The concept of calculating Mahalanobis distance (MD) was introduced in order to describe welding faults. First, a set of weldments without any faults were generated in a number of repeated sessions in order to be used as references. The values of Mahalanobis distance obtained from the reference weldments were taken as a reference or a standard. Then, additional weldments were fashioned while artificial changing the flow rate of shielding gas and types of contact tips and simultaneously obtaining values for arc voltage and current at a rate of more than 8000 samples per second. Last, Mahalanobis distances for voltage and current values were calculated and used for qualitative and quantitative analysis with comparison to values obtained from the reference welds. The results described in this article confirm that Mahalanobis distances based on the short-term changes of welding parameters can be feasibly and effectively used for quality rating of welding faults in gas metal arc welding.