The Weldability of $6mm^t$ Primer-coated Steel for Shipbuilding by $CO_2$ Laser( I ) - Effects of Primer Coating Condition and Gap Clearance -

$6mm^t$조선용 프라이머 코팅강판의 $CO_2$레이저 용접성( I ) - 프라이머 코팅조건과 갭 간극의 영향 -

  • Kim Jong-Do (Division of Marine System Engineering, Korea Maritime University) ;
  • Park Hyun-Joon (Graduate School, Korea Maritime University)
  • 김종도 (한국해양대학교 기관시스템공학부) ;
  • 박현준 (한국해양대학교 대학원)
  • Published : 2005.06.01


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 zinc. So we performed experiment with objectives of understanding spatter and porosity formation mechanism and producing sound weld beads in 6mmt primer coated steels by a $CO_2$ CW laser. The 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 zinc of primer has a boiling point that is lower than melting point of steel. Zinc 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 zinc 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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