Depth Of Molten Pool Research Articles

Vacuum Arc Remelting Process of High-Alloy Bearing Steel and Multi-Scale Control of Solidification Structure

Utilizing Pro-cast software, the whole vacuum arc remelting process of high-alloy bearing steel ingot (the diameter was 160 mm and the high was 600 mm) was simulated. And moving face quality and moving boundary conditions were added to the simulation. Purposes of the simulation were to explore the influence of smelting powers on the temperature field, pool shape and solidification microstructure in vacuum arc remelting process. The depth of molten bath gradually increased and stabilized finally and the pool shape transferred from flat to funnel. When smelting power increased, the depth of molten pool became deeper and the width of mushy zone slightly reduced; the size of primary dendrite and secondary dendrite spacing increased significantly; the percentage and size of columnar crystals also increased. A reasonable power-time cure was given to guide industrial melting after simulation, the size of molten pool morphology and microstructure were controlled in an ideal range under the reasonable cure. The simulated grain morphology agreed well with the experimental pickling result.

Effects of welding parameters on weld geometry during high-power laser welding of thick plate

During high-power deep-penetration laser welding of thick plate, the geometrical characteristics of weld cross section were investigated under different welding conditions. The molten metal behaviors were observed by using the high-speed camera and X-ray imaging system to study the formation mechanism of weld cross section. With the increase of welding speed, the width and depth of weld seam decreased, and the geometry of weld cross section changed from big-head shape to needle-like shape. The change of focal position of laser beam led to the variation of molten metal behavior which thus resulted in different geometries of weld cross sections during laser welding. The accumulation of high-temperature molten metal at both the top surface of molten pool and the middle depth of molten pool could lead to a higher heat-transferring efficiency of the molten metal which could lead to a wider weld width. The stable molten metal behavior on the molten pool surface resulted in a low heat-transferring efficiency, and the sound appearance of weld seam could be obtained when the focal position was inside the metal.

Molten Depth Modeling of Laser Transmission Welding Based on Temperature Distribution of Moving Point Heat Source

Laser transmission welding (LTW) is a new and efficient technology. During LTW of polymers, the size and morphology of the weld have great influence on the welding quality. In order to better evaluate the welding quality and optimize process parameters, many researches on the morphology and mathematical analytical model of the molten pool have been conducted. This study attempts to build an analytical model for calculating the depth of the molten pool (molten depth), based on the temperature field distribution theory of the moving point heat source acting on the semi-infinite body. The influence of the welding power and welding speed on the molten depth is studied emphatically. The mathematical analytical model is solved through MATLAB mathematical software. Subsequently, the test experiment about LTW of PA66 is conducted to validate the model. During the test experiment, the upper layer contains 30 wt. % glass fibers (GF) and the bottom layer contains 30 wt. % carbon fiber (CF). The result shows that the mathematical analytical model can well predict the trend of the molten depth. However, the error exists indeed. The detailed analysis about the error is also made in this article.

Parametric analysis of thermal behavior during selective laser melting additive manufacturing of aluminum alloy powder

Simulation of temperature fields during selective laser melting (SLM) additive manufacturing of AlSi10Mg powder was performed using the finite element method (FEM). The effects of laser power and scan speed on the SLM thermal behavior were investigated. It showed that the cooling rate of the molten pool elevated slightly from 2.13×106°C/s to 2.97×106°C/s as the laser power increased from 150W to 300W, but it enhanced significantly from 1.25×106°C/s to 6.17×106°C/s as the scan speed increased from 100mm/s to 400mm/s. The combination of a low laser power (200W) and a high scan speed (400mm/s) yielded a low temperature (1059°C) and an extremely short liquid lifetime (0.19ms), resulting in the poor wettability and occurrence of micropores in SLM-produced parts. The temperature gradient along the depth direction of the molten pool increased considerably from 10.6°C/μm to 21.7°C/μm as the laser power elevated from 150W to 300W, while it decreased slightly from 14.9°C/μm to 13.5°C/μm as the scan speed increased from 100mm/s to 400mm/s. The proper molten pool width (111.4μm) and depth (67.5μm) were obtained for a successful SLM process using the laser power of 250W and scan speed of 200mm/s. SLM of AlSi10Mg powder was also experimentally performed using different laser processing conditions and the microstructures of the SLM-fabricated samples were investigated to verify the reliability of the physical model. A sound metallurgical bonding between the neighboring fully dense layers was achieved at laser power of 250W and scan speed of 200mm/s, due to the larger molten pool depth (67.5μm) as relative to the layer thickness (50μm).

Growth Characteristics of TiCxNy Ceramics under Laser Melting Conditions

By laser melting technique, TiCxNy ceramics are prepared under the laser powers of 300, 400, 500, 600, and 700 W, respectively. The size of molten pool decreases with the increase of scanning speed from 1 to 4 mm/s at a certain power. TiCxNy microstructure continuously changes from the top to bottom of molten pool. Based on the XRD spectrum, the composition of ceramic can be confirmed as Ti(O0.19C0.53N0.32), C0.7N0.3Ti, C2MoTi, and Ti8C5. Based on the analysis of the growth process, the growth conditions can be confirmed. The maximum depth of molten pool obtained at the laser energy density of 500 W/cm2. The more deviation from this value, the more shallow the pool. The corrosion experiment result shows that TiCxNy ceramic has good corrosion resistance to various corrosive agents except HNO3.

W042008 プラスチック/金属異材直接接合のプロセスとその接合体強度([W04100]機械材料・材料加工部門企画,締結・接合のプロセスと接合部・界面の信頼性評価)

Dissimilar materials laser direct joining between plastic and metal was studied in lap joint configuration. Laser was irradiated from transparent plastic material side. Joining state was strongly depending on material properties of metallic materials because heat energy was generated at the metallic surface. Depth of molten pool formed in metallic material side affected tensile shear strength of the joint. Oxide layer at metallic surface changed absorptivity of laser and might affect chemical bonding between plastic and metal. Bubbles were formed inside plastic nearby the interface. Strength of the joint decreased with increase in density of bubbles. In order to improve strength of the joint, it is necessary to optimize laser irradiation condition with taking several factors influenced into account.

Numerical Modeling of Heat Distribution in the Electron Beam Melting® of Ti-6Al-4V

Electron beam melting® (EBM) is one of the fastest growing additive manufacturing processes capable of building parts with complex geometries, made predominantly of Ti-alloys. Providing an understanding of the effects of process parameters on the heat distribution in a specimen built by EBM®, could be the preliminary step toward the microstructural and consequently mechanical properties control. Numerical modeling is a useful tool for the optimization of processing parameters, because it decreases the level of required experimentation and significantly saves on time and cost. So far, a few numerical models are developed to investigate the effects of EBM® process parameters on the heat distribution and molten pool geometry. All of the numerical models have ignored the material convection inside the molten pool that affects the real presentation of the temperature distribution and the geometry of molten pool. In this study, a moving electron beam heat source and temperature dependent properties of Ti-6Al-4V were used in order to provide a 3D thermal-fluid flow model of EBM®. The influence of process parameters including electron beam scanning speed, electron beam current, and the powder bed density were studied. Also, the effects of flow convection in temperature distribution and molten pool geometry were investigated by comparing a pure-thermal with the developed thermal-fluid flow model. According to the results, the negative temperature coefficient of surface tension in Ti-6Al-4V was responsible for the formation of an outward flow in the molten pool. Also, results showed that ignoring the material convection inside the molten pool resulted in the formation of a molten pool with narrower width and shorter length, while it had a deeper penetration and higher maximum temperature in the molten pool. Increasing the powder bed density was accompanied with an increase in the thermal conductivity of the powder bed that resulted in a reduction in the molten pool width on the powder bed top surface. Experimental measurements of molten pool width and depth are performed to validate the numerical model.

Effect of Molten Pool Shape on Tensile Shear Strength of Dissimilar Materials Laser Spot Joint between Plastic and Metal

Dissimilar materials laser spot joining between polyethylene terephthalate (PET) and aluminum alloy (A5052) was studied by using pulse YAG laser. The results showed that it was possible to make a joint in a wide range of heat input. Molten pool was formed at the interface of A5052 and depth of molten pool increased with increase in heat input. Tensile shear test was carried out to evaluate strength of the joints. The result showed that tensile shear strength increased with increase in the heat input when the molten pool filled with molten or softened PET. On the other hand, instability of joining state inside the molten pool might induce variation in the strength. FEM analysis was carried out to investigate effect of molten pool shape on the strength. The result showed that molten pool radius did not significantly affect tensile shear strength. In contrast, the joint strength increased with increase in the molten pool depth as observed in result of the experiment. It is proposed that taking into account the mechanical effect such as molten pool shape is an important approach to improve the joining strength under tensile shear loading.

Effect of remelting current on molten pool profile of titanium alloy ingot during vacuum arc remelting process

The performance of vacuum arc remelting (VAR) ingot depends largely on ingot structure and chemical uniformity, which are strongly influenced by molten pool profile that is influenced by VAR process. To better understand the effect of remelting current on molten pool profile of titanium alloy ingot during VAR process, a 3D finite element model is developed by the ANSYS software. The results show that there are three remelting stages during VAR process when the remelting current is 2.0 kA. The molten pool depth increases gradually from 30 to 320 s, then the change of molten pool depth is very small during the steady state stage from 320 to 386 s, and lastly the molten pool depth becomes shallow after 386 s. The melting rate and temperature of superheat increase with the remelting current increasing, which leads to the augment of molten pool volume. In the end, the total remelting time and steady state molten pool time decrease with the melting current from 1.6 to 2.8 kA.

Finite Element Analysis of Molten Pool Depth and Dilution Rate in Laser Clad TiC/NiCrBSiC Coatings on Ti6Al4V

A three-dimensional model was proposed to simulate high power laser clad TiC/NiCrBSiC composite coatings on Ti6Al4V alloys. Molten pool depth and dilution rate were obtained and compared with the experimental results. The calculated molten pool depth in the sample is about 0.76 mm and dilution rate is 21 %. The experimental data molten pool depth and dilution rate were 0.81 mm and 26%, respectively. There is a good agreement between the numerical and experimental results. A good quality laser clad TiC/NiCrBSiC coating with low dilution rate and excellent metallurgical bond can be prepared under the optimal parameters.

Mathematical modeling of dynamics of fast phase transitions and overheated metastable states during nano- and femtosecond laser treatment of metal targets

For a mathematical description of pulsed laser heating, melting, and evaporation of an aluminium target in an ambient atmosphere, a one dimensional, multifront hydrodynamic Stephan problem was used, written for both phases (liquid and solid). On the boundary of solid and gaseous forms, the Stephan problem is combined with radiation gas-dynamic equations, with thermal conductivity, and describes processes in the evaporated material and surrounding gas. For the numerical solution, finite difference method of dynamic adaptation, which gives an opportunity of explicitly tracking interphase boundaries and shock waves, was applied. As a result, in the process of the solution, the problem had 6 computational regions and 7 boundaries, 6 of them were moving, including 2 shock waves and one free boundary in the atmosphere. We used this model to calculate the pulsed laser interaction with an aluminium target with the following parameters: λ = 0.8 μm, τ = 10−8–10−15 s, and G0 = 10−9–10−16 W/cm2. Modeling revealed that in the case of long ∼1 ns pulses, most of the energy is spent on melting and heating the liquid. The depth of the molten pool depth constitutes about 1.2 μm. In the case of femtosecond pulses, most of the energy is spent on heating the solid body and the formation of shock waves in it. The depth of the molten pool does not exceed 0.03 μm. Even though the evaporated layers were of almost the same thickness. For nanosecond laser pulses with fluence J less than 30 J/cm2, there is no plasma formation in the evaporated material. For the same fluence of femtosecond laser pulses, plasma is formed after the pulses and is thermal by nature.

Comparison of nano- and femtosecond laser ablation of aluminum

For mathematical description of pulsed laser heating, melting and evaporation of aluminum target in ambient atmosphere was used one dimensional, multi front hydrodynamic Stephan problem, written for both phases (liquid and solid). On the boundary of solid and gaseous forms Stephan problem is combined with radiation gas dynamic equations, with thermo conductivity, and describes processes in evaporated material and surrounding gas. For numerical solution finite difference dynamic adaptation method, which gives opportunity of explicit tracking of inter phase boundaries and shockwaves. As a result, in the process of the solution the problem had 6 computation regions and 7 boundaries, 6 of them were moving, including 2 shockwaves and free boundary in atmosphere. We used this model to calculate pulsed laser interaction with aluminum target with following parameters: A = 0.8, τ = 10−8−10−15 s and G 0 = 109−1016 W/cm2. Modeling revealed that in case of long ∼1 ns pulses greater part of the energy is spend on melting and heating of the liquid. Molten pool depth is about 1.2 μm. In case of femtosecond pulses greater part of the energy is spent on heating of the solid and for the formation of shockwave in solid. The depth of the molten pool does not exceeds 0.03 μm. Although evaporated layers were almost the same thickness. For nanosecond laser pulses with fluence J less than 30 J/cm2, there is no plasma formation in the evaporated material. For the same fluence for femtosecond laser pulse plasma is formed after the pulse and has thermal nature.

Calculation of the molten pool depth in vacuum arc remelting of alloy Vt3-1

This paper is devoted to a simple heat model of vacuum arc remelting (VAR) including the solution of a nonlinear heat conduction equation with nonlinear boundary conditions typical for VAR. A finite-difference analog of the model’s initial equation is obtained by the finite-volume method. The system obtained is solved by a two-cyclic scheme of component-wise splitting. A simplified model neglecting the magnetohydrodynamic phenomena in the molten pool is tested by comparison of the results of numerical calculations of the pool depth in remelting of the Russian titanium alloy Vt3-1 (Ti-6.5Al-2.5Mo-1.5Cr-0.5Fe-0.3Si) with the results of radiographic experiments. It has been shown that the model fits the experimental data well under various remelting conditions (the ingot diameter and operating current intensity).

Numerical simulation of multiphase transient field during plasma deposition manufacturing

A transient solid/liquid/vapor unified mathematical model for plasma deposition manufacturing was developed to investigate the fluid flow and heat transfer of the molten pool and deposition layer. The level-set approach was adopted to deal with the liquid/vapor interface boundary conditions, which considered surface tension gradient (the major driving forces for the melt flow), interface curvatures, buoyancy, and convection heat loss. The mixture continuum model was applied to describe melting and solidification processes at the solid/liquid interface. Moreover, the effects of main processing parameters on the thickness of the deposition layer, full depth of the molten pool and penetration depth of the substrate have been studied further. The experiments agree well with the simulation results.

Melting and precision casting of Ti-6Al-4V alloy by use of electron beam furnace

For melting and casting of Ti-6Al-4V alloy by use of an electron beam furnace, key technologies have been developed: measurement and control of temperature, amount, and chemical composition of molten pool. Temperature in the molten pool was measurred by applying three devices; a thermocouple, a two color pyrometer and the rate of vaporization from the molten pool. Temperature measured by an optical pyrometer without influence of plasma by shifting the wave lengths of the light for the optical pyrometry from those of plasma evolved above the molten pool was in a good accordance with that estimated from the vaporization rate. By combining temperatures measured by three methods, the temperature gradient in the molten pool was estimated to be a level of 100 K/cm. In order to derive an empirical equation for the depth of molten pool of various metals, the depth of the molten pool was determined for Ti, Ti-6Al-4V alloy, solar grade Si, low carbon steel, and stainless steel by chemical etching of vertical cross section of an ingot melted and solidified in a skull crucible. Chemical compositions of Ti-6Al-4V alloy melt before casting was adjusted by adding an aluminum block into the pool before pouring, which compensated vaporization loss of Al from the pool surface under high vacuum. Since, a key to settle Al content in the specified range is the yield and distribution of Al in every castparts, influences of operating variables on the yield have been studied by paying attention to rapid temperature change observed immediately after addition of aluminum.

A‐TIG welding of UR 52N+ superduplex stainless steel

Summary The improved performance due to the use of flux in automatic welding of a superduplex stainless steel with the A‐TIG process is presented. The flux used during welding enables molten pool depth to be increased in a single pass, with complete penetration of a plate 5.6 mm thick and without edge preparation. Welding energy is located in the range of values recommended for this type of steel. The beads obtained were observed using optical micrography and were subjected to mechanical and corrosion tests, as well as ferrite content measurement testing. In addition, the influence of flux grain measurement and the nature of welding gas on flux effectiveness were studied. These tests reveal that the use of flux not only enables superduplex stainless steels 5.6 mm thick to be welded in a single pass but it also improves mechanical properties, corrosion characteristics and austenite content of welded joints, while maintaining an austenite volume fraction identical to that of the parent metal.

ＣＷ‐ＹＡＧレーザによる軟鋼の溶接特性

Penetration mechanisms of welding by continuous wave (CW) YAG laser beam for mild steel were discussed. Bead-on-plate tests were carried out varing laser beam power and welding speed, and the cross-sectional shapes of the welds were measured. The fundamental welding characteristics for mild steel by YAG laser beam were estimated in comparison with those by CO2 laser beam. The results obtaine are as follows. (1) The penetration mechanism of key-hole welding in a steady state by YAG laser beam agrees with the heat conduction theory for a wedge type volume heat source model, like that by CO2 laser beam. (2) YAG laser beam has lower threshold power to enter fusion of mild steel and its absorption efficiency is less dependent upon the cavity depth of molten pool than CO2 laser beam. Then, input power can be controlled to adjust the irradiating beam power, that is necessary to slow down penetration depth at the end of weld.

Melting and Flow Behavior of Fe–O Melts Heated by Plasma Arc

In order to clarify the mechanism of change in molten pool geometry by plasma arc heating, the effects of oxygen contents of Fe-O melts on the geometry and flow behavior of molten pool were investigated. Also, the temperature coefficients of surface tension of Fe-O melts were examined in a temperature range from 1823 to 2023 K. The depth of molten pool increased and the width of it decreased with increasing oxygen contents. Outward flow was observed at the surface of molten pool in the case of a low oxygen level and inward flow was observed in the case of a high oxygen level