Welding quality of electron beam welded joint is usually susceptible to the stability of keyhole during welding process.The more stable the keyhole,the better the welding quality.To reveal the evolution mechanism of k...Welding quality of electron beam welded joint is usually susceptible to the stability of keyhole during welding process.The more stable the keyhole,the better the welding quality.To reveal the evolution mechanism of keyhole and welding quality of the electron beam welded joint of magnesium-gadolinium alloy under different scanning path,numerical simulation was conducted for the changes in morphology of keyhole and liquid flow in molten pool.The magnesium-gadolinium alloy was welded by electron beam in vacuum with two different scanning paths,sinusoid path and cochleoid path,indicating the identical heat input,welding speed,and focusing state.The stability of keyhole was mainly related to the frequency of keyhole collapse.When the sinusoid scanning path was adopted,the fluids both inside the molten pool and at keyhole wall were disorder,corresponding to the numerous independent vortices and dramatically chaotic flows at their junctions.The maximum velocity of fluids ranged from 0.79 m/s to 1.02 m/s.The average and maximum depth of keyhole were 3.48 mm and 4.51 mm,respectively,meaning that the keyhole collapsed frequently.As the scanning path was changed into cochleoid mode,the electron beam scanned in a homogeneous manner without abrupt change in direction and speed like sinusoid path at its peaks and troughs.The maximum velocity of fluids was more uniform without drastic variation,ranging from 0.90 m/s to 1.01 m/s.The average and maximum depth of keyhole were decreased to 3.30 mm and 4.05 mm,respectively,indicating the more stable keyhole and alleviated collapse.Both the actual in-situ capture of molten pool signature and porosity inside the weld corresponded to the analysis of the change in keyhole stability.展开更多
The influence of the longitudinal acceleration and the angular acceleration of detecting target based on vortex electromagnetic waves in keyhole space are analyzed.The spectrum spreads of different orbital angular mom...The influence of the longitudinal acceleration and the angular acceleration of detecting target based on vortex electromagnetic waves in keyhole space are analyzed.The spectrum spreads of different orbital angular momentum(OAM)modes in different non-line-of-sight situations are simulated.The errors of target accelerations in detection are calculated and compared based on the OAM spectra spreading by using two combinations of composite OAM modes in the keyhole space.According to the research,the effects about spectrum spreads of higher OAM modes are more obvious.The error in detection is mainly affected by OAM spectrum spreading,which can be reduced by reasonably using different combinations of OAM modes in different practical situations.The above results provide a reference idea for investigating keyhole effect when vortex electromagnetic wave is used to detect accelerations.展开更多
In order to obtain good welding quality, it is necessary to apply quality control because there are many influencing factors in laser welding process. The key to realize welding quality control is to obtain the qualit...In order to obtain good welding quality, it is necessary to apply quality control because there are many influencing factors in laser welding process. The key to realize welding quality control is to obtain the quality information. Abundant weld quality information is contained in weld pool and keyhole. Aiming at Nd：YAG laser welding of stainless steel, a coaxial visual sensing system was constructed. The images of weld pool and keyhole were obtained. Based on the gray character of weld pool and keyhole in images, an image processing algorithm was designed. The search start point and search criteria of weld pool and keyhole edge were determined respectively.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
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
Sensing of keyhole shape and size is important for controlling of plasma arc welding process. In this study, a synchronous vision system is developed by using two CCD cameras to observe the keyhole entrance and exit s...Sensing of keyhole shape and size is important for controlling of plasma arc welding process. In this study, a synchronous vision system is developed by using two CCD cameras to observe the keyhole entrance and exit simultaneously. Experiments are conducted on stainless steel workpiece, Whole keyhole exit image and part of keyhole entrance image are captured synchronously under different welding conditions. Image processing and calibration algorithms are proposed. The boundary and front point of the keyhole entrance and exit are extracted respectively. The effects of welding current and welding speed on ,front point of keyhole entrance and exit are analyzed. Compared to the front point of the keyhole entrance, the position of the front point of the keyhole exit is better to reflect the variation of the welding parameters.展开更多
The double side image sensing of the keyhole puddle in the variable polarity plasma arc welding of aluminum alloys has been investigated in this paper, to extract the characteristically geometrical size of the keyhol...The double side image sensing of the keyhole puddle in the variable polarity plasma arc welding of aluminum alloys has been investigated in this paper, to extract the characteristically geometrical size of the keyhole and to realize the feedback controlling for weld formation in the welding process. Some geometrical sizes of the visible keyhole in the front and back images such as the width, height, area, etc. can be used to monitor both the keyhole puddle and the weld formation in the welding process. Under the condition of the varied heat sink, varied gap and misalignment, the trend from normal welding to cutting can be reflected from the variations of geometrical sizes of the keyhole puddle respectively. The keyhole area, the keyhole height and the shape parameters of the keyhole puddle are the key parameters which reflect the trend from normal welding to cutting when meeting the condition of the varied heat sink, varied gap and misalignment respectively. The algorithm for the image processing of the keyhole puddle and the periphery extracting of the visible keyhole developed in the paper can be used to determine real timely the geometrical sizes of the visible keyhole. Artificial neural network is applied to establish the model for predicting the geometrical sizes of the back keyhole puddle. The inputs of the model are the geometrical sizes of the front keyhole puddle and the weld parameters, the outputs of the model are the geometrical sizes of the back keyhole puddle. The model can be used to control the stability of keyhole and the weld formation.展开更多
Endoscopic cervical foraminotomy is increasingly used for cervical spondylotic radiculopathy(CSR),but there is great concern about radiation exposure because of the heavy dependence of this surgical method on fluorosc...Endoscopic cervical foraminotomy is increasingly used for cervical spondylotic radiculopathy(CSR),but there is great concern about radiation exposure because of the heavy dependence of this surgical method on fluoroscopy.The objective of this study was to introduce in detail an advanced surgical technique of keyhole foraminotomy via a percutaneous posterior full-endoscopic approach as a treatment for CSR and investigate its clinical outcomes.We retrospectively reviewed 33 consecutive patients with CSR who underwent keyhole foraminotomy via a percutaneous posterior full-endoscopic approach from October 2015 to April 2017.The patients’general characteristics,including operative time,blood loss,hospital stay,complications,and recurrence,were obtained.Clinical outcomes were evaluated using the visual analogue scale(VAS)for radicular pain,the neck disability index(NDI)for functional assessment,and the modified MacNab criteria for patient satisfaction.All operations were successfully performed(mean operation time,62 min),with no measurable blood loss or severe related complications.The mean follow-up was 25 months.The VAS and NDI scores were significantly improved as compared with those in the preoperative period(preoperative vs.final follow-up:7.6±1.6 vs.3.83±7.34 for VAS,P<0.01;69.5%±10.5%vs.17.54%±13.40%for NDI,P<0.01).Of the 33 patients,32(97.0%)had good-to-excellent global outcomes and all patients obtained symptomatic improvement.In conclusion,keyhole foraminotomy via a percutaneous posterior full-endoscopic approach is an efficient,safe,and feasible procedure for the treatment of CSR.Its simplified single-step blunt incision for localization appears to decrease radiation exposure risks.展开更多
Keyhole gas tungsten arc welding(K-TIG)of Q345 low alloy steel plates was simulated by using SYSWELD software.The temperature field of the K-TIG welding process was simulated with three different combined heat sources...Keyhole gas tungsten arc welding(K-TIG)of Q345 low alloy steel plates was simulated by using SYSWELD software.The temperature field of the K-TIG welding process was simulated with three different combined heat sources and was compared with the weld profile that was obtained experimentally.The temperature field that was obtained by a combination of a double ellipsoid heat source on the upper half and a three-dimensional Gauss heat source on the lower half was similar to the real situation.The effects of plate thickness,gap and welding speed on the deformation and stress of the K-TIG welded joints were investigated by K-TIG welding numerical simulation.A reduction in the thickness of the weld plates reduced the z-direction deformation and transverse residual stress;an appropriate gap reduced the residual stress and an increase in the welding speed reduced deformation after welding,but did not help to control the residual stress after welding.展开更多
In the double-sided arc welding system (DSAW) composing of PAW+TIG arcs, the PAW arc is guided by the TIG arc so that the current mostly flows through the direction of the workpiece thickness and the penetration is gr...In the double-sided arc welding system (DSAW) composing of PAW+TIG arcs, the PAW arc is guided by the TIG arc so that the current mostly flows through the direction of the workpiece thickness and the penetration is greatly improved. To analyze the current density distribution in DSAW is beneficial to understanding of this process. Considering all kinds of dynamic factors acting on the weldpool, this paper discusses firstly the surface deformation of the weldpool and the keyhole formation in PAW+TIG DSAW process on the basis of the magnetohydrodynamic theory and variation principles. Hence, a model of the current density distribution is developed. Through numerical simulation, the current density distribution in PAW+TIG DSAW process is quantitatively analyzed. It shows that the minimal radius of keyhole formed in PAW+TIG DSAW process is 0.5 mm and 89.5 percent of current flows through the keyhole.展开更多
基金financially supported by China National Postdoctoral Program for Innovative Talents(BX20230269)National Key R&D Program of China(2022YFB4600800)Fundamental Research Funds for The Central Universities(2042024kf0015).
文摘Welding quality of electron beam welded joint is usually susceptible to the stability of keyhole during welding process.The more stable the keyhole,the better the welding quality.To reveal the evolution mechanism of keyhole and welding quality of the electron beam welded joint of magnesium-gadolinium alloy under different scanning path,numerical simulation was conducted for the changes in morphology of keyhole and liquid flow in molten pool.The magnesium-gadolinium alloy was welded by electron beam in vacuum with two different scanning paths,sinusoid path and cochleoid path,indicating the identical heat input,welding speed,and focusing state.The stability of keyhole was mainly related to the frequency of keyhole collapse.When the sinusoid scanning path was adopted,the fluids both inside the molten pool and at keyhole wall were disorder,corresponding to the numerous independent vortices and dramatically chaotic flows at their junctions.The maximum velocity of fluids ranged from 0.79 m/s to 1.02 m/s.The average and maximum depth of keyhole were 3.48 mm and 4.51 mm,respectively,meaning that the keyhole collapsed frequently.As the scanning path was changed into cochleoid mode,the electron beam scanned in a homogeneous manner without abrupt change in direction and speed like sinusoid path at its peaks and troughs.The maximum velocity of fluids was more uniform without drastic variation,ranging from 0.90 m/s to 1.01 m/s.The average and maximum depth of keyhole were decreased to 3.30 mm and 4.05 mm,respectively,indicating the more stable keyhole and alleviated collapse.Both the actual in-situ capture of molten pool signature and porosity inside the weld corresponded to the analysis of the change in keyhole stability.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11804073 and 61775050).
文摘The influence of the longitudinal acceleration and the angular acceleration of detecting target based on vortex electromagnetic waves in keyhole space are analyzed.The spectrum spreads of different orbital angular momentum(OAM)modes in different non-line-of-sight situations are simulated.The errors of target accelerations in detection are calculated and compared based on the OAM spectra spreading by using two combinations of composite OAM modes in the keyhole space.According to the research,the effects about spectrum spreads of higher OAM modes are more obvious.The error in detection is mainly affected by OAM spectrum spreading,which can be reduced by reasonably using different combinations of OAM modes in different practical situations.The above results provide a reference idea for investigating keyhole effect when vortex electromagnetic wave is used to detect accelerations.
基金Project (10776020) supported by the Joint Foundation of the National Natural Science Foundation of China and China Academy of Engineering Physics
文摘In order to obtain good welding quality, it is necessary to apply quality control because there are many influencing factors in laser welding process. The key to realize welding quality control is to obtain the quality information. Abundant weld quality information is contained in weld pool and keyhole. Aiming at Nd：YAG laser welding of stainless steel, a coaxial visual sensing system was constructed. The images of weld pool and keyhole were obtained. Based on the gray character of weld pool and keyhole in images, an image processing algorithm was designed. The search start point and search criteria of weld pool and keyhole edge were determined respectively.
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 for this research from the Natural Science Foundation of Shandong Province under grant No.ZR2011EEM013 and Independent Innovation Foundation of Shandong University under grant No.2010TS108
文摘Sensing of keyhole shape and size is important for controlling of plasma arc welding process. In this study, a synchronous vision system is developed by using two CCD cameras to observe the keyhole entrance and exit simultaneously. Experiments are conducted on stainless steel workpiece, Whole keyhole exit image and part of keyhole entrance image are captured synchronously under different welding conditions. Image processing and calibration algorithms are proposed. The boundary and front point of the keyhole entrance and exit are extracted respectively. The effects of welding current and welding speed on ,front point of keyhole entrance and exit are analyzed. Compared to the front point of the keyhole entrance, the position of the front point of the keyhole exit is better to reflect the variation of the welding parameters.
基金This work was supported by National Minister of Areospace and National Key Labora tory of Advanced Welding Production Technology.
文摘The double side image sensing of the keyhole puddle in the variable polarity plasma arc welding of aluminum alloys has been investigated in this paper, to extract the characteristically geometrical size of the keyhole and to realize the feedback controlling for weld formation in the welding process. Some geometrical sizes of the visible keyhole in the front and back images such as the width, height, area, etc. can be used to monitor both the keyhole puddle and the weld formation in the welding process. Under the condition of the varied heat sink, varied gap and misalignment, the trend from normal welding to cutting can be reflected from the variations of geometrical sizes of the keyhole puddle respectively. The keyhole area, the keyhole height and the shape parameters of the keyhole puddle are the key parameters which reflect the trend from normal welding to cutting when meeting the condition of the varied heat sink, varied gap and misalignment respectively. The algorithm for the image processing of the keyhole puddle and the periphery extracting of the visible keyhole developed in the paper can be used to determine real timely the geometrical sizes of the visible keyhole. Artificial neural network is applied to establish the model for predicting the geometrical sizes of the back keyhole puddle. The inputs of the model are the geometrical sizes of the front keyhole puddle and the weld parameters, the outputs of the model are the geometrical sizes of the back keyhole puddle. The model can be used to control the stability of keyhole and the weld formation.
文摘Endoscopic cervical foraminotomy is increasingly used for cervical spondylotic radiculopathy(CSR),but there is great concern about radiation exposure because of the heavy dependence of this surgical method on fluoroscopy.The objective of this study was to introduce in detail an advanced surgical technique of keyhole foraminotomy via a percutaneous posterior full-endoscopic approach as a treatment for CSR and investigate its clinical outcomes.We retrospectively reviewed 33 consecutive patients with CSR who underwent keyhole foraminotomy via a percutaneous posterior full-endoscopic approach from October 2015 to April 2017.The patients’general characteristics,including operative time,blood loss,hospital stay,complications,and recurrence,were obtained.Clinical outcomes were evaluated using the visual analogue scale(VAS)for radicular pain,the neck disability index(NDI)for functional assessment,and the modified MacNab criteria for patient satisfaction.All operations were successfully performed(mean operation time,62 min),with no measurable blood loss or severe related complications.The mean follow-up was 25 months.The VAS and NDI scores were significantly improved as compared with those in the preoperative period(preoperative vs.final follow-up:7.6±1.6 vs.3.83±7.34 for VAS,P<0.01;69.5%±10.5%vs.17.54%±13.40%for NDI,P<0.01).Of the 33 patients,32(97.0%)had good-to-excellent global outcomes and all patients obtained symptomatic improvement.In conclusion,keyhole foraminotomy via a percutaneous posterior full-endoscopic approach is an efficient,safe,and feasible procedure for the treatment of CSR.Its simplified single-step blunt incision for localization appears to decrease radiation exposure risks.
基金Key Research and Development Project of Shandong Province(2016ZDJS05B03)Key Research and Development Project of Shandong Province(2017CXGC0812)。
文摘Keyhole gas tungsten arc welding(K-TIG)of Q345 low alloy steel plates was simulated by using SYSWELD software.The temperature field of the K-TIG welding process was simulated with three different combined heat sources and was compared with the weld profile that was obtained experimentally.The temperature field that was obtained by a combination of a double ellipsoid heat source on the upper half and a three-dimensional Gauss heat source on the lower half was similar to the real situation.The effects of plate thickness,gap and welding speed on the deformation and stress of the K-TIG welded joints were investigated by K-TIG welding numerical simulation.A reduction in the thickness of the weld plates reduced the z-direction deformation and transverse residual stress;an appropriate gap reduced the residual stress and an increase in the welding speed reduced deformation after welding,but did not help to control the residual stress after welding.
基金The authors wish to express their gratitude to the financial support to this project from the project foundation of the National Key Laboratory of Advanced Welding Production Technology of Harbin Institute of Technology and the US National Science Foundation under grant No.DMI 9812981
文摘In the double-sided arc welding system (DSAW) composing of PAW+TIG arcs, the PAW arc is guided by the TIG arc so that the current mostly flows through the direction of the workpiece thickness and the penetration is greatly improved. To analyze the current density distribution in DSAW is beneficial to understanding of this process. Considering all kinds of dynamic factors acting on the weldpool, this paper discusses firstly the surface deformation of the weldpool and the keyhole formation in PAW+TIG DSAW process on the basis of the magnetohydrodynamic theory and variation principles. Hence, a model of the current density distribution is developed. Through numerical simulation, the current density distribution in PAW+TIG DSAW process is quantitatively analyzed. It shows that the minimal radius of keyhole formed in PAW+TIG DSAW process is 0.5 mm and 89.5 percent of current flows through the keyhole.
