are taken to avoid confusion.
- The lack of smart technology to detect errors, for example use of a pneumatic tool which does not allow torque monitoring and does not have the required precision in terms of the torque applied.
- Missing components such as washers or the overtightening of a screw or bolt.
Typical causes of tightening errors
To find out more about the specific benefits of seating control for users, read the second part of our Expert Hub article .
Download our flyer "Joint analysis with seating point detection":