The invention relates to a method and a device for interlocking stackwise plastic bags, especially bags for automatic machines, by welding, wherein welding is effected by an interlocking device integrated into the grip hand of a robot with the purpose of simplifying welding. If CSI mode 1 is selected RI and W1 are jointly encoded using codebook sub-sampling in report 1. 1 to 10 times is used as the sealing member so as to obtain excellent sealing performance, durability, safety and environmental friendliness. The at least one lateral portion 36 extends part way only along the length of the main portion 34.