Metal Flow Velocity Research Articles

Variation of Surface Tension of Liquid Metal with Fluorides in Tungsten Inert Gas Welding

Real-time measuring and obtaining surface tension of liquid metal during the arc welding process is critical for studying the behavior of the weld pool, such as Marangoni flow and flow velocity. The dynamic variation of surface tension of weld pool during tungsten inert gas welding process with and without fluoride flux was measured by weld pool oscillation sensing system, and the effect of fluoride flux on surface tension and pool behavior was analyzed. The results show that the surface tension gradient of liquid metal can convert from a negative to a positive value in a critical arc time. The flow velocity of liquid metal and critical arc time significantly increased and decreased, respectively, with fluoride flux. The variation of surface tension, flow velocity, and critical arc time with fluoride flux was induced by arc temperature increasing.

Microstructure forming mechanism of inconel 625 alloy fabricated by laser/ultra-high (UHF) induction hybrid deposition method

To reveal the microstructure forming mechanism of laser/ultra-high frequency (UHF) induction deposition, this paper developed a microscopic phase-field (PF) model to numerically investigate dendrite growth during solidification. The macroscopic model of molten pool evolution is adopted to provide the solidification conditions for the microscopic PF model. The dendrite growth during laser deposition is simulated to evaluate the effect of UHF induction heat on the dendrite growth. Results show that because of the high temperature gradient and cooling rate, the PDAS of laser-UHF induction hybrid deposited layer is less than that of the laser deposited layer. The UHF induction heat also leads to a high flow velocity of the molten metal during laser-UHF induction hybrid deposition. The high flow velocity contributes to the decrease in PDAS by inhibiting the interdendritic enrichment of solute. During laser-UHF induction hybrid deposition, a higher solute gradient is present in the tip region of dendrite arm, leading to a faster dendrite growth rate. The UHF induction heat also increases the solute distribution coefficient during deposition, which further inhibits the element segregation. Under the action of UHF induction heat, a low interdendritic solute gradient and an evenly distributed solute can be obtained, thus helping increase interdendritic undercooling degrees and decreasing the PDAS. The simulated PDAS and solute distribution have good consistency with the experimental results. The spectral analysis of EDS line detection indicates that the laser-UHF induction hybrid deposited layer has a more refined microstructure and weaker element segregation than the laser deposited layer does.

Numerical simulation study on the cold thread rolling forming of Ti-6Al-4V alloy fasteners with external threads and their defects.

Abstract A three-dimensional numerical finite element model for cold rolling forming of external threads on Ti-6Al-4V alloy fasteners for aerospace applications was established using DEFORM-3D. This model was employed to investigate the characteristics of the cold rolling forming process and analyze the defects associated with the rolling operation. The stability of the ratio between torque and tangential load at the radius value of the rolling wheel (72.5) validates the accuracy of the model. The research results indicate that due to the unevenness of the extrusion force, the metal flow velocity is higher adjacent to the tooth-shaped surface compared to the central position. This causes the metal on both sides to accumulate and squeeze towards the middle position at the tooth top, ultimately resulting in tooth top folding defects.

Finite Element Simulation of Multi-Pass Rolling of a Pure Aluminum Target under Different Rolling Routes and Methods

By coordinating the rolling direction and mode, a multi-rolling plastic deformation process for an aluminum (Al) sputter target is proposed to achieve multiple excellent properties, including a uniform and fine grain structure and low defect risk, which are significant in producing high-quality sputtered films. In this work, therefore, DEFORM 3D 10.2 software is adopted to establish three strategies, clock-synchronous rolling, cross-synchronous rolling, and clock–snake rolling. The effect of different rolling routes and modes on the metal flow velocity (MFV), effective strain distribution (ESD), grain size distribution (GSD), damage, and rolling force (RF) are comparatively investigated. The simulation results show that clock–snake rolling can increase the MFV and effective strain by producing a deeper deformation than the others. It provides sufficient energy for dynamic recrystallization to promote grain refinement. In combination with the microstructure homogeneity promoted by the clock rolling route, the GSD from 6.5 to 44.3 μm accounts for about 80.5% of all the grains because of the fact that a randomly oriented grain region is full of high-angle grain boundaries. Compared with the synchronous rolling mode, the decrement in RF maximum reaches up to 51% during the asynchronous rolling process because component energy is consumed to form cross-sheering stress. It remarkably reduces the risk of defects, with a damage value of less than 73%, and simultaneously improves energy efficiency owing to smaller and uniform grains caused by less RF. The results obtained in this work are of great significance as they can guide practical production in the metal target industry.

Modeling for plastic instability in multi-directional rotary forging of thin-walled components with three ribs

Multi-directional rotary forging has the great potential to form thin-walled components with three ribs because of its incremental deformation characteristic and smaller forging load. However, for the components with thin-walled sterna and thick ribs, the plastic instability is easier to occur at the bottom of thick ribs in multi-directional rotary forging, resulting in the waste of components. Therefore, the aim of this paper is to establish the model for predicting plastic instability in multi-directional rotary forging of thin-walled components with three ribs. Firstly, the models for calculating actual and critical radial stresses on both sides of rib are established by analyzing complicated stress states caused by time-varying thinning deformation of sterna and thickening deformation of rib. It is found that the critical radial stress is mainly determined by ratio of deformation energy and external force work, while the actual radial stress is mainly determined by dissipated power and metal flow velocity. By combining actual and critical radial stresses, a unified model for simultaneously predicting plastic instability of ribs at different positions is proposed. Then, the influence laws of different technical parameters on critical conditions of plastic instability are revealed. It is found that the plastic instability is mainly determined by initial thickness of workpiece and width of rib, i.e., the critical deformation amount increases with increasing initial thickness of workpiece or decreasing width of rib, and vice versa. Finally, the experiments are conducted to verify that the proposed model for predicting plastic instability in multi-directional rotary forging of thin-walled components with three ribs is reliable. This paper provides a guideline to establish the model for predicting plastic instability under complicated stress states and metal flow modes.

Analysis of molten metal fluid flow mechanisms in variable polarity plasma arc welding of aluminum alloys

The stability and quality of welding in variable polarity plasma arc welding are determined by the directional fluid flow within the molten pool. In this study, the particle tracking method was employed to obtain flow traces and velocity of the molten metal on the walls of the keyhole using a high-speed camera system. Additionally, a confocal laser scanning microscope was utilized to capture the 3D morphology of the keyhole, while the flow channels were obtained through sectioning. By correlating the flow traces and velocity with the 3D keyhole morphology, the experimental results revealed the presence of saddle points on both the front and rear walls of the keyhole. The front saddle point represents the region where the flow velocity in the depth direction is minimum, causing the keyhole front side to converge upward and downward. The depth and volume of fluid flow to the keyhole sidewall are determined by this front saddle point. On the other hand, the rear saddle point is located at the center of the molten pool, marking the entry and exit sides of the keyhole rear wall where the melting metal eventually reaches. The location of the post-settlement point will affect the weld state. During the welding process, the double saddle points of the molten pool remain dynamically stable, and their position is influenced by shear force, gravity, arc pressure, keyhole morphology, and flow channels. These findings contribute to controlling the process characteristics necessary for stable welding of the keyhole in the molten pool.

Deformation Behaviors of 2219 Aluminium Alloy in Hot Multi-direcrional Forging Process

The hot multi-direcrional forging (MDF) process of 2219 aluminium alloy was simulated and the MDF test was carried out. The deformation behaviors of 2219 aluminium alloy were investigated in this paper, and the metal flow rule, temperature field variation and the strain variation were focused on. The results show that in the forging process, the metal flow velocity decreases gradually from top to bottom of the forgings. Meanwhile, on a horizontal section, the closer to four vertical edges, the smaller velocity of metal flow was obtained. After the forging process, the highest temperature appeared in the central area inside the forgings, followed by the four long edges, and the lowest temperature area is the eight sharp corners. The strain in each part of the forgings increased gradually with the increase of forging times. The maximum cumulative strain (12.5) and minimum cumulative strain (4.9) appeared in the central area inside the forgings and in the center area of the forging surface, respectively. In addition, in the whole MDF process, the highest temperature of 2219 aluminum alloy forging was 470 ℃, which is lower than their over burnt temperature.

Numerical simulation of arc-droplet-weld pool behaviors during the external magnetic field-assisted MIG welding-brazing of aluminum to steel

The alternative longitudinal external magnetic field (LEMF) was verified to be effective to enhance the spreading and wetting capacity of the molten aluminum metal in metal inert gas (MIG) welding-brazing of aluminum to steel. This study proposed a three-dimensional arc plasma-molten aluminum-solid steel coupled model of LEMF-assisted MIG welding-brazing of aluminum to steel. The effect of LEMF on the arc plasma, metal transfer, weld pool behavior and temperature evolution at the brazing interface was analyzed. It was found that the alternative LEMF caused the periodical swinging of the arc plasma along the weld width direction and increased the velocity of the arc plasma under the undetached filler metal. The droplet velocity was decreased due to the deflection of the arc plasma force and the additional electromagnetic force. The periodical inclination of the droplet and arc plasma increased the lateral flow velocity of the molten aluminum metal so the spreading ability of the liquid aluminum on the surface of steel was improved. The heating area at the brazing interface between the molten aluminum and solid steel was expanded to improve the wetting of the molten metal. Besides, the peak temperature at the brazing interface decreased, which may suppress the growth of the intermetallic compound.

Suppression of humping bead defects in high-speed triple-wire gas indirect arc welding through compensation gas

Triple-wire gas indirect arc welding (TW-GIA) has significant advantages of high deposition rate and low heat input. However, the humping bead defects in high-speed TW-GIA welding limits the improvement of welding speed. In this article, the feasibility of compensation gas to suppress the humping bead in TW-GIA was explored, and the influence on molten pool flow and arc stability was revealed. The results show that the compensation gas with jet angle of 90 °has the ability to suppress the humping bead and reduces the oxygen content of the weld. When the compensation gas flow rate is less than 30 L/min, the decrease of arc pressure leads to the decrease of reverse flow velocity of liquid metal. And the vertical downward impact force caused by compensation gas can directly inhibit the uplift of the liquid metal, which is beneficial to suppress the humping bead. In addition, the compensation gas carry in high ionization energy gas, which reduces the welding current and increases the range of conductive channel. The low gas flow rate with the jet angle of 90° has little effect on the arc stability, but the flow rate exceeding 30 L/min significantly increases the degree of arc disorder.

Thermal process and flow behavior during laser/ultra-high frequency (UHF) induction hybrid deposition

In this study, ultra-high frequency (UHF) induction heat was combined with laser deposition, which is referred to as laser–UHF induction hybrid deposition. On the one hand, this method takes the conventional laser induction hybrid deposition as reference, which uses the heat effect of UHF induction heat to optimize the residual stress of the deposited layer. On the other, this method utilizes the strong Lorentz force generated by the UHF induction heat to accelerate the flow velocity of the molten metal, which will be beneficial for microstructure refinement. Given that the thermal process and flow behavior during deposition are critical factors for the microstructure, a numerical model coupled with temperature field, electromagnetic field, flow field, and mass transfer field was developed to investigate the thermal process and flow behavior during laser–UHF induction hybrid deposition. Results showed that the UHF induction heat in laser-UHF induction hybrid deposition has pre-heating and slow-cooling effects on the deposited layer compared with laser deposition. The Lorentz force generated by UHF induction heat enhanced the flow velocity and the heat convection in molten pool. Research on the UHF induction heat parameters indicates that increasing the current frequency or current density can strengthen the slow-cooling effect of the UHF induction heat, and the flow velocity of the molten metal can be increased by 12.1% and 24.6%. Moreover, the maximum temperature in the molten pool decreased with increasing current frequency or current density because of the enhanced heat convection. Laser–UHF induction hybrid deposition experiment was also conducted, and the detected elemental content of the deposited layer and temperature showed good consistency with the simulated results. The grain size in the microstructure of the experimental laser–UHF induction hybrid deposited layer can be refined to approximately 3.358 μm at high current density conditions because of the enhanced fluid flow and heat convection in molten pool. This work provides an effective tool for predicting the thermal process and flow behavior during laser–UHF induction hybrid deposition, which will be an essential reference for evaluating microstructure quality.

The Modification of the Runner and Ingate Geometry to eliminate Misrun Defects on the Piston using Gravity Die Casting

Piston is an essential component of an engine because it plays a crucial role in the combustion process that drives the motorcycle. Gravity dies casting has become an ideal method for producing pistons owing to its high-quality product, cost-effective with excellent dimensional accuracy, good surface finish, and performance characteristics. However, misrun defect may occur during metal filling and solidification. This study aims to find the suitable dimensions for motorcycle piston products without the presence of misrun using MAGMASoft. The geometry modification introduced in this research are an ingate area of 176, 264, and 352 mm2 as well as the angle of runner of 60, 160, and 180o. Modifying the ingate area to 264 mm2 and the angle of the runner to 160o eliminated the misrun defect in the piston product. This phenomenon results from the laminar flow, higher temperature, and quicker flow velocity of the molten metal as it fills the window (the thinnest part of the piston).

Radially loading rotary extrusion for manufacturing large-size conical cylinders with inner transverse high ribs

The Large-size Conical Cylinders with Inner Transverse High Ribs (LCCWITHR) can reduce the weight of the parts while maintaining high rigidity and strength. Radially Loading Rotary Extrusion (RLRE) forming technology can achieve integral forming of LCCWITHR through the synergy of radial and rotary movements of dies. The flow law of the material during the forming process is the key to forming large-size inner ribs. At present, there is no unified understanding of the metal flow law of RLRE forming technology. An analytical expression was derived to predict the Radial Direction (RD) deformation loads. The FE simulation and process experiment were carried out to investigate the effects of the inclination angle, thickness factor and transition arc radius of the split top dies on the spacing of the metal diversion plane, the metal flow velocity of the rib area and the final radius of the inner rib. The influence of the split top dies loading distance and the bottom die rotation angle of each pass on the inner radius of the inner rib was verified. And the optimal combination of dies shape parameters and loading paths which can make the metal flow orderly was obtained: the inclination angle is 140°, the thickness factor is 3.64, the transition arc radius is 16 mm; the top dies loading distance is 15 mm, the bottom die rotation angle is 45°. The FE simulation results have been found to be in close agreement with physics experiment. The research results reveal the metal flow law of rib growth in the RLRE of LCCWITHR, which lays a theoretical foundation for subsequent thorough research and process optimization.

Effect of scanning speed on molten metal behaviour under angled irradiation with a continuous-wave laser

Laser processing is one of the most suitable technologies for fabricating controlled structures consisting of grooves or holes having a depth of several tens of micrometres on a metal surface. These structures are expected to improve the characteristics of the surface, such as its adhesiveness to metal and plastics. To control the surface structures, it is important to understand the dynamic behaviours during laser processing. Surface processing using an angled continuous-wave (CW) laser irradiation has been proposed for high-speed surface structuring. Distinct structures consisting of high upheavals on the incident side of the irradiated laser beam and wide grooves on the reflection side are formed on metal surfaces using this proposed method. The dynamic phenomena of molten metal during laser irradiation were investigated by examining the effect of scanning speed via experiments and thermal fluid analyses under the conditions of an average power of 200 W, an irradiation angle of 60°, and a scanning speed of 0.5–2.0 m/s. High-speed camera observations and fluid analysis revealed that the molten metal flow velocity from the reflection side to incident side significantly increased with an increase in scanning speed. Thus, the molten metal was dispersed on the reflection side and accumulated on the incident side. These asymmetric molten metal behaviours resulted in the formation of distinct surface structures. The detailed analyses of molten metal behaviours conducted in this study will help clarify the phenomena associated with high-speed laser surface structuring.

Die design and process optimization for aluminum flat tube profile with offset small channel

Aluminum tube with single row of small channels used in frequency conversion module of air-conditioner for heat radiation is manufactured by porthole extrusion, which has the characteristics of thin wall and large wall thickness difference. Due to the tiny dimension and offset distribution of channels, the design of process and die faces great challenges. In this study, a porthole extrusion die for aluminum flat tube with offset small channel was designed, and the offset porthole was used to balance the force on the both sides of the die core. The numerical simulation model of porthole extrusion process was established, and then, the structure of the extrusion die was optimized by taking the uniformity of metal flow velocity on the cross-section of the profile at the exit of the die. The effects of extrusion temperature, extrusion speed and die temperature on the displacement of the core, extrusion load, flow velocity and temperature of the metal at the exit of the die were studied. The optimal parameter combination of extrusion speed and temperature was obtained. The result showed that the dimensional accuracy of profile meets requirements. This study can provide guidance for the die design and process optimization of aluminum flat tube profile with offset small channel.

Effect of molten pool behaviors on welding defects in tandem NG-GMAW based on CFD simulation

The simulation of tandem narrow-gap GMAW based on computational fluid dynamics (CFD) was carried out to establish the relationship between the molten pool behaviors and weld bead formation under different wire feed rates (vf) and welding speed (vw). Inclined arcs were considered in the model by a novel rotated coordinate system. The variation of effective arc radius with welding current was also taken into consideration in the model. The experimental results illustrate that small vfor large vw easily leads to lack-of-fusion (LOF) defect. However, large vf also causes finger penetration. The simulation results indicate that a clockwise vortex in the right sidewall and an anticlockwise vertex in the left sidewall enhance the transverse transmission of fluid and heat, which is conducive to forming a concave weld bead. When vf is small or vw is large, due to low arc heat input, the groove sidewall cannot be melted and the transverse flow in the molten pool is weak. Furthermore, owing to the small flow velocity and large solidification rate of molten metal, the preferentially solidified metal further hinders the spreading of liquid metal to the sidewalls. As a result of high vf, the droplet that has high transition frequency and velocity transfers the arc heat and the high momentum to the molten pool bottom. The downward flow in the molten pool center is enhanced and its velocity is also increased, resulting in finger penetration.

Effect of Scanning Speed on Properties of Laser Surface Remelted 304 Stainless Steel

In order to study the microstructure and properties of stainless steel after laser surface remelting, based on the theory of laser surface remelting, a simulation model of nanosecond-pulsed laser surface remelted stainless steel was established to study the evolution law of the Marangoni force of the molten pool during laser surface remelting. A single-lane laser remelting experiment was performed to study the variation of the scanning speed on the remelting width, roughness, and layer microtopography. The “S” scanning path was used to remelt the stainless steel surface to investigate the bonding force between the remelted layer and the substrate, the hardness, microscopic morphology, and corrosion resistance. The results show that the viscosity of the liquid metal in the molten pool increases with the increase of the scanning speed. Larger liquid viscosity and smaller surface tension temperature gradients promote a weaker flow of liquid metal, which reduces the velocity of the liquid metal flow in the molten pool. With the increase of scanning speed, the remelting width gradually decreases, but the roughness gradually increases. When the element content of Cr increases, the element content of Fe and O decreases. The surface is covered with an oxide film, the main components of which are oxides of Cr and Fe, the remelted layer is greater than that of the substrate, and the corrosion resistance is improved. Laser surface remelting technology can improve the structure and properties of 304 stainless steel.

A Novel 2D Metal Flow Model for Hot Rolling of Aluminum Alloy Thick Plate

Considering the serious inhomogeneous distribution of plastic deformation in the rolling process of thick plate, a novel 2D metal flow model is proposed with a quadratic distribution of flow velocity in the thickness direction instead of an equal value used in traditional metal flow models. According to the energy method, this model is solved. Through comparing with the experimental data of rolling force, the accuracy of this model is validated. Then, it is found that with the increase in roll speed, the neutral point moves towards the exit of the deformation zone. However, compared with other models of metal flow in rolling process, the neutral point is distributed much closer to the entrance of the deformation zone. That is because with the quadratic distribution of flow velocity in thickness direction, flow velocity of metal at the surface increases faster than average flow velocity of metal, so that the neutral point appears earlier.

Experimental sensing of molten flow velocity, weld pool and keyhole geometries in ultrasonic-assisted plasma arc welding

• Comparative experiments were performed to investigate the ultrasonic effect in plasma arc welding. • The molten flow velocity on the weld pool surface was measured by tracer particle approach. • With ultrasonic vibration, the front wall and the back wall of the keyhole became steeper. • With ultrasonic vibration, the backward flow velocity of the molten metal decreased obviously. • Ultrasonic vibration causes small sizes of weld pool and keyhole but enhanced keyholing/penetrating capability. Comparative experiments were performed to investigate how the ultrasonic vibration exerted on the tungsten electrode affect the molten metal flow on weld pool surface and the sizes of weld pool and keyhole in plasma arc welding (PAW). The fluid flow velocity on the molten pool surface was measured by tracer particle approach. The images of front molten pool and keyhole entrance were captured synchronously from different directions with two CCD cameras. Special algorithms were developed to calibrate and integrate the weld pool and keyhole images into a single picture in one coordinate system. It was found that when ultrasonic vibration was applied, the keyhole shape was changed, the front wall and the back wall of the keyhole became steeper, and the backward flow velocity of the molten metal decreased obviously. The size of the molten pool and the keyhole entrance in ultrasonic-assisted PAW was smaller than that in PAW, and the keyholing/penetrating capability was enhanced.

Influencing mechanism of an external magnetic field on fluid flow, heat transfer and microstructure in aluminum resistance spot welding

ABSTRACT The magnetically assisted resistance spot welding (MA-RSW) method provides a promising approach for improving weld performance. However, the MA-RSW process involves complex multiphysics fields that make numerical modeling very challenging. Thus, most resistance spot welding (RSW) models adopt electrothermal-mechanical coupling and ignore the influence of fluid flows caused by electromagnetic forces on nugget growth. In this paper, a magnetohydrodynamic (MHD) model, which couples the electric, thermal, magnetic and flow fields, is developed to explore the influencing mechanism of an external magnetic field (EMF) on the flow patterns and microstructures of aluminum resistance spot welds. Numerical results show that the application of an EMF can lead to the formation of Lorentz force in the liquid nugget, which transforms the flow pattern from an in-plane flow to a combined in-plane and out-of-plane flow. The flow velocity of molten metal in the MA-RSW process is 5 times higher than that of the RSW process, and the maximum temperature of the MA-RSW model is reduced from 774°C in the MHD RSW model to 725°C. Therefore, the MA-RSW joint exhibits a 25.5% larger nugget diameter, a more than 20% finer grain structure, and fewer defects than the RSW joint in the experimental results.

STRESS STATE STUDY DURING ROLLING IN A BOX CALIBER WITH A CHILLED SURFACE

The article deals with the influence of the uneven distribution of the temperature field of the billet on the stress state of the strip when rolling in a box-shaped caliber for the production of pipe billets. Until recently, in the study of deformed and stressed state there were problems ones related to the accounting accuracy of the non-uniformity of deformation in the caliber itself, which when rolling in box-shaped calibers is significant due to the fact that the studied deformation zone has signs of a high zone. In addition, the shape of the caliber imposes its own imprint on the flow of the metal. It leads to the fact that in reality the deformation zone is much more complicated than it is represented. Therefore, a complex variation of the velocity field is formed during rolling along the length of the deformation zone consequently; a complex stress field is formed. The situation is even more complicated when trying to account for the influence of temperature fields on the metal flow and stress state. The studies were carried out for the modes and deformation schemes existing in production line. The finite element method for approximation of metal flow velocity fields and the variation principle of continuum mechanics were used as a mathematical apparatus. The occurrence of the zone of tensile transverse stresses is shown in the part of the strip under the horizontal contact surface. The reason for the occurrence of this zone is that when the length is reduced of a part of the strip heavily crimp by sides of the caliber, it tends to widen. Naturally, metal particles tend to flow not towards the vertical axis of symmetry of the caliber, but in the opposite direction. In addition, the central part of the strip tends to broaden itself. This leads to compressive transverse stresses at the side parts and tensile stresses at the contact center part. It is shown that from the point of view of defect formation, the most severe stress state pattern arises in places corresponding to the horizontal part of the contact surface of the strip after the strip leaves the rolls and the zone of the lateral surface located slightly below the corners of the workpiece.