The semi-automatic CO2 welding usually adopts the method of burst arc ignition. Before arc striking, select the appropriate arc striking position to keep a certain distance between the welding wire and the workpiece. Press the start button on the welding gun to send the welding wire in and contact with the workpiece. The welding wire will melt and explode under the action of large short circuit current to ignite the arc.

The key to reliable arc striking is to make the welding wire slightly contact with the workpiece. Too tight contact or poor contact will cause excessive wire burn out length, leading to serious spatter and insufficient penetration at the arc striking point. Therefore, the following points should be noted.

①Before arc striking, the extension length of the welding wire must be adjusted properly to keep a distance of 2~3mm between the end of the welding wire and the weldment, and the distance between the contact tip and the weldment is 10~15mm, The operation method is: click the control switch on the welding gun and move the wire feed to make the extension length of the welding wire be 2~3mm less than the distance between the nozzle and the workpiece.

②If there is a metal ball at the end of the welding wire, it must be cut off with pliers, otherwise it is easy to cause serious spatter and weld defects at the arc striking position, or even difficult to achieve reliable arc striking.

③After the welding wire contacts with the workpiece, the welding gun tends to be jacked up by the welding wire. Therefore, slightly press the welding gun downward to prevent the arc from being extinguished due to stretching.

④When welding important welds or automatic welding, it is better to add the run on plate and start the arc on the run on plate.

⑤If it is not possible to add an arc strike plate, the arc is usually struck at 10~20mm from the starting end during semi-automatic welding, and then the arc is moved to the starting end after the arc is stable.

Generally, the initial welding end is prone to defects such as too high weld bead and insufficient penetration. To avoid these defects, firstly lengthen the arc slightly, preheat the end properly, and then compress the arc to normal length for normal welding. To avoid incomplete penetration, penetration, porosity and other defects at the arc striking position of the weld.

⑥ If the run on plate cannot be added, it shall generally move quickly at the arc starting point during automatic welding to obtain a narrow weld bead and create conditions for the weld bead joint.