Three-dimensional Transient Temperature Field Research Articles

Numerical simulation of the thermal behaviors for two typical damping alloys during selective laser melting

In this work, the three-dimensional transient temperature field model of two typical damping alloys (i.e., AZ31 Mg alloy and Mn-Cu alloy) were developed during selective laser melting (SLM) using ANSYS finite element analysis software, considering thermophysical properties and phase transformation latent heat of the materials. The simulated molten pool width values of the Mn-Cu alloy show a 6 % error with the experimental SLMed Mn-Cu sample, verifying that the developed model agrees well with the experimental results. Based on the developed numerical model, the temperature distribution, temperature gradients, and cooling rates of the two alloys were investigated during horizontal deposition and vertical deposition of SLM at different scanning speeds (300–700 mm/s). The results showed that the simulated peak temperatures of the AZ31 Mg alloy during the SLM process show a small fluctuation and are well below its boiling point (1107 °C) at the scanning speed of 500–700 mm/s. The temperature gradient increases from 8.5 × 106 °C/m to 20.2 × 106 °C/m with the laser scanning speed. The cooling rate increases from 1.7 × 106 °C/s to 4.1 × 106 °C/s, then reaches stable at 500–600 mm/s. As for Mn-Cu alloy, the cooling rate fluctuates between 7.5 and 8.8 × 106 °C/s during the SLM process at a scanning speed of 300–700 mm/s. By comparing the thermal behavior of the two alloys, the peak temperatures, temperature gradients, and cooling rate of both alloys are closely associated with their thermophysical properties and the laser energy input.

Hygrothermal dynamic behavior of fiber metal laminated structure under dual-ellipse distribution heat source

Refined plate theory could account for parabolic variation of transverse shear stress through the thickness, and satisfy the zero traction boundary conditions on the top and bottom surfaces of the plate without introducing shear correction factor, of which all displacement variables can be depicted in functions of shear and bending components. Based on three-dimensional transient thermal conduction theory and the refined plate theory, an analytical solution of fiber metal laminated (FML) plate under hygrothermal environment is presented. In present work, distinct from other literatures, the separate variable method and Newton-Cotes method is applied to solve the three-dimensional transient temperature field (subjected to moving dual-ellipse distribution laser heat source) firstly. Secondly, the constitutive equations and geometrical equations are derived. Subsequently, the governing equations in hygrothermal environment are obtained. Finally, the Newmark method and Galerkin method are used to solve the governing equations of which in terms of displacement functions. The results show that fiber orientation affects the bending stiffness, the selection of (45°/ 0°) fiber orientation is more resistance to deformation and normal stress, and bending part is more sensitive to shear factor between layers.

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.

Optimal Temperature Rise Control for a Large-Scale Vertical Quench Furnace System

An optimal switching heating control strategy based on minimum margin (OS-MM) is proposed for high efficiency, low energy consumption, and high-uniformity fine control in a large-scale vertical quench furnace. This work was stimulated by the need for solving the contradiction between the heating rate and temperature overshoot to achieve a rapid rise in temperature with no overshoot. Based on a three-dimensional (3-D) transient temperature field model of the quenching furnace, the temperature field optimization control problem is transformed into a boundary optimization control problem of rapid heating, whereby it is rigorously proved that the fastest rise in temperature is attained by the full-power heating, which satisfies the bang-bang characteristics. The key parameter that determines the overshoot in the full-power heating mode is introduced and defined as the minimum margin in the temperature-rising process. The analytical expression for solving the minimum margin is calculated by the eigenfunction expansion method and using the strong metal thermal inertia of the internal temperature field, the OS-MM method is designed to stop the heating in advance at a calculated switching point to optimize full-power heating, thus conserving energy by reducing its consumption. The results of simulation and industrial experiments show that this strategy greatly shortens the temperature adjusting time, significantly reduces energy consumption, and effectively improves the control performance indices, such as overshoot and static error in the temperature holding period of the thermal treatment process, as compared to the existing heating methods.

Dynamics and temperature field analysis of piezoelectric driven three-stator multi-degree-of-freedom ultrasonic motor

Since the temperature has a great effect on the service behavior of the ultrasonic motor, high temperature will affect its mechanical characteristics and service life. This article is on a model of a piezoelectric driven three-stator multi-degree-of-freedom ultrasonic motor. Firstly, the motion mechanism is analyzed, and the main causes of temperature rise are determined to be friction heat generation and vibration heat generation. Then, the theoretical model of temperature rise is built, and the temperature rise characteristics of the ultrasonic motor are simulated and analyzed by establishing a three-dimensional transient temperature field model. Finally, it is verified by temperature test experiment. The results show that the simulation analyses are consistent with the experimental results, and this analysis can correctly reflect the temperature rise characteristics of the motor. It provides a reference for further seeking the effect of the body temperature rise on the service behavior of the ultrasonic motor and improving the operating characteristics of the ultrasonic motor.

Analysis and Optimization on Non-uniformity of Temperature Distribution in Hydrophobic Cycloaliphatic Epoxy Resin Insulators during the Curing Process

Hydrophobic cycloaliphatic epoxy resin (HCEP) insulators are a new generation of outdoor transmission line insulators with good application prospects. However, the HCEP has obvious curing internal stress due to the uneven internal temperature distribution. In this paper, the curing reaction of HCEP mixture is analyzed and a three-dimensional transient temperature field model of HCEP insulator is established. The internal temperature field of HCEP insulator during curing is analyzed for the first time. The results show that the curing reaction of HCEP mixture conforms to autocatalytic reaction. The structure of umbrella skirt causes the uneven temperature distribution inside HCEP insulator. Based on a surrogate model, it is found that thermal conductivity has a great influence on axial temperature distribution, while curing temperature plays a leading role in curing degree and temperature overshoot. The optimal curing temperature is found according to Pareto front. This paper is beneficial for the theoretical analysis and engineering guidance for manufacture of HCEP insulators.

Research on water jet-guided laser micro-hole machining of 6061 aluminum alloy

With the rapid development of the information age, electronic components are developing toward miniaturization, which makes the manufacturing of chips more and more difficult. Water jet-guided laser processing technology (WJGL) is a composite processing technology that combines pulsed laser and water jet, which can ensure the accuracy and efficiency of processing while small size parts machining. This paper is based on the “element birth and death” technique in the finite element method and the three-dimensional transient temperature field and subsequent material removal model of 6061 aluminum alloy are established. The effects of laser average power, pulse repetition frequency, and pulse action time on the transient thermal distribution, aperture, taper, and other forming qualities with the two technologies of fixed-point drilling and spiral drilling, respectively, are studied. Combining the experimental process, the general rule of morphology change of the micro-hole is obtained. The results show that WJGL of micro-hole is based on the combined effect of thermal ablation and real-time cooling. Spiral drilling can maintain a better hole shape but fixed-point drilling can achieve a smaller hole taper. With the increase of laser power, the hole taper increases, reaching saturation at 8 W. The repetition frequency is between 50 and 70 kHz to obtain better hole morphology while maintaining better processing efficiency, and the minimum hole taper is 8.21°.

Research on the Mechanism of Micro-Water Jet-Guided Laser Precision Drilling in Metal Sheet.

As the microporous structure has been widely used in the field of precision machining, at the same time, the requirements for the quality of microporous machining are continuously increasing. Water jet-guide laser processing technology (WJGL) has been gradually applied for its high machining precision. However, there are a few researches on the heat conduction process of WJGL processing metal materials. Therefore, it is of great significance to study the transient thermal effect of metal materials and the mechanism of material removal to improve the processing quality. In order to explore the heat conduction model of WJGL processing metal materials, this paper is based on the “element birth and death” technique in the finite element method, and the three-dimensional transient temperature field of four typical metal materials (titanium alloy, stainless steel, aluminum alloy, copper) and material removal model are established. Under this model, the removal mechanism of different metal materials and the influence of different process parameters on the temperature field distribution of the material are studied, and the influence of fixed-position drilling and helix drilling on the microporous morphology is compared. The results show that copper and aluminum alloys can obtain a larger depth-to-diameter ratio and a smaller hole taper. Titanium alloy and stainless steel have better hole roundness, lower hole edge temperature, and smaller thermal deformation. Hole roundness error and hole taper decrease with the increase of laser power. The roundness error of each material is reduced to within 10 μm when the laser power is 10 W, and the average hole taper is 8.73°.

Research on Model Slice and Forming Method of Thin-walled Parts

According to the structural characteristics of thin-walled parts, a model slicing method is proposed, and its mathematical process is established. The three-dimensional transient temperature field in the process of synchronous powder feeding laser cladding is studied and verified by numerical simulation method, and the thin-walled parts formed by later experimental processing are processed by the results of numerical simulation. Using the simulation results of temperature field as the basis for optimizing the processing parameters, the forming path of thin-walled parts is programmed and optimized, and the experimental verification shows the reliability of this method.

Numerical simulation of water jet–guided laser micromachining of CFRP

Carbon fiber-reinforced plastics (CFRP) composites are increasingly used in the aerospace and automotive industries due to their excellent properties, which require higher processing accuracy to ensure their performance. Water jet-guided laser processing technology is a modern processing method, which can effectively reduce the thermal damage caused by laser processing. In order to understand the transient thermal effect of water jet-guided laser processing on CFRP materials and its removal mechanism and the influence of the duty cycle of laser pulse on the temperature field distribution of materials, this paper is based on the “element birth and death” technique in the finite element method, the three-dimensional transient temperature field of heterogeneous fiber matrix and the subsequent material removal model are established. The results show that the CFRP composites processed by water jet-guided laser processing can obtain better processing results over traditional laser processing. Adjusting the duty cycle of laser pulses can significantly affects the shape and temperature distribution of the composites after drilling.

Online Determining Heat Transfer Coefficient for Monitoring Transient Thermal Stresses

This paper proposes an effective method for determining thermal stresses in structural elements with a three-dimensional transient temperature field. This is the situation in the case of pressure elements of complex shapes. When the thermal stresses are determined by the finite element method (FEM), the temperature of the fluid and the heat transfer coefficient on the internal surface must be known. Both values are very difficult to determine under industrial conditions. In this paper, an inverse space marching method was proposed for the determination of the heat transfer coefficient on the active surface of the thick-walled plate. The temperature and heat flux on the exposed surface were obtained by measuring the unsteady temperature in a small region on the insulated external surface of a pressure component that is easily accessible. Three different procedures for the determination of the heat transfer coefficient on the water-spray surface were presented, with the division of the plate into three or four finite volumes in the normal direction to the plate surface. Calculation and experimental tests were carried out in order to validate the method. The results of the measurements and calculations agreed very well. The computer calculation time is short, so the technique can be used for online stress determination. The proposed method can be applied to monitor thermal stresses in the components of the power unit in thermal power plants, both conventional and nuclear.

Numerical Simulation of Temperature Field of 12crni2 by Laser Melting Deposition

Based on the heat transfer theory, and the fact that thermal physical parameters, latent heat of phase change and heat transfer coefficient which vary with temperature is taken into considered, a three-dimensional transient temperature field model of 12CrNi2 by Laser Melting Deposition (LMD) is established by using the parametric design language of ANSYS. Optimum process parameters were determined by single-layer and single-track experiments of LMD. Microstructure observation by optical microscope shows that the width of heat affected zone increased with the increase of laser power and decreased with the increase of printing speed. The top of the deposited layer is mainly composed of equiaxed dendrites, and the middle and bottom of the deposited layer are columnar crystals with epitaxial growth characteristics. At the same time, the accuracy and reliability of temperature field model are verified by comparing the morphology of molten pool. The simulation results show that in the process of LMD, the peak temperature of molten pool increases with the increase of layers; the peak temperature of the node increases with the increase of laser power and the decrease of printing speed. The research results in this paper would be reference for LMD of 12CrNi2 alloy steel.

Numerical investigation of Transient Temperature Field on the Selective Laser Melting process with Al6063

The finite element simulation of the selective laser melting process with Al6063 metal powder was carried out by using ABAQUS. The loading of the laser Gaussian moving heat source is realized, and a model of the three-dimensional transient temperature field is established. The effects of scanning speed and scanning pitch on temperature distribution and temperature changes on different scanning channels were investigated. The simulation results show that due to the heat accumulation effect and heat conduction, the previous scan will have effect on the surrounding powder, which results the rise of temperature. Different scanning speed and the scanning pitch have influence on the temperature distribution. As the scanning speed increases, the temperature gradually decreases, and the increase in the scanning pitch also lead to lower temperature of the powder layer.

Thermo-Mechanical Coupling Analyses for Al Alloy Brake Discs with Al2O3-SiC(3D)/Al Alloy Composite Wear-Resisting Surface Layer for High-Speed Trains.

In the present work, a theoretical model of three-dimensional (3D) transient temperature field for Al alloy brake discs with Al2O3-SiC(3D)/Al alloy wear-resisting surface layer was established. 3D transient thermo-stress coupling finite element (FE) and computational fluid dynamic (CFD) models of the brake discs was presented. The variation regularities of transient temperature and internal temperature gradient of the brake discs under different emergency braking conditions were obtained. The effects of initial braking velocity (IBV) and thickness of Al2O3-SiC(3D)/Al alloy composite wear-resisting layer on the maximum friction temperature evolution of the disc were discussed. The results indicated the lower temperature and thermal stress distributed uniformly on the wear-resisting surface, which was dominated by high conductivity and cooling ability of the Al alloy brake disc. The maximum friction temperature was not obviously affected by the thickness of the wear-resisting layer. The maximum friction temperature of the brake discs increased with the increase of the IBV, the maximum friction temperature and thermal stress of the brake discs is about 517 °C and 192 MPa at IBV = 97 m/s considering air cooling, respectively. The lower thermal stress and fewer thermal cracks are produced during the braking process, which relatively decrease the damage. The friction behavior of the tribo-couple predicted using FE method correlated well with the experimental results obtained by sub-scale testing.

Temperature of a sliding contact between wire rope and friction lining

Abstract This paper studies the three-dimensional (3d) transient temperature field of a friction lining and a sliding wire rope. An efficient multigrid solver is developed. The multigrid code is validated by a comparison with a well-known analytical solution. The influence of several parameters on the temperature rise is investigated. Sliding velocity has a great influence: the larger the velocity, the larger the average temperature rise and the temperature fluctuation at a certain time. Two approximate solutions characterized by simple heat flux forms are proposed, using only a limited computational effort. A comparison of the temperature rise by the original and the two simplified schemes is performed. It is found that the heat flux shape influence is limited to the surface temperature and the temperature rise far below the contact surface depends only on the total heat flow.

Three-dimensional transient thermodynamic analysis of laser surface treatment for a fiber laminated plate with a coating layer

Based on the method of separation of variables and equivalent temperature method, three-dimensional transient temperature field for a fiber metal laminated (FML) plate with a coating layer (total structure is named as a CFML structure) during laser surface treatment process is firstly obtained. Subsequently, the three-dimensional transient thermodynamic governing equations for the CFML structure under such laser work condition are solved by applying the finite difference method and Newmark method in space domain and time domain, respectively. The aim of this research is to give the analytical solution of three-dimensional transient temperature field for CFML structure under laser surface treatment technology, understand the influence of number of fiber species, laser moving velocity, number of FML layers and selected coating layer’s heat conduction coefficient on the deflection, normal stress, shear stress and vibration frequency of the CFML structure. Besides, it could guide engineers designing the CFML structure to adapt to hostile laser surface treatment environment.

Thermoviscoelastic dynamic response for a rectangular steel plate under laser processing

The thermoviscoelastic dynamic response of a simply supported rectangular steel plate under laser processing is studied in this paper. Three-dimensional transient temperature field of the laser processing thermoviscoelastic rectangular steel plate is solved by the method of separation of variables. Meanwhile, based on von Karman nonlinear strain–displacement relationships and classical thin plate theory, a list of nonlinear dynamic equilibrium equations for a rectangular thermoviscoelastic steel plate are deduced. Then the entire problem is solved by utilizing the Newmark method and the iterative method. Finally, numerical results show that laser moving speed, laser power density and thickness-to-length ratio have a great influence on the thermoviscoelastic response of the rectangular DP980 steel plate.

High-energy laser shock processing for a rectangular HSLA steel plate considering solid-liquid-vapor phase change

Three-dimensional thermodynamic analysis of a high strength and low alloy (HSLA) rectangular steel plate under high-energy laser shock processing is carried out in this paper. Considering the solid-liquid-vapor phase-change process, three-dimensional transient temperature field, mass fraction of liquid phase and vapor phase for the rectangular HSLA steel plate are solved by the method of separation of variables. Meanwhile, the displacement and stress fields are derived by using the state-space method. It could be found that laser shock processing time increases the three-phase temperature a lot. The greater the coordinate x and y are, the larger is the mass fraction of liquid phase. The laser moving speed and length to thickness ratio also have great influences on the displacement and stress fields. Variation of deflection curve across the thickness of plate is no longer smooth from top surface to bottom surface because of high-energy laser shock processing at instantaneous time which could be ignored.

Reconstruction of 3D transient temperature field for fusion welding processes on basis of discrete experimental data

This paper presents an approach to reconstruct the three-dimensional transient temperature field for fusion welding processes as input data for computational weld mechanics. The methodology to solve this inverse heat conduction problem fast and automatically focuses on analytical temperature field models for volumetric heat sources and application of global optimisation. The important issue addressed here is the question which experimental data is needed to guarantee a unique reconstruction of the experimental temperature field. Different computational-experimental test cases are executed to determine the influence of various sets of discrete experimental data on the solvability of the optimisation problem. The application of energy distributions utilised for laser beam welding allows reconstructing the temperature field efficiently. Furthermore, the heat input into the workpiece determined by the simulation contributes to the evaluation of the thermal efficiency of the welding process.

PMMA激光融化三维瞬态温度场数值模拟

PMMA激光融化三维瞬态温度场数值模拟