Role of Capillary and Thermocapillary Forces in Laser Polishing of Metals

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Chi Zhang ◽  
Jing Zhou ◽  
Hong Shen
Keyword(s):  
Capillary Force ◽  
Molten Pool ◽  
Continuous Wave ◽  
Flow Behavior ◽  
Marangoni Effect ◽  
Cost Effective ◽  
Underlying Mechanism ◽  
Thermocapillary Force ◽  
Laser Polishing ◽  
Coupled Heat Transfer

As one of emerging novel surface treatment techniques, laser polishing offers a cost-effective and efficient solution to reduce surface roughness of precision components at micro-/mesoscale. Although it has been applied for industrial and biomedical purposes, the underlying mechanism has not been fully revealed. This paper presents a study to understand the basic fundamentals of continuous wave fiber laser polishing of Ti6Al4V samples. A two-dimensional numerical model that coupled heat transfer and fluid flow is developed to illustrate the molten flow behavior. The roles of capillary and thermocapillary flow in the process of laser polishing are investigated to assist the understanding of the contributions of surface tension (capillary force) and Marangoni effect (thermocapillary force) in the polishing process. Capillary force dominates the molten pool at the initial stage of melting, while thermocapillary force becomes predominant when the molten pool fully develops.

Numerical Simulation of the Influence of Different Surface Morphologies on Molten Pool Flow under Moving Heat Source

2021 ◽  
Vol 904 ◽  
pp. 9-13
Author(s):  
Jie Yin ◽  
Zhen Yu Zhao ◽  
Hou Ming Zhou ◽  
Kai Li ◽  
Hao Zhou
Keyword(s):  
Heat Source ◽  
Surface Topography ◽  
Capillary Force ◽  
Molten Pool ◽  
Moving Heat Source ◽  
Element Analysis ◽  
Thermocapillary Force ◽  
Initial Shape ◽  
Transient Model ◽  
Laser Polishing

In order to study the influence of different initial topography on the molten pool flow under a moving heat source, the finite element analysis method was used to establish a two-dimensional transient model of laser polishing to simulate the evolution of the surface topography of the material during laser polishing. In the simulation process, a moving laser beam was used as the heat source, and the free surface of the actual material was profiled through a three-dimensional profiler. A very similar simulation model surface was constructed, coupled with the flow field and temperature field in the laser polishing process, and the capillary force was considered comprehensively. Combined with thermocapillary force. The results show that under the combined action of capillary force and thermocapillary force, the surface of the polished material has a peak-filling effect, which makes the surface of the material achieve a good polishing effect. The initial shape will affect the polishing effect, the greater the curvature, the faster the flow rate of the molten pool. In molten pools with large spatial curvatures, capillary forces dominate. Keywords: Laser polishing; molten pool; surface topography; numerical analysis; capillary force; thermocapillary force.

Investigation on the coupling interaction in electron beam welded Al–Cu bimetallic sheet

2020 ◽  
pp. 146442072097669
Author(s):  
FS Li ◽  
ZC Wei ◽  
XF Li ◽  
HD Kang ◽  
Z Li ◽  
...  
Keyword(s):  
Electron Beam ◽  
Intermetallic Compounds ◽  
Fusion Zone ◽  
Molten Pool ◽  
Electron Beam Welding ◽  
Flow Behavior ◽  
Marangoni Effect ◽  
Interface Zone ◽  
Fracture Characteristics ◽  
Bimetallic Sheet

Two sound joints of Al–Cu bimetallic sheet with 6.5 mm in thickness were obtained in Cu (upper)–Al (lower) and Al (upper)–Cu (lower) welding configurations via the electron beam welding and their distinct coupling models were developed to well understand their flow behavior of the molten pool and microstructure evolution mechanisms during the electron beam welding. For the electron beam welding of the Cu–Al bimetallic sheet, liquid Al and Cu flowed into each other and fully combined in the fusion zone and the interface zone under high-temperature environment, forming large amount of intermetallic compounds. For the electron beam welding of the Al–Cu bimetallic sheet, liquid Al was floating on the Cu substrate, while liquid Cu was flowing at the bottom of the molten pool and mutually combined with liquid Al at the interface, forming a relatively small amount of intermetallic compounds. Moreover, a part of liquid Al flowed back to the seam root under the influence of the Marangoni effect. Therefore, the fusion zone and the interface zone with various phase compositions were formed in these two Al–Cu bimetallic joints and the mechanical properties of the corresponding joints were determined. Furthermore, the average tensile strengths of Cu–Al and Al–Cu bimetallic joints were 59 MPa and 67 MPa, respectively. The fracture locations of these two joints were both at the edge of the fusion zone along the Al2Cu intermetallic compound interlayer. Moreover, the fracture characteristics of these joints were mainly cleavage fracture.

scholarly journals CO$$_{2}$$ Convection in Hydrocarbon Under Flowing Conditions

2021 ◽  
Author(s):  
Trine S. Mykkeltvedt ◽  
Sarah E. Gasda ◽  
Tor Harald Sandve
Keyword(s):  
Enhanced Oil Recovery ◽  
Oil Recovery ◽  
Flow Behavior ◽  
Cost Effective ◽  
Fine Grid ◽  
Cost Effective Method ◽  
Gravity Effects ◽  
Petroleum Resources ◽  
Nearby Point ◽  
Diffusive Processes

AbstractCarbon-neutral oil production is one way to improve the sustainability of petroleum resources. The emissions from produced hydrocarbons can be offset by injecting capture CO$$_{2}$$ 2 from a nearby point source into a saline aquifer for storage or a producing oil reservoir. The latter is referred to as enhanced oil recovery (EOR) and would enhance the economic viability of CO$$_{2}$$ 2 sequestration. The injected CO$$_{2}$$ 2 will interact with the oil and cause it to flow more freely within the reservoir. Consequently, the overall recovery of oil from the reservoir will increase. This enhanced oil recovery (EOR) technique is perceived as the most cost-effective method for disposing captured CO$$_{2}$$ 2 emissions and has been performed for many decades with the focus on oil recovery. The interaction between existing oil and injected CO$$_{2}$$ 2 needs to be fully understood to effectively manage CO$$_{2}$$ 2 migration and storage efficiency. When CO$$_{2}$$ 2 and oil mix in a fully miscible setting, the density can change non-linearly and cause density instabilities. These instabilities involve complex convective-diffusive processes, which are hard to model and simulate. The interactions occur at the sub-centimeter scale, and it is important to understand its implications for the field scale migration of CO$$_{2}$$ 2 and oil. In this work, we simulate gravity effects, namely gravity override and convective mixing, during miscible displacement of CO$$_{2}$$ 2 and oil. The flow behavior due to the competition between viscous and gravity effects is complex, and can only be accurately simulated with a very fine grid. We demonstrate that convection occurs rapidly, and has a strong effect on breakthrough of CO$$_{2}$$ 2 at the outlet. This work for the first time quantifies these effects for a simple system under realistic conditions.

scholarly journals Numerical Simulation of Effect of Different Initial Morphologies on Melt Hydrodynamics in Laser Polishing of Ti6Al4V

Micromachines ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 581
Author(s):  
Kai Li ◽  
Zhenyu Zhao ◽  
Houming Zhou ◽  
Hao Zhou ◽  
Jie Yin ◽  
...  
Keyword(s):  
Flow Behavior ◽  
Processing Parameters ◽  
Surface Finishing ◽  
Polished Surface ◽  
Laser Polishing ◽  
Starting Position ◽  
Double Spiral ◽  
The Difference ◽  
Thermocapillary Forces ◽  
Surface Morphologies

As a surface finishing technique for rapid remelting and re-solidification, laser polishing can effectively eliminate the asperities so as to approach the feature size. Nevertheless, the polished surface quality is significantly sensitive to the processing parameters, especially with respect to melt hydrodynamics. In this paper, a transient two-dimensional model was developed to demonstrate the molten flow behavior for different surface morphologies of the Ti6Al4V alloy. It is illustrated that the complex evolution of the melt hydrodynamics involving heat conduction, thermal convection, thermal radiation, melting and solidification during laser polishing. Results show that the uniformity of the distribution of surface peaks and valleys can improve the molten flow stability and obtain better smoothing effect. The high cooling rate of the molten pool resulting in a shortening of the molten lifetime, which prevents the peaks from being removed by capillary and thermocapillary forces. It is revealed that the mechanism of secondary roughness formation on polished surface. Moreover, the double spiral nest Marangoni convection extrudes the molten to the outsides. It results in the formation of expansion and depression, corresponding to nearby the starting position and at the edges of the polished surface. It is further found that the difference between the simulation and experimental depression depths is only about 2 μm. Correspondingly, the errors are approximately 8.3%, 14.3% and 13.3%, corresponding to Models 1, 2 and 3, respectively. The aforementioned results illustrated that the predicted surface profiles agree reasonably well with the experimentally measured surface height data.

scholarly journals In-Situ Laser Polishing Additive Manufactured AlSi10Mg: Effect of Laser Polishing Strategy on Surface Morphology, Roughness and Microhardness

Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 393
Author(s):  
Jiantao Zhou ◽  
Xu Han ◽  
Hui Li ◽  
Sheng Liu ◽  
Shengnan Shen ◽  
...  
Keyword(s):  
Surface Quality ◽  
Molten Pool ◽  
Surface Defects ◽  
Polished Surface ◽  
Transient Model ◽  
Surface Evolution ◽  
Powder Bed ◽  
Laser Polishing ◽  
Surface Morphologies

Laser polishing is a widely used technology to improve the surface quality of the products. However, the investigation on the physical mechanism is still lacking. In this paper, the established numerical transient model reveals the rough surface evolution mechanism during laser polishing. Mass transfer driven by Marangoni force, surface tension and gravity appears in the laser-induced molten pool so that the polished surface topography tends to be smoother. The AlSi10Mg samples fabricated by laser-based powder bed fusion were polished at different laser hatching spaces, passes and directions to gain insight into the variation of the surface morphologies, roughness and microhardness in this paper. The experimental results show that after laser polishing, the surface roughness of Ra and Sa of the upper surface can be reduced from 12.5 μm to 3.7 μm and from to 29.3 μm to 8.4 μm, respectively, due to sufficient wetting in the molten pool. The microhardness of the upper surface can be elevated from 112.3 HV to 176.9 HV under the combined influence of the grain refinement, elements distribution change and surface defects elimination. Better surface quality can be gained by decreasing the hatching space, increasing polishing pass or choosing apposite laser direction.

scholarly journals High-speed high-resolution laser diode-based photoacoustic microscopy for in vivo microvasculature imaging

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Xiufeng Li ◽  
Victor T C Tsang ◽  
Lei Kang ◽  
Yan Zhang ◽  
Terence T W Wong
Keyword(s):  
High Resolution ◽  
High Speed ◽  
High Performance ◽  
Continuous Wave ◽  
Signal To Noise Ratio ◽  
Cost Effective ◽  
High Signal ◽  
Photoacoustic Microscopy ◽  
Mouse Ear

AbstractLaser diodes (LDs) have been considered as cost-effective and compact excitation sources to overcome the requirement of costly and bulky pulsed laser sources that are commonly used in photoacoustic microscopy (PAM). However, the spatial resolution and/or imaging speed of previously reported LD-based PAM systems have not been optimized simultaneously. In this paper, we developed a high-speed and high-resolution LD-based PAM system using a continuous wave LD, operating at a pulsed mode, with a repetition rate of 30 kHz, as an excitation source. A hybrid scanning mechanism that synchronizes a one-dimensional galvanometer mirror and a two-dimensional motorized stage is applied to achieve a fast imaging capability without signal averaging due to the high signal-to-noise ratio. By optimizing the optical system, a high lateral resolution of 4.8 μm has been achieved. In vivo microvasculature imaging of a mouse ear has been demonstrated to show the high performance of our LD-based PAM system.

AC Electrodeposition of Uniform High Aspect-Ratio Metal Nanowires in Porous Aluminum Oxide Templates

2005 ◽  
Vol 879 ◽  
Author(s):  
Nathan J. Gerein ◽  
Shazma S. Mithani ◽  
Joel A. Haber
Keyword(s):  
Aluminum Oxide ◽  
Continuous Wave ◽  
Cost Effective ◽  
Fractional Factorial ◽  
Metal Nanowires ◽  
Porous Aluminum ◽  
Multiple Variables ◽  
Porous Aluminum Oxide ◽  
Iron Nanowires ◽  
The Impact

AbstractThe use of alternating current (ac) electrodeposition permits deposition through the resistive Al2O3 barrier layer, enabling the use of the as-grown porous aluminum oxide (PAO) template. This results in a process that is cost effective, simple, and scalable. However, achieving uniform filling using this technique is challenging. We have carried out a systematic study of the effect of multiple variables on the ac electrodeposition of copper nanowires using a fractional factorial design of experiment (FFDOE). This experiment led to the identification of template damage that occurs when continuous wave ac deposition conditions are employed, as well as to effective pulsed wave ac electrodeposition conditions. Subsequent examination of the effect of wave shape has identified the impact of this variable on electrodeposition, producing a further optimized set of ac electrodeposition conditions. The utility of these electrodeposition conditions has also been extended to the deposition of iron nanowires with similar results.

Laser polishing of additive manufactured tool steel components using pulsed or continuous-wave lasers

2019 ◽  
Vol 105 (1-4) ◽  
pp. 425-440 ◽  
Author(s):  
K. C. Yung ◽  
S. S. Zhang ◽  
L. Duan ◽  
H. S. Choy ◽  
Z. X. Cai
Keyword(s):  
Tool Steel ◽  
Continuous Wave ◽  
Laser Polishing

scholarly journals On the MHD Casson Axisymmetric Marangoni Forced Convective Flow of Nanofluids

Mathematics ◽  
2019 ◽  
Vol 7 (11) ◽  
pp. 1087 ◽  
Author(s):  
Anum Shafiq ◽  
Islam Zari ◽  
Ghulam Rasool ◽  
Iskander Tlili ◽  
Tahir Saeed Khan
Keyword(s):  
Differential Equations ◽  
Convective Flow ◽  
Flow Behavior ◽  
Marangoni Effect ◽  
Casson Fluid ◽  
Linear Ordinary Differential Equations ◽  
Metallic Particles ◽  
Flow Parameters ◽  
Forced Convective Flow ◽  
The Impact

The proposed investigation concerns the impact of inclined magnetohydrodynamics (MHD) in a Casson axisymmetric Marangoni forced convective flow of nanofluids. Axisymmetric Marangoni convective flow has been driven by concentration and temperature gradients due to an infinite disk. Brownian motion appears due to concentration of the nanosize metallic particles in a typical base fluid. Thermophoretic attribute and heat source are considered. The analysis of flow pattern is perceived in the presence of certain distinct fluid parameters. Using appropriate transformations, the system of Partial Differential Equations (PDEs) is reduced into non-linear Ordinary Differential Equations (ODEs). Numerical solution of this problem is achieved invoking Runge–Kutta fourth-order algorithm. To observe the effect of inclined MHD in axisymmetric Marangoni convective flow, some suitable boundary conditions are incorporated. To figure out the impact of heat/mass phenomena on flow behavior, different physical and flow parameters are addressed for velocity, concentration and temperature profiles with the aid of tables and graphs. The results indicate that Casson fluid parameter and angle of inclination of MHD are reducing factors for fluid movement; however, stronger Marangoni effect is sufficient to improve the velocity profile.

A Micropump Driven by Marangoni Effect

2007 ◽  
Author(s):  
Kenji Sugimoto ◽  
Kaoru Iwamoto ◽  
Hiroshi Kawamura
Keyword(s):  
Flow Structure ◽  
Marangoni Number ◽  
Marangoni Effect ◽  
Surface Forces ◽  
Present Calculation ◽  
Central Field ◽  
Liquid Region ◽  
Liquid Interfaces ◽  
Thermocapillary Force ◽  
Driven System

A micropump driven by the thermocapillary convection is proposed. The purpose of this study is to elucidate the flow structure in liquid region and the effect of the geometry on the performance of the present micropump. There are two significant advantages in the thermocapillary-driven system. First, the surface forces become more dominant than the volume forces with decreasing scale. The present micropump driven by the surface forces shows an advantage in the micro scale over a diaphragm pump driven by the volume forces. Secondary, the thermocapillary driven system contains no movable parts; thus, it allows a very simple structure compared to the diaphragm one. In the present micropump system, a number of ribs are distributed along the flow circuit between a heater and a cooler (see Fig. A-1). An appropriate amount of gas is trapped between the ribs; the gas-liquid interfaces formed between the ribs are the source of the pumping power. Since heat transfer from these ribs to the working liquid imposes temperature gradients along the gas-liquid interfaces, the flow from the hot to the cold side is induced by the Marangoni effect. Fundamental characteristics of the present micropump are studied on the basis of three-dimensional simulation conducted taking the gas, liquid and ribs into account. Since the surface tension is controlled by the temperature of the ribs, the equations for liquid and gas phases are formulated by coupling them with the heat conduction equation for the ribs. The intensity of the flow induced by the thermocapillary force can be described by using the Marangoni number. In this study, the flow structure corresponding to the temperature field was observed (see Fig. A-2). Since the high temperature fluid is convected downstream, the temperature of the central liquid region exceeds the temperature of the ribs at the same streamwise position. Therefore, the flow from the central field to the ribs is induced by the Marangoni effect on the gas-liquid interfaces. The present calculation has revealed that the flow field exhibits a transition from steady flow to oscillatory flow when the Marangoni number exceeds a critical value of about 2,000 – 2,500. An experiment was also performed. The liquid flow driven by the present micropump system was confirmed through the experiment.

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