Moving Heat Source Research Articles

Effects of latent heat in additive manufacturing

We analyzed the effects of latent heat in conditions related to the additive manufacturing technology by solving the free boundary problem of a moving heat source. The most important finding of our analysis is a possibility of a genuine (not constitutional) supercooling at the fusion edge of the melt pool. It is measured by the structure forming number of the system, which changes significantly compared to the latent-heat-free system. Other findings of the present treatment are the increase of the longitudinal size and decrease of the maximum temperature of the melt pool due to the latent heat and the role of the surface heat losses in the process. There are several important physical properties, which were not accounted for by the free-boundary model developed in this treatment. They can be accounted for by a phase-field model, which we plan to develop in the future. The latter may also be useful for other technologies, like laser melting, electron (ion)-beam irradiation, and fusion welding.

Investigation of Effect of Processing Parameters for Direct Energy Deposition Additive Manufacturing Technologies

In order to capitalize on the cost-effectiveness of additive manufacturing (AM), it is critical to understand how to build components with consistency and high quality. Directed energy deposition (DED) is an AM method for creating parts layer by layer through the use of a moving heat source and powder material inserted into the melt pool generated on the substrate. DED, like most AM processes, is highly complex due to the rapid thermal gradients experienced during processing. These thermal gradients are determined by a variety of processing parameters, which include laser power, powder feed rate, travel speed, layer height hatch spacing, etc. A lot of effort has been carried out in the additive manufacturing community to understand what these critical parameters are and how they influence the thermal gradients. Despite all these efforts, AM industries rely on a trial-and-error-based approach to find the right set of parameters to produce a quality part. This is time-consuming and not a cost-effective use of AM technology. The aim of our research is to reduce the amount of experimental data in combination with numerical analysis to optimize this relationship. Physics-based two-dimensional melt-pool modeling and experimental results from an OPTOMEC 850M LENS will be utilized to investigate the effects of processing parameters on melt-pool geometry, and the results from this study will provide key processing guidelines to achieve desirable clad geometry and powder efficiency for the DED method.

Phase change heat transfer analysis of anisotropic structures with moving heat source using the element-free Galerkin method

The computational model of phase change heat transfer analysis for anisotropic structures with moving heat sources is established using the element-free Galerkin method (EFGM), and the accuracy and superiority of the proposed model are verified by experimental results and two butt welding examples of anisotropic plates. The influence of off-angle and thermal conductivity factors on the temperature field, welding pool, and weld seam is investigated. The results show that EFGM temperature and welding pool have higher accuracy compared with the finite element method solutions. It is demonstrated that EFGM has a distinct advantage in the tracing of moving heat sources and dynamic phase interfaces during the butt welding process, whether along straight or complex paths. There is a high-quality welding pool and a uniform temperature in butt welding of anisotropic structures compared with isotropic structures. The increase of thermal conductivity factor can accelerate the phase change process and its reasonable range is suggested to be 2–4. It can reduce the temperature concentration and accelerate the solidification speed of weld seam when the off-angle is enlarged, and its recommended range is 30°–45°.

Calculation of thermal features in welding and additive manufacturing

This paper summarizes multiple engineering expressions that enable the prediction of thermal magnitudes of interest associated with moving heat sources. The expressions use only fundamental parameters available before performing any experiments, and their calculation is algebraic, without the need for numerical methods. All expressions are based on the fundamental governing equations of heat transfer in the solid. The magnitudes predicted include maximum width and its location, maximum penetration, thickness of HAZ, maximum temperature and its location, leading and trailing edge of an isotherm, heating and cooling rate, aspect ratio of an isotherm, melting efficiency, cooling time from 800°C to 500°C, solidification time, and maximum distribution of a heat source to reach a target temperature. Parameters involved include heat source power and speed, thermal conductivity and diffusivity of the substrate material, temperature of interest and preheat or interpass temperature. Temperature-dependent properties are accounted for by the use of effective properties. The expressions proposed can be extended into sophisticated geometries for welding and specific additive manufacturing cases.

Enhancement of a quasi-analytical solution for modelling additive manufacturing processes

Numerical modelling methods (e.g. finite element) can provide accurate descriptions of long-range temperature fields in laser or electron-beam melting processes, however the high computational costs at part-scale make them unsuitable for process modelling in additive manufacturing (AM). Alternative methods such as semi-analytical solutions based on a moving heat source reduce the computational expense but at the cost of unrealistic assumptions. Radiation, temperature-dependent physical properties and latent heat are not considered in the semi-analytical approach but can have a significant effect on the thermal history. In this study, the error associated with each of these contributions are assessed against the conduction-only semi-analytical solution for a range of processing parameters for surface melting on solid Ti-6Al-4V. The semi-analytical model is then “enhanced” using results from finite element simulations to better account for the heat transfer in the AM process.

Numerical simulation of the temperature field of T2 copper/304 steel dissimilar metal electron beam welding

ANSYS workbench finite element analysis software was adopted to simulate and study the thermal process of electron beam welding of T2 copper and 304 steel heterogeneous materials in this paper. A solid model was established according to the size of the specimens, and a double ellipsoidal moving heat source model of the temperature field of the specimens of the three-dimensional dynamic simulation was imposed. Copper and steel welding transient temperature field distribution pattern and molten pool morphology were studied, and the temperature field welding thermal cycle curve was analyzed. The results show that the peak temperature of the steel side is higher than the copper side, the morphology of the welding pool is basically biased toward the steel side, and the highest temperature during the welding process appears in the center of the weld on the steel side about 0.5 mm.

Thermal mapping of SS316L experimental and simulation for GTA welding process with moving heat source model using FEA

Thermal mapping of SS316L experimental and simulation for GTA welding process with moving heat source model using FEA

Dynamic response of a one‐dimensional hexagonal quasicrystal rod in the framework of fractional‐order thermoelasticity

AbstractBased on the fractional‐order thermoelastic theory, the dynamic response of a finite quasicrystal (QC) rod fixed at both ends and subjected to a moving heat source is analyzed. The governing equations of one‐dimensional (1D) hexagonal QC rod are derived. And then the numerical solution is obtained by using the Laplace transform and its numerical inversion. The effects of time; the velocity of heat source; and fractional‐order parameter on displacement, stress, and temperature of the QCs are discussed and compared with classical materials in this paper.

Observation and simulation investigation for the crater formation under discharge plasma movement in RT-WEDM

Observations of the discharge gap were conducted to investigate the discharge plasma motion in reciprocated traveling wire electrical discharge machining (RT-WEDM). It was found that a discharge plasma continuously slides on the surface of a workpiece. An oscillating moving heat source is proposed to better describe the characteristics of discharge plasma motions. Based on an oscillating moving heat source, a novel thermal-fluid coupling model by adopting a level-set method is proposed to investigate the formation of a crater and the effects of machining parameters on craters. Discharge plasma sliding, latent heat, and molten pool forces are comprehensively considered in the proposed model. Simulation and experimental results show that a sliding discharge plasma has a significant effect on a crater. At the end of a discharge, a considerable proportion of molten materials remains in the molten pool. A high sliding speed of discharge plasma can lead to a low aspect ratio in a crater and a thin recast layer. Due to discharge plasma sliding, an increase in pulse duration can significantly increase the length of a crater and decrease the aspect ratio, while an increase in peak current can significantly increase the depth and volume of the crater. Simulation and experimental results also show that morphologies of the simulated crater and experimental craters are consistent, verifying the feasibility and accuracy of the proposed simulation model in explaining the mechanism of crater formation in RT-WEDM.

Laser welding simulation of large-scale assembly module of stainless steel side-wall

Due to the advantageous characteristics of laser welding technology, it is being increasingly used for constructing stainless steel rail vehicles. It can improve the appearance of a vehicle, enable designs with a relatively high degree of flatness, and ensure higher-quality connections between different parts of a vehicle. Moreover, it can improve the strength and stiffness of the components of the vehicle. In this study, a large-scale assembly module of a stainless steel side-wall was considered as the research object. The combined heat source model of a Gaussian heat source and a cylindrical volume heat source was used to obtain the heat source parameters of laser welding to match the experimental data. Based on the thermal cycle curve method (TCCM), the influence of the number of weld segments and mesh divisions of the local model on the efficiency and accuracy of laser welding simulations was investigated. Thereafter, the research results were applied to the welding simulation of the whole side-wall module. The shape of the molten pool obtained using the combined heat source was closer to that of the experiments (error < 10%), demonstrating the accuracy and effectiveness of the developed the heat source model for laser welding simulation. For local model laser welding using the TCCM, a coarse mesh was used, and the weld was divided into four segments, and highly accurate results were obtained. This calculation time was only 5.97% of that of a moving heat source in case of the thermo-elastic-plastic method (TEPM). Residual stress and welding deformation of the stainless steel side-wall module were calculated according to actual process parameters and the results of local model simulation. Residual stress was discontinuously distributed at the weld segments, and it only slightly influenced the overall stress distribution. The maximum residual stress (462.15 MPa) occurred at the weld of the large crossbeam. Welding eight small and two large crossbeams influenced the deformation change and the maximum deformation (1.26 mm) appeared in the middle position of the left side-wall. The findings of this study show that the TCCM has high calculation accuracy and is sufficiently economical for predicting laser welding of large structures.

Thermoelastic Analysis of Circular and Rectangular Objects with Moving Heat Source: A Review of Recent Literature

The article investigates the present review of thermoelastic theories of circular and rectangular objects with moving heat sources published on paper after 1950. The main theme of thermoelastic problems on circular and rectangular structures is to establish operational methods to solve governing differential equations. In the thermoelastic problems, we have considered a few practical problems of technical interest, taking into account the circular and rectangular shape geometry with moving heat sources by using integral transform techniques. AMS Subject classifications: 35B07; 35G30; 35K05: 44A10 Keywords: circular and rectangular objects, temperature distribution, thermal stresses, integral transform.

Flaw Detection in Multi-Laser Powder Bed Fusion Using In Situ Coaxial Multi-Spectral Sensing and Deep Learning

Abstract Multi-laser powder bed fusion (M-LPBF) systems are garnering increased attention in metal additive manufacturing as they promise increased productivity and part size without sacrificing feature resolution or mechanical properties. However, M-LPBF introduces unique problems related to the interaction of multiple moving heat sources not observed in single laser systems, possibly leading to unexpected flaws and other process anomalies. Careful process modeling, planning, and monitoring are required to fully exploit M-LPBF. We present a novel in situ sensing and machine learning-based flaw detection for M-LPBF. Specifically, we consider a configuration where on-axis multi-spectral sensors are integrated and synchronized with each of the three lasers on a 3D Systems DMP Factory 500 printer. Each multi-spectral sensor monitors spectral emissions at two material-dependent wavelengths. The time series data generated from the multiple multi-spectral sensors are converted into a rasterized image per layer to be fed into a supervised deep learning (DL)-based semantic segmentation pipeline. To discriminate nominal process variations from anomalies, we explore a novel framework to incorporate context into the DL model which includes factors such as laser scan direction, processing parameters, and multi-laser proximity. We demonstrate our framework on in situ monitoring data collected during a build of carefully selected specimens seeded with surrogate lack of fusion flaws. Post-build X-ray computed tomography data are registered to the in situ data to generate ground truth labels for training and validation of the DL model.

Thermal contact resistance for stationary and moving heat sources in angular contact ball bearings

Sliding friction is a common tribological effect that occurs between the contact surfaces of the inner components (inner race, outer race and balls) of a spindle rolling bearing during operation. This friction generally generates heat, which can affect the performance of the rolling bearing. To date, numerous studies have assumed that the contact surface between the inner components of the bearing is circular and stationary. While this assumption has yielded adequate results, it is not sufficient in the case of angular contact ball bearings, where the contact surfaces are elliptical and could be treated as either stationary or moving heat sources. This paper presents solutions for both, stationary and moving heat sources for elliptical contact surfaces in a spindle rolling bearing. The primary objective is to find the thermal contact resistances which are dependent on the shape of contact, the loads, the rotational speed and the material properties thereof, applying the mathematical expressions developed by Muzychka and Yovanovich. These expressions were used to calculate various thermal resistances, providing results applicable to the analysis of thermal models in spindle rolling elements. Through finite element analysis (FEA) performed in Ansys Workbench, the stationary and moving heat sources were compared, finding the heat distribution along the elements of the bearing. The findings herein are suitable for the creation of thermal networks in rolling bearings, which are essential to predict their thermal behaviour.

Adaptive step size controllers based on Runge-Kutta and linear-neighbor methods for solving the non-stationary heat conduction equation

&lt;abstract&gt;&lt;p&gt;We systematically test families of explicit adaptive step size controllers for solving the diffusion or heat equation. After discretizing the space variables as in the conventional method of lines, we are left with a system of ordinary differential equations (ODEs). Different methods for estimating the local error and techniques for changing the step size when solving a system of ODEs were suggested previously by researchers. In this paper, those local error estimators and techniques are used to generate different types of adaptive step size controllers. Those controllers are applied to a system of ODEs resulting from discretizing diffusion equations. The performances of the controllers were compared in the cases of three different experiments. The first and the second system are heat conduction in homogeneous and inhomogeneous media, while the third one contains a moving heat source that can correspond to a welding process.&lt;/p&gt;&lt;/abstract&gt;

ПРОСТАЯ АНАЛИТИЧЕСКАЯ МОДЕЛЬ ТЕПЛОВЫХ ПОЛЕЙ ДЛЯ РАЗРАБОТКИ ЦИФРОВЫХ ДВОЙНИКОВ ПРОЦЕССА ПРОМЫШЛЕННОЙ ДУГОВОЙ СВАРКИ

A digital twin is the virtual representation of a physical object, system, or process using computerized digital technologies. Creating digital twins becomes much more difficult for dynamic manufacturing processes, such as welding, when simulation time should not exceed a few seconds. This paper presents a method for modeling thermal fields in industrial welding in real time, based on physical processes. The method can be used to create a digital twin at the process level. The method uses analytical solutions to the problem of temperature distribution around a weld which is a moving heat source.

Simulation of the distribution of temperature, stresses and deformations during splined shafts hardfacing

This article describes the process of modeling the restoration operations of the destroyed segment of the spline and its complete restoration using modern methods, such as hardfacing in a protective gas environment with a consumable electrode. The ANSYS Workbench 19.2 software with an additional Welding Distortion and Moving Heat Source extension was used to simulate the process of hardfacing a damaged surface. The thermomechanical behavior of the deposited layer on the outer surface of the splined shaft is analysed. Dependences of the value of temperature fields on the parameters of the hardfacing mode in one and two passes depending on time are established. Dependences of residual stresses (0.413-239 MPa) and deformations (0.02-0.23 mm) in the process of semi-automatic hardfacing are determined. Experimental studies of samples during hardfacing were carried out for comparison with the geometry of the weld during modeling. The simulation results are in good agreement with the experimental data.

Thermo-Mechanical Analysis of Girth Welding Process on Flange Pipe Joints using Moving Heat Source Extension

This paper forecasts the transient thermal temperature history during girth welding with a single pass over the welded area on pipe ASME class 300 flange joints of low carbon steel using the moving heat source extension model. Using ANSYS ACT extension for the model of the moving, heat source is simulated for the forecast of the distribution of temperature over the welded region during the welding process like gas metal arc welding. Then due to the residual stress induced by the thermal load of the welding, heat source on the joints is analysed and then comparison of the various heat distribution by changing welding parameters is analysed for optimal welding parameters to reduce the stress. The analysis was carried out on transient thermal and transient structural processes to predict the temperature distribution and residual stress respectively.

Reliability analysis of thermal cycle method on the prediction of residual stresses in arc-welded ultra-high strength steels

The large amount of calculation time is one of the major obstacles to the industrial application of numerical welding simulation. The thermal cycle method is a newly developed approach, which can significantly reduce the computational time. The present work aims to systematically analyze the reliability of the thermal cycle method in the prediction of residual stresses in the arc-welded ultra-high strength steels (UHSS). Both numerical simulation and experiments have been performed for estimating and validating its feasibility in this study. The increasingly used ultra-high strength structural steel S960 in industrial sectors was selected for investigation here. The results indicate that the calculated longitudinal residual stress applying the moving heat source and thermal cycle method is almost the same in and near the weld, while that is quite different mainly in the base metal directly under the weld area for UHSS. The predicted transverse residual stress using the thermal cycle method and moving heat source is significantly different, especially for the transforming UHSS. Although the thermal cycle method can obviously reduce the computing time, the moving heat source gives much better agreement with experimental results than the thermal cycle method in the assessment of welding residual stresses (WRS) overall in UHSS thick plates. Thus, the thermal cycle method is not reliable to predict WRS in thick structures made of UHSS. Furthermore, it is not recommended to use the thermal cycle method in numerical welding simulation for UHSS thin-walled structures.

Transient thermal error modeling of a ball screw feed system

The thermal behaviors of the ball screw feed system significantly affect the machining accuracy of the machine tool, which is widely valued by users and manufacturers. In the current ball screws thermal error models, the moving heat source at nuts is simplified to a fixed heat source to simplify the calculation, which can decrease the model’s prediction accuracy. A novel thermal error modeling method for the ball screw feed system is proposed by this paper based on the FEM. In the proposed method, the moving heat source at the nut is loaded into the model by changing the grid distribution at different time steps. Meanwhile, a series of thermal experiments are carried out to collect the thermodynamic data with the machine tool’s feed drive system operating at a different speed. And then the multi-objective optimization method is introduced to obtain the heat generated by the nuts and the convection coefficient between the air and the screw. The experimental results show that the thermal error of the ball screw feed system is different when the feed system runs in different intervals, even if the temperature rise at measuring points is the same. In the final, experiments under different conditions are carried out, and the proposed model is accurate enough to predict the thermal error of the ball screw feed system.

Preventing Crack in an Aluminum Alloy Complex Structure during Welding Process Based on Numerical Simulation Technology

Aluminum alloy structures are widely used for weight reduction in aviation, shipbuilding, rail vehicles and automotive industries. Fusion welding technology is one of the most important joining methods for lightweight structure assembly due to its advantages such as flexibility in design, high production efficiency, and low cost. However, the local centralized heating during fusion welding inevitably produces residual stress and welding deformation. For actual engineering structures, if the product design is unreasonable or the external restraint is inappropriate, the transient stress or residual stress become a key factor resulting in cracking during the assembly process. In the current study, an effective computational approach was developed based on the MSC Marc software to simulate transient and residual stress fields for complex aluminum alloy structures during the welding process. In the developed computational approach, according to the location and arrangement of welding lines, an instantaneous heat source model was used to replace the traditional moving heat source model, and as a result significanlty improved the calculation efficiency to meet actual engineering needs. The welding stresses, including transient and residual stress, of an A6061 aluminum alloy complex structure were calculated by the developed numerical simulation technology. The simulation results indicated that the cracking was produced by excessive transient stress during welding process. Subsequently, the effect of external restraint intensity on welding stress at the key location was examined numerically. Based on the simulation results, measures to reduce welding stress and cracking risk were put forward based on adjusting the external restraint intensity.