2015 Vol. 36 No. 3
Abstract:
An approach of detecting the offset between the micro-gap seam and the laser beam focus based on wavelet transform was presented during fiber laser butt-joint welding of Type 304 austenitic stainless steel plate with a high power 10 kW continuous wave fiber laser. This offset is less than 0.1 mm. To study the details of seam offset characteristics, an infrared sensitive high-speed video camera was used to capture the dynamic images of the molten pools. Multi-scale decomposition was implemented to the interested area of a molten pool image by using the wavelet function. The collected horizontal coordinate of high frequency coefficient was defined as a keyhole deformation parameter, and then this keyhole deformation parameter was deemed as a keyhole eigenvalue. Through the analysis of the relationship between the eigenvalue and welding seam offset, it was found that the offset between the micro-gap seam and the laser beam focus could be estimated by the keyhole deformation parameter effectively.
An approach of detecting the offset between the micro-gap seam and the laser beam focus based on wavelet transform was presented during fiber laser butt-joint welding of Type 304 austenitic stainless steel plate with a high power 10 kW continuous wave fiber laser. This offset is less than 0.1 mm. To study the details of seam offset characteristics, an infrared sensitive high-speed video camera was used to capture the dynamic images of the molten pools. Multi-scale decomposition was implemented to the interested area of a molten pool image by using the wavelet function. The collected horizontal coordinate of high frequency coefficient was defined as a keyhole deformation parameter, and then this keyhole deformation parameter was deemed as a keyhole eigenvalue. Through the analysis of the relationship between the eigenvalue and welding seam offset, it was found that the offset between the micro-gap seam and the laser beam focus could be estimated by the keyhole deformation parameter effectively.
2015, 36(3): 5-8,13.
Abstract:
Aimed at the zero-voltage soft-switching of leading-leg power devices in full load range, the resonant process of leading-leg parallel resonant network was analyzed fully after decoupling of the leading-leg parallel resonant network and transformer primary side series resonant network in phase-shift controlled full-bridge soft-switching power converter. Based on the theoretical computation and circuit simulation, the influence laws of power output current, resonant inductance and capacitance on the switching dead-time and loss of leading-leg power devices were researched. Taking the loss of resonant inductance into account, a design approach of resonant inductance and capacitance was provided. On the above basis, by experiments, the data of dead-time changing with output current for leading-leg power devices was acquired; the voltage and current waveforms at no-load state were also measured. The experimental data and waveforms agreed well with the theory and simulation results.
Aimed at the zero-voltage soft-switching of leading-leg power devices in full load range, the resonant process of leading-leg parallel resonant network was analyzed fully after decoupling of the leading-leg parallel resonant network and transformer primary side series resonant network in phase-shift controlled full-bridge soft-switching power converter. Based on the theoretical computation and circuit simulation, the influence laws of power output current, resonant inductance and capacitance on the switching dead-time and loss of leading-leg power devices were researched. Taking the loss of resonant inductance into account, a design approach of resonant inductance and capacitance was provided. On the above basis, by experiments, the data of dead-time changing with output current for leading-leg power devices was acquired; the voltage and current waveforms at no-load state were also measured. The experimental data and waveforms agreed well with the theory and simulation results.
Abstract:
During laser strengthening mould surface, a tiny wave of defocusing amount will generate splash as laser energy reach a certain value, which has strong effect on mould surface strengthening quality. By real-time collecting and processing the picture while laser strengthening the mould surface using CCD coaxial visual, the width of weld bead was extracted as the characteristic quantity of splash under fixed current. Acoustic signal strength has direct relation with laser energy and the relationship between acoustical signal RMS and splash was also investigated. Coaxial visual supplemented by acoustical signal achieve detecting laser strengthening splash using different sensor, improving remarkably the accuracy of splash detecting.
During laser strengthening mould surface, a tiny wave of defocusing amount will generate splash as laser energy reach a certain value, which has strong effect on mould surface strengthening quality. By real-time collecting and processing the picture while laser strengthening the mould surface using CCD coaxial visual, the width of weld bead was extracted as the characteristic quantity of splash under fixed current. Acoustic signal strength has direct relation with laser energy and the relationship between acoustical signal RMS and splash was also investigated. Coaxial visual supplemented by acoustical signal achieve detecting laser strengthening splash using different sensor, improving remarkably the accuracy of splash detecting.
Abstract:
To solve the problems of the instability seam-tracking signal and poor welding formability of the magnetic-control sensor in submerged arc welding, a Box-Behnken design (BBD) test method was proposed. The mathematical models of automatic submerged arc welding seam-tracking of magnetic-control sensor parameters such as excitation frequency, excitation current, magnetic pole height were built and response seam-tracking and weld width values were built based on the response surface method. By examining the fitting situation of the mathematical model on the test points, the sensor parameters were optimized according to the requirement of the quality of the seam-tracking signal and weld forming. Through the optimization of the sensor parameters, the quality of the seam-tracking signal and weld fusion width were predicted in submerged arc welding. The best combination between the seam-tracking signal and weld forming was realized, so as to the seam-tracking precision of the magnetic-control submerged arc welding and the welding quality were improved.
To solve the problems of the instability seam-tracking signal and poor welding formability of the magnetic-control sensor in submerged arc welding, a Box-Behnken design (BBD) test method was proposed. The mathematical models of automatic submerged arc welding seam-tracking of magnetic-control sensor parameters such as excitation frequency, excitation current, magnetic pole height were built and response seam-tracking and weld width values were built based on the response surface method. By examining the fitting situation of the mathematical model on the test points, the sensor parameters were optimized according to the requirement of the quality of the seam-tracking signal and weld forming. Through the optimization of the sensor parameters, the quality of the seam-tracking signal and weld fusion width were predicted in submerged arc welding. The best combination between the seam-tracking signal and weld forming was realized, so as to the seam-tracking precision of the magnetic-control submerged arc welding and the welding quality were improved.
2015, 36(3): 18-22.
Abstract:
Since the presence of CO2, the droplet control to MAG welding has always been a difficult problem. Based on preliminary studies, ultrasonic standing wave field, as a new method of droplet regulation, was introduced into MAG welding in this paper. In different conditions of shielding gas composition, the effect of ultrasound on droplet transfer was also studied. Under the conditions of low CO2 content, ultrasonic effect was still very significant. But with the increase of CO2 content, especially more than 20%, in short transition, the compression effect of ultrasound-arc tended to a constant and minimum. In droplet transition, this electromagnetic force gradually increased and eventually offset the downward ultrasound radiation force. Finally,the conclusions of the above analysis was verified by pure CO2 ultrasonic-MAG welding experiment.
Since the presence of CO2, the droplet control to MAG welding has always been a difficult problem. Based on preliminary studies, ultrasonic standing wave field, as a new method of droplet regulation, was introduced into MAG welding in this paper. In different conditions of shielding gas composition, the effect of ultrasound on droplet transfer was also studied. Under the conditions of low CO2 content, ultrasonic effect was still very significant. But with the increase of CO2 content, especially more than 20%, in short transition, the compression effect of ultrasound-arc tended to a constant and minimum. In droplet transition, this electromagnetic force gradually increased and eventually offset the downward ultrasound radiation force. Finally,the conclusions of the above analysis was verified by pure CO2 ultrasonic-MAG welding experiment.
2015, 36(3): 23-26.
Abstract:
Characteristic of laser beam-variable polarity plasma arc (LB-VPPA) hybrid heat source was studied for joining process of Al-Mn aluminum alloy. Arc shape was achieved by Y4-S2 high-speed camera, and welding current and arc voltage were obtained by Hannover welding quality analyzer. The results show that VPPA arc is attracted by laser and the mechanism which laser acts on arc is different for both positive polarity and negative polarity periods. Laser is concentrated on the roof of arc in positive polarity, while there is a protuberance-like plasma cylinder in negative polarity period. Roof plasma of VPPA arc absorbs laser by inverse bremsstroblung, and cross sectional area of arc becomes large as temperature increase. Meanwhile, laser provides plenty of free electrons to VPPA arc, thus current density and conductivity increase. Arc voltage decreases about 3-4 volts as resistance decreases. With the increasing of laser power, it obviously enhances the effects on VPPA arc.
Characteristic of laser beam-variable polarity plasma arc (LB-VPPA) hybrid heat source was studied for joining process of Al-Mn aluminum alloy. Arc shape was achieved by Y4-S2 high-speed camera, and welding current and arc voltage were obtained by Hannover welding quality analyzer. The results show that VPPA arc is attracted by laser and the mechanism which laser acts on arc is different for both positive polarity and negative polarity periods. Laser is concentrated on the roof of arc in positive polarity, while there is a protuberance-like plasma cylinder in negative polarity period. Roof plasma of VPPA arc absorbs laser by inverse bremsstroblung, and cross sectional area of arc becomes large as temperature increase. Meanwhile, laser provides plenty of free electrons to VPPA arc, thus current density and conductivity increase. Arc voltage decreases about 3-4 volts as resistance decreases. With the increasing of laser power, it obviously enhances the effects on VPPA arc.
2015, 36(3): 27-30.
Abstract:
SiCp/2024 matrix composites reinforced with SiC particles and 2219 aluminium alloy were joined by centered electron beam welding and deflection beam welding, respectively, and the microstructures and mechanical properties of these joints were studied. The results show that SiC particles were more likely to segregate by centered electron beam welding, meanwhile lots of Al4C3 brittle intermetallic compounds formed for serious interface reactions. Moreover, the tensile strength of the joints was about 104 MPa. The interface reaction was restrained by choosing deflection electron beam welding,and there was a little Al4C3 intermetallic compounds formed at the top of the joint and heat affected zone of SiCp/Al. The quasi-cleavage fracture occurred at the interface reaction layer of the base metal. There was a hardness transition zone near the SiCp/2024 fusion zone for both methods. The brittle intermetallic compounds Al4C3 formed in this zone results in the high hardness.
SiCp/2024 matrix composites reinforced with SiC particles and 2219 aluminium alloy were joined by centered electron beam welding and deflection beam welding, respectively, and the microstructures and mechanical properties of these joints were studied. The results show that SiC particles were more likely to segregate by centered electron beam welding, meanwhile lots of Al4C3 brittle intermetallic compounds formed for serious interface reactions. Moreover, the tensile strength of the joints was about 104 MPa. The interface reaction was restrained by choosing deflection electron beam welding,and there was a little Al4C3 intermetallic compounds formed at the top of the joint and heat affected zone of SiCp/Al. The quasi-cleavage fracture occurred at the interface reaction layer of the base metal. There was a hardness transition zone near the SiCp/2024 fusion zone for both methods. The brittle intermetallic compounds Al4C3 formed in this zone results in the high hardness.
2015, 36(3): 31-34.
Abstract:
As to the gas pool coupled activating TIG arc with the outer gas being the mixture of nitrogen and oxygen, Boltzmann plot method was applied to analyze the temperature distributions of the arc plasma and the regularity for change of the arc voltage when they were under different coupling degrees, and then the results were compared with the traditional TIG arc and the gas pool coupled activating TIG arc only using oxygen as the outer gas, respectively. The results show that both the plasma temperature of central zone and the arc voltage of the gas pool coupled activating TIG arc with the outer gas being the mixture of nitrogen and oxygen are higher than those of the TIG arc and gas pool coupled activating TIG arc with oxygen being introduced only. When the coupling degree h is changed from 0 to +2, both the arc plasma temperature of central zone and arc voltage are increased slightly.
As to the gas pool coupled activating TIG arc with the outer gas being the mixture of nitrogen and oxygen, Boltzmann plot method was applied to analyze the temperature distributions of the arc plasma and the regularity for change of the arc voltage when they were under different coupling degrees, and then the results were compared with the traditional TIG arc and the gas pool coupled activating TIG arc only using oxygen as the outer gas, respectively. The results show that both the plasma temperature of central zone and the arc voltage of the gas pool coupled activating TIG arc with the outer gas being the mixture of nitrogen and oxygen are higher than those of the TIG arc and gas pool coupled activating TIG arc with oxygen being introduced only. When the coupling degree h is changed from 0 to +2, both the arc plasma temperature of central zone and arc voltage are increased slightly.
Abstract:
In order to determine the temperature field of WC-12Co coating, mathematical model of heat conduction was established by utilizing suitable heat source and the thermal boundary conditions. Numerical simulation was carried out by commercial finite element code ANSYS, and iso-surface, the temperature distribution curve and temperature variation curve were derived. The areas of melting and gasification zone were measured by setting of contour lines of temperature field. Furthermore, the influence of process parameters on the areas of melting and gasification zone was researched and the optimized process parameters were predicted. To verify the prediction, electro spark deposition experiments were carried out and the optimized process parameters were determined.
In order to determine the temperature field of WC-12Co coating, mathematical model of heat conduction was established by utilizing suitable heat source and the thermal boundary conditions. Numerical simulation was carried out by commercial finite element code ANSYS, and iso-surface, the temperature distribution curve and temperature variation curve were derived. The areas of melting and gasification zone were measured by setting of contour lines of temperature field. Furthermore, the influence of process parameters on the areas of melting and gasification zone was researched and the optimized process parameters were predicted. To verify the prediction, electro spark deposition experiments were carried out and the optimized process parameters were determined.
2015, 36(3): 39-42.
Abstract:
Vibro-acoustic modulation technique (VAM) is a novel nonlinear ultrasonic method. The principle of VAM was briefly introduced, and then VAM with sine wave excitation and swept probing excitation was utilized to detect the fillet weld of small diameter nozzle stubs sample. It was found that the modulation intensity of defect sample was larger than reference sample, this difference would be much larger in some special high frequency range, which would be more beneficial to distinguish the weld quality. And the proper high frequency range can be quickly obtained by the swept probing excitation technique. Compared with the ultrasonic C-scan results, it was indicated that the VAM technique can be used to evaluate the quality of the fillet weld, however, further work is required to locate and quantitatively detect the damage.
Vibro-acoustic modulation technique (VAM) is a novel nonlinear ultrasonic method. The principle of VAM was briefly introduced, and then VAM with sine wave excitation and swept probing excitation was utilized to detect the fillet weld of small diameter nozzle stubs sample. It was found that the modulation intensity of defect sample was larger than reference sample, this difference would be much larger in some special high frequency range, which would be more beneficial to distinguish the weld quality. And the proper high frequency range can be quickly obtained by the swept probing excitation technique. Compared with the ultrasonic C-scan results, it was indicated that the VAM technique can be used to evaluate the quality of the fillet weld, however, further work is required to locate and quantitatively detect the damage.
2015, 36(3): 43-46.
Abstract:
The effects of gas mixture ratio in hyperbaric environment on pulsed MAG welding splash ratio and the shape of weld pool were analysed. Experimental results showed that more active gas made the weld arc instable, the spatter increase and the welding process extremely unstable in the same condition. In order to obtain the stable welding process and reduce the rate of spatter in hyperbaric environment and then prevent the formation of defects, the ratio of Ar was increased to reduce energy loss. Taking into consideration the influence of the splash ratio, the stability of droplet and the shape of weld pool, experiments results showed that 90%Ar+10%CO2 gas mixtures in 0.3 MPa can make the best welding quality. The effective control of gas mixture ratio has a significant effect on the stability of pulse MAG welding in hyperbaric environment.
The effects of gas mixture ratio in hyperbaric environment on pulsed MAG welding splash ratio and the shape of weld pool were analysed. Experimental results showed that more active gas made the weld arc instable, the spatter increase and the welding process extremely unstable in the same condition. In order to obtain the stable welding process and reduce the rate of spatter in hyperbaric environment and then prevent the formation of defects, the ratio of Ar was increased to reduce energy loss. Taking into consideration the influence of the splash ratio, the stability of droplet and the shape of weld pool, experiments results showed that 90%Ar+10%CO2 gas mixtures in 0.3 MPa can make the best welding quality. The effective control of gas mixture ratio has a significant effect on the stability of pulse MAG welding in hyperbaric environment.
Abstract:
Tin coating were brush electroplated on BAg34CuZnSn brazing filler metals. The surface microstructure and crystallization orientation of tin coatings were observed by scanning electron microscopy and X-ray diffraction patterns. The effect of tin content on melting temperature, wettability and tensile strength of brazing filler metals were analyzed using the differential scanning calorimetry, wetting test furnace and tensile test machine, respectively. The electrical resistivity and elongation of the brazing filler metals were also discussed after brush electroplated tin. The results show that a smooth and uniform surface morphology of tin coating with small grain size and porosity is obtained, and its crystallization orientation is (200) and (112) crystal faces. The DSC endothermic peak shift to the left, the melting temperature of brazing filler metals decreases with the increasing of tin content. The wettability area and elongation of the brazing filler metals are improved, but the electrical resistivity and tensile strength of brazing filler metals are decreased. When the content of tin in the film is 2.0 %(wt.%), the wettability area and elongation of AgCuZnSn brazing filler metals are maximum, while its melting temperature, resistivity and tensile strength are minimum.
Tin coating were brush electroplated on BAg34CuZnSn brazing filler metals. The surface microstructure and crystallization orientation of tin coatings were observed by scanning electron microscopy and X-ray diffraction patterns. The effect of tin content on melting temperature, wettability and tensile strength of brazing filler metals were analyzed using the differential scanning calorimetry, wetting test furnace and tensile test machine, respectively. The electrical resistivity and elongation of the brazing filler metals were also discussed after brush electroplated tin. The results show that a smooth and uniform surface morphology of tin coating with small grain size and porosity is obtained, and its crystallization orientation is (200) and (112) crystal faces. The DSC endothermic peak shift to the left, the melting temperature of brazing filler metals decreases with the increasing of tin content. The wettability area and elongation of the brazing filler metals are improved, but the electrical resistivity and tensile strength of brazing filler metals are decreased. When the content of tin in the film is 2.0 %(wt.%), the wettability area and elongation of AgCuZnSn brazing filler metals are maximum, while its melting temperature, resistivity and tensile strength are minimum.
Abstract:
Cold metal transfer(CMT) welding-brazing of Al6061 and TA2 was carried out using ER4043 filler metal. The microstructure characteristics of the Ti/Al joints were analyzed by optical microscopy, scanning electron microscopy and energy dispersive spectrometer, respectively. Mechanical properties of the joints were characterized by measurement of the tensile strength. The results indicate that a welding-brazing joint was formed by CMT method, which included a welding joint at the aluminium sheet side and a brazing joint at the titanium sheet side. The intermetallic compound at the brazing interface consisted of two different layers. Among them, the continuous layer near titanium substrate was composed of Ti3Al intermetallic compound, while the serration-shaped layer next to the weld metal was composed of TiAl3 intermetallic compound. When groove angle 30° of titanium sheet was used during the welding process, uniform intermetallics would be formed at the brazing interface, thus sound joint which had a tensile strength of 197.5 MPa was obtained and the failure location of this joint was at Al HAZ.
Cold metal transfer(CMT) welding-brazing of Al6061 and TA2 was carried out using ER4043 filler metal. The microstructure characteristics of the Ti/Al joints were analyzed by optical microscopy, scanning electron microscopy and energy dispersive spectrometer, respectively. Mechanical properties of the joints were characterized by measurement of the tensile strength. The results indicate that a welding-brazing joint was formed by CMT method, which included a welding joint at the aluminium sheet side and a brazing joint at the titanium sheet side. The intermetallic compound at the brazing interface consisted of two different layers. Among them, the continuous layer near titanium substrate was composed of Ti3Al intermetallic compound, while the serration-shaped layer next to the weld metal was composed of TiAl3 intermetallic compound. When groove angle 30° of titanium sheet was used during the welding process, uniform intermetallics would be formed at the brazing interface, thus sound joint which had a tensile strength of 197.5 MPa was obtained and the failure location of this joint was at Al HAZ.
2015, 36(3): 55-58.
Abstract:
Aimed at solving the problem of double welding robots collision in the same workspace, this research presented a method of collision-free path planning based on assuming correction strategy and genetic algorithm. Envelope model of robot was established with sphere and cylinder, and the analytical expression of shortest distance between two robots was calculated in local coordinate system using space geometry principle. An assuming path was given by ideal constraint's condition, the planning of arc welding process and the shortest distance between solder joints. Fitness function was related to the quality of arc welding, the shortest distance of spot welding, the shortest distance between two robots, the range of joints. Genetic algorithm was used to search for safe configuration. Taking stud welding station an example, this paper did collision-free path planning and emulation experiments with MATLAB and DELMIA software. The method was proved correct and feasible, planning a quality and safe path for double robots.
Aimed at solving the problem of double welding robots collision in the same workspace, this research presented a method of collision-free path planning based on assuming correction strategy and genetic algorithm. Envelope model of robot was established with sphere and cylinder, and the analytical expression of shortest distance between two robots was calculated in local coordinate system using space geometry principle. An assuming path was given by ideal constraint's condition, the planning of arc welding process and the shortest distance between solder joints. Fitness function was related to the quality of arc welding, the shortest distance of spot welding, the shortest distance between two robots, the range of joints. Genetic algorithm was used to search for safe configuration. Taking stud welding station an example, this paper did collision-free path planning and emulation experiments with MATLAB and DELMIA software. The method was proved correct and feasible, planning a quality and safe path for double robots.
Abstract:
FGH95 nickel-based superalloy laser cladding layer was strengthened by ultrasonic impact treatment(UIT). The microstructure of laser cladding with and without UIT was studied by metallurgical microscope, the grain size was calculated by the Image-Pro Plus software, and the sectional microhardness of laser cladding was also analyzed after UIT. Results show that plastic deformation of cladding layer was formed with UIT and the varying degrees of grain refined behavior were obvious in depth direction. Dislocation pile up phenomenon was significant in strong plastic deformation zone with refined small crystal block. Sub-plastic deformation zone was depth range of 0.1-0.25 mm and the microstructure of this zone was refinement tree dendrite. The microstructure of micro-plastic deformation zone was mainly refined equiaxed grains into 5.4μm depth to 0.7 mm. The microhardness of cladding layer was enhanced significantly and the maximum value of surface microhardness was 594.25 HV by 1.3 fold after UIT.
FGH95 nickel-based superalloy laser cladding layer was strengthened by ultrasonic impact treatment(UIT). The microstructure of laser cladding with and without UIT was studied by metallurgical microscope, the grain size was calculated by the Image-Pro Plus software, and the sectional microhardness of laser cladding was also analyzed after UIT. Results show that plastic deformation of cladding layer was formed with UIT and the varying degrees of grain refined behavior were obvious in depth direction. Dislocation pile up phenomenon was significant in strong plastic deformation zone with refined small crystal block. Sub-plastic deformation zone was depth range of 0.1-0.25 mm and the microstructure of this zone was refinement tree dendrite. The microstructure of micro-plastic deformation zone was mainly refined equiaxed grains into 5.4μm depth to 0.7 mm. The microhardness of cladding layer was enhanced significantly and the maximum value of surface microhardness was 594.25 HV by 1.3 fold after UIT.
Abstract:
The pulsed MAG welding current and voltage waveforms in different air environmental pressures were analyzed using statistical method. The relationship between probability density distribution of arc voltage and current and the hyperbaric welding arc stability under different ambient pressure were also investigated in this paper. It is shown that the arc energy loss intensifies with increasing the environment pressure resulting in less stable welding process. A useful method to raise arc voltage setting to compensate the arc energy loss was used to obtain stable welding process. When arc voltage setting was increased 3 V and 5 V respectively in 0.3 MPa and 0.5 MPa hyperbaric environment, a stable welding process comparable with normal atmospheric welding has been realized. It is concluded that welding stability of hyperbaric pulsed MAG welding arc can be improved by higher arc voltage. This paper provided theoretical basis and experimental foundation for the hyperbaric pulse MAG welding to optimize and match the welding parameter.
The pulsed MAG welding current and voltage waveforms in different air environmental pressures were analyzed using statistical method. The relationship between probability density distribution of arc voltage and current and the hyperbaric welding arc stability under different ambient pressure were also investigated in this paper. It is shown that the arc energy loss intensifies with increasing the environment pressure resulting in less stable welding process. A useful method to raise arc voltage setting to compensate the arc energy loss was used to obtain stable welding process. When arc voltage setting was increased 3 V and 5 V respectively in 0.3 MPa and 0.5 MPa hyperbaric environment, a stable welding process comparable with normal atmospheric welding has been realized. It is concluded that welding stability of hyperbaric pulsed MAG welding arc can be improved by higher arc voltage. This paper provided theoretical basis and experimental foundation for the hyperbaric pulse MAG welding to optimize and match the welding parameter.
2015, 36(3): 67-70.
Abstract:
The present study introduces a path planning algorithm of the two-robot coordinate system in welding task of complex curve seam. Furthermore, a leader-follower scheme has been proposed, according to the molten pool of each points on whole seam are nearly vertical or horizontal,which guarantee one robot catching work piece to adjust seam lying in the flat position under pose constraint and the other tracking and welding. In this research, the two-robot coordinate system and coordinate mathematical model has been established for constrained pose. Moreover, the paper study on path planning in two-robot coordinate which saddle-shape weld seam as study objects. Finally, test on path planning was done in order to prove the theory results, while the test results and analysis show that the two-robot coordinate system can realize continuous welding for complex curve seam.
The present study introduces a path planning algorithm of the two-robot coordinate system in welding task of complex curve seam. Furthermore, a leader-follower scheme has been proposed, according to the molten pool of each points on whole seam are nearly vertical or horizontal,which guarantee one robot catching work piece to adjust seam lying in the flat position under pose constraint and the other tracking and welding. In this research, the two-robot coordinate system and coordinate mathematical model has been established for constrained pose. Moreover, the paper study on path planning in two-robot coordinate which saddle-shape weld seam as study objects. Finally, test on path planning was done in order to prove the theory results, while the test results and analysis show that the two-robot coordinate system can realize continuous welding for complex curve seam.
Abstract:
Low cycle fatigue tests on 96.5Sn-3Ag-0.5Cu solder joints were carried out using micro-uniaxial fatigue testing system at 25 ℃ with different dwell time (1-20 s) and different strain rates (0.01-0.08 mm/s). The results show that dwell time of 1-20 s has little influence on fatigue life of solder joints at 25 ℃. With the increasing of strain rates, the fatigue life of solder joints reduced gradually, and fracture mode was transformed from ductile fracture to brittle fracture. Fatigue cracks tended to initiate around the solder/IMC interfaces at the edge of the joints with different loading speeds, and then propagated within the solder proximately along the IMC interfaces. The fracture morphology of solder joints with different strain rates consisted mainly of propagation region and final fracture region.
Low cycle fatigue tests on 96.5Sn-3Ag-0.5Cu solder joints were carried out using micro-uniaxial fatigue testing system at 25 ℃ with different dwell time (1-20 s) and different strain rates (0.01-0.08 mm/s). The results show that dwell time of 1-20 s has little influence on fatigue life of solder joints at 25 ℃. With the increasing of strain rates, the fatigue life of solder joints reduced gradually, and fracture mode was transformed from ductile fracture to brittle fracture. Fatigue cracks tended to initiate around the solder/IMC interfaces at the edge of the joints with different loading speeds, and then propagated within the solder proximately along the IMC interfaces. The fracture morphology of solder joints with different strain rates consisted mainly of propagation region and final fracture region.
Abstract:
Numerical model of temperature field and fluid flow field was built to study the effects of gravity on different welding positions and different gravity values. Temperature field and fluid flow field of flat position, 45° position and 90° position with downward speed were calculated, respectively. The results showed that fluid flow of 90° position was far more intense than the one of flat position, which affected the temperature distribution and caused molten metal flowing downward. The presence of gravity had no influence on fluid flow distribution morphology, but affected the flowing speed significantly. Conclusions of this study can be used on the research of welding pool instability judgment basis and deciding parameters of all position TIG or MAG welding.
Numerical model of temperature field and fluid flow field was built to study the effects of gravity on different welding positions and different gravity values. Temperature field and fluid flow field of flat position, 45° position and 90° position with downward speed were calculated, respectively. The results showed that fluid flow of 90° position was far more intense than the one of flat position, which affected the temperature distribution and caused molten metal flowing downward. The presence of gravity had no influence on fluid flow distribution morphology, but affected the flowing speed significantly. Conclusions of this study can be used on the research of welding pool instability judgment basis and deciding parameters of all position TIG or MAG welding.
2015, 36(3): 80-84.
Abstract:
The void extraction method of solder joints based on global threshold segmentation is inaccurate. Moreover, once the solder joint in the image is shaded, the extraction of BGA solder joint's voids will become difficult. In order to detect the void defects of BGA solder joints under complex X-ray imaging background, it was detected that the unobstructed solder joints based on thresholding, solder roundness and solder area, and an interactive method of X-ray contour extraction to detect the obstructed solder joints was propose. According to the characteristics of solder buddle, an integrated method of solder joint's void extraction was presented based on grayscale morphology, histogram stretching, fuzzy enhancement and BLOB analysis. The result of comparison experiment shows that the method presented in this research possesses high accuracy in detecting the void defect of BGA solder joints.
The void extraction method of solder joints based on global threshold segmentation is inaccurate. Moreover, once the solder joint in the image is shaded, the extraction of BGA solder joint's voids will become difficult. In order to detect the void defects of BGA solder joints under complex X-ray imaging background, it was detected that the unobstructed solder joints based on thresholding, solder roundness and solder area, and an interactive method of X-ray contour extraction to detect the obstructed solder joints was propose. According to the characteristics of solder buddle, an integrated method of solder joint's void extraction was presented based on grayscale morphology, histogram stretching, fuzzy enhancement and BLOB analysis. The result of comparison experiment shows that the method presented in this research possesses high accuracy in detecting the void defect of BGA solder joints.
Abstract:
13mm diameter bars of 600MPa grade ultra-fine grain steel were welded by friction welding. Experimental results show that ultra-fine grain steel has good weldability of friction welding when the friction welding process parameters were properly controlled. Ultra-fine grain steel friction welding joint was mainly composed of four zones: welding seam, thermo-mechanically affected zone (TMAZ), heat affected zone(HAZ) and base material. The grain size was about 9-11 μm in the HAZ, which was slightly larger than the one of the base metal. Mechanical properties results showed that joint strength of the ultrafine-grained steel friction welding was up to 715 MPa with 22% elongation and 68% contraction ratio of cross section, and impact toughness was about 98 J. Meanwhile typical ductile fracture was obtained for this kind of joint.
13mm diameter bars of 600MPa grade ultra-fine grain steel were welded by friction welding. Experimental results show that ultra-fine grain steel has good weldability of friction welding when the friction welding process parameters were properly controlled. Ultra-fine grain steel friction welding joint was mainly composed of four zones: welding seam, thermo-mechanically affected zone (TMAZ), heat affected zone(HAZ) and base material. The grain size was about 9-11 μm in the HAZ, which was slightly larger than the one of the base metal. Mechanical properties results showed that joint strength of the ultrafine-grained steel friction welding was up to 715 MPa with 22% elongation and 68% contraction ratio of cross section, and impact toughness was about 98 J. Meanwhile typical ductile fracture was obtained for this kind of joint.
Abstract:
AC magnetic field was employed in welding of 5 mm thick AZ91 magnesium alloy plate by TIG method. The effects of post weld heat treatment on properties and microstructure of welded joints were studied through the analysis of the microstructure, mechanical properties and corrosion resistance. The results showed that the grain size was refined for AZ91 magnesium alloy joint with solution treatment; and more dispersed β-Mg17Al12 phase precipitates in α-Mg were found for the joint with solution and aging treatment; intermittent and dispersal precipitations of β-Mg17Al12 phase was smaller for joint with aging treatment. Meanwhile, the hardness, strength and plasticity of the weld joints were improved after heat treatment.
AC magnetic field was employed in welding of 5 mm thick AZ91 magnesium alloy plate by TIG method. The effects of post weld heat treatment on properties and microstructure of welded joints were studied through the analysis of the microstructure, mechanical properties and corrosion resistance. The results showed that the grain size was refined for AZ91 magnesium alloy joint with solution treatment; and more dispersed β-Mg17Al12 phase precipitates in α-Mg were found for the joint with solution and aging treatment; intermittent and dispersal precipitations of β-Mg17Al12 phase was smaller for joint with aging treatment. Meanwhile, the hardness, strength and plasticity of the weld joints were improved after heat treatment.
2015, 36(3): 93-96.
Abstract:
The Fe-Cr-Ti-C series of wear-resistant flux cored wire was surfaced on low carbon steel by GTAW method. The phase composition, distribution and growth mechanism of hard phase in surfacing layer were studied. The reasons for the increasing of abrasion resistance and surface hardness were discussed as well. The results show that the alloy elements of flux cored wire could effectively translate into surfacing layer, in-situ synthesis of (Fe,Cr)7C3 and TiC hard phase were obtained. TiC preferentially nucleated and grew up by attaching to external interface, the nucleation and growth of eutectic (Fe,Cr)7C3 hard phase was dependent on the primary martensite phase and TiC. Most of TiC hard phase was punctate, the minority was the strip and cross shaped. They dispersed in the matrix of martensite, and formed composite hard phase with (Fe,Cr)7C3, which could significantly improve the wear resistance of the surfacing layer.
The Fe-Cr-Ti-C series of wear-resistant flux cored wire was surfaced on low carbon steel by GTAW method. The phase composition, distribution and growth mechanism of hard phase in surfacing layer were studied. The reasons for the increasing of abrasion resistance and surface hardness were discussed as well. The results show that the alloy elements of flux cored wire could effectively translate into surfacing layer, in-situ synthesis of (Fe,Cr)7C3 and TiC hard phase were obtained. TiC preferentially nucleated and grew up by attaching to external interface, the nucleation and growth of eutectic (Fe,Cr)7C3 hard phase was dependent on the primary martensite phase and TiC. Most of TiC hard phase was punctate, the minority was the strip and cross shaped. They dispersed in the matrix of martensite, and formed composite hard phase with (Fe,Cr)7C3, which could significantly improve the wear resistance of the surfacing layer.
2015, 36(3): 97-100.
Abstract:
The ring of Al-12Si self-fluxing filler metals has been prepared by hot pressed sintering. The wetting property, microhardness, microscopic structure of self-fluxing on different sintering pressure were studied. The results showed that the spreading areas of the self-fluxing filler metals were affected with sintering pressure. And the spreading areas of the self-fluxing filler metals was up to 152 mm2 when the sintering pressure was at 222 MPa. With increasing of the sintering pressure, the density, microhardness of the self-fluxing filler metals increased, but the tendency of increasing became slowly. The microscopic structure of self-fluxing filler metals was composed of black large lump and white small particles which was evenly distributed on the gray matrix; XRD results showed that self-fluxing filler metals was only composed of α-Al solid solution, primary crystal silicium and Nocolok filler metals, which denoted that the filler metals prepared by hot pressed sintering did not occur oxidation reactions and hydrolysis reactions. The activation of silicium ensured the high activity of filler metals.
The ring of Al-12Si self-fluxing filler metals has been prepared by hot pressed sintering. The wetting property, microhardness, microscopic structure of self-fluxing on different sintering pressure were studied. The results showed that the spreading areas of the self-fluxing filler metals were affected with sintering pressure. And the spreading areas of the self-fluxing filler metals was up to 152 mm2 when the sintering pressure was at 222 MPa. With increasing of the sintering pressure, the density, microhardness of the self-fluxing filler metals increased, but the tendency of increasing became slowly. The microscopic structure of self-fluxing filler metals was composed of black large lump and white small particles which was evenly distributed on the gray matrix; XRD results showed that self-fluxing filler metals was only composed of α-Al solid solution, primary crystal silicium and Nocolok filler metals, which denoted that the filler metals prepared by hot pressed sintering did not occur oxidation reactions and hydrolysis reactions. The activation of silicium ensured the high activity of filler metals.
2015, 36(3): 101-104.
Abstract:
Traditional stress measurement methods are time-consuming and destructive. Ultrasonic stress measurement method was used to overcome these disadvantages based on the acoustoelasticity theory. Ultrasonic stress measurement experimental equipment was established with Lcr waves. This method has proved its accuracy and reliability by actual measurement of such industrial structures as electric multiple units(EMU) and rockets. The entire envelope weighting algorithm was proposed to reduce the influencing factors for measurement accuracy, by which uncertainty of the system is lower than threshold method.
Traditional stress measurement methods are time-consuming and destructive. Ultrasonic stress measurement method was used to overcome these disadvantages based on the acoustoelasticity theory. Ultrasonic stress measurement experimental equipment was established with Lcr waves. This method has proved its accuracy and reliability by actual measurement of such industrial structures as electric multiple units(EMU) and rockets. The entire envelope weighting algorithm was proposed to reduce the influencing factors for measurement accuracy, by which uncertainty of the system is lower than threshold method.
Abstract:
A professional friction stir welding simulation software MORFEO was used to observe flow characteristics of different thickness. 2024 aluminum alloy sheets of 4 mm thickness were butt jointed. Two local 3D models of two kinds of pin profiles were set up, namely cylindrical and conical shapes. Compared with other simulation software, MORFEO provided a more convenient and parameterized way to demonstrate each level's streamlines and gave a quasi steady state description of the material deposition which helped to predict defects caused by insufficient flow. The material close to the shoulder tended to move farther around the pin. Both sides' material flowed around the pin to the retreating side behind the moving pin and lefe large vacant space on the advancing side. Whereas when the pin was tapered and had an appropriate rotation speed such as 600 r/min in this paper, the material could be taken to both sides behind the pin on each level. Similar results had also been observed in the experiment conducted with the marker technique.
A professional friction stir welding simulation software MORFEO was used to observe flow characteristics of different thickness. 2024 aluminum alloy sheets of 4 mm thickness were butt jointed. Two local 3D models of two kinds of pin profiles were set up, namely cylindrical and conical shapes. Compared with other simulation software, MORFEO provided a more convenient and parameterized way to demonstrate each level's streamlines and gave a quasi steady state description of the material deposition which helped to predict defects caused by insufficient flow. The material close to the shoulder tended to move farther around the pin. Both sides' material flowed around the pin to the retreating side behind the moving pin and lefe large vacant space on the advancing side. Whereas when the pin was tapered and had an appropriate rotation speed such as 600 r/min in this paper, the material could be taken to both sides behind the pin on each level. Similar results had also been observed in the experiment conducted with the marker technique.
Abstract:
The inverse-welding method, post welding cooling treatment(PWCT) to eliminate residual stress, was analyzed by deactive element method using commercial finite element code ABAQUS. The residual stresses eliminated in post welding cooling treatment of P122 steel were quantitatively analysed with different heat treatment temperatures, the cooling media, the cooling rates and cooling times. Results show that both the Mises residual stress and transverse residual stress were reduced obviously after PWCT. And the effect of heat treatment temperature on PWCT method was the most remarkable. Then the effects of cooling time, cooling rate of cooling medium during the PWCT were reduced sequentially. When the heat treatment temperature is 400 ℃, the cooling time is 20 s, this method could not only eliminate the welding residual stress but also form compressive stress layer of 1.3 mm depth in the surface of the treatment.
The inverse-welding method, post welding cooling treatment(PWCT) to eliminate residual stress, was analyzed by deactive element method using commercial finite element code ABAQUS. The residual stresses eliminated in post welding cooling treatment of P122 steel were quantitatively analysed with different heat treatment temperatures, the cooling media, the cooling rates and cooling times. Results show that both the Mises residual stress and transverse residual stress were reduced obviously after PWCT. And the effect of heat treatment temperature on PWCT method was the most remarkable. Then the effects of cooling time, cooling rate of cooling medium during the PWCT were reduced sequentially. When the heat treatment temperature is 400 ℃, the cooling time is 20 s, this method could not only eliminate the welding residual stress but also form compressive stress layer of 1.3 mm depth in the surface of the treatment.