Small amount of active gases CO 2 and O 2 were added into pure argon inert shielding gas to impro... more Small amount of active gases CO 2 and O 2 were added into pure argon inert shielding gas to improve the weld formation of pulsed-current narrow-gap gas metal arc welding (NG-GMAW) of mild steel. Their effects on droplet transfer and arc behavior were investigated. A high-speed visual sensing system was utilized to observe the metal transfer process and arc morphology. When the proportion of CO 2 , being added into the pure argon shielding gas, changes from 5% to 5%, the metal transfer mode changes from pulsed spray streaming transfer to pulsed projected spray transfer, while it remains the pulsed spray streaming transfer when 2% to 10% O 2 is added. Both CO 2 and O 2 are favorable to stabilizing arc and welding process. O 2 is even more effective than CO 2 . However, O 2 is more likely to cause the inclusion defects in the weld, while CO 2 can improve the weld appearance in some sense. The weld surface concavity, which is sensitive to the formation of lack-of-fusion defect in NG-GMA...
The International Journal of Advanced Manufacturing Technology, 2017
The lack of fusion at sidewall is one of the most frequently occurred problems in narrow-gap gas ... more The lack of fusion at sidewall is one of the most frequently occurred problems in narrow-gap gas metal arc welding for joining thick plates of aluminum alloys. For better understanding the sidewall fusion mechanism and eventually solving such a problem, a series of welding experiments were carried out to investigate the sidewall penetration characteristics for 5083 Al alloys under various technological conditions. A Taguchi method was adopted to study the effect of welding current, arc voltage, and welding speed on the sidewall penetration and surface concavity, which is related to the quality of welding joint. The result shows that higher welding current or lower welding speed will contribute to a better fusion between weld bead and sidewalls; thus, optimized welding parameters can be obtained. The analysis of formation mechanism for lack of fusion defect shows that the molten pool surface tension, which is greatly influenced by temperature and oxide, is a main reason. Therefore, increasing the heat input to sidewalls by arc-swing, improving the gas protection of molten pool against oxidization, or reducing the heat dispersion of molten pool by preheating, are all effective measures for eliminating the lack of sidewall fusion defect.
ABSTRACT In order to better reveal the oscillation mechanism of the pulsed gas metal arc welding ... more ABSTRACT In order to better reveal the oscillation mechanism of the pulsed gas metal arc welding (GMAW-P) process due to an alternately varied welding current, arc plasma and molten pool oscillation were simulated through a self-consistent three-dimensional model. Based on an experimental analysis of the dynamic variation of the arc plasma and molten pool captured by a high-speed camera, the model was validated by comparison of the measured and predicted results. The calculated results showed that arc pressure was the key factor causing the molten pool to oscillate. The variation in arc size and temperature from peak time to base time resulted in a great difference in the heat input and arc pressure acting on the molten pool. The surface deformation of the molten pool due to the varying degrees of arc pressure induced alternate displacement and backflow in the molten metal. The periodic iteration of deeper and shallower surface deformation, drain and backflow of molten metal caused the molten pool to oscillate at a certain frequency. In this condition, the arc pressure at the peak time is more than six times higher than that at the base time, and the maximum surface depression is 1.4 mm and 0.6 mm, respectively, for peak time and base time.
ABSTRACT A novel light scanning system based on circular laser trajectory for welding robot is de... more ABSTRACT A novel light scanning system based on circular laser trajectory for welding robot is developed. With the help of image processing technique, intelligent laser welding could be realized. According to laser triangulation algorithm and Scheimpflug condition, mathematical model for circular laser vision is built. This scanning system projects circular laser onto welded seams and recovers the depth of the welded seams, escapes from shortcomings of less information, explains ambiguity and single tracking direction inherent in "spot" or "line" type laser trajectory. Three-dimensional (3D) model for welded seams could be recognized after depth recovery. The imaging error is investigated also.
The interface deformation between welding arc and weld pool is important in dynamic coupling nume... more The interface deformation between welding arc and weld pool is important in dynamic coupling numerical simulation on arc and pool. To reveal the interaction between welding arc and weld pool, unified mathematic model of TIG welding arc and pool was established ...
ABSTRACT Area-array CCD vision sensor based on circular laser trajectory used for weld seam locat... more ABSTRACT Area-array CCD vision sensor based on circular laser trajectory used for weld seam location and seam tracking was developed. In order to meet the requirement of 3D recovery, order-statistic filtering method based on one-third value instead of mean value was presented to make the circular laser trajectory perfect. Two-step segmentation (TSS) technique under GTAW (gas tungsten arc welding) arc condition or without welding arc condition was investigated. Using proposed 3D calculation algorithm, seam tracking for ramp welded seam was studied. The results showed, this vision sensor could measure the 3D change of welded seams at the same time, and 3D seam tracking could be realized. Proposed vision sensor manifested a promising result with high precision and high efficiency.
Small amount of active gases CO 2 and O 2 were added into pure argon inert shielding gas to impro... more Small amount of active gases CO 2 and O 2 were added into pure argon inert shielding gas to improve the weld formation of pulsed-current narrow-gap gas metal arc welding (NG-GMAW) of mild steel. Their effects on droplet transfer and arc behavior were investigated. A high-speed visual sensing system was utilized to observe the metal transfer process and arc morphology. When the proportion of CO 2 , being added into the pure argon shielding gas, changes from 5% to 5%, the metal transfer mode changes from pulsed spray streaming transfer to pulsed projected spray transfer, while it remains the pulsed spray streaming transfer when 2% to 10% O 2 is added. Both CO 2 and O 2 are favorable to stabilizing arc and welding process. O 2 is even more effective than CO 2 . However, O 2 is more likely to cause the inclusion defects in the weld, while CO 2 can improve the weld appearance in some sense. The weld surface concavity, which is sensitive to the formation of lack-of-fusion defect in NG-GMA...
The International Journal of Advanced Manufacturing Technology, 2017
The lack of fusion at sidewall is one of the most frequently occurred problems in narrow-gap gas ... more The lack of fusion at sidewall is one of the most frequently occurred problems in narrow-gap gas metal arc welding for joining thick plates of aluminum alloys. For better understanding the sidewall fusion mechanism and eventually solving such a problem, a series of welding experiments were carried out to investigate the sidewall penetration characteristics for 5083 Al alloys under various technological conditions. A Taguchi method was adopted to study the effect of welding current, arc voltage, and welding speed on the sidewall penetration and surface concavity, which is related to the quality of welding joint. The result shows that higher welding current or lower welding speed will contribute to a better fusion between weld bead and sidewalls; thus, optimized welding parameters can be obtained. The analysis of formation mechanism for lack of fusion defect shows that the molten pool surface tension, which is greatly influenced by temperature and oxide, is a main reason. Therefore, increasing the heat input to sidewalls by arc-swing, improving the gas protection of molten pool against oxidization, or reducing the heat dispersion of molten pool by preheating, are all effective measures for eliminating the lack of sidewall fusion defect.
ABSTRACT In order to better reveal the oscillation mechanism of the pulsed gas metal arc welding ... more ABSTRACT In order to better reveal the oscillation mechanism of the pulsed gas metal arc welding (GMAW-P) process due to an alternately varied welding current, arc plasma and molten pool oscillation were simulated through a self-consistent three-dimensional model. Based on an experimental analysis of the dynamic variation of the arc plasma and molten pool captured by a high-speed camera, the model was validated by comparison of the measured and predicted results. The calculated results showed that arc pressure was the key factor causing the molten pool to oscillate. The variation in arc size and temperature from peak time to base time resulted in a great difference in the heat input and arc pressure acting on the molten pool. The surface deformation of the molten pool due to the varying degrees of arc pressure induced alternate displacement and backflow in the molten metal. The periodic iteration of deeper and shallower surface deformation, drain and backflow of molten metal caused the molten pool to oscillate at a certain frequency. In this condition, the arc pressure at the peak time is more than six times higher than that at the base time, and the maximum surface depression is 1.4 mm and 0.6 mm, respectively, for peak time and base time.
ABSTRACT A novel light scanning system based on circular laser trajectory for welding robot is de... more ABSTRACT A novel light scanning system based on circular laser trajectory for welding robot is developed. With the help of image processing technique, intelligent laser welding could be realized. According to laser triangulation algorithm and Scheimpflug condition, mathematical model for circular laser vision is built. This scanning system projects circular laser onto welded seams and recovers the depth of the welded seams, escapes from shortcomings of less information, explains ambiguity and single tracking direction inherent in "spot" or "line" type laser trajectory. Three-dimensional (3D) model for welded seams could be recognized after depth recovery. The imaging error is investigated also.
The interface deformation between welding arc and weld pool is important in dynamic coupling nume... more The interface deformation between welding arc and weld pool is important in dynamic coupling numerical simulation on arc and pool. To reveal the interaction between welding arc and weld pool, unified mathematic model of TIG welding arc and pool was established ...
ABSTRACT Area-array CCD vision sensor based on circular laser trajectory used for weld seam locat... more ABSTRACT Area-array CCD vision sensor based on circular laser trajectory used for weld seam location and seam tracking was developed. In order to meet the requirement of 3D recovery, order-statistic filtering method based on one-third value instead of mean value was presented to make the circular laser trajectory perfect. Two-step segmentation (TSS) technique under GTAW (gas tungsten arc welding) arc condition or without welding arc condition was investigated. Using proposed 3D calculation algorithm, seam tracking for ramp welded seam was studied. The results showed, this vision sensor could measure the 3D change of welded seams at the same time, and 3D seam tracking could be realized. Proposed vision sensor manifested a promising result with high precision and high efficiency.
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Papers by Xinhua Tang