Material Flow Behavior on Weld Pool Surface in Plasma Arc Welding Process Considering Dominant Driving Forces
TL;DR: In this article, the effect of oxygen in the shielding gas on the material flow behavior of the weld pool surface was discussed to clarify the dominant driving weld pool force in keyhole plasma arc welding (KPAW).
Abstract: In this study, the effect of oxygen in the shielding gas on the material flow behavior of the weld pool surface was discussed to clarify the dominant driving weld pool force in keyhole plasma arc welding (KPAW). To address this issue, the convection flow on the top surface of weld pool was observed using a high-speed video camera. The temperature distribution on the surface along keyhole wall was measured using the two-color pyrometry method to confirm the Marangoni force activity on the weld pool. The results show that the inclination angle of the keyhole wall (keyhole shape) increased especially near the top surface due to the decrease in the surface tension of weld pool through surface oxidation when a shielding gas of Ar + 0.5% O2 was used. Due to the change in the keyhole shape, the upward and backward shear force compositions created a large inclination angle at the top surface of the keyhole. From the temperature measurement results, the Marangoni force was found to alter the direction when 0.5% O2 was mixed with the shielding gas. The shear force was found to be the strongest force among the four driving forces. The buoyant force and Lorentz force were very weak. The Marangoni force was stronger than the Lorentz force but was weaker than shear force. The interaction of shear force and Marangoni force controlled the behavior and speed of material flow on the weld pool surface. A strong upward and backward flow was observed in the case of mixture shielding gas, whereas a weak upward flow was observed for pure Ar. The heat transportation due to the weld pool convection significantly changed when only a small amount of oxygen was admixed in the shielding gas. The results can be applied to control the penetration ratio in KPAW.
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TL;DR: In this paper, the formation process of welding defects in plasma keyhole arc welding was investigated based on the formation of eddies inside the weld pool using an advanced X-ray visualization system.
16 citations
TL;DR: In this paper , the effects of different magnetic field intensity on WC particle distribution, microstructure, phase composition, microhardness and wear are compared. And the mechanism of alternating magnetic fields on cladding layers is briefly analyzed.
Abstract: Ni60A/WC composite coating is prepared on 45 steel substrate by alternating-magnetic-field-assisted laser cladding. We compare the effects of different magnetic field intensity on WC particle distribution, microstructure, phase composition, microhardness and wear; in addition, the mechanism of alternating magnetic fields on cladding layers is briefly analyzed. The results show that an alternating magnetic field can significantly homogenize the distribution of WC particles. WC particles at the bottom are stirred and dispersed to the middle and upper area of the laser pool. The distribution of WC in the bottom region 6 of the coating decreases from 19.1% to 10%, the distribution of WC in the bottom region 5 decreases from 46.46% to 33.3%, the WC distribution in the top region 1 of the coating increases from 0 to 7.7% and the WC distribution in the top region 2 of the coating increases from 8.08% to 12.2%. The stirring of alternating magnetic fields strengthens the solute convection in the laser pool, refines the snowflake-shaped carbide hard phase and improves the coating microhardness and wear property, and adhesive wear and abrasive wear decrease gradually with increasing magnetic field strength.
3 citations
TL;DR: In this article, a nanowire flux activated TIG welding with a full penetration and a narrow bead geometry was used as flux and compared with micro-scale Fe2O3 flux.
Abstract: Economic welding of thick steel plates is an emerging challenge for various engineering applications. However, tungsten inert gas (TIG) arc welding, as an economic and widely used method, is not regarded as a suitable tool to weld thick steel plates due to the shallow penetration in a single-pass operation. In this technical progress, the joining of austenitic high manganese steel of 8 mm thickness was successfully performed using nanowire flux activated TIG welding with a full penetration and a narrow bead geometry. Fe2O3 nanowire was used as flux and compared with microscale Fe2O3 flux. Experimental results showed that with nanowire fluxes, the welding yielded the maximum of more than 8 mm thick penetration (full penetration and melt over the plate) with proper operating parameters in a single pass. In sharp contrast, the penetration is only less than 4 mm for a single pass welding without Fe2O3 flux with the similar parameters. Arc voltage—time variation during welding process was analyzed and the angular distortion was measured after welding to understand the activating effect of optimized flux mixture. Compared to welding joint without flux and with microscale Fe2O3 flux, nanoscale Fe2O3 flux has a larger arc voltage and higher energy efficiency, higher joint strength and less angular distortion. The developed joint with nanowire flux qualified the tensile test with tensile strength of 700.7 MPa (82.38% of base material strength) and 34.1% elongation. This work may pave a way for nanotechnology-enabling welding innovation for engineering application.
3 citations
TL;DR: In this article , the feasibility studies on the effect of process parameters of keyhole plasma arc welding (KPAW) joints were conducted and the results showed that the failure region reflects the presence of coarse grains; because of the heat dissipation from the fusion zone.
Abstract: Abstract AISI 304HCu is a super austenitic stainless steel with alloying elements adding its capacity to retain the ability to withstand mechanical and corrosion resistance at extreme service conditions. The investigation focuses on the feasibility studies on the effect of process parameters of Keyhole Plasma Arc Welding (KPAW). The stability of the keyhole on 9 mm thick tubes is by the action of welding current, gas flow rate and the standoff distance. The autogenous joint had a wine glass bead morphology with a minimum heat-affected zone. The influence of current is on the penetration, whereas the gas flow rate and standoff distance govern the geometric appearance. The fusion zone consists of vermicular δ ferrites within the austenitic matrix. The refined vermicular ferrite grains in the fusion zone of the KPAW joint record a maximum strength of 610 MPa and hardness of 230 HV. The failure region reflects the presence of coarse grains; because of the heat dissipation from the fusion zone. The cooling rate is high that it restricts the growth of the grains in the HAZ. The failure is by the ductile manner in KPAW joints.
2 citations
13 Sep 2021
TL;DR: In this paper, the effects of low and high currents of plasma arc welding on the material flow and thermodynamics of molten pool and its relationship to the welding defects were investigated using a high-speed video camera.
Abstract: The material flow dynamic and velocity distribution on the melted domain surface play a crucial role on the joint quality and formation of welding defects. In this study, authors investigated the effects of the low and high currents of plasma arc welding on the material flow and thermodynamics of molten pool and its relationship to the welding defects. The high-speed video camera (HSVC) was used to observe the convection of the melted domain and welded-joint appearance. Furthermore, to consider the Marangoni force activation, the temperature on the melted domain was measured by a thermal HSVC. The results revealed that the velocity distribution on the weld pool surface was higher than that inside the molten weld pool. Moreover, in the case of 80 A welding current, the convection speed of molten was faster than that in other cases (120 A and 160 A). The serious undercut and humping could be seen on the top surface (upper side) and unstable weld bead was visualized on the back side (bottom surface). In the case of 160 A welding current, the convection on the weld pool surface was much more complex in comparison with 80 A and 120 A cases. The excessive convex defect at the bottom side and the concave defect at the top surface were observed. In the case of 120 A welding current, two convection patterns with the main flow in the backward direction were seen. Almost no welding defect could be found. The interaction between the shear force and Marangoni force played a solid state on the convection and heat transportation processes in the plasma arc welding process.
1 citations
References
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01 Jun 1988-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this paper, the Gibbs and Langmuir adsorption isotherms were used to calculate the entropy and enthalpy of surface active components such as oxygen, sulfur, selenium, and tellurium.
Abstract: Since the fluid flow, heat transfer, and the resulting weld properties are significantly affected by interfacial tension driven flow, the variation of interfacial tension in dilute binary solutions is studied as a function of both composition and temperature. Entropy and enthalpy of adsorption of surface active components such as oxygen, sulfur, selenium, and tellurium in Fe-O, Fe-S, Fe-Se, Cu-O, Cu-S, Cu-Se, Cu-Te, Ag-O, and Sn-Te systems were calculated from the analysis of the published data on interfacial tension of these systems. For these calculations, a formalism based on the combination of Gibbs and Langmuir adsorption isotherms was used. Interfacial tensions in Cr-O, Co-S, and Ni-S systems, where the data are scarce, were predicted by using certain approximations. The computed values were found to be in reasonable agreement with the data available in the literature. Temperature coefficients of interfacial tensions were calculated for several binary systems. It was demonstrated that in dilute solutions, the temperature coefficient of interfacial tension is strongly influenced by the heat of adsorption which, in turn, is influenced by the difference in electronegativity between the solute and solvent ions.
470 citations
TL;DR: In this paper, a review of recent papers which have led to the capability of the prediction of weld depths for gas tungsten arc welding, for any given arc current, electrode shape or separation and welding gas, is given.
Abstract: This paper gives a review of recent papers which have led to the capability of the prediction of weld depths for gas tungsten arc welding, for any given arc current, electrode shape or separation and welding gas. The methodology is given for deriving plasma composition as a function of temperature and pressure from basic atomic and molecular properties. Transport coefficients of density, specific heat, enthalpy, electrical conductivity, thermal conductivity, viscosity and radiation emission coefficients can then be derived as a function of temperature. The conservation equations of fluid dynamics are then used to derive weld profiles for stainless steel for welding gases such as argon, helium, carbon dioxide and a 10% mixture of hydrogen in argon. The markedly different weld depths which are obtained are related to basic material functions such as specific heat, electrical and thermal conductivity. The temperature dependence of the surface tension coefficient has a marked effect on weld depth and profiles because it can influence the direction of circulatory flow in the weld pool. Electric arcs in helium and carbon dioxide are more constricted than arcs in argon and as a consequence the magnetic pinch pressure of the arc, transmitted to the weld pool, can force strong downward flows in the weld pool and thus lead to a deep weld. It is found that because of the interactions of the arc and the weld pool through effects such as viscous drag forces of the plasma on the weld pool, it is necessary to treat the arc, the electrode and the weld pool in a unified system.
231 citations
TL;DR: In this article, the basic principles of plasma arc welding (PAW) and a survey of the latest research and applications in the field are provided, along with a novel PAW process variant, the controlled pulse keyholing process and the corresponding experimental system.
114 citations
TL;DR: In this article, the authors investigated the effect of active flux on the Marangoni convection in the welding pool, and showed that the depth/width ratio of the weld pool was closely related to the oxygen content in the pool.
Abstract: Active flux can modify the fusion zone geometry dramatically in GTA welding (A-TIG). In the present study, in order to investigate the effect of the active flux on the Marangoni convection in the welding pool, bead-on-plate specimens are made on SUS304 stainless steel pre-placed with single active flux, Cu 2 O, NiO, Cr 2 O 3 , SiO 2 and TiO 2 by the GTA process. Weld pool cross-sections and the bead surface morphology are analyzed by optical microscopy after welding. The oxygen content in the weld metal is measured using a HORIBA EMGA-520 Oxygen/Nitrogen Analyzer. The results showed that the depth/width ratio of the weld pool was closely related to the oxygen content in the pool. The oxygen content in the weld metal increases with the quantity of fluxes, Cu 2 O, NiO, Cr 2 O 3 , SiO 2 and TiO 2 . However, for the TiO 2 oxide flux, the highest oxygen content in the weld metal is below 200 ppm. As the oxygen content in the weld metal is in a certain range of 70-300 ppm, the depth/width ratio increases to 1.5 to 2.0 times. Too low or too high oxygen content in the pool does not increase the depth/width ratio. The oxygen from the decomposition of the flux in the welding pool alters the surface tension gradients on the weld pool surface, and hence, changes the Marangoni convection direction and the weld pool penetration depth.
103 citations
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77 citations