For CO2 laser welding of large output, when a deep penetration welding in single pass is done in the ambient atmosphere, it is known that blowholes may occur because of the in-keyhole gas being entrapped in molten metal. Keeping this problem in mind and changing the parameters, we conducted welding tests with full-penetration bead-on-plate welding, and checked by radiographic test for welding defects.The experimental results demonstrated that the larger is the specimen thickness, the more frequently occur welding defects, and that generation of welding defects depends upon the amount of welding heat input.Welding defects such as blowholes remain in metal, because the gas once entrapped into keyhole floats up in molten metal, and it is enclosed in the course of solidification. From this, we can verify the theory that a larger welding heat input, in the case of the full-penetration bead-on-plate welding, may be favorable for preventing welding blowholes. It can be assumed, therefore, that a larger heat input may hinder cooling of molten metal, and need a longer time for metal solidification; in this longer span of time, in-molten metal gas may escape while the metal is sufficiently heated.
AMPI introduced a CO2 laser processing system of 50kW that was the greatest output in the world. And, fundamental studies for welding of thick plates have been carried out.In this paper, the observation of plasma behavior with high-speed camera and the relationship between penetration depth and plasma configuration are studied. Then through the investigations, the welding characteristics with great output power CO2 laser by using the selected suitable supply condition of assist gas was investigated. And, to confirm limits of full penetration thickness, appearance of weld beads that tested full penetration welding were evaluated, and then proper welding conditions were examined.
The AMPI has introduced CO2 laser processing equipment featuring 50kW class output which is the greatest in the world. The equipment integrates a 50kW class CO2 laser oscillator, with a portal three-dimensional processing device and an internal path type CO2 laser robot, that is, robot with an integrated laser path. It offers a high degree of freedom in access to workpieces, enabling thereby flexible processing.The essential parameters which exert significant influence upon the laser welding performance are the defocused distance at the laser-irradiated point, the stand-off height (distance between welding nozzle and workpiece), as well as the kind and flow rate of shielding gas. The authors investigated the relationship between the penetration depth and these parameters for workpieces of mild steel and stainless steel respectively, in order to determine optimal values of the parameters. Besides, on the basis of the optimal values thus obtained, the relationship between penetration depth and welding speed was studied.This paper reports the summary of the equipment and main characteristics of the high power CO2 laser robot demonstrated by the investigation.
The AMPI has introduced CO{sub 2} laser processing equipment featuring 50kW class output which is the greatest in the world. The equipment integrates a 50kW class CO{sub 2} laser oscillator, with a portal three-dimensional processing device and an internal path type CO{sub 2} laser robot, that is, robot with an integrated laser path. It offers a high degree of freedom in access to workpieces, enabling thereby flexible processing. The essential parameters which exert significant influence upon the laser welding performance are the defocused distance at the laser-irradiated point, the stand-off height (distance between welding nozzle and workpiece), as well as the kind and flow rate of shielding gas. The authors investigated the relationship between the penetration depth and these parameters for workpieces of mild steel and stainless steel respectively, in order to determine optimal values of the parameters. Besides, on the basis of the optimal values thus obtained, the relationship between penetration depth and welding speed was studied. This paper reports the summary of the equipment and main characteristics of the high power CO{sub 2} laser robot demonstrated by the investigation.
The authors have examined proper welding condition which enclosed good weld beads in terms of welding appearance for full penetration welding. For CO2 laser welding of large output, it is generally known that porosity may occur in the weld bead when a deep penetration welding in single pass is performed in the ambient atmosphere. Welding defects mainly including porosity also occur more frequently with increase of plate thickness even though in the case of using proper welding condition.In order to spread laser welding generally, porosity is one of the most important problems to be solved. It is thought that formation mechanism of porosity is expressed as follows. Bubbles are generated mainly at the bottom of keyhole, which are trapped in molten metal during floating up and remain as porosity in metal.In this context, to reduce welding defects in welded bead, the authors paid attention to the following two conceptions; the first is that long heat input time would enable to delay beginning of molten metal solidification; the second is that molten metal could be fluidified smoothly by changing direction of recoil pressure. The authors adopted use of twin spot condensing system and improvement for the radiation angle of laser to test piece to accomplish these conception. Twin spot welding was the method of welding with two spot lasers which were condensed two laser beams which were divided from an uncondensed laser beam so that heat input increased in spite of decrease of penetration depth. Forehand welding was performed using a method of inclined laser radiation so that molten metal could be fluidified smoothly by changing direction of recoil pressure.In this report, the authors discuss in detail the prevention of welding defects which are generated by mainly porosity for thick plates.
For CO2 laser welding of large output, when a deep penetration welding in single pass is done in the ambient atmosphere, it is known that blowholes may occur because of the in-keyhole gas being entrapped in molten metal. Keeping this problem in mind and changing the parameters, we conducted welding tests with full-penetration bead-on-plate welding, and checked by radiographic test for welding defects. The experimental results demonstrated that the larger the specimen thickness, the more frequently welding defects occur, and that generation of welding defects depends upon the amount of welding heat input. Welding defects such as blowholes remain in metal, because the gas once entrapped into keyhole floats up in molten metal, and it is enclosed in the course of solidification. From this, we can verify the theory that a larger welding heat input, in the case of the good appearance full-penetration bead-on-plate welding, may be favorable for preventing welding blowholes. It can be assumed, therefore, that a larger heat input may hinder cooling of molten metal, and need a longer time for metal solidification; in this longer span of time, in-molten metal gas may escape while the metal is sufficiently heated.
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