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Article Citation - WoS: 42Citation - Scopus: 50Numerical Simulation of Various Cross Sectional Workpieces Using Conventional Deep Drawing and Hydroforming Technologies(Elsevier Sci Ltd, 2008) Onder, Erkan; Tekkaya, A. ErmanThis study focuses on the determination of optimum sheet metal forming process and process parameters for various cross sectional workpieces by comparing the numerical results of high-pressure sheet metal forming, hydro-mechanical deep drawing (DD) and conventional DD simulations. Within the range of each cross section, depth, characteristic dimensions ratio and fillet radius have been altered systematically. Steel of types St14 and DC04 have been used as the specimen material in the numerical analyses and the experimental verification throughout the study. All numerical simulations have been carried out by using a dynamic-explicit commercial finite element code and an elasto-plastic material model. During the analyses each workpiece was simulated by the three competing processes. The results of analyses, such as sheet thickness distribution, necking, forming of radii etc., are used for assessing the success of each forming process alternative. The analyses revealed that depending on the workpiece geometry and dimensional properties certain processes are preferable for obtaining more satisfactory products. Working windows for each process have been established based on the analyzed parameters of the circular, elliptic, rectangular and square cross sectional product geometries. This data is expected to be useful for selecting the appropriate production process for a given workpiece geometry and understand the limits of each sheet metal forming processes. (c) 2007 Elsevier Ltd. All rights reserved.Article Citation - WoS: 64Citation - Scopus: 69A Semi-Empirical Approach for Residual Stresses in Electric Discharge Machining (edm)(Elsevier Sci Ltd, 2006) Ekmekci, Bulent; Tekkaya, A. Erman; Erden, AbdulkadirHigh residual stresses are developed on the surfaces of electric discharge machined parts. In this study, layer removal method is used to measure the residual stress profile as a function of depth beneath the surface caused by die sinking type EDM. Cracking and its consequences on residual stresses are also studied on samples machined at long pulse durations. A modified empirical equation is developed for scaling residual stresses in machined surfaces with respect to operating conditions. In this model, a unit amplitude shape function representing change in curvature with respect to removal depth is proposed. The proposed form is found to be a special form of a Gauss Distribution. It is the sum of two Gaussian peaks, with the same amplitude and pulse width but opposite center location. The form can be represented by three constant coefficients. These coefficients depend on the released energy by a power function. (C) 2005 Elsevier Ltd. All rights reserved.
