Ultrasonic monitoring and controlling of a screwing process

Ultrasonic pulses are repeatedly coupled into the screw starting from the head of the screw using a pulse-echo method before and during the tightening process and the time it takes the ultrasonic pulses to traverse the length of the screw (propagation time) is measured. Before starting the tightening process, a dependency of the propagation time of the ultrasonic pulse on the predetermined tension of the screw is calculated from the material-specific characteristic values of the screw utilizing the measured propagation time through the load-free screw. Comparison of a change in propagation time dependent on a screw parameter with a calculated change in propagation time dependent on the predetermined tension of the screw permits drawing conclusions about the control of the screwing process. Thus, in particular, significant deviations indicate poor adherence to the specifications or thread damage, whereas minor deviations can be utilized to control the screwing process.