Heat Balance In Resistance Welding

Heat Balance in Resistance Welding

A weld is said to have good heat balance if the parts being welded reach the required temperature on either side of the weld interface at the same time. Designing the weld joint for proper heat balance is one of the most important requirements for a successful and robust welding process. If the weld has poor heat balance then the welds will either not be strong enough or have a tendency to stick to the electrodes. There are multiple ways to improve heat balance and are discussed below:

Electrode Material Selection
Typically, a copper electrode will be placed against a resistive alloy such as stainless steel to keep the stainless for getting too hot. Similarly, a tungsten or molybdenum electrode will be used against a conductive alloy such as copper to keep the copper from loosing too much heat.
Electrode Size
If the welding application requires welding of thinner foil to a thicker sheet, a smaller diameter electrode should be used against the thinner foil and larger diameter electrode on the sheet. Doing so helps to focus the welding current density at the weld interface.
Polarity
The flow of current across a dissimilar metal junction, such as between a copper electrode and steel sheet has the capability to heat or cool the junction depending on the direction of current flow. This heating/cooling is different from the conventional resistive heating that is only dependent on the magnitude of the current and not the direction.
Projection
If one of the parts being welded is too big and does not get hot enough, a projection should be machined/stamped/coined into the big parts. The projection helps focus the welding heat and ensures that both the big and smaller part reach welding temperature at the same time.
Weld Location
Position of the weld on the part also changes heat balance by changing the heat loss to the adjacent material that is not taking part in the welding. For example, a weld on the edge of steel sheet will be hotter than a weld at the center.
Pulsation
Use of pulsation mode welding can also help in focusing the weld heat at the interface. Additional details in the following paper on pulsation welding ( pdf, link).