working principle
During the formation process of seam welded joints (intermittent) seam welding, each solder joint also goes through three stages of pre-pressing, electrified heating and cooling and crystallization. However, due to the rapid change of the relative position between the roller electrode and the weldment during seam welding, these three stages are not as obvious as those in spot welding. It can be considered that: 1) Under the direct pressing of the roller electrode, the metal being heated by electricity is in the "electric heating stage". 2) The adjacent metal that is about to enter under the roller electrode is subjected to certain preheating and partial pressure of the roller electrode, and it is in the "pre-pressing stage". 3) The adjacent metal that has just come out from under the roller electrode begins to cool on the one hand, and at the same time is subjected to the partial pressure of the roller electrode, which is in the "cooling and crystallization stage". Therefore, the welding area under the roller electrode and the metal materials on both sides adjacent to it will be in different stages at the same time. For any solder joint on the weld, the process of passing under the roller is also a three-stage process of "pre-pressing-electric heating-cooling and crystallization". Since the process is carried out dynamically, the pressure during the pre-pressing and cooling crystallization stages is not sufficient, so the quality of seam welded joints is generally worse than that of spot welding, and defects such as cracks and shrinkage holes are prone to occur.
According to the mechanical-electrical coordination method of the rotation of the roller electrode (movement of the weldment) and the passage of the welding current (energization), it can be divided into the following three types.
continuous seam welding
The roller electrode rotates continuously, the weldment moves at a constant speed, and the welding current passes continuously, forming a welding spot every half-circle. Welding speed can reach 10～20m/min Due to the poor surface quality of the weld, the practical application is limited
Intermittent seam welding
The weldment moves continuously and at the same speed, and the welding current passes through intermittently, and a welding spot is formed every "on-off" time. 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 sealing welds of ferrous metals.
Step seam welding
The weldment moves intermittently, and the welding current passes through when the weldment is stationary, and a welding spot is formed every "on-movement", and forging pressure can be applied. Joint formation is very similar to spot welding. The welding speed is low, generally only 0.2~0.6m/min. It is only used to manufacture high-sealing welds such as aluminum alloys and magnesium alloys.
