Roller seam welding
In addition to spot and projection welding, roller seam welding (abbreviation RR) is used relatively frequently. Here, too, the same process-related principles apply as for resistance spot welding. Simplified, roller seam welding can be viewed as a sequence of individual points. Depending on the speed and sequence of the individual points, a tight weld seam can be achieved. A pair of rollers, usually one of them driven, replaces the electrodes. The pair of rollers touches the workpieces in a point-like manner like two electrodes and allows welding to take place when current passes through.
By rotating the electrodes, the welding spot “migrates” further and ultimately leads to a weld seam. Since different contact points of the rollers always ensure the end, a uniform and very low electrode load is achieved. The spot sequence can be varied by continuous current or a current programme (current pulse and current pause alternately) to obtain a sealed seam or a tacked seam.
This always depends on the specific application and the workpiece material.
As the duty cycle is very high due to the fast spot sequence or continuous welding, care must be taken to ensure appropriate connection power. Due to the process, the metallic components often dip into the secondary discharge and lead to inductive losses. For this reason, controls with constant current control are used with AC machines, or DC machines are also very often used for roller seam welding because of the high welding power.
Here, too, the trend towards medium frequency is becoming increasingly prevalent. By means of medium-frequency controls, it becomes possible to set the pulse-pause ratios in the millisecond range.
The DVS 2906 information sheet provides further details and interesting facts about roller seam welding.