LASER BEAM WELDING METHOD OF METAL THICK PLATE

PURPOSE:To enable the piercing welding not having melt down by setting a heat input quantity to the prescribed condition at executing flat/butt welding of thick plate by laser beam. CONSTITUTION:When a metal thick plate is subjected to flat/butt welding with using laser beam, a heat input quantity Q by laser beam is set so as to satisfy the condition in the inequality and welding is executed. In the inequality, Q: heat input quantity (KJ/cm), h: plate thickness (mm), V: welding speed (cm/min) sigma: surface tension of molten metal (dyn/cm ), rho: density of metal (g/cm ), t: constant obtained relationship between laser output and piercing thickness, g: acceleration of gravity (cm/sec ). When heat input quantity Q can not satisfy the condition of the inequality, piercing welding becomes impossible due to insufficient melt down. When heat input quantity Q exceeds the condition of the inequality, because a molten metal quantity becomes excessive, melt down of molten metal is generated, sound bead is not formed.