Papers by Author: Branko Grizelj

Abstract: In the paper, firstly on the basis of different theoretical methods and by means of different strain determining criteria the analytic modeling of backward extrusion process was done. Analyzed analytical models are derived directly from the mathematical description of the backward extrusion physical phenomena and their mathematical description has been presented. Afterwards, numerical modeling of strain energy by means of ABAQUS 6.4.1. software [1] was done. Also, stochastic modeling, founded on the statistic processing of experimental data according to the mathematical theory of experimental design, has been examined. For establishing of process strain energy, the second order stochastic model has been introduced. Analytic, numerical and stochastic research and experiments were performed according to central composite design (type CCC). As industrial case, the material AlCu5Pb Bi was chosen. The power law which describes material compression properties is obtained as 334.33 . = ⋅ϕ 0.192 f k The extrusion strain energy is dependent on the change in section size, friction coefficient, and material properties. Because of that, these parameters were varied variables at the all points of CCC design. The diameter of workpiece used in this design was set predetermined as industrial case, but both coefficient of friction and wall thickness of workpiece has been varied according to experimental design. The best results in modeling were derived by means of stochastic modeling, and the best strain energy model in the form 2 2 W = -1111.82 − 88.7 ⋅μ − 3200 ⋅μ + 625 ⋅μ ⋅ s + 816.43 ⋅ s − 42.25 ⋅ s has been obtained.

Abstract: Cold extrusion is a technology which offers a number of advantages when compared to other manufacturing technologies. High mechanical properties of extruded component, short production time as well as significant cost effectiveness which can be achieved by implementation of this technology are the main characteristics of cold extrusion process. In order to design the complete extrusion process in optimal way it is crucial to know the main process parameters such as load, die pressure, stress and strain distribution within deformation zone etc. There is a number of methods for the analysis of cold extrusion processes. Current paper gives the insight into the possibilities of process analysis in three different cases of cold extrusion. Radial extrusion of gear like elements has been analyzed theoretically (Upper Bound method), numerically by FE simulation and experimentally. Die stressing has been measured by special device (pin load cell) in the process of forward extrusion. Third analyzed process was backward extrusion with profiled punch. In this process loading characteristics as well as some of the mechanical properties of extruded component were obtained experimentally.

Abstract: The paper analyses the process of simulation forward-backward extrusion. In metal forming industries, many products have to be formed in large numbers and with highly accurate dimensions. To save energy and material it is necessary to understand the behavior of material and to know the intermediate shapes of the formed parts and the mutual effects between tool and formed party during the forming process. These are normally based on numerical methods which take into account all physical conditions of the deformed material during the process. For this purpose, the finite element method has been developed in the past in different ways. The paper highlights the finite element simulation as a very useful technique in studying, where there is a generally close correlation in the load results obtained with finite elements method and those obtained experimentally.

Abstract: In order to determine the forming force in deep drawing and backward extrusion processes (on Al 99.5F7 specimens) the analytical, numerical and stochastic modeling and analysis of forming force on the basis of the Box-Wilson’s multi factorial experimental designs by use of rotatable experimental design were carried out. The goal of the paper is to predict the force in these different forming processes giving identical parts by means of different modeling approaches. This study will seek to compare the results of these modeling solutions with experimental results serving to check the correction and the verification of analytic, stochastic and numerically obtained results. Also, the scope of the present paper is to evaluate different parameters affecting these processes and to examine some experimental procedures in laboratory scale for the listed material in order to give more useful information in numerical and stochastic computations and also, to define the correlation among the parameters of these processes in order to improve the existing one and to raise it to a higher techno economic level. The increasing tendency for industrial parts cost reduction, quality improvement, materials savings, and the shortening of design and manufacturing time is more focused on this way of analysis of processes. These investigations are a basis for general conclusions about the forming force and they have a direct application in the projecting of these processes, tools and forming systems.

Abstract: The paper is concerned with the numerical method of determination bending force and calibration force in plate bending. For numeric procedure the finite element method is used. Calibration force is determined when bending force and calibration coefficient are known. Significant factors for determination of bending force are: material of the circular plate, bending radius circular plate, diameter of the circular plate, thickness of the circular plate and method of loading of the circular plate. The calibration coefficient is determined by experiment. The analysis of bending plate is limited to the facts and figures used so far in the fabrication of spherical tanks, i.e. for deformations up to 1 %.