Upgrading of the 2167P-50 tensile machine for investigation of the strength of welded joints

The purpose of the work is to upgrade the 2167P-50 tensile machine and to investigate the strength of welded joints made by contact (resistance) welding, ob-tained by welding on a machine equipped with a developed heat energy stabiliza-tion device. The microcontroller based control unit for the tensile machine has been developed and built. The microcontroller software performs closed-loop speed control of the tensile machine DC drive built using half-controlled single phase bridge rectifier (two diodes + two thyristors), measurement of a tensile force using strain gauge, measurement of the clamp displacement using incremental optical encoder and transmitting the data to the PC via RS232 interface. Special PC software has been written that allows to export the results to MS Excel for further processing. With the help of an upgraded tensile machine, the welded joints made with a resistance welding machine with a developed heat stabilization device were tested. Heat stabilization device performs measurement of voltage and current of the primary winding of the welding transformer and, knowing the transformer parameters, calculates the active power dissipated in the contact (welding) area. This active power is then integrated giving the heat energy in the welding area, and compared against preset threshold value. When calculated energy exceeds threshold, the welding current is switched off – the welding cycle ends. As a result of the conducted investigations it was established that when ferromagnetic masses are put into the welding current loop, the strength of the welded joints decreases. The equipment of resistance welding machines with the developed heat stabilization device makes it possible to reduce the effect of changing the resistance of the welding circuit, which leads to an increase in the strength of welded joints compared to the operation of the machine without a specific device. The practical value of the proposed device is to improve the quality of welded joints by reducing the influence of external disturbances on the welding process