Please tell us how to decide the welding parameters for spot welding.

First, tentatively determine the electrode force, welding time, and electrode tip shape by referring to the welding parameter charts, etc.
Under these parameters, gradually increase the current from a lower value to identify the current value that provides the required nugget diameter and the current value that causes expulsion.The optimal current range is between these two values. The mid value in this range should be adopted as the welding parameter.If you want to determine the more precise welding parameters, make weld lobes as shown in the figure.
Generally, in the case of galvanized steel sheet, a higher electrode force, a longer weld time, and a higher current are required.Also, electrodes should be dressed frequently because plating tends to adhere to electrodes.
In the case of high tensile strength steel sheets, generally a higher electrode force, a longer weld time, and a lower current are adopted.In addition, if a higher electrode force is not enough to eliminate the sheet gap, it may be effective to weld twice or three times.Materials are quenched during welding. In the case of high-tensile steel, the material ductility can be increased by adding the tempering current.
In the case of stainless steel, welding is possible with a lower current because of high resistivity.
However, in the case of martensitic type, the tempering current needs to be applied in the same way as in the case of high tensile steel.