The present paper aims to develop an effective analytical solution for laser directed energy deposition through powder feeding (LDED-PF). Three heat source models are introduced and compared to ...analytically describe the transient temperature field in the process. These models are known as point (1D) heat source, circular (2D) heat source, and semi-spherical (3D) heat source. For the validation tests, single-track deposition of Ti-5Al-5 V-5Mo-3Cr powder on Ti-6Al-4 V substrate is conducted at different laser powers, scanning speeds, and powder feed rates. The temperature field is validated using the measurement of melt-pool/deposit geometry. In order to improve the model fidelity, the enhanced thermal diffusivity and heat source radius are calibrated in terms of linear functions. It is found that the 2D Gaussian heat source model, which is in agreement with the underlying physics of the process, establishes a better match between the predicted and experimental data. The developed model only needs the basic information from the LDED-PF setup and material thermal properties to predict the thermal history and melt-pool geometry at different processing parameters.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•Parallel-flow four-channel four-fluid heat exchanger is investigated.•Transient temperature field is determined semi-analytically.•Laplace transform and numerical inverse algorithm are ...used.•Semi-analytical solutions are validated by numerical and analytical solutions.
A set of partial differential equations which describes transient behavior of parallel-flow four-channel four-fluid heat exchangers is solved using Laplace transform and numerical inverse algorithm. A case of a temperature disturbance in one channel and the homogeneous initial conditions is studied. To validate the semi-analytical solutions, they are compared with pure numerical and analytical solutions. The agreement is very good.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•An improved version of algorithm for thermal analysis of pressure components.•Experimental validation of the presented algorithm.•The influence of accidental measurement error on the accuracy of the ...solution.•Transient thermal analysis of thick-walled pressure component.
The article aims to determine and experimentally validate the transient temperature fields in a cylindrical component. The applied in-house algorithm, which is based on the inverse heat conduction method, is solved by means of the finite volume method. On the basis of temperature measurements on the outer surface of the element, the algorithm enables thermomechanical analysis of the element. In order to perform experimental validation of the algorithm, the existing laboratory set-up was modernized. During the experiment, the thick-walled steam manifold was heated up rapidly with dry saturated steam. To reconstruct the unsteady temperature distribution within the element, 19 thermocouples were used and 3 thermocouples were inserted inside the wall of the element. The 3 thermocouple locations correspond with nodal positions in the numerical algorithm, thus allowingvalidation of the unstable temperature fields. The analysis of the time-step selection and of the influence of the accidental temperature measurement error on the accuracy of the solution have also been analyzed. Moreover, the algorithm has been validated based on the analytical method. The algorithm does not require knowledge of the boundary conditions on the element’s barely accessible internal surface – a highly valued feature in industrial applications.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Large three-dimensional metallic parts can be printed layer-by-layer using gas metal arc directed energy deposition (GMA-DED) process at a high deposition rate and with little or no material wastage. ...Fast responsive real-time monitoring of GMA-DED process signatures and their transient variations is required for printing of dimensionally accurate and structurally sound parts. A systematic experimental investigation is presented here on multi-layer GMA-DED with two different scanning strategies using a high strength low alloy (HSLA) filler wire. The dynamic metal transfer, melt pool temperature field and its longitudinal cross-section, and arc voltage and current are monitored synchronously. The transient arc heat input and the melt pool solidification cooling rate are estimated from the monitored signals. The layer-wise variations of the melt pool dimension, surface temperature profile, thermal cycles, and solidification cooling rate are examined for different scanning strategies. It is comprehended that the part defects can be minimized, and the mass production of zero-defect parts can be achieved in GMA-DED process with synchronized monitoring and assessment of the real-time process signatures.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The mechanism of laser-induced backside wet etching (LIBWE) of sapphire substrate with CuSO4 solution is considered as a two-step process. First, it deposits the layer from copper sulfate solution on ...the backside of sapphire substrate by 1064nm laser irradiation. Then it is followed by the absorption of deposited layer to laser irradiation, resulting in the etching of the sapphire. Therefore, the material removal of LIBWE is based on laser interaction with multilayer materials (sapphire substrate--deposition layer--liquid solution). A three-dimensional thermal model is established to simulate the material removal during the LIBWE process by considering the material data variations of temperature, enthalpy change and latent heat fusion. The model can predict the groove shape influenced by the laser processing parameters (laser fluence, scanning velocity and scanning pass). The simulation results indicate that the groove depth increases with the decreasing of scanning velocity, the increasing of laser fluence and the scanning pass. The groove width is comparable with the focal beam diameter. Some peaks and valleys occur at the bottom of the groove. A comparison between the modeling and experiment indicates that the groove shape in simulation agrees well with the experiment data at laser pulse energy of 4.3mJ/pulse, scanning velocity of 15mm/s and the scanning pass of 4. i.e, the present physical model is effective and feasible.
•Cuprous oxide/copper oxides species are deposited on the rear sapphire surface.•Material removal mechanism is based on laser interaction with multilayer materials.•Model is built up by considering the material data variations.•Model predicts the groove shape influenced by the processing parameters.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The temperature field caused by solar radiation can seriously affect the electromagnetic (EM) performances of large-aperture and high-frequency radio telescopes, and achieving the EM performance ...improvements under solar radiation is of great importance. In this study, combining temperature simulation and measurement, a fast estimation method of the temperature field is presented. First, a temperature database based on transient temperature field simulation is constructed in advance, and by utilising the telescope's axisymmetric structure, the dimension of the database can be greatly reduced. Then, a small number of temperature sensors are installed and the real-time measured data are applied to correct the simulation temperature field extracted from the above temperature database by the table look-up method, which can ensure the temperature field estimation speed. Thus, based on the real-time estimated temperature field and the telescope's finite element model, thermal deformations can be calculated in real-time and used for deformation compensation. A 7.3 m reflector antenna with 21 temperature sensors is adopted to verify the proposed strategy, and the results show the effectiveness and feasibility of the strategy. This study can provide helpful guidance for the real-time compensation of thermal deformations derived from large axisymmetric telescopes.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The braking characteristics of an elevator block brake greatly affect its safety. However, the braking capacity cannot be directly tested owing to the elevator’s structure and mode of operation. In ...this study, a new method for analyzing emergency braking characteristics based on thermal–structural coupling is proposed. A 3D model of an elevator block brake was built using SolidWorks software and then, imported into Workbench finite element analysis software to analyze the brake characteristics based on thermal–structural coupling. Combined with three elevator speeds, the braking process was simulated using direct coupling to analyze the change law of the transient temperature and stress fields of the brake wheel and to determine the coupling relationship between the temperature and stress fields. Moreover, in accordance with the finite element analysis results as well as the form and cause of fatigue failure of the brake wheel, the thermal fatigue life of the brake wheel was predicted based on the Manson–Coffin equation. The simulation results show that the surface temperature of the brake wheel first increases and then, decreases during the braking process. Furthermore, when the braking pressure is 1.7 MPa, the service life of the brake wheel is 147, 142, and 99 times, corresponding to the rated speeds of 1.5, 2, and 2.5 m/s, respectively. The simulation results confirm the theoretical foundation formulated in this study and provide a reference for optimizing the structural parameters and braking performance of elevator block brakes.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In the selective laser melting process, metal powder melted by the laser heat source generates large instantaneous energy, resulting in transient high temperature and complex stress distribution. ...Different temperature gradients and anisotropy finally determine the microstructure after melting and affect the build quality and mechanical properties as a result. It is important to monitor and investigate the temperature and stress distribution evolution. Due to the difficulties in online monitoring, finite element methods (FEM) are used to simulate and predict the building process in real time. In this paper, a thermo-mechanical coupled FEM model is developed to predict the thermal behaviors of the melt pool by using Gaussian moving heat source. The model could simulate the shapes of the melt pool, distributions of temperature and stress under different process parameters through FEM. The influences of scanning speed, laser power, and spot diameter on the distribution of the melt pool temperature and stress are investigated in the SLM process of Al6063, which is widely applied in aerospace, transportation, construction and other fields due to its good corrosion resistance, sufficient strength and excellent process performance. Based on transient analysis, the relationships are identified among these process parameters and the melt pool morphology, distribution of temperature and thermal stress. It is shown that the maximum temperature at the center point of the scanning tracks will gradually increase with the increment of laser power under the effect of thermal accumulation and heat conduction, as the preceded scanning will preheat the subsequent scanning tracks. It is recommended that the parameters with optimized laser power (
= 175-200 W), scanning speed (
= 200-300 mm/s) and spot diameter (
= 0.1-0.15 mm) of aluminum alloy powder can produce a high building quality of the SLM parts under the pre-set conditions.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The presented paper deals with the problems associated with laser machining of metal materials. Specifically, it solves the question of structural changes that occur as a result of the transfer of ...heat to the material. Experimental machining of selected technical materials was carried out, and on the basis of the hardness measurement near the cutting point, the heat-affected zone was evaluated after passing the laser beam. To confirm the detection of the affected zone width the models of transient temperature field were arranged, to represent the distribution of temperature in the vicinity of the cutting edge.
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