Spot welding is the most common welding method for cold rolled and galvanized steel sheets. The method is rapid and due to the low heat input the distortion of the welded sheets is normally very low.
Measurement of weld size
The weld size is normally determined by measuring the plug diameter in a peel test (Figure 1) or a cross-tension test (Figure 2).
Figure 1: Peel test. A common method used to measure the plug diameter of spot welds.
Available welding current range
To determine the spot weldability of steels the available welding current range is normally evaluated. This current range can be determined from the graph “plug diameter vs welding current”. The available welding current range is defined by the maximum current without splash and the minimum current still giving an acceptable size of the plug diameter. This minimum plug diameter often varies between different companies but for sheet thicknesses <1,5 mm a value of 4 mm is often used. The corresponding value of the minimum plug diameter for sheet thicknesses >1,5 mm is often 6 mm.