Aluminum specimens with and without chemically cleaning were welded by electron beam to investigate the effect of Al2O3 film on weld appearance. The removal mechanism of Al2O3 film during vacuum electron beam welding ...Aluminum specimens with and without chemically cleaning were welded by electron beam to investigate the effect of Al2O3 film on weld appearance. The removal mechanism of Al2O3 film during vacuum electron beam welding of aluminum was analyzed and the effect of Al2O3 film on molten pool flow behavior and weld appearance was investigated. The results showed that the weld width of the specimen was enlarged by chemically cleaning. The solid Al2O3 film transformed into gaseous Al2O3 via the reaction with liquid aluminum at the temperature higher than 1 350 K was the main reason for the removal of the film. The weld width was narrowed down by the oxide film due to the inhibition of outward flow driven by the surface tension gradient and the drag force between the Al2O3 film and liquid Al. The weld penetration was reduced in the initial stage and then enhanced in the metastable stage.展开更多
In this paper, an automatic inspection system for weld surface appearance using machine vision has been developed to recognize weld surface defects such as porosities, cracks, etc. It can replace conventional manual v...In this paper, an automatic inspection system for weld surface appearance using machine vision has been developed to recognize weld surface defects such as porosities, cracks, etc. It can replace conventional manual visual inspection method, which is tedious, time-consuming, subjective, experience-depended, and sometimes biased. The system consists of a CCD camera, a self-designed annular light source, a sensor controller, a frame grabbing card, a computer and so on. After acquiring weld surface appearance images using CCD, the images are preprocessed using median filtering and a series of image enhancement algorithms. Then a dynamic threshold and morphology algorithms are applied to segment defect object. Finally, defect features information is obtained by eight neighborhoods boundary chain code algorithm. Experimental results show that the developed system is capable of inspecting most surface defects such as porosities, cracks with high reliability and accuracy.展开更多
In order to increase the absorption of laser energy and improve the weld appearance in laser welding of Al alloy, 1.8 mm- 6013 Al alloy plate was welded by activating flux CO2 laser welding. Activating flux includes o...In order to increase the absorption of laser energy and improve the weld appearance in laser welding of Al alloy, 1.8 mm- 6013 Al alloy plate was welded by activating flux CO2 laser welding. Activating flux includes oxide and fluoride, which was coated on the workpiece surface before welding. The experimental results show that the activating flux can effectively improve the absorption of CO2 laser energy and increase the amount of the molten base metal. The improvement on the absorption of laser energy by oxide activating flux is greater than that by fluoride activating flux or two-component activating flux, but the slag detachability made from both the single activating flux and two-activating flux is poor. The gas pore sensitivity with oxide activating flux is much higher than that with fluoride activating flux in CO2 laser welding of 6013 Al alloy.展开更多
LF6 aluminum alloy plates with 4.5 mm thickness are welded in this experiment. Welding is carried out by using the CO2 laser-MIG paraxial hybrid welding in fiat position. The experimental results indicate that the inh...LF6 aluminum alloy plates with 4.5 mm thickness are welded in this experiment. Welding is carried out by using the CO2 laser-MIG paraxial hybrid welding in fiat position. The experimental results indicate that the inherent droplet transfer cycle time of conventional MIG arc is changed due to the interaction between CO2 laser beam and MIG arc in the short-circuiting mode of laser-MIG hybrid welding. Because of the preheating action of CO2 laser to electrode and base material, the droplet transfer frequency of MIG arc is increased in the hybrid welding process. When laser power is increased to a certain degree, the droplet transfer frequency is decreased due to the effect of laser-induced keyhole. Furthermore, through analyzing the MIG welding current and arc voltage waveforms and the characteristics of droplet transfer in the hybrid welding process, the effect of laser energy and the action point between laser beam and arc on the frequency of droplet transfer and weld appearance is investigated in details.展开更多
The metal transfer mode of electron beam welding （EBW） with filler wire was studied experimentally. The spatial position between the electron beam and the filler wire was defined. Basing on the charge coupled device...The metal transfer mode of electron beam welding （EBW） with filler wire was studied experimentally. The spatial position between the electron beam and the filler wire was defined. Basing on the charge coupled device （CCD） visual sensing system, the metal transfer mode of filler wire was investigated. The results showed that there were five transfer modes during EBW process due to different wire feed rates and spatial positions between beam and filler wire, such as short-circuiting mode, molten metal bridge mode, small droplet mode, big droplet mode and mixed mode. By comparing the weld appearance of different transfer modes, the molten metal bridge transfer was proved to be the best transfer mode.展开更多
The ultrasonic assisted GMAW （U-GMAW） method is proposed to achieve a more stable welding process and better weld quality. Tbe U-GMA W system is dereloped, which consists of power supplies, ultrasonic vibration syst...The ultrasonic assisted GMAW （U-GMAW） method is proposed to achieve a more stable welding process and better weld quality. Tbe U-GMA W system is dereloped, which consists of power supplies, ultrasonic vibration system and specially designed u＇elding torch. The U-GMA W process and eonventional GMA W process are compared through bead-on-plate welding. The weld beads arc continuous and well protected, while the weld surface appearances by GMA W and U-GMA W are apparently diffierent. The metal transfe ,node changes from globular transfer to short-circuiting transfer after ultrasonic wave is applied onto the arc.展开更多
基金supported by the International S&T Cooperation Program of China(Grant No.2011DFR60)
文摘Aluminum specimens with and without chemically cleaning were welded by electron beam to investigate the effect of Al2O3 film on weld appearance. The removal mechanism of Al2O3 film during vacuum electron beam welding of aluminum was analyzed and the effect of Al2O3 film on molten pool flow behavior and weld appearance was investigated. The results showed that the weld width of the specimen was enlarged by chemically cleaning. The solid Al2O3 film transformed into gaseous Al2O3 via the reaction with liquid aluminum at the temperature higher than 1 350 K was the main reason for the removal of the film. The weld width was narrowed down by the oxide film due to the inhibition of outward flow driven by the surface tension gradient and the drag force between the Al2O3 film and liquid Al. The weld penetration was reduced in the initial stage and then enhanced in the metastable stage.
文摘In this paper, an automatic inspection system for weld surface appearance using machine vision has been developed to recognize weld surface defects such as porosities, cracks, etc. It can replace conventional manual visual inspection method, which is tedious, time-consuming, subjective, experience-depended, and sometimes biased. The system consists of a CCD camera, a self-designed annular light source, a sensor controller, a frame grabbing card, a computer and so on. After acquiring weld surface appearance images using CCD, the images are preprocessed using median filtering and a series of image enhancement algorithms. Then a dynamic threshold and morphology algorithms are applied to segment defect object. Finally, defect features information is obtained by eight neighborhoods boundary chain code algorithm. Experimental results show that the developed system is capable of inspecting most surface defects such as porosities, cracks with high reliability and accuracy.
基金supported by State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, China
文摘In order to increase the absorption of laser energy and improve the weld appearance in laser welding of Al alloy, 1.8 mm- 6013 Al alloy plate was welded by activating flux CO2 laser welding. Activating flux includes oxide and fluoride, which was coated on the workpiece surface before welding. The experimental results show that the activating flux can effectively improve the absorption of CO2 laser energy and increase the amount of the molten base metal. The improvement on the absorption of laser energy by oxide activating flux is greater than that by fluoride activating flux or two-component activating flux, but the slag detachability made from both the single activating flux and two-activating flux is poor. The gas pore sensitivity with oxide activating flux is much higher than that with fluoride activating flux in CO2 laser welding of 6013 Al alloy.
文摘LF6 aluminum alloy plates with 4.5 mm thickness are welded in this experiment. Welding is carried out by using the CO2 laser-MIG paraxial hybrid welding in fiat position. The experimental results indicate that the inherent droplet transfer cycle time of conventional MIG arc is changed due to the interaction between CO2 laser beam and MIG arc in the short-circuiting mode of laser-MIG hybrid welding. Because of the preheating action of CO2 laser to electrode and base material, the droplet transfer frequency of MIG arc is increased in the hybrid welding process. When laser power is increased to a certain degree, the droplet transfer frequency is decreased due to the effect of laser-induced keyhole. Furthermore, through analyzing the MIG welding current and arc voltage waveforms and the characteristics of droplet transfer in the hybrid welding process, the effect of laser energy and the action point between laser beam and arc on the frequency of droplet transfer and weld appearance is investigated in details.
文摘The metal transfer mode of electron beam welding （EBW） with filler wire was studied experimentally. The spatial position between the electron beam and the filler wire was defined. Basing on the charge coupled device （CCD） visual sensing system, the metal transfer mode of filler wire was investigated. The results showed that there were five transfer modes during EBW process due to different wire feed rates and spatial positions between beam and filler wire, such as short-circuiting mode, molten metal bridge mode, small droplet mode, big droplet mode and mixed mode. By comparing the weld appearance of different transfer modes, the molten metal bridge transfer was proved to be the best transfer mode.
文摘The ultrasonic assisted GMAW （U-GMAW） method is proposed to achieve a more stable welding process and better weld quality. Tbe U-GMA W system is dereloped, which consists of power supplies, ultrasonic vibration system and specially designed u＇elding torch. The U-GMA W process and eonventional GMA W process are compared through bead-on-plate welding. The weld beads arc continuous and well protected, while the weld surface appearances by GMA W and U-GMA W are apparently diffierent. The metal transfe ,node changes from globular transfer to short-circuiting transfer after ultrasonic wave is applied onto the arc.
