Spatter during laser powder bed fusion(LPBF)can induce surface defects,impacting the fatigue performance of the fabricated components.Here,we reveal and explain the links between vapour depression shape and spatter dy...Spatter during laser powder bed fusion(LPBF)can induce surface defects,impacting the fatigue performance of the fabricated components.Here,we reveal and explain the links between vapour depression shape and spatter dynamics during LPBF of an Al-Fe-Zr aluminium alloy using high-speed synchrotron x-ray imaging.We quantify the number,trajectory angle,velocity,and kinetic energy of the spatter as a function of vapour depression zone/keyhole morphology under industry-relevant processing conditions.The depression zone/keyhole morphology was found to influence the spatter ejection angle in keyhole versus conduction melting modes:(i)the vapour-pressure driven plume in conduction mode with a quasi-semi-circular depression zone leads to backward spatter whereas;and(ii)the keyhole rear wall redirects the gas/vapour flow to cause vertical spatter ejection and rear rim droplet spatter.Increasing the opening of the keyhole or vapour depression zone can reduce entrainment of solid spatter.We discover a spatter-induced cavity mechanism in which small spatter particles are accelerated towards the powder bed after laser-spatter interaction,inducing powder denudation and cavities on the printed surface.By quantifying these laser-spatter interactions,we suggest a printing strategy for minimising defects and improving the surface quality of LPBF parts.展开更多
Laser powder bed fusion(LPBF)is a highly dynamic and complex physical process,and single-track de-fects tend to accumulate into non-negligible internal defects of parts.The nickel-based superalloy single track was fab...Laser powder bed fusion(LPBF)is a highly dynamic and complex physical process,and single-track de-fects tend to accumulate into non-negligible internal defects of parts.The nickel-based superalloy single track was fabricated by LPBF,and its plume and spattering behavior were monitored in situ and recorded in real time based on image recognition and tracking in this study.The relationship among laser energy density,melt flow,plume and spattering behavior during LPBF was discussed.Volumetric energy density had limitations as a design parameter for LPBF.However,we found that plume and spattering behavior can be used as real-time design parameters for the processing of LPBF parts and implemented the initial velocity statistics for LPBF single-track spattering based on the centroid extraction algorithm.The influ-ence of melt flow evolution paths on the spattering and plume behavior in three different melting modes was revealed,and a shift in plume behavior was found in the overlap region of the additive substrate.This study provides a new method for obtaining statistics of spattering-related physical quantities in the melting mode,which is beneficial for the development of processing methods to mitigate the instability of the LPBF process.展开更多
Classification of plume and spatter images was studied to evaluate the welding stability. A high-speed camera was used to capture the instantaneous images of plume and spatters during high power disk laser welding. Ch...Classification of plume and spatter images was studied to evaluate the welding stability. A high-speed camera was used to capture the instantaneous images of plume and spatters during high power disk laser welding. Characteristic parameters such as the area and number of spatters, the average grayscale of a spatter image, the entropy of a spatter grayscale image, the coordinate ratio of the plume centroid and the welding point, the polar coordinates of the plume centroid were defined and extracted. Karhunen-Loeve transform method was used to change the seven characteristics into three primary characteristics to reduce the dimensions. Also, K-nearest neighbor method was used to classify the plume and spatter images into two categories such as good and poor welding quality. The results show that plume and spatter have a close relationship with the welding stability, and two categories could be recognized effectively using K-nearest neighbor method based on Karhunen-Loeve transform.展开更多
Welding spatter cause many problems during the welding process and this issue is particularly important for cellulose electrode welding. The hot flying spatter balls often deteriorate the working environment, and decr...Welding spatter cause many problems during the welding process and this issue is particularly important for cellulose electrode welding. The hot flying spatter balls often deteriorate the working environment, and decrease the welding efficiency. Many factors affect the welding spatter, and metal transfer behavior is one of the main factors. Many studies concerning the spatter mechanism in arc welding process were made; most of them focused on the solid wire welding and the study on cellulose electrode is rarely reported. In this paper the metal transfer behavior and the weld spatter characteristics of three commercial cellulose electrodes were studied experimentally by using a high speed camera for visually capturing the metal transfer. The relationship between the metal transfer and the welding spatter was analyzed experimentally by comparing the spatter loss coefficient, which is for quantitative evaluation of welding spatter, with the statistical analysis of the large droplet transfer mode. The results showed that short circuiting transfer, large droplet spray transfer, fine droplet spray transfer and explosive transfer govern the metal transfer modes in cellulose electrode welding. Weld spatter occurred mainly in the deflection of large droplet process, explosive transfer process and fine droplet spraying process. Different metal transfer modes lead to different spatter. The deflection of large droplet and explosive transfer are the main factors of the spatter formation. Minimizing the droplet size and reducing the deflection of large droplet and explosive transfer leads to the reduction the amount of spatter in cellulose electrode welding.展开更多
Aim at improving the stability of the Short-circuiting Gas Metal Arc Welding （GMAW-S） process for the enhanced speed usage, effects of current waveform parameters during short-term on the welding stability have been...Aim at improving the stability of the Short-circuiting Gas Metal Arc Welding （GMAW-S） process for the enhanced speed usage, effects of current waveform parameters during short-term on the welding stability have been investigated by experimental method. The welding power source used for the research is an inverter with a special current waveform control. It is shown that the spatter decreases at first then increases with each increase of the low current period, current increase rate and the maximum current limit. The test results are provided for welding of 1 mm and 3 mm mild steel at speed of 1.2 m/min. The stable GMA W-S process under high speed welding condition has been achieved by optimizing the parameters.展开更多
Welding spatter seriously affects the surface quality of the product. Aiming at the automatic detection problem of spatter on welding plate surface, an in-situ detection algorithm of welding spatter based on machine v...Welding spatter seriously affects the surface quality of the product. Aiming at the automatic detection problem of spatter on welding plate surface, an in-situ detection algorithm of welding spatter based on machine vision is designed. In the extraction process of the welding spatter, the two-dimensional Fourier transform is adopted to obtain the frequency and phase information of image, and the elliptical high-pass filter is introduced to filter the low-frequency signal. The experimental results show that the proposed algorithm has higher extraction rate and extraction accuracy rate of welding spatter than the threshold method, the rectangular high-pass filter and the Canny operator, and it has the characteristics of high efficiency, high precision, and good robustness.展开更多
During the selective laser melting process,a high-energy laser beam acts on the powder,a molten pool is rapidly generated and the characteristic parameters are constantly changing.Among them,temperature is one of the ...During the selective laser melting process,a high-energy laser beam acts on the powder,a molten pool is rapidly generated and the characteristic parameters are constantly changing.Among them,temperature is one of the important parameters in the forming process.Due to the generation of splash particles,there will be defects in the microstructure,which will seriously affect the formation quality of the prepared parts.Therefore,it is necessary to study the relationships between the splash behavior,molten pool characteristics and product quality.The finite element simulation of the transient temperature field was performed by ANSYS software.Time-series images at different frame rates were obtained with a high-speed camera,and the dynamic process of splashing was observed.Using IN718 alloy powder,the influence of the laser energy density on the light intensity of the molten pool was studied.The appearance of splash particles and the deviation of the powder chemical elements caused by the splash were analyzed.The results show that the transient temperature field with drastic change is easy to cause spatter,which is consistent with the experimental results.There are large differences in the splash at different shooting frame rates.Increasing the frame rate can allow the observation of details such as the shape,size and number of splash particles,which is beneficial for studying the process of splash formation.At the moment when the splash occurs,the light intensity of the molten pool always first increases and then decreases,depending on the energy input.The higher the energy input is,the more intense the light intensity of the molten pool and the higher the peak interval distribution.Compared with fresh powder,the contents of Al and Ti in powder reused 5 times were reduced by 0.15%and 0.02%,respectively.The increases of these two elements in the splash were 16.18%and 29.62%,respectively,and the content of Nb even exceeded the standard range.When the energy density decreased from 229.17 J/mm3 to 130.95 J/mm3,the relative density of the part increased from 91.82%to 99.83%.This shows that reducing the energy input can reduce the splash to suppress the generation of defects,along with the weakening of the overall light intensity of the molten pool.These results can provide a basis for feature extraction of the molten pool,which is of great significance for real-time monitoring and online control in manufacturing processes and ensuring product quality.展开更多
Welding polarity has influence on welding stability to some extent, but the specific relationship between welding polarity and weld quality has not been found, especially under the hyperbaric environment. Based on a h...Welding polarity has influence on welding stability to some extent, but the specific relationship between welding polarity and weld quality has not been found, especially under the hyperbaric environment. Based on a hyperbaric dry welding experiment system, gas metal arc welding（GMAW） experiments with direct current electrode positive（DCEP） and direct current electrode negative（DCEN） operations are carried out under the ambient pressures of 0.1 MPa, 0.4 MPa, 0.7 MPa and 1.0 MPa to find the influence rule of different welding polarities on welding spatters and weld bead geometry. The effects of welding polarities on the weld bead geometry such as the reinforcement, the weld width and the penetration are discussed. The experimental results show that the welding spatters gradually grow in quantity and size for GMAW with DCEP, while GMAW with DCEN can produce fewer spatters comparatively with the increase of the ambient pressure. Compared with DCEP, the welding current and arc voltage waveforms for DCEN is more stable and the distribution of welding current probability density for DCEN is more concentrated under the hyperbaric environment. When the ambient pressure is increased from 0.1 MPa to 1.0 MPa, the effects of welding polarities on the reinforcement, the weld width and the penetration are as follows： an increase of 0.8 mm for the weld reinforcement is produced by GMAW with DCEN and 1.3 mm by GMAW with DCEP, a decrease of 7.2 mm for the weld width is produced by DCEN and 6.1 mm by DCEP; and an increase of 3.9 mm for the penetration is produced by DCEN and 1.9 mm by DCEP. The proposed research indicates that the desirable stability in the welding procedure can be achieved by GMAW with DCEN operation under the hyperbaric environment.展开更多
During deep penetration laser welding,there exist plume（weak plasma） and spatters,which are the results of weld material ejection due to strong laser heating.The characteristics of plume and spatters are related to ...During deep penetration laser welding,there exist plume（weak plasma） and spatters,which are the results of weld material ejection due to strong laser heating.The characteristics of plume and spatters are related to welding stability and quality.Characteristics of metallic plume and spatters were investigated during high-power disk laser bead-on-plate welding of Type 304 austenitic stainless steel plates at a continuous wave laser power of 10 kW.An ultraviolet and visible sensitive high-speed camera was used to capture the metallic plume and spatter images.Plume area,laser beam path through the plume,swing angle,distance between laser beam focus and plume image centroid,abscissa of plume centroid and spatter numbers are defined as eigenvalues,and the weld bead width was used as a characteristic parameter that reflected welding stability.Welding status was distinguished by SVM（support vector machine） after data normalization and characteristic analysis.Also,PCA（principal components analysis） feature extraction was used to reduce the dimensions of feature space,and PSO（particle swarm optimization） was used to optimize the parameters of SVM.Finally a classification model based on SVM was established to estimate the weld bead width and welding stability.Experimental results show that the established algorithm based on SVM could effectively distinguish the variation of weld bead width,thus providing an experimental example of monitoring high-power disk laser welding quality.展开更多
This paper analyzes the drop transfer process in gas metal arc welding in short-circuit transfer mode （GMAW-S） in order to develop an optimized spatter rate model that can be used on line. According to thermodynamic...This paper analyzes the drop transfer process in gas metal arc welding in short-circuit transfer mode （GMAW-S） in order to develop an optimized spatter rate model that can be used on line. According to thermodynamic characters and practical behavior, a complete arcing process is divided into three sub-processes： arc re-ignition, energy output and shorting preparation. Shorting process is then divided as drop spread, bridge sustention and bridge destabilization. Nine process variables and their distribution are analyzed based on welding experiments with high-speed photos and synchronous current and voltage signals. Method of variation coefficient is used to reflect process consistency and to design characteristic parameters. Partial least square regression （PLSR） is utilized to set up spatter rate model because of severe correlativity among the above characteristic parameters. PLSR is a new multivariate statistical analysis method, in which regression modeling, data simplification and relativity analysis are included in a single algorithm. Experiment results show that the regression equation based on PLSR is effective for on-line predicting spatter rate of its corresponding welding condition.展开更多
基金support from the UKRI-EPSRC,Grants Numbered EP/W006774/1,EP/P006566/1,EP/W003333/1,and EP/V061798/1funded by the support from a Royal Academy of Engineering Chair in Emerging Technologies(CiET1819/10)+1 种基金CLAL is funded in part by EP/W037483/1 and IPG Photonics/Royal Academy of Engineering Senior Research Fellowship in SEARCH(ref:RCSRF2324-18-71)This research used resources of the European Synchrotron Radiation Facility(ESRF)in Beamline ID19(ME-1573).
文摘Spatter during laser powder bed fusion(LPBF)can induce surface defects,impacting the fatigue performance of the fabricated components.Here,we reveal and explain the links between vapour depression shape and spatter dynamics during LPBF of an Al-Fe-Zr aluminium alloy using high-speed synchrotron x-ray imaging.We quantify the number,trajectory angle,velocity,and kinetic energy of the spatter as a function of vapour depression zone/keyhole morphology under industry-relevant processing conditions.The depression zone/keyhole morphology was found to influence the spatter ejection angle in keyhole versus conduction melting modes:(i)the vapour-pressure driven plume in conduction mode with a quasi-semi-circular depression zone leads to backward spatter whereas;and(ii)the keyhole rear wall redirects the gas/vapour flow to cause vertical spatter ejection and rear rim droplet spatter.Increasing the opening of the keyhole or vapour depression zone can reduce entrainment of solid spatter.We discover a spatter-induced cavity mechanism in which small spatter particles are accelerated towards the powder bed after laser-spatter interaction,inducing powder denudation and cavities on the printed surface.By quantifying these laser-spatter interactions,we suggest a printing strategy for minimising defects and improving the surface quality of LPBF parts.
基金Defense Industrial Technology Development Program(No.JCKY2019205A002)National Science and Technology Major Project(Nos.J2019-IV-0012-0080,J2019-VII-0004-0144,and Y2022-VII-0007).
文摘Laser powder bed fusion(LPBF)is a highly dynamic and complex physical process,and single-track de-fects tend to accumulate into non-negligible internal defects of parts.The nickel-based superalloy single track was fabricated by LPBF,and its plume and spattering behavior were monitored in situ and recorded in real time based on image recognition and tracking in this study.The relationship among laser energy density,melt flow,plume and spattering behavior during LPBF was discussed.Volumetric energy density had limitations as a design parameter for LPBF.However,we found that plume and spattering behavior can be used as real-time design parameters for the processing of LPBF parts and implemented the initial velocity statistics for LPBF single-track spattering based on the centroid extraction algorithm.The influ-ence of melt flow evolution paths on the spattering and plume behavior in three different melting modes was revealed,and a shift in plume behavior was found in the overlap region of the additive substrate.This study provides a new method for obtaining statistics of spattering-related physical quantities in the melting mode,which is beneficial for the development of processing methods to mitigate the instability of the LPBF process.
基金Project (51175095) supported by the National Natural Science Foundation of ChinaProjects (10251009001000001,9151009001000020) supported by the Natural Science Foundation of Guangdong Province,ChinaProject (20104420110001) supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China
文摘Classification of plume and spatter images was studied to evaluate the welding stability. A high-speed camera was used to capture the instantaneous images of plume and spatters during high power disk laser welding. Characteristic parameters such as the area and number of spatters, the average grayscale of a spatter image, the entropy of a spatter grayscale image, the coordinate ratio of the plume centroid and the welding point, the polar coordinates of the plume centroid were defined and extracted. Karhunen-Loeve transform method was used to change the seven characteristics into three primary characteristics to reduce the dimensions. Also, K-nearest neighbor method was used to classify the plume and spatter images into two categories such as good and poor welding quality. The results show that plume and spatter have a close relationship with the welding stability, and two categories could be recognized effectively using K-nearest neighbor method based on Karhunen-Loeve transform.
文摘Welding spatter cause many problems during the welding process and this issue is particularly important for cellulose electrode welding. The hot flying spatter balls often deteriorate the working environment, and decrease the welding efficiency. Many factors affect the welding spatter, and metal transfer behavior is one of the main factors. Many studies concerning the spatter mechanism in arc welding process were made; most of them focused on the solid wire welding and the study on cellulose electrode is rarely reported. In this paper the metal transfer behavior and the weld spatter characteristics of three commercial cellulose electrodes were studied experimentally by using a high speed camera for visually capturing the metal transfer. The relationship between the metal transfer and the welding spatter was analyzed experimentally by comparing the spatter loss coefficient, which is for quantitative evaluation of welding spatter, with the statistical analysis of the large droplet transfer mode. The results showed that short circuiting transfer, large droplet spray transfer, fine droplet spray transfer and explosive transfer govern the metal transfer modes in cellulose electrode welding. Weld spatter occurred mainly in the deflection of large droplet process, explosive transfer process and fine droplet spraying process. Different metal transfer modes lead to different spatter. The deflection of large droplet and explosive transfer are the main factors of the spatter formation. Minimizing the droplet size and reducing the deflection of large droplet and explosive transfer leads to the reduction the amount of spatter in cellulose electrode welding.
文摘Aim at improving the stability of the Short-circuiting Gas Metal Arc Welding （GMAW-S） process for the enhanced speed usage, effects of current waveform parameters during short-term on the welding stability have been investigated by experimental method. The welding power source used for the research is an inverter with a special current waveform control. It is shown that the spatter decreases at first then increases with each increase of the low current period, current increase rate and the maximum current limit. The test results are provided for welding of 1 mm and 3 mm mild steel at speed of 1.2 m/min. The stable GMA W-S process under high speed welding condition has been achieved by optimizing the parameters.
基金supported by the National Natural Science Foundation of China(No.51175304)the Natural Science Foundation of Shandong Province(No.ZR2017MEE052)
文摘Welding spatter seriously affects the surface quality of the product. Aiming at the automatic detection problem of spatter on welding plate surface, an in-situ detection algorithm of welding spatter based on machine vision is designed. In the extraction process of the welding spatter, the two-dimensional Fourier transform is adopted to obtain the frequency and phase information of image, and the elliptical high-pass filter is introduced to filter the low-frequency signal. The experimental results show that the proposed algorithm has higher extraction rate and extraction accuracy rate of welding spatter than the threshold method, the rectangular high-pass filter and the Canny operator, and it has the characteristics of high efficiency, high precision, and good robustness.
基金supported by the National Natural Science Foundation of China(Nos.91860136 and 51801231,Zhou,X.,http://www.nsfc.gov.cn/)the Key R&D plan of Guangdong Province(No.2018B090905001,Zhou,X.,http://pro.gdstc.gov.cn/)the Key Science and Technology project of Shaanxi Province(No.2018zdzx01-04-01,Zhou,X.,http://kjt.shaanxi.gov.cn/).
文摘During the selective laser melting process,a high-energy laser beam acts on the powder,a molten pool is rapidly generated and the characteristic parameters are constantly changing.Among them,temperature is one of the important parameters in the forming process.Due to the generation of splash particles,there will be defects in the microstructure,which will seriously affect the formation quality of the prepared parts.Therefore,it is necessary to study the relationships between the splash behavior,molten pool characteristics and product quality.The finite element simulation of the transient temperature field was performed by ANSYS software.Time-series images at different frame rates were obtained with a high-speed camera,and the dynamic process of splashing was observed.Using IN718 alloy powder,the influence of the laser energy density on the light intensity of the molten pool was studied.The appearance of splash particles and the deviation of the powder chemical elements caused by the splash were analyzed.The results show that the transient temperature field with drastic change is easy to cause spatter,which is consistent with the experimental results.There are large differences in the splash at different shooting frame rates.Increasing the frame rate can allow the observation of details such as the shape,size and number of splash particles,which is beneficial for studying the process of splash formation.At the moment when the splash occurs,the light intensity of the molten pool always first increases and then decreases,depending on the energy input.The higher the energy input is,the more intense the light intensity of the molten pool and the higher the peak interval distribution.Compared with fresh powder,the contents of Al and Ti in powder reused 5 times were reduced by 0.15%and 0.02%,respectively.The increases of these two elements in the splash were 16.18%and 29.62%,respectively,and the content of Nb even exceeded the standard range.When the energy density decreased from 229.17 J/mm3 to 130.95 J/mm3,the relative density of the part increased from 91.82%to 99.83%.This shows that reducing the energy input can reduce the splash to suppress the generation of defects,along with the weakening of the overall light intensity of the molten pool.These results can provide a basis for feature extraction of the molten pool,which is of great significance for real-time monitoring and online control in manufacturing processes and ensuring product quality.
基金Supported by National Natural Science Foundation of China(Grant No.51275051)Innovation and Improvement Plan of Beijing Education Commission,China(Grant No.TJSHG201510017023)
文摘Welding polarity has influence on welding stability to some extent, but the specific relationship between welding polarity and weld quality has not been found, especially under the hyperbaric environment. Based on a hyperbaric dry welding experiment system, gas metal arc welding（GMAW） experiments with direct current electrode positive（DCEP） and direct current electrode negative（DCEN） operations are carried out under the ambient pressures of 0.1 MPa, 0.4 MPa, 0.7 MPa and 1.0 MPa to find the influence rule of different welding polarities on welding spatters and weld bead geometry. The effects of welding polarities on the weld bead geometry such as the reinforcement, the weld width and the penetration are discussed. The experimental results show that the welding spatters gradually grow in quantity and size for GMAW with DCEP, while GMAW with DCEN can produce fewer spatters comparatively with the increase of the ambient pressure. Compared with DCEP, the welding current and arc voltage waveforms for DCEN is more stable and the distribution of welding current probability density for DCEN is more concentrated under the hyperbaric environment. When the ambient pressure is increased from 0.1 MPa to 1.0 MPa, the effects of welding polarities on the reinforcement, the weld width and the penetration are as follows： an increase of 0.8 mm for the weld reinforcement is produced by GMAW with DCEN and 1.3 mm by GMAW with DCEP, a decrease of 7.2 mm for the weld width is produced by DCEN and 6.1 mm by DCEP; and an increase of 3.9 mm for the penetration is produced by DCEN and 1.9 mm by DCEP. The proposed research indicates that the desirable stability in the welding procedure can be achieved by GMAW with DCEN operation under the hyperbaric environment.
基金partly supported by National Natural Science Foundation of China(No.51175095)Guangdong Provincial Natural Science Foundation of China(No.10251009001000001)the Guangdong Provincial Project of Science and Technology Innovation of Discipline Construction,China(No.2013KJCX0063)
文摘During deep penetration laser welding,there exist plume（weak plasma） and spatters,which are the results of weld material ejection due to strong laser heating.The characteristics of plume and spatters are related to welding stability and quality.Characteristics of metallic plume and spatters were investigated during high-power disk laser bead-on-plate welding of Type 304 austenitic stainless steel plates at a continuous wave laser power of 10 kW.An ultraviolet and visible sensitive high-speed camera was used to capture the metallic plume and spatter images.Plume area,laser beam path through the plume,swing angle,distance between laser beam focus and plume image centroid,abscissa of plume centroid and spatter numbers are defined as eigenvalues,and the weld bead width was used as a characteristic parameter that reflected welding stability.Welding status was distinguished by SVM（support vector machine） after data normalization and characteristic analysis.Also,PCA（principal components analysis） feature extraction was used to reduce the dimensions of feature space,and PSO（particle swarm optimization） was used to optimize the parameters of SVM.Finally a classification model based on SVM was established to estimate the weld bead width and welding stability.Experimental results show that the established algorithm based on SVM could effectively distinguish the variation of weld bead width,thus providing an experimental example of monitoring high-power disk laser welding quality.
文摘This paper analyzes the drop transfer process in gas metal arc welding in short-circuit transfer mode （GMAW-S） in order to develop an optimized spatter rate model that can be used on line. According to thermodynamic characters and practical behavior, a complete arcing process is divided into three sub-processes： arc re-ignition, energy output and shorting preparation. Shorting process is then divided as drop spread, bridge sustention and bridge destabilization. Nine process variables and their distribution are analyzed based on welding experiments with high-speed photos and synchronous current and voltage signals. Method of variation coefficient is used to reflect process consistency and to design characteristic parameters. Partial least square regression （PLSR） is utilized to set up spatter rate model because of severe correlativity among the above characteristic parameters. PLSR is a new multivariate statistical analysis method, in which regression modeling, data simplification and relativity analysis are included in a single algorithm. Experiment results show that the regression equation based on PLSR is effective for on-line predicting spatter rate of its corresponding welding condition.
