Applications of single-mode fiber-lasers to novel microwelding

High power single-mode fiber-lasers with CW output power 40-200W was applied to microwelding. Thermal conduction equations of a square heat source were derived to calculate the temperature distribution and the mean temperature within the beam area. The penetration depth can be predicted assuming the beam- irradiation area is heated up to the boiling temperature of the material. High-speed photographs showed that a keyhole with the size of approximately focused beam spot is formed in the molten pool, of which diameter is in good agreement with the measured spot size. The humping defect can be suppressed by using fine beam spot size, because the width of the flow channel beside the keyhole is kept widely even at very high welding speeds resulting in stable flow of the molten metal. Ultra-high speed welding up to a velocity of 1500mm/s was attained without humping in SUS304 stainless steel foil. Sound lap welding of thin foils of 10muM to 30mum is demonstrated at welding speed of 920mm/s. Penetration welding of 800mum in thickness was achieved at laser power of 200W.