Resistance ratios for spot welding
As already known, the heat required for welding is generated by the current flow via the electrical resistance of the welding zone.
The contact resistance between the sheets is decisive for heat generation and thus for lens formation. This must be significantly larger than all other resistors in the secondary circuit. The total contact resistance consists of the described contact resistance sheet-metal-sheet, the two contact resistances electrode-sheet and sheet-metal-electrode, as well as the material resistances of the two sheets and the electrodes.
During welding, the individual resistances change. As the electrode force and temperature increase, the contact area increases and the contact resistance decreases. Due to the increasing temperature as the current time progresses, the now increasing material resistances predominate.
Typical for the welding of structural steels is a collapse of the total resistance in the first periods of the welding time and a subsequent increase up to a maximum. Then, due to the repositioning of the electrodes, the thickness is reduced and the resistance decreases again.
You can obtain more information during training courses at our company, which we offer on a customer-specific basis.