It is of great significance to model the keyhole shape and dimensions to optimize the plasma arc welding process parameters. In this study, through employing a combined volumetric heat source mode, the weld pool in ke...It is of great significance to model the keyhole shape and dimensions to optimize the plasma arc welding process parameters. In this study, through employing a combined volumetric heat source mode, the weld pool in keyhole plasma arc welding is determined firstly, and then the dynamic force-balance condition on the interface between the plasma jet and the molten metal is dealt with in describing the keyhole formation inside the weld pool. The effects of welding current on the shape and size of keyhole are numerically analyzed. The sharp transformation from a partial keyhole to a full-penetration keyhole is quantitatively demonstrated.展开更多
Based on the characteristics of ＂one keyhole in a pulse＂ in pulsed current plasma arc welding （PAW） , the transient variation process of weld pool in a pulse cycle is simulated through the establishment of corresp...Based on the characteristics of ＂one keyhole in a pulse＂ in pulsed current plasma arc welding （PAW） , the transient variation process of weld pool in a pulse cycle is simulated through the establishment of corresponding heat source model. And considering the effects of gravitational force, plasma arc pressure and surface tension on the weld pool surface, the dynamic change features of the keyhole shape in a pulse cycle are calculated by using surface deformation equation. Experiments are conducted and validate that the calctdated weld fusion line is in good agreement with the experimental results.展开更多
An adaptive heat source mode is proposed to account for the keyhole effect and the characteristics of volumetric distribution along the direction of the workpiece thickness. Finite element analysis of the temperature ...An adaptive heat source mode is proposed to account for the keyhole effect and the characteristics of volumetric distribution along the direction of the workpiece thickness. Finite element analysis of the temperature field in keyhole plasma arc welding is conducted and the weld geometry is obtained. The predicted results are in agreement with the measured ones.展开更多
Modeling and simulation of fluid flow and heat transfer in keyhole plasma arc welding is of great significance for optimizing the process parameters. In this study, a three-dimensional transient model is established t...Modeling and simulation of fluid flow and heat transfer in keyhole plasma arc welding is of great significance for optimizing the process parameters. In this study, a three-dimensional transient model is established to analyze numerically the heat transfer and fluid flow phenomena in keyhole plasma arc welding. VOF （volume of fluid） method is used to track the boundary of the keyhole. The dynamic developments of keyhole geometry, the fluid velocity field and temperature profiles are numerically simulated. And the changing Of the fluid velocity and pressure distribution on the keyhole wall in the forming process of the keyhole are analyzed.展开更多
During stable keyhole plasma arc welding, the pilot arc and the transferred arc exist at the meantime, and the arcs can be considered as a composition of two parts inside and outside the nozzle, respectively. Under th...During stable keyhole plasma arc welding, the pilot arc and the transferred arc exist at the meantime, and the arcs can be considered as a composition of two parts inside and outside the nozzle, respectively. Under the mechanical constriction and thermal contraction effects, the inside arc has certain arc length, electron density and arc profile etc. inducing constant tungsten-to-nozzle voltage. However, the arc outside the nozzle diverges at about 5 degrees and has certain characteristics similar to the free arcs. The nozzle-to-workpiece voltage （NTWV） depends mainly on the length of the arc, which gets bigger as increasing of the weld penetration and keyhole size. The NTWV sensor is developed for monitoring NTWV in real time. The welding experiments are designed to get different penetrations and keyhole sizes. It is found that as the weld penetration and the keyhole size increase, NTWV also increases linearly. The NTWV signals can be used as the feedback variable in automatic control of keyhole plasma arc welding.展开更多
Keyhole plasma arc welding experiments are conducted to measure the weld geometry and penetration at different moments during the initial phase from igniting arc to quasi-steady state. Indirect information on keyhole ...Keyhole plasma arc welding experiments are conducted to measure the weld geometry and penetration at different moments during the initial phase from igniting arc to quasi-steady state. Indirect information on keyhole formation and evolution in plasma arc welding can be extracted based on the weld macrophotograph at cross section. It has laid foundation to verify the mathematical models of keyhole plasma arc welding.展开更多
A new kind of control system for keyhole plasma arc welding （K-PAW） was developed based on the computer and the Graphics Language--LabVIEW. It can set and output the required current waveforms with desired decreasin...A new kind of control system for keyhole plasma arc welding （K-PAW） was developed based on the computer and the Graphics Language--LabVIEW. It can set and output the required current waveforms with desired decreasing slopes so that the corresponding ＂opening and closing＂ of keyhole can occur periodically. With this control strategy of welding current waveforms, the workpiece is fully penetrated while no burn-through Occurs. Keyhole plasma arc welding experiments were conducted to verify the stability and reliability of the developed system.展开更多
The key problem for numerical simulation of plasma arc welding （PAW） process is to develop a suitable and adaptive volumetric heat source mode which reflects the physical characteristics of keyhole PAW. To this end,...The key problem for numerical simulation of plasma arc welding （PAW） process is to develop a suitable and adaptive volumetric heat source mode which reflects the physical characteristics of keyhole PAW. To this end, the keyhole geometry under different PAW process conditions must be predicted. In this paper, a mathematical model for determining the keyhole shape is developed with considering the mass and momentum conservation of the in-keyhole plasma jet as well as the pressure equilibrium at the plasma jet/liquid metal boundary. A suitable heat source model related to the keyhole shape is applied to the calculation of PAW weld dimensions. The predicted results are in good agreement with the experimental ones.展开更多
The development of closed-loop control systems is one of the most effective ways to improve the stability of the keyhole status during keyhole plasma arc welding （K-PAW）. Due to the disadvantages of the ＂one-pulse-...The development of closed-loop control systems is one of the most effective ways to improve the stability of the keyhole status during keyhole plasma arc welding （K-PAW）. Due to the disadvantages of the ＂one-pulse-one-keyhole＂ technology based on the conventional square current waveform, the controlled pulse welding current waveform is newly applied to control the keyhole open and close periodically. In order to realize the real-time control on the keyhole behavior with this advanced current waveform, welding experiments and system identification are conducted based on the classical control theory. One complete welding cycle can be divided into 3 periods. The keyhole establishing time is the most important time variable, which determines the keyhole behavior and welding process stability. At the same time, the averaged effiux plasma arc voltage during one pulse cycle can reflect the real keyhole dimension and status in a real-time manner. Therefore, two single-input-single-output （SISO） systems are proposed, in which keyhole establishing time and keyhole average dimension are taken as the system controlled variables respectively. Welding experiments are designed with the peak current varying randomly. Experiments show that the keyhole establishing time changes in an opposite direction to the varied peak current, and the averaged efflux plasma arc voltage varies with the same trend as the peak current. Based on the least squares technique and F test of classical system identification, second order difference equation for keyhole establishing time/peak current system and first order difference equation for keyhole average dimension/peak current system are obtained. It is proved that the calculated data by the two mathematical expressions are well matched with the measured data. The proposed research provides mathematical expressions and theoretical analysis to develop closed-loop systems for the controlled pulse K-PAW.展开更多
Numerical analysis of keyhole shape and keyhole establishment time is of great significance for selection and optimization of the process parameters in keyhole plasma arc welding. In this paper, a three-dimensional tr...Numerical analysis of keyhole shape and keyhole establishment time is of great significance for selection and optimization of the process parameters in keyhole plasma arc welding. In this paper, a three-dimensional transient model is developed to analyze the evolutions of keyhole shape and keyhole establishment time in continuous current plasma arc welding process. Firstly, a combined volumetric heat source model is used to simulate the transient variation of temperature field. And then the surface deformation equation is adopted to calculate dynamic features of the keyhole shape and keyhole establishment time inside weld pool, in which the force action on weld pool surface is considered. Experiment is cond^ted to validate the numerical simulation results. The predicted keyhole size and keyhole establishment time are in agreement with the experimental measurement. And the calculated fusion zone geometry is consistent with the measured one.展开更多
A three-dimensional mathematical model for the transferred-type argon arc was developed to describe arc force on the anode surface. The software ANSYS was employed to solve the model. The model includes a part of torc...A three-dimensional mathematical model for the transferred-type argon arc was developed to describe arc force on the anode surface. The software ANSYS was employed to solve the model. The model includes a part of torch and tungsten electrode to achieve more reasonable resuits. The arc temperature and flow fields were derived. And the influences of welding parameters on arc force were also studied. The simulated results show that arc pressure at the anode are dependent on the welding current, plasma gas flow rate and electrode neck-in, while not sensitive to arc length.展开更多
A unified numerical model is developed to couple the plasma arc, weld pool and keyhole in a self consistent way. The plasma arc/anode interface and the melt/solid interface are treated specially, the VOF method is use...A unified numerical model is developed to couple the plasma arc, weld pool and keyhole in a self consistent way. The plasma arc/anode interface and the melt/solid interface are treated specially, the VOF method is used to trace the moving keyhole wall, and the fluid flow and heat transfer in both the plasma arc and weld pool are numerically simulated. The distributions of current density and arc pressure on the weld pool surface during the keyhole formation process are analyzed using the coupled model. The predicted arc pressure and current density are compared with the experimentally measured results, and both are in good agreement.展开更多
According to the strategy of controlled pulse key-holing,a new sensing and control system was developed for monitoring and controlling the keyhole condition during plasma arc welding(PAW). Through sensing and processi...According to the strategy of controlled pulse key-holing,a new sensing and control system was developed for monitoring and controlling the keyhole condition during plasma arc welding(PAW). Through sensing and processing the efflux plasma voltage signals,the quantitative relationship among the welding current,efflux plasma voltage and backside weld width of the weld was established. PAW experiments show that the efflux plasma voltage can reflect the state of keyhole and backside weld width accurately. The closed-loop control tests validate the stability and reliability of the developed keyhole PAW system.展开更多
Weld shape control is a fundamental issue in automatic welding. In this paper, a double side visual system is established for pulsed gas metal arc welding （ P-GMAW） , and both topside and backside weld pool images c...Weld shape control is a fundamental issue in automatic welding. In this paper, a double side visual system is established for pulsed gas metal arc welding （ P-GMAW） , and both topside and backside weld pool images can be captured and stored continuously in real time. By analyzing the weld shape regulation with the molten metal volume, some topside weld pool characterized parameters （WPCPs） are proposed for determining penetration in butt welding of thin mild steel. Moreover, some BP network models are established to predict backside Weld pool width with welding parameters and WPCPs as inputs.展开更多
The dynamic behaviors of the keyhole and weld pool are coupled together in plasma arc welding, and the geometric variations of both the keyhole and the weld pool determine the weld quality. It is of great significance...The dynamic behaviors of the keyhole and weld pool are coupled together in plasma arc welding, and the geometric variations of both the keyhole and the weld pool determine the weld quality. It is of great significance to simultaneously sense and monitor the keyhole and the weld pool behaviors by using a single low-cost vision sensor in plasma arc welding process. In this study, the keyhole and weld pool were observed and measured under different levels of welding current by using the near infrared sensing technology and the charge coupled device （CCD） sensing system. The shapes and relative position of weld pool and keyhole under different conditions were compared and analyzed. The observation results lay solid foundation for controlling weld quality and understanding the underlying process mechanisms.展开更多
The plasma arc pressure plays an important role in determining the keyhole formation and size. So it is of great significance to choose adaptive distribution mode of the plasma arc pressure for determining keyhole sha...The plasma arc pressure plays an important role in determining the keyhole formation and size. So it is of great significance to choose adaptive distribution mode of the plasma arc pressure for determining keyhole shape and size. In this study, through employing a double-elliptic distribution mode of plasma arc pressure, three-dimensional keyhole was numerically simulated. The unsymmetric feature of the keyhole inside the weld pool was described. The development of keyhole was demonstrated under different levels of welding current. The critical current required to form an open keyhole was obtained for the study cases .展开更多
The physical characteristics of a plasma arc affect the stability of the keyhole and weld pool directly during keyhole plasma arc welding(KPAW).There will be significant change for these characteristics because of the...The physical characteristics of a plasma arc affect the stability of the keyhole and weld pool directly during keyhole plasma arc welding(KPAW).There will be significant change for these characteristics because of the interaction between the keyhole weld pool and plasma arc after penetration.Therefore,in order to obtain the temperature field,flow field,and arc pressure of a plasma arc under the reaction of the keyhole,the physical model of a plasma arc with a pre-set keyhole was established.In addition,the tungsten and base metal were established into the calculated domain,which can reflect the effect of plasma arc to weld pool further.Based on magneto hydrodynamics and Maxwell equations,a twoSdimensional steady state mathematical model was established.Considering the heat production of anode and cathode,the distribution of temperature field,flow field,welding current density,and plasma arc pressure were solved out by the finite difference method.From the calculated results,it is found that the plasma arc was compressed a second time by the keyhole.This additional constraint results in an obvious rise of the plasma arc pressure and flow velocity at the minimum diameter place of the keyhole,while the temperature field is impacted slightly.Finally,the observational and metallographic experiments are conducted,and the shapes of plasma arc and fusion line agree with the simulated results generally.展开更多
Variable polarity plasma arc-gas metal arc welding(VPPA-GMAW)integrates the advantages of VPPA and GMAW,and it is particularly applied to weld thick-plates aluminum alloys.High-speed camera and data acquisition system...Variable polarity plasma arc-gas metal arc welding(VPPA-GMAW)integrates the advantages of VPPA and GMAW,and it is particularly applied to weld thick-plates aluminum alloys.High-speed camera and data acquisition system were used to analyze the arc shape and the welding process electrical signal.According to the analysis of arc swing amplitude and the approximate entropy of arc voltage signal denoised by wavelet threshold method,the influence of VPPA frequency on the arc stability was studied.The results show that the approximate entropy of GMAW arc voltage decreases with the increase of VPPA frequency in a certain range,and the stability of the hybrid arc is significantly improved.The spectral analysis shows that the arc stability is reduced due to the resonance effect between the VPPA and the GMAW arc when the VPPA frequency closes to the GMAW arc pulse frequency.The results are helpful to understand hybrid welding mechanism and the selection of welding process parameters.展开更多
Pulsed current Micro Plasma Arc Welding is used to joint thin sheets of AISI 304L sheets, which are used in manufacturing of metallic bellows and diaphragms. In this article the effects of pulsing current parameters o...Pulsed current Micro Plasma Arc Welding is used to joint thin sheets of AISI 304L sheets, which are used in manufacturing of metallic bellows and diaphragms. In this article the effects of pulsing current parameters on weld pool geometry namely front width, back width, front height and back height of pulsed current micro plasma arc welded AISI 304L stainless steel sheets was analyzed. Four factors, five levels, central composite design was used to develop mathematical models, incorporating pulsed current parameters and weld pool geometry. The mathematical models have been developed by Response Surface Method. The adequacy of the models was checked by ANOVA technique. Variation of output responses with input process variables are discussed. By using the developed mathematical models, weld pool geometry parameters can be predicted.展开更多
文摘It is of great significance to model the keyhole shape and dimensions to optimize the plasma arc welding process parameters. In this study, through employing a combined volumetric heat source mode, the weld pool in keyhole plasma arc welding is determined firstly, and then the dynamic force-balance condition on the interface between the plasma jet and the molten metal is dealt with in describing the keyhole formation inside the weld pool. The effects of welding current on the shape and size of keyhole are numerically analyzed. The sharp transformation from a partial keyhole to a full-penetration keyhole is quantitatively demonstrated.
文摘Based on the characteristics of ＂one keyhole in a pulse＂ in pulsed current plasma arc welding （PAW） , the transient variation process of weld pool in a pulse cycle is simulated through the establishment of corresponding heat source model. And considering the effects of gravitational force, plasma arc pressure and surface tension on the weld pool surface, the dynamic change features of the keyhole shape in a pulse cycle are calculated by using surface deformation equation. Experiments are conducted and validate that the calctdated weld fusion line is in good agreement with the experimental results.
文摘An adaptive heat source mode is proposed to account for the keyhole effect and the characteristics of volumetric distribution along the direction of the workpiece thickness. Finite element analysis of the temperature field in keyhole plasma arc welding is conducted and the weld geometry is obtained. The predicted results are in agreement with the measured ones.
文摘Modeling and simulation of fluid flow and heat transfer in keyhole plasma arc welding is of great significance for optimizing the process parameters. In this study, a three-dimensional transient model is established to analyze numerically the heat transfer and fluid flow phenomena in keyhole plasma arc welding. VOF （volume of fluid） method is used to track the boundary of the keyhole. The dynamic developments of keyhole geometry, the fluid velocity field and temperature profiles are numerically simulated. And the changing Of the fluid velocity and pressure distribution on the keyhole wall in the forming process of the keyhole are analyzed.
基金the financial support for this research from the National Natural Science Foundation of China (Grant No 50540420570)the Innovative Conception Fund of Chinese Welding Society (No 07-12-002)
文摘During stable keyhole plasma arc welding, the pilot arc and the transferred arc exist at the meantime, and the arcs can be considered as a composition of two parts inside and outside the nozzle, respectively. Under the mechanical constriction and thermal contraction effects, the inside arc has certain arc length, electron density and arc profile etc. inducing constant tungsten-to-nozzle voltage. However, the arc outside the nozzle diverges at about 5 degrees and has certain characteristics similar to the free arcs. The nozzle-to-workpiece voltage （NTWV） depends mainly on the length of the arc, which gets bigger as increasing of the weld penetration and keyhole size. The NTWV sensor is developed for monitoring NTWV in real time. The welding experiments are designed to get different penetrations and keyhole sizes. It is found that as the weld penetration and the keyhole size increase, NTWV also increases linearly. The NTWV signals can be used as the feedback variable in automatic control of keyhole plasma arc welding.
基金The authors are grateful to the financial support to this research from the National Natural Science Foundation of China under Grant No. 50540420570.
文摘Keyhole plasma arc welding experiments are conducted to measure the weld geometry and penetration at different moments during the initial phase from igniting arc to quasi-steady state. Indirect information on keyhole formation and evolution in plasma arc welding can be extracted based on the weld macrophotograph at cross section. It has laid foundation to verify the mathematical models of keyhole plasma arc welding.
文摘A new kind of control system for keyhole plasma arc welding （K-PAW） was developed based on the computer and the Graphics Language--LabVIEW. It can set and output the required current waveforms with desired decreasing slopes so that the corresponding ＂opening and closing＂ of keyhole can occur periodically. With this control strategy of welding current waveforms, the workpiece is fully penetrated while no burn-through Occurs. Keyhole plasma arc welding experiments were conducted to verify the stability and reliability of the developed system.
基金The authors are grateful to the financial support to this research from the National Nature Science Foundation of China under Grant No. 50540420570.
文摘The key problem for numerical simulation of plasma arc welding （PAW） process is to develop a suitable and adaptive volumetric heat source mode which reflects the physical characteristics of keyhole PAW. To this end, the keyhole geometry under different PAW process conditions must be predicted. In this paper, a mathematical model for determining the keyhole shape is developed with considering the mass and momentum conservation of the in-keyhole plasma jet as well as the pressure equilibrium at the plasma jet/liquid metal boundary. A suitable heat source model related to the keyhole shape is applied to the calculation of PAW weld dimensions. The predicted results are in good agreement with the experimental ones.
基金supported by National Natural Science Foundation of China(Grant No. 50936003)
文摘The development of closed-loop control systems is one of the most effective ways to improve the stability of the keyhole status during keyhole plasma arc welding （K-PAW）. Due to the disadvantages of the ＂one-pulse-one-keyhole＂ technology based on the conventional square current waveform, the controlled pulse welding current waveform is newly applied to control the keyhole open and close periodically. In order to realize the real-time control on the keyhole behavior with this advanced current waveform, welding experiments and system identification are conducted based on the classical control theory. One complete welding cycle can be divided into 3 periods. The keyhole establishing time is the most important time variable, which determines the keyhole behavior and welding process stability. At the same time, the averaged effiux plasma arc voltage during one pulse cycle can reflect the real keyhole dimension and status in a real-time manner. Therefore, two single-input-single-output （SISO） systems are proposed, in which keyhole establishing time and keyhole average dimension are taken as the system controlled variables respectively. Welding experiments are designed with the peak current varying randomly. Experiments show that the keyhole establishing time changes in an opposite direction to the varied peak current, and the averaged efflux plasma arc voltage varies with the same trend as the peak current. Based on the least squares technique and F test of classical system identification, second order difference equation for keyhole establishing time/peak current system and first order difference equation for keyhole average dimension/peak current system are obtained. It is proved that the calculated data by the two mathematical expressions are well matched with the measured data. The proposed research provides mathematical expressions and theoretical analysis to develop closed-loop systems for the controlled pulse K-PAW.
文摘Numerical analysis of keyhole shape and keyhole establishment time is of great significance for selection and optimization of the process parameters in keyhole plasma arc welding. In this paper, a three-dimensional transient model is developed to analyze the evolutions of keyhole shape and keyhole establishment time in continuous current plasma arc welding process. Firstly, a combined volumetric heat source model is used to simulate the transient variation of temperature field. And then the surface deformation equation is adopted to calculate dynamic features of the keyhole shape and keyhole establishment time inside weld pool, in which the force action on weld pool surface is considered. Experiment is cond^ted to validate the numerical simulation results. The predicted keyhole size and keyhole establishment time are in agreement with the experimental measurement. And the calculated fusion zone geometry is consistent with the measured one.
基金National Natural Science Foundation of China(No.50275106)
文摘A three-dimensional mathematical model for the transferred-type argon arc was developed to describe arc force on the anode surface. The software ANSYS was employed to solve the model. The model includes a part of torch and tungsten electrode to achieve more reasonable resuits. The arc temperature and flow fields were derived. And the influences of welding parameters on arc force were also studied. The simulated results show that arc pressure at the anode are dependent on the welding current, plasma gas flow rate and electrode neck-in, while not sensitive to arc length.
基金The authors are grateful to the financial support for this project from the National Natural Science Foundation of China （No. 50936003 ）.
文摘A unified numerical model is developed to couple the plasma arc, weld pool and keyhole in a self consistent way. The plasma arc/anode interface and the melt/solid interface are treated specially, the VOF method is used to trace the moving keyhole wall, and the fluid flow and heat transfer in both the plasma arc and weld pool are numerically simulated. The distributions of current density and arc pressure on the weld pool surface during the keyhole formation process are analyzed using the coupled model. The predicted arc pressure and current density are compared with the experimentally measured results, and both are in good agreement.
基金Project(50540420570) supported by the National Natural Science Foundation of ChinaProject(07-12-002) supported by the Innovative Conception Fund of the Welding Institution of Chinese Mechanical Engineering Society
文摘According to the strategy of controlled pulse key-holing,a new sensing and control system was developed for monitoring and controlling the keyhole condition during plasma arc welding(PAW). Through sensing and processing the efflux plasma voltage signals,the quantitative relationship among the welding current,efflux plasma voltage and backside weld width of the weld was established. PAW experiments show that the efflux plasma voltage can reflect the state of keyhole and backside weld width accurately. The closed-loop control tests validate the stability and reliability of the developed keyhole PAW system.
文摘Weld shape control is a fundamental issue in automatic welding. In this paper, a double side visual system is established for pulsed gas metal arc welding （ P-GMAW） , and both topside and backside weld pool images can be captured and stored continuously in real time. By analyzing the weld shape regulation with the molten metal volume, some topside weld pool characterized parameters （WPCPs） are proposed for determining penetration in butt welding of thin mild steel. Moreover, some BP network models are established to predict backside Weld pool width with welding parameters and WPCPs as inputs.
文摘The dynamic behaviors of the keyhole and weld pool are coupled together in plasma arc welding, and the geometric variations of both the keyhole and the weld pool determine the weld quality. It is of great significance to simultaneously sense and monitor the keyhole and the weld pool behaviors by using a single low-cost vision sensor in plasma arc welding process. In this study, the keyhole and weld pool were observed and measured under different levels of welding current by using the near infrared sensing technology and the charge coupled device （CCD） sensing system. The shapes and relative position of weld pool and keyhole under different conditions were compared and analyzed. The observation results lay solid foundation for controlling weld quality and understanding the underlying process mechanisms.
基金Acknowledgement The authors are grateful to the financial support for this project from the National Natural Science Foundation of China under grant No. 50540420570.
文摘The plasma arc pressure plays an important role in determining the keyhole formation and size. So it is of great significance to choose adaptive distribution mode of the plasma arc pressure for determining keyhole shape and size. In this study, through employing a double-elliptic distribution mode of plasma arc pressure, three-dimensional keyhole was numerically simulated. The unsymmetric feature of the keyhole inside the weld pool was described. The development of keyhole was demonstrated under different levels of welding current. The critical current required to form an open keyhole was obtained for the study cases .
基金Project supported by the National Natural Science Foundation of China(Grant No.51505008)the National Science and Technology Major Project of China(Grant No.2014ZX04001-171)
文摘The physical characteristics of a plasma arc affect the stability of the keyhole and weld pool directly during keyhole plasma arc welding(KPAW).There will be significant change for these characteristics because of the interaction between the keyhole weld pool and plasma arc after penetration.Therefore,in order to obtain the temperature field,flow field,and arc pressure of a plasma arc under the reaction of the keyhole,the physical model of a plasma arc with a pre-set keyhole was established.In addition,the tungsten and base metal were established into the calculated domain,which can reflect the effect of plasma arc to weld pool further.Based on magneto hydrodynamics and Maxwell equations,a twoSdimensional steady state mathematical model was established.Considering the heat production of anode and cathode,the distribution of temperature field,flow field,welding current density,and plasma arc pressure were solved out by the finite difference method.From the calculated results,it is found that the plasma arc was compressed a second time by the keyhole.This additional constraint results in an obvious rise of the plasma arc pressure and flow velocity at the minimum diameter place of the keyhole,while the temperature field is impacted slightly.Finally,the observational and metallographic experiments are conducted,and the shapes of plasma arc and fusion line agree with the simulated results generally.
基金supported by the National Natural Science Foundation of China(51665044)Natural Science Foundation of Inner Mongolia(2019LH05017)+1 种基金Science and Technology Programs of Inner Mongolia(2020GG0313)Major Basic Research Open Subjects of Inner Mongolia Autonomous Region.
文摘Variable polarity plasma arc-gas metal arc welding(VPPA-GMAW)integrates the advantages of VPPA and GMAW,and it is particularly applied to weld thick-plates aluminum alloys.High-speed camera and data acquisition system were used to analyze the arc shape and the welding process electrical signal.According to the analysis of arc swing amplitude and the approximate entropy of arc voltage signal denoised by wavelet threshold method,the influence of VPPA frequency on the arc stability was studied.The results show that the approximate entropy of GMAW arc voltage decreases with the increase of VPPA frequency in a certain range,and the stability of the hybrid arc is significantly improved.The spectral analysis shows that the arc stability is reduced due to the resonance effect between the VPPA and the GMAW arc when the VPPA frequency closes to the GMAW arc pulse frequency.The results are helpful to understand hybrid welding mechanism and the selection of welding process parameters.
文摘Pulsed current Micro Plasma Arc Welding is used to joint thin sheets of AISI 304L sheets, which are used in manufacturing of metallic bellows and diaphragms. In this article the effects of pulsing current parameters on weld pool geometry namely front width, back width, front height and back height of pulsed current micro plasma arc welded AISI 304L stainless steel sheets was analyzed. Four factors, five levels, central composite design was used to develop mathematical models, incorporating pulsed current parameters and weld pool geometry. The mathematical models have been developed by Response Surface Method. The adequacy of the models was checked by ANOVA technique. Variation of output responses with input process variables are discussed. By using the developed mathematical models, weld pool geometry parameters can be predicted.
