This paper describes investigations of a process monitoring system—window monitoring for clinching techniques. This window technique was used in the study of evaluating the quality of joints. In the research a clinching machine from the type Eckold, steel DC04 with different thicknesses and steel H340 with a thickness 1.00 mm as well as a window monitoring system Digiforce 9306 were utilized. Monitoring functions were investigated under different applying conditions: change of clinched materials, change of sheet metal thicknesses and change of clinching machine tools etc. The results showed that the window monitoring method had an outstanding capability of monitoring changes of applying conditions so that a reproducible quality of joints could be ensured. Comparing with the conventional tolerance monitoring method window monitoring method has two extra advantages: one is its short time consume during a monitoring phase, another one is that with windows there is more information about a monitoring situation, to distinguish which errors occur during a clinch joining.