Technical Information

Principle of the Resistance Welding Process

Resistance spot welding is a process in which metal parts are joined together by applying heat and pressure. The heat is generated by conversion of the electrical energy applied (welding current). The high electrical resistance of the materials being welded causes them to be heated to such an extent that they melt at their interface, forming a weld nugget. This nugget produces a firm joint between the material when it solidifies. This process is based on the equation:

Q = I² · R · t
Q = Quantity of heat (Qw)
I = Welding current (Iw)
R = total restistance (sum of R1-Rn)
t = Welding time (tw)

Depending on the type of material, sheet thickness and surface finish of the materials being joined, welding currents (lw) between 6.000 A and 35.000 A are needed to generate the heat (Q). The currents for iron-based materials lie at the lower end of the overall range and those for aluminium and its alloys at the upper end.

To transmit high currents while simultaneously applying the high electrode force (Fel) required in a range of 2.5-5 kN, electrode materials with high electrical conductivity and mechanical hardness at room and higher temperatures are needed. Among other grades Duro Metall supplies the qualities Elmedur X, Elmedur HA and Elmedur Z for this application.