Analysis of resistance welding processes and expulsion of liquid metal from the weld nugget

The article presents the process of resistance welding in relation to the expulsion of liquid metal from the weld nugget. The research-related tests involved the synchronic recording of welding process parameters such as welding current and voltage as well as electrode force and travel. The phenomenon of expulsion was filmed using a high speed camera. The tests aimed to determine the most effective parameter as regards the detection of expulsion as well as the accurate determination of the moment of expulsion in relation to the above-named parameter. During the tests it appeared that the most favourable parameter was the force of electrodes. The tests required the precise synchronisation of the recording of process parameters with the recording of images (using the camera). The uncertainty of expulsion time determination was estimated at 0.1ms. The research-related experimental tests were focused on the possibility of eliminating expulsion by stopping (blocking) the flow of welding current. In the case of expulsion, the process of welding was continued with a delayed second current pulse. The force signal, on the basis of which the expulsion detection was performed, was analysed using a dedicated controller which implementing the algorithm of discreet differentiation. The tests were performed using an inverter welding machine having an internal transformation frequency of 10kHz. In this study, SORPAS software-aided FEM analysis was performed to analyse the possibility of the effective reduction of the expulsion phenomenon.