Volumetric Heat Source Model Research Articles

A Dynamic Volumetric Heat Source Model for Laser Additive Manufacturing

Melt pool scale models of laser powder bed fusion (LPBF) offer insights into the process-structure-property relationships in additive manufacturing (AM). These models often neglect physical phenomena such as vapor cavity formation and fluid mechanics to reduce computational demands. Instead, volumetric heat source models are used to represent the effects that these phenomena have on the predicted melt pool dimensions. Generally, the dimensions and effective absorption of the volumetric heat source are calibrated to reproduce melt pool dimensions observed in metallographic cross sections taken from single-track experiments on bare plate. However, the transient nature of LPBF often deviates the melt pool dimensions from the assumed steady-state conditions of single-track experiments, motivating the need for a volumetric heat source model that more generally considers the dynamic relationship between melt pool shape and laser-material interactions. Here, we introduce a two-parameter volumetric heat source model that integrates several existing models into a generalized mathematical expression, providing independent control over the radial heat distribution via the parameter k and the volumetric shape of the heat source via the parameter m. This parameterization enables the calibration of melt pool shape predictions through simultaneous adjustment of these parameters, while keeping the radial heat source dimensions consistent with the experimental spot size (D4σ) and constraining the heat source depth and absorption to physically derived expressions for cavities. Consequently, the proposed volumetric heat source model adapts to changes in the local melt pool conditions due to scanning strategy and part geometry by dynamically adjusting the heat source depth and absorption. We demonstrate the capabilities of the proposed model through comparisons with a collection of experiments from the Additive Manufacturing Benchmark (AMBench).

Heat source models for numerical simulation of laser welding processes – a short review

In recent decades, numerical modeling and computer simulation have become an integral part of the design, analysis and optimization of fusion welding processes, including laser welding. In general, laser welding processes involve the interaction of multiple physical phenomena, such as thermal, fluid, metallurgical, chemical, mechanical, and diffusion effects, which makes the development of a simulation model difficult and complex. In addition to the geometric characteristics of the parts to be welded, their material properties must be specified in a wide temperature range, as well as the conditions for heat removal to the environment or shielding gas. One of the most complex tasks in the preparation of a simulation model of the laser welding processes consists in the selection of an appropriate heat source model to accurately determine the heat input to the weld. Very important is also the process of experimental verification and validation of the developed simulation models. In this paper, a short examination of significant mathematical heat source models for numerical simulation of laser welding is provided. Numerical analysis of laser welding of sheets made of S650MC steel is accomplished using conical 3D heat source model with the support of the ANSYS code. The effect of geometrical characteristics of the conical volumetric heat source model on the computed width, length, and depth of the weld pool is discussed, along with evaluation of maximum weld pool temperature.

Three-dimensional transient heat transfer analysis of micro-plasma arc welding process using volumetric heat source models

Abstract The micro plasma arc welding process is associated with different physical phenomena simultaneously. This results in complexities to comprehend the actual mechanism involved during the process. Therefore, a robust numerical model that can compute the weld pool shape, temperature distribution, and thermal history needs to be addressed. Unlike, other arc welding processes, the micro plasma arc welding process utilizes thin sheets of thickness between 0.5 and 2 mm. However, joining thin sheets using a high-density arc welding process quickens the welding defects such as burn-through, thermal stresses, and welding-induced distortions. The incorporation of a surface heat source model for computational modeling of the high energy density welding process impedes heat transfer analysis. In that respect, researchers have developed numerous volumetric heat source models to examine the welding process holistically. Although, selecting volumetric heat source models for miniature welding is a significant task. The present work emphasis developing a rigorous yet efficient model to evaluate weld pool shape, temperature distribution, and thermal history of plasma arc welded Ti6Al4V sheets. The computational modeling is performed using a commercially available COMSOL Multiphysics 5.4 package with a finite element approach. Two different prominent thermal models, namely, Parabolic Gaussian and Conical power energy distribution models are used. A comparative analysis is carried out to determine the most suitable heat source model for evaluating temperature distribution, peak temperature, and thermal history. The analysis is done by juxtaposing the simulated half-cross-section weld macrographs with the published experimental results from independent literature. The numerical results showed that the proximity of top bead width magnitude was obtained using the Parabolic Gaussian heat source model for low heat input magnitude of 47.52 and high heat input magnitude of 65.47 J·mm−1, respectively. In terms of percentage error, the maximum top bead width percentage error for the Parabolic heat source model is 13.26%. However, the maximum top bead width percentage error for the Conical heat source model is 18.36%. Likewise, the maximum bottom bead width percentage error for the Parabolic heat source model and the Conical heat source model is 12.3 and 25.8%, respectively. Overall, it was observed that the Parabolic heat source model produces the least deviating outcomes when compared with the Conical distribution. It was assessed that the Parabolic Gaussian heat source model can be a viable heat source model for numerically evaluating micro-plasma arc welded Ti6Al4V alloy of thin sheets.

Numerical study on multiphase evolution and molten pool dynamics of underwater wet laser welding in shallow water environment

Underwater wet laser welding (UWLW) is a promising and labor-saving in-situ repair technique in aquatic environments, which simplifies the arduous dismantling and transportation processes of repairing underwater equipment on land. However, the thermo-physical mechanism during UWLW is still unclear. This study presents, for the first time, a thermal multi-phase flow model to study the heat transfer, fluid dynamics, and phase transitions involved in the UWLW process at shallow water column depths (water depth ≤ 4 mm). A dual-cone volumetric heat source model considering the laser energy distribution in both the water and metal is proposed. The driving forces, including gravity, surface tension, and the water/metal vapor recoil pressure are taken into account. The simulated weld profiles are in good agreement with the experimental results. The results indicate that in the UWLW process, laser heating creates a water keyhole, forming a localized dry region (LDR) above the molten pool. The LDR isolates the water from the molten pool and protects the laser-metal interactions, thereby making the welding environment similar to that of in air laser welding (IALW). Due to the water evaporation, the upper rear and sides of the molten pool during the UWLW pocessess a higher cooling rate compared to the IALW case, resulting in a higher temperature gradient and smaller molten pool dimensions. The results contribute to a better understanding of the complex interactions in UWLW process.

A volumetric heat source model for the approximation of the melting pool in laser beam welding

AbstractLaser beam welding is a metal fusion technique that, with its high advance speed and low thermal distortion, is used more frequently nowadays in industry. During welding, the solidification front is located in the so‐called mushy zone, which forms the transition region between the completely solidified and mixture zone of solid and fluid material behind the laser beam. In this zone, various process parameters can lead to the formation of included melt areas that may cause cracking when they solidify and shrink. The properties of the solidification region are influenced by several parameters. Factors such as welding speed, temperature gradient, and chemical composition affect the likelihood of solidification cracking. To study the heat affected zone more accurately, different models describing the melting pool in finite element approaches using a heat source are discussed. The goal is to develop a volumetric heat source model based on the conical model, which closely represents the temperature distribution illustrated by the Lamé curves. Boundary value problems are presented to showcase the results.

An equivalent volumetric heat source model for thermal conduction of plate forming by inducted line heating

An equivalent volumetric heat source model for thermal conduction of plate forming by inducted line heating

Modelling and validation of laser based DED processes reinforced with nanoparticles in view of the effect of wetting

Although the observation of wetting phenomena has a long history both in science and in everyday life, nanoscale wetting properties leave open a multitude of questions. Improving the properties of Direct Energy Deposition (DED) products through reinforcement with nanoparticles (NPs) is attractive. Due to the involved NPs, the wetting behaviour of the deposition differs from that in macroscales. Modelling and validation of a laser-based DED process reinforced with NPs in view of the effect of wetting is demonstrated in this study. Metal alloys reinforced with NPs (Ti6Al4V- and Al7075-TiC) are melted by laser light and deposit on a substrate. Heating of the alloys by laser light is tackled using a volumetric heat source model. A three-phase (solid, liquid and gas) melting and solidification simulation methodology is established in a continuum approach. Nanoparticles are treated in the Lagrangian framework. Effect of nanoparticle reinforcement on the wetting behaviour of melt bead during the printing process is investigated numerically, taking into account the influence of nanoparticles on contact angle and surface tension. Simulation results are compared with the experimental deposition of Ti6Al4V and Al7075 alloys through dimensional analysis of the tracks by macrography.

Numerical Simulation of Laser Transmission Welding-A Review on Temperature Field, Stress Field, Melt Flow Field, and Thermal Degradation.

Laser transmission welding (LTW) is an excellent process for joining plastics and is widely used in industry. Numerical simulation is an important method and area for studying LTW. It can effectively shorten the experimental time and reduce research costs, aid in understanding the welding mechanism, and enable the acquisition of ideal process parameters. To enhance understanding of numerical simulation studies on LTW and facilitate research in this area, this paper presents a comprehensive overview of the progress made in numerical simulation of LTW, covering the following aspects: (a) characteristics of the three heat source models for LTW temperature field simulation, including surface heat source model, volumetric heat source model, and hybrid heat source model, along with the methods, results, and applications of temperature field simulation based on these models and experimental validation; (b) numerical simulation of thermal and residual stresses based on the temperature field; (c) numerical simulation of the melt flow field; and (d) predictive simulation of material degradation. The conclusion of the review and the prospects for further research work are eventually addressed.

Numerical study of beam oscillation and its effect on the solidification parameters and grain morphology in remote laser welding of high-strength aluminium alloys

This study investigated the effect of beam oscillation on the solidification behaviour during laser welding of Al-5754 to Al-6061 alloy. In this study, a finite element model has been developed to simulate temperature and fluid flow fields by implementing different combinations of volumetric heat source models. Solidification parameters such as temperature gradient (G), solidification rate (R), cooling rate (G × R) and G/R are evaluated to understand the mechanism of microstructure formation. It was found that beam oscillation improves the tensile strength by 21.4% for full penetration welding due to an increase in the percentage of formation of equiaxed grains. Modelling results revealed that the cooling rate increases with an increase in oscillation frequency. However, tensile strength followed a parabolic distribution with a peak at the oscillation frequency of 300 Hz.

Evaluation of residual stresses in CO2 laser beam welding of SS316L weldments using FEA

Laser welding is used in critical component production when tight tolerances like minimal distortions and residual stresses are required. Laser beam welding offers a lower heat input, a smaller heat affected zone, lower residual stresses, minimum distortions, and greater mechanical joint characteristics than conventional welding does. In order to simulate the laser welding process used on SS316L plates, the Gaussian heat source model was used. The model is developed and simulated with volumetric heat source model with APDL coding using ANSYS. The thermal profiles at the joint cross sections via welded area, interface across joints is taken for the analysis. The maximum temperature was observed at the fusion zone and associated zones. The residual stresses are analysed in the same path and found the stresses are in safe limits of base material. Predicted and experimentally measured residual stresses are close agreement with 10%.

Investigation of heat input effects on the joint characteristics of CMT welded Aa6061 sheets

Cold Metal Transfer (CMT) arc welding is an updated version of the GMAW process, in which heat input is significantly reduced due to the push-pull action of filler wire feeding during welding. The aluminium alloy sheets are welded by the CMT arc welding process using different heat input levels in this research work. The temperature distribution during welding is experimentally measured with the help of an infrared thermometer, and finite element analysis (volumetric heat source model) is used to predict the temperature distribution, and these results are equated. The influence of heat input on joint characteristics such as bead geometry, microhardness variation, microstructure analysis and tensile properties is also being investigated experimentally. The temperature study reveals that the results of numerical modelling for temperature distribution using various heat inputs were very close to the experimental condition, with a less significant difference ±5. In addition, the well-controlled heat input at 210 J/mm was attributed to eradicating porosity, which was confirmed by Non-destructive evaluation, macrostructure and microstructure analysis. As a result, the joint produced a better tensile strength of 241 MPa due to the achievement of fine grain refinement of 17 µm in the weld zone, reduced heat affect zone, and 6.45% volume fraction of Mg2Si particles. The intercept length of 18.937 microns is measured as the average value, and the misorientation angle of 25.2922 was also found as the average in the fusion zone, which is more significant when compared to the base metal value of 20 μm.

A semi-analytical approach for analysis of thermal behaviors coupling heat loss in powder bed fusion

The build-up of the heat losses induced by a high-temperature gradient during laser additive manufacturing process has a significant effect on the thermal behaviors and the formation of parts’ defect. In this paper, considering heat losses caused by conduction, convection and radiation, a semi-analytical model for predicting three-dimensional transient temperature field distributions is established, which is verified by comparison with results from the literature. The temperature distributions coupled with heat losses for typical surface and volumetric heat source models are obtained by using the separation of variables. The effect of process parameters and heat source model on peak temperature, temperature gradient, molten pool dimensions and heat losses is analyzed. In addition, the effect of the surface and volumetric heat source model on formation quality during the powder bed fusion (PBF) process is discussed in detail. The results show that higher average temperature and lower heat losses occur for the volumetric heat source model. Moreover, heat losses increase as the power, energy absorptivity and effective radius of the laser beam, while decrease with a decrease of scan speed. The results could be helpful to enable process optimization of the PBF to improve as-built parts quality.

On the importance of heat source model determination for numerical modeling of selective laser melting of IN625

Accurate prediction of temperature distribution and melt pool geometry in metal additive manufacturing is highly dependent on the appropriate selection of heat source models. In the present study, a three-dimensional (3D) finite element (FE) heat transfer model is developed utilizing Abaqus by integrating different heat source models focusing on the surface heat source model and volumetric heat source model for selective laser melting (SLM) of Inconel 625 (IN625). All of the predicted peak temperatures, molten pool width, and depth are evaluated and compared with the experimental results cited from open literature. The relative error in simulated peak temperature and melt pool geometry from the surface heat source model is much higher in comparison to the volumetric heat transfer model. Further, a hybrid heat source model incorporating surface and volumetric heat models is developed to fulfill the numerical modeling of SLM of IN625 with high accuracy, which is highly recommended for the in-depth simulation study.

A simplified modelling approach for thermal behaviour analysis in hybrid plasma arc-laser additive manufacturing

Hybrid plasma transferred arc (PTA)-laser additive manufacturing (AM) has the potential to build large-scale metal components with high deposition rate and near-net shape. However, the process is complex with many parameters adjustable for process control, which determine the thermal behaviour and thus the final structure and properties of the deposited components. In this study, a three-dimensional steady-state finite element model with two independent circular surface heat sources was developed, validated, and used to analyse the thermal behaviour in hybrid PTA-laser AM of Ti-6Al-4V. Artificial conductivity in three orthogonal directions was applied in the melt pool to compensate for the melt pool convection effect. The predicted melt pool geometry, heat-affected zone and thermal cycles had good agreement with the corresponding experimental data. This model has advantages over the widely used volumetric heat source model, since it is more representative of the energy sources used, giving accurate thermal prediction for a wide range of process parameters. As the heat source parameters in this model are directly linked to the actual arc/laser size, it enables to capture heat source size effect on the hybrid process. In addition, it is easier to calibrate compared to the model with volumetric heat sources due to the fewer empirical parameters involved. It was found that in the investigated ranges of all the parameters, the melt pool geometry is more sensitive to laser power and travel speed compared to arc-laser separation distance and laser beam size. The full-field distributions of the cooling rate and temperature gradient in the hybrid process were obtained and the roles that different process parameters played on them were also studied, which provided useful thermal information for metallurgical analysis.

A Review on Modelling and Simulation of Laser Additive Manufacturing: Heat Transfer, Microstructure Evolutions and Mechanical Properties

Modelling and simulation are very important for revealing the relationship between process parameters and internal variables like grain morphology in solidification, precipitate evolution, and solid-state phase transformation in laser additive manufacturing. The impact of the microstructural changes on mechanical behaviors is also a hot topic in laser additive manufacturing. Here we reviewed key developments in thermal modelling, microstructural simulations, and the predictions of mechanical properties in laser additive manufacturing. A volumetric heat source model, including the Gaussian and double ellipsoid heat sources, is introduced. The main methods used in the simulation of microstructures, including Monte Carlo method, cellular automaton, and phase field method, are mainly described. The impacts of the microstructures on mechanical properties are revealed by the physics-based models including a precipitate evolution based model and dislocation evolution based model and by the crystal plasticity model. The key issues in the modelling and simulation of laser additive manufacturing are addressed.

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.

Laser-particle interaction-based heat source model of laser powder bed fusion additive manufacturing

The use of powder is one of the special features in laser powder bed fusion additive manufacturing (L-PBF AM). How the powder affects the L-PBF process is the basic mechanism determining the accurate prediction of the melt pool and the temperatures in finite element heat transfer simulations. The laser is treated as electromagnetic wave essentially and the powder particles can be heated by the formation of the inducted current on the particle surfaces. The laser energy density absorbed by the powder particles was calculated based on the laser-particle interaction. Based on the statistical analysis of particles in spatial distribution, the new volumetric heat source model was obtained and then applied to finite element heat transfer simulations. Results indicate that the temperature rise of the individual particle is not uniform and relates to the distribution of electromagnetic energy density on the surface of particles. The distribution of electromagnetic energy density on the surface of the individual particle at different positions is different. The energy absorbed by the upper particles is mainly determined by the direct irradiation of the laser. The energy absorbed by the bottom particles is mainly caused by the laser reflections. Due to the change of the mechanism for energy absorption, the maximum energy absorption occurs at the location which is near the average diameter away from the top surface of the powder bed. When the powder bed thickness is small, the laser energy density along build direction is in Gaussian distribution. With the increase of the powder bed thickness, the laser energy density distribution along build direction can be fit for 4-order polynomial function.

Volumetric heat source model for laser-based powder bed fusion process in additive manufacturing

Laser-based powder bed fusion (L-PBF) is one of the most widely used additive manufacturing methods. Its most striking feature is the melt pool in the powder bed, which is formed by a laser heat source. Many physical phenomena occur as a result of the interaction of the heat source with metal powders. Spattering, melting and sintering to each other of the metal powders (phase and shape change), liquid metal movement induced by buoyancy force and surface tension gradient, high evaporation and resulting recoil pressure, fluctuations and deteriorations on the liquid metal surface, plume type structures can be given as examples. The most important point in terms of L-PBF and similar methods is to predict the melt pool dimensions and temperature distribution in the powder bed. However, the phenomena mentioned above complicate the process considerably and require high calculation costs. Volumetric heat sources are a frequently used prescription in terms of simplifying the modeling of the process and reducing the calculation cost. However, such heat source models may contain many non-standard parameters and do not always produce reasonable results. In this study, a dynamic heat source model is presented for use in powder bed systems. Some discussions related to the problems such as uncertainties in absorptivity ratios used in L-PBF are also presented.

Analytical model for three-dimensional non-uniform temperature field and welding stress of thick plates via friction stir weld

The non-uniform thermal field for thick plates jointed by friction stir welding (FSW) easily causes the complex stress state and affects the mechanical behaviour of welded components. The transient non-uniform temperature field for thick plates by FSW is analytically studied based on the heat conduction problem solved by three-dimensional Green’s function. The asymmetric volumetric heat source model is developed by considering the flux distributions in the thickness direction, which is used to obtain the semi-analytical temperature field for welded plates with nonhomogeneous boundary conditions. Then, the analytical model for welding stress is proposed for thick plates by FSW according to the non-uniform temperature field in the weld. The elastic-plastic boundary and the variations of welding stress in the thickness direction are discussed based on the temperature gradient in the welding process. The non-uniform stress distribution in the weld may be analytically predicted in the welding process. The residual stress in the weld is numerically calculated in the cooling process and compared with experiment data to verify the models for the non-uniform temperature field and stress distribution of thick plates. The results show that the three-dimensional temperature field may be used effectively to provide insights into the mechanical response by FSW.

The well-distributed volumetric heat source model for numerical simulation of wire arc additive manufacturing process

Wire arc additive manufacturing (WAAM) is a promising alternative to laser-powder based additive manufacturing for fabricating large metallic components due to its high productivity and low cost. The high heat input of the arc welding process causes significant thermal stresses resulting in large distortion of the components. Finite element methods are widely used to analysis arc welding and additive manufacturing process, while the commonly used Gaussian or Double ellipsoid volumetric heat source model requires a large number of mesh points suffering from computational expensive and time consuming. This paper describes the well-distributed volumetric heat source model for numerical simulation of wire arc additive manufacturing process on large components. The proposed well-distributed heat source model is insensitive to mesh, showing a significant advantage with respect to the computational time. The simulated temperature history and distribution are verified by comparison with the experimental results from thermocouples and a high-temperature thermal imaging camera.