Pool Length Research Articles

Optimization of Weld Parameters in Wire and Arc-Based Directed Energy Deposition of High Strength Low Alloy Steels

This paper aims to investigate the fabrication of high strength low alloy (HSLA) steels by wire and arc-based directed energy deposition (WADED). Firstly, the relationship between the process variables (including the travel speed-V, the current-C, and the voltage-U) and the geometrical characteristics of weld beads (including the bead height (BH), bead width (BW), and melting pool length (MPL)) was investigated. Secondly, the optimal process variables were identified using the desirability approach. The results indicate that voltage-U has the highest impact on BW and MPL, meanwhile the travel speed-V is the most impacting factor on BH. The optimal variables for the WADED process of HSAL steels are V = 0.3 m/min, C = 160 A, and U = 19 V. The component fabricated with the optimal variables is fully dense without spatters and defects, confirming the efficiency of the WADED process for HSLA steels.

Neural Network-Based Prediction of Potential Ribonucleic Acid Aptamers to Target Protein

Aptamers are short strands of nucleic acid with a single strand that may unite to target a certain molecule in a selective and specific manner. SELEX experiments are the typical method used for identifying aptamers in vitro (systematic evolution of ligands by exponential enrichment). Several different computational methods have been developed to locate aptamers. The purpose of this research is to identify and make predictions on the possible RNA aptamers that may be used to target the protein. To do this, we propose the use of a multi-layer perceptron neural network with sixteen layers that are trained to locate possible aptamers of a protein target. This network is trained by extracting the main properties of RNA sequences. The outcome of our proposed model is compared to the output of two well-known machine learning classifiers, namely random forest (RF) and support vector machine (SVM). Additionally, we undertake the independent testing of our model on the benchmark dataset, which allows us to reach the highest accuracy possible. As a consequence of this, our model obtains an accuracy of 98.44% and an MCC of 0.9123 during the 15-fold cross-validation, and it achieves an accuracy of 98.10% and an MCC of 0.9354 when the leave-one-out cross-validation is performed. We are certain that our approach will contribute to a reduction in the amount of money and time spent on in vitro testing. Therefore, restricting the length of the initial pool of potential nucleic acid pattern combinations.

Comparative analysis between the laser beam welding and low current pulsed GMA assisted high-power laser welding by numerical simulation

By introducing the low current pulsed gas metal arc (GMA), the bridging ability of the laser beam welding (LBW) can be effectively improved. However, the impact mechanism of the additive GMA is hard to investigate by experimental methods. In this paper, the three-dimensional transient mass and heat transfer models of the low current pulsed GMA assisted high-power laser welding and single LBW are established. The pulsed arc and laser heat source models are optimized based on the arc morphology images, arc voltage and welding current. The drop transfer and arc pressure models are improved by comprehensively considering the effect of the molten pool surface deformation and the interaction of laser and arc on the arc heat flow distribution. Based on the established welding models, a comparative analysis is conducted to investigate the evolution characteristics of the temperature and flow fields in the molten pool. The simulated results show that the additive low current pulsed GMA in novel hybrid welding significantly increases the high temperature region of the molten pool, while allowing the liquid metal to expand transversely, thereby increasing the length and width of the molten pool. These greatly improve the bridging ability of LBW and extend its application range.

Sensitivity of Melt Pool Size and Porosity Appearing to Base Plate Preheating in Laser Powder Bed Fusion Process

The base plate temperature ranks among the crucial building parameters whose effect on melt pool dimensions and porosity defects generation has not been sufficiently discussed in literature. In the current study, with the aim to explore the dependence between melt pool dimensions, porosity defects and base plate preheating, a 3-dimensional thermal finite element model is carried out to create IN718 single beads, at various base plate temperatures. The dimensions of the melt pool behave favourably with the base plate preheating. Indeed, the melt pool depth, width and length increase continuously with the heat of the base plate, from 20 °C to 500 °C. The melt pool width is more responsive to the base plate temperature than the melt pool depth. Numerical results also indicate that the melt dimensions become more responsive to the temperature of the base plate at a slower scan speed. The degree of porosity is predicted under multiple values of base plate temperature and the results show that porosity tends to disappear with further preheating of the base plate. A satisfying accordance between the numerical finding and the experimental results from literature is identified.

Analytical Prediction of Molten Pool Dimensions in Powder Bed Fusion Considering Process Conditions-Dependent Laser Absorptivity

This research proposes an analytical method for the prediction of molten pool size in laser-based powder bed fusion (LPBF) additive manufacturing with the consideration of process conditions-dependent absorptivity. Under different process conditions, the melting modes in LPBF are different, which induces the difference in laser absorptivity. An empirical model of absorptivity was used to calculate the laser absorptivity under various process conditions. An analytical point-moving heat source model was employed to calculate the temperature distribution of the build-in LPBF, with absorptivity, material properties, and process conditions as inputs. The molten pool width, length, and depth were determined by comparing the predicted temperature profile with the melting temperature of the material. To validate the proposed method, the predicted molten pool width, and depth of Ti6Al4V were compared with the reported experimental measurements under various process conditions. The predicted molten pool widths were very close to the measured results, and the predictions of molten pool depth were also acceptable. The computational time of the presented model is less than 200s, which shows better computational efficiency than most methods based on numerical iterations, such as the finite element method (FEM). The sensitivity of molten pool width and depth to normalized enthalpy w also discussed. The presented analytical method can be a potential tool for the research of molten pool size and related defects in LPBF.

Thermal monitoring for directed energy deposition of stainless steel, bronze, and cobalt-based alloy

Laser cladding and Directed Energy Deposition are two related processes that allow the deposition of specific surface coatings and the production of additively manufactured parts. In both processes, the selection of optimised parameters results in the deposition of high-density material with low dilution. However, the thermal and geometrical conditions constantly change during the process and the parameters need to be continually adapted in order to avoid defects or poor properties. In this context, the development of closed-loop monitoring systems is crucial in order to widen the field of possible applications towards more complexity, with a more stable process and higher materials properties. In this research, the possibility of thermal monitoring with middle-wave and long-wave infra-red cameras is investigated for Directed Energy Deposition of 316L, Stellite 21 and CuSn10. The melt pool length and the cooling rate are extracted from thermal imaging while the laser power was varied, and these results are compared to the materials properties of the deposited tracks. The main results show that an increase of melt pool length results in a decrease of porosity and an increase of dilution, which induces a change of hardness. The melt pool length can be regulated by adjusting the laser power in order to keep both the porosity and the dilution within acceptable values.

Investigating the laser metal deposition of Inconel 718 superalloy using the numerical and experimental methods

In this research, a volume of fluid (VOF) model was developed to investigate the effect of laser deposition parameters on the geometry of molten pool and deposited layer in the Inconel 718 superalloy. For this purpose, the process parameters of laser power, laser beam diameter and scanning speed were considered to estimate the geometric characteristics of the molten pool and deposited layer. In the following, the laser deposition process of Inconel 718 superalloy was carried out experimentally to validate the results of simulation. It was observed that an increase in the laser power from 100 to 400 W resulted in an improvement in the length, width and depth of molten pool, while an increase in the values of laser beam diameter (from 1 to 2 mm) and scanning speed (from 2 to 10 mm s−1) was associated with a reduction in the length, width and depth of molten pool. From the results of both simulation and experiments, a reduction was observed in the wetting angle of deposited layer when the values of laser power and scanning speed increased up to 400 W and 10 mm s−1 respectively, while the increase of feeding rate from 48 to 62 mgr s−1 indicated an improvement in the wetting angle. It was also observed that the maximum penetration depth was obtained in the rear part of molten pool due to Marangoni convection currents that pushed the melt toward the end of molten pool. The comparison of the experimental results and those predicted by the VOF model indicated that the model is capable of predicting the shape of deposition layer with sensible error.

Aquatic Systems of the Wichita State University Biological Field Station: Youngmeyer Ranch, Elk County, Kansas

Intermittent streams and rivers account for over half of the world's waterways and yet they are still vastly understudied compared to permanent streams and rivers. Wichita State University Biological Field Station: Youngmeyer Ranch presents an opportunity to study intermittent streams and stream pools across 1902 hectares of Flint Hills tall grass prairie ecosystems. We used a freely available satellite imagery program (Google Earth Pro©) to map and provide an initial inventory of streams, intermittent stream pools, and cattle ponds. We also used historic images to create connectivity (percent of downstream length with water) and hydroperiod indices (number of years out of four that pools held water). In total, we mapped 58.2 km of major (2nd to 3rd order) and minor (1st order) streams, and 13 cattle pond impoundments on the property. We used a systematic random sample to select a subset of seven stream reaches (out of 83) within the property for on-the-ground surveys of intermittent stream pools. Within selected streams, a subset of 117 stream pools were sampled in the summer of 2020 and data was collected on the average stream pool width, max depth, length, volume, and biological communities. Stream pools averaged 6.5 ± 9.7 m3 (mean ± SD) in volume, 12.50 ± 9.3 m in length, 2.97 ± 1.7 m in width, and 0.38 ± 0.26 m in depth. Stream and stream pool permanence varied widely across the landscape with pools holding water 3.2 ± 0.8 out of the four years with high resolution satellite imagery. We provided an initial baseline of aquatic systems at Youngmeyer Ranch and characterized representative intermittent stream pools in the Flint Hills and the Great Plains. We also demonstrated the viability of using Google Earth Pro© for mapping and taking inventory of aquatic systems without proprietary software or on-site access.

Numerical investigation of flammable vapour cloud formation from pools of heated organic liquids

The aim of this work is to study the effects of wind velocity, pool length and thickness on the flammable vapour cloud formation from pools of heated organic liquids, covering a wide range of substance properties such as molecular weights and boiling temperatures. To achieve that goal, the computational fluid dynamics (CFD) model has been built and implemented in the commercial CFD code ANSYS Fluent. The mathematical model is validated against published experimental data with respect to both pool evaporation and vapour dispersion simulation. The vapour cloud formation is studied in terms of evaporated mass per unit area of the pool, flammable mass of vapours and its fraction of the total released mass, and maximum downwind extent of the flammable cloud. The results of numerical simulation presented in this work provide a better understanding of evaporation and dispersion processes accompanying the formation of a flammable vapour cloud from pools of heated hydrocarbon liquids.

Evaluation of narrowed weld pool shapes and their effect on resulting potential defects during deep penetration laser beam welding

This study presents mechanisms of the evolution of a narrowed region in the weld pool center during deep penetration laser beam welding. In numerous numerical studies presented in this study, it was also found that the local reduction of the weld pool size can cause detrimental effects on the melt flow behavior and the resulting properties of the welds. A particularly large influence of this effect was identified in three aspects. First, the local variation of the solidification sequence of the weld pool causes an increase in the hot-cracking susceptibility due to a locally delayed solidification. Second, it was proven that a change in the local length and width of the weld pool is associated with an adverse impact on the potential flow routes of the molten material that induces stronger local variations of its solidification. Thus, the element mixing, e.g., during the welding with filler materials, is blocked. This leads to a nonhomogeneous chemical composition of the final weld and can cause undesired effects on the final material properties. Finally, another observed effect is related to the reduced ability of process pores to reach the top surface. As this type of porosity is usually produced around the keyhole tip, the change of the fluid flow regime above this area plays a significant role in determining the final path of the pores until the premature solidification in the middle of the weld pool captures them. This study summarizes mainly numerical results that were supported by selected experimental validation results.

Effect of thermal-fluidic transport on the temperature distribution and the melt pool in laser powder bed fusion of Ti6Al4V

The thermal-fluidic transport affects the temperature distribution and melt pool size in laser powder bed fusion due to its large temperature gradient. A finite element model is established to predict the temperature and melt pool size with considering the thermal-fluidic transport effect. The enthalpy-porosity method is adopted to determine the solid-liquid interface with considering the momentum dissipation during the solidification of the melt pool. A parabolic optical penetration depth (POPD) volumetric heat source model is deduced based on the cylinder heat source model satisfying energy conservation. In the proposed model, the material properties are dependent on the temperature and the powder porosity. The proposed model is validated by comparing to published experimental data of melt pool size. Based on the validated finite element model, the thermal-fluidic transport effects on the temperature distribution and the melt pool are discussed. Results show that in terms of the melt pool width, the prediction accuracy of the surface heat source model is slightly higher than that of POPD volumetric heat source model. In terms of the melt pool depth, surface heat source model is appropriate for the low energy density, while POPD volumetric heat source model is suited for the medium energy density. The thermal-fluidic transport effect increases the melt pool width and length under the surface heat source model, and its effect on the melt pool depth is not obvious. While the thermal-fluidic transport effect decreases the melt pool length under POPD volumetric heat source model, and its effect of the melt pool width and depth is not significant.

Paddle propulsive force and power balance: a new approach to performance assessment in flatwater kayaking

ABSTRACT This study aims to determine the propulsive force (Fp) and its timing of application during the paddle stroke confirming the dynamic balance between propulsive and drag powers (Pp = Pd) in kayaking performance. Ten male sub-elite paddlers participated in the study. The athletes carried out three trials of 50 m at three different velocity ranges: 2.70 – 3.00 m/ s; 3.01 – 3.50 m/s and 3.51 – 4.00 m/ s. A constant velocity during each trial was maintained and the section between 15 and 40 m of the total pool length was considered for further analysis. Data were collected using the E-kayak system provided of an instrumented paddle and 2D video analysis. It was observed that the propulsive force increases in intensity (up to 90% of the peak force) as the velocity increases. The dynamic balance between Pd and Pp was confirmed with a Bland and Altman plot (estimated bias: 0.2; LoA: 12.8 and 13.3 W). The related comparisons between the power parameters showed no significant difference (p > 0.050) in each of the considered velocity. By applying the dynamic balance theory between Pp = Pd on the data obtained from the interaction among GPS, force on the paddle and 2D video analysis, it is possible to acquire essential information (Fp, Pp) to monitor the flatwater kayaking performance.

Effect of Parameters of Pool Geometry on Flow Structure in Nature-like Fishway.

Many uncertainties such as variable irregular structure and complex flow conditions bring difficulties to the design of a nature-like fishway. This study defines the main factors and parameters affecting flow conditions such as permeability ratio, offset ratio, bottom slope and pool length to simplify and generalize the irregular geometry of the nature-like fishway. According to the engineering requirements of the Mopiling nature-like fishway, the effect of the above parameters of pool geometry on the flow structure is investigated through a 3D turbulent numerical simulation, and the parameter thresholds are summarized according to the optimization of the flow conditions. The results show that under the same conditions, the maximum velocity of the control section increases with the increase in permeability ratio, bottom slope and pool length, and the offset ratio has limited effect on the maximum velocity of the control section. It is recommended that when the bottom slope is 1/250 and the pool length is 10 m, the permeability ratio should not be greater than 0.30 and the offset ratio should be located between 0.15 and 0.60. When the bottom slope is adjusted to 1/200, it is recommended to control the permeability ratio below 0.20, the offset ratio between 0.30 and 0.60, and the pool length can be adjusted to 8 m. Within the above threshold range of the design parameters, the maximum velocity in the fishway can be basically controlled at about 1.0 m/s. The mainstream in the pool is clear and the flow pattern is good, which can basically satisfy the requirements of fish passing. The relevant design parameters and optimization strategies can provide reference for similar projects.

Neuro-fuzzy estimation of the most influential factors of laser melt pool depth during direct deposition process

In this article the main aim was to identify the most influential attributes for optimal conditions for directed energy deposition through the melt pool optimization and monitoring. The main goal is to track the melt pool geometries such as width and depth. The goal of this study is to use an adaptive neural fuzzy inference system (ANFIS) to categorize the various melt pool depth input values. The procedure was optimized using ANFIS based on seven processing factors. Laser power (P), scanning speed (V), melt pool width (W), melt pool length (L), build height (BH), melt pool height (H), and melt pool tilt are the input parameters (I). Skillful prediction might be critical in achieving optimal circumstances throughout the deposition process. According to the findings, laser power has the greatest influence on melt pool depth. The combination of laser power and melt pool width produces the least training error and hence has the greatest impact on melt pool depth. The study, which takes into account many input parameters at the same time, is thought to be the first on a modest scale and will pique everyone's curiosity.

CFD-Based Feasibility Study of Laser-Directed Energy Deposition With a Metal Wire for On-Orbit Manufacturing

Additive manufacturing of parts on-site in space requires investigating the feasibility of adapting to zero-gravity and near-vacuum conditions, a technology applied today on Earth at standard conditions. While a few studies have been conducted for powder bed fusion, a feasibility study remains to be explored for direct energy deposition using a laser beam and a metal wire. This is the purpose of this study, which is conducted using a modeling approach based on computational fluid dynamics. The simulation model developed includes melting, re-solidification, vaporization, prediction of beam energy absorption as a function of the local surface temperature and curvature, ray tracing, tracking of free surface deformation and metal transfer, and wire-resistive heating. The study is carried out by starting from process parameters suited for stable on-Earth metal deposition. These conditions were also studied experimentally to validate the simulation model, leading to satisfactorily results. A total of three other test cases with ambient pressure lowered down to near-vacuum and/or gravitation down to zero are investigated. It is found that, compared to on-Earth conditions, in-space conditions can induce vaporization of the metal alloy that is large enough to result in a curvature of the melt pool free surface but too small to lead to the formation of a keyhole. The in-space conditions can also modify the force balance at the liquid melt bridge between the wire and the melt pool, leading to small changes in the curvature and temperature field at the free surface of the wire tip. Among the observed consequences are a small increase of the melt pool length and a small elevation of the bead height. More importantly, for process control, changing to in-space conditions might also affect the stability of the process, which could be assessed through the width of the liquid metal bridge. However, by using appropriate process control to maintain a continuous liquid metal bridge, it is concluded that direct energy deposition of metal using a laser and a wire could be used for manufacturing metal parts in-space in a tempered atmosphere.

An effective method for large-scale temperature simulation in SLM based on the finite difference

Numerical simulation is an effective approach to analyze the selective laser melting (SLM) process and reduce the production development cost. Based on the finite difference method (FDM), the nonuniform grid algorithm (NUGA) is developed to simulate the thermal behavior in SLM process concerning the variable thermophysical parameters of materials with different status. The NUGA can effectively improve computing efficiency, and the calculation speed using NUGA is 610 times than that without using NUGA. Different heat transfer strategies are used on each side of the two critical scanning speeds, 68.95 mm/s and 6895 mm/s, respectively, and the results of temperature calculations are highly consistent. The correctness of the heat transfer strategy under different speeds is analyzed using the NUGA. The effects of processing parameters (laser power, scanning speed and building height) on the shape and volume of the molten pool are investigated. As the scanning speed ranged from 100 mm/s to 500 mm/s, the width and depth of the molten pool decrease, while the length increases. As the laser power ranged from 100 W to 500 W, the length, width and depth of molten pool all increase. The length of the molten pool increases 11.68% from 264.94 of layer 1 to 295.88 of layer 5. The molten pool volume decreases, then increases and decreases finally from the start to the end of single molten path. The molten pool volume increases with increasing laser power and building height, while decreases with increasing scanning speed in general. The NUGA is an effective method for temperature simulation of large-size parts, which expands the application range of temperature simulation in SLM process.

Cross-Scale Simulation Research on the Macro/Microstructure of TC4 Alloy Wire Laser Additive Manufacturing

A cross-scale model of macro-micro coupling is established for the wire laser additive manufacturing process of the TC4 titanium alloy. The model reproduces the dynamic evolution process of the molten pool shape, reveals the temperature change law in the molten pool, and simulates the microstructure and morphology of different regions of the molten pool. Finally, the model is used to quantitatively analyze the effects of process parameters (laser power, scanning speed) on the growth morphology of dendrites during solidification. The research shows that with the increase in laser power and the decrease in scanning speed, the peak temperature of the molten pool increases rapidly, and the size of the molten pool increases gradually. When the laser scanning speed is greater than 5 mm/s, the molten pool length decreases significantly. After solidification, an asymmetrically distributed equiaxed grain structure is formed at the upper part of the molten pool, the bottom of the molten pool is made up of slender columnar crystals, and the columnar-to-equiaxed transition (CET) occurs in the middle of the molten pool. With the decrease in laser power and the increase in scanning speed, the growth rate of dendrites becomes faster, the arm spacing and the overall morphology of dendrites become smaller, and the arrangement of columnar crystals have a tighter microstructure.

Optimization of Surface Roughness and Density of Overhang Structures Fabricated by Laser Powder Bed Fusion.

Laser powder bed fusion (LPBF) provides a rapid and versatile approach for producing parts with complex geometries. However, many parts with intricate geometries have overhang structures, which are not easily fabricated by using LPBF and are often downgraded by staircase effects, warpage, cracks, and dross formation. Thus, the present study proposes a combined numerical and experimental approach for determining the optimal settings of the laser power and scanning speed that minimize the surface roughness and maximize the density of Inconel 718 LPBF overhang structures. In the proposed approach, the heat transfer simulations are employed to determine the melt pool depth, the melt pool length, and the solid cooling rate within the feasible input space of laser power and scanning speed combinations. Notably, the simulations take account of both the difference in the material properties of the solid and powder materials, respectively, and the variation of the laser absorptivity in the depth direction of the powder layer. The simulation results are then used to train artificial neural networks for predicting the melt pool depth for 3600 combinations of the laser power and scanning speed within the input space. The resulting processing maps are screened in accordance with three quality criteria (namely the melt pool depth, the melt pool length, and the solid cooling rate) to determine the optimal processing region, which improves the surface roughness. The feasibility of the proposed approach is demonstrated by fabricating 10 × 10 and 20 × 20 mm2 horizontal overhang structures using parameter settings chosen from the optimal processing map. It shows that the optimal processing conditions result in a low surface roughness and a maximum density of 99.78%.

Laser additive manufacturing of bulk and powder ceramic materials: mathematical modeling with experimental correlations

PurposeThis paper aims to develop efficient and simple models for thermal distribution, melt pool dimensions and controlled phase change in the laser additive manufacturing (AM) of bulk and powder particles ceramic materials.Design/methodology/approachThis paper proposes new analytical models for the AM of bulk and powder bed ceramic materials. A volumetric moving heat source, along with the complete melting of bulk and powder particle materials, is taken into account. Different values of laser absorption coefficient in solid and liquid states have been used to investigate the phase transformation. Furthermore, the pores and voids dimensions are also included in the modeling. Theoretical predictions have been compared with the experimental analyses and finite element simulations in laser to silicon nitride and laser to alumina interaction. The analysis focuses on the impact of laser power and scanning speed on the melt pool width and depth evolution into the bulk substrate and powder bed.FindingsThis study shows that the powder particles exhibit a higher thermal distribution value than the bulk substrate because of voids in the powder layer. The laser beam experiences multiple reflections in the presence of porosity/voids, thus increasing the surface absorption coefficient, which becomes relevant with the increment in the pore/void dimension. A direct relationship has been found between the laser power and melt pool dimensions, while the scanning speed displayed an inverse relationship for the melt pool width and length. Larger melt dimensions were inferred in the case of laser–powder particle interaction compared with laser–bulk substrate interaction. A close correlation was found between the analytical simulations, experimental investigations and numerical simulation results within the range of 4%–8%.Originality/valueThis paper fulfills an identified need to develop efficient and simplified models for ceramics laser AM by taking into account different laser absorption coefficients in solid and liquid form, voids and pores dimensions and controlled phase transformation to avoid vapors and plasma formation. The limitation of the finite element simulation model is that the solution is strongly dependent on the mesh quality and accuracy directly linked to the computation efficiency and time. A finer mesh requires a longer computing time than a coarse mesh. Finite element simulations require, however, specialized skills.

Study of weld pool monitoring system based on spatial filtering

The observable information of the welding process mainly includes the weld pool, weld seam, and arc length, which can be used to predict the penetration depth, perform weld tracking, and provide early warning of weld defects. Welding monitoring technology based on machine vision has been widely researched to improve the quality and efficiency of welding. This paper proposes a novel weld pool image acquisition system based on spatial filtering and Abbe’s theory of image formation. A high-pass spatial filter was designed to eliminate the low frequency background noise so that the contour of the weld pool, weld seam, and arc shape were acquired. Compared with the weld pool monitoring system based on an optical filter, this method more effectively solved the problem of the large radiation gradient in the weld pool area, and the weld pool could be more clearly observed. It provided a new method to image the weld pool image system with the advantages of low cost and ease of implementation.