Lukáš Koudela, Václav Kotlan and Ivo Doležel
The paper aims to deal with shape optimization of a novel thermoelastic clutch working on the principle of induction heating. The clutch consists of a driving part, with a…
Abstract
Purpose
The paper aims to deal with shape optimization of a novel thermoelastic clutch working on the principle of induction heating. The clutch consists of a driving part, with a ferromagnetic ring, and a driven part. The driving part rotates in a static field produced by appropriately arranged static permanent magnet. Currents induced in the rotating ferromagnetic ring cause its temperature to rise and increase its internal and external radii. As soon as its external diameter reaches the diameter of head of the driven part, it starts also rotating because of mechanical friction between both parts.
Design/methodology/approach
Presented is the complete mathematical model of the device, taking into account all relevant nonlinearities (saturation curve of the processed steel material and temperature dependences of its physical parameters). The forward solution is realized by the finite element method, and the shape optimization is solved using heuristic algorithms.
Findings
The clutch was found to be fully functional and may be used in applications with limited access into the device.
Research limitations/implications
The coefficient of expansion of material of the driven part must be substantially lower than the same coefficient of the driving part to keep the necessary friction torque. The clutch can be only used in applications where higher temperatures (such as 300°C) are not dangerous to the environment.
Practical implications
The presented model and methodology of its solution may represent a basis for design of devices for transfer of generally mechanical forces and torques.
Originality/value
This paper presents an idea of induction-produced thermoelastic connection of two parts capable of transferring mechanical forces and torques.
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Ivo Doležel, Václav Kotlan, Roman Hamar and David Pánek
This paper aims to present a three-dimensional (3D) model of hybrid laser welding of a steel plate. Before welding, the plate is pre- and/or post-heated by induction to avoid…
Abstract
Purpose
This paper aims to present a three-dimensional (3D) model of hybrid laser welding of a steel plate. Before welding, the plate is pre- and/or post-heated by induction to avoid mechanical stresses in material due to high gradients of temperature. Welding itself is realized by laser beam without welding rod. The model takes into account existence of both solid and liquid phases in the weld.
Design/methodology/approach
Presented is the complete mathematical model of the above heat treatment process, taking into account all relevant nonlinearities (saturation curve of the processed steel material and temperature dependences of its physical parameters). Its numerical solution is realized by the finite element method. Some important results are compared with experimental data.
Findings
In comparison with the former model developed by the authors that did not take into account the phase change, the results are more realistic and exhibit a better accordance with measurements. On the other hand, they strongly depend on sufficiently accurate knowledge of material parameters in both solid and liquid levels (that represent the input data).
Research limitations/implications
The quality of calculated results strongly depends on the material properties and their temperature dependencies. In case of alloys (whose chemical composition may vary in some range), such data are often unavailable and must be estimated on the basis of experiments. Another quantity that has to be calibrated is the time dependence of power delivered by the laser beam, which is due to the production of a plasma cloud above the exposed spot.
Practical implications
The presented model and methodology of its solution may represent a basis for design of the complete technology of laser welding with induction pre-heating and/or post-heating.
Originality/value
Fully 3D model of hybrid laser welding (supplemented with pre- and/or post-heating by magnetic induction) taking into account both solid and liquid phases of welded metal and influence of the plasma cloud is presented.
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David Pánek, Václav Kotlan, Roman Hamar and Ivo Doležel
This paper aims to present a methodology of finding temperature dependencies of selected physical parameters of metals. The method is based on the combination of measurement of…
Abstract
Purpose
This paper aims to present a methodology of finding temperature dependencies of selected physical parameters of metals. The method is based on the combination of measurement of the surface temperature of material during the process of heating and subsequent solution of the inverse problem using multi-parametric optimization.
Design/methodology/approach
The methodology is based on measurements and numerical solution of the forward and inverse problem, taking into account all involved nonlinearities (saturation curve of the processed steel material and temperature dependences of its physical parameters). The inverse problem is solved by a genetic algorithm.
Findings
The suggested methodology was successfully verified on several metal materials whose temperature-dependent parameters are known. The calculated and measured results exhibit a very good accordance (the differences do not exceed about 10 per cent for room and higher temperatures).
Research limitations/implications
At this moment, the methodology successfully works when the temperature dependence of just one material parameter is to be found (which means that the temperature dependencies of other parameters are known). The accuracy of results also depends on the correctness of other input data.
Practical implications
This paper provides a relatively easy possibility of finding the temperature dependencies of thermal conductivity or heat capacity of various alloys.
Originality/value
The paper proposes a methodology of finding the temperature dependence of a given material parameter that is not known in advance (which is of great importance in case of alloys).
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Václav Kotlan, Roman Hamar, Ivan Alexandrovich Smolyanov and Ivo Doležel
The paper aims to describe the modeling of the induction-assisted laser welding process taking into account the keyhole effect and phase changes in the material.
Abstract
Purpose
The paper aims to describe the modeling of the induction-assisted laser welding process taking into account the keyhole effect and phase changes in the material.
Design/methodology/approach
A sophisticated mathematical model of the above heat treatment process is presented, taking into account the above phenomena and all available nonlinearities of the material. Its numerical solution is carried out using the finite element method incorporating algorithms for the deformation of geometry and solution of the flow field.
Findings
Unlike various simplified models solved in the past, this approach incorporating a sophisticated model of heat transfer and flow of melt is able to reach a very accurate solution, differing only by a small error (not more than 8 per cent) from the experiment.
Research limitations/implications
The presented model does not consider several subtle phenomena related to the evaporation of metal after irradiation of the material by a laser beam. In fact, at the heated spot, all three phases of the material coexist. The evaporated metal forms a capillary leak off and forms a cloud above the spot of irradiation. Due to the absorption of laser power in this cloud, the process of heating decelerates, which leads to a decrease in the process efficiency.
Practical implications
The presented model and methodology of its solution may represent a basis for design of the process of laser welding.
Originality/value
The main value is the proposal of numerical model for solution a complex multiphysical model with respecting several physical phenomena whose results are available in a short time and still with a good agreement with the experimental verification.
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Václav Kotlan, Roman Hamar, Lenka Šroubová and Ivo Doležel
A model of hybrid fillet welding is built and solved. No additional material (welding rod, etc.) is used. Heating of the welded parts is realized by laser beam with induction…
Abstract
Purpose
A model of hybrid fillet welding is built and solved. No additional material (welding rod, etc.) is used. Heating of the welded parts is realized by laser beam with induction preheating and/or postheating. The purpose of these operations is to reduce the temperature gradient in welded parts in the course of both heating and cooling, which reduces the resultant hardness of the weld and its neighborhood and also reduces undesirable internal mechanical strains and stresses in material.
Design/methodology/approach
The complete mathematical model of the combined welding process is presented, taking into account all relevant nonlinearities. The model is then solved numerically by the finite element method. The methodology is illustrated with an example, the results of which are compared with experiment.
Findings
The proposed model provided satisfactory results even when some subtle phenomena were not taken into account (flow of melt in the pool after irradiation of the laser beam driven by the buoyancy and gravitational forces and evaporation of molten metal and influence of plasma cloud above the irradiated spot).
Research limitations/implications
Accuracy of the results depends on the accuracy of physical parameters of materials entering the model and their temperature dependencies. These quantities are functions of chemical composition of the materials used, and may more or less differ from the values delivered by manufacturers. Also, the above subtle physical phenomena exhibit stochastic character and their modeling may be accompanied by non-negligible uncertainties.
Practical implications
The presented model and methodology of its solution may represent a basis for design of welding processes in various branches of industry.
Originality/value
The model of a complex multiphysics problem (induction-assisted laser welding) provides reasonable results confirmed by experiments.
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Ivan Alexandrovich Smolyanov, Václav Kotlan and Ivo Doležel
This paper aims to propose a number of approaches to reduce the temperature gradient of titanium billets in the heat treatment process.
Abstract
Purpose
This paper aims to propose a number of approaches to reduce the temperature gradient of titanium billets in the heat treatment process.
Design/methodology/approach
Modeling physical processes in the induction unit is calculated by the finite element method. Required power was calculated based on the fact that all the induced power is allocated in a certain layer and there are loss flows and heating flows. Also, an opportunity is offered to reduce temperature difference using numerical optimization, control system based on proportional-integral regulator and ballast blank.
Findings
The asymmetry of the magnetic field at the ends of the inductor significantly affects the temperature uniformity along the length of the workpiece. Increasing the length of the workpiece by adding ballast blanks reduces the temperature drop. Also, increasing the non-magnetic gap in some cases it is possible to improve the quality of through heating.
Research limitations/implications
The results of this study are verified only for a number of titanium alloys. Therefore, this knowledge is appropriate to apply for this type of materials. In future studies, it is possible to expand the possibilities of the considered approaches for other types of materials.
Practical implications
Part of the study will be used to industrial plant for purpose of heat treatment of titanium alloys workpiece. Especially, control system will be basically made based on the model.
Originality/value
A novel methodology of induction heating of titanium alloy Ti6Al4V in the form of cylindrical billets is presented that simplifies the process and improves temperature uniformity along the radius and length of the billet by optimizing the shape of the inductor and selecting suitable power modes.
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Iveta Petrasova, Václav Kotlan, Lenka Šroubová, Pavel Karban and Ivo Doležel
The purpose of this paper is to present the calibration of a laser welding model suitable for solving problems with input data that are either unknown or known only approximately.
Abstract
Purpose
The purpose of this paper is to present the calibration of a laser welding model suitable for solving problems with input data that are either unknown or known only approximately.
Design/methodology/approach
The calibration starts from the measured temperature profile of the weld, and the aim is to get a similar profile by the solution of the model. The corresponding procedure is based on replacing the material characteristics that are known only approximately by polynomial or rational functions whose coefficients are determined using a suitable optimization process. The algorithm is supplemented with a simplified model of the keyhole shape.
Findings
The big advantage of the proposed approach is the velocity of solution of the problem and low consumption of the sources (hardware and software). In comparison with solving the full model of laser welding, the methodology provides results of a still acceptable accuracy by several orders faster. On the other hand, the results also depend on the strategy of selecting the points at which the temperature is verified and on “manual” setting of the deformation parameters.
Research limitations/implications
Application of the methodology is conditioned by several experiments with the used material (without experiment it is impossible to carry out the calibration and set the shape of the keyhole), while the full model allows it. On the other hand, the full model is not able to predict the errors in the case when some input data is unknown or known only approximately and the results have to be also confirmed experimentally.
Practical implications
The presented methodology may be used for determining unknown material characteristics and faster modelling of laser welding.
Originality/value
This paper proposes a novel methodology for evaluation of quality of laser welds in cases of unknown or partially unknown material parameters and substantial acceleration (by 2-3 orders) of the numerical solution of the model of laser welding.
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Václav Kotlan, Roman Hamar, David Pánek and Ivo Doležel
The purpose of this paper is to propose and analyze a combined heat treatment of metal materials, consisting in classic induction pre-heating and/or post-heating and full heating…
Abstract
Purpose
The purpose of this paper is to propose and analyze a combined heat treatment of metal materials, consisting in classic induction pre-heating and/or post-heating and full heating by laser beam. This technology is prospective for some kinds of surface hardening and welding because its application leads to lowering of temperature gradients at the heated spots, which substantially reduces local residual mechanical strains and stresses.
Design/methodology/approach
The task was solved like the 3D hard-coupled problem for electromagnetic field, temperature field and field of displacements. It was solved numerically using the techniques based on the FEM. For solution was used commercial software COMSOL Multiphysics, some parts were solved using own scripts in the software Agros.
Findings
In the paper are shown results of the numerical solution and experimental measured data. Due the work the authors found that the influence of the pre-heating and post-heating really leads to limit the temperature gradients and from other measurements is clear that also to improving of the welding.
Originality/value
The paper presents fully 3D nonlinear and nonstationary mathematical model of hybrid laser welding, its numerical solution experimental verification.