The welding deviation detection is the basis of robotic tracking welding, but the on-line real-time measurement of welding deviation is still not well solved by the existing methods. There is plenty of information in ...The welding deviation detection is the basis of robotic tracking welding, but the on-line real-time measurement of welding deviation is still not well solved by the existing methods. There is plenty of information in the gas metal arc welding(GMAW) molten pool images that is very important for the control of welding seam tracking. The physical meaning for the curvature extremum of molten pool contour is revealed by researching the molten pool images, that is, the deviation information points of welding wire center and the molten tip center are the maxima and the local maxima of the contour curvature, and the horizontal welding deviation is the position difference of these two extremum points. A new method of weld deviation detection is presented, including the process of preprocessing molten pool images, extracting and segmenting the contours, obtaining the contour extremum points, and calculating the welding deviation, etc. Extracting the contours is the premise, segmenting the contour lines is the foundation, and obtaining the contour extremum points is the key. The contour images can be extracted with the method of discrete dyadic wavelet transform, which is divided into two sub contours including welding wire and molten tip separately. The curvature value of each point of the two sub contour lines is calculated based on the approximate curvature formula of multi-points for plane curve, and the two points of the curvature extremum are the characteristics needed for the welding deviation calculation. The results of the tests and analyses show that the maximum error of the obtained on-line welding deviation is 2 pixels(0.16 ram), and the algorithm is stable enough to meet the requirements of the pipeline in real-time control at a speed of less than 500 mm/min. The method can be applied to the on-line automatic welding deviation detection.展开更多
An experimental setup of acquiring the coaxial visual image of the molten pool and keyhole in high power Nd:YAG laser welding is introduced in this paper. It is one of the most difficult problems in acquiring coaxial ...An experimental setup of acquiring the coaxial visual image of the molten pool and keyhole in high power Nd:YAG laser welding is introduced in this paper. It is one of the most difficult problems in acquiring coaxial image that the coaxial imaging signal of molten pool and keyhole must be separated from the laser beam with high power. This problem was resolved by designing a dichroitic spectroscope. The characteristics of imaging signal were analyzed and the coaxial image of molten pool and keyhole was acquired. A smoothing filter and a homomorphic filter were designed to remove the low frequency noise and to enhance the image according to the characteristics of imaging signal. At last, edges of molten pool and keyhole were detected and extracted based on image segmentation with threshold.展开更多
Body-fitted coordinate transformation equation was deduced and used to generate the body-fitted grids of molten pool for twin-roll strip casting.The orthogonality of the grids on the boundary was modified by adjusting...Body-fitted coordinate transformation equation was deduced and used to generate the body-fitted grids of molten pool for twin-roll strip casting.The orthogonality of the grids on the boundary was modified by adjusting source item.The energy equation and the boundary conditions were transformed from physical space to computational space.The velocity field model proposed by Hirohiko Takuda was used to calculate the temperature field of molten steel,and the influence of technical factors was also discussed.展开更多
The effect of the laser processing parameters on the composition uniformity and shape coefficient of fusion zone with laser surface alloyed Cr plated on medium carbon low alloy steel has been studied.It was found that...The effect of the laser processing parameters on the composition uniformity and shape coefficient of fusion zone with laser surface alloyed Cr plated on medium carbon low alloy steel has been studied.It was found that the composition uniformity depends on the shape coefficient of fusion zone,and the later is a function of both power density and interaction time.If the power density is fixed to a certain value,the shape coefficient is directly,propor- tional to the interaction time.A completely,uniform molten pool can be obtained,when the shape coefficient is between 1.6 and 3.0.展开更多
Two measuring methods, high-speed camera and optical monitoring system, were used to study processes of laser welding. Molten pool, cooling time and temperature field were analyzed based on real measured images and op...Two measuring methods, high-speed camera and optical monitoring system, were used to study processes of laser welding. Molten pool, cooling time and temperature field were analyzed based on real measured images and optical signal data. The results show that the width of molten pool is almost equal to the width of weld, and length is about 7. 8 mm. The solidification time is about 0. 5 s and the temperature gradient is great, so HAZ is very small. The method and results will be of benefit to build the relationship between welding parameters and microstructure.展开更多
Due to the disturbances of spatters, dusts and strong arc light, it is difficult to detect the molten pool edge and the weld line location in CO_2 welding processes. The median filtering and self-multiplication was em...Due to the disturbances of spatters, dusts and strong arc light, it is difficult to detect the molten pool edge and the weld line location in CO_2 welding processes. The median filtering and self-multiplication was employed to preprocess the image of the CO_2 welding in order to detect effectively the edge of molten pool and the location of weld line. The B-spline wavelet algorithm has been investigated, the influence of different scales and thresholds on the results of the edge detection have been compared and analyzed. The experimental results show that better performance to extract the edge of the molten pool and the location of weld line can be obtained by using the B-spline wavelet transform. The proposed edge detection approach can be further applied to the control of molten depth and the seam tracking.展开更多
Intermetallic compounds produced in laser additive manufacturing are the main factors restricting the joint performance of dissimilar metals.To solve this problem,a dual molten pool interface interlocking mechanism wa...Intermetallic compounds produced in laser additive manufacturing are the main factors restricting the joint performance of dissimilar metals.To solve this problem,a dual molten pool interface interlocking mechanism was proposed in this study.Based on a dual molten pool interface interlocking mechanism,the dissimilar metals,aluminum alloy and stainless steel,were produced as single-layer and multilayer samples,using the wire-feed laser additive manufacturing directed energy deposition technology.The preferred parameters for the dual molten pool interface interlocking mechanism process of the dissimilar metals,aluminum alloy and stainless steel,were obtained.The matching relationship between the interface connection of dissimilar metals and the process parameters was established.The results demonstrated excellent mechanical occlusion at the connection interface and no apparent intermetallic compound layer.Good feature size and high microhardness were observed under a laser power of 660 W,a wire feeding speed of 55 mm/s,and a platform moving speed of 10 mm/s.Molecular dynamics simulations demonstrated a faster rate of aluminum diffusion in the aluminum alloy substrate to stainless steel under the action of the initial contact force than without the initial contact force.Thus,the dual molten pool interface interlocking mechanism can effectively reduce the intermetallic compound layer when dissimilar metals are connected in the aerospace field.展开更多
Submerged arc welding process has been simulated to investigate the molten pool features of EH36 shipbuilding steel.One case only involved the surface tension model,and another one involved both the surface tension mo...Submerged arc welding process has been simulated to investigate the molten pool features of EH36 shipbuilding steel.One case only involved the surface tension model,and another one involved both the surface tension model and the interface tension model.The role of interface tension during welding is revealed,and the evolution of molten pool morphology is understood by comparing the surface temperature distribution,surface tension and interface tension distribution,and the streamline of the molten pool for the two cases.When the interface tension model is disregarded,a flow conducive to the outward expansion is formed in the surface area of the molten pool,resulting in a small weld depth-to-width ratio.After applying the interface tension model,the expanding outward flow is restrained,which leads to a deep penetration morphology with a large weld depth-to-width ratio due to the inward flow governed by the Marangoni forces.The simulation results involving the interface tension model have been verified with satisfactory predictability.展开更多
The performance of vacuum arc remelting (VAR) ingot depends largely on ingot structure and chemical uniformity,which are strongly influenced by molten pool profile that is influenced by VAR process.To better understan...The performance of vacuum arc remelting (VAR) ingot depends largely on ingot structure and chemical uniformity,which are strongly influenced by molten pool profile that is influenced by VAR process.To better understand the effect of remelting current on molten pool profile of titanium alloy ingot during VAR process,a 3D finite element model is developed by the ANSYS software.The results show that there are three remelting stages during VAR process when the remelting current is 2.0 kA.The molten pool depth increases gradually from 30 to 320 s,then the change of molten pool depth is very small during the steady state stage from 320 to 386 s,and lastly the molten pool depth becomes shallow after 386 s.The melting rate and temperature of superheat increase with the remelting current increasing,which leads to the augment of molten pool volume.In the end,the total remelting time and steady state molten pool time decrease with the melting current from 1.6 to 2.8 kA.展开更多
基金Supported by National Natural Science Foundation of China(Grant Nos.51275051,51505035)National Hi-tech Research and Development Program of China(863 Program,Grant No.2009AA04Z208)Beijing Education Commission Innovation Ability Upgrade Program of China(Grant No.TJSHG201510017023)
文摘The welding deviation detection is the basis of robotic tracking welding, but the on-line real-time measurement of welding deviation is still not well solved by the existing methods. There is plenty of information in the gas metal arc welding(GMAW) molten pool images that is very important for the control of welding seam tracking. The physical meaning for the curvature extremum of molten pool contour is revealed by researching the molten pool images, that is, the deviation information points of welding wire center and the molten tip center are the maxima and the local maxima of the contour curvature, and the horizontal welding deviation is the position difference of these two extremum points. A new method of weld deviation detection is presented, including the process of preprocessing molten pool images, extracting and segmenting the contours, obtaining the contour extremum points, and calculating the welding deviation, etc. Extracting the contours is the premise, segmenting the contour lines is the foundation, and obtaining the contour extremum points is the key. The contour images can be extracted with the method of discrete dyadic wavelet transform, which is divided into two sub contours including welding wire and molten tip separately. The curvature value of each point of the two sub contour lines is calculated based on the approximate curvature formula of multi-points for plane curve, and the two points of the curvature extremum are the characteristics needed for the welding deviation calculation. The results of the tests and analyses show that the maximum error of the obtained on-line welding deviation is 2 pixels(0.16 ram), and the algorithm is stable enough to meet the requirements of the pipeline in real-time control at a speed of less than 500 mm/min. The method can be applied to the on-line automatic welding deviation detection.
文摘An experimental setup of acquiring the coaxial visual image of the molten pool and keyhole in high power Nd:YAG laser welding is introduced in this paper. It is one of the most difficult problems in acquiring coaxial image that the coaxial imaging signal of molten pool and keyhole must be separated from the laser beam with high power. This problem was resolved by designing a dichroitic spectroscope. The characteristics of imaging signal were analyzed and the coaxial image of molten pool and keyhole was acquired. A smoothing filter and a homomorphic filter were designed to remove the low frequency noise and to enhance the image according to the characteristics of imaging signal. At last, edges of molten pool and keyhole were detected and extracted based on image segmentation with threshold.
文摘Body-fitted coordinate transformation equation was deduced and used to generate the body-fitted grids of molten pool for twin-roll strip casting.The orthogonality of the grids on the boundary was modified by adjusting source item.The energy equation and the boundary conditions were transformed from physical space to computational space.The velocity field model proposed by Hirohiko Takuda was used to calculate the temperature field of molten steel,and the influence of technical factors was also discussed.
文摘The effect of the laser processing parameters on the composition uniformity and shape coefficient of fusion zone with laser surface alloyed Cr plated on medium carbon low alloy steel has been studied.It was found that the composition uniformity depends on the shape coefficient of fusion zone,and the later is a function of both power density and interaction time.If the power density is fixed to a certain value,the shape coefficient is directly,propor- tional to the interaction time.A completely,uniform molten pool can be obtained,when the shape coefficient is between 1.6 and 3.0.
文摘Two measuring methods, high-speed camera and optical monitoring system, were used to study processes of laser welding. Molten pool, cooling time and temperature field were analyzed based on real measured images and optical signal data. The results show that the width of molten pool is almost equal to the width of weld, and length is about 7. 8 mm. The solidification time is about 0. 5 s and the temperature gradient is great, so HAZ is very small. The method and results will be of benefit to build the relationship between welding parameters and microstructure.
文摘Due to the disturbances of spatters, dusts and strong arc light, it is difficult to detect the molten pool edge and the weld line location in CO_2 welding processes. The median filtering and self-multiplication was employed to preprocess the image of the CO_2 welding in order to detect effectively the edge of molten pool and the location of weld line. The B-spline wavelet algorithm has been investigated, the influence of different scales and thresholds on the results of the edge detection have been compared and analyzed. The experimental results show that better performance to extract the edge of the molten pool and the location of weld line can be obtained by using the B-spline wavelet transform. The proposed edge detection approach can be further applied to the control of molten depth and the seam tracking.
基金supported by the National Natural Science Foundation of China(Grant No.51901162)the support of the National Talent Program of China。
文摘Intermetallic compounds produced in laser additive manufacturing are the main factors restricting the joint performance of dissimilar metals.To solve this problem,a dual molten pool interface interlocking mechanism was proposed in this study.Based on a dual molten pool interface interlocking mechanism,the dissimilar metals,aluminum alloy and stainless steel,were produced as single-layer and multilayer samples,using the wire-feed laser additive manufacturing directed energy deposition technology.The preferred parameters for the dual molten pool interface interlocking mechanism process of the dissimilar metals,aluminum alloy and stainless steel,were obtained.The matching relationship between the interface connection of dissimilar metals and the process parameters was established.The results demonstrated excellent mechanical occlusion at the connection interface and no apparent intermetallic compound layer.Good feature size and high microhardness were observed under a laser power of 660 W,a wire feeding speed of 55 mm/s,and a platform moving speed of 10 mm/s.Molecular dynamics simulations demonstrated a faster rate of aluminum diffusion in the aluminum alloy substrate to stainless steel under the action of the initial contact force than without the initial contact force.Thus,the dual molten pool interface interlocking mechanism can effectively reduce the intermetallic compound layer when dissimilar metals are connected in the aerospace field.
基金The authors sincerely thank the National Natural Science Foundation of China(Grant Nos.U20A20277,52150610494,52104295,52011530180 and 52050410341)Research Fund for Central Universities(Grant Nos.N2125016 and N2025025)Young Elite Scientists Sponsorship Program by CAST(YESS)(Grant No.2021-2023QNRC001).
文摘Submerged arc welding process has been simulated to investigate the molten pool features of EH36 shipbuilding steel.One case only involved the surface tension model,and another one involved both the surface tension model and the interface tension model.The role of interface tension during welding is revealed,and the evolution of molten pool morphology is understood by comparing the surface temperature distribution,surface tension and interface tension distribution,and the streamline of the molten pool for the two cases.When the interface tension model is disregarded,a flow conducive to the outward expansion is formed in the surface area of the molten pool,resulting in a small weld depth-to-width ratio.After applying the interface tension model,the expanding outward flow is restrained,which leads to a deep penetration morphology with a large weld depth-to-width ratio due to the inward flow governed by the Marangoni forces.The simulation results involving the interface tension model have been verified with satisfactory predictability.
基金the National Basic Research Program(973) of China (No.2007CB613802)
文摘The performance of vacuum arc remelting (VAR) ingot depends largely on ingot structure and chemical uniformity,which are strongly influenced by molten pool profile that is influenced by VAR process.To better understand the effect of remelting current on molten pool profile of titanium alloy ingot during VAR process,a 3D finite element model is developed by the ANSYS software.The results show that there are three remelting stages during VAR process when the remelting current is 2.0 kA.The molten pool depth increases gradually from 30 to 320 s,then the change of molten pool depth is very small during the steady state stage from 320 to 386 s,and lastly the molten pool depth becomes shallow after 386 s.The melting rate and temperature of superheat increase with the remelting current increasing,which leads to the augment of molten pool volume.In the end,the total remelting time and steady state molten pool time decrease with the melting current from 1.6 to 2.8 kA.