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Journal of KWJS 2005;23(3):76-82.
Published online July 15, 2005.
The Weldability of 6㎜^t Primer-coated Steel for Shipbuilding by CO₂ Laser(Ⅰ) - Effects of Primer Coating Condition and Gap Clearance -
Jong-Do Kim, Hyun-Joon Park
Abstract
Recently the application of laser welding technology has been considered to shipbuilding structure. However, when this technology is applied to primer coated steel, good quality weld beads are not easily obtained. Because the primer-coated layer caused the spatter, humping bead and porosity which are main part of the welding defect attributed to the powerful vaporizing pressure of zine. So we performed experiment with objectives of understanding spatter and porosity formation mechanism and producing sound weld beads in 6㎜t primer coated steels by a CO₂ CW laser. The effects of welding parameters; defocused distance, welding speed, coated thickness and coated position; were effects of welding parameters; defocused distance, welding speed, coated thickness and coated position; were investigated in the bead shape and penetration depth on bead and lap welding. Alternative idea was suggested to suspend the welding defect by giving a reasonable gap clearance for primer coated thickness. The zine of primer has a boiling point that is lower than melting point of steel. Zine vapor builds up at the interface between the two sheets and this tends to deteriorate the quality of the weld by ejecting weld material from lap position or leaving porosity. Significant effects of primer coated position was lap side rather than surface. Therefore introducing a small gap clearance in the lap position, the zine vapor could escape through it and sound weld beads can be acquired. In conclusion, formation and suspension mechanism of the welding defects was suggested by controling the factors.


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