Research On Plasma In High Power CO₂ Laser Welding Of Domain Ship Plate

Plasma in CO₂ laser welding influencs the welding process stability and welding joint quality. Especially in high power CO₂ laser welding, because of the high input energy and laser density, the plasma is more active.With this as a reserch background, the thesis conducts a detailed study on the plasma in high power CO₂ laser welding of domainship plate based on the LabView image processing technology.Firstly, choosing the height of plasma image along the laser incident direction to represent the absorption. And selecting the area of plasma image to represent the plasma refraction.Secondly researching the influencing factor and the function of plasma in differernt welding parameters and conditions to obtain the following conclusion: (1) line energy is the crucial parameter. The plasma size could be controlled and welding process could be stable, when the line energy is appropriate. That is important to spread the high power laser welding. (2) In the problem usually happened during welding, workpieces decling and oversize gap are more disadvantageous than misalignment, oil and rust. (3) The plasme shape and size are changed unconspicuously in laser filler wire weldig.Finally, researching the shielding gas in different flow rate, nozzle position and gas component to get the following conclusion: (1) With the increasing flow rate, the plasma size is diminish. But when the flow over 40L/min, the change is small (2) The nozzle position is important to high power laser welding. X position may change in the range from -4 to +2mm, 0²mm is recommended; The Y position must guarantee in the laser point; Z position should be in 8¹5mm; Thenazzle angle maintains at 30o⁵0o. (3) Compared with pure helium, when using the mix-gas (75%Ar+25%He), the height of plasma is depressed and the area of plasma is increased, and could't get the qualified welding joint. When using the mix-gas (60%Ar+40%He), the welding joint quality and welding efficiency are accepted.