The improvement of bolted joints model via finite element model updating method

Efficient schemes to represent mathematical model of thin-sheet metal structures jointed by bolted joints for accurately predict the structure dynamic behaviour has been a significant unresolved issue in structural dynamics community. The biggest challenge is to efficiently incorporate the joints local deformation effects on the developed mathematical model via finite element (FE) method. Generally, the joints local deformation typically exerts on the joints mating area. To solve this issue, this paper proposes efficient schemes to represent mathematical model of thin-sheet metal structures jointed by bolted joints with application to accurately calculate the structure dynamic behaviour using FE model updating method. The initial FE model of the assembled structure was developed by employed Fastener Connector (CFAST) in MSC NASTRAN software to represent the bolted joints while, the inclusion of the local deformation effects at the bolted joints mating area was represented by contact elements. Then, the responses obtained from the FE model was evaluated by weight up with experimental data. FE model updating (FEMU) method then was utilised for minimising prediction discrepancies originated from the initial FE model based on the experimental data. The proposed scheme shows the accuracy of the initial prediction was improved from 25.03 % to 14.65 % while the accuracy of the predicted mode shapes via modal assurance criterion (MAC) analysis were above 0.8. Therefore, the findings offer useful schemes for improving the quality of predicted dynamic behaviour, particularly in the thin-sheet metal jointed structure and the developed model can be used with confident for any subsequence dynamic analyses.

Characterisation of the plane anisotropy and its effect on interstitial free steel thin sheet metal forming simulation

The main purpose of this paper is to study the orthotropic plastic behaviour of the cold-rolled interstitial free steel HC260Y when it is submitted to various loading directions under monotonic tests. The experimental database included tensile tests carried out on specimens (in the as-received condition and after undergoing an annealing heat treatment) cut in different orientations according to the rolling direction. A model was proposed, depending on a plasticity criterion, a hardening law and an evolution law, which takes into account the anisotropy of the material. To validate the proposed identification strategy, a comparison with the experimental results of the planar tension tests, carried out on specimens cut parallel to the rolling direction, was considered. The obtained results allowed the prediction of the behaviour of this material when it is subjected to other solicitations whether simple or compound.

МОДЕЛЮВАННЯ ПРОЦЕСІВ ВИРУБКИ-ПРОБИВКИ ПЕРЕДАВАЛЬНИМИ СЕРЕДОВИЩАМИ

During improvement of the quality of products and reducing its cost, sheet metal stamping production, being the basis for the aerospace industry, should more intensively introduce modern production technologies, especially design. There are a large number of factors influencing the stamping process (especially parts with complex geometry), more comprehensive consideration of which would allow to optimize such processes, thereby reducing the manufacturing cost and improving the quality. Currently the processes of forming and separation of complex parts by of an elastic pad are of interest from the point of view of optimization and the final determination of the nature of the behavior of the material. This includes the refinement of such parameters as the maximum permissible thinning, the strength of the die. Clarification of these and other parameters will significantly reduce energy required. Determination of these and other parameters of sheet metal stamping is possible due to application of the modern analysis methods. For numerical studies in the sheet stamping production, the variational method or FEM is the most suitable. Computer modeling makes it possible to investigate the behavior of the material, the kinematics of the workpiece movement during forming process, select the correct loading scheme for the workpiece, and also makes it possible to consider several options for the location of the workpiece in the die, which is very important for stamping thin sheet metal blanks. It provides a significant reduction of the time and costs for carrying out natural experiments, and decrease of technological preproduction preparation of sheet metal stamping. The development of a mathematical model based on the FEM makes it possible to determine not only the required parameters of the process, but also to consider the forming process during its certain stages, to determine the stress-strain state, indicating at the same time the problem zones of excessive thinning, loss of stability, the need to apply a die with a back pressure for cutting of thin sheet metal blanks. It allows to evaluate the quality of a ready product according to the calculated parameters, to use the results obtained for the design of elastic pad

IMPROVING OF ROUND HOLE CUTTING PROCESS IN THE SHEET METAL

Improving existing technological processes is an important stage in the development of all industries. As a consequence, this article is devoted to the analysis of the process of flanging round holes in sheet steel. The existing typical technological process, with a detailed analysis, gives grounds for substantiating the idea of an innovative solution. Changing the sequence of the traditional flanging method will ensure high productivity and material savings. Of the many promising methods of metal forming by pressure, which include flanging of round holes, two are given for comparison: the traditional one and the improved one. The methodology of the traditional direction, worked out over the years, provides for a clear sequence of the technological process using tools for marking, centering, making a hole and using tools for flanging. The final, after the previous operations of marking the centers of the holes, punching, making holes, is the flanging stage. The tapered punch (usually a metal rod) prevents the small-diameter hole from deviating from the marking lines and ensures the centering of the punch-blank-matrix system. Following the above steps, the conventional workflow involves positioning the workpiece over the surface of the punch hole to guide the tool in the desired direction. For the manufacture of a flanged hole, a special sharpening of the working part of the punch is performed so that the diameter of the central part of the tool is equal to the difference between the diameters of the guide hole of the matrix and the inner diameter of the workpiece of the part. To avoid further displacement of the hole, the workpiece is centered by placing it on the die and the next operation is supposed to lower the punch to flang the hole. As a result, the article touches on the topic, taking into account the widespread use of thin sheet metal, including in the agricultural sector, the feasibility of using an innovative idea to improve the technological process associated with the processing of sheet material, namely thin metal sheets. It is advisable to note that, for example, a material is considered that is characterized by its versatility, namely steel. Despite numerous sources devoted to the study of improving the flanging technological process, there are a number of issues, in particular, the extension of this direction to numerous varieties of metal materials that have surfaces with and without coating, various thicknesses within thin-walled rolled products. The most significant result is the improved technological process of flanging will find application in the system of efficient servicing of agricultural machinery.

SUSPENSION LARGE SPAN ROOFS STRUCTURES IN RUSSIA

Сonsidered are large-span structures with suspended roof structures with a span of up to 200 m, erected in Russia over the past 40 years. Among them, there are differen types of structures for covering sports facilities: cablestayed systems, structures of the "bicycle wheel" type, combined systems, thin-sheet metal hanging shells, etc. The main technical characteristics of structures, principles of operation of structures, their advantages and disadvantages are given. The development of technologies in recent decades has determined the emergence of new forms, materials, design and construction methods. Unique large-span structures have an increased level of responsibility; their collapse can lead to severe economic and social consequences. In this regard, it is relevant to analyze the experience in the design and construction of large-span suspended structures.

Media-based forming of micro-flow channels into thin sheet metal by electromagnetically driven tools

The use of high-speed forming technologies can contribute to satisfying current social and political demands on production technology such as sustainability and climate protection in manufacturing. These technologies have a very high potential for shaping complex, sharp-edged parts and constitute a key means of reducing a component’s weight. One exemplary high-speed forming technology is electromagnetic forming. It uses the energy density of pulsed magnetic fields to impose forces on electrically conductive materials, which leads to plastic deformation when reaching the yield stress of the material. However, for very thin sheet materials this effect can result in an uncontrolled deformation of the work piece. In order to overcome this effect, electromagnetically driven tools the use of can be appropriate. An additional benefit is that this process is no longer restricted to electrically highly conductive work piece materials. This paper describes a media-based process using electromagnetically driven tools to form micro-flow channels, which are often used in bipolar plates, into thin sheet metals. The principles are explained and first results are shown.

Numerical and Experimental Investigation of the Impact of the Electromagnetic Properties of the Die Materials in Electromagnetic Forming of Thin Sheet Metal

In electromagnetic forming of thin sheet metal, the die is located within the effective range of the electromagnetic wave. Correspondingly, a current is induced not only in the sheet metal, but also in the die. Like the current in the workpiece, also the current in the die interacts with the electromagnetic wave, resulting in Lorentz forces and changes of the electromagnetic field. With the aim to study the influence of different electromagnetic die properties in terms of specific electric resistance and relative magnetic permeability, electromagnetic simulations were carried out. A change in the resulting forming forces in the sheet metals was determined. To confirm the simulation results, electromagnetic forming and embossing tests were carried out with the corresponding die materials. The results from simulation and experiment were in good agreement.