ISQ

Intelligent welding gun control for quality monitoring during spot welding

A fiber Bragg grating sensor (FBG sensor) with an evaluation unit, already tested in previous projects, is used. Here, strain-time curves on the surface of the welding gun during the welding process are first recorded, digitized and provided as control variables by means of interference-optical and thus independent of the process variables. The core of the control system is digital filtering and the calculation of the control variable. The filtering is intended to eliminate noise components and periodic disturbance variables and, if necessary, to amplify quality-defining characteristics. The signal processing shall be designed in such a way that the filtered signal allows sufficiently statistically assured conclusions to be drawn about the expected quality of the weld spot already at the beginning of a welding process and that the control system can be used to take corrective action.

The test equipment was adapted and first basic tests were carried out on a spot welding robot of SLV Halle. The evaluation of the sensor signals recorded during these tests resulted in the basic functional verification of the measuring principle on a welding robot. Control and filter algorithms were designed and simulated with modelled signal characteristics. The results were used to determine filter characteristics and evaluation parameters for subsequent experimental investigations.

For further work, welding tests with the recording and evaluation of sensor signals are primarily planned. The materials of the welding samples as well as the technological welding parameters, including deliberate inducement of welding defects, are to be varied in order to be able to analyse their influences on the signal characteristics. Finally, experiments to control the welding process are planned in the subsequent work.