In the process of seam formation (intermittent) seam welding, each welding spot also undergoes three stages of pre-compression, electric heating and cooling and crystallization. However, due to the rapid changes in the relative position of the roller electrode and the weldment during seam welding, these three stages are not as distinct as those during spot welding. It can be concluded that: 1) Under the direct pressing of the roller electrode, the metal heated by electricity is at "Electrical heating stage". 2) The adjacent metal that is about to enter under the roller electrode is subject to a certain preheating and partial pressure of the roller electrode, and is in the "pre-loading stage". 3) On the one hand, the adjacent metal that has just come out from under the roller electrode begins to cool while still under the partial pressure of the roller electrode and is in the "cooling crystallization stage". Therefore, the welding area under the roller electrode and the metal materials on both sides adjacent to it will be at different stages at the same time. For any welding spot on the weld, the process of passing under the roller is a three-stage process of "pre-pressing-energizing heating-cooling and crystallization". Because the process is dynamic and the pressure in the pre-pressing and cooling crystallization stages is not enough, the quality of seam welded joints is generally different from that of spot welding, and defects such as cracks and shrinkage holes are prone to appear.

Working method of seam welder

According to the electromechanical coordination mode of roller electrode rotation (weld piece movement) and welding current passing (energization), it can be divided into the following three types.

Continuous seam welding

The roller electrode continuously rotates, the weldment moves at a constant speed, and the welding current passes continuously, forming a welding spot every half circle. The welding speed can reach 10 ~ 20m/min. Due to the poor surface quality of the weld, practical applications are limited.

Intermittent seam welding

The weldment moves continuously at a uniform speed, and the welding current passes intermittently, forming a welding spot every time it is "on and off". According to the thickness of the plate, the welding speed can reach 0.5 ~ 4.3m/min. It is widely used and mainly produces gas, water and oil sealed welds of ferrous metals.

Step seam welding

The weldment moves intermittently, and the welding current passes when the weldment is stationary, so that each "movement" will form a welding spot, and forging pressure can be applied. The formation of joints is very similar to spot welding. The welding speed is low, generally only 0.2~0.6m/min. It is only used to make high-sealing welds such as aluminum alloys and magnesium alloys.