Mitigation Solutions for the Magnetic Field Produced by MFDC Spot Welding Guns

Among the different welding technologies, portable welding guns are one of the most critical devices in relation to human exposure to electromagnetic fields. This paper focuses on medium frequency (MF) direct current guns proposing two actions aimed to the mitigation of the magnetic field generated during the welding process. The first action consists in the adoption of a passive shield for the on-board MF transformer. The analysis points out that the transformer alone produces a magnetic field that can exceed the prescribed limits. Therefore, a suitable mitigation system is identified. The second action aims to mitigate the predominant magnetic field that is generated by the electrodes of the welding gun. The analysis of the field waveforms shows that the rise time of the welding current pulse is the main parameter affecting the exposure index. The effect of the increase of the rise time is investigated through experimental and numerical analyses. The results prove that a small increase of the rise time causes a significant reduction of the exposure level. It is noteworthy that the two mitigation actions can be adopted on both existing and newly developed welding guns as they do not require any structural modification of the welding device